User Guide for AMDGPU Backend

Introduction

The AMDGPU backend provides ISA code generation for AMD GPUs, starting with the R600 family up until the current GCN families. It lives in the llvm/lib/Target/AMDGPU directory.

LLVM

Target Triples

Use the Clang option -target <Architecture>-<Vendor>-<OS>-<Environment> to specify the target triple:

Table 18 AMDGPU Architectures

Architecture

Description

r600

AMD GPUs HD2XXX-HD6XXX for graphics and compute shaders.

amdgcn

AMD GPUs GCN GFX6 onwards for graphics and compute shaders.
Table 19 AMDGPU Vendors

Vendor

Description

amd

Can be used for all AMD GPU usage.

mesa

Can be used if the OS is mesa3d.
Table 20 AMDGPU Operating Systems

OS

Description

<empty>

Defaults to the unknown OS.

amdhsa

Compute kernels executed on HSA [HSA] compatible runtimes such as:

  • AMD’s ROCm™ runtime [AMD-ROCm] using the rocm-amdhsa loader on Linux. See AMD ROCm Platform Release Notes [AMD-ROCm-Release-Notes] for supported hardware and software.

  • AMD’s PAL runtime using the pal-amdhsa loader on Windows.

amdpal

Graphic shaders and compute kernels executed on AMD’s PAL runtime using the pal-amdpal loader on Windows and Linux Pro.

mesa3d

Graphic shaders and compute kernels executed on AMD’s Mesa 3D runtime using the mesa-mesa3d loader on Linux.
Table 21 AMDGPU Environments

Environment

Description

<empty>

Default.

Processors

Use the Clang options -mcpu=<target-id> or --offload-arch=<target-id> to specify the AMDGPU processor together with optional target features. See Target ID and Target Features for AMD GPU target specific information.

Every processor supports every OS ABI (see AMDGPU Operating Systems) with the following exceptions:

  • amdhsa is not supported in r600 architecture (see AMDGPU Architectures).

    Table 22 AMDGPU Processors

    Processor

    Alternative Processor

    Target Triple Architecture

    dGPU/ APU

    Target Features Supported

    Target Properties

    OS Support (see amdgpu-os and corresponding runtime release notes for current information and level of support)

    Example Products

    Radeon HD 2000/3000 Series (R600) [AMD-RADEON-HD-2000-3000]

    r600

    r600

    dGPU

    • Does not support generic address space

    r630

    r600

    dGPU

    • Does not support generic address space

    rs880

    r600

    dGPU

    • Does not support generic address space

    rv670

    r600

    dGPU

    • Does not support generic address space

    Radeon HD 4000 Series (R700) [AMD-RADEON-HD-4000]

    rv710

    r600

    dGPU

    • Does not support generic address space

    rv730

    r600

    dGPU

    • Does not support generic address space

    rv770

    r600

    dGPU

    • Does not support generic address space

    Radeon HD 5000 Series (Evergreen) [AMD-RADEON-HD-5000]

    cedar

    r600

    dGPU

    • Does not support generic address space

    cypress

    r600

    dGPU

    • Does not support generic address space

    juniper

    r600

    dGPU

    • Does not support generic address space

    redwood

    r600

    dGPU

    • Does not support generic address space

    sumo

    r600

    dGPU

    • Does not support generic address space

    Radeon HD 6000 Series (Northern Islands) [AMD-RADEON-HD-6000]

    barts

    r600

    dGPU

    • Does not support generic address space

    caicos

    r600

    dGPU

    • Does not support generic address space

    cayman

    r600

    dGPU

    • Does not support generic address space

    turks

    r600

    dGPU

    • Does not support generic address space

    GCN GFX6 (Southern Islands (SI)) [AMD-GCN-GFX6]

    gfx600

    • tahiti

    amdgcn

    dGPU

    • Does not support generic address space

    • pal-amdpal

    gfx601

    • pitcairn

    • verde

    amdgcn

    dGPU

    • Does not support generic address space

    • pal-amdpal

    gfx602

    • hainan

    • oland

    amdgcn

    dGPU

    • Does not support generic address space

    • pal-amdpal

    GCN GFX7 (Sea Islands (CI)) [AMD-GCN-GFX7]

    gfx700

    • kaveri

    amdgcn

    APU

    • Offset flat scratch

    • rocm-amdhsa

    • pal-amdhsa

    • pal-amdpal

    • A6-7000

    • A6 Pro-7050B

    • A8-7100

    • A8 Pro-7150B

    • A10-7300

    • A10 Pro-7350B

    • FX-7500

    • A8-7200P

    • A10-7400P

    • FX-7600P

    gfx701

    • hawaii

    amdgcn

    dGPU

    • Offset flat scratch

    • rocm-amdhsa

    • pal-amdhsa

    • pal-amdpal

    • FirePro W8100

    • FirePro W9100

    • FirePro S9150

    • FirePro S9170

    gfx702

    amdgcn

    dGPU

    • Offset flat scratch

    • rocm-amdhsa

    • pal-amdhsa

    • pal-amdpal

    • Radeon R9 290

    • Radeon R9 290x

    • Radeon R390

    • Radeon R390x

    gfx703

    • kabini

    • mullins

    amdgcn

    APU

    • Offset flat scratch

    • pal-amdhsa

    • pal-amdpal

    • E1-2100

    • E1-2200

    • E1-2500

    • E2-3000

    • E2-3800

    • A4-5000

    • A4-5100

    • A6-5200

    • A4 Pro-3340B

    gfx704

    • bonaire

    amdgcn

    dGPU

    • Offset flat scratch

    • pal-amdhsa

    • pal-amdpal

    • Radeon HD 7790

    • Radeon HD 8770

    • R7 260

    • R7 260X

    gfx705

    amdgcn

    APU

    • Offset flat scratch

    • pal-amdhsa

    • pal-amdpal

    TBA

    GCN GFX8 (Volcanic Islands (VI)) [AMD-GCN-GFX8]

    gfx801

    • carrizo

    amdgcn

    APU

    • xnack

    • Offset flat scratch

    • rocm-amdhsa

    • pal-amdhsa

    • pal-amdpal

    • A6-8500P

    • Pro A6-8500B

    • A8-8600P

    • Pro A8-8600B

    • FX-8800P

    • Pro A12-8800B

    • A10-8700P

    • Pro A10-8700B

    • A10-8780P

    • A10-9600P

    • A10-9630P

    • A12-9700P

    • A12-9730P

    • FX-9800P

    • FX-9830P

    • E2-9010

    • A6-9210

    • A9-9410

    gfx802

    • iceland

    • tonga

    amdgcn

    dGPU

    • Offset flat scratch

    • rocm-amdhsa

    • pal-amdhsa

    • pal-amdpal

    • Radeon R9 285

    • Radeon R9 380

    • Radeon R9 385

    gfx803

    • fiji

    amdgcn

    dGPU

    • rocm-amdhsa

    • pal-amdhsa

    • pal-amdpal

    • Radeon R9 Nano

    • Radeon R9 Fury

    • Radeon R9 FuryX

    • Radeon Pro Duo

    • FirePro S9300x2

    • Radeon Instinct MI8

    • polaris10

    amdgcn

    dGPU

    • Offset flat scratch

    • rocm-amdhsa

    • pal-amdhsa

    • pal-amdpal

    • Radeon RX 470

    • Radeon RX 480

    • Radeon Instinct MI6

    • polaris11

    amdgcn

    dGPU

    • Offset flat scratch

    • rocm-amdhsa

    • pal-amdhsa

    • pal-amdpal

    • Radeon RX 460

    gfx805

    • tongapro

    amdgcn

    dGPU

    • Offset flat scratch

    • rocm-amdhsa

    • pal-amdhsa

    • pal-amdpal

    • FirePro S7150

    • FirePro S7100

    • FirePro W7100

    • Mobile FirePro M7170

    gfx810

    • stoney

    amdgcn

    APU

    • xnack

    • Offset flat scratch

    • rocm-amdhsa

    • pal-amdhsa

    • pal-amdpal

    TBA

    GCN GFX9 (Vega) [AMD-GCN-GFX900-GFX904-VEGA] [AMD-GCN-GFX906-VEGA7NM] [AMD-GCN-GFX908-CDNA1] [AMD-GCN-GFX90A-CDNA2] [AMD-GCN-GFX940-GFX942-CDNA3]

    gfx900

    amdgcn

    dGPU

    • xnack

    • Absolute flat scratch

    • rocm-amdhsa

    • pal-amdhsa

    • pal-amdpal

    • Radeon Vega Frontier Edition

    • Radeon RX Vega 56

    • Radeon RX Vega 64

    • Radeon RX Vega 64 Liquid

    • Radeon Instinct MI25

    gfx902

    amdgcn

    APU

    • xnack

    • Absolute flat scratch

    • rocm-amdhsa

    • pal-amdhsa

    • pal-amdpal

    • Ryzen 3 2200G

    • Ryzen 5 2400G

    gfx904

    amdgcn

    dGPU

    • xnack

    • rocm-amdhsa

    • pal-amdhsa

    • pal-amdpal

    TBA

    gfx906

    amdgcn

    dGPU

    • sramecc

    • xnack

    • Absolute flat scratch

    • rocm-amdhsa

    • pal-amdhsa

    • pal-amdpal

    • Radeon Instinct MI50

    • Radeon Instinct MI60

    • Radeon VII

    • Radeon Pro VII

    gfx908

    amdgcn

    dGPU

    • sramecc

    • xnack

    • Absolute flat scratch

    • rocm-amdhsa

    • AMD Instinct MI100 Accelerator

    gfx909

    amdgcn

    APU

    • xnack

    • Absolute flat scratch

    • pal-amdpal

    TBA

    gfx90a

    amdgcn

    dGPU

    • sramecc

    • tgsplit

    • xnack

    • kernarg preload

    • Absolute flat scratch

    • Packed work-item IDs

    • rocm-amdhsa

    • rocm-amdhsa

    • rocm-amdhsa

    • AMD Instinct MI210 Accelerator

    • AMD Instinct MI250 Accelerator

    • AMD Instinct MI250X Accelerator

    gfx90c

    amdgcn

    APU

    • xnack

    • Absolute flat scratch

    • pal-amdpal

    • Ryzen 7 4700G

    • Ryzen 7 4700GE

    • Ryzen 5 4600G

    • Ryzen 5 4600GE

    • Ryzen 3 4300G

    • Ryzen 3 4300GE

    • Ryzen Pro 4000G

    • Ryzen 7 Pro 4700G

    • Ryzen 7 Pro 4750GE

    • Ryzen 5 Pro 4650G

    • Ryzen 5 Pro 4650GE

    • Ryzen 3 Pro 4350G

    • Ryzen 3 Pro 4350GE

    gfx940

    amdgcn

    dGPU

    • sramecc

    • tgsplit

    • xnack

    • kernarg preload

    • Architected flat scratch

    • Packed work-item IDs

    TBA

    gfx941

    amdgcn

    dGPU

    • sramecc

    • tgsplit

    • xnack

    • kernarg preload

    • Architected flat scratch

    • Packed work-item IDs

    TBA

    gfx942

    amdgcn

    dGPU

    • sramecc

    • tgsplit

    • xnack

    • kernarg preload

    • Architected flat scratch

    • Packed work-item IDs

    TBA

    GCN GFX10.1 (RDNA 1) [AMD-GCN-GFX10-RDNA1]

    gfx1010

    amdgcn

    dGPU

    • cumode

    • wavefrontsize64

    • xnack

    • Absolute flat scratch

    • rocm-amdhsa

    • pal-amdhsa

    • pal-amdpal

    • Radeon RX 5700

    • Radeon RX 5700 XT

    • Radeon Pro 5600 XT

    • Radeon Pro 5600M

    gfx1011

    amdgcn

    dGPU

    • cumode

    • wavefrontsize64

    • xnack

    • Absolute flat scratch

    • rocm-amdhsa

    • pal-amdhsa

    • pal-amdpal

    • Radeon Pro V520

    gfx1012

    amdgcn

    dGPU

    • cumode

    • wavefrontsize64

    • xnack

    • Absolute flat scratch

    • rocm-amdhsa

    • pal-amdhsa

    • pal-amdpal

    • Radeon RX 5500

    • Radeon RX 5500 XT

    gfx1013

    amdgcn

    APU

    • cumode

    • wavefrontsize64

    • xnack

    • Absolute flat scratch

    • rocm-amdhsa

    • pal-amdhsa

    • pal-amdpal

    TBA

    GCN GFX10.3 (RDNA 2) [AMD-GCN-GFX10-RDNA2]

    gfx1030

    amdgcn

    dGPU

    • cumode

    • wavefrontsize64

    • Absolute flat scratch

    • rocm-amdhsa

    • pal-amdhsa

    • pal-amdpal

    • Radeon RX 6800

    • Radeon RX 6800 XT

    • Radeon RX 6900 XT

    gfx1031

    amdgcn

    dGPU

    • cumode

    • wavefrontsize64

    • Absolute flat scratch

    • rocm-amdhsa

    • pal-amdhsa

    • pal-amdpal

    • Radeon RX 6700 XT

    gfx1032

    amdgcn

    dGPU

    • cumode

    • wavefrontsize64

    • Absolute flat scratch

    • rocm-amdhsa

    • pal-amdhsa

    • pal-amdpal

    TBA

    gfx1033

    amdgcn

    APU

    • cumode

    • wavefrontsize64

    • Absolute flat scratch

    • pal-amdpal

    TBA

    gfx1034

    amdgcn

    dGPU

    • cumode

    • wavefrontsize64

    • Absolute flat scratch

    • pal-amdpal

    TBA

    gfx1035

    amdgcn

    APU

    • cumode

    • wavefrontsize64

    • Absolute flat scratch

    • pal-amdpal

    TBA

    gfx1036

    amdgcn

    APU

    • cumode

    • wavefrontsize64

    • Absolute flat scratch

    • pal-amdpal

    TBA

    GCN GFX11 (RDNA 3) [AMD-GCN-GFX11-RDNA3]

    gfx1100

    amdgcn

    dGPU

    • cumode

    • wavefrontsize64

    • Architected flat scratch

    • Packed work-item IDs

    • pal-amdpal

    TBA

    gfx1101

    amdgcn

    dGPU

    • cumode

    • wavefrontsize64

    • Architected flat scratch

    • Packed work-item IDs

    TBA

    gfx1102

    amdgcn

    dGPU

    • cumode

    • wavefrontsize64

    • Architected flat scratch

    • Packed work-item IDs

    TBA

    gfx1103

    amdgcn

    APU

    • cumode

    • wavefrontsize64

    • Architected flat scratch

    • Packed work-item IDs

    TBA

    gfx1150

    amdgcn

    APU

    • cumode

    • wavefrontsize64

    • Architected flat scratch

    • Packed work-item IDs

    TBA

    gfx1151

    amdgcn

    APU

    • cumode

    • wavefrontsize64

    • Architected flat scratch

    • Packed work-item IDs

    TBA

    gfx1152

    amdgcn

    APU

    • cumode

    • wavefrontsize64

    • Architected flat scratch

    • Packed work-item IDs

    TBA

    gfx1200

    amdgcn

    dGPU

    • cumode

    • wavefrontsize64

    • Architected flat scratch

    • Packed work-item IDs

    TBA

    gfx1201

    amdgcn

    dGPU

    • cumode

    • wavefrontsize64

    • Architected flat scratch

    • Packed work-item IDs

    TBA

Generic processors allow execution of a single code object on any of the processors that it supports. Such code objects may not perform as well as those for the non-generic processors.

Generic processors are only available on code object V6 and above (see ELF Code Object).

Generic processor code objects are versioned. See Generic Processor Versioning for more information on how versioning works.

Table 23 AMDGPU Generic Processors

Processor

Target Triple Architecture

Supported Processors

Target Features Supported

Target Properties

Target Restrictions

gfx9-generic

amdgcn

  • gfx900

  • gfx902

  • gfx904

  • gfx906

  • gfx909

  • gfx90c

  • xnack

  • Absolute flat scratch

  • v_mad_mix instructions are not available on gfx900, gfx902, gfx909, gfx90c

  • v_fma_mix instructions are not available on gfx904

  • sramecc is not available on gfx906

  • The following instructions are not available on gfx906:

    • v_fmac_f32

    • v_xnor_b32

    • v_dot4_i32_i8

    • v_dot8_i32_i4

    • v_dot2_i32_i16

    • v_dot2_u32_u16

    • v_dot4_u32_u8

    • v_dot8_u32_u4

    • v_dot2_f32_f16

gfx10-1-generic

amdgcn

  • gfx1010

  • gfx1011

  • gfx1012

  • gfx1013

  • xnack

  • wavefrontsize64

  • cumode

  • Absolute flat scratch

  • The following instructions are not available on gfx1011 and gfx1012

    • v_dot4_i32_i8

    • v_dot8_i32_i4

    • v_dot2_i32_i16

    • v_dot2_u32_u16

    • v_dot2c_f32_f16

    • v_dot4c_i32_i8

    • v_dot4_u32_u8

    • v_dot8_u32_u4

    • v_dot2_f32_f16

  • BVH Ray Tracing instructions are not available on gfx1013

gfx10-3-generic

amdgcn

  • gfx1030

  • gfx1031

  • gfx1032

  • gfx1033

  • gfx1034

  • gfx1035

  • gfx1036

  • wavefrontsize64

  • cumode

  • Absolute flat scratch

No restrictions.

gfx11-generic

amdgcn

  • gfx1100

  • gfx1101

  • gfx1102

  • gfx1103

  • gfx1150

  • gfx1151

  • gfx1152

  • wavefrontsize64

  • cumode

  • Architected flat scratch

  • Packed work-item IDs

Various codegen pessimizations are applied to work around some hazards specific to some targets within this family.

Not all VGPRs can be used on:

  • gfx1100

  • gfx1101

  • gfx1151

  • gfx1152

SALU floating point instructions and single-use VGPR hint instructions are not available on:

  • gfx1150

  • gfx1151

  • gfx1152

SGPRs are not supported for src1 in dpp instructions for:

  • gfx1150

  • gfx1151

  • gfx1152

gfx12-generic

amdgcn

  • gfx1200

  • gfx1201

  • wavefrontsize64

  • cumode

  • Architected flat scratch

  • Packed work-item IDs

No restrictions.

Generic Processor Versioning

Generic processor (see AMDGPU Generic Processors) code objects are versioned (see AMDGPU ELF Header e_flags for Code Object V6 and After) between 1 and 255. The version of non-generic code objects is always set to 0.

For a generic code object, adding a new supported processor may require the code generated for the generic target to be changed so it can continue to execute on the previously supported processors as well as on the new one. When this happens, the generic code object version number is incremented at the same time as the generic target is updated.

Each supported processor of a generic target is mapped to the version it was introduced in. A generic code object can execute on a supported processor if the version of the code object being loaded is greater than or equal to the version in which the processor was added to the generic target.

Target Features

Target features control how code is generated to support certain processor specific features. Not all target features are supported by all processors. The runtime must ensure that the features supported by the device used to execute the code match the features enabled when generating the code. A mismatch of features may result in incorrect execution, or a reduction in performance.

The target features supported by each processor is listed in Processors.

Target features are controlled by exactly one of the following Clang options:

-mcpu=<target-id> or --offload-arch=<target-id>

The -mcpu and --offload-arch can specify the target feature as optional components of the target ID. If omitted, the target feature has the any value. See Target ID.

-m[no-]<target-feature>

Target features not specified by the target ID are specified using a separate option. These target features can have an on or off value. on is specified by omitting the no- prefix, and off is specified by including the no- prefix. The default if not specified is off.

For example:

-mcpu=gfx908:xnack+

Enable the xnack feature.

-mcpu=gfx908:xnack-

Disable the xnack feature.

-mcumode

Enable the cumode feature.

-mno-cumode

Disable the cumode feature.

Table 24 AMDGPU Target Features

Target Feature

Clang Option to Control

Description

Name

cumode

  • -m[no-]cumode

Control the wavefront execution mode used when generating code for kernels. When disabled native WGP wavefront execution mode is used, when enabled CU wavefront execution mode is used (see Memory Model).

sramecc

  • -mcpu

  • --offload-arch

If specified, generate code that can only be loaded and executed in a process that has a matching setting for SRAMECC.

If not specified for code object V2 to V3, generate code that can be loaded and executed in a process with SRAMECC enabled.

If not specified for code object V4 or above, generate code that can be loaded and executed in a process with either setting of SRAMECC.

tgsplit

-m[no-]tgsplit

Enable/disable generating code that assumes work-groups are launched in threadgroup split mode. When enabled the waves of a work-group may be launched in different CUs.

wavefrontsize64

  • -m[no-]wavefrontsize64

Control the wavefront size used when generating code for kernels. When disabled native wavefront size 32 is used, when enabled wavefront size 64 is used.

xnack

  • -mcpu

  • --offload-arch

If specified, generate code that can only be loaded and executed in a process that has a matching setting for XNACK replay.

If not specified for code object V2 to V3, generate code that can be loaded and executed in a process with XNACK replay enabled.

If not specified for code object V4 or above, generate code that can be loaded and executed in a process with either setting of XNACK replay.

XNACK replay can be used for demand paging and page migration. If enabled in the device, then if a page fault occurs the code may execute incorrectly unless generated with XNACK replay enabled, or generated for code object V4 or above without specifying XNACK replay. Executing code that was generated with XNACK replay enabled, or generated for code object V4 or above without specifying XNACK replay, on a device that does not have XNACK replay enabled will execute correctly but may be less performant than code generated for XNACK replay disabled.

Target ID

AMDGPU supports target IDs. See Clang Offload Bundler for a general description. The AMDGPU target specific information is:

processor

Is an AMDGPU processor or alternative processor name specified in AMDGPU Processors. The non-canonical form target ID allows both the primary processor and alternative processor names. The canonical form target ID only allow the primary processor name.

target-feature

Is a target feature name specified in AMDGPU Target Features that is supported by the processor. The target features supported by each processor is specified in AMDGPU Processors. Those that can be specified in a target ID are marked as being controlled by -mcpu and --offload-arch. Each target feature must appear at most once in a target ID. The non-canonical form target ID allows the target features to be specified in any order. The canonical form target ID requires the target features to be specified in alphabetic order.

Code Object V2 to V3 Target ID

The target ID syntax for code object V2 to V3 is the same as defined in Clang Offload Bundler except when used in the .amdgcn_target <target-triple> “-” <target-id> assembler directive and the bundle entry ID. In those cases it has the following BNF syntax:

<target-id> ::== <processor> ( "+" <target-feature> )*

Where a target feature is omitted if Off and present if On or Any.

Note

The code object V2 to V3 cannot represent Any and treats it the same as On.

Embedding Bundled Code Objects

AMDGPU supports the HIP and OpenMP languages that perform code object embedding as described in Clang Offload Bundler.

Note

The target ID syntax used for code object V2 to V3 for a bundle entry ID differs from that used elsewhere. See Code Object V2 to V3 Target ID.

Address Spaces

The AMDGPU architecture supports a number of memory address spaces. The address space names use the OpenCL standard names, with some additions.

The AMDGPU address spaces correspond to target architecture specific LLVM address space numbers used in LLVM IR.

The AMDGPU address spaces are described in AMDGPU Address Spaces. Only 64-bit process address spaces are supported for the amdgcn target.

Table 25 AMDGPU Address Spaces

64-Bit Process Address Space

Address Space Name

LLVM IR Address Space Number

HSA Segment Name

Hardware Name

Address Size

NULL Value

Generic

0

flat

flat

64

0x0000000000000000

Global

1

global

global

64

0x0000000000000000

Region

2

N/A

GDS

32

not implemented for AMDHSA

Local

3

group

LDS

32

0xFFFFFFFF

Constant

4

constant

same as global

64

0x0000000000000000

Private

5

private

scratch

32

0xFFFFFFFF

Constant 32-bit

6

TODO

0x00000000

Buffer Fat Pointer

7

N/A

N/A

160

0

Buffer Resource

8

N/A

V#

128

0x00000000000000000000000000000000

Buffer Strided Pointer (experimental)

9

TODO

Streamout Registers

128

N/A

GS_REGS
Generic

The generic address space is supported unless the Target Properties column of AMDGPU Processors specifies Does not support generic address space.

The generic address space uses the hardware flat address support for two fixed ranges of virtual addresses (the private and local apertures), that are outside the range of addressable global memory, to map from a flat address to a private or local address. This uses FLAT instructions that can take a flat address and access global, private (scratch), and group (LDS) memory depending on if the address is within one of the aperture ranges.

Flat access to scratch requires hardware aperture setup and setup in the kernel prologue (see Flat Scratch). Flat access to LDS requires hardware aperture setup and M0 (GFX7-GFX8) register setup (see M0).

To convert between a private or group address space address (termed a segment address) and a flat address the base address of the corresponding aperture can be used. For GFX7-GFX8 these are available in the HSA AQL Queue the address of which can be obtained with Queue Ptr SGPR (see Initial Kernel Execution State). For GFX9-GFX11 the aperture base addresses are directly available as inline constant registers SRC_SHARED_BASE/LIMIT and SRC_PRIVATE_BASE/LIMIT. In 64-bit address mode the aperture sizes are 2^32 bytes and the base is aligned to 2^32 which makes it easier to convert from flat to segment or segment to flat.

A global address space address has the same value when used as a flat address so no conversion is needed.

Global and Constant

The global and constant address spaces both use global virtual addresses, which are the same virtual address space used by the CPU. However, some virtual addresses may only be accessible to the CPU, some only accessible by the GPU, and some by both.

Using the constant address space indicates that the data will not change during the execution of the kernel. This allows scalar read instructions to be used. As the constant address space could only be modified on the host side, a generic pointer loaded from the constant address space is safe to be assumed as a global pointer since only the device global memory is visible and managed on the host side. The vector and scalar L1 caches are invalidated of volatile data before each kernel dispatch execution to allow constant memory to change values between kernel dispatches.

Region

The region address space uses the hardware Global Data Store (GDS). All wavefronts executing on the same device will access the same memory for any given region address. However, the same region address accessed by wavefronts executing on different devices will access different memory. It is higher performance than global memory. It is allocated by the runtime. The data store (DS) instructions can be used to access it.

Local

The local address space uses the hardware Local Data Store (LDS) which is automatically allocated when the hardware creates the wavefronts of a work-group, and freed when all the wavefronts of a work-group have terminated. All wavefronts belonging to the same work-group will access the same memory for any given local address. However, the same local address accessed by wavefronts belonging to different work-groups will access different memory. It is higher performance than global memory. The data store (DS) instructions can be used to access it.

Private

The private address space uses the hardware scratch memory support which automatically allocates memory when it creates a wavefront and frees it when a wavefronts terminates. The memory accessed by a lane of a wavefront for any given private address will be different to the memory accessed by another lane of the same or different wavefront for the same private address.

If a kernel dispatch uses scratch, then the hardware allocates memory from a pool of backing memory allocated by the runtime for each wavefront. The lanes of the wavefront access this using dword (4 byte) interleaving. The mapping used from private address to backing memory address is:

wavefront-scratch-base + ((private-address / 4) * wavefront-size * 4) + (wavefront-lane-id * 4) + (private-address % 4)

If each lane of a wavefront accesses the same private address, the interleaving results in adjacent dwords being accessed and hence requires fewer cache lines to be fetched.

There are different ways that the wavefront scratch base address is determined by a wavefront (see Initial Kernel Execution State).

Scratch memory can be accessed in an interleaved manner using buffer instructions with the scratch buffer descriptor and per wavefront scratch offset, by the scratch instructions, or by flat instructions. Multi-dword access is not supported except by flat and scratch instructions in GFX9-GFX11.

Code that manipulates the stack values in other lanes of a wavefront, such as by addrspacecast-ing stack pointers to generic ones and taking offsets that reach other lanes or by explicitly constructing the scratch buffer descriptor, triggers undefined behavior when it modifies the scratch values of other lanes. The compiler may assume that such modifications do not occur. When using code object V5 LIBOMPTARGET_STACK_SIZE may be used to provide the private segment size in bytes, for cases where a dynamic stack is used.

Constant 32-bit

TODO

Buffer Fat Pointer

The buffer fat pointer is an experimental address space that is currently unsupported in the backend. It exposes a non-integral pointer that is in the future intended to support the modelling of 128-bit buffer descriptors plus a 32-bit offset into the buffer (in total encapsulating a 160-bit pointer), allowing normal LLVM load/store/atomic operations to be used to model the buffer descriptors used heavily in graphics workloads targeting the backend.

The buffer descriptor used to construct a buffer fat pointer must be raw: the stride must be 0, the “add tid” flag must be 0, the swizzle enable bits must be off, and the extent must be measured in bytes. (On subtargets where bounds checking may be disabled, buffer fat pointers may choose to enable it or not).

Buffer Resource

The buffer resource pointer, in address space 8, is the newer form for representing buffer descriptors in AMDGPU IR, replacing their previous representation as <4 x i32>. It is a non-integral pointer that represents a 128-bit buffer descriptor resource (V#).

Since, in general, a buffer resource supports complex addressing modes that cannot be easily represented in LLVM (such as implicit swizzled access to structured buffers), it is illegal to perform non-trivial address computations, such as getelementptr operations, on buffer resources. They may be passed to AMDGPU buffer intrinsics, and they may be converted to and from i128.

Casting a buffer resource to a buffer fat pointer is permitted and adds an offset of 0.

Buffer resources can be created from 64-bit pointers (which should be either generic or global) using the llvm.amdgcn.make.buffer.rsrc intrinsic, which takes the pointer, which becomes the base of the resource, the 16-bit stride (and swzizzle control) field stored in bits 63:48 of a V#, the 32-bit NumRecords/extent field (bits 95:64), and the 32-bit flags field (bits 127:96). The specific interpretation of these fields varies by the target architecture and is detailed in the ISA descriptions.

Buffer Strided Pointer

The buffer index pointer is an experimental address space. It represents a 128-bit buffer descriptor and a 32-bit offset, like the Buffer Fat Pointer. Additionally, it contains an index into the buffer, which allows the direct addressing of structured elements. These components appear in that order, i.e., the descriptor comes first, then the 32-bit offset followed by the 32-bit index.

The bits in the buffer descriptor must meet the following requirements: the stride is the size of a structured element, the “add tid” flag must be 0, and the swizzle enable bits must be off.

Streamout Registers

Dedicated registers used by the GS NGG Streamout Instructions. The register file is modelled as a memory in a distinct address space because it is indexed by an address-like offset in place of named registers, and because register accesses affect LGKMcnt. This is an internal address space used only by the compiler. Do not use this address space for IR pointers.

Memory Scopes

This section provides LLVM memory synchronization scopes supported by the AMDGPU backend memory model when the target triple OS is amdhsa (see Memory Model and Target Triples).

The memory model supported is based on the HSA memory model [HSA] which is based in turn on HRF-indirect with scope inclusion [HRF]. The happens-before relation is transitive over the synchronizes-with relation independent of scope and synchronizes-with allows the memory scope instances to be inclusive (see table AMDHSA LLVM Sync Scopes).

This is different to the OpenCL [OpenCL] memory model which does not have scope inclusion and requires the memory scopes to exactly match. However, this is conservatively correct for OpenCL.

Table 26 AMDHSA LLVM Sync Scopes

LLVM Sync Scope

Description

none

The default: system.

Synchronizes with, and participates in modification and seq_cst total orderings with, other operations (except image operations) for all address spaces (except private, or generic that accesses private) provided the other operation’s sync scope is:

  • system.

  • agent and executed by a thread on the same agent.

  • workgroup and executed by a thread in the same work-group.

  • wavefront and executed by a thread in the same wavefront.

agent

Synchronizes with, and participates in modification and seq_cst total orderings with, other operations (except image operations) for all address spaces (except private, or generic that accesses private) provided the other operation’s sync scope is:

  • system or agent and executed by a thread on the same agent.

  • workgroup and executed by a thread in the same work-group.

  • wavefront and executed by a thread in the same wavefront.

workgroup

Synchronizes with, and participates in modification and seq_cst total orderings with, other operations (except image operations) for all address spaces (except private, or generic that accesses private) provided the other operation’s sync scope is:

  • system, agent or workgroup and executed by a thread in the same work-group.

  • wavefront and executed by a thread in the same wavefront.

wavefront

Synchronizes with, and participates in modification and seq_cst total orderings with, other operations (except image operations) for all address spaces (except private, or generic that accesses private) provided the other operation’s sync scope is:

  • system, agent, workgroup or wavefront and executed by a thread in the same wavefront.

singlethread

Only synchronizes with and participates in modification and seq_cst total orderings with, other operations (except image operations) running in the same thread for all address spaces (for example, in signal handlers).

one-as

Same as system but only synchronizes with other operations within the same address space.

agent-one-as

Same as agent but only synchronizes with other operations within the same address space.

workgroup-one-as

Same as workgroup but only synchronizes with other operations within the same address space.

wavefront-one-as

Same as wavefront but only synchronizes with other operations within the same address space.

singlethread-one-as

Same as singlethread but only synchronizes with other operations within the same address space.

LLVM IR Intrinsics

The AMDGPU backend implements the following LLVM IR intrinsics.

This section is WIP.

Table 27 AMDGPU LLVM IR Intrinsics

LLVM Intrinsic

Description

llvm.amdgcn.sqrt

Provides direct access to v_sqrt_f64, v_sqrt_f32 and v_sqrt_f16 (on targets with half support). Performs sqrt function.

llvm.amdgcn.log

Provides direct access to v_log_f32 and v_log_f16 (on targets with half support). Performs log2 function.

llvm.amdgcn.exp2

Provides direct access to v_exp_f32 and v_exp_f16 (on targets with half support). Performs exp2 function.

llvm.frexp

Implemented for half, float and double.

llvm.log2

Implemented for float and half (and vectors of float or half). Not implemented for double. Hardware provides 1ULP accuracy for float, and 0.51ULP for half. Float instruction does not natively support denormal inputs.

llvm.sqrt

Implemented for double, float and half (and vectors).

llvm.log

Implemented for float and half (and vectors).

llvm.exp

Implemented for float and half (and vectors).

llvm.log10

Implemented for float and half (and vectors).

llvm.exp2

Implemented for float and half (and vectors of float or half). Not implemented for double. Hardware provides 1ULP accuracy for float, and 0.51ULP for half. Float instruction does not natively support denormal inputs.

llvm.stacksave.p5

Implemented, must use the alloca address space.

llvm.stackrestore.p5

Implemented, must use the alloca address space.

llvm.get.fpmode.i32

The natural floating-point mode type is i32. This implemented by extracting relevant bits out of the MODE register with s_getreg_b32. The first 10 bits are the core floating-point mode. Bits 12:18 are the exception mask. On gfx9+, bit 23 is FP16_OVFL. Bitfields not relevant to floating-point instructions are 0s.

llvm.get.rounding

AMDGPU supports two separately controllable rounding modes depending on the floating-point type. One controls float, and the other controls both double and half operations. If both modes are the same, returns one of the standard return values. If the modes are different, returns one of 12 extended values describing the two modes.

To nearest, ties away from zero is not a supported mode. The raw rounding mode values in the MODE register do not exactly match the FLT_ROUNDS values, so a conversion is performed.

llvm.set.rounding

Input value expected to be one of the valid results from ‘llvm.get.rounding’. Rounding mode is undefined if not passed a valid input. This should be a wave uniform value. In case of a divergent input value, the first active lane’s value will be used.

llvm.get.fpenv

Returns the current value of the AMDGPU floating point environment. This stores information related to the current rounding mode, denormalization mode, enabled traps, and floating point exceptions. The format is a 64-bit concatenation of the MODE and TRAPSTS registers.

llvm.set.fpenv

Sets the floating point environment to the specifies state.

llvm.amdgcn.readfirstlane

Provides direct access to v_readfirstlane_b32. Returns the value in the lowest active lane of the input operand. Currently implemented for i16, i32, float, half, bfloat, <2 x i16>, <2 x half>, <2 x bfloat>, i64, double, pointers, multiples of the 32-bit vectors.

llvm.amdgcn.readlane

Provides direct access to v_readlane_b32. Returns the value in the specified lane of the first input operand. The second operand specifies the lane to read from. Currently implemented for i16, i32, float, half, bfloat, <2 x i16>, <2 x half>, <2 x bfloat>, i64, double, pointers, multiples of the 32-bit vectors.

llvm.amdgcn.writelane

Provides direct access to v_writelane_b32. Writes value in the first input operand to the specified lane of divergent output. The second operand specifies the lane to write. Currently implemented for i16, i32, float, half, bfloat, <2 x i16>, <2 x half>, <2 x bfloat>, i64, double, pointers, multiples of the 32-bit vectors.

llvm.amdgcn.wave.reduce.umin

Performs an arithmetic unsigned min reduction on the unsigned values provided by each lane in the wavefront. Intrinsic takes a hint for reduction strategy using second operand 0: Target default preference, 1: Iterative strategy, and 2: DPP. If target does not support the DPP operations (e.g. gfx6/7), reduction will be performed using default iterative strategy. Intrinsic is currently only implemented for i32.

llvm.amdgcn.wave.reduce.umax

Performs an arithmetic unsigned max reduction on the unsigned values provided by each lane in the wavefront. Intrinsic takes a hint for reduction strategy using second operand 0: Target default preference, 1: Iterative strategy, and 2: DPP. If target does not support the DPP operations (e.g. gfx6/7), reduction will be performed using default iterative strategy. Intrinsic is currently only implemented for i32.

llvm.amdgcn.permlane16

Provides direct access to v_permlane16_b32. Performs arbitrary gather-style operation within a row (16 contiguous lanes) of the second input operand. The third and fourth inputs must be scalar values. these are combined into a single 64-bit value representing lane selects used to swizzle within each row. Currently implemented for i16, i32, float, half, bfloat, <2 x i16>, <2 x half>, <2 x bfloat>, i64, double, pointers, multiples of the 32-bit vectors.

llvm.amdgcn.permlanex16

Provides direct access to v_permlanex16_b32. Performs arbitrary gather-style operation across two rows of the second input operand (each row is 16 contiguous lanes). The third and fourth inputs must be scalar values. these are combined into a single 64-bit value representing lane selects used to swizzle within each row. Currently implemented for i16, i32, float, half, bfloat, <2 x i16>, <2 x half>, <2 x bfloat>, i64, double, pointers, multiples of the 32-bit vectors.

llvm.amdgcn.permlane64

Provides direct access to v_permlane64_b32. Performs a specific permutation across lanes of the input operand where the high half and low half of a wave64 are swapped. Performs no operation in wave32 mode. Currently implemented for i16, i32, float, half, bfloat, <2 x i16>, <2 x half>, <2 x bfloat>, i64, double, pointers, multiples of the 32-bit vectors.

llvm.amdgcn.udot2

Provides direct access to v_dot2_u32_u16 across targets which support such instructions. This performs unsigned dot product with two v2i16 operands, summed with the third i32 operand. The i1 fourth operand is used to clamp the output.

llvm.amdgcn.udot4

Provides direct access to v_dot4_u32_u8 across targets which support such instructions. This performs unsigned dot product with two i32 operands (holding a vector of 4 8bit values), summed with the third i32 operand. The i1 fourth operand is used to clamp the output.

llvm.amdgcn.udot8

Provides direct access to v_dot8_u32_u4 across targets which support such instructions. This performs unsigned dot product with two i32 operands (holding a vector of 8 4bit values), summed with the third i32 operand. The i1 fourth operand is used to clamp the output.

llvm.amdgcn.sdot2

Provides direct access to v_dot2_i32_i16 across targets which support such instructions. This performs signed dot product with two v2i16 operands, summed with the third i32 operand. The i1 fourth operand is used to clamp the output. When applicable (e.g. no clamping), this is lowered into v_dot2c_i32_i16 for targets which support it.

llvm.amdgcn.sdot4

Provides direct access to v_dot4_i32_i8 across targets which support such instructions. This performs signed dot product with two i32 operands (holding a vector of 4 8bit values), summed with the third i32 operand. The i1 fourth operand is used to clamp the output. When applicable (i.e. no clamping / operand modifiers), this is lowered into v_dot4c_i32_i8 for targets which support it. RDNA3 does not offer v_dot4_i32_i8, and rather offers v_dot4_i32_iu8 which has operands to hold the signedness of the vector operands. Thus, this intrinsic lowers to the signed version of this instruction for gfx11 targets.

llvm.amdgcn.sdot8

Provides direct access to v_dot8_u32_u4 across targets which support such instructions. This performs signed dot product with two i32 operands (holding a vector of 8 4bit values), summed with the third i32 operand. The i1 fourth operand is used to clamp the output. When applicable (i.e. no clamping / operand modifiers), this is lowered into v_dot8c_i32_i4 for targets which support it. RDNA3 does not offer v_dot8_i32_i4, and rather offers v_dot4_i32_iu4 which has operands to hold the signedness of the vector operands. Thus, this intrinsic lowers to the signed version of this instruction for gfx11 targets.

llvm.amdgcn.sudot4

Provides direct access to v_dot4_i32_iu8 on gfx11 targets. This performs dot product with two i32 operands (holding a vector of 4 8bit values), summed with the fifth i32 operand. The i1 sixth operand is used to clamp the output. The i1s preceding the vector operands decide the signedness.

llvm.amdgcn.sudot8

Provides direct access to v_dot8_i32_iu4 on gfx11 targets. This performs dot product with two i32 operands (holding a vector of 8 4bit values), summed with the fifth i32 operand. The i1 sixth operand is used to clamp the output. The i1s preceding the vector operands decide the signedness.

llvm.amdgcn.sched_barrier

Controls the types of instructions that may be allowed to cross the intrinsic during instruction scheduling. The parameter is a mask for the instruction types that can cross the intrinsic.

  • 0x0000: No instructions may be scheduled across sched_barrier.

  • 0x0001: All, non-memory, non-side-effect producing instructions may be scheduled across sched_barrier, i.e. allow ALU instructions to pass.

  • 0x0002: VALU instructions may be scheduled across sched_barrier.

  • 0x0004: SALU instructions may be scheduled across sched_barrier.

  • 0x0008: MFMA/WMMA instructions may be scheduled across sched_barrier.

  • 0x0010: All VMEM instructions may be scheduled across sched_barrier.

  • 0x0020: VMEM read instructions may be scheduled across sched_barrier.

  • 0x0040: VMEM write instructions may be scheduled across sched_barrier.

  • 0x0080: All DS instructions may be scheduled across sched_barrier.

  • 0x0100: All DS read instructions may be scheduled accoss sched_barrier.

  • 0x0200: All DS write instructions may be scheduled across sched_barrier.

  • 0x0400: All Transcendental (e.g. V_EXP) instructions may be scheduled across sched_barrier.

llvm.amdgcn.sched_group_barrier

Creates schedule groups with specific properties to create custom scheduling pipelines. The ordering between groups is enforced by the instruction scheduler. The intrinsic applies to the code that preceeds the intrinsic. The intrinsic takes three values that control the behavior of the schedule groups.

  • Mask : Classify instruction groups using the llvm.amdgcn.sched_barrier mask values.

  • Size : The number of instructions that are in the group.

  • SyncID : Order is enforced between groups with matching values.

The mask can include multiple instruction types. It is undefined behavior to set values beyond the range of valid masks.

Combining multiple sched_group_barrier intrinsics enables an ordering of specific instruction types during instruction scheduling. For example, the following enforces a sequence of 1 VMEM read, followed by 1 VALU instruction, followed by 5 MFMA instructions.

// 1 VMEM read
__builtin_amdgcn_sched_group_barrier(32, 1, 0)
// 1 VALU
__builtin_amdgcn_sched_group_barrier(2, 1, 0)
// 5 MFMA
__builtin_amdgcn_sched_group_barrier(8, 5, 0)

llvm.amdgcn.iglp_opt

An experimental intrinsic for instruction group level parallelism. The intrinsic implements predefined intruction scheduling orderings. The intrinsic applies to the surrounding scheduling region. The intrinsic takes a value that specifies the strategy. The compiler implements two strategies.

  1. Interleave DS and MFMA instructions for small GEMM kernels.

  2. Interleave DS and MFMA instructions for single wave small GEMM kernels.

Only one iglp_opt intrinsic may be used in a scheduling region. The iglp_opt intrinsic cannot be combined with sched_barrier or sched_group_barrier.

The iglp_opt strategy implementations are subject to change.

llvm.amdgcn.atomic.cond.sub.u32

Provides direct access to flat_atomic_cond_sub_u32, global_atomic_cond_sub_u32 and ds_cond_sub_u32 based on address space on gfx12 targets. This performs subtraction only if the memory value is greater than or equal to the data value.

llvm.amdgcn.s.getpc

Provides access to the s_getpc_b64 instruction, but with the return value sign-extended from the width of the underlying PC hardware register even on processors where the s_getpc_b64 instruction returns a zero-extended value.

LLVM IR Metadata

The AMDGPU backend implements the following target custom LLVM IR metadata.

‘amdgpu.last.use’ Metadata

Sets TH_LOAD_LU temporal hint on load instructions that support it. Takes priority over nontemporal hint (TH_LOAD_NT). This takes no arguments.

%val = load i32, ptr %in, align 4, !amdgpu.last.use !{}

‘amdgpu.no.remote.memory’ Metadata

Asserts a memory operation does not access bytes in host memory, or remote connected peer device memory (the address must be device local). This is intended for use with atomicrmw and other atomic instructions. This is required to emit a native hardware instruction for some system scope atomic operations on some subtargets. For most integer atomic operations, this is a sufficient restriction to emit a native atomic instruction.

An atomicrmw without metadata will be treated conservatively as required to preserve the operation behavior in all cases. This will typically be used in conjunction with !amdgpu.no.fine.grained.memory.

; Indicates the atomic does not access fine-grained memory, or
; remote device memory.
%old0 = atomicrmw sub ptr %ptr0, i32 1 acquire, !amdgpu.no.fine.grained.memory !0, !amdgpu.no.remote.memory !0

; Indicates the atomic does not access peer device memory.
%old2 = atomicrmw sub ptr %ptr2, i32 1 acquire, !amdgpu.no.remote.memory !0

!0 = !{}

‘amdgpu.no.fine.grained.memory’ Metadata

Asserts a memory access does not access bytes allocated in fine-grained allocated memory. This is intended for use with atomicrmw and other atomic instructions. This is required to emit a native hardware instruction for some system scope atomic operations on some subtargets. An atomicrmw without metadata will be treated conservatively as required to preserve the operation behavior in all cases. This will typically be used in conjunction with !amdgpu.no.remote.memory.access.

; Indicates the access does not access fine-grained memory, or
; remote device memory.
%old0 = atomicrmw sub ptr %ptr0, i32 1 acquire, !amdgpu.no.fine.grained.memory !0, !amdgpu.no.remote.memory.access !0

; Indicates the access does not access fine-grained memory
%old2 = atomicrmw sub ptr %ptr2, i32 1 acquire, !amdgpu.no.fine.grained.memory !0

!0 = !{}

‘amdgpu.ignore.denormal.mode’ Metadata

For use with atomicrmw floating-point operations. Indicates the handling of denormal inputs and results is insignificant and may be inconsistent with the expected floating-point mode. This is necessary to emit a native atomic instruction on some targets for some address spaces where float denormals are unconditionally flushed. This is typically used in conjunction with !amdgpu.no.remote.memory.access and !amdgpu.no.fine.grained.memory

%res0 = atomicrmw fadd ptr addrspace(1) %ptr, float %value seq_cst, align 4, !amdgpu.ignore.denormal.mode !0
%res1 = atomicrmw fadd ptr addrspace(1) %ptr, float %value seq_cst, align 4, !amdgpu.ignore.denormal.mode !0, !amdgpu.no.fine.grained.memory !0, !amdgpu.no.remote.memory.access !0

!0 = !{}

LLVM IR Attributes

The AMDGPU backend supports the following LLVM IR attributes.

Table 28 AMDGPU LLVM IR Attributes

LLVM Attribute

Description

“amdgpu-flat-work-group-size”=”min,max”

Specify the minimum and maximum flat work group sizes that will be specified when the kernel is dispatched. Generated by the amdgpu_flat_work_group_size CLANG attribute [CLANG-ATTR]. The IR implied default value is 1,1024. Clang may emit this attribute with more restrictive bounds depending on language defaults. If the actual block or workgroup size exceeds the limit at any point during the execution, the behavior is undefined. For example, even if there is only one active thread but the thread local id exceeds the limit, the behavior is undefined.

“amdgpu-implicitarg-num-bytes”=”n”

Number of kernel argument bytes to add to the kernel argument block size for the implicit arguments. This varies by OS and language (for OpenCL see OpenCL kernel implicit arguments appended for AMDHSA OS).

“amdgpu-num-sgpr”=”n”

Specifies the number of SGPRs to use. Generated by the amdgpu_num_sgpr CLANG attribute [CLANG-ATTR].

“amdgpu-num-vgpr”=”n”

Specifies the number of VGPRs to use. Generated by the amdgpu_num_vgpr CLANG attribute [CLANG-ATTR].

“amdgpu-waves-per-eu”=”m,n”

Specify the minimum and maximum number of waves per execution unit. Generated by the amdgpu_waves_per_eu CLANG attribute [CLANG-ATTR]. This is an optimization hint, and the backend may not be able to satisfy the request. If the specified range is incompatible with the function’s “amdgpu-flat-work-group-size” value, the implied occupancy bounds by the workgroup size takes precedence.

“amdgpu-ieee” true/false.

GFX6-GFX11 Only Specify whether the function expects the IEEE field of the mode register to be set on entry. Overrides the default for the calling convention.

“amdgpu-dx10-clamp” true/false.

GFX6-GFX11 Only Specify whether the function expects the DX10_CLAMP field of the mode register to be set on entry. Overrides the default for the calling convention.

“amdgpu-no-workitem-id-x”

Indicates the function does not depend on the value of the llvm.amdgcn.workitem.id.x intrinsic. If a function is marked with this attribute, or reached through a call site marked with this attribute, and that intrinsic is called, the behavior of the program is undefined. (Whole-program undefined behavior is used here because, for example, the absence of a required workitem ID in the preloaded register set can mean that all other preloaded registers are earlier than the compilation assumed they would be.) The backend can generally infer this during code generation, so typically there is no benefit to frontends marking functions with this.

“amdgpu-no-workitem-id-y”

The same as amdgpu-no-workitem-id-x, except for the llvm.amdgcn.workitem.id.y intrinsic.

“amdgpu-no-workitem-id-z”

The same as amdgpu-no-workitem-id-x, except for the llvm.amdgcn.workitem.id.z intrinsic.

“amdgpu-no-workgroup-id-x”

The same as amdgpu-no-workitem-id-x, except for the llvm.amdgcn.workgroup.id.x intrinsic.

“amdgpu-no-workgroup-id-y”

The same as amdgpu-no-workitem-id-x, except for the llvm.amdgcn.workgroup.id.y intrinsic.

“amdgpu-no-workgroup-id-z”

The same as amdgpu-no-workitem-id-x, except for the llvm.amdgcn.workgroup.id.z intrinsic.

“amdgpu-no-dispatch-ptr”

The same as amdgpu-no-workitem-id-x, except for the llvm.amdgcn.dispatch.ptr intrinsic.

“amdgpu-no-implicitarg-ptr”

The same as amdgpu-no-workitem-id-x, except for the llvm.amdgcn.implicitarg.ptr intrinsic.

“amdgpu-no-dispatch-id”

The same as amdgpu-no-workitem-id-x, except for the llvm.amdgcn.dispatch.id intrinsic.

“amdgpu-no-queue-ptr”

Similar to amdgpu-no-workitem-id-x, except for the llvm.amdgcn.queue.ptr intrinsic. Note that unlike the other ABI hint attributes, the queue pointer may be required in situations where the intrinsic call does not directly appear in the program. Some subtargets require the queue pointer for to handle some addrspacecasts, as well as the llvm.amdgcn.is.shared, llvm.amdgcn.is.private, llvm.trap, and llvm.debug intrinsics.

“amdgpu-no-hostcall-ptr”

Similar to amdgpu-no-implicitarg-ptr, except specific to the implicit kernel argument that holds the pointer to the hostcall buffer. If this attribute is absent, then the amdgpu-no-implicitarg-ptr is also removed.

“amdgpu-no-heap-ptr”

Similar to amdgpu-no-implicitarg-ptr, except specific to the implicit kernel argument that holds the pointer to an initialized memory buffer that conforms to the requirements of the malloc/free device library V1 version implementation. If this attribute is absent, then the amdgpu-no-implicitarg-ptr is also removed.

“amdgpu-no-multigrid-sync-arg”

Similar to amdgpu-no-implicitarg-ptr, except specific to the implicit kernel argument that holds the multigrid synchronization pointer. If this attribute is absent, then the amdgpu-no-implicitarg-ptr is also removed.

“amdgpu-no-default-queue”

Similar to amdgpu-no-implicitarg-ptr, except specific to the implicit kernel argument that holds the default queue pointer. If this attribute is absent, then the amdgpu-no-implicitarg-ptr is also removed.

“amdgpu-no-completion-action”

Similar to amdgpu-no-implicitarg-ptr, except specific to the implicit kernel argument that holds the completion action pointer. If this attribute is absent, then the amdgpu-no-implicitarg-ptr is also removed.

“amdgpu-lds-size”=”min[,max]”

Min is the minimum number of bytes that will be allocated in the Local Data Store at address zero. Variables are allocated within this frame using absolute symbol metadata, primarily by the AMDGPULowerModuleLDS pass. Optional max is the maximum number of bytes that will be allocated. Note that min==max indicates that no further variables can be added to the frame. This is an internal detail of how LDS variables are lowered, language front ends should not set this attribute.

“amdgpu-gds-size”

Bytes expected to be allocated at the start of GDS memory at entry.

“amdgpu-git-ptr-high”

The hard-wired high half of the address of the global information table for AMDPAL OS type. 0xffffffff represents no hard-wired high half, since current hardware only allows a 16 bit value.

“amdgpu-32bit-address-high-bits”

Assumed high 32-bits for 32-bit address spaces which are really truncated 64-bit addresses (i.e., addrspace(6))

“amdgpu-color-export”

Indicates shader exports color information if set to 1. Defaults to 1 for amdgpu_ps, and 0 for other calling conventions. Determines the necessity and type of null exports when a shader terminates early by killing lanes.

“amdgpu-depth-export”

Indicates shader exports depth information if set to 1. Determines the necessity and type of null exports when a shader terminates early by killing lanes. A depth-only shader will export to depth channel when no null export target is available (GFX11+).

“InitialPSInputAddr”

Set the initial value of the spi_ps_input_addr register for amdgpu_ps shaders. Any bits enabled by this value will be enabled in the final register value.

“amdgpu-wave-priority-threshold”

VALU instruction count threshold for adjusting wave priority. If exceeded, temporarily raise the wave priority at the start of the shader function until its last VMEM instructions to allow younger waves to issue their VMEM instructions as well.

“amdgpu-memory-bound”

Set internally by backend

“amdgpu-wave-limiter”

Set internally by backend

“amdgpu-unroll-threshold”

Set base cost threshold preference for loop unrolling within this function, default is 300. Actual threshold may be varied by per-loop metadata or reduced by heuristics.

“amdgpu-max-num-workgroups”=”x,y,z”

Specify the maximum number of work groups for the kernel dispatch in the X, Y, and Z dimensions. Generated by the amdgpu_max_num_work_groups CLANG attribute [CLANG-ATTR]. Clang only emits this attribute when all the three numbers are >= 1.

“amdgpu-no-agpr”

Indicates the function will not require allocating AGPRs. This is only relevant on subtargets with AGPRs. The behavior is undefined if a function which requires AGPRs is reached through any function marked with this attribute.

Calling Conventions

The AMDGPU backend supports the following calling conventions:

Table 29 AMDGPU Calling Conventions

Calling Convention

Description

ccc

The C calling convention. Used by default. See Non-Kernel Functions for more details.

fastcc

The fast calling convention. Mostly the same as the ccc.

coldcc

The cold calling convention. Mostly the same as the ccc.

amdgpu_cs

Used for Mesa/AMDPAL compute shaders. ..TODO:: Describe.

amdgpu_cs_chain

Similar to amdgpu_cs, with differences described below.

Functions with this calling convention cannot be called directly. They must instead be launched via the llvm.amdgcn.cs.chain intrinsic.

Arguments are passed in SGPRs, starting at s0, if they have the inreg attribute, and in VGPRs otherwise, starting at v8. Using more SGPRs or VGPRs than available in the subtarget is not allowed. On subtargets that use a scratch buffer descriptor (as opposed to scratch_{load,store}_* instructions), the scratch buffer descriptor is passed in s[48:51]. This limits the SGPR / inreg arguments to the equivalent of 48 dwords; using more than that is not allowed.

The return type must be void. Varargs, sret, byval, byref, inalloca, preallocated are not supported.

Values in scalar registers as well as v0-v7 are not preserved. Values in VGPRs starting at v8 are not preserved for the active lanes, but must be saved by the callee for inactive lanes when using WWM.

Wave scratch is “empty” at function boundaries. There is no stack pointer input or output value, but functions are free to use scratch starting from an initial stack pointer. Calls to amdgpu_gfx functions are allowed and behave like they do in amdgpu_cs functions.

All counters (lgkmcnt, vmcnt, storecnt, etc.) are presumed in an unknown state at function entry.

A function may have multiple exits (e.g. one chain exit and one plain ret void for when the wave ends), but all llvm.amdgcn.cs.chain exits must be in uniform control flow.

amdgpu_cs_chain_preserve

Same as amdgpu_cs_chain, but active lanes for VGPRs starting at v8 are preserved. Calls to amdgpu_gfx functions are not allowed, and any calls to llvm.amdgcn.cs.chain must not pass more VGPR arguments than the caller’s VGPR function parameters.

amdgpu_es

Used for AMDPAL shader stage before geometry shader if geometry is in use. So either the domain (= tessellation evaluation) shader if tessellation is in use, or otherwise the vertex shader. ..TODO:: Describe.

amdgpu_gfx

Used for AMD graphics targets. Functions with this calling convention cannot be used as entry points. ..TODO:: Describe.

amdgpu_gs

Used for Mesa/AMDPAL geometry shaders. ..TODO:: Describe.

amdgpu_hs

Used for Mesa/AMDPAL hull shaders (= tessellation control shaders). ..TODO:: Describe.

amdgpu_kernel

See Kernel Functions

amdgpu_ls

Used for AMDPAL vertex shader if tessellation is in use. ..TODO:: Describe.

amdgpu_ps

Used for Mesa/AMDPAL pixel shaders. ..TODO:: Describe.

amdgpu_vs

Used for Mesa/AMDPAL last shader stage before rasterization (vertex shader if tessellation and geometry are not in use, or otherwise copy shader if one is needed). ..TODO:: Describe.

AMDGPU MCExpr

As part of the AMDGPU MC layer, AMDGPU provides the following target specific MCExprs.

Table 30 AMDGPU MCExpr types:

MCExpr

Operands

Return value

max(arg, ...)

1 or more

Variadic signed operation that returns the maximum value of all its arguments.

or(arg, ...)

1 or more

Variadic signed operation that returns the bitwise-or result of all its arguments.

ELF Code Object

The AMDGPU backend generates a standard ELF [ELF] relocatable code object that can be linked by lld to produce a standard ELF shared code object which can be loaded and executed on an AMDGPU target.

Sections

An AMDGPU target ELF code object has the standard ELF sections which include:

Table 38 AMDGPU ELF Sections

Name

Type

Attributes

.bss

SHT_NOBITS

SHF_ALLOC + SHF_WRITE

.data

SHT_PROGBITS

SHF_ALLOC + SHF_WRITE

.debug_*

SHT_PROGBITS

none

.dynamic

SHT_DYNAMIC

SHF_ALLOC

.dynstr

SHT_PROGBITS

SHF_ALLOC

.dynsym

SHT_PROGBITS

SHF_ALLOC

.got

SHT_PROGBITS

SHF_ALLOC + SHF_WRITE

.hash

SHT_HASH

SHF_ALLOC

.note

SHT_NOTE

none

.relaname

SHT_RELA

none

.rela.dyn

SHT_RELA

none

.rodata

SHT_PROGBITS

SHF_ALLOC

.shstrtab

SHT_STRTAB

none

.strtab

SHT_STRTAB

none

.symtab

SHT_SYMTAB

none

.text

SHT_PROGBITS

SHF_ALLOC + SHF_EXECINSTR

These sections have their standard meanings (see [ELF]) and are only generated if needed.

.debug*

The standard DWARF sections. See DWARF Debug Information for information on the DWARF produced by the AMDGPU backend.

.dynamic, .dynstr, .dynsym, .hash

The standard sections used by a dynamic loader.

.note

See Note Records for the note records supported by the AMDGPU backend.

.relaname, .rela.dyn

For relocatable code objects, name is the name of the section that the relocation records apply. For example, .rela.text is the section name for relocation records associated with the .text section.

For linked shared code objects, .rela.dyn contains all the relocation records from each of the relocatable code object’s .relaname sections.

See Relocation Records for the relocation records supported by the AMDGPU backend.

.text

The executable machine code for the kernels and functions they call. Generated as position independent code. See Code Conventions for information on conventions used in the isa generation.

Note Records

The AMDGPU backend code object contains ELF note records in the .note section. The set of generated notes and their semantics depend on the code object version; see Code Object V2 Note Records and Code Object V3 and Above Note Records.

As required by ELFCLASS32 and ELFCLASS64, minimal zero-byte padding must be generated after the name field to ensure the desc field is 4 byte aligned. In addition, minimal zero-byte padding must be generated to ensure the desc field size is a multiple of 4 bytes. The sh_addralign field of the .note section must be at least 4 to indicate at least 8 byte alignment.

Code Object V2 Note Records

Warning

Code object V2 generation is no longer supported by this version of LLVM.

The AMDGPU backend code object uses the following ELF note record in the .note section when compiling for code object V2.

The note record vendor field is “AMD”.

Additional note records may be present, but any which are not documented here are deprecated and should not be used.

Table 39 AMDGPU Code Object V2 ELF Note Records

Name

Type

Description

“AMD”

NT_AMD_HSA_CODE_OBJECT_VERSION

Code object version.

“AMD”

NT_AMD_HSA_HSAIL

HSAIL properties generated by the HSAIL Finalizer and not the LLVM compiler.

“AMD”

NT_AMD_HSA_ISA_VERSION

Target ISA version.

“AMD”

NT_AMD_HSA_METADATA

Metadata null terminated string in YAML [YAML] textual format.

“AMD”

NT_AMD_HSA_ISA_NAME

Target ISA name.
Table 40 AMDGPU Code Object V2 ELF Note Record Enumeration Values

Name

Value

NT_AMD_HSA_CODE_OBJECT_VERSION

1

NT_AMD_HSA_HSAIL

2

NT_AMD_HSA_ISA_VERSION

3

reserved

4-9

NT_AMD_HSA_METADATA

10

NT_AMD_HSA_ISA_NAME

11
NT_AMD_HSA_CODE_OBJECT_VERSION

Specifies the code object version number. The description field has the following layout:

struct amdgpu_hsa_note_code_object_version_s {
  uint32_t major_version;
  uint32_t minor_version;
};

The major_version has a value less than or equal to 2.

NT_AMD_HSA_HSAIL

Specifies the HSAIL properties used by the HSAIL Finalizer. The description field has the following layout:

struct amdgpu_hsa_note_hsail_s {
  uint32_t hsail_major_version;
  uint32_t hsail_minor_version;
  uint8_t profile;
  uint8_t machine_model;
  uint8_t default_float_round;
};
NT_AMD_HSA_ISA_VERSION

Specifies the target ISA version. The description field has the following layout:

struct amdgpu_hsa_note_isa_s {
  uint16_t vendor_name_size;
  uint16_t architecture_name_size;
  uint32_t major;
  uint32_t minor;
  uint32_t stepping;
  char vendor_and_architecture_name[1];
};

vendor_name_size and architecture_name_size are the length of the vendor and architecture names respectively, including the NUL character.

vendor_and_architecture_name contains the NUL terminates string for the vendor, immediately followed by the NUL terminated string for the architecture.

This note record is used by the HSA runtime loader.

Code object V2 only supports a limited number of processors and has fixed settings for target features. See AMDGPU Code Object V2 Supported Processors and Fixed Target Feature Settings for a list of processors and the corresponding target ID. In the table the note record ISA name is a concatenation of the vendor name, architecture name, major, minor, and stepping separated by a “:”.

The target ID column shows the processor name and fixed target features used by the LLVM compiler. The LLVM compiler does not generate a NT_AMD_HSA_HSAIL note record.

A code object generated by the Finalizer also uses code object V2 and always generates a NT_AMD_HSA_HSAIL note record. The processor name and sramecc target feature is as shown in AMDGPU Code Object V2 Supported Processors and Fixed Target Feature Settings but the xnack target feature is specified by the EF_AMDGPU_FEATURE_XNACK_V2 e_flags bit.

NT_AMD_HSA_ISA_NAME

Specifies the target ISA name as a non-NUL terminated string.

This note record is not used by the HSA runtime loader.

See the NT_AMD_HSA_ISA_VERSION note record description of the code object V2’s limited support of processors and fixed settings for target features.

See AMDGPU Code Object V2 Supported Processors and Fixed Target Feature Settings for a mapping from the string to the corresponding target ID. If the xnack target feature is supported and enabled, the string produced by the LLVM compiler will may have a +xnack appended. The Finlizer did not do the appending and instead used the EF_AMDGPU_FEATURE_XNACK_V2 e_flags bit.

NT_AMD_HSA_METADATA

Specifies extensible metadata associated with the code objects executed on HSA [HSA] compatible runtimes (see AMDGPU Operating Systems). It is required when the target triple OS is amdhsa (see Target Triples). See Code Object V2 Metadata for the syntax of the code object metadata string.

Table 41 AMDGPU Code Object V2 Supported Processors and Fixed Target Feature Settings

Note Record ISA Name

Target ID

AMD:AMDGPU:6:0:0

gfx600

AMD:AMDGPU:6:0:1

gfx601

AMD:AMDGPU:6:0:2

gfx602

AMD:AMDGPU:7:0:0

gfx700

AMD:AMDGPU:7:0:1

gfx701

AMD:AMDGPU:7:0:2

gfx702

AMD:AMDGPU:7:0:3

gfx703

AMD:AMDGPU:7:0:4

gfx704

AMD:AMDGPU:7:0:5

gfx705

AMD:AMDGPU:8:0:0

gfx802

AMD:AMDGPU:8:0:1

gfx801:xnack+

AMD:AMDGPU:8:0:2

gfx802

AMD:AMDGPU:8:0:3

gfx803

AMD:AMDGPU:8:0:4

gfx803

AMD:AMDGPU:8:0:5

gfx805

AMD:AMDGPU:8:1:0

gfx810:xnack+

AMD:AMDGPU:9:0:0

gfx900:xnack-

AMD:AMDGPU:9:0:1

gfx900:xnack+

AMD:AMDGPU:9:0:2

gfx902:xnack-

AMD:AMDGPU:9:0:3

gfx902:xnack+

AMD:AMDGPU:9:0:4

gfx904:xnack-

AMD:AMDGPU:9:0:5

gfx904:xnack+

AMD:AMDGPU:9:0:6

gfx906:sramecc-:xnack-

AMD:AMDGPU:9:0:7

gfx906:sramecc-:xnack+

AMD:AMDGPU:9:0:12

gfx90c:xnack-

Code Object V3 and Above Note Records

The AMDGPU backend code object uses the following ELF note record in the .note section when compiling for code object V3 and above.

The note record vendor field is “AMDGPU”.

Additional note records may be present, but any which are not documented here are deprecated and should not be used.

Table 42 AMDGPU Code Object V3 and Above ELF Note Records

Name

Type

Description

“AMDGPU”

NT_AMDGPU_METADATA

Metadata in Message Pack [MsgPack] binary format.
Table 43 AMDGPU Code Object V3 and Above ELF Note Record Enumeration Values

Name

Value

reserved

0-31

NT_AMDGPU_METADATA

32
NT_AMDGPU_METADATA

Specifies extensible metadata associated with an AMDGPU code object. It is encoded as a map in the Message Pack [MsgPack] binary data format. See Code Object V3 Metadata, Code Object V4 Metadata and Code Object V5 Metadata for the map keys defined for the amdhsa OS.

Symbols

Symbols include the following:

Table 44 AMDGPU ELF Symbols

Name

Type

Section

Description

link-name

STT_OBJECT

  • .data

  • .rodata

  • .bss

Global variable

link-name.kd

STT_OBJECT

  • .rodata

Kernel descriptor

link-name

STT_FUNC

  • .text

Kernel entry point

link-name

STT_OBJECT

  • SHN_AMDGPU_LDS

Global variable in LDS
Global variable

Global variables both used and defined by the compilation unit.

If the symbol is defined in the compilation unit then it is allocated in the appropriate section according to if it has initialized data or is readonly.

If the symbol is external then its section is STN_UNDEF and the loader will resolve relocations using the definition provided by another code object or explicitly defined by the runtime.

If the symbol resides in local/group memory (LDS) then its section is the special processor specific section name SHN_AMDGPU_LDS, and the st_value field describes alignment requirements as it does for common symbols.

Kernel descriptor

Every HSA kernel has an associated kernel descriptor. It is the address of the kernel descriptor that is used in the AQL dispatch packet used to invoke the kernel, not the kernel entry point. The layout of the HSA kernel descriptor is defined in Kernel Descriptor.

Kernel entry point

Every HSA kernel also has a symbol for its machine code entry point.

Relocation Records

The AMDGPU backend generates Elf64_Rela relocation records for AMDHSA or Elf64_Rel relocation records for Mesa/AMDPAL. Supported relocatable fields are:

word32

This specifies a 32-bit field occupying 4 bytes with arbitrary byte alignment. These values use the same byte order as other word values in the AMDGPU architecture.

word64

This specifies a 64-bit field occupying 8 bytes with arbitrary byte alignment. These values use the same byte order as other word values in the AMDGPU architecture.

Following notations are used for specifying relocation calculations:

A

Represents the addend used to compute the value of the relocatable field. If the addend field is smaller than 64 bits then it is zero-extended to 64 bits for use in the calculations below. (In practice this only affects _HI relocation types on Mesa/AMDPAL, where the addend comes from the 32-bit field but the result of the calculation depends on the high part of the full 64-bit address.)

G

Represents the offset into the global offset table at which the relocation entry’s symbol will reside during execution.

GOT

Represents the address of the global offset table.

P

Represents the place (section offset for et_rel or address for et_dyn) of the storage unit being relocated (computed using r_offset).

S

Represents the value of the symbol whose index resides in the relocation entry. Relocations not using this must specify a symbol index of STN_UNDEF.

B

Represents the base address of a loaded executable or shared object which is the difference between the ELF address and the actual load address. Relocations using this are only valid in executable or shared objects.

The following relocation types are supported:

Table 45 AMDGPU ELF Relocation Records

Relocation Type

Kind

Value

Field

Calculation

R_AMDGPU_NONE

0

none

none

R_AMDGPU_ABS32_LO

Static, Dynamic

1

word32

(S + A) & 0xFFFFFFFF

R_AMDGPU_ABS32_HI

Static, Dynamic

2

word32

(S + A) >> 32

R_AMDGPU_ABS64

Static, Dynamic

3

word64

S + A

R_AMDGPU_REL32

Static

4

word32

S + A - P

R_AMDGPU_REL64

Static

5

word64

S + A - P

R_AMDGPU_ABS32

Static, Dynamic

6

word32

S + A

R_AMDGPU_GOTPCREL

Static

7

word32

G + GOT + A - P

R_AMDGPU_GOTPCREL32_LO

Static

8

word32

(G + GOT + A - P) & 0xFFFFFFFF

R_AMDGPU_GOTPCREL32_HI

Static

9

word32

(G + GOT + A - P) >> 32

R_AMDGPU_REL32_LO

Static

10

word32

(S + A - P) & 0xFFFFFFFF

R_AMDGPU_REL32_HI

Static

11

word32

(S + A - P) >> 32

reserved

12

R_AMDGPU_RELATIVE64

Dynamic

13

word64

B + A

R_AMDGPU_REL16

Static

14

word16

((S + A - P) - 4) / 4

R_AMDGPU_ABS32_LO and R_AMDGPU_ABS32_HI are only supported by the mesa3d OS, which does not support R_AMDGPU_ABS64.

There is no current OS loader support for 32-bit programs and so R_AMDGPU_ABS32 is not used.

Loaded Code Object Path Uniform Resource Identifier (URI)

The AMD GPU code object loader represents the path of the ELF shared object from which the code object was loaded as a textual Uniform Resource Identifier (URI). Note that the code object is the in memory loaded relocated form of the ELF shared object. Multiple code objects may be loaded at different memory addresses in the same process from the same ELF shared object.

The loaded code object path URI syntax is defined by the following BNF syntax:

code_object_uri ::== file_uri | memory_uri
file_uri        ::== "file://" file_path [ range_specifier ]
memory_uri      ::== "memory://" process_id range_specifier
range_specifier ::== [ "#" | "?" ] "offset=" number "&" "size=" number
file_path       ::== URI_ENCODED_OS_FILE_PATH
process_id      ::== DECIMAL_NUMBER
number          ::== HEX_NUMBER | DECIMAL_NUMBER | OCTAL_NUMBER
number

Is a C integral literal where hexadecimal values are prefixed by “0x” or “0X”, and octal values by “0”.

file_path

Is the file’s path specified as a URI encoded UTF-8 string. In URI encoding, every character that is not in the regular expression [a-zA-Z0-9/_.~-] is encoded as two uppercase hexadecimal digits proceeded by “%”. Directories in the path are separated by “/”.

offset

Is a 0-based byte offset to the start of the code object. For a file URI, it is from the start of the file specified by the file_path, and if omitted defaults to 0. For a memory URI, it is the memory address and is required.

size

Is the number of bytes in the code object. For a file URI, if omitted it defaults to the size of the file. It is required for a memory URI.

process_id

Is the identity of the process owning the memory. For Linux it is the C unsigned integral decimal literal for the process ID (PID).

For example:

file:///dir1/dir2/file1
file:///dir3/dir4/file2#offset=0x2000&size=3000
memory://1234#offset=0x20000&size=3000

DWARF Debug Information

Warning

This section describes provisional support for AMDGPU DWARF [DWARF] that is not currently fully implemented and is subject to change.

AMDGPU generates DWARF [DWARF] debugging information ELF sections (see ELF Code Object) which contain information that maps the code object executable code and data to the source language constructs. It can be used by tools such as debuggers and profilers. It uses features defined in DWARF Extensions For Heterogeneous Debugging that are made available in DWARF Version 4 and DWARF Version 5 as an LLVM vendor extension.

This section defines the AMDGPU target architecture specific DWARF mappings.

Register Identifier

This section defines the AMDGPU target architecture register numbers used in DWARF operation expressions (see DWARF Version 5 section 2.5 and A.2.5.4 DWARF Operation Expressions) and Call Frame Information instructions (see DWARF Version 5 section 6.4 and A.6.4 Call Frame Information).

A single code object can contain code for kernels that have different wavefront sizes. The vector registers and some scalar registers are based on the wavefront size. AMDGPU defines distinct DWARF registers for each wavefront size. This simplifies the consumer of the DWARF so that each register has a fixed size, rather than being dynamic according to the wavefront size mode. Similarly, distinct DWARF registers are defined for those registers that vary in size according to the process address size. This allows a consumer to treat a specific AMDGPU processor as a single architecture regardless of how it is configured at run time. The compiler explicitly specifies the DWARF registers that match the mode in which the code it is generating will be executed.

DWARF registers are encoded as numbers, which are mapped to architecture registers. The mapping for AMDGPU is defined in AMDGPU DWARF Register Mapping. All AMDGPU targets use the same mapping.

Table 46 AMDGPU DWARF Register Mapping

DWARF Register

AMDGPU Register

Bit Size

Description

0

PC_32

32

Program Counter (PC) when executing in a 32-bit process address space. Used in the CFI to describe the PC of the calling frame.

1

EXEC_MASK_32

32

Execution Mask Register when executing in wavefront 32 mode.

2-15

Reserved

Reserved for highly accessed registers using DWARF shortcut.

16

PC_64

64

Program Counter (PC) when executing in a 64-bit process address space. Used in the CFI to describe the PC of the calling frame.

17

EXEC_MASK_64

64

Execution Mask Register when executing in wavefront 64 mode.

18-31

Reserved

Reserved for highly accessed registers using DWARF shortcut.

32-95

SGPR0-SGPR63

32

Scalar General Purpose Registers.

96-127

Reserved

Reserved for frequently accessed registers using DWARF 1-byte ULEB.

128

STATUS

32

Status Register.

129-511

Reserved

Reserved for future Scalar Architectural Registers.

512

VCC_32

32

Vector Condition Code Register when executing in wavefront 32 mode.

513-767

Reserved

Reserved for future Vector Architectural Registers when executing in wavefront 32 mode.

768

VCC_64

64

Vector Condition Code Register when executing in wavefront 64 mode.

769-1023

Reserved

Reserved for future Vector Architectural Registers when executing in wavefront 64 mode.

1024-1087

Reserved

Reserved for padding.

1088-1129

SGPR64-SGPR105

32

Scalar General Purpose Registers.

1130-1535

Reserved

Reserved for future Scalar General Purpose Registers.

1536-1791

VGPR0-VGPR255

32*32

Vector General Purpose Registers when executing in wavefront 32 mode.

1792-2047

Reserved

Reserved for future Vector General Purpose Registers when executing in wavefront 32 mode.

2048-2303

AGPR0-AGPR255

32*32

Vector Accumulation Registers when executing in wavefront 32 mode.

2304-2559

Reserved

Reserved for future Vector Accumulation Registers when executing in wavefront 32 mode.

2560-2815

VGPR0-VGPR255

64*32

Vector General Purpose Registers when executing in wavefront 64 mode.

2816-3071

Reserved

Reserved for future Vector General Purpose Registers when executing in wavefront 64 mode.

3072-3327

AGPR0-AGPR255

64*32

Vector Accumulation Registers when executing in wavefront 64 mode.

3328-3583

Reserved

Reserved for future Vector Accumulation Registers when executing in wavefront 64 mode.

The vector registers are represented as the full size for the wavefront. They are organized as consecutive dwords (32-bits), one per lane, with the dword at the least significant bit position corresponding to lane 0 and so forth. DWARF location expressions involving the DW_OP_LLVM_offset and DW_OP_LLVM_push_lane operations are used to select the part of the vector register corresponding to the lane that is executing the current thread of execution in languages that are implemented using a SIMD or SIMT execution model.

If the wavefront size is 32 lanes then the wavefront 32 mode register definitions are used. If the wavefront size is 64 lanes then the wavefront 64 mode register definitions are used. Some AMDGPU targets support executing in both wavefront 32 and wavefront 64 mode. The register definitions corresponding to the wavefront mode of the generated code will be used.

If code is generated to execute in a 32-bit process address space, then the 32-bit process address space register definitions are used. If code is generated to execute in a 64-bit process address space, then the 64-bit process address space register definitions are used. The amdgcn target only supports the 64-bit process address space.

Memory Space Identifier

The DWARF memory space represents the source language memory space. See DWARF Version 5 section 2.12 which is updated by the DWARF Extensions For Heterogeneous Debugging section A.2.14 Memory Spaces.

The DWARF memory space mapping used for AMDGPU is defined in AMDGPU DWARF Memory Space Mapping.

Table 47 AMDGPU DWARF Memory Space Mapping

DWARF

AMDGPU

Memory Space Name

Value

Memory Space

DW_MSPACE_LLVM_none

0x0000

Generic (Flat)

DW_MSPACE_LLVM_global

0x0001

Global

DW_MSPACE_LLVM_constant

0x0002

Global

DW_MSPACE_LLVM_group

0x0003

Local (group/LDS)

DW_MSPACE_LLVM_private

0x0004

Private (Scratch)

DW_MSPACE_AMDGPU_region

0x8000

Region (GDS)

The DWARF memory space values defined in the DWARF Extensions For Heterogeneous Debugging section A.2.14 Memory Spaces are used.

In addition, DW_ADDR_AMDGPU_region is encoded as a vendor extension. This is available for use for the AMD extension for access to the hardware GDS memory which is scratchpad memory allocated per device.

For AMDGPU if no DW_AT_LLVM_memory_space attribute is present, then the default memory space of DW_MSPACE_LLVM_none is used.

See Address Space Identifier for information on the AMDGPU mapping of DWARF memory spaces to DWARF address spaces, including address size and NULL value.

Address Space Identifier

DWARF address spaces correspond to target architecture specific linear addressable memory areas. See DWARF Version 5 section 2.12 and DWARF Extensions For Heterogeneous Debugging section A.2.13 Address Spaces.

The DWARF address space mapping used for AMDGPU is defined in AMDGPU DWARF Address Space Mapping.

Table 48 AMDGPU DWARF Address Space Mapping

DWARF

AMDGPU

Notes

Address Space Name

Value

Address

Bit Size

LLVM IR Address Space

64-bit process address space

32-bit process address space

DW_ASPACE_LLVM_none

0x00

64

32

Global

default address space

DW_ASPACE_AMDGPU_generic

0x01

64

32

Generic (Flat)

DW_ASPACE_AMDGPU_region

0x02

32

32

Region (GDS)

DW_ASPACE_AMDGPU_local

0x03

32

32

Local (group/LDS)

Reserved

0x04

DW_ASPACE_AMDGPU_private_lane

0x05

32

32

Private (Scratch)

focused lane

DW_ASPACE_AMDGPU_private_wave

0x06

32

32

Private (Scratch)

unswizzled wavefront

See Address Spaces for information on the AMDGPU LLVM IR address spaces including address size and NULL value.

The DW_ASPACE_LLVM_none address space is the default target architecture address space used in DWARF operations that do not specify an address space. It therefore has to map to the global address space so that the DW_OP_addr* and related operations can refer to addresses in the program code.

The DW_ASPACE_AMDGPU_generic address space allows location expressions to specify the flat address space. If the address corresponds to an address in the local address space, then it corresponds to the wavefront that is executing the focused thread of execution. If the address corresponds to an address in the private address space, then it corresponds to the lane that is executing the focused thread of execution for languages that are implemented using a SIMD or SIMT execution model.

Note

CUDA-like languages such as HIP that do not have address spaces in the language type system, but do allow variables to be allocated in different address spaces, need to explicitly specify the DW_ASPACE_AMDGPU_generic address space in the DWARF expression operations as the default address space is the global address space.

The DW_ASPACE_AMDGPU_local address space allows location expressions to specify the local address space corresponding to the wavefront that is executing the focused thread of execution.

The DW_ASPACE_AMDGPU_private_lane address space allows location expressions to specify the private address space corresponding to the lane that is executing the focused thread of execution for languages that are implemented using a SIMD or SIMT execution model.

The DW_ASPACE_AMDGPU_private_wave address space allows location expressions to specify the unswizzled private address space corresponding to the wavefront that is executing the focused thread of execution. The wavefront view of private memory is the per wavefront unswizzled backing memory layout defined in Address Spaces, such that address 0 corresponds to the first location for the backing memory of the wavefront (namely the address is not offset by wavefront-scratch-base). The following formula can be used to convert from a DW_ASPACE_AMDGPU_private_lane address to a DW_ASPACE_AMDGPU_private_wave address:

private-address-wavefront =
  ((private-address-lane / 4) * wavefront-size * 4) +
  (wavefront-lane-id * 4) + (private-address-lane % 4)

If the DW_ASPACE_AMDGPU_private_lane address is dword aligned, and the start of the dwords for each lane starting with lane 0 is required, then this simplifies to:

private-address-wavefront =
  private-address-lane * wavefront-size

A compiler can use the DW_ASPACE_AMDGPU_private_wave address space to read a complete spilled vector register back into a complete vector register in the CFI. The frame pointer can be a private lane address which is dword aligned, which can be shifted to multiply by the wavefront size, and then used to form a private wavefront address that gives a location for a contiguous set of dwords, one per lane, where the vector register dwords are spilled. The compiler knows the wavefront size since it generates the code. Note that the type of the address may have to be converted as the size of a DW_ASPACE_AMDGPU_private_lane address may be smaller than the size of a DW_ASPACE_AMDGPU_private_wave address.

Lane identifier

DWARF lane identifies specify a target architecture lane position for hardware that executes in a SIMD or SIMT manner, and on which a source language maps its threads of execution onto those lanes. The DWARF lane identifier is pushed by the DW_OP_LLVM_push_lane DWARF expression operation. See DWARF Version 5 section 2.5 which is updated by DWARF Extensions For Heterogeneous Debugging section A.2.5.4 DWARF Operation Expressions.

For AMDGPU, the lane identifier corresponds to the hardware lane ID of a wavefront. It is numbered from 0 to the wavefront size minus 1.

Operation Expressions

DWARF expressions are used to compute program values and the locations of program objects. See DWARF Version 5 section 2.5 and A.2.5.4 DWARF Operation Expressions.

DWARF location descriptions describe how to access storage which includes memory and registers. When accessing storage on AMDGPU, bytes are ordered with least significant bytes first, and bits are ordered within bytes with least significant bits first.

For AMDGPU CFI expressions, DW_OP_LLVM_select_bit_piece is used to describe unwinding vector registers that are spilled under the execution mask to memory: the zero-single location description is the vector register, and the one-single location description is the spilled memory location description. The DW_OP_LLVM_form_aspace_address is used to specify the address space of the memory location description.

In AMDGPU expressions, DW_OP_LLVM_select_bit_piece is used by the DW_AT_LLVM_lane_pc attribute expression where divergent control flow is controlled by the execution mask. An undefined location description together with DW_OP_LLVM_extend is used to indicate the lane was not active on entry to the subprogram. See DW_AT_LLVM_lane_pc for an example.

Debugger Information Entry Attributes

This section describes how certain debugger information entry attributes are used by AMDGPU. See the sections in DWARF Version 5 section 3.3.5 and 3.1.1 which are updated by DWARF Extensions For Heterogeneous Debugging section A.3.3.5 Low-Level Information and A.3.1.1 Full and Partial Compilation Unit Entries.

DW_AT_LLVM_lane_pc

For AMDGPU, the DW_AT_LLVM_lane_pc attribute is used to specify the program location of the separate lanes of a SIMT thread.

If the lane is an active lane then this will be the same as the current program location.

If the lane is inactive, but was active on entry to the subprogram, then this is the program location in the subprogram at which execution of the lane is conceptual positioned.

If the lane was not active on entry to the subprogram, then this will be the undefined location. A client debugger can check if the lane is part of a valid work-group by checking that the lane is in the range of the associated work-group within the grid, accounting for partial work-groups. If it is not, then the debugger can omit any information for the lane. Otherwise, the debugger may repeatedly unwind the stack and inspect the DW_AT_LLVM_lane_pc of the calling subprogram until it finds a non-undefined location. Conceptually the lane only has the call frames that it has a non-undefined DW_AT_LLVM_lane_pc.

The following example illustrates how the AMDGPU backend can generate a DWARF location list expression for the nested IF/THEN/ELSE structures of the following subprogram pseudo code for a target with 64 lanes per wavefront.

 1SUBPROGRAM X
 2BEGIN
 3  a;
 4  IF (c1) THEN
 5    b;
 6    IF (c2) THEN
 7      c;
 8    ELSE
 9      d;
10    ENDIF
11    e;
12  ELSE
13    f;
14  ENDIF
15  g;
16END

The AMDGPU backend may generate the following pseudo LLVM MIR to manipulate the execution mask (EXEC) to linearize the control flow. The condition is evaluated to make a mask of the lanes for which the condition evaluates to true. First the THEN region is executed by setting the EXEC mask to the logical AND of the current EXEC mask with the condition mask. Then the ELSE region is executed by negating the EXEC mask and logical AND of the saved EXEC mask at the start of the region. After the IF/THEN/ELSE region the EXEC mask is restored to the value it had at the beginning of the region. This is shown below. Other approaches are possible, but the basic concept is the same.

 1$lex_start:
 2  a;
 3  %1 = EXEC
 4  %2 = c1
 5$lex_1_start:
 6  EXEC = %1 & %2
 7$if_1_then:
 8    b;
 9    %3 = EXEC
10    %4 = c2
11$lex_1_1_start:
12    EXEC = %3 & %4
13$lex_1_1_then:
14      c;
15    EXEC = ~EXEC & %3
16$lex_1_1_else:
17      d;
18    EXEC = %3
19$lex_1_1_end:
20    e;
21  EXEC = ~EXEC & %1
22$lex_1_else:
23    f;
24  EXEC = %1
25$lex_1_end:
26  g;
27$lex_end:

To create the DWARF location list expression that defines the location description of a vector of lane program locations, the LLVM MIR DBG_VALUE pseudo instruction can be used to annotate the linearized control flow. This can be done by defining an artificial variable for the lane PC. The DWARF location list expression created for it is used as the value of the DW_AT_LLVM_lane_pc attribute on the subprogram’s debugger information entry.

A DWARF procedure is defined for each well nested structured control flow region which provides the conceptual lane program location for a lane if it is not active (namely it is divergent). The DWARF operation expression for each region conceptually inherits the value of the immediately enclosing region and modifies it according to the semantics of the region.

For an IF/THEN/ELSE region the divergent program location is at the start of the region for the THEN region since it is executed first. For the ELSE region the divergent program location is at the end of the IF/THEN/ELSE region since the THEN region has completed.

The lane PC artificial variable is assigned at each region transition. It uses the immediately enclosing region’s DWARF procedure to compute the program location for each lane assuming they are divergent, and then modifies the result by inserting the current program location for each lane that the EXEC mask indicates is active.

By having separate DWARF procedures for each region, they can be reused to define the value for any nested region. This reduces the total size of the DWARF operation expressions.

The following provides an example using pseudo LLVM MIR.

  1$lex_start:
  2  DEFINE_DWARF %__uint_64 = DW_TAG_base_type[
  3    DW_AT_name = "__uint64";
  4    DW_AT_byte_size = 8;
  5    DW_AT_encoding = DW_ATE_unsigned;
  6  ];
  7  DEFINE_DWARF %__active_lane_pc = DW_TAG_dwarf_procedure[
  8    DW_AT_name = "__active_lane_pc";
  9    DW_AT_location = [
 10      DW_OP_regx PC;
 11      DW_OP_LLVM_extend 64, 64;
 12      DW_OP_regval_type EXEC, %uint_64;
 13      DW_OP_LLVM_select_bit_piece 64, 64;
 14    ];
 15  ];
 16  DEFINE_DWARF %__divergent_lane_pc = DW_TAG_dwarf_procedure[
 17    DW_AT_name = "__divergent_lane_pc";
 18    DW_AT_location = [
 19      DW_OP_LLVM_undefined;
 20      DW_OP_LLVM_extend 64, 64;
 21    ];
 22  ];
 23  DBG_VALUE $noreg, $noreg, %DW_AT_LLVM_lane_pc, DIExpression[
 24    DW_OP_call_ref %__divergent_lane_pc;
 25    DW_OP_call_ref %__active_lane_pc;
 26  ];
 27  a;
 28  %1 = EXEC;
 29  DBG_VALUE %1, $noreg, %__lex_1_save_exec;
 30  %2 = c1;
 31$lex_1_start:
 32  EXEC = %1 & %2;
 33$lex_1_then:
 34    DEFINE_DWARF %__divergent_lane_pc_1_then = DW_TAG_dwarf_procedure[
 35      DW_AT_name = "__divergent_lane_pc_1_then";
 36      DW_AT_location = DIExpression[
 37        DW_OP_call_ref %__divergent_lane_pc;
 38        DW_OP_addrx &lex_1_start;
 39        DW_OP_stack_value;
 40        DW_OP_LLVM_extend 64, 64;
 41        DW_OP_call_ref %__lex_1_save_exec;
 42        DW_OP_deref_type 64, %__uint_64;
 43        DW_OP_LLVM_select_bit_piece 64, 64;
 44      ];
 45    ];
 46    DBG_VALUE $noreg, $noreg, %DW_AT_LLVM_lane_pc, DIExpression[
 47      DW_OP_call_ref %__divergent_lane_pc_1_then;
 48      DW_OP_call_ref %__active_lane_pc;
 49    ];
 50    b;
 51    %3 = EXEC;
 52    DBG_VALUE %3, %__lex_1_1_save_exec;
 53    %4 = c2;
 54$lex_1_1_start:
 55    EXEC = %3 & %4;
 56$lex_1_1_then:
 57      DEFINE_DWARF %__divergent_lane_pc_1_1_then = DW_TAG_dwarf_procedure[
 58        DW_AT_name = "__divergent_lane_pc_1_1_then";
 59        DW_AT_location = DIExpression[
 60          DW_OP_call_ref %__divergent_lane_pc_1_then;
 61          DW_OP_addrx &lex_1_1_start;
 62          DW_OP_stack_value;
 63          DW_OP_LLVM_extend 64, 64;
 64          DW_OP_call_ref %__lex_1_1_save_exec;
 65          DW_OP_deref_type 64, %__uint_64;
 66          DW_OP_LLVM_select_bit_piece 64, 64;
 67        ];
 68      ];
 69      DBG_VALUE $noreg, $noreg, %DW_AT_LLVM_lane_pc, DIExpression[
 70        DW_OP_call_ref %__divergent_lane_pc_1_1_then;
 71        DW_OP_call_ref %__active_lane_pc;
 72      ];
 73      c;
 74    EXEC = ~EXEC & %3;
 75$lex_1_1_else:
 76      DEFINE_DWARF %__divergent_lane_pc_1_1_else = DW_TAG_dwarf_procedure[
 77        DW_AT_name = "__divergent_lane_pc_1_1_else";
 78        DW_AT_location = DIExpression[
 79          DW_OP_call_ref %__divergent_lane_pc_1_then;
 80          DW_OP_addrx &lex_1_1_end;
 81          DW_OP_stack_value;
 82          DW_OP_LLVM_extend 64, 64;
 83          DW_OP_call_ref %__lex_1_1_save_exec;
 84          DW_OP_deref_type 64, %__uint_64;
 85          DW_OP_LLVM_select_bit_piece 64, 64;
 86        ];
 87      ];
 88      DBG_VALUE $noreg, $noreg, %DW_AT_LLVM_lane_pc, DIExpression[
 89        DW_OP_call_ref %__divergent_lane_pc_1_1_else;
 90        DW_OP_call_ref %__active_lane_pc;
 91      ];
 92      d;
 93    EXEC = %3;
 94$lex_1_1_end:
 95    DBG_VALUE $noreg, $noreg, %DW_AT_LLVM_lane_pc, DIExpression[
 96      DW_OP_call_ref %__divergent_lane_pc;
 97      DW_OP_call_ref %__active_lane_pc;
 98    ];
 99    e;
100  EXEC = ~EXEC & %1;
101$lex_1_else:
102    DEFINE_DWARF %__divergent_lane_pc_1_else = DW_TAG_dwarf_procedure[
103      DW_AT_name = "__divergent_lane_pc_1_else";
104      DW_AT_location = DIExpression[
105        DW_OP_call_ref %__divergent_lane_pc;
106        DW_OP_addrx &lex_1_end;
107        DW_OP_stack_value;
108        DW_OP_LLVM_extend 64, 64;
109        DW_OP_call_ref %__lex_1_save_exec;
110        DW_OP_deref_type 64, %__uint_64;
111        DW_OP_LLVM_select_bit_piece 64, 64;
112      ];
113    ];
114    DBG_VALUE $noreg, $noreg, %DW_AT_LLVM_lane_pc, DIExpression[
115      DW_OP_call_ref %__divergent_lane_pc_1_else;
116      DW_OP_call_ref %__active_lane_pc;
117    ];
118    f;
119  EXEC = %1;
120$lex_1_end:
121  DBG_VALUE $noreg, $noreg, %DW_AT_LLVM_lane_pc DIExpression[
122    DW_OP_call_ref %__divergent_lane_pc;
123    DW_OP_call_ref %__active_lane_pc;
124  ];
125  g;
126$lex_end:

The DWARF procedure %__active_lane_pc is used to update the lane pc elements that are active, with the current program location.

Artificial variables %__lex_1_save_exec and %__lex_1_1_save_exec are created for the execution masks saved on entry to a region. Using the DBG_VALUE pseudo instruction, location list entries will be created that describe where the artificial variables are allocated at any given program location. The compiler may allocate them to registers or spill them to memory.

The DWARF procedures for each region use the values of the saved execution mask artificial variables to only update the lanes that are active on entry to the region. All other lanes retain the value of the enclosing region where they were last active. If they were not active on entry to the subprogram, then will have the undefined location description.

Other structured control flow regions can be handled similarly. For example, loops would set the divergent program location for the region at the end of the loop. Any lanes active will be in the loop, and any lanes not active must have exited the loop.

An IF/THEN/ELSEIF/ELSEIF/... region can be treated as a nest of IF/THEN/ELSE regions.

The DWARF procedures can use the active lane artificial variable described in DW_AT_LLVM_active_lane rather than the actual EXEC mask in order to support whole or quad wavefront mode.

DW_AT_LLVM_active_lane

The DW_AT_LLVM_active_lane attribute on a subprogram debugger information entry is used to specify the lanes that are conceptually active for a SIMT thread.

The execution mask may be modified to implement whole or quad wavefront mode operations. For example, all lanes may need to temporarily be made active to execute a whole wavefront operation. Such regions would save the EXEC mask, update it to enable the necessary lanes, perform the operations, and then restore the EXEC mask from the saved value. While executing the whole wavefront region, the conceptual execution mask is the saved value, not the EXEC value.

This is handled by defining an artificial variable for the active lane mask. The active lane mask artificial variable would be the actual EXEC mask for normal regions, and the saved execution mask for regions where the mask is temporarily updated. The location list expression created for this artificial variable is used to define the value of the DW_AT_LLVM_active_lane attribute.

DW_AT_LLVM_augmentation

For AMDGPU, the DW_AT_LLVM_augmentation attribute of a compilation unit debugger information entry has the following value for the augmentation string:

[amdgpu:v0.0]

The “vX.Y” specifies the major X and minor Y version number of the AMDGPU extensions used in the DWARF of the compilation unit. The version number conforms to [SEMVER].

Call Frame Information

DWARF Call Frame Information (CFI) describes how a consumer can virtually unwind call frames in a running process or core dump. See DWARF Version 5 section 6.4 and A.6.4 Call Frame Information.

For AMDGPU, the Common Information Entry (CIE) fields have the following values:

  1. augmentation string contains the following null-terminated UTF-8 string:

    [amd:v0.0]

    The vX.Y specifies the major X and minor Y version number of the AMDGPU extensions used in this CIE or to the FDEs that use it. The version number conforms to [SEMVER].

  2. address_size for the Global address space is defined in Address Space Identifier.

  3. segment_selector_size is 0 as AMDGPU does not use a segment selector.

  4. code_alignment_factor is 4 bytes.

  5. data_alignment_factor is 4 bytes.

  6. return_address_register is PC_32 for 32-bit processes and PC_64 for 64-bit processes defined in Register Identifier.

  7. initial_instructions Since a subprogram X with fewer registers can be called from subprogram Y that has more allocated, X will not change any of the extra registers as it cannot access them. Therefore, the default rule for all columns is same value.

For AMDGPU the register number follows the numbering defined in Register Identifier.

For AMDGPU the instructions are variable size. A consumer can subtract 1 from the return address to get the address of a byte within the call site instructions. See DWARF Version 5 section 6.4.4.

Accelerated Access

See DWARF Version 5 section 6.1.

Lookup By Name Section Header

See DWARF Version 5 section 6.1.1.4.1 and A.6.1.1 Lookup By Name.

For AMDGPU the lookup by name section header table:

augmentation_string_size (uword)

Set to the length of the augmentation_string value which is always a multiple of 4.

augmentation_string (sequence of UTF-8 characters)

Contains the following UTF-8 string null padded to a multiple of 4 bytes:

[amdgpu:v0.0]

The “vX.Y” specifies the major X and minor Y version number of the AMDGPU extensions used in the DWARF of this index. The version number conforms to [SEMVER].

Note

This is different to the DWARF Version 5 definition that requires the first 4 characters to be the vendor ID. But this is consistent with the other augmentation strings and does allow multiple vendor contributions. However, backwards compatibility may be more desirable.

Lookup By Address Section Header

See DWARF Version 5 section 6.1.2.

For AMDGPU the lookup by address section header table:

address_size (ubyte)

Match the address size for the Global address space defined in Address Space Identifier.

segment_selector_size (ubyte)

AMDGPU does not use a segment selector so this is 0. The entries in the .debug_aranges do not have a segment selector.

Line Number Information

See DWARF Version 5 section 6.2 and A.6.2 Line Number Information.

AMDGPU does not use the isa state machine registers and always sets it to 0. The instruction set must be obtained from the ELF file header e_flags field in the EF_AMDGPU_MACH bit position (see ELF Header). See DWARF Version 5 section 6.2.2.

For AMDGPU the line number program header fields have the following values (see DWARF Version 5 section 6.2.4):

address_size (ubyte)

Matches the address size for the Global address space defined in Address Space Identifier.

segment_selector_size (ubyte)

AMDGPU does not use a segment selector so this is 0.

minimum_instruction_length (ubyte)

For GFX9-GFX11 this is 4.

maximum_operations_per_instruction (ubyte)

For GFX9-GFX11 this is 1.

Source text for online-compiled programs (for example, those compiled by the OpenCL language runtime) may be embedded into the DWARF Version 5 line table. See DWARF Version 5 section 6.2.4.1 which is updated by DWARF Extensions For Heterogeneous Debugging section DW_LNCT_LLVM_source.

The Clang option used to control source embedding in AMDGPU is defined in AMDGPU Clang Debug Options.

Table 49 AMDGPU Clang Debug Options

Debug Flag

Description

-g[no-]embed-source

Enable/disable embedding source text in DWARF debug sections. Useful for environments where source cannot be written to disk, such as when performing online compilation.

For example:

-gembed-source

Enable the embedded source.

-gno-embed-source

Disable the embedded source.

32-Bit and 64-Bit DWARF Formats

See DWARF Version 5 section 7.4 and A.7.4 32-Bit and 64-Bit DWARF Formats.

For AMDGPU:

  • For the amdgcn target architecture only the 64-bit process address space is supported.

  • The producer can generate either 32-bit or 64-bit DWARF format. LLVM generates the 32-bit DWARF format.

Unit Headers

For AMDGPU the following values apply for each of the unit headers described in DWARF Version 5 sections 7.5.1.1, 7.5.1.2, and 7.5.1.3:

address_size (ubyte)

Matches the address size for the Global address space defined in Address Space Identifier.

Code Conventions

This section provides code conventions used for each supported target triple OS (see Target Triples).

AMDHSA

This section provides code conventions used when the target triple OS is amdhsa (see Target Triples).

Code Object Metadata

The code object metadata specifies extensible metadata associated with the code objects executed on HSA [HSA] compatible runtimes (see AMDGPU Operating Systems). The encoding and semantics of this metadata depends on the code object version; see Code Object V2 Metadata, Code Object V3 Metadata, Code Object V4 Metadata and Code Object V5 Metadata.

Code object metadata is specified in a note record (see Note Records) and is required when the target triple OS is amdhsa (see Target Triples). It must contain the minimum information necessary to support the HSA compatible runtime kernel queries. For example, the segment sizes needed in a dispatch packet. In addition, a high-level language runtime may require other information to be included. For example, the AMD OpenCL runtime records kernel argument information.

Code Object V2 Metadata

Warning

Code object V2 generation is no longer supported by this version of LLVM.

Code object V2 metadata is specified by the NT_AMD_HSA_METADATA note record (see Code Object V2 Note Records).

The metadata is specified as a YAML formatted string (see [YAML] and YAML I/O).

The metadata is represented as a single YAML document comprised of the mapping defined in table AMDHSA Code Object V2 Metadata Map and referenced tables.

For boolean values, the string values of false and true are used for false and true respectively.

Additional information can be added to the mappings. To avoid conflicts, any non-AMD key names should be prefixed by “vendor-name.”.

Table 50 AMDHSA Code Object V2 Metadata Map

String Key

Value Type

Required?

Description

“Version”

sequence of 2 integers

Required

  • The first integer is the major version. Currently 1.

  • The second integer is the minor version. Currently 0.

“Printf”

sequence of strings

Each string is encoded information about a printf function call. The encoded information is organized as fields separated by colon (‘:’):

ID:N:S[0]:S[1]:...:S[N-1]:FormatString

where:

ID

A 32-bit integer as a unique id for each printf function call

N

A 32-bit integer equal to the number of arguments of printf function call minus 1

S[i] (where i = 0, 1, … , N-1)

32-bit integers for the size in bytes of the i-th FormatString argument of the printf function call

FormatString

The format string passed to the printf function call.

“Kernels”

sequence of mapping

Required

Sequence of the mappings for each kernel in the code object. See AMDHSA Code Object V2 Kernel Metadata Map for the definition of the mapping.
Table 51 AMDHSA Code Object V2 Kernel Metadata Map

String Key

Value Type

Required?

Description

“Name”

string

Required

Source name of the kernel.

“SymbolName”

string

Required

Name of the kernel descriptor ELF symbol.

“Language”

string

Source language of the kernel. Values include:

  • “OpenCL C”

  • “OpenCL C++”

  • “HCC”

  • “OpenMP”

“LanguageVersion”

sequence of 2 integers

  • The first integer is the major version.

  • The second integer is the minor version.

“Attrs”

mapping

Mapping of kernel attributes. See AMDHSA Code Object V2 Kernel Attribute Metadata Map for the mapping definition.

“Args”

sequence of mapping

Sequence of mappings of the kernel arguments. See AMDHSA Code Object V2 Kernel Argument Metadata Map for the definition of the mapping.

“CodeProps”

mapping

Mapping of properties related to the kernel code. See AMDHSA Code Object V2 Kernel Code Properties Metadata Map for the mapping definition.
Table 52 AMDHSA Code Object V2 Kernel Attribute Metadata Map

String Key

Value Type

Required?

Description

“ReqdWorkGroupSize”

sequence of 3 integers

If not 0, 0, 0 then all values must be >=1 and the dispatch work-group size X, Y, Z must correspond to the specified values. Defaults to 0, 0, 0.

Corresponds to the OpenCL reqd_work_group_size attribute.

“WorkGroupSizeHint”

sequence of 3 integers

The dispatch work-group size X, Y, Z is likely to be the specified values.

Corresponds to the OpenCL work_group_size_hint attribute.

“VecTypeHint”

string

The name of a scalar or vector type.

Corresponds to the OpenCL vec_type_hint attribute.

“RuntimeHandle”

string

The external symbol name associated with a kernel. OpenCL runtime allocates a global buffer for the symbol and saves the kernel’s address to it, which is used for device side enqueueing. Only available for device side enqueued kernels.
Table 53 AMDHSA Code Object V2 Kernel Argument Metadata Map

String Key

Value Type

Required?

Description

“Name”

string

Kernel argument name.

“TypeName”

string

Kernel argument type name.

“Size”

integer

Required

Kernel argument size in bytes.

“Align”

integer

Required

Kernel argument alignment in bytes. Must be a power of two.

“ValueKind”

string

Required

Kernel argument kind that specifies how to set up the corresponding argument. Values include:

“ByValue”

The argument is copied directly into the kernarg.

“GlobalBuffer”

A global address space pointer to the buffer data is passed in the kernarg.

“DynamicSharedPointer”

A group address space pointer to dynamically allocated LDS is passed in the kernarg.

“Sampler”

A global address space pointer to a S# is passed in the kernarg.

“Image”

A global address space pointer to a T# is passed in the kernarg.

“Pipe”

A global address space pointer to an OpenCL pipe is passed in the kernarg.

“Queue”

A global address space pointer to an OpenCL device enqueue queue is passed in the kernarg.

“HiddenGlobalOffsetX”

The OpenCL grid dispatch global offset for the X dimension is passed in the kernarg.

“HiddenGlobalOffsetY”

The OpenCL grid dispatch global offset for the Y dimension is passed in the kernarg.

“HiddenGlobalOffsetZ”

The OpenCL grid dispatch global offset for the Z dimension is passed in the kernarg.

“HiddenNone”

An argument that is not used by the kernel. Space needs to be left for it, but it does not need to be set up.

“HiddenPrintfBuffer”

A global address space pointer to the runtime printf buffer is passed in kernarg. Mutually exclusive with “HiddenHostcallBuffer”.

“HiddenHostcallBuffer”

A global address space pointer to the runtime hostcall buffer is passed in kernarg. Mutually exclusive with “HiddenPrintfBuffer”.

“HiddenDefaultQueue”

A global address space pointer to the OpenCL device enqueue queue that should be used by the kernel by default is passed in the kernarg.

“HiddenCompletionAction”

A global address space pointer to help link enqueued kernels into the ancestor tree for determining when the parent kernel has finished.

“HiddenMultiGridSyncArg”

A global address space pointer for multi-grid synchronization is passed in the kernarg.

“ValueType”

string

Unused and deprecated. This should no longer be emitted, but is accepted for compatibility.

“PointeeAlign”

integer

Alignment in bytes of pointee type for pointer type kernel argument. Must be a power of 2. Only present if “ValueKind” is “DynamicSharedPointer”.

“AddrSpaceQual”

string

Kernel argument address space qualifier. Only present if “ValueKind” is “GlobalBuffer” or “DynamicSharedPointer”. Values are:

  • “Private”

  • “Global”

  • “Constant”

  • “Local”

  • “Generic”

  • “Region”

“AccQual”

string

Kernel argument access qualifier. Only present if “ValueKind” is “Image” or “Pipe”. Values are:

  • “ReadOnly”

  • “WriteOnly”

  • “ReadWrite”

“ActualAccQual”

string

The actual memory accesses performed by the kernel on the kernel argument. Only present if “ValueKind” is “GlobalBuffer”, “Image”, or “Pipe”. This may be more restrictive than indicated by “AccQual” to reflect what the kernel actual does. If not present then the runtime must assume what is implied by “AccQual” and “IsConst”. Values are:

  • “ReadOnly”

  • “WriteOnly”

  • “ReadWrite”

“IsConst”

boolean

Indicates if the kernel argument is const qualified. Only present if “ValueKind” is “GlobalBuffer”.

“IsRestrict”

boolean

Indicates if the kernel argument is restrict qualified. Only present if “ValueKind” is “GlobalBuffer”.

“IsVolatile”

boolean

Indicates if the kernel argument is volatile qualified. Only present if “ValueKind” is “GlobalBuffer”.

“IsPipe”

boolean

Indicates if the kernel argument is pipe qualified. Only present if “ValueKind” is “Pipe”.
Table 54 AMDHSA Code Object V2 Kernel Code Properties Metadata Map

String Key

Value Type

Required?

Description

“KernargSegmentSize”

integer

Required

The size in bytes of the kernarg segment that holds the values of the arguments to the kernel.

“GroupSegmentFixedSize”

integer

Required

The amount of group segment memory required by a work-group in bytes. This does not include any dynamically allocated group segment memory that may be added when the kernel is dispatched.

“PrivateSegmentFixedSize”

integer

Required

The amount of fixed private address space memory required for a work-item in bytes. If the kernel uses a dynamic call stack then additional space must be added to this value for the call stack.

“KernargSegmentAlign”

integer

Required

The maximum byte alignment of arguments in the kernarg segment. Must be a power of 2.

“WavefrontSize”

integer

Required

Wavefront size. Must be a power of 2.

“NumSGPRs”

integer

Required

Number of scalar registers used by a wavefront for GFX6-GFX11. This includes the special SGPRs for VCC, Flat Scratch (GFX7-GFX10) and XNACK (for GFX8-GFX10). It does not include the 16 SGPR added if a trap handler is enabled. It is not rounded up to the allocation granularity.

“NumVGPRs”

integer

Required

Number of vector registers used by each work-item for GFX6-GFX11

“MaxFlatWorkGroupSize”

integer

Required

Maximum flat work-group size supported by the kernel in work-items. Must be >=1 and consistent with ReqdWorkGroupSize if not 0, 0, 0.

“NumSpilledSGPRs”

integer

Number of stores from a scalar register to a register allocator created spill location.

“NumSpilledVGPRs”

integer

Number of stores from a vector register to a register allocator created spill location.
Code Object V3 Metadata

Warning

Code object V3 generation is no longer supported by this version of LLVM.

Code object V3 and above metadata is specified by the NT_AMDGPU_METADATA note record (see Code Object V3 and Above Note Records).

The metadata is represented as Message Pack formatted binary data (see [MsgPack]). The top level is a Message Pack map that includes the keys defined in table AMDHSA Code Object V3 Metadata Map and referenced tables.

Additional information can be added to the maps. To avoid conflicts, any key names should be prefixed by “vendor-name.” where vendor-name can be the name of the vendor and specific vendor tool that generates the information. The prefix is abbreviated to simply “.” when it appears within a map that has been added by the same vendor-name.

Table 55 AMDHSA Code Object V3 Metadata Map

String Key

Value Type

Required?

Description

“amdhsa.version”

sequence of 2 integers

Required

  • The first integer is the major version. Currently 1.

  • The second integer is the minor version. Currently 0.

“amdhsa.printf”

sequence of strings

Each string is encoded information about a printf function call. The encoded information is organized as fields separated by colon (‘:’):

ID:N:S[0]:S[1]:...:S[N-1]:FormatString

where:

ID

A 32-bit integer as a unique id for each printf function call

N

A 32-bit integer equal to the number of arguments of printf function call minus 1

S[i] (where i = 0, 1, … , N-1)

32-bit integers for the size in bytes of the i-th FormatString argument of the printf function call

FormatString

The format string passed to the printf function call.

“amdhsa.kernels”

sequence of map

Required

Sequence of the maps for each kernel in the code object. See AMDHSA Code Object V3 Kernel Metadata Map for the definition of the keys included in that map.
Table 56 AMDHSA Code Object V3 Kernel Metadata Map

String Key

Value Type

Required?

Description

“.name”

string

Required

Source name of the kernel.

“.symbol”

string

Required

Name of the kernel descriptor ELF symbol.

“.language”

string

Source language of the kernel. Values include:

  • “OpenCL C”

  • “OpenCL C++”

  • “HCC”

  • “HIP”

  • “OpenMP”

  • “Assembler”

“.language_version”

sequence of 2 integers

  • The first integer is the major version.

  • The second integer is the minor version.

“.args”

sequence of map

Sequence of maps of the kernel arguments. See AMDHSA Code Object V3 Kernel Argument Metadata Map for the definition of the keys included in that map.

“.reqd_workgroup_size”

sequence of 3 integers

If not 0, 0, 0 then all values must be >=1 and the dispatch work-group size X, Y, Z must correspond to the specified values. Defaults to 0, 0, 0.

Corresponds to the OpenCL reqd_work_group_size attribute.

“.workgroup_size_hint”

sequence of 3 integers

The dispatch work-group size X, Y, Z is likely to be the specified values.

Corresponds to the OpenCL work_group_size_hint attribute.

“.vec_type_hint”

string

The name of a scalar or vector type.

Corresponds to the OpenCL vec_type_hint attribute.

“.device_enqueue_symbol”

string

The external symbol name associated with a kernel. OpenCL runtime allocates a global buffer for the symbol and saves the kernel’s address to it, which is used for device side enqueueing. Only available for device side enqueued kernels.

“.kernarg_segment_size”

integer

Required

The size in bytes of the kernarg segment that holds the values of the arguments to the kernel.

“.group_segment_fixed_size”

integer

Required

The amount of group segment memory required by a work-group in bytes. This does not include any dynamically allocated group segment memory that may be added when the kernel is dispatched.

“.private_segment_fixed_size”

integer

Required

The amount of fixed private address space memory required for a work-item in bytes. If the kernel uses a dynamic call stack then additional space must be added to this value for the call stack.

“.kernarg_segment_align”

integer

Required

The maximum byte alignment of arguments in the kernarg segment. Must be a power of 2.

“.wavefront_size”

integer

Required

Wavefront size. Must be a power of 2.

“.sgpr_count”

integer

Required

Number of scalar registers required by a wavefront for GFX6-GFX9. A register is required if it is used explicitly, or if a higher numbered register is used explicitly. This includes the special SGPRs for VCC, Flat Scratch (GFX7-GFX9) and XNACK (for GFX8-GFX9). It does not include the 16 SGPR added if a trap handler is enabled. It is not rounded up to the allocation granularity.

“.vgpr_count”

integer

Required

Number of vector registers required by each work-item for GFX6-GFX9. A register is required if it is used explicitly, or if a higher numbered register is used explicitly.

“.agpr_count”

integer

Required

Number of accumulator registers required by each work-item for GFX90A, GFX908.

“.max_flat_workgroup_size”

integer

Required

Maximum flat work-group size supported by the kernel in work-items. Must be >=1 and consistent with ReqdWorkGroupSize if not 0, 0, 0.

“.sgpr_spill_count”

integer

Number of stores from a scalar register to a register allocator created spill location.

“.vgpr_spill_count”

integer

Number of stores from a vector register to a register allocator created spill location.

“.kind”

string

The kind of the kernel with the following values:

“normal”

Regular kernels.

“init”

These kernels must be invoked after loading the containing code object and must complete before any normal and fini kernels in the same code object are invoked.

“fini”

These kernels must be invoked before unloading the containing code object and after all init and normal kernels in the same code object have been invoked and completed.

If omitted, “normal” is assumed.

“.max_num_work_groups_{x,y,z}”

integer

The max number of launched work-groups in the X, Y, and Z dimensions. Each number must be >=1.
Table 57 AMDHSA Code Object V3 Kernel Argument Metadata Map

String Key

Value Type

Required?

Description

“.name”

string

Kernel argument name.

“.type_name”

string

Kernel argument type name.

“.size”

integer

Required

Kernel argument size in bytes.

“.offset”

integer

Required

Kernel argument offset in bytes. The offset must be a multiple of the alignment required by the argument.

“.value_kind”

string

Required

Kernel argument kind that specifies how to set up the corresponding argument. Values include:

“by_value”

The argument is copied directly into the kernarg.

“global_buffer”

A global address space pointer to the buffer data is passed in the kernarg.

“dynamic_shared_pointer”

A group address space pointer to dynamically allocated LDS is passed in the kernarg.

“sampler”

A global address space pointer to a S# is passed in the kernarg.

“image”

A global address space pointer to a T# is passed in the kernarg.

“pipe”

A global address space pointer to an OpenCL pipe is passed in the kernarg.

“queue”

A global address space pointer to an OpenCL device enqueue queue is passed in the kernarg.

“hidden_global_offset_x”

The OpenCL grid dispatch global offset for the X dimension is passed in the kernarg.

“hidden_global_offset_y”

The OpenCL grid dispatch global offset for the Y dimension is passed in the kernarg.

“hidden_global_offset_z”

The OpenCL grid dispatch global offset for the Z dimension is passed in the kernarg.

“hidden_none”

An argument that is not used by the kernel. Space needs to be left for it, but it does not need to be set up.

“hidden_printf_buffer”

A global address space pointer to the runtime printf buffer is passed in kernarg. Mutually exclusive with “hidden_hostcall_buffer” before Code Object V5.

“hidden_hostcall_buffer”

A global address space pointer to the runtime hostcall buffer is passed in kernarg. Mutually exclusive with “hidden_printf_buffer” before Code Object V5.

“hidden_default_queue”

A global address space pointer to the OpenCL device enqueue queue that should be used by the kernel by default is passed in the kernarg.

“hidden_completion_action”

A global address space pointer to help link enqueued kernels into the ancestor tree for determining when the parent kernel has finished.

“hidden_multigrid_sync_arg”

A global address space pointer for multi-grid synchronization is passed in the kernarg.

“.value_type”

string

Unused and deprecated. This should no longer be emitted, but is accepted for compatibility.

“.pointee_align”

integer

Alignment in bytes of pointee type for pointer type kernel argument. Must be a power of 2. Only present if “.value_kind” is “dynamic_shared_pointer”.

“.address_space”

string

Kernel argument address space qualifier. Only present if “.value_kind” is “global_buffer” or “dynamic_shared_pointer”. Values are:

  • “private”

  • “global”

  • “constant”

  • “local”

  • “generic”

  • “region”

“.access”

string

Kernel argument access qualifier. Only present if “.value_kind” is “image” or “pipe”. Values are:

  • “read_only”

  • “write_only”

  • “read_write”

“.actual_access”

string

The actual memory accesses performed by the kernel on the kernel argument. Only present if “.value_kind” is “global_buffer”, “image”, or “pipe”. This may be more restrictive than indicated by “.access” to reflect what the kernel actual does. If not present then the runtime must assume what is implied by “.access” and “.is_const” . Values are:

  • “read_only”

  • “write_only”

  • “read_write”

“.is_const”

boolean

Indicates if the kernel argument is const qualified. Only present if “.value_kind” is “global_buffer”.

“.is_restrict”

boolean

Indicates if the kernel argument is restrict qualified. Only present if “.value_kind” is “global_buffer”.

“.is_volatile”

boolean

Indicates if the kernel argument is volatile qualified. Only present if “.value_kind” is “global_buffer”.

“.is_pipe”

boolean

Indicates if the kernel argument is pipe qualified. Only present if “.value_kind” is “pipe”.
Code Object V4 Metadata
. warning::

Code object V4 is not the default code object version emitted by this version of LLVM.

Code object V4 metadata is the same as Code Object V3 Metadata with the changes and additions defined in table AMDHSA Code Object V4 Metadata Map Changes.

Table 58 AMDHSA Code Object V4 Metadata Map Changes

String Key

Value Type

Required?

Description

“amdhsa.version”

sequence of 2 integers

Required

  • The first integer is the major version. Currently 1.

  • The second integer is the minor version. Currently 1.

“amdhsa.target”

string

Required

The target name of the code using the syntax:

<target-triple> [ "-" <target-id> ]

A canonical target ID must be used. See Target Triples and Target ID.
Code Object V5 Metadata

Code object V5 metadata is the same as Code Object V4 Metadata with the changes defined in table AMDHSA Code Object V5 Metadata Map Changes, table AMDHSA Code Object V5 Kernel Metadata Map Additions and table AMDHSA Code Object V5 Kernel Argument Metadata Map Additions and Changes.

Table 59 AMDHSA Code Object V5 Metadata Map Changes

String Key

Value Type

Required?

Description

“amdhsa.version”

sequence of 2 integers

Required

  • The first integer is the major version. Currently 1.

  • The second integer is the minor version. Currently 2.
Table 60 AMDHSA Code Object V5 Kernel Metadata Map Additions

String Key

Value Type

Required?

Description

“.uses_dynamic_stack”

boolean

Indicates if the generated machine code is using a dynamically sized stack.

“.workgroup_processor_mode”

boolean

(GFX10+) Controls ENABLE_WGP_MODE in Code Object V3 Kernel Descriptor.
Table 61 AMDHSA Code Object V5 Kernel Attribute Metadata Map

String Key

Value Type

Required?

Description

“.uniform_work_group_size”

integer

Indicates if the kernel requires that each dimension of global size is a multiple of corresponding dimension of work-group size. Value of 1 implies true and value of 0 implies false. Metadata is only emitted when value is 1.
Table 62 AMDHSA Code Object V5 Kernel Argument Metadata Map Additions and Changes

String Key

Value Type

Required?

Description

“.value_kind”

string

Required

Kernel argument kind that specifies how to set up the corresponding argument. Values include: the same as code object V3 metadata (see AMDHSA Code Object V3 Kernel Argument Metadata Map) with the following additions:

“hidden_block_count_x”

The grid dispatch work-group count for the X dimension is passed in the kernarg. Some languages, such as OpenCL, support a last work-group in each dimension being partial. This count only includes the non-partial work-group count. This is not the same as the value in the AQL dispatch packet, which has the grid size in work-items.

“hidden_block_count_y”

The grid dispatch work-group count for the Y dimension is passed in the kernarg. Some languages, such as OpenCL, support a last work-group in each dimension being partial. This count only includes the non-partial work-group count. This is not the same as the value in the AQL dispatch packet, which has the grid size in work-items. If the grid dimensionality is 1, then must be 1.

“hidden_block_count_z”

The grid dispatch work-group count for the Z dimension is passed in the kernarg. Some languages, such as OpenCL, support a last work-group in each dimension being partial. This count only includes the non-partial work-group count. This is not the same as the value in the AQL dispatch packet, which has the grid size in work-items. If the grid dimensionality is 1 or 2, then must be 1.

“hidden_group_size_x”

The grid dispatch work-group size for the X dimension is passed in the kernarg. This size only applies to the non-partial work-groups. This is the same value as the AQL dispatch packet work-group size.

“hidden_group_size_y”

The grid dispatch work-group size for the Y dimension is passed in the kernarg. This size only applies to the non-partial work-groups. This is the same value as the AQL dispatch packet work-group size. If the grid dimensionality is 1, then must be 1.

“hidden_group_size_z”

The grid dispatch work-group size for the Z dimension is passed in the kernarg. This size only applies to the non-partial work-groups. This is the same value as the AQL dispatch packet work-group size. If the grid dimensionality is 1 or 2, then must be 1.

“hidden_remainder_x”

The grid dispatch work group size of the partial work group of the X dimension, if it exists. Must be zero if a partial work group does not exist in the X dimension.

“hidden_remainder_y”

The grid dispatch work group size of the partial work group of the Y dimension, if it exists. Must be zero if a partial work group does not exist in the Y dimension.

“hidden_remainder_z”

The grid dispatch work group size of the partial work group of the Z dimension, if it exists. Must be zero if a partial work group does not exist in the Z dimension.

“hidden_grid_dims”

The grid dispatch dimensionality. This is the same value as the AQL dispatch packet dimensionality. Must be a value between 1 and 3.

“hidden_heap_v1”

A global address space pointer to an initialized memory buffer that conforms to the requirements of the malloc/free device library V1 version implementation.

“hidden_dynamic_lds_size”

Size of the dynamically allocated LDS memory is passed in the kernarg.

“hidden_private_base”

The high 32 bits of the flat addressing private aperture base. Only used by GFX8 to allow conversion between private segment and flat addresses. See Flat Scratch.

“hidden_shared_base”

The high 32 bits of the flat addressing shared aperture base. Only used by GFX8 to allow conversion between shared segment and flat addresses. See Flat Scratch.

“hidden_queue_ptr”

A global memory address space pointer to the ROCm runtime struct amd_queue_t structure for the HSA queue of the associated dispatch AQL packet. It is only required for pre-GFX9 devices for the trap handler ABI (see Trap Handler ABI).

Kernel Dispatch

The HSA architected queuing language (AQL) defines a user space memory interface that can be used to control the dispatch of kernels, in an agent independent way. An agent can have zero or more AQL queues created for it using an HSA compatible runtime (see AMDGPU Operating Systems), in which AQL packets (all of which are 64 bytes) can be placed. See the HSA Platform System Architecture Specification [HSA] for the AQL queue mechanics and packet layouts.

The packet processor of a kernel agent is responsible for detecting and dispatching HSA kernels from the AQL queues associated with it. For AMD GPUs the packet processor is implemented by the hardware command processor (CP), asynchronous dispatch controller (ADC) and shader processor input controller (SPI).

An HSA compatible runtime can be used to allocate an AQL queue object. It uses the kernel mode driver to initialize and register the AQL queue with CP.

To dispatch a kernel the following actions are performed. This can occur in the CPU host program, or from an HSA kernel executing on a GPU.

  1. A pointer to an AQL queue for the kernel agent on which the kernel is to be executed is obtained.

  2. A pointer to the kernel descriptor (see Kernel Descriptor) of the kernel to execute is obtained. It must be for a kernel that is contained in a code object that was loaded by an HSA compatible runtime on the kernel agent with which the AQL queue is associated.

  3. Space is allocated for the kernel arguments using the HSA compatible runtime allocator for a memory region with the kernarg property for the kernel agent that will execute the kernel. It must be at least 16-byte aligned.

  4. Kernel argument values are assigned to the kernel argument memory allocation. The layout is defined in the HSA Programmer’s Language Reference [HSA]. For AMDGPU the kernel execution directly accesses the kernel argument memory in the same way constant memory is accessed. (Note that the HSA specification allows an implementation to copy the kernel argument contents to another location that is accessed by the kernel.)

  5. An AQL kernel dispatch packet is created on the AQL queue. The HSA compatible runtime api uses 64-bit atomic operations to reserve space in the AQL queue for the packet. The packet must be set up, and the final write must use an atomic store release to set the packet kind to ensure the packet contents are visible to the kernel agent. AQL defines a doorbell signal mechanism to notify the kernel agent that the AQL queue has been updated. These rules, and the layout of the AQL queue and kernel dispatch packet is defined in the HSA System Architecture Specification [HSA].

  6. A kernel dispatch packet includes information about the actual dispatch, such as grid and work-group size, together with information from the code object about the kernel, such as segment sizes. The HSA compatible runtime queries on the kernel symbol can be used to obtain the code object values which are recorded in the Code Object Metadata.

  7. CP executes micro-code and is responsible for detecting and setting up the GPU to execute the wavefronts of a kernel dispatch.

  8. CP ensures that when the a wavefront starts executing the kernel machine code, the scalar general purpose registers (SGPR) and vector general purpose registers (VGPR) are set up as required by the machine code. The required setup is defined in the Kernel Descriptor. The initial register state is defined in Initial Kernel Execution State.

  9. The prolog of the kernel machine code (see Kernel Prolog) sets up the machine state as necessary before continuing executing the machine code that corresponds to the kernel.

  10. When the kernel dispatch has completed execution, CP signals the completion signal specified in the kernel dispatch packet if not 0.

Memory Spaces

The memory space properties are:

Table 63 AMDHSA Memory Spaces

Memory Space Name

HSA Segment Name

Hardware Name

Address Size

NULL Value

Private

private

scratch

32

0x00000000

Local

group

LDS

32

0xFFFFFFFF

Global

global

global

64

0x0000000000000000

Constant

constant

same as global

64

0x0000000000000000

Generic

flat

flat

64

0x0000000000000000

Region

N/A

GDS

32

not implemented for AMDHSA

The global and constant memory spaces both use global virtual addresses, which are the same virtual address space used by the CPU. However, some virtual addresses may only be accessible to the CPU, some only accessible by the GPU, and some by both.

Using the constant memory space indicates that the data will not change during the execution of the kernel. This allows scalar read instructions to be used. The vector and scalar L1 caches are invalidated of volatile data before each kernel dispatch execution to allow constant memory to change values between kernel dispatches.

The local memory space uses the hardware Local Data Store (LDS) which is automatically allocated when the hardware creates work-groups of wavefronts, and freed when all the wavefronts of a work-group have terminated. The data store (DS) instructions can be used to access it.

The private memory space uses the hardware scratch memory support. If the kernel uses scratch, then the hardware allocates memory that is accessed using wavefront lane dword (4 byte) interleaving. The mapping used from private address to physical address is:

wavefront-scratch-base + (private-address * wavefront-size * 4) + (wavefront-lane-id * 4)

There are different ways that the wavefront scratch base address is determined by a wavefront (see Initial Kernel Execution State). This memory can be accessed in an interleaved manner using buffer instruction with the scratch buffer descriptor and per wavefront scratch offset, by the scratch instructions, or by flat instructions. If each lane of a wavefront accesses the same private address, the interleaving results in adjacent dwords being accessed and hence requires fewer cache lines to be fetched. Multi-dword access is not supported except by flat and scratch instructions in GFX9-GFX11.

The generic address space uses the hardware flat address support available in GFX7-GFX11. This uses two fixed ranges of virtual addresses (the private and local apertures), that are outside the range of addressible global memory, to map from a flat address to a private or local address.

FLAT instructions can take a flat address and access global, private (scratch) and group (LDS) memory depending on if the address is within one of the aperture ranges. Flat access to scratch requires hardware aperture setup and setup in the kernel prologue (see Flat Scratch). Flat access to LDS requires hardware aperture setup and M0 (GFX7-GFX8) register setup (see M0).

To convert between a segment address and a flat address the base address of the apertures address can be used. For GFX7-GFX8 these are available in the HSA AQL Queue the address of which can be obtained with Queue Ptr SGPR (see Initial Kernel Execution State). For GFX9-GFX11 the aperture base addresses are directly available as inline constant registers SRC_SHARED_BASE/LIMIT and SRC_PRIVATE_BASE/LIMIT. In 64 bit address mode the aperture sizes are 2^32 bytes and the base is aligned to 2^32 which makes it easier to convert from flat to segment or segment to flat.

Image and Samplers

Image and sample handles created by an HSA compatible runtime (see AMDGPU Operating Systems) are 64-bit addresses of a hardware 32-byte V# and 48 byte S# object respectively. In order to support the HSA query_sampler operations two extra dwords are used to store the HSA BRIG enumeration values for the queries that are not trivially deducible from the S# representation.

HSA Signals

HSA signal handles created by an HSA compatible runtime (see AMDGPU Operating Systems) are 64-bit addresses of a structure allocated in memory accessible from both the CPU and GPU. The structure is defined by the runtime and subject to change between releases. For example, see [AMD-ROCm-github].

HSA AQL Queue

The HSA AQL queue structure is defined by an HSA compatible runtime (see AMDGPU Operating Systems) and subject to change between releases. For example, see [AMD-ROCm-github]. For some processors it contains fields needed to implement certain language features such as the flat address aperture bases. It also contains fields used by CP such as managing the allocation of scratch memory.

Kernel Descriptor

A kernel descriptor consists of the information needed by CP to initiate the execution of a kernel, including the entry point address of the machine code that implements the kernel.

Code Object V3 Kernel Descriptor

CP microcode requires the Kernel descriptor to be allocated on 64-byte alignment.

The fields used by CP for code objects before V3 also match those specified in Code Object V3 Kernel Descriptor.

Table 64 Code Object V3 Kernel Descriptor

Bits

Size

Field Name

Description

31:0

4 bytes

GROUP_SEGMENT_FIXED_SIZE

The amount of fixed local address space memory required for a work-group in bytes. This does not include any dynamically allocated local address space memory that may be added when the kernel is dispatched.

63:32

4 bytes

PRIVATE_SEGMENT_FIXED_SIZE

The amount of fixed private address space memory required for a work-item in bytes. When this cannot be predicted, code object v4 and older sets this value to be higher than the minimum requirement.

95:64

4 bytes

KERNARG_SIZE

The size of the kernarg memory pointed to by the AQL dispatch packet. The kernarg memory is used to pass arguments to the kernel.

  • If the kernarg pointer in the dispatch packet is NULL then there are no kernel arguments.

  • If the kernarg pointer in the dispatch packet is not NULL and this value is 0 then the kernarg memory size is unspecified.

  • If the kernarg pointer in the dispatch packet is not NULL and this value is not 0 then the value specifies the kernarg memory size in bytes. It is recommended to provide a value as it may be used by CP to optimize making the kernarg memory visible to the kernel code.

127:96

4 bytes

Reserved, must be 0.

191:128

8 bytes

KERNEL_CODE_ENTRY_BYTE_OFFSET

Byte offset (possibly negative) from base address of kernel descriptor to kernel’s entry point instruction which must be 256 byte aligned.

351:192

20 bytes

Reserved, must be 0.

383:352

4 bytes

COMPUTE_PGM_RSRC3
GFX6-GFX9

Reserved, must be 0.

GFX90A, GFX940

Compute Shader (CS) program settings used by CP to set up COMPUTE_PGM_RSRC3 configuration register. See compute_pgm_rsrc3 for GFX90A, GFX940.

GFX10-GFX11

Compute Shader (CS) program settings used by CP to set up COMPUTE_PGM_RSRC3 configuration register. See compute_pgm_rsrc3 for GFX10-GFX11.

GFX12

Compute Shader (CS) program settings used by CP to set up COMPUTE_PGM_RSRC3 configuration register. See compute_pgm_rsrc3 for GFX12.

415:384

4 bytes

COMPUTE_PGM_RSRC1

Compute Shader (CS) program settings used by CP to set up COMPUTE_PGM_RSRC1 configuration register. See compute_pgm_rsrc1 for GFX6-GFX12.

447:416

4 bytes

COMPUTE_PGM_RSRC2

Compute Shader (CS) program settings used by CP to set up COMPUTE_PGM_RSRC2 configuration register. See compute_pgm_rsrc2 for GFX6-GFX12.

458:448

7 bits

See separate bits below.

Enable the setup of the SGPR user data registers (see Initial Kernel Execution State).

The total number of SGPR user data registers requested must not exceed 16 and match value in compute_pgm_rsrc2.user_sgpr.user_sgpr_count. Any requests beyond 16 will be ignored.

>448

1 bit

ENABLE_SGPR_PRIVATE_SEGMENT _BUFFER

If the Target Properties column of AMDGPU Processors specifies Architected flat scratch then not supported and must be 0,

>449

1 bit

ENABLE_SGPR_DISPATCH_PTR

>450

1 bit

ENABLE_SGPR_QUEUE_PTR

>451

1 bit

ENABLE_SGPR_KERNARG_SEGMENT_PTR

>452

1 bit

ENABLE_SGPR_DISPATCH_ID

>453

1 bit

ENABLE_SGPR_FLAT_SCRATCH_INIT

If the Target Properties column of AMDGPU Processors specifies Architected flat scratch then not supported and must be 0,

>454

1 bit

ENABLE_SGPR_PRIVATE_SEGMENT _SIZE

457:455

3 bits

Reserved, must be 0.

458

1 bit

ENABLE_WAVEFRONT_SIZE32
GFX6-GFX9

Reserved, must be 0.

GFX10-GFX11

  • If 0 execute in wavefront size 64 mode.

  • If 1 execute in native wavefront size 32 mode.

459

1 bit

USES_DYNAMIC_STACK

Indicates if the generated machine code is using a dynamically sized stack. This is only set in code object v5 and later.

463:460

4 bits

Reserved, must be 0.

470:464

7 bits

KERNARG_PRELOAD_SPEC_LENGTH
GFX6-GFX9

  • Reserved, must be 0.

GFX90A, GFX940

  • The number of dwords from the kernarg segment to preload into User SGPRs before kernel execution. (see Preloaded Kernel Arguments).

479:471

9 bits

KERNARG_PRELOAD_SPEC_OFFSET
GFX6-GFX9

  • Reserved, must be 0.

GFX90A, GFX940

511:480

4 bytes

Reserved, must be 0.

512

Total size 64 bytes.
Table 65 compute_pgm_rsrc1 for GFX6-GFX12

Bits

Size

Field Name

Description

5:0

6 bits

GRANULATED_WORKITEM_VGPR_COUNT

Number of vector register blocks used by each work-item; granularity is device specific:

GFX6-GFX9

  • vgprs_used 0..256

  • max(0, ceil(vgprs_used / 4) - 1)

GFX90A, GFX940

  • vgprs_used 0..512

  • vgprs_used = align(arch_vgprs, 4)

    • acc_vgprs

  • max(0, ceil(vgprs_used / 8) - 1)

GFX10-GFX12 (wavefront size 64)

  • max_vgpr 1..256

  • max(0, ceil(vgprs_used / 4) - 1)

GFX10-GFX12 (wavefront size 32)

  • max_vgpr 1..256

  • max(0, ceil(vgprs_used / 8) - 1)

Where vgprs_used is defined as the highest VGPR number explicitly referenced plus one.

Used by CP to set up COMPUTE_PGM_RSRC1.VGPRS.

The Assembler calculates this automatically for the selected processor from values provided to the .amdhsa_kernel directive by the .amdhsa_next_free_vgpr nested directive (see AMDHSA Kernel Assembler Directives).

9:6

4 bits

GRANULATED_WAVEFRONT_SGPR_COUNT

Number of scalar register blocks used by a wavefront; granularity is device specific:

GFX6-GFX8

  • sgprs_used 0..112

  • max(0, ceil(sgprs_used / 8) - 1)

GFX9

  • sgprs_used 0..112

  • 2 * max(0, ceil(sgprs_used / 16) - 1)

GFX10-GFX12

Reserved, must be 0. (128 SGPRs always allocated.)

Where sgprs_used is defined as the highest SGPR number explicitly referenced plus one, plus a target specific number of additional special SGPRs for VCC, FLAT_SCRATCH (GFX7+) and XNACK_MASK (GFX8+), and any additional target specific limitations. It does not include the 16 SGPRs added if a trap handler is enabled.

The target specific limitations and special SGPR layout are defined in the hardware documentation, which can be found in the Processors table.

Used by CP to set up COMPUTE_PGM_RSRC1.SGPRS.

The Assembler calculates this automatically for the selected processor from values provided to the .amdhsa_kernel directive by the .amdhsa_next_free_sgpr and .amdhsa_reserve_* nested directives (see AMDHSA Kernel Assembler Directives).

11:10

2 bits

PRIORITY

Must be 0.

Start executing wavefront at the specified priority.

CP is responsible for filling in COMPUTE_PGM_RSRC1.PRIORITY.

13:12

2 bits

FLOAT_ROUND_MODE_32

Wavefront starts execution with specified rounding mode for single (32 bit) floating point precision floating point operations.

Floating point rounding mode values are defined in Floating Point Rounding Mode Enumeration Values.

Used by CP to set up COMPUTE_PGM_RSRC1.FLOAT_MODE.

15:14

2 bits

FLOAT_ROUND_MODE_16_64

Wavefront starts execution with specified rounding denorm mode for half/double (16 and 64-bit) floating point precision floating point operations.

Floating point rounding mode values are defined in Floating Point Rounding Mode Enumeration Values.

Used by CP to set up COMPUTE_PGM_RSRC1.FLOAT_MODE.

17:16

2 bits

FLOAT_DENORM_MODE_32

Wavefront starts execution with specified denorm mode for single (32 bit) floating point precision floating point operations.

Floating point denorm mode values are defined in Floating Point Denorm Mode Enumeration Values.

Used by CP to set up COMPUTE_PGM_RSRC1.FLOAT_MODE.

19:18

2 bits

FLOAT_DENORM_MODE_16_64

Wavefront starts execution with specified denorm mode for half/double (16 and 64-bit) floating point precision floating point operations.

Floating point denorm mode values are defined in Floating Point Denorm Mode Enumeration Values.

Used by CP to set up COMPUTE_PGM_RSRC1.FLOAT_MODE.

20

1 bit

PRIV

Must be 0.

Start executing wavefront in privilege trap handler mode.

CP is responsible for filling in COMPUTE_PGM_RSRC1.PRIV.

21

1 bit

ENABLE_DX10_CLAMP

WG_RR_EN
GFX9-GFX11

Wavefront starts execution with DX10 clamp mode enabled. Used by the vector ALU to force DX10 style treatment of NaN’s (when set, clamp NaN to zero, otherwise pass NaN through).

Used by CP to set up COMPUTE_PGM_RSRC1.DX10_CLAMP.

GFX12

If 1, wavefronts are scheduled in a round-robin fashion with respect to the other wavefronts of the SIMD. Otherwise, wavefronts are scheduled in oldest age order.

CP is responsible for filling in COMPUTE_PGM_RSRC1.WG_RR_EN.

22

1 bit

DEBUG_MODE

Must be 0.

Start executing wavefront in single step mode.

CP is responsible for filling in COMPUTE_PGM_RSRC1.DEBUG_MODE.

23

1 bit

ENABLE_IEEE_MODE

DISABLE_PERF
GFX9-GFX11

Wavefront starts execution with IEEE mode enabled. Floating point opcodes that support exception flag gathering will quiet and propagate signaling-NaN inputs per IEEE 754-2008. Min_dx10 and max_dx10 become IEEE 754-2008 compliant due to signaling-NaN propagation and quieting.

Used by CP to set up COMPUTE_PGM_RSRC1.IEEE_MODE.

GFX12

Reserved. Must be 0.

24

1 bit

BULKY

Must be 0.

Only one work-group allowed to execute on a compute unit.

CP is responsible for filling in COMPUTE_PGM_RSRC1.BULKY.

25

1 bit

CDBG_USER

Must be 0.

Flag that can be used to control debugging code.

CP is responsible for filling in COMPUTE_PGM_RSRC1.CDBG_USER.

26

1 bit

FP16_OVFL
GFX6-GFX8

Reserved, must be 0.

GFX9-GFX12

Wavefront starts execution with specified fp16 overflow mode.

  • If 0, fp16 overflow generates +/-INF values.

  • If 1, fp16 overflow that is the result of an +/-INF input value or divide by 0 produces a +/-INF, otherwise clamps computed overflow to +/-MAX_FP16 as appropriate.

Used by CP to set up COMPUTE_PGM_RSRC1.FP16_OVFL.

28:27

2 bits

Reserved, must be 0.

29

1 bit

WGP_MODE
GFX6-GFX9

Reserved, must be 0.

GFX10-GFX12

  • If 0 execute work-groups in CU wavefront execution mode.

  • If 1 execute work-groups on in WGP wavefront execution mode.

See Memory Model.

Used by CP to set up COMPUTE_PGM_RSRC1.WGP_MODE.

30

1 bit

MEM_ORDERED
GFX6-GFX9

Reserved, must be 0.

GFX10-GFX12

Controls the behavior of the s_waitcnt’s vmcnt and vscnt counters.

  • If 0 vmcnt reports completion of load and atomic with return out of order with sample instructions, and the vscnt reports the completion of store and atomic without return in order.

  • If 1 vmcnt reports completion of load, atomic with return and sample instructions in order, and the vscnt reports the completion of store and atomic without return in order.

Used by CP to set up COMPUTE_PGM_RSRC1.MEM_ORDERED.

31

1 bit

FWD_PROGRESS
GFX6-GFX9

Reserved, must be 0.

GFX10-GFX12

  • If 0 execute SIMD wavefronts using oldest first policy.

  • If 1 execute SIMD wavefronts to ensure wavefronts will make some forward progress.

Used by CP to set up COMPUTE_PGM_RSRC1.FWD_PROGRESS.

32

Total size 4 bytes
Table 66 compute_pgm_rsrc2 for GFX6-GFX12

Bits

Size

Field Name

Description

0

1 bit

ENABLE_PRIVATE_SEGMENT

Used by CP to set up COMPUTE_PGM_RSRC2.SCRATCH_EN.

5:1

5 bits

USER_SGPR_COUNT

The total number of SGPR user data registers requested. This number must be greater than or equal to the number of user data registers enabled.

Used by CP to set up COMPUTE_PGM_RSRC2.USER_SGPR.

6

1 bit

ENABLE_TRAP_HANDLER
GFX6-GFX11

Must be 0.

This bit represents COMPUTE_PGM_RSRC2.TRAP_PRESENT, which is set by the CP if the runtime has installed a trap handler.

GFX12

Reserved, must be 0.

7

1 bit

ENABLE_SGPR_WORKGROUP_ID_X

Enable the setup of the system SGPR register for the work-group id in the X dimension (see Initial Kernel Execution State).

Used by CP to set up COMPUTE_PGM_RSRC2.TGID_X_EN.

8

1 bit

ENABLE_SGPR_WORKGROUP_ID_Y

Enable the setup of the system SGPR register for the work-group id in the Y dimension (see Initial Kernel Execution State).

Used by CP to set up COMPUTE_PGM_RSRC2.TGID_Y_EN.

9

1 bit

ENABLE_SGPR_WORKGROUP_ID_Z

Enable the setup of the system SGPR register for the work-group id in the Z dimension (see Initial Kernel Execution State).

Used by CP to set up COMPUTE_PGM_RSRC2.TGID_Z_EN.

10

1 bit

ENABLE_SGPR_WORKGROUP_INFO

Enable the setup of the system SGPR register for work-group information (see Initial Kernel Execution State).

Used by CP to set up COMPUTE_PGM_RSRC2.TGID_SIZE_EN.

12:11

2 bits

ENABLE_VGPR_WORKITEM_ID

Enable the setup of the VGPR system registers used for the work-item ID. System VGPR Work-Item ID Enumeration Values defines the values.

Used by CP to set up COMPUTE_PGM_RSRC2.TIDIG_CMP_CNT.

13

1 bit

ENABLE_EXCEPTION_ADDRESS_WATCH

Must be 0.

Wavefront starts execution with address watch exceptions enabled which are generated when L1 has witnessed a thread access an address of interest.

CP is responsible for filling in the address watch bit in COMPUTE_PGM_RSRC2.EXCP_EN_MSB according to what the runtime requests.

14

1 bit

ENABLE_EXCEPTION_MEMORY

Must be 0.

Wavefront starts execution with memory violation exceptions exceptions enabled which are generated when a memory violation has occurred for this wavefront from L1 or LDS (write-to-read-only-memory, mis-aligned atomic, LDS address out of range, illegal address, etc.).

CP sets the memory violation bit in COMPUTE_PGM_RSRC2.EXCP_EN_MSB according to what the runtime requests.

23:15

9 bits

GRANULATED_LDS_SIZE

Must be 0.

CP uses the rounded value from the dispatch packet, not this value, as the dispatch may contain dynamically allocated group segment memory. CP writes directly to COMPUTE_PGM_RSRC2.LDS_SIZE.

Amount of group segment (LDS) to allocate for each work-group. Granularity is device specific:

GFX6

roundup(lds-size / (64 * 4))

GFX7-GFX11

roundup(lds-size / (128 * 4))

24

1 bit

ENABLE_EXCEPTION_IEEE_754_FP _INVALID_OPERATION

Wavefront starts execution with specified exceptions enabled.

Used by CP to set up COMPUTE_PGM_RSRC2.EXCP_EN (set from bits 0..6).

IEEE 754 FP Invalid Operation

25

1 bit

ENABLE_EXCEPTION_FP_DENORMAL _SOURCE

FP Denormal one or more input operands is a denormal number

26

1 bit

ENABLE_EXCEPTION_IEEE_754_FP _DIVISION_BY_ZERO

IEEE 754 FP Division by Zero

27

1 bit

ENABLE_EXCEPTION_IEEE_754_FP _OVERFLOW

IEEE 754 FP FP Overflow

28

1 bit

ENABLE_EXCEPTION_IEEE_754_FP _UNDERFLOW

IEEE 754 FP Underflow

29

1 bit

ENABLE_EXCEPTION_IEEE_754_FP _INEXACT

IEEE 754 FP Inexact

30

1 bit

ENABLE_EXCEPTION_INT_DIVIDE_BY _ZERO

Integer Division by Zero (rcp_iflag_f32 instruction only)

31

1 bit

RESERVED

Reserved, must be 0.

32

Total size 4 bytes.
Table 67 compute_pgm_rsrc3 for GFX90A, GFX940

Bits

Size

Field Name

Description

5:0

6 bits

ACCUM_OFFSET

Offset of a first AccVGPR in the unified register file. Granularity 4. Value 0-63. 0 - accum-offset = 4, 1 - accum-offset = 8, …, 63 - accum-offset = 256.

15:6

10 bits

Reserved, must be 0.

16

1 bit

TG_SPLIT

  • If 0 the waves of a work-group are launched in the same CU.

  • If 1 the waves of a work-group can be launched in different CUs. The waves cannot use S_BARRIER or LDS.

31:17

15 bits

Reserved, must be 0.

32

Total size 4 bytes.
Table 68 compute_pgm_rsrc3 for GFX10-GFX11

Bits

Size

Field Name

Description

3:0

4 bits

SHARED_VGPR_COUNT

Number of shared VGPR blocks when executing in subvector mode. For wavefront size 64 the value is 0-15, representing 0-120 VGPRs (granularity of 8), such that (compute_pgm_rsrc1.vgprs +1)*4 + shared_vgpr_count*8 does not exceed 256. For wavefront size 32 shared_vgpr_count must be 0.

9:4

6 bits

INST_PREF_SIZE
GFX10

Reserved, must be 0.

GFX11

Number of instruction bytes to prefetch, starting at the kernel’s entry point instruction, before wavefront starts execution. The value is 0..63 with a granularity of 128 bytes.

10

1 bit

TRAP_ON_START
GFX10

Reserved, must be 0.

GFX11

Must be 0.

If 1, wavefront starts execution by trapping into the trap handler.

CP is responsible for filling in the trap on start bit in COMPUTE_PGM_RSRC3.TRAP_ON_START according to what the runtime requests.

11

1 bit

TRAP_ON_END
GFX10

Reserved, must be 0.

GFX11

Must be 0.

If 1, wavefront execution terminates by trapping into the trap handler.

CP is responsible for filling in the trap on end bit in COMPUTE_PGM_RSRC3.TRAP_ON_END according to what the runtime requests.

30:12

19 bits

Reserved, must be 0.

31

1 bit

IMAGE_OP
GFX10

Reserved, must be 0.

GFX11

If 1, the kernel execution contains image instructions. If executed as part of a graphics pipeline, image read instructions will stall waiting for any necessary WAIT_SYNC fence to be performed in order to indicate that earlier pipeline stages have completed writing to the image.

Not used for compute kernels that are not part of a graphics pipeline and must be 0.

32

Total size 4 bytes.
Table 69 compute_pgm_rsrc3 for GFX12

Bits

Size

Field Name

Description

3:0

4 bits

RESERVED

Reserved, must be 0.

11:4

8 bits

INST_PREF_SIZE

Number of instruction bytes to prefetch, starting at the kernel’s entry point instruction, before wavefront starts execution. The value is 0..255 with a granularity of 128 bytes.

12

1 bit

RESERVED

Reserved, must be 0.

13

1 bit

GLG_EN

If 1, group launch guarantee will be enabled for this dispatch

30:14

17 bits

RESERVED

Reserved, must be 0.

31

1 bit

IMAGE_OP

If 1, the kernel execution contains image instructions. If executed as part of a graphics pipeline, image read instructions will stall waiting for any necessary WAIT_SYNC fence to be performed in order to indicate that earlier pipeline stages have completed writing to the image.

Not used for compute kernels that are not part of a graphics pipeline and must be 0.

32

Total size 4 bytes.
Table 70 Floating Point Rounding Mode Enumeration Values

Enumeration Name

Value

Description

FLOAT_ROUND_MODE_NEAR_EVEN

0

Round Ties To Even

FLOAT_ROUND_MODE_PLUS_INFINITY

1

Round Toward +infinity

FLOAT_ROUND_MODE_MINUS_INFINITY

2

Round Toward -infinity

FLOAT_ROUND_MODE_ZERO

3

Round Toward 0
Table 71 Extended FLT_ROUNDS Enumeration Values

F32 NEAR_EVEN

F32 PLUS_INFINITY

F32 MINUS_INFINITY

F32 ZERO

F64/F16 NEAR_EVEN

1

11

14

17

F64/F16 PLUS_INFINITY

8

2

15

18

F64/F16 MINUS_INFINITY

9

12

3

19

F64/F16 ZERO

10

13

16

0
Table 72 Floating Point Denorm Mode Enumeration Values

Enumeration Name

Value

Description

FLOAT_DENORM_MODE_FLUSH_SRC_DST

0

Flush Source and Destination Denorms

FLOAT_DENORM_MODE_FLUSH_DST

1

Flush Output Denorms

FLOAT_DENORM_MODE_FLUSH_SRC

2

Flush Source Denorms

FLOAT_DENORM_MODE_FLUSH_NONE

3

No Flush

Denormal flushing is sign respecting. i.e. the behavior expected by "denormal-fp-math"="preserve-sign". The behavior is undefined with "denormal-fp-math"="positive-zero"

Table 73 System VGPR Work-Item ID Enumeration Values

Enumeration Name

Value

Description

SYSTEM_VGPR_WORKITEM_ID_X

0

Set work-item X dimension ID.

SYSTEM_VGPR_WORKITEM_ID_X_Y

1

Set work-item X and Y dimensions ID.

SYSTEM_VGPR_WORKITEM_ID_X_Y_Z

2

Set work-item X, Y and Z dimensions ID.

SYSTEM_VGPR_WORKITEM_ID_UNDEFINED

3

Undefined.

Initial Kernel Execution State

This section defines the register state that will be set up by the packet processor prior to the start of execution of every wavefront. This is limited by the constraints of the hardware controllers of CP/ADC/SPI.

The order of the SGPR registers is defined, but the compiler can specify which ones are actually setup in the kernel descriptor using the enable_sgpr_* bit fields (see Kernel Descriptor). The register numbers used for enabled registers are dense starting at SGPR0: the first enabled register is SGPR0, the next enabled register is SGPR1 etc.; disabled registers do not have an SGPR number.

The initial SGPRs comprise up to 16 User SGPRs that are set by CP and apply to all wavefronts of the grid. It is possible to specify more than 16 User SGPRs using the enable_sgpr_* bit fields, in which case only the first 16 are actually initialized. These are then immediately followed by the System SGPRs that are set up by ADC/SPI and can have different values for each wavefront of the grid dispatch.

SGPR register initial state is defined in SGPR Register Set Up Order.

Table 74 SGPR Register Set Up Order

SGPR Order

Name (kernel descriptor enable field)

Number of SGPRs

Description

First

Private Segment Buffer (enable_sgpr_private _segment_buffer)

4

See Private Segment Buffer.

then

Dispatch Ptr (enable_sgpr_dispatch_ptr)

2

64-bit address of AQL dispatch packet for kernel dispatch actually executing.

then

Queue Ptr (enable_sgpr_queue_ptr)

2

64-bit address of amd_queue_t object for AQL queue on which the dispatch packet was queued.

then

Kernarg Segment Ptr (enable_sgpr_kernarg _segment_ptr)

2

64-bit address of Kernarg segment. This is directly copied from the kernarg_address in the kernel dispatch packet.

Having CP load it once avoids loading it at the beginning of every wavefront.

then

Dispatch Id (enable_sgpr_dispatch_id)

2

64-bit Dispatch ID of the dispatch packet being executed.

then

Flat Scratch Init (enable_sgpr_flat_scratch _init)

2

See Flat Scratch.

then

Preloaded Kernargs (kernarg_preload_spec _length)

N/A

See Preloaded Kernel Arguments.

then

Private Segment Size (enable_sgpr_private _segment_size)

1

The 32-bit byte size of a single work-item’s memory allocation. This is the value from the kernel dispatch packet Private Segment Byte Size rounded up by CP to a multiple of DWORD.

Having CP load it once avoids loading it at the beginning of every wavefront.

This is not used for GFX7-GFX8 since it is the same value as the second SGPR of Flat Scratch Init. However, it may be needed for GFX9-GFX11 which changes the meaning of the Flat Scratch Init value.

then

Work-Group Id X (enable_sgpr_workgroup_id _X)

1

32-bit work-group id in X dimension of grid for wavefront.

then

Work-Group Id Y (enable_sgpr_workgroup_id _Y)

1

32-bit work-group id in Y dimension of grid for wavefront.

then

Work-Group Id Z (enable_sgpr_workgroup_id _Z)

1

32-bit work-group id in Z dimension of grid for wavefront.

then

Work-Group Info (enable_sgpr_workgroup _info)

1

{first_wavefront, 14’b0000, ordered_append_term[10:0], threadgroup_size_in_wavefronts[5:0]}

then

Scratch Wavefront Offset (enable_sgpr_private _segment_wavefront_offset)

1

See Flat Scratch. and Private Segment Buffer.

The order of the VGPR registers is defined, but the compiler can specify which ones are actually setup in the kernel descriptor using the enable_vgpr* bit fields (see Kernel Descriptor). The register numbers used for enabled registers are dense starting at VGPR0: the first enabled register is VGPR0, the next enabled register is VGPR1 etc.; disabled registers do not have a VGPR number.

There are different methods used for the VGPR initial state:

  • Unless the Target Properties column of AMDGPU Processors specifies otherwise, a separate VGPR register is used per work-item ID. The VGPR register initial state for this method is defined in VGPR Register Set Up Order for Unpacked Work-Item ID Method.

  • If Target Properties column of AMDGPU Processors specifies Packed work-item IDs, the initial value of VGPR0 register is used for all work-item IDs. The register layout for this method is defined in Register Layout for Packed Work-Item ID Method.

    Table 75 VGPR Register Set Up Order for Unpacked Work-Item ID Method

    VGPR Order

    Name (kernel descriptor enable field)

    Number of VGPRs

    Description

    First

    Work-Item Id X (Always initialized)

    1

    32-bit work-item id in X dimension of work-group for wavefront lane.

    then

    Work-Item Id Y (enable_vgpr_workitem_id > 0)

    1

    32-bit work-item id in Y dimension of work-group for wavefront lane.

    then

    Work-Item Id Z (enable_vgpr_workitem_id > 1)

    1

    32-bit work-item id in Z dimension of work-group for wavefront lane.
Table 76 Register Layout for Packed Work-Item ID Method

Bits

Size

Field Name

Description

0:9

10 bits

Work-Item Id X

Work-item id in X dimension of work-group for wavefront lane.

Always initialized.

10:19

10 bits

Work-Item Id Y

Work-item id in Y dimension of work-group for wavefront lane.

Initialized if enable_vgpr_workitem_id > 0, otherwise set to 0.

20:29

10 bits

Work-Item Id Z

Work-item id in Z dimension of work-group for wavefront lane.

Initialized if enable_vgpr_workitem_id > 1, otherwise set to 0.

30:31

2 bits

Reserved, set to 0.

The setting of registers is done by GPU CP/ADC/SPI hardware as follows:

  1. SGPRs before the Work-Group Ids are set by CP using the 16 User Data registers.

  2. Work-group Id registers X, Y, Z are set by ADC which supports any combination including none.

  3. Scratch Wavefront Offset is set by SPI in a per wavefront basis which is why its value cannot be included with the flat scratch init value which is per queue (see Flat Scratch).

  4. The VGPRs are set by SPI which only supports specifying either (X), (X, Y) or (X, Y, Z).

  5. Flat Scratch register pair initialization is described in Flat Scratch.

The global segment can be accessed either using buffer instructions (GFX6 which has V# 64-bit address support), flat instructions (GFX7-GFX11), or global instructions (GFX9-GFX11).

If buffer operations are used, then the compiler can generate a V# with the following properties:

  • base address of 0

  • no swizzle

  • ATC: 1 if IOMMU present (such as APU)

  • ptr64: 1

  • MTYPE set to support memory coherence that matches the runtime (such as CC for APU and NC for dGPU).

Preloaded Kernel Arguments

On hardware that supports this feature, kernel arguments can be preloaded into User SGPRs, up to the maximum number of User SGPRs available. The allocation of Preload SGPRs occurs directly after the last enabled non-kernarg preload User SGPR. (See Initial Kernel Execution State)

The data preloaded is copied from the kernarg segment, the amount of data is determined by the value specified in the kernarg_preload_spec_length field of the kernel descriptor. This data is then loaded into consecutive User SGPRs. The number of SGPRs receiving preloaded kernarg data corresponds with the value given by kernarg_preload_spec_length. The preloading starts at the dword offset within the kernarg segment, which is specified by the kernarg_preload_spec_offset field.

If the kernarg_preload_spec_length is non-zero, the CP firmware will append an additional 256 bytes to the kernel_code_entry_byte_offset. This addition facilitates the incorporation of a prologue to the kernel entry to handle cases where code designed for kernarg preloading is executed on hardware equipped with incompatible firmware. If hardware has compatible firmware the 256 bytes at the start of the kernel entry will be skipped. Additionally, the compiler backend may insert a trap instruction at the start of the kernel prologue to manage situations where kernarg preloading is attempted on hardware with incompatible firmware.

Kernel Prolog

The compiler performs initialization in the kernel prologue depending on the target and information about things like stack usage in the kernel and called functions. Some of this initialization requires the compiler to request certain User and System SGPRs be present in the Initial Kernel Execution State via the Kernel Descriptor.

CFI

  1. The CFI return address is undefined.

  2. The CFI CFA is defined using an expression which evaluates to a location description that comprises one memory location description for the DW_ASPACE_AMDGPU_private_lane address space address 0.

M0
GFX6-GFX8

The M0 register must be initialized with a value at least the total LDS size if the kernel may access LDS via DS or flat operations. Total LDS size is available in dispatch packet. For M0, it is also possible to use maximum possible value of LDS for given target (0x7FFF for GFX6 and 0xFFFF for GFX7-GFX8).

GFX9-GFX11

The M0 register is not used for range checking LDS accesses and so does not need to be initialized in the prolog.

Stack Pointer

If the kernel has function calls it must set up the ABI stack pointer described in Non-Kernel Functions by setting SGPR32 to the unswizzled scratch offset of the address past the last local allocation.

Frame Pointer

If the kernel needs a frame pointer for the reasons defined in SIFrameLowering then SGPR33 is used and is always set to 0 in the kernel prolog. If a frame pointer is not required then all uses of the frame pointer are replaced with immediate 0 offsets.

Flat Scratch

There are different methods used for initializing flat scratch:

  • If the Target Properties column of AMDGPU Processors specifies Does not support generic address space:

    Flat scratch is not supported and there is no flat scratch register pair.

  • If the Target Properties column of AMDGPU Processors specifies Offset flat scratch:

    If the kernel or any function it calls may use flat operations to access scratch memory, the prolog code must set up the FLAT_SCRATCH register pair (FLAT_SCRATCH_LO/FLAT_SCRATCH_HI). Initialization uses Flat Scratch Init and Scratch Wavefront Offset SGPR registers (see Initial Kernel Execution State):

    1. The low word of Flat Scratch Init is the 32-bit byte offset from SH_HIDDEN_PRIVATE_BASE_VIMID to the base of scratch backing memory being managed by SPI for the queue executing the kernel dispatch. This is the same value used in the Scratch Segment Buffer V# base address.

      CP obtains this from the runtime. (The Scratch Segment Buffer base address is SH_HIDDEN_PRIVATE_BASE_VIMID plus this offset.)

      The prolog must add the value of Scratch Wavefront Offset to get the wavefront’s byte scratch backing memory offset from SH_HIDDEN_PRIVATE_BASE_VIMID.

      The Scratch Wavefront Offset must also be used as an offset with Private segment address when using the Scratch Segment Buffer.

      Since FLAT_SCRATCH_LO is in units of 256 bytes, the offset must be right shifted by 8 before moving into FLAT_SCRATCH_HI.

      FLAT_SCRATCH_HI corresponds to SGPRn-4 on GFX7, and SGPRn-6 on GFX8 (where SGPRn is the highest numbered SGPR allocated to the wavefront). FLAT_SCRATCH_HI is multiplied by 256 (as it is in units of 256 bytes) and added to SH_HIDDEN_PRIVATE_BASE_VIMID to calculate the per wavefront FLAT SCRATCH BASE in flat memory instructions that access the scratch aperture.

    2. The second word of Flat Scratch Init is 32-bit byte size of a single work-items scratch memory usage.

      CP obtains this from the runtime, and it is always a multiple of DWORD. CP checks that the value in the kernel dispatch packet Private Segment Byte Size is not larger and requests the runtime to increase the queue’s scratch size if necessary.

      CP directly loads from the kernel dispatch packet Private Segment Byte Size field and rounds up to a multiple of DWORD. Having CP load it once avoids loading it at the beginning of every wavefront.

      The kernel prolog code must move it to FLAT_SCRATCH_LO which is SGPRn-3 on GFX7 and SGPRn-5 on GFX8. FLAT_SCRATCH_LO is used as the FLAT SCRATCH SIZE in flat memory instructions.

  • If the Target Properties column of AMDGPU Processors specifies Absolute flat scratch:

    If the kernel or any function it calls may use flat operations to access scratch memory, the prolog code must set up the FLAT_SCRATCH register pair (FLAT_SCRATCH_LO/FLAT_SCRATCH_HI which are in SGPRn-4/SGPRn-3). Initialization uses Flat Scratch Init and Scratch Wavefront Offset SGPR registers (see Initial Kernel Execution State):

    The Flat Scratch Init is the 64-bit address of the base of scratch backing memory being managed by SPI for the queue executing the kernel dispatch.

    CP obtains this from the runtime.

    The kernel prolog must add the value of the wave’s Scratch Wavefront Offset and move the result as a 64-bit value to the FLAT_SCRATCH SGPR register pair which is SGPRn-6 and SGPRn-5. It is used as the FLAT SCRATCH BASE in flat memory instructions.

    The Scratch Wavefront Offset must also be used as an offset with Private segment address when using the Scratch Segment Buffer (see Private Segment Buffer).

  • If the Target Properties column of AMDGPU Processors specifies Architected flat scratch:

    If ENABLE_PRIVATE_SEGMENT is enabled in compute_pgm_rsrc2 for GFX6-GFX12 then the FLAT_SCRATCH register pair will be initialized to the 64-bit address of the base of scratch backing memory being managed by SPI for the queue executing the kernel dispatch plus the value of the wave’s Scratch Wavefront Offset for use as the flat scratch base in flat memory instructions.

Private Segment Buffer

If the Target Properties column of AMDGPU Processors specifies Architected flat scratch then a Private Segment Buffer is not supported. Instead the flat SCRATCH instructions are used.

Otherwise, Private Segment Buffer SGPR register is used to initialize 4 SGPRs that are used as a V# to access scratch. CP uses the value provided by the runtime. It is used, together with Scratch Wavefront Offset as an offset, to access the private memory space using a segment address. See Initial Kernel Execution State.

The scratch V# is a four-aligned SGPR and always selected for the kernel as follows:

  • If it is known during instruction selection that there is stack usage, SGPR0-3 is reserved for use as the scratch V#. Stack usage is assumed if optimizations are disabled (-O0), if stack objects already exist (for locals, etc.), or if there are any function calls.

  • Otherwise, four high numbered SGPRs beginning at a four-aligned SGPR index are reserved for the tentative scratch V#. These will be used if it is determined that spilling is needed.

    • If no use is made of the tentative scratch V#, then it is unreserved, and the register count is determined ignoring it.

    • If use is made of the tentative scratch V#, then its register numbers are shifted to the first four-aligned SGPR index after the highest one allocated by the register allocator, and all uses are updated. The register count includes them in the shifted location.

    • In either case, if the processor has the SGPR allocation bug, the tentative allocation is not shifted or unreserved in order to ensure the register count is higher to workaround the bug.

    Note

    This approach of using a tentative scratch V# and shifting the register numbers if used avoids having to perform register allocation a second time if the tentative V# is eliminated. This is more efficient and avoids the problem that the second register allocation may perform spilling which will fail as there is no longer a scratch V#.

When the kernel prolog code is being emitted it is known whether the scratch V# described above is actually used. If it is, the prolog code must set it up by copying the Private Segment Buffer to the scratch V# registers and then adding the Private Segment Wavefront Offset to the queue base address in the V#. The result is a V# with a base address pointing to the beginning of the wavefront scratch backing memory.

The Private Segment Buffer is always requested, but the Private Segment Wavefront Offset is only requested if it is used (see Initial Kernel Execution State).

Memory Model

This section describes the mapping of the LLVM memory model onto AMDGPU machine code (see Memory Model for Concurrent Operations).

The AMDGPU backend supports the memory synchronization scopes specified in Memory Scopes.

The code sequences used to implement the memory model specify the order of instructions that a single thread must execute. The s_waitcnt and cache management instructions such as buffer_wbinvl1_vol are defined with respect to other memory instructions executed by the same thread. This allows them to be moved earlier or later which can allow them to be combined with other instances of the same instruction, or hoisted/sunk out of loops to improve performance. Only the instructions related to the memory model are given; additional s_waitcnt instructions are required to ensure registers are defined before being used. These may be able to be combined with the memory model s_waitcnt instructions as described above.

The AMDGPU backend supports the following memory models:

HSA Memory Model [HSA]

The HSA memory model uses a single happens-before relation for all address spaces (see Address Spaces).

OpenCL Memory Model [OpenCL]

The OpenCL memory model which has separate happens-before relations for the global and local address spaces. Only a fence specifying both global and local address space, and seq_cst instructions join the relationships. Since the LLVM memfence instruction does not allow an address space to be specified the OpenCL fence has to conservatively assume both local and global address space was specified. However, optimizations can often be done to eliminate the additional s_waitcnt instructions when there are no intervening memory instructions which access the corresponding address space. The code sequences in the table indicate what can be omitted for the OpenCL memory. The target triple environment is used to determine if the source language is OpenCL (see OpenCL).

ds/flat_load/store/atomic instructions to local memory are termed LDS operations.

buffer/global/flat_load/store/atomic instructions to global memory are termed vector memory operations.

Private address space uses buffer_load/store using the scratch V# (GFX6-GFX8), or scratch_load/store (GFX9-GFX11). Since only a single thread is accessing the memory, atomic memory orderings are not meaningful, and all accesses are treated as non-atomic.

Constant address space uses buffer/global_load instructions (or equivalent scalar memory instructions). Since the constant address space contents do not change during the execution of a kernel dispatch it is not legal to perform stores, and atomic memory orderings are not meaningful, and all accesses are treated as non-atomic.

A memory synchronization scope wider than work-group is not meaningful for the group (LDS) address space and is treated as work-group.

The memory model does not support the region address space which is treated as non-atomic.

Acquire memory ordering is not meaningful on store atomic instructions and is treated as non-atomic.

Release memory ordering is not meaningful on load atomic instructions and is treated a non-atomic.

Acquire-release memory ordering is not meaningful on load or store atomic instructions and is treated as acquire and release respectively.

The memory order also adds the single thread optimization constraints defined in table AMDHSA Memory Model Single Thread Optimization Constraints.

Table 77 AMDHSA Memory Model Single Thread Optimization Constraints

LLVM Memory

Optimization Constraints

Ordering

unordered

none

monotonic

none

acquire

  • If a load atomic/atomicrmw then no following load/load atomic/store/store atomic/atomicrmw/fence instruction can be moved before the acquire.

  • If a fence then same as load atomic, plus no preceding associated fence-paired-atomic can be moved after the fence.

release

  • If a store atomic/atomicrmw then no preceding load/load atomic/store/store atomic/atomicrmw/fence instruction can be moved after the release.

  • If a fence then same as store atomic, plus no following associated fence-paired-atomic can be moved before the fence.

acq_rel

Same constraints as both acquire and release.

seq_cst

  • If a load atomic then same constraints as acquire, plus no preceding sequentially consistent load atomic/store atomic/atomicrmw/fence instruction can be moved after the seq_cst.

  • If a store atomic then the same constraints as release, plus no following sequentially consistent load atomic/store atomic/atomicrmw/fence instruction can be moved before the seq_cst.

  • If an atomicrmw/fence then same constraints as acq_rel.

The code sequences used to implement the memory model are defined in the following sections:

Fence and Address Spaces

LLVM fences do not have address space information, thus, fence codegen usually needs to conservatively synchronize all address spaces.

In the case of OpenCL, where fences only need to synchronize user-specified address spaces, this can result in extra unnecessary waits. For instance, a fence that is supposed to only synchronize local memory will also have to wait on all global memory operations, which is unnecessary.

Memory Model Relaxation Annotations can be used as an optimization hint for fences to solve this problem. The AMDGPU backend recognizes the following tags on fences:

  • amdgpu-as:local - fence only the local address space

  • amdgpu-as:global- fence only the global address space

Note

As an optimization hint, those tags are not guaranteed to survive until code generation. Optimizations are free to drop the tags to allow for better code optimization, at the cost of synchronizing additional address spaces.

Memory Model GFX6-GFX9

For GFX6-GFX9:

  • Each agent has multiple shader arrays (SA).

  • Each SA has multiple compute units (CU).

  • Each CU has multiple SIMDs that execute wavefronts.

  • The wavefronts for a single work-group are executed in the same CU but may be executed by different SIMDs.

  • Each CU has a single LDS memory shared by the wavefronts of the work-groups executing on it.

  • All LDS operations of a CU are performed as wavefront wide operations in a global order and involve no caching. Completion is reported to a wavefront in execution order.

  • The LDS memory has multiple request queues shared by the SIMDs of a CU. Therefore, the LDS operations performed by different wavefronts of a work-group can be reordered relative to each other, which can result in reordering the visibility of vector memory operations with respect to LDS operations of other wavefronts in the same work-group. A s_waitcnt lgkmcnt(0) is required to ensure synchronization between LDS operations and vector memory operations between wavefronts of a work-group, but not between operations performed by the same wavefront.

  • The vector memory operations are performed as wavefront wide operations and completion is reported to a wavefront in execution order. The exception is that for GFX7-GFX9 flat_load/store/atomic instructions can report out of vector memory order if they access LDS memory, and out of LDS operation order if they access global memory.

  • The vector memory operations access a single vector L1 cache shared by all SIMDs a CU. Therefore, no special action is required for coherence between the lanes of a single wavefront, or for coherence between wavefronts in the same work-group. A buffer_wbinvl1_vol is required for coherence between wavefronts executing in different work-groups as they may be executing on different CUs.

  • The scalar memory operations access a scalar L1 cache shared by all wavefronts on a group of CUs. The scalar and vector L1 caches are not coherent. However, scalar operations are used in a restricted way so do not impact the memory model. See Memory Spaces.

  • The vector and scalar memory operations use an L2 cache shared by all CUs on the same agent.

  • The L2 cache has independent channels to service disjoint ranges of virtual addresses.

  • Each CU has a separate request queue per channel. Therefore, the vector and scalar memory operations performed by wavefronts executing in different work-groups (which may be executing on different CUs) of an agent can be reordered relative to each other. A s_waitcnt vmcnt(0) is required to ensure synchronization between vector memory operations of different CUs. It ensures a previous vector memory operation has completed before executing a subsequent vector memory or LDS operation and so can be used to meet the requirements of acquire and release.

  • The L2 cache can be kept coherent with other agents on some targets, or ranges of virtual addresses can be set up to bypass it to ensure system coherence.

Scalar memory operations are only used to access memory that is proven to not change during the execution of the kernel dispatch. This includes constant address space and global address space for program scope const variables. Therefore, the kernel machine code does not have to maintain the scalar cache to ensure it is coherent with the vector caches. The scalar and vector caches are invalidated between kernel dispatches by CP since constant address space data may change between kernel dispatch executions. See Memory Spaces.

The one exception is if scalar writes are used to spill SGPR registers. In this case the AMDGPU backend ensures the memory location used to spill is never accessed by vector memory operations at the same time. If scalar writes are used then a s_dcache_wb is inserted before the s_endpgm and before a function return since the locations may be used for vector memory instructions by a future wavefront that uses the same scratch area, or a function call that creates a frame at the same address, respectively. There is no need for a s_dcache_inv as all scalar writes are write-before-read in the same thread.

For kernarg backing memory:

  • CP invalidates the L1 cache at the start of each kernel dispatch.

  • On dGPU the kernarg backing memory is allocated in host memory accessed as MTYPE UC (uncached) to avoid needing to invalidate the L2 cache. This also causes it to be treated as non-volatile and so is not invalidated by *_vol.

  • On APU the kernarg backing memory it is accessed as MTYPE CC (cache coherent) and so the L2 cache will be coherent with the CPU and other agents.

Scratch backing memory (which is used for the private address space) is accessed with MTYPE NC_NV (non-coherent non-volatile). Since the private address space is only accessed by a single thread, and is always write-before-read, there is never a need to invalidate these entries from the L1 cache. Hence all cache invalidates are done as *_vol to only invalidate the volatile cache lines.

The code sequences used to implement the memory model for GFX6-GFX9 are defined in table AMDHSA Memory Model Code Sequences GFX6-GFX9.

Table 78 AMDHSA Memory Model Code Sequences GFX6-GFX9

LLVM Instr

LLVM Memory Ordering

LLVM Memory Sync Scope

AMDGPU Address Space

AMDGPU Machine Code GFX6-GFX9

Non-Atomic

load

none

none

  • global

  • generic

  • private

  • constant

  • !volatile & !nontemporal

    1. buffer/global/flat_load

  • !volatile & nontemporal

    1. buffer/global/flat_load glc=1 slc=1

  • volatile

    1. buffer/global/flat_load glc=1

    2. s_waitcnt vmcnt(0)

    • Must happen before any following volatile global/generic load/store.

    • Ensures that volatile operations to different addresses will not be reordered by hardware.

load

none

none

  • local

  1. ds_load

store

none

none

  • global

  • generic

  • private

  • constant

  • !volatile & !nontemporal

    1. buffer/global/flat_store

  • !volatile & nontemporal

    1. buffer/global/flat_store glc=1 slc=1

  • volatile

    1. buffer/global/flat_store

    2. s_waitcnt vmcnt(0)

    • Must happen before any following volatile global/generic load/store.

    • Ensures that volatile operations to different addresses will not be reordered by hardware.

store

none

none

  • local

  1. ds_store

Unordered Atomic

load atomic

unordered

any

any

Same as non-atomic.

store atomic

unordered

any

any

Same as non-atomic.

atomicrmw

unordered

any

any

Same as monotonic atomic.

Monotonic Atomic

load atomic

monotonic

  • singlethread

  • wavefront

  • workgroup

  • global

  • local

  • generic

  1. buffer/global/ds/flat_load

load atomic

monotonic

  • agent

  • system

  • global

  • generic

  1. buffer/global/flat_load glc=1

store atomic

monotonic

  • singlethread

  • wavefront

  • workgroup

  • agent

  • system

  • global

  • generic

  1. buffer/global/flat_store

store atomic

monotonic

  • singlethread

  • wavefront

  • workgroup

  • local

  1. ds_store

atomicrmw

monotonic

  • singlethread

  • wavefront

  • workgroup

  • agent

  • system

  • global

  • generic

  1. buffer/global/flat_atomic

atomicrmw

monotonic

  • singlethread

  • wavefront

  • workgroup

  • local

  1. ds_atomic

Acquire Atomic

load atomic

acquire

  • singlethread

  • wavefront

  • global

  • local

  • generic

  1. buffer/global/ds/flat_load

load atomic

acquire

  • workgroup

  • global

  1. buffer/global_load

load atomic

acquire

  • workgroup

  • local

  • generic

  1. ds/flat_load

  2. s_waitcnt lgkmcnt(0)

  • If OpenCL, omit.

  • Must happen before any following global/generic load/load atomic/store/store atomic/atomicrmw.

  • Ensures any following global data read is no older than a local load atomic value being acquired.

load atomic

acquire

  • agent

  • system

  • global

  1. buffer/global_load glc=1

  2. s_waitcnt vmcnt(0)

  • Must happen before following buffer_wbinvl1_vol.

  • Ensures the load has completed before invalidating the cache.

  1. buffer_wbinvl1_vol

  • Must happen before any following global/generic load/load atomic/atomicrmw.

  • Ensures that following loads will not see stale global data.

load atomic

acquire

  • agent

  • system

  • generic

  1. flat_load glc=1

  2. s_waitcnt vmcnt(0) & lgkmcnt(0)

  • If OpenCL omit lgkmcnt(0).

  • Must happen before following buffer_wbinvl1_vol.

  • Ensures the flat_load has completed before invalidating the cache.

  1. buffer_wbinvl1_vol

  • Must happen before any following global/generic load/load atomic/atomicrmw.

  • Ensures that following loads will not see stale global data.

atomicrmw

acquire

  • singlethread

  • wavefront

  • global

  • local

  • generic

  1. buffer/global/ds/flat_atomic

atomicrmw

acquire

  • workgroup

  • global

  1. buffer/global_atomic

atomicrmw

acquire

  • workgroup

  • local

  • generic

  1. ds/flat_atomic

  2. s_waitcnt lgkmcnt(0)

  • If OpenCL, omit.

  • Must happen before any following global/generic load/load atomic/store/store atomic/atomicrmw.

  • Ensures any following global data read is no older than a local atomicrmw value being acquired.

atomicrmw

acquire

  • agent

  • system

  • global

  1. buffer/global_atomic

  2. s_waitcnt vmcnt(0)

  • Must happen before following buffer_wbinvl1_vol.

  • Ensures the atomicrmw has completed before invalidating the cache.

  1. buffer_wbinvl1_vol

  • Must happen before any following global/generic load/load atomic/atomicrmw.

  • Ensures that following loads will not see stale global data.

atomicrmw

acquire

  • agent

  • system

  • generic

  1. flat_atomic

  2. s_waitcnt vmcnt(0) & lgkmcnt(0)

  • If OpenCL, omit lgkmcnt(0).

  • Must happen before following buffer_wbinvl1_vol.

  • Ensures the atomicrmw has completed before invalidating the cache.

  1. buffer_wbinvl1_vol

  • Must happen before any following global/generic load/load atomic/atomicrmw.

  • Ensures that following loads will not see stale global data.

fence

acquire

  • singlethread

  • wavefront

none

none

fence

acquire

  • workgroup

none

  1. s_waitcnt lgkmcnt(0)

  • If OpenCL and address space is not generic, omit.

  • See Fence and Address Spaces for more details on fencing specific address spaces.

  • Must happen after any preceding local/generic load atomic/atomicrmw with an equal or wider sync scope and memory ordering stronger than unordered (this is termed the fence-paired-atomic).

  • Must happen before any following global/generic load/load atomic/store/store atomic/atomicrmw.

  • Ensures any following global data read is no older than the value read by the fence-paired-atomic.

fence

acquire

  • agent

  • system

none

  1. s_waitcnt lgkmcnt(0) & vmcnt(0)

  • If OpenCL and address space is not generic, omit lgkmcnt(0).

  • See Fence and Address Spaces for more details on fencing specific address spaces.

  • Could be split into separate s_waitcnt vmcnt(0) and s_waitcnt lgkmcnt(0) to allow them to be independently moved according to the following rules.

  • s_waitcnt vmcnt(0) must happen after any preceding global/generic load atomic/atomicrmw with an equal or wider sync scope and memory ordering stronger than unordered (this is termed the fence-paired-atomic).

  • s_waitcnt lgkmcnt(0) must happen after any preceding local/generic load atomic/atomicrmw with an equal or wider sync scope and memory ordering stronger than unordered (this is termed the fence-paired-atomic).

  • Must happen before the following buffer_wbinvl1_vol.

  • Ensures that the fence-paired atomic has completed before invalidating the cache. Therefore any following locations read must be no older than the value read by the fence-paired-atomic.

  1. buffer_wbinvl1_vol

  • Must happen before any following global/generic load/load atomic/store/store atomic/atomicrmw.

  • Ensures that following loads will not see stale global data.

Release Atomic

store atomic

release

  • singlethread

  • wavefront

  • global

  • local

  • generic

  1. buffer/global/ds/flat_store

store atomic

release

  • workgroup

  • global

  • generic

  1. s_waitcnt lgkmcnt(0)

  • If OpenCL, omit.

  • Must happen after any preceding local/generic load/store/load atomic/store atomic/atomicrmw.

  • Must happen before the following store.

  • Ensures that all memory operations to local have completed before performing the store that is being released.

  1. buffer/global/flat_store

store atomic

release

  • workgroup

  • local

  1. ds_store

store atomic

release

  • agent

  • system

  • global

  • generic

  1. s_waitcnt lgkmcnt(0) & vmcnt(0)

  • If OpenCL and address space is not generic, omit lgkmcnt(0).

  • Could be split into separate s_waitcnt vmcnt(0) and s_waitcnt lgkmcnt(0) to allow them to be independently moved according to the following rules.

  • s_waitcnt vmcnt(0) must happen after any preceding global/generic load/store/load atomic/store atomic/atomicrmw.

  • s_waitcnt lgkmcnt(0) must happen after any preceding local/generic load/store/load atomic/store atomic/atomicrmw.

  • Must happen before the following store.

  • Ensures that all memory operations to memory have completed before performing the store that is being released.

  1. buffer/global/flat_store

atomicrmw

release

  • singlethread

  • wavefront

  • global

  • local

  • generic

  1. buffer/global/ds/flat_atomic

atomicrmw

release

  • workgroup

  • global

  • generic

  1. s_waitcnt lgkmcnt(0)

  • If OpenCL, omit.

  • Must happen after any preceding local/generic load/store/load atomic/store atomic/atomicrmw.

  • Must happen before the following atomicrmw.

  • Ensures that all memory operations to local have completed before performing the atomicrmw that is being released.

  1. buffer/global/flat_atomic

atomicrmw

release

  • workgroup

  • local

  1. ds_atomic

atomicrmw

release

  • agent

  • system

  • global

  • generic

  1. s_waitcnt lgkmcnt(0) & vmcnt(0)

  • If OpenCL, omit lgkmcnt(0).

  • Could be split into separate s_waitcnt vmcnt(0) and s_waitcnt lgkmcnt(0) to allow them to be independently moved according to the following rules.

  • s_waitcnt vmcnt(0) must happen after any preceding global/generic load/store/load atomic/store atomic/atomicrmw.

  • s_waitcnt lgkmcnt(0) must happen after any preceding local/generic load/store/load atomic/store atomic/atomicrmw.

  • Must happen before the following atomicrmw.

  • Ensures that all memory operations to global and local have completed before performing the atomicrmw that is being released.

  1. buffer/global/flat_atomic

fence

release

  • singlethread

  • wavefront

none

none

fence

release

  • workgroup

none

  1. s_waitcnt lgkmcnt(0)

  • If OpenCL and address space is not generic, omit.

  • See Fence and Address Spaces for more details on fencing specific address spaces.

  • Must happen after any preceding local/generic load/load atomic/store/store atomic/atomicrmw.

  • Must happen before any following store atomic/atomicrmw with an equal or wider sync scope and memory ordering stronger than unordered (this is termed the fence-paired-atomic).

  • Ensures that all memory operations to local have completed before performing the following fence-paired-atomic.

fence

release

  • agent

  • system

none

  1. s_waitcnt lgkmcnt(0) & vmcnt(0)

  • If OpenCL and address space is not generic, omit lgkmcnt(0).

  • If OpenCL and address space is local, omit vmcnt(0).

  • See Fence and Address Spaces for more details on fencing specific address spaces.

  • Could be split into separate s_waitcnt vmcnt(0) and s_waitcnt lgkmcnt(0) to allow them to be independently moved according to the following rules.

  • s_waitcnt vmcnt(0) must happen after any preceding global/generic load/store/load atomic/store atomic/atomicrmw.

  • s_waitcnt lgkmcnt(0) must happen after any preceding local/generic load/store/load atomic/store atomic/atomicrmw.

  • Must happen before any following store atomic/atomicrmw with an equal or wider sync scope and memory ordering stronger than unordered (this is termed the fence-paired-atomic).

  • Ensures that all memory operations have completed before performing the following fence-paired-atomic.

Acquire-Release Atomic

atomicrmw

acq_rel

  • singlethread

  • wavefront

  • global

  • local

  • generic

  1. buffer/global/ds/flat_atomic

atomicrmw

acq_rel

  • workgroup

  • global

  1. s_waitcnt lgkmcnt(0)

  • If OpenCL, omit.

  • Must happen after any preceding local/generic load/store/load atomic/store atomic/atomicrmw.

  • Must happen before the following atomicrmw.

  • Ensures that all memory operations to local have completed before performing the atomicrmw that is being released.

  1. buffer/global_atomic

atomicrmw

acq_rel

  • workgroup

  • local

  1. ds_atomic

  2. s_waitcnt lgkmcnt(0)

  • If OpenCL, omit.

  • Must happen before any following global/generic load/load atomic/store/store atomic/atomicrmw.

  • Ensures any following global data read is no older than the local load atomic value being acquired.

atomicrmw

acq_rel

  • workgroup

  • generic

  1. s_waitcnt lgkmcnt(0)

  • If OpenCL, omit.

  • Must happen after any preceding local/generic load/store/load atomic/store atomic/atomicrmw.

  • Must happen before the following atomicrmw.

  • Ensures that all memory operations to local have completed before performing the atomicrmw that is being released.

  1. flat_atomic

  2. s_waitcnt lgkmcnt(0)

  • If OpenCL, omit.

  • Must happen before any following global/generic load/load atomic/store/store atomic/atomicrmw.

  • Ensures any following global data read is no older than a local load atomic value being acquired.

atomicrmw

acq_rel

  • agent

  • system

  • global

  1. s_waitcnt lgkmcnt(0) & vmcnt(0)

  • If OpenCL, omit lgkmcnt(0).

  • Could be split into separate s_waitcnt vmcnt(0) and s_waitcnt lgkmcnt(0) to allow them to be independently moved according to the following rules.

  • s_waitcnt vmcnt(0) must happen after any preceding global/generic load/store/load atomic/store atomic/atomicrmw.

  • s_waitcnt lgkmcnt(0) must happen after any preceding local/generic load/store/load atomic/store atomic/atomicrmw.

  • Must happen before the following atomicrmw.

  • Ensures that all memory operations to global have completed before performing the atomicrmw that is being released.

  1. buffer/global_atomic

  2. s_waitcnt vmcnt(0)

  • Must happen before following buffer_wbinvl1_vol.

  • Ensures the atomicrmw has completed before invalidating the cache.

  1. buffer_wbinvl1_vol

  • Must happen before any following global/generic load/load atomic/atomicrmw.

  • Ensures that following loads will not see stale global data.

atomicrmw

acq_rel

  • agent

  • system

  • generic

  1. s_waitcnt lgkmcnt(0) & vmcnt(0)

  • If OpenCL, omit lgkmcnt(0).

  • Could be split into separate s_waitcnt vmcnt(0) and s_waitcnt lgkmcnt(0) to allow them to be independently moved according to the following rules.

  • s_waitcnt vmcnt(0) must happen after any preceding global/generic load/store/load atomic/store atomic/atomicrmw.

  • s_waitcnt lgkmcnt(0) must happen after any preceding local/generic load/store/load atomic/store atomic/atomicrmw.

  • Must happen before the following atomicrmw.

  • Ensures that all memory operations to global have completed before performing the atomicrmw that is being released.

  1. flat_atomic

  2. s_waitcnt vmcnt(0) & lgkmcnt(0)

  • If OpenCL, omit lgkmcnt(0).

  • Must happen before following buffer_wbinvl1_vol.

  • Ensures the atomicrmw has completed before invalidating the cache.

  1. buffer_wbinvl1_vol

  • Must happen before any following global/generic load/load atomic/atomicrmw.

  • Ensures that following loads will not see stale global data.

fence

acq_rel

  • singlethread

  • wavefront

none

none

fence

acq_rel

  • workgroup

none

  1. s_waitcnt lgkmcnt(0)

  • If OpenCL and address space is not generic, omit.

  • However, since LLVM currently has no address space on the fence need to conservatively always generate (see comment for previous fence).

  • Must happen after any preceding local/generic load/load atomic/store/store atomic/atomicrmw.

  • Must happen before any following global/generic load/load atomic/store/store atomic/atomicrmw.

  • Ensures that all memory operations to local have completed before performing any following global memory operations.

  • Ensures that the preceding local/generic load atomic/atomicrmw with an equal or wider sync scope and memory ordering stronger than unordered (this is termed the acquire-fence-paired-atomic) has completed before following global memory operations. This satisfies the requirements of acquire.

  • Ensures that all previous memory operations have completed before a following local/generic store atomic/atomicrmw with an equal or wider sync scope and memory ordering stronger than unordered (this is termed the release-fence-paired-atomic). This satisfies the requirements of release.

fence

acq_rel

  • agent

  • system

none

  1. s_waitcnt lgkmcnt(0) & vmcnt(0)

  • If OpenCL and address space is not generic, omit lgkmcnt(0).

  • See Fence and Address Spaces for more details on fencing specific address spaces.

  • Could be split into separate s_waitcnt vmcnt(0) and s_waitcnt lgkmcnt(0) to allow them to be independently moved according to the following rules.

  • s_waitcnt vmcnt(0) must happen after any preceding global/generic load/store/load atomic/store atomic/atomicrmw.

  • s_waitcnt lgkmcnt(0) must happen after any preceding local/generic load/store/load atomic/store atomic/atomicrmw.

  • Must happen before the following buffer_wbinvl1_vol.

  • Ensures that the preceding global/local/generic load atomic/atomicrmw with an equal or wider sync scope and memory ordering stronger than unordered (this is termed the acquire-fence-paired-atomic) has completed before invalidating the cache. This satisfies the requirements of acquire.

  • Ensures that all previous memory operations have completed before a following global/local/generic store atomic/atomicrmw with an equal or wider sync scope and memory ordering stronger than unordered (this is termed the release-fence-paired-atomic). This satisfies the requirements of release.

  1. buffer_wbinvl1_vol

  • Must happen before any following global/generic load/load atomic/store/store atomic/atomicrmw.

  • Ensures that following loads will not see stale global data. This satisfies the requirements of acquire.

Sequential Consistent Atomic

load atomic

seq_cst

  • singlethread

  • wavefront

  • global

  • local

  • generic

Same as corresponding load atomic acquire, except must generate all instructions even for OpenCL.

load atomic

seq_cst

  • workgroup

  • global

  • generic

  1. s_waitcnt lgkmcnt(0)

  • Must happen after preceding local/generic load atomic/store atomic/atomicrmw with memory ordering of seq_cst and with equal or wider sync scope. (Note that seq_cst fences have their own s_waitcnt lgkmcnt(0) and so do not need to be considered.)

  • Ensures any preceding sequential consistent local memory instructions have completed before executing this sequentially consistent instruction. This prevents reordering a seq_cst store followed by a seq_cst load. (Note that seq_cst is stronger than acquire/release as the reordering of load acquire followed by a store release is prevented by the s_waitcnt of the release, but there is nothing preventing a store release followed by load acquire from completing out of order. The s_waitcnt could be placed after seq_store or before the seq_load. We choose the load to make the s_waitcnt be as late as possible so that the store may have already completed.)

  1. Following instructions same as corresponding load atomic acquire, except must generate all instructions even for OpenCL.

load atomic

seq_cst

  • workgroup

  • local

Same as corresponding load atomic acquire, except must generate all instructions even for OpenCL.

load atomic

seq_cst

  • agent

  • system

  • global

  • generic

  1. s_waitcnt lgkmcnt(0) & vmcnt(0)

  • Could be split into separate s_waitcnt vmcnt(0) and s_waitcnt lgkmcnt(0) to allow them to be independently moved according to the following rules.

  • s_waitcnt lgkmcnt(0) must happen after preceding global/generic load atomic/store atomic/atomicrmw with memory ordering of seq_cst and with equal or wider sync scope. (Note that seq_cst fences have their own s_waitcnt lgkmcnt(0) and so do not need to be considered.)

  • s_waitcnt vmcnt(0) must happen after preceding global/generic load atomic/store atomic/atomicrmw with memory ordering of seq_cst and with equal or wider sync scope. (Note that seq_cst fences have their own s_waitcnt vmcnt(0) and so do not need to be considered.)

  • Ensures any preceding sequential consistent global memory instructions have completed before executing this sequentially consistent instruction. This prevents reordering a seq_cst store followed by a seq_cst load. (Note that seq_cst is stronger than acquire/release as the reordering of load acquire followed by a store release is prevented by the s_waitcnt of the release, but there is nothing preventing a store release followed by load acquire from completing out of order. The s_waitcnt could be placed after seq_store or before the seq_load. We choose the load to make the s_waitcnt be as late as possible so that the store may have already completed.)

  1. Following instructions same as corresponding load atomic acquire, except must generate all instructions even for OpenCL.

store atomic

seq_cst

  • singlethread

  • wavefront

  • workgroup

  • agent

  • system

  • global

  • local

  • generic

Same as corresponding store atomic release, except must generate all instructions even for OpenCL.

atomicrmw

seq_cst

  • singlethread

  • wavefront

  • workgroup

  • agent

  • system

  • global

  • local

  • generic

Same as corresponding atomicrmw acq_rel, except must generate all instructions even for OpenCL.

fence

seq_cst

  • singlethread

  • wavefront

  • workgroup

  • agent

  • system

none

Same as corresponding fence acq_rel, except must generate all instructions even for OpenCL.
Memory Model GFX90A

For GFX90A:

  • Each agent has multiple shader arrays (SA).

  • Each SA has multiple compute units (CU).

  • Each CU has multiple SIMDs that execute wavefronts.

  • The wavefronts for a single work-group are executed in the same CU but may be executed by different SIMDs. The exception is when in tgsplit execution mode when the wavefronts may be executed by different SIMDs in different CUs.

  • Each CU has a single LDS memory shared by the wavefronts of the work-groups executing on it. The exception is when in tgsplit execution mode when no LDS is allocated as wavefronts of the same work-group can be in different CUs.

  • All LDS operations of a CU are performed as wavefront wide operations in a global order and involve no caching. Completion is reported to a wavefront in execution order.

  • The LDS memory has multiple request queues shared by the SIMDs of a CU. Therefore, the LDS operations performed by different wavefronts of a work-group can be reordered relative to each other, which can result in reordering the visibility of vector memory operations with respect to LDS operations of other wavefronts in the same work-group. A s_waitcnt lgkmcnt(0) is required to ensure synchronization between LDS operations and vector memory operations between wavefronts of a work-group, but not between operations performed by the same wavefront.

  • The vector memory operations are performed as wavefront wide operations and completion is reported to a wavefront in execution order. The exception is that flat_load/store/atomic instructions can report out of vector memory order if they access LDS memory, and out of LDS operation order if they access global memory.

  • The vector memory operations access a single vector L1 cache shared by all SIMDs a CU. Therefore:

    • No special action is required for coherence between the lanes of a single wavefront.

    • No special action is required for coherence between wavefronts in the same work-group since they execute on the same CU. The exception is when in tgsplit execution mode as wavefronts of the same work-group can be in different CUs and so a buffer_wbinvl1_vol is required as described in the following item.

    • A buffer_wbinvl1_vol is required for coherence between wavefronts executing in different work-groups as they may be executing on different CUs.

  • The scalar memory operations access a scalar L1 cache shared by all wavefronts on a group of CUs. The scalar and vector L1 caches are not coherent. However, scalar operations are used in a restricted way so do not impact the memory model. See Memory Spaces.

  • The vector and scalar memory operations use an L2 cache shared by all CUs on the same agent.

    • The L2 cache has independent channels to service disjoint ranges of virtual addresses.

    • Each CU has a separate request queue per channel. Therefore, the vector and scalar memory operations performed by wavefronts executing in different work-groups (which may be executing on different CUs), or the same work-group if executing in tgsplit mode, of an agent can be reordered relative to each other. A s_waitcnt vmcnt(0) is required to ensure synchronization between vector memory operations of different CUs. It ensures a previous vector memory operation has completed before executing a subsequent vector memory or LDS operation and so can be used to meet the requirements of acquire and release.

    • The L2 cache of one agent can be kept coherent with other agents by: using the MTYPE RW (read-write) or MTYPE CC (cache-coherent) with the PTE C-bit for memory local to the L2; and using the MTYPE NC (non-coherent) with the PTE C-bit set or MTYPE UC (uncached) for memory not local to the L2.

      • Any local memory cache lines will be automatically invalidated by writes from CUs associated with other L2 caches, or writes from the CPU, due to the cache probe caused by coherent requests. Coherent requests are caused by GPU accesses to pages with the PTE C-bit set, by CPU accesses over XGMI, and by PCIe requests that are configured to be coherent requests.

      • XGMI accesses from the CPU to local memory may be cached on the CPU. Subsequent access from the GPU will automatically invalidate or writeback the CPU cache due to the L2 probe filter and and the PTE C-bit being set.

      • Since all work-groups on the same agent share the same L2, no L2 invalidation or writeback is required for coherence.

      • To ensure coherence of local and remote memory writes of work-groups in different agents a buffer_wbl2 is required. It will writeback dirty L2 cache lines of MTYPE RW (used for local coarse grain memory) and MTYPE NC ()used for remote coarse grain memory). Note that MTYPE CC (used for local fine grain memory) causes write through to DRAM, and MTYPE UC (used for remote fine grain memory) bypasses the L2, so both will never result in dirty L2 cache lines.

      • To ensure coherence of local and remote memory reads of work-groups in different agents a buffer_invl2 is required. It will invalidate L2 cache lines with MTYPE NC (used for remote coarse grain memory). Note that MTYPE CC (used for local fine grain memory) and MTYPE RW (used for local coarse memory) cause local reads to be invalidated by remote writes with with the PTE C-bit so these cache lines are not invalidated. Note that MTYPE UC (used for remote fine grain memory) bypasses the L2, so will never result in L2 cache lines that need to be invalidated.

    • PCIe access from the GPU to the CPU memory is kept coherent by using the MTYPE UC (uncached) which bypasses the L2.

Scalar memory operations are only used to access memory that is proven to not change during the execution of the kernel dispatch. This includes constant address space and global address space for program scope const variables. Therefore, the kernel machine code does not have to maintain the scalar cache to ensure it is coherent with the vector caches. The scalar and vector caches are invalidated between kernel dispatches by CP since constant address space data may change between kernel dispatch executions. See Memory Spaces.

The one exception is if scalar writes are used to spill SGPR registers. In this case the AMDGPU backend ensures the memory location used to spill is never accessed by vector memory operations at the same time. If scalar writes are used then a s_dcache_wb is inserted before the s_endpgm and before a function return since the locations may be used for vector memory instructions by a future wavefront that uses the same scratch area, or a function call that creates a frame at the same address, respectively. There is no need for a s_dcache_inv as all scalar writes are write-before-read in the same thread.

For kernarg backing memory:

  • CP invalidates the L1 cache at the start of each kernel dispatch.

  • On dGPU over XGMI or PCIe the kernarg backing memory is allocated in host memory accessed as MTYPE UC (uncached) to avoid needing to invalidate the L2 cache. This also causes it to be treated as non-volatile and so is not invalidated by *_vol.

  • On APU the kernarg backing memory is accessed as MTYPE CC (cache coherent) and so the L2 cache will be coherent with the CPU and other agents.

Scratch backing memory (which is used for the private address space) is accessed with MTYPE NC_NV (non-coherent non-volatile). Since the private address space is only accessed by a single thread, and is always write-before-read, there is never a need to invalidate these entries from the L1 cache. Hence all cache invalidates are done as *_vol to only invalidate the volatile cache lines.

The code sequences used to implement the memory model for GFX90A are defined in table AMDHSA Memory Model Code Sequences GFX90A.

Table 79 AMDHSA Memory Model Code Sequences GFX90A

LLVM Instr

LLVM Memory Ordering

LLVM Memory Sync Scope

AMDGPU Address Space

AMDGPU Machine Code GFX90A

Non-Atomic

load

none

none

  • global

  • generic

  • private

  • constant

  • !volatile & !nontemporal

    1. buffer/global/flat_load

  • !volatile & nontemporal

    1. buffer/global/flat_load glc=1 slc=1

  • volatile

    1. buffer/global/flat_load glc=1

    2. s_waitcnt vmcnt(0)

    • Must happen before any following volatile global/generic load/store.

    • Ensures that volatile operations to different addresses will not be reordered by hardware.

load

none

none

  • local

  1. ds_load

store

none

none

  • global

  • generic

  • private

  • constant

  • !volatile & !nontemporal

    1. buffer/global/flat_store

  • !volatile & nontemporal

    1. buffer/global/flat_store glc=1 slc=1

  • volatile

    1. buffer/global/flat_store

    2. s_waitcnt vmcnt(0)

    • Must happen before any following volatile global/generic load/store.

    • Ensures that volatile operations to different addresses will not be reordered by hardware.

store

none

none

  • local

  1. ds_store

Unordered Atomic

load atomic

unordered

any

any

Same as non-atomic.

store atomic

unordered

any

any

Same as non-atomic.

atomicrmw

unordered

any

any

Same as monotonic atomic.

Monotonic Atomic

load atomic

monotonic

  • singlethread

  • wavefront

  • global

  • generic

  1. buffer/global/flat_load

load atomic

monotonic

  • workgroup

  • global

  • generic

  1. buffer/global/flat_load glc=1

  • If not TgSplit execution mode, omit glc=1.

load atomic

monotonic

  • singlethread

  • wavefront

  • workgroup

  • local

If TgSplit execution mode, local address space cannot be used.

  1. ds_load

load atomic

monotonic

  • agent

  • global

  • generic

  1. buffer/global/flat_load glc=1

load atomic

monotonic

  • system

  • global

  • generic

  1. buffer/global/flat_load glc=1

store atomic

monotonic

  • singlethread

  • wavefront

  • workgroup

  • agent

  • global

  • generic

  1. buffer/global/flat_store

store atomic

monotonic

  • system

  • global

  • generic

  1. buffer/global/flat_store

store atomic

monotonic

  • singlethread

  • wavefront

  • workgroup

  • local

If TgSplit execution mode, local address space cannot be used.

  1. ds_store

atomicrmw

monotonic

  • singlethread

  • wavefront

  • workgroup

  • agent

  • global

  • generic

  1. buffer/global/flat_atomic

atomicrmw

monotonic

  • system

  • global

  • generic

  1. buffer/global/flat_atomic

atomicrmw

monotonic

  • singlethread

  • wavefront

  • workgroup

  • local

If TgSplit execution mode, local address space cannot be used.

  1. ds_atomic

Acquire Atomic

load atomic

acquire

  • singlethread

  • wavefront

  • global

  • local

  • generic

  1. buffer/global/ds/flat_load

load atomic

acquire

  • workgroup

  • global

  1. buffer/global_load glc=1

  • If not TgSplit execution mode, omit glc=1.

  1. s_waitcnt vmcnt(0)

  • If not TgSplit execution mode, omit.

  • Must happen before the following buffer_wbinvl1_vol.

  1. buffer_wbinvl1_vol

  • If not TgSplit execution mode, omit.

  • Must happen before any following global/generic load/load atomic/store/store atomic/atomicrmw.

  • Ensures that following loads will not see stale data.

load atomic

acquire

  • workgroup

  • local

If TgSplit execution mode, local address space cannot be used.

  1. ds_load

  2. s_waitcnt lgkmcnt(0)

  • If OpenCL, omit.

  • Must happen before any following global/generic load/load atomic/store/store atomic/atomicrmw.

  • Ensures any following global data read is no older than the local load atomic value being acquired.

load atomic

acquire

  • workgroup

  • generic

  1. flat_load glc=1

  • If not TgSplit execution mode, omit glc=1.

  1. s_waitcnt lgkm/vmcnt(0)

  • Use lgkmcnt(0) if not TgSplit execution mode and vmcnt(0) if TgSplit execution mode.

  • If OpenCL, omit lgkmcnt(0).

  • Must happen before the following buffer_wbinvl1_vol and any following global/generic load/load atomic/store/store atomic/atomicrmw.

  • Ensures any following global data read is no older than a local load atomic value being acquired.

  1. buffer_wbinvl1_vol

  • If not TgSplit execution mode, omit.

  • Ensures that following loads will not see stale data.

load atomic

acquire

  • agent

  • global

  1. buffer/global_load glc=1

  2. s_waitcnt vmcnt(0)

  • Must happen before following buffer_wbinvl1_vol.

  • Ensures the load has completed before invalidating the cache.

  1. buffer_wbinvl1_vol

  • Must happen before any following global/generic load/load atomic/atomicrmw.

  • Ensures that following loads will not see stale global data.

load atomic

acquire

  • system

  • global

  1. buffer/global/flat_load glc=1

  2. s_waitcnt vmcnt(0)

  • Must happen before following buffer_invl2 and buffer_wbinvl1_vol.

  • Ensures the load has completed before invalidating the cache.

  1. buffer_invl2; buffer_wbinvl1_vol

  • Must happen before any following global/generic load/load atomic/atomicrmw.

  • Ensures that following loads will not see stale L1 global data, nor see stale L2 MTYPE NC global data. MTYPE RW and CC memory will never be stale in L2 due to the memory probes.

load atomic

acquire

  • agent

  • generic

  1. flat_load glc=1

  2. s_waitcnt vmcnt(0) & lgkmcnt(0)

  • If TgSplit execution mode, omit lgkmcnt(0).

  • If OpenCL omit lgkmcnt(0).

  • Must happen before following buffer_wbinvl1_vol.

  • Ensures the flat_load has completed before invalidating the cache.

  1. buffer_wbinvl1_vol

  • Must happen before any following global/generic load/load atomic/atomicrmw.

  • Ensures that following loads will not see stale global data.

load atomic

acquire

  • system

  • generic

  1. flat_load glc=1

  2. s_waitcnt vmcnt(0) & lgkmcnt(0)

  • If TgSplit execution mode, omit lgkmcnt(0).

  • If OpenCL omit lgkmcnt(0).

  • Must happen before following buffer_invl2 and buffer_wbinvl1_vol.

  • Ensures the flat_load has completed before invalidating the caches.

  1. buffer_invl2; buffer_wbinvl1_vol

  • Must happen before any following global/generic load/load atomic/atomicrmw.

  • Ensures that following loads will not see stale L1 global data, nor see stale L2 MTYPE NC global data. MTYPE RW and CC memory will never be stale in L2 due to the memory probes.

atomicrmw

acquire

  • singlethread

  • wavefront

  • global

  • generic

  1. buffer/global/flat_atomic

atomicrmw

acquire

  • singlethread

  • wavefront

  • local

If TgSplit execution mode, local address space cannot be used.

  1. ds_atomic

atomicrmw

acquire

  • workgroup

  • global

  1. buffer/global_atomic

  2. s_waitcnt vmcnt(0)

  • If not TgSplit execution mode, omit.

  • Must happen before the following buffer_wbinvl1_vol.

  • Ensures the atomicrmw has completed before invalidating the cache.

  1. buffer_wbinvl1_vol

  • If not TgSplit execution mode, omit.

  • Must happen before any following global/generic load/load atomic/atomicrmw.

  • Ensures that following loads will not see stale global data.

atomicrmw

acquire

  • workgroup

  • local

If TgSplit execution mode, local address space cannot be used.

  1. ds_atomic

  2. s_waitcnt lgkmcnt(0)

  • If OpenCL, omit.

  • Must happen before any following global/generic load/load atomic/store/store atomic/atomicrmw.

  • Ensures any following global data read is no older than the local atomicrmw value being acquired.

atomicrmw

acquire

  • workgroup

  • generic

  1. flat_atomic

  2. s_waitcnt lgkm/vmcnt(0)

  • Use lgkmcnt(0) if not TgSplit execution mode and vmcnt(0) if TgSplit execution mode.

  • If OpenCL, omit lgkmcnt(0).

  • Must happen before the following buffer_wbinvl1_vol and any following global/generic load/load atomic/store/store atomic/atomicrmw.

  • Ensures any following global data read is no older than a local atomicrmw value being acquired.

  1. buffer_wbinvl1_vol

  • If not TgSplit execution mode, omit.

  • Ensures that following loads will not see stale data.

atomicrmw

acquire

  • agent

  • global

  1. buffer/global_atomic

  2. s_waitcnt vmcnt(0)

  • Must happen before following buffer_wbinvl1_vol.

  • Ensures the atomicrmw has completed before invalidating the cache.

  1. buffer_wbinvl1_vol

  • Must happen before any following global/generic load/load atomic/atomicrmw.

  • Ensures that following loads will not see stale global data.

atomicrmw

acquire

  • system

  • global

  1. buffer/global_atomic

  2. s_waitcnt vmcnt(0)

  • Must happen before following buffer_invl2 and buffer_wbinvl1_vol.

  • Ensures the atomicrmw has completed before invalidating the caches.

  1. buffer_invl2; buffer_wbinvl1_vol

  • Must happen before any following global/generic load/load atomic/atomicrmw.

  • Ensures that following loads will not see stale L1 global data, nor see stale L2 MTYPE NC global data. MTYPE RW and CC memory will never be stale in L2 due to the memory probes.

atomicrmw

acquire

  • agent

  • generic

  1. flat_atomic

  2. s_waitcnt vmcnt(0) & lgkmcnt(0)

  • If TgSplit execution mode, omit lgkmcnt(0).

  • If OpenCL, omit lgkmcnt(0).

  • Must happen before following buffer_wbinvl1_vol.

  • Ensures the atomicrmw has completed before invalidating the cache.

  1. buffer_wbinvl1_vol

  • Must happen before any following global/generic load/load atomic/atomicrmw.

  • Ensures that following loads will not see stale global data.

atomicrmw

acquire

  • system

  • generic

  1. flat_atomic

  2. s_waitcnt vmcnt(0) & lgkmcnt(0)

  • If TgSplit execution mode, omit lgkmcnt(0).

  • If OpenCL, omit lgkmcnt(0).

  • Must happen before following buffer_invl2 and buffer_wbinvl1_vol.

  • Ensures the atomicrmw has completed before invalidating the caches.

  1. buffer_invl2; buffer_wbinvl1_vol

  • Must happen before any following global/generic load/load atomic/atomicrmw.

  • Ensures that following loads will not see stale L1 global data, nor see stale L2 MTYPE NC global data. MTYPE RW and CC memory will never be stale in L2 due to the memory probes.

fence

acquire

  • singlethread

  • wavefront

none

none

fence

acquire

  • workgroup

none

  1. s_waitcnt lgkm/vmcnt(0)

  • Use lgkmcnt(0) if not TgSplit execution mode and vmcnt(0) if TgSplit execution mode.

  • If OpenCL and address space is not generic, omit lgkmcnt(0).

  • If OpenCL and address space is local, omit vmcnt(0).

  • See Fence and Address Spaces for more details on fencing specific address spaces.

  • s_waitcnt vmcnt(0) must happen after any preceding global/generic load atomic/ atomicrmw with an equal or wider sync scope and memory ordering stronger than unordered (this is termed the fence-paired-atomic).

  • s_waitcnt lgkmcnt(0) must happen after any preceding local/generic load atomic/atomicrmw with an equal or wider sync scope and memory ordering stronger than unordered (this is termed the fence-paired-atomic).

  • Must happen before the following buffer_wbinvl1_vol and any following global/generic load/load atomic/store/store atomic/atomicrmw.

  • Ensures any following global data read is no older than the value read by the fence-paired-atomic.

  1. buffer_wbinvl1_vol

  • If not TgSplit execution mode, omit.

  • Ensures that following loads will not see stale data.

fence

acquire

  • agent

none

  1. s_waitcnt lgkmcnt(0) & vmcnt(0)

  • If TgSplit execution mode, omit lgkmcnt(0).

  • If OpenCL and address space is not generic, omit lgkmcnt(0).

  • See Fence and Address Spaces for more details on fencing specific address spaces.

  • Could be split into separate s_waitcnt vmcnt(0) and s_waitcnt lgkmcnt(0) to allow them to be independently moved according to the following rules.

  • s_waitcnt vmcnt(0) must happen after any preceding global/generic load atomic/atomicrmw with an equal or wider sync scope and memory ordering stronger than unordered (this is termed the fence-paired-atomic).

  • s_waitcnt lgkmcnt(0) must happen after any preceding local/generic load atomic/atomicrmw with an equal or wider sync scope and memory ordering stronger than unordered (this is termed the fence-paired-atomic).

  • Must happen before the following buffer_wbinvl1_vol.

  • Ensures that the fence-paired atomic has completed before invalidating the cache. Therefore any following locations read must be no older than the value read by the fence-paired-atomic.

  1. buffer_wbinvl1_vol

  • Must happen before any following global/generic load/load atomic/store/store atomic/atomicrmw.

  • Ensures that following loads will not see stale global data.

fence

acquire

  • system

none

  1. s_waitcnt lgkmcnt(0) & vmcnt(0)

  • If TgSplit execution mode, omit lgkmcnt(0).

  • If OpenCL and address space is not generic, omit lgkmcnt(0).

  • See Fence and Address Spaces for more details on fencing specific address spaces.

  • Could be split into separate s_waitcnt vmcnt(0) and s_waitcnt lgkmcnt(0) to allow them to be independently moved according to the following rules.

  • s_waitcnt vmcnt(0) must happen after any preceding global/generic load atomic/atomicrmw with an equal or wider sync scope and memory ordering stronger than unordered (this is termed the fence-paired-atomic).

  • s_waitcnt lgkmcnt(0) must happen after any preceding local/generic load atomic/atomicrmw with an equal or wider sync scope and memory ordering stronger than unordered (this is termed the fence-paired-atomic).

  • Must happen before the following buffer_invl2 and buffer_wbinvl1_vol.

  • Ensures that the fence-paired atomic has completed before invalidating the cache. Therefore any following locations read must be no older than the value read by the fence-paired-atomic.

  1. buffer_invl2; buffer_wbinvl1_vol

  • Must happen before any following global/generic load/load atomic/store/store atomic/atomicrmw.

  • Ensures that following loads will not see stale L1 global data, nor see stale L2 MTYPE NC global data. MTYPE RW and CC memory will never be stale in L2 due to the memory probes.

Release Atomic

store atomic

release

  • singlethread

  • wavefront

  • global

  • generic

  1. buffer/global/flat_store

store atomic

release

  • singlethread

  • wavefront

  • local

If TgSplit execution mode, local address space cannot be used.

  1. ds_store

store atomic

release

  • workgroup

  • global

  • generic

  1. s_waitcnt lgkm/vmcnt(0)

  • Use lgkmcnt(0) if not TgSplit execution mode and vmcnt(0) if TgSplit execution mode.

  • If OpenCL, omit lgkmcnt(0).

  • s_waitcnt vmcnt(0) must happen after any preceding global/generic load/store/ load atomic/store atomic/ atomicrmw.

  • s_waitcnt lgkmcnt(0) must happen after any preceding local/generic load/store/load atomic/store atomic/atomicrmw.

  • Must happen before the following store.

  • Ensures that all memory operations have completed before performing the store that is being released.

  1. buffer/global/flat_store

store atomic

release

  • workgroup

  • local

If TgSplit execution mode, local address space cannot be used.

  1. ds_store

store atomic

release

  • agent

  • global

  • generic

  1. s_waitcnt lgkmcnt(0) & vmcnt(0)

  • If TgSplit execution mode, omit lgkmcnt(0).

  • If OpenCL and address space is not generic, omit lgkmcnt(0).

  • Could be split into separate s_waitcnt vmcnt(0) and s_waitcnt lgkmcnt(0) to allow them to be independently moved according to the following rules.

  • s_waitcnt vmcnt(0) must happen after any preceding global/generic load/store/load atomic/store atomic/atomicrmw.

  • s_waitcnt lgkmcnt(0) must happen after any preceding local/generic load/store/load atomic/store atomic/atomicrmw.

  • Must happen before the following store.

  • Ensures that all memory operations to memory have completed before performing the store that is being released.

  1. buffer/global/flat_store

store atomic

release

  • system

  • global

  • generic

  1. buffer_wbl2

  • Must happen before following s_waitcnt.

  • Performs L2 writeback to ensure previous global/generic store/atomicrmw are visible at system scope.

  1. s_waitcnt lgkmcnt(0) & vmcnt(0)

  • If TgSplit execution mode, omit lgkmcnt(0).

  • If OpenCL and address space is not generic, omit lgkmcnt(0).

  • Could be split into separate s_waitcnt vmcnt(0) and s_waitcnt lgkmcnt(0) to allow them to be independently moved according to the following rules.

  • s_waitcnt vmcnt(0) must happen after any preceding global/generic load/store/load atomic/store atomic/atomicrmw.

  • s_waitcnt lgkmcnt(0) must happen after any preceding local/generic load/store/load atomic/store atomic/atomicrmw.

  • Must happen before the following store.

  • Ensures that all memory operations to memory and the L2 writeback have completed before performing the store that is being released.

  1. buffer/global/flat_store

atomicrmw

release

  • singlethread

  • wavefront

  • global

  • generic

  1. buffer/global/flat_atomic

atomicrmw

release

  • singlethread

  • wavefront

  • local

If TgSplit execution mode, local address space cannot be used.

  1. ds_atomic

atomicrmw

release

  • workgroup

  • global

  • generic

  1. s_waitcnt lgkm/vmcnt(0)

  • Use lgkmcnt(0) if not TgSplit execution mode and vmcnt(0) if TgSplit execution mode.

  • If OpenCL, omit lgkmcnt(0).

  • s_waitcnt vmcnt(0) must happen after any preceding global/generic load/store/ load atomic/store atomic/ atomicrmw.

  • s_waitcnt lgkmcnt(0) must happen after any preceding local/generic load/store/load atomic/store atomic/atomicrmw.

  • Must happen before the following atomicrmw.

  • Ensures that all memory operations have completed before performing the atomicrmw that is being released.

  1. buffer/global/flat_atomic

atomicrmw

release

  • workgroup

  • local

If TgSplit execution mode, local address space cannot be used.

  1. ds_atomic

atomicrmw

release

  • agent

  • global

  • generic

  1. s_waitcnt lgkmcnt(0) & vmcnt(0)

  • If TgSplit execution mode, omit lgkmcnt(0).

  • If OpenCL, omit lgkmcnt(0).

  • Could be split into separate s_waitcnt vmcnt(0) and s_waitcnt lgkmcnt(0) to allow them to be independently moved according to the following rules.

  • s_waitcnt vmcnt(0) must happen after any preceding global/generic load/store/load atomic/store atomic/atomicrmw.

  • s_waitcnt lgkmcnt(0) must happen after any preceding local/generic load/store/load atomic/store atomic/atomicrmw.

  • Must happen before the following atomicrmw.

  • Ensures that all memory operations to global and local have completed before performing the atomicrmw that is being released.

  1. buffer/global/flat_atomic

atomicrmw

release

  • system

  • global

  • generic

  1. buffer_wbl2

  • Must happen before following s_waitcnt.

  • Performs L2 writeback to ensure previous global/generic store/atomicrmw are visible at system scope.

  1. s_waitcnt lgkmcnt(0) & vmcnt(0)

  • If TgSplit execution mode, omit lgkmcnt(0).

  • If OpenCL, omit lgkmcnt(0).

  • Could be split into separate s_waitcnt vmcnt(0) and s_waitcnt lgkmcnt(0) to allow them to be independently moved according to the following rules.

  • s_waitcnt vmcnt(0) must happen after any preceding global/generic load/store/load atomic/store atomic/atomicrmw.

  • s_waitcnt lgkmcnt(0) must happen after any preceding local/generic load/store/load atomic/store atomic/atomicrmw.

  • Must happen before the following atomicrmw.

  • Ensures that all memory operations to memory and the L2 writeback have completed before performing the store that is being released.

  1. buffer/global/flat_atomic

fence

release

  • singlethread

  • wavefront

none

none

fence

release

  • workgroup

none

  1. s_waitcnt lgkm/vmcnt(0)

  • Use lgkmcnt(0) if not TgSplit execution mode and vmcnt(0) if TgSplit execution mode.

  • If OpenCL and address space is not generic, omit lgkmcnt(0).

  • If OpenCL and address space is local, omit vmcnt(0).

  • See Fence and Address Spaces for more details on fencing specific address spaces.

  • s_waitcnt vmcnt(0) must happen after any preceding global/generic load/store/ load atomic/store atomic/ atomicrmw.

  • s_waitcnt lgkmcnt(0) must happen after any preceding local/generic load/load atomic/store/store atomic/atomicrmw.

  • Must happen before any following store atomic/atomicrmw with an equal or wider sync scope and memory ordering stronger than unordered (this is termed the fence-paired-atomic).

  • Ensures that all memory operations have completed before performing the following fence-paired-atomic.

fence

release

  • agent

none

  1. s_waitcnt lgkmcnt(0) & vmcnt(0)

  • If TgSplit execution mode, omit lgkmcnt(0).

  • If OpenCL and address space is not generic, omit lgkmcnt(0).

  • If OpenCL and address space is local, omit vmcnt(0).

  • See Fence and Address Spaces for more details on fencing specific address spaces.

  • Could be split into separate s_waitcnt vmcnt(0) and s_waitcnt lgkmcnt(0) to allow them to be independently moved according to the following rules.

  • s_waitcnt vmcnt(0) must happen after any preceding global/generic load/store/load atomic/store atomic/atomicrmw.

  • s_waitcnt lgkmcnt(0) must happen after any preceding local/generic load/store/load atomic/store atomic/atomicrmw.

  • Must happen before any following store atomic/atomicrmw with an equal or wider sync scope and memory ordering stronger than unordered (this is termed the fence-paired-atomic).

  • Ensures that all memory operations have completed before performing the following fence-paired-atomic.

fence

release

  • system

none

  1. buffer_wbl2

  • If OpenCL and address space is local, omit.

  • Must happen before following s_waitcnt.

  • Performs L2 writeback to ensure previous global/generic store/atomicrmw are visible at system scope.

  1. s_waitcnt lgkmcnt(0) & vmcnt(0)

  • If TgSplit execution mode, omit lgkmcnt(0).

  • If OpenCL and address space is not generic, omit lgkmcnt(0).

  • If OpenCL and address space is local, omit vmcnt(0).

  • See Fence and Address Spaces for more details on fencing specific address spaces.

  • Could be split into separate s_waitcnt vmcnt(0) and s_waitcnt lgkmcnt(0) to allow them to be independently moved according to the following rules.

  • s_waitcnt vmcnt(0) must happen after any preceding global/generic load/store/load atomic/store atomic/atomicrmw.

  • s_waitcnt lgkmcnt(0) must happen after any preceding local/generic load/store/load atomic/store atomic/atomicrmw.

  • Must happen before any following store atomic/atomicrmw with an equal or wider sync scope and memory ordering stronger than unordered (this is termed the fence-paired-atomic).

  • Ensures that all memory operations have completed before performing the following fence-paired-atomic.

Acquire-Release Atomic

atomicrmw

acq_rel

  • singlethread

  • wavefront

  • global

  • generic

  1. buffer/global/flat_atomic

atomicrmw

acq_rel

  • singlethread

  • wavefront

  • local

If TgSplit execution mode, local address space cannot be used.

  1. ds_atomic

atomicrmw

acq_rel

  • workgroup

  • global

  1. s_waitcnt lgkm/vmcnt(0)

  • Use lgkmcnt(0) if not TgSplit execution mode and vmcnt(0) if TgSplit execution mode.

  • If OpenCL, omit lgkmcnt(0).

  • Must happen after any preceding local/generic load/store/load atomic/store atomic/atomicrmw.

  • s_waitcnt vmcnt(0) must happen after any preceding global/generic load/store/ load atomic/store atomic/ atomicrmw.

  • s_waitcnt lgkmcnt(0) must happen after any preceding local/generic load/store/load atomic/store atomic/atomicrmw.

  • Must happen before the following atomicrmw.

  • Ensures that all memory operations have completed before performing the atomicrmw that is being released.

  1. buffer/global_atomic

  2. s_waitcnt vmcnt(0)

  • If not TgSplit execution mode, omit.

  • Must happen before the following buffer_wbinvl1_vol.

  • Ensures any following global data read is no older than the atomicrmw value being acquired.

  1. buffer_wbinvl1_vol

  • If not TgSplit execution mode, omit.

  • Ensures that following loads will not see stale data.

atomicrmw

acq_rel

  • workgroup

  • local

If TgSplit execution mode, local address space cannot be used.

  1. ds_atomic

  2. s_waitcnt lgkmcnt(0)

  • If OpenCL, omit.

  • Must happen before any following global/generic load/load atomic/store/store atomic/atomicrmw.

  • Ensures any following global data read is no older than the local load atomic value being acquired.

atomicrmw

acq_rel

  • workgroup

  • generic

  1. s_waitcnt lgkm/vmcnt(0)

  • Use lgkmcnt(0) if not TgSplit execution mode and vmcnt(0) if TgSplit execution mode.

  • If OpenCL, omit lgkmcnt(0).

  • s_waitcnt vmcnt(0) must happen after any preceding global/generic load/store/ load atomic/store atomic/ atomicrmw.

  • s_waitcnt lgkmcnt(0) must happen after any preceding local/generic load/store/load atomic/store atomic/atomicrmw.

  • Must happen before the following atomicrmw.

  • Ensures that all memory operations have completed before performing the atomicrmw that is being released.

  1. flat_atomic

  2. s_waitcnt lgkmcnt(0) & vmcnt(0)

  • If not TgSplit execution mode, omit vmcnt(0).

  • If OpenCL, omit lgkmcnt(0).

  • Must happen before the following buffer_wbinvl1_vol and any following global/generic load/load atomic/store/store atomic/atomicrmw.

  • Ensures any following global data read is no older than a local load atomic value being acquired.

  1. buffer_wbinvl1_vol

  • If not TgSplit execution mode, omit.

  • Ensures that following loads will not see stale data.

atomicrmw

acq_rel

  • agent

  • global

  1. s_waitcnt lgkmcnt(0) & vmcnt(0)

  • If TgSplit execution mode, omit lgkmcnt(0).

  • If OpenCL, omit lgkmcnt(0).

  • Could be split into separate s_waitcnt vmcnt(0) and s_waitcnt lgkmcnt(0) to allow them to be independently moved according to the following rules.

  • s_waitcnt vmcnt(0) must happen after any preceding global/generic load/store/load atomic/store atomic/atomicrmw.

  • s_waitcnt lgkmcnt(0) must happen after any preceding local/generic load/store/load atomic/store atomic/atomicrmw.

  • Must happen before the following atomicrmw.

  • Ensures that all memory operations to global have completed before performing the atomicrmw that is being released.

  1. buffer/global_atomic

  2. s_waitcnt vmcnt(0)

  • Must happen before following buffer_wbinvl1_vol.

  • Ensures the atomicrmw has completed before invalidating the cache.

  1. buffer_wbinvl1_vol

  • Must happen before any following global/generic load/load atomic/atomicrmw.

  • Ensures that following loads will not see stale global data.

atomicrmw

acq_rel

  • system

  • global

  1. buffer_wbl2

  • Must happen before following s_waitcnt.

  • Performs L2 writeback to ensure previous global/generic store/atomicrmw are visible at system scope.

  1. s_waitcnt lgkmcnt(0) & vmcnt(0)

  • If TgSplit execution mode, omit lgkmcnt(0).

  • If OpenCL, omit lgkmcnt(0).

  • Could be split into separate s_waitcnt vmcnt(0) and s_waitcnt lgkmcnt(0) to allow them to be independently moved according to the following rules.

  • s_waitcnt vmcnt(0) must happen after any preceding global/generic load/store/load atomic/store atomic/atomicrmw.

  • s_waitcnt lgkmcnt(0) must happen after any preceding local/generic load/store/load atomic/store atomic/atomicrmw.

  • Must happen before the following atomicrmw.

  • Ensures that all memory operations to global and L2 writeback have completed before performing the atomicrmw that is being released.

  1. buffer/global_atomic

  2. s_waitcnt vmcnt(0)

  • Must happen before following buffer_invl2 and buffer_wbinvl1_vol.

  • Ensures the atomicrmw has completed before invalidating the caches.

  1. buffer_invl2; buffer_wbinvl1_vol

  • Must happen before any following global/generic load/load atomic/atomicrmw.

  • Ensures that following loads will not see stale L1 global data, nor see stale L2 MTYPE NC global data. MTYPE RW and CC memory will never be stale in L2 due to the memory probes.

atomicrmw

acq_rel

  • agent

  • generic

  1. s_waitcnt lgkmcnt(0) & vmcnt(0)

  • If TgSplit execution mode, omit lgkmcnt(0).

  • If OpenCL, omit lgkmcnt(0).

  • Could be split into separate s_waitcnt vmcnt(0) and s_waitcnt lgkmcnt(0) to allow them to be independently moved according to the following rules.

  • s_waitcnt vmcnt(0) must happen after any preceding global/generic load/store/load atomic/store atomic/atomicrmw.

  • s_waitcnt lgkmcnt(0) must happen after any preceding local/generic load/store/load atomic/store atomic/atomicrmw.

  • Must happen before the following atomicrmw.

  • Ensures that all memory operations to global have completed before performing the atomicrmw that is being released.

  1. flat_atomic

  2. s_waitcnt vmcnt(0) & lgkmcnt(0)

  • If TgSplit execution mode, omit lgkmcnt(0).

  • If OpenCL, omit lgkmcnt(0).

  • Must happen before following buffer_wbinvl1_vol.

  • Ensures the atomicrmw has completed before invalidating the cache.

  1. buffer_wbinvl1_vol

  • Must happen before any following global/generic load/load atomic/atomicrmw.

  • Ensures that following loads will not see stale global data.

atomicrmw

acq_rel

  • system

  • generic

  1. buffer_wbl2

  • Must happen before following s_waitcnt.

  • Performs L2 writeback to ensure previous global/generic store/atomicrmw are visible at system scope.

  1. s_waitcnt lgkmcnt(0) & vmcnt(0)

  • If TgSplit execution mode, omit lgkmcnt(0).

  • If OpenCL, omit lgkmcnt(0).

  • Could be split into separate s_waitcnt vmcnt(0) and s_waitcnt lgkmcnt(0) to allow them to be independently moved according to the following rules.

  • s_waitcnt vmcnt(0) must happen after any preceding global/generic load/store/load atomic/store atomic/atomicrmw.

  • s_waitcnt lgkmcnt(0) must happen after any preceding local/generic load/store/load atomic/store atomic/atomicrmw.

  • Must happen before the following atomicrmw.

  • Ensures that all memory operations to global and L2 writeback have completed before performing the atomicrmw that is being released.

  1. flat_atomic

  2. s_waitcnt vmcnt(0) & lgkmcnt(0)

  • If TgSplit execution mode, omit lgkmcnt(0).

  • If OpenCL, omit lgkmcnt(0).

  • Must happen before following buffer_invl2 and buffer_wbinvl1_vol.

  • Ensures the atomicrmw has completed before invalidating the caches.

  1. buffer_invl2; buffer_wbinvl1_vol

  • Must happen before any following global/generic load/load atomic/atomicrmw.

  • Ensures that following loads will not see stale L1 global data, nor see stale L2 MTYPE NC global data. MTYPE RW and CC memory will never be stale in L2 due to the memory probes.

fence

acq_rel

  • singlethread

  • wavefront

none

none

fence

acq_rel

  • workgroup

none

  1. s_waitcnt lgkm/vmcnt(0)

  • Use lgkmcnt(0) if not TgSplit execution mode and vmcnt(0) if TgSplit execution mode.

  • If OpenCL and address space is not generic, omit lgkmcnt(0).

  • If OpenCL and address space is local, omit vmcnt(0).

  • However, since LLVM currently has no address space on the fence need to conservatively always generate (see comment for previous fence).

  • s_waitcnt vmcnt(0) must happen after any preceding global/generic load/store/ load atomic/store atomic/ atomicrmw.

  • s_waitcnt lgkmcnt(0) must happen after any preceding local/generic load/load atomic/store/store atomic/atomicrmw.

  • Must happen before any following global/generic load/load atomic/store/store atomic/atomicrmw.

  • Ensures that all memory operations have completed before performing any following global memory operations.

  • Ensures that the preceding local/generic load atomic/atomicrmw with an equal or wider sync scope and memory ordering stronger than unordered (this is termed the acquire-fence-paired-atomic) has completed before following global memory operations. This satisfies the requirements of acquire.

  • Ensures that all previous memory operations have completed before a following local/generic store atomic/atomicrmw with an equal or wider sync scope and memory ordering stronger than unordered (this is termed the release-fence-paired-atomic). This satisfies the requirements of release.

  • Must happen before the following buffer_wbinvl1_vol.

  • Ensures that the acquire-fence-paired atomic has completed before invalidating the cache. Therefore any following locations read must be no older than the value read by the acquire-fence-paired-atomic.

  1. buffer_wbinvl1_vol

  • If not TgSplit execution mode, omit.

  • Ensures that following loads will not see stale data.

fence

acq_rel

  • agent

none

  1. s_waitcnt lgkmcnt(0) & vmcnt(0)

  • If TgSplit execution mode, omit lgkmcnt(0).

  • If OpenCL and address space is not generic, omit lgkmcnt(0).

  • See Fence and Address Spaces for more details on fencing specific address spaces.

  • Could be split into separate s_waitcnt vmcnt(0) and s_waitcnt lgkmcnt(0) to allow them to be independently moved according to the following rules.

  • s_waitcnt vmcnt(0) must happen after any preceding global/generic load/store/load atomic/store atomic/atomicrmw.

  • s_waitcnt lgkmcnt(0) must happen after any preceding local/generic load/store/load atomic/store atomic/atomicrmw.

  • Must happen before the following buffer_wbinvl1_vol.

  • Ensures that the preceding global/local/generic load atomic/atomicrmw with an equal or wider sync scope and memory ordering stronger than unordered (this is termed the acquire-fence-paired-atomic) has completed before invalidating the cache. This satisfies the requirements of acquire.

  • Ensures that all previous memory operations have completed before a following global/local/generic store atomic/atomicrmw with an equal or wider sync scope and memory ordering stronger than unordered (this is termed the release-fence-paired-atomic). This satisfies the requirements of release.

  1. buffer_wbinvl1_vol

  • Must happen before any following global/generic load/load atomic/store/store atomic/atomicrmw.

  • Ensures that following loads will not see stale global data. This satisfies the requirements of acquire.

fence

acq_rel

  • system

none

  1. buffer_wbl2

  • If OpenCL and address space is local, omit.

  • Must happen before following s_waitcnt.

  • Performs L2 writeback to ensure previous global/generic store/atomicrmw are visible at system scope.

  1. s_waitcnt lgkmcnt(0) & vmcnt(0)

  • If TgSplit execution mode, omit lgkmcnt(0).

  • If OpenCL and address space is not generic, omit lgkmcnt(0).

  • See Fence and Address Spaces for more details on fencing specific address spaces.

  • Could be split into separate s_waitcnt vmcnt(0) and s_waitcnt lgkmcnt(0) to allow them to be independently moved according to the following rules.

  • s_waitcnt vmcnt(0) must happen after any preceding global/generic load/store/load atomic/store atomic/atomicrmw.

  • s_waitcnt lgkmcnt(0) must happen after any preceding local/generic load/store/load atomic/store atomic/atomicrmw.

  • Must happen before the following buffer_invl2 and buffer_wbinvl1_vol.

  • Ensures that the preceding global/local/generic load atomic/atomicrmw with an equal or wider sync scope and memory ordering stronger than unordered (this is termed the acquire-fence-paired-atomic) has completed before invalidating the cache. This satisfies the requirements of acquire.

  • Ensures that all previous memory operations have completed before a following global/local/generic store atomic/atomicrmw with an equal or wider sync scope and memory ordering stronger than unordered (this is termed the release-fence-paired-atomic). This satisfies the requirements of release.

  1. buffer_invl2; buffer_wbinvl1_vol

  • Must happen before any following global/generic load/load atomic/store/store atomic/atomicrmw.

  • Ensures that following loads will not see stale L1 global data, nor see stale L2 MTYPE NC global data. MTYPE RW and CC memory will never be stale in L2 due to the memory probes.

Sequential Consistent Atomic

load atomic

seq_cst

  • singlethread

  • wavefront

  • global

  • local

  • generic

Same as corresponding load atomic acquire, except must generate all instructions even for OpenCL.

load atomic

seq_cst

  • workgroup

  • global

  • generic

  1. s_waitcnt lgkm/vmcnt(0)

  • Use lgkmcnt(0) if not TgSplit execution mode and vmcnt(0) if TgSplit execution mode.

  • s_waitcnt lgkmcnt(0) must happen after preceding local/generic load atomic/store atomic/atomicrmw with memory ordering of seq_cst and with equal or wider sync scope. (Note that seq_cst fences have their own s_waitcnt lgkmcnt(0) and so do not need to be considered.)

  • s_waitcnt vmcnt(0) must happen after preceding global/generic load atomic/store atomic/atomicrmw with memory ordering of seq_cst and with equal or wider sync scope. (Note that seq_cst fences have their own s_waitcnt vmcnt(0) and so do not need to be considered.)

  • Ensures any preceding sequential consistent global/local memory instructions have completed before executing this sequentially consistent instruction. This prevents reordering a seq_cst store followed by a seq_cst load. (Note that seq_cst is stronger than acquire/release as the reordering of load acquire followed by a store release is prevented by the s_waitcnt of the release, but there is nothing preventing a store release followed by load acquire from completing out of order. The s_waitcnt could be placed after seq_store or before the seq_load. We choose the load to make the s_waitcnt be as late as possible so that the store may have already completed.)

  1. Following instructions same as corresponding load atomic acquire, except must generate all instructions even for OpenCL.

load atomic

seq_cst

  • workgroup

  • local

If TgSplit execution mode, local address space cannot be used.

Same as corresponding load atomic acquire, except must generate all instructions even for OpenCL.

load atomic

seq_cst

  • agent

  • system

  • global

  • generic

  1. s_waitcnt lgkmcnt(0) & vmcnt(0)

  • If TgSplit execution mode, omit lgkmcnt(0).

  • Could be split into separate s_waitcnt vmcnt(0) and s_waitcnt lgkmcnt(0) to allow them to be independently moved according to the following rules.

  • s_waitcnt lgkmcnt(0) must happen after preceding global/generic load atomic/store atomic/atomicrmw with memory ordering of seq_cst and with equal or wider sync scope. (Note that seq_cst fences have their own s_waitcnt lgkmcnt(0) and so do not need to be considered.)

  • s_waitcnt vmcnt(0) must happen after preceding global/generic load atomic/store atomic/atomicrmw with memory ordering of seq_cst and with equal or wider sync scope. (Note that seq_cst fences have their own s_waitcnt vmcnt(0) and so do not need to be considered.)

  • Ensures any preceding sequential consistent global memory instructions have completed before executing this sequentially consistent instruction. This prevents reordering a seq_cst store followed by a seq_cst load. (Note that seq_cst is stronger than acquire/release as the reordering of load acquire followed by a store release is prevented by the s_waitcnt of the release, but there is nothing preventing a store release followed by load acquire from completing out of order. The s_waitcnt could be placed after seq_store or before the seq_load. We choose the load to make the s_waitcnt be as late as possible so that the store may have already completed.)

  1. Following instructions same as corresponding load atomic acquire, except must generate all instructions even for OpenCL.

store atomic

seq_cst

  • singlethread

  • wavefront

  • workgroup

  • agent

  • system

  • global

  • local

  • generic

Same as corresponding store atomic release, except must generate all instructions even for OpenCL.

atomicrmw

seq_cst

  • singlethread

  • wavefront

  • workgroup

  • agent

  • system

  • global

  • local

  • generic

Same as corresponding atomicrmw acq_rel, except must generate all instructions even for OpenCL.

fence

seq_cst

  • singlethread

  • wavefront

  • workgroup

  • agent

  • system

none

Same as corresponding fence acq_rel, except must generate all instructions even for OpenCL.
Memory Model GFX942

For GFX942:

  • Each agent has multiple shader arrays (SA).

  • Each SA has multiple compute units (CU).

  • Each CU has multiple SIMDs that execute wavefronts.

  • The wavefronts for a single work-group are executed in the same CU but may be executed by different SIMDs. The exception is when in tgsplit execution mode when the wavefronts may be executed by different SIMDs in different CUs.

  • Each CU has a single LDS memory shared by the wavefronts of the work-groups executing on it. The exception is when in tgsplit execution mode when no LDS is allocated as wavefronts of the same work-group can be in different CUs.

  • All LDS operations of a CU are performed as wavefront wide operations in a global order and involve no caching. Completion is reported to a wavefront in execution order.

  • The LDS memory has multiple request queues shared by the SIMDs of a CU. Therefore, the LDS operations performed by different wavefronts of a work-group can be reordered relative to each other, which can result in reordering the visibility of vector memory operations with respect to LDS operations of other wavefronts in the same work-group. A s_waitcnt lgkmcnt(0) is required to ensure synchronization between LDS operations and vector memory operations between wavefronts of a work-group, but not between operations performed by the same wavefront.

  • The vector memory operations are performed as wavefront wide operations and completion is reported to a wavefront in execution order. The exception is that flat_load/store/atomic instructions can report out of vector memory order if they access LDS memory, and out of LDS operation order if they access global memory.

  • The vector memory operations access a single vector L1 cache shared by all SIMDs a CU. Therefore:

    • No special action is required for coherence between the lanes of a single wavefront.

    • No special action is required for coherence between wavefronts in the same work-group since they execute on the same CU. The exception is when in tgsplit execution mode as wavefronts of the same work-group can be in different CUs and so a buffer_inv sc0 is required which will invalidate the L1 cache.

    • A buffer_inv sc0 is required to invalidate the L1 cache for coherence between wavefronts executing in different work-groups as they may be executing on different CUs.

    • Atomic read-modify-write instructions implicitly bypass the L1 cache. Therefore, they do not use the sc0 bit for coherence and instead use it to indicate if the instruction returns the original value being updated. They do use sc1 to indicate system or agent scope coherence.

  • The scalar memory operations access a scalar L1 cache shared by all wavefronts on a group of CUs. The scalar and vector L1 caches are not coherent. However, scalar operations are used in a restricted way so do not impact the memory model. See Memory Spaces.

  • The vector and scalar memory operations use an L2 cache.

    • The gfx942 can be configured as a number of smaller agents with each having a single L2 shared by all CUs on the same agent, or as fewer (possibly one) larger agents with groups of CUs on each agent each sharing separate L2 caches.

    • The L2 cache has independent channels to service disjoint ranges of virtual addresses.

    • Each CU has a separate request queue per channel for its associated L2. Therefore, the vector and scalar memory operations performed by wavefronts executing with different L1 caches and the same L2 cache can be reordered relative to each other.

    • A s_waitcnt vmcnt(0) is required to ensure synchronization between vector memory operations of different CUs. It ensures a previous vector memory operation has completed before executing a subsequent vector memory or LDS operation and so can be used to meet the requirements of acquire and release.

    • An L2 cache can be kept coherent with other L2 caches by using the MTYPE RW (read-write) for memory local to the L2, and MTYPE NC (non-coherent) with the PTE C-bit set for memory not local to the L2.

      • Any local memory cache lines will be automatically invalidated by writes from CUs associated with other L2 caches, or writes from the CPU, due to the cache probe caused by the PTE C-bit.

      • XGMI accesses from the CPU to local memory may be cached on the CPU. Subsequent access from the GPU will automatically invalidate or writeback the CPU cache due to the L2 probe filter.

      • To ensure coherence of local memory writes of CUs with different L1 caches in the same agent a buffer_wbl2 is required. It does nothing if the agent is configured to have a single L2, or will writeback dirty L2 cache lines if configured to have multiple L2 caches.

      • To ensure coherence of local memory writes of CUs in different agents a buffer_wbl2 sc1 is required. It will writeback dirty L2 cache lines.

      • To ensure coherence of local memory reads of CUs with different L1 caches in the same agent a buffer_inv sc1 is required. It does nothing if the agent is configured to have a single L2, or will invalidate non-local L2 cache lines if configured to have multiple L2 caches.

      • To ensure coherence of local memory reads of CUs in different agents a buffer_inv sc0 sc1 is required. It will invalidate non-local L2 cache lines if configured to have multiple L2 caches.

    • PCIe access from the GPU to the CPU can be kept coherent by using the MTYPE UC (uncached) which bypasses the L2.

Scalar memory operations are only used to access memory that is proven to not change during the execution of the kernel dispatch. This includes constant address space and global address space for program scope const variables. Therefore, the kernel machine code does not have to maintain the scalar cache to ensure it is coherent with the vector caches. The scalar and vector caches are invalidated between kernel dispatches by CP since constant address space data may change between kernel dispatch executions. See Memory Spaces.

The one exception is if scalar writes are used to spill SGPR registers. In this case the AMDGPU backend ensures the memory location used to spill is never accessed by vector memory operations at the same time. If scalar writes are used then a s_dcache_wb is inserted before the s_endpgm and before a function return since the locations may be used for vector memory instructions by a future wavefront that uses the same scratch area, or a function call that creates a frame at the same address, respectively. There is no need for a s_dcache_inv as all scalar writes are write-before-read in the same thread.

For kernarg backing memory:

  • CP invalidates the L1 cache at the start of each kernel dispatch.

  • On dGPU over XGMI or PCIe the kernarg backing memory is allocated in host memory accessed as MTYPE UC (uncached) to avoid needing to invalidate the L2 cache. This also causes it to be treated as non-volatile and so is not invalidated by *_vol.

  • On APU the kernarg backing memory is accessed as MTYPE CC (cache coherent) and so the L2 cache will be coherent with the CPU and other agents.

Scratch backing memory (which is used for the private address space) is accessed with MTYPE NC_NV (non-coherent non-volatile). Since the private address space is only accessed by a single thread, and is always write-before-read, there is never a need to invalidate these entries from the L1 cache. Hence all cache invalidates are done as *_vol to only invalidate the volatile cache lines.

The code sequences used to implement the memory model for GFX940, GFX941, GFX942 are defined in table AMDHSA Memory Model Code Sequences GFX940, GFX941, GFX942.

Table 80 AMDHSA Memory Model Code Sequences GFX940, GFX941, GFX942

LLVM Instr

LLVM Memory Ordering

LLVM Memory Sync Scope

AMDGPU Address Space

AMDGPU Machine Code GFX940, GFX941, GFX942

Non-Atomic

load

none

none

  • global

  • generic

  • private

  • constant

  • !volatile & !nontemporal

    1. buffer/global/flat_load

  • !volatile & nontemporal

    1. buffer/global/flat_load nt=1

  • volatile

    1. buffer/global/flat_load sc0=1 sc1=1

    2. s_waitcnt vmcnt(0)

    • Must happen before any following volatile global/generic load/store.

    • Ensures that volatile operations to different addresses will not be reordered by hardware.

load

none

none

  • local

  1. ds_load

store

none

none

  • global

  • generic

  • private

  • constant

  • !volatile & !nontemporal

    1. GFX940, GFX941

      buffer/global/flat_store sc0=1 sc1=1

      GFX942

      buffer/global/flat_store

  • !volatile & nontemporal

    1. GFX940, GFX941

      buffer/global/flat_store nt=1 sc0=1 sc1=1

      GFX942

      buffer/global/flat_store nt=1

  • volatile

    1. buffer/global/flat_store sc0=1 sc1=1

    2. s_waitcnt vmcnt(0)

    • Must happen before any following volatile global/generic load/store.

    • Ensures that volatile operations to different addresses will not be reordered by hardware.

store

none

none

  • local

  1. ds_store

Unordered Atomic

load atomic

unordered

any

any

Same as non-atomic.

store atomic

unordered

any

any

Same as non-atomic.

atomicrmw

unordered

any

any

Same as monotonic atomic.

Monotonic Atomic

load atomic

monotonic

  • singlethread

  • wavefront

  • global

  • generic

  1. buffer/global/flat_load

load atomic

monotonic

  • workgroup

  • global

  • generic

  1. buffer/global/flat_load sc0=1

load atomic

monotonic

  • singlethread

  • wavefront

  • workgroup

  • local

If TgSplit execution mode, local address space cannot be used.

  1. ds_load

load atomic

monotonic

  • agent

  • global

  • generic

  1. buffer/global/flat_load sc1=1

load atomic

monotonic

  • system

  • global

  • generic

  1. buffer/global/flat_load sc0=1 sc1=1

store atomic

monotonic

  • singlethread

  • wavefront

  • global

  • generic

  1. buffer/global/flat_store

store atomic

monotonic

  • workgroup

  • global

  • generic

  1. buffer/global/flat_store sc0=1

store atomic

monotonic

  • agent

  • global

  • generic

  1. buffer/global/flat_store sc1=1

store atomic

monotonic

  • system

  • global

  • generic

  1. buffer/global/flat_store sc0=1 sc1=1

store atomic

monotonic

  • singlethread

  • wavefront

  • workgroup

  • local

If TgSplit execution mode, local address space cannot be used.

  1. ds_store

atomicrmw

monotonic

  • singlethread

  • wavefront

  • workgroup

  • agent

  • global

  • generic

  1. buffer/global/flat_atomic

atomicrmw

monotonic

  • system

  • global

  • generic

  1. buffer/global/flat_atomic sc1=1

atomicrmw

monotonic

  • singlethread

  • wavefront

  • workgroup

  • local

If TgSplit execution mode, local address space cannot be used.

  1. ds_atomic

Acquire Atomic

load atomic

acquire

  • singlethread

  • wavefront

  • global

  • local

  • generic

  1. buffer/global/ds/flat_load

load atomic

acquire

  • workgroup

  • global

  1. buffer/global_load sc0=1

  2. s_waitcnt vmcnt(0)

  • If not TgSplit execution mode, omit.

  • Must happen before the following buffer_inv.

  1. buffer_inv sc0=1

  • If not TgSplit execution mode, omit.

  • Must happen before any following global/generic load/load atomic/store/store atomic/atomicrmw.

  • Ensures that following loads will not see stale data.

load atomic

acquire

  • workgroup

  • local

If TgSplit execution mode, local address space cannot be used.

  1. ds_load

  2. s_waitcnt lgkmcnt(0)

  • If OpenCL, omit.

  • Must happen before any following global/generic load/load atomic/store/store atomic/atomicrmw.

  • Ensures any following global data read is no older than the local load atomic value being acquired.

load atomic

acquire

  • workgroup

  • generic

  1. flat_load sc0=1

  2. s_waitcnt lgkm/vmcnt(0)

  • Use lgkmcnt(0) if not TgSplit execution mode and vmcnt(0) if TgSplit execution mode.

  • If OpenCL, omit lgkmcnt(0).

  • Must happen before the following buffer_inv and any following global/generic load/load atomic/store/store atomic/atomicrmw.

  • Ensures any following global data read is no older than a local load atomic value being acquired.

  1. buffer_inv sc0=1

  • If not TgSplit execution mode, omit.

  • Ensures that following loads will not see stale data.

load atomic

acquire

  • agent

  • global

  1. buffer/global_load sc1=1

  2. s_waitcnt vmcnt(0)

  • Must happen before following buffer_inv.

  • Ensures the load has completed before invalidating the cache.

  1. buffer_inv sc1=1

  • Must happen before any following global/generic load/load atomic/atomicrmw.

  • Ensures that following loads will not see stale global data.

load atomic

acquire

  • system

  • global

  1. buffer/global/flat_load sc0=1 sc1=1

  2. s_waitcnt vmcnt(0)

  • Must happen before following buffer_inv.

  • Ensures the load has completed before invalidating the cache.

  1. buffer_inv sc0=1 sc1=1

  • Must happen before any following global/generic load/load atomic/atomicrmw.

  • Ensures that following loads will not see stale MTYPE NC global data. MTYPE RW and CC memory will never be stale due to the memory probes.

load atomic

acquire

  • agent

  • generic

  1. flat_load sc1=1

  2. s_waitcnt vmcnt(0) & lgkmcnt(0)

  • If TgSplit execution mode, omit lgkmcnt(0).

  • If OpenCL omit lgkmcnt(0).

  • Must happen before following buffer_inv.

  • Ensures the flat_load has completed before invalidating the cache.

  1. buffer_inv sc1=1

  • Must happen before any following global/generic load/load atomic/atomicrmw.

  • Ensures that following loads will not see stale global data.

load atomic

acquire

  • system

  • generic

  1. flat_load sc0=1 sc1=1

  2. s_waitcnt vmcnt(0) & lgkmcnt(0)

  • If TgSplit execution mode, omit lgkmcnt(0).

  • If OpenCL omit lgkmcnt(0).

  • Must happen before the following buffer_inv.

  • Ensures the flat_load has completed before invalidating the caches.

  1. buffer_inv sc0=1 sc1=1

  • Must happen before any following global/generic load/load atomic/atomicrmw.

  • Ensures that following loads will not see stale MTYPE NC global data. MTYPE RW and CC memory will never be stale due to the memory probes.

atomicrmw

acquire

  • singlethread

  • wavefront

  • global

  • generic

  1. buffer/global/flat_atomic

atomicrmw

acquire

  • singlethread

  • wavefront

  • local

If TgSplit execution mode, local address space cannot be used.

  1. ds_atomic

atomicrmw

acquire

  • workgroup

  • global

  1. buffer/global_atomic

  2. s_waitcnt vmcnt(0)

  • If not TgSplit execution mode, omit.

  • Must happen before the following buffer_inv.

  • Ensures the atomicrmw has completed before invalidating the cache.

  1. buffer_inv sc0=1

  • If not TgSplit execution mode, omit.

  • Must happen before any following global/generic load/load atomic/atomicrmw.

  • Ensures that following loads will not see stale global data.

atomicrmw

acquire

  • workgroup

  • local

If TgSplit execution mode, local address space cannot be used.

  1. ds_atomic

  2. s_waitcnt lgkmcnt(0)

  • If OpenCL, omit.

  • Must happen before any following global/generic load/load atomic/store/store atomic/atomicrmw.

  • Ensures any following global data read is no older than the local atomicrmw value being acquired.

atomicrmw

acquire

  • workgroup

  • generic

  1. flat_atomic

  2. s_waitcnt lgkm/vmcnt(0)

  • Use lgkmcnt(0) if not TgSplit execution mode and vmcnt(0) if TgSplit execution mode.

  • If OpenCL, omit lgkmcnt(0).

  • Must happen before the following buffer_inv and any following global/generic load/load atomic/store/store atomic/atomicrmw.

  • Ensures any following global data read is no older than a local atomicrmw value being acquired.

  1. buffer_inv sc0=1

  • If not TgSplit execution mode, omit.

  • Ensures that following loads will not see stale data.

atomicrmw

acquire

  • agent

  • global

  1. buffer/global_atomic

  2. s_waitcnt vmcnt(0)

  • Must happen before following buffer_inv.

  • Ensures the atomicrmw has completed before invalidating the cache.

  1. buffer_inv sc1=1

  • Must happen before any following global/generic load/load atomic/atomicrmw.

  • Ensures that following loads will not see stale global data.

atomicrmw

acquire

  • system

  • global

  1. buffer/global_atomic sc1=1

  2. s_waitcnt vmcnt(0)

  • Must happen before following buffer_inv.

  • Ensures the atomicrmw has completed before invalidating the caches.

  1. buffer_inv sc0=1 sc1=1

  • Must happen before any following global/generic load/load atomic/atomicrmw.

  • Ensures that following loads will not see stale MTYPE NC global data. MTYPE RW and CC memory will never be stale due to the memory probes.

atomicrmw

acquire

  • agent

  • generic

  1. flat_atomic

  2. s_waitcnt vmcnt(0) & lgkmcnt(0)

  • If TgSplit execution mode, omit lgkmcnt(0).

  • If OpenCL, omit lgkmcnt(0).

  • Must happen before following buffer_inv.

  • Ensures the atomicrmw has completed before invalidating the cache.

  1. buffer_inv sc1=1

  • Must happen before any following global/generic load/load atomic/atomicrmw.

  • Ensures that following loads will not see stale global data.

atomicrmw

acquire

  • system

  • generic

  1. flat_atomic sc1=1

  2. s_waitcnt vmcnt(0) & lgkmcnt(0)

  • If TgSplit execution mode, omit lgkmcnt(0).

  • If OpenCL, omit lgkmcnt(0).

  • Must happen before following buffer_inv.

  • Ensures the atomicrmw has completed before invalidating the caches.

  1. buffer_inv sc0=1 sc1=1

  • Must happen before any following global/generic load/load atomic/atomicrmw.

  • Ensures that following loads will not see stale MTYPE NC global data. MTYPE RW and CC memory will never be stale due to the memory probes.

fence

acquire

  • singlethread

  • wavefront

none

none

fence

acquire

  • workgroup

none

  1. s_waitcnt lgkm/vmcnt(0)

  • Use lgkmcnt(0) if not TgSplit execution mode and vmcnt(0) if TgSplit execution mode.

  • If OpenCL and address space is not generic, omit lgkmcnt(0).

  • If OpenCL and address space is local, omit vmcnt(0).

  • See Fence and Address Spaces for more details on fencing specific address spaces.

  • s_waitcnt vmcnt(0) must happen after any preceding global/generic load atomic/ atomicrmw with an equal or wider sync scope and memory ordering stronger than unordered (this is termed the fence-paired-atomic).

  • s_waitcnt lgkmcnt(0) must happen after any preceding local/generic load atomic/atomicrmw with an equal or wider sync scope and memory ordering stronger than unordered (this is termed the fence-paired-atomic).

  • Must happen before the following buffer_inv and any following global/generic load/load atomic/store/store atomic/atomicrmw.

  • Ensures any following global data read is no older than the value read by the fence-paired-atomic.

  1. buffer_inv sc0=1

  • If not TgSplit execution mode, omit.

  • Ensures that following loads will not see stale data.

fence

acquire

  • agent

none

  1. s_waitcnt lgkmcnt(0) & vmcnt(0)

  • If TgSplit execution mode, omit lgkmcnt(0).

  • If OpenCL and address space is not generic, omit lgkmcnt(0).

  • See Fence and Address Spaces for more details on fencing specific address spaces.

  • Could be split into separate s_waitcnt vmcnt(0) and s_waitcnt lgkmcnt(0) to allow them to be independently moved according to the following rules.

  • s_waitcnt vmcnt(0) must happen after any preceding global/generic load atomic/atomicrmw with an equal or wider sync scope and memory ordering stronger than unordered (this is termed the fence-paired-atomic).

  • s_waitcnt lgkmcnt(0) must happen after any preceding local/generic load atomic/atomicrmw with an equal or wider sync scope and memory ordering stronger than unordered (this is termed the fence-paired-atomic).

  • Must happen before the following buffer_inv.

  • Ensures that the fence-paired atomic has completed before invalidating the cache. Therefore any following locations read must be no older than the value read by the fence-paired-atomic.

  1. buffer_inv sc1=1

  • Must happen before any following global/generic load/load atomic/store/store atomic/atomicrmw.

  • Ensures that following loads will not see stale global data.

fence

acquire

  • system

none

  1. s_waitcnt lgkmcnt(0) & vmcnt(0)

  • If TgSplit execution mode, omit lgkmcnt(0).

  • If OpenCL and address space is not generic, omit lgkmcnt(0).

  • See Fence and Address Spaces for more details on fencing specific address spaces.

  • Could be split into separate s_waitcnt vmcnt(0) and s_waitcnt lgkmcnt(0) to allow them to be independently moved according to the following rules.

  • s_waitcnt vmcnt(0) must happen after any preceding global/generic load atomic/atomicrmw with an equal or wider sync scope and memory ordering stronger than unordered (this is termed the fence-paired-atomic).

  • s_waitcnt lgkmcnt(0) must happen after any preceding local/generic load atomic/atomicrmw with an equal or wider sync scope and memory ordering stronger than unordered (this is termed the fence-paired-atomic).

  • Must happen before the following buffer_inv.

  • Ensures that the fence-paired atomic has completed before invalidating the cache. Therefore any following locations read must be no older than the value read by the fence-paired-atomic.

  1. buffer_inv sc0=1 sc1=1

  • Must happen before any following global/generic load/load atomic/store/store atomic/atomicrmw.

  • Ensures that following loads will not see stale global data.

Release Atomic

store atomic

release

  • singlethread

  • wavefront

  • global

  • generic
  1. GFX940, GFX941

    buffer/global/flat_store sc0=1 sc1=1

    GFX942

    buffer/global/flat_store

store atomic

release

  • singlethread

  • wavefront

  • local

If TgSplit execution mode, local address space cannot be used.

  1. ds_store

store atomic

release

  • workgroup

  • global

  • generic

  1. s_waitcnt lgkm/vmcnt(0)

  • Use lgkmcnt(0) if not TgSplit execution mode and vmcnt(0) if TgSplit execution mode.

  • If OpenCL, omit lgkmcnt(0).

  • s_waitcnt vmcnt(0) must happen after any preceding global/generic load/store/ load atomic/store atomic/ atomicrmw.

  • s_waitcnt lgkmcnt(0) must happen after any preceding local/generic load/store/load atomic/store atomic/atomicrmw.

  • Must happen before the following store.

  • Ensures that all memory operations have completed before performing the store that is being released.

  1. GFX940, GFX941

    buffer/global/flat_store sc0=1 sc1=1

    GFX942

    buffer/global/flat_store sc0=1

store atomic

release

  • workgroup

  • local

If TgSplit execution mode, local address space cannot be used.

  1. ds_store

store atomic

release

  • agent

  • global

  • generic

  1. buffer_wbl2 sc1=1

  • Must happen before following s_waitcnt.

  • Performs L2 writeback to ensure previous global/generic store/atomicrmw are visible at agent scope.

  1. s_waitcnt lgkmcnt(0) & vmcnt(0)

  • If TgSplit execution mode, omit lgkmcnt(0).

  • If OpenCL and address space is not generic, omit lgkmcnt(0).

  • Could be split into separate s_waitcnt vmcnt(0) and s_waitcnt lgkmcnt(0) to allow them to be independently moved according to the following rules.

  • s_waitcnt vmcnt(0) must happen after any preceding global/generic load/store/load atomic/store atomic/atomicrmw.

  • s_waitcnt lgkmcnt(0) must happen after any preceding local/generic load/store/load atomic/store atomic/atomicrmw.

  • Must happen before the following store.

  • Ensures that all memory operations to memory have completed before performing the store that is being released.

  1. GFX940, GFX941

    buffer/global/flat_store sc0=1 sc1=1

    GFX942

    buffer/global/flat_store sc1=1

store atomic

release

  • system

  • global

  • generic

  1. buffer_wbl2 sc0=1 sc1=1

  • Must happen before following s_waitcnt.

  • Performs L2 writeback to ensure previous global/generic store/atomicrmw are visible at system scope.

  1. s_waitcnt lgkmcnt(0) & vmcnt(0)

  • If TgSplit execution mode, omit lgkmcnt(0).

  • If OpenCL and address space is not generic, omit lgkmcnt(0).

  • Could be split into separate s_waitcnt vmcnt(0) and s_waitcnt lgkmcnt(0) to allow them to be independently moved according to the following rules.

  • s_waitcnt vmcnt(0) must happen after any preceding global/generic load/store/load atomic/store atomic/atomicrmw.

  • s_waitcnt lgkmcnt(0) must happen after any preceding local/generic load/store/load atomic/store atomic/atomicrmw.

  • Must happen before the following store.

  • Ensures that all memory operations to memory and the L2 writeback have completed before performing the store that is being released.

  1. buffer/global/flat_store sc0=1 sc1=1

atomicrmw

release

  • singlethread

  • wavefront

  • global

  • generic

  1. buffer/global/flat_atomic

atomicrmw

release

  • singlethread

  • wavefront

  • local

If TgSplit execution mode, local address space cannot be used.

  1. ds_atomic

atomicrmw

release

  • workgroup

  • global

  • generic

  1. s_waitcnt lgkm/vmcnt(0)

  • Use lgkmcnt(0) if not TgSplit execution mode and vmcnt(0) if TgSplit execution mode.

  • If OpenCL, omit lgkmcnt(0).

  • s_waitcnt vmcnt(0) must happen after any preceding global/generic load/store/ load atomic/store atomic/ atomicrmw.

  • s_waitcnt lgkmcnt(0) must happen after any preceding local/generic load/store/load atomic/store atomic/atomicrmw.

  • Must happen before the following atomicrmw.

  • Ensures that all memory operations have completed before performing the atomicrmw that is being released.

  1. buffer/global/flat_atomic sc0=1

atomicrmw

release

  • workgroup

  • local

If TgSplit execution mode, local address space cannot be used.

  1. ds_atomic

atomicrmw

release

  • agent

  • global

  • generic

  1. buffer_wbl2 sc1=1

  • Must happen before following s_waitcnt.

  • Performs L2 writeback to ensure previous global/generic store/atomicrmw are visible at agent scope.

  1. s_waitcnt lgkmcnt(0) & vmcnt(0)

  • If TgSplit execution mode, omit lgkmcnt(0).

  • If OpenCL, omit lgkmcnt(0).

  • Could be split into separate s_waitcnt vmcnt(0) and s_waitcnt lgkmcnt(0) to allow them to be independently moved according to the following rules.

  • s_waitcnt vmcnt(0) must happen after any preceding global/generic load/store/load atomic/store atomic/atomicrmw.

  • s_waitcnt lgkmcnt(0) must happen after any preceding local/generic load/store/load atomic/store atomic/atomicrmw.

  • Must happen before the following atomicrmw.

  • Ensures that all memory operations to global and local have completed before performing the atomicrmw that is being released.

  1. buffer/global/flat_atomic sc1=1

atomicrmw

release

  • system

  • global

  • generic

  1. buffer_wbl2 sc0=1 sc1=1

  • Must happen before following s_waitcnt.

  • Performs L2 writeback to ensure previous global/generic store/atomicrmw are visible at system scope.

  1. s_waitcnt lgkmcnt(0) & vmcnt(0)

  • If TgSplit execution mode, omit lgkmcnt(0).

  • If OpenCL, omit lgkmcnt(0).

  • Could be split into separate s_waitcnt vmcnt(0) and s_waitcnt lgkmcnt(0) to allow them to be independently moved according to the following rules.

  • s_waitcnt vmcnt(0) must happen after any preceding global/generic load/store/load atomic/store atomic/atomicrmw.

  • s_waitcnt lgkmcnt(0) must happen after any preceding local/generic load/store/load atomic/store atomic/atomicrmw.

  • Must happen before the following atomicrmw.

  • Ensures that all memory operations to memory and the L2 writeback have completed before performing the store that is being released.

  1. buffer/global/flat_atomic sc0=1 sc1=1

fence

release

  • singlethread

  • wavefront

none

none

fence

release

  • workgroup

none

  1. s_waitcnt lgkm/vmcnt(0)

  • Use lgkmcnt(0) if not TgSplit execution mode and vmcnt(0) if TgSplit execution mode.

  • If OpenCL and address space is not generic, omit lgkmcnt(0).

  • If OpenCL and address space is local, omit vmcnt(0).

  • See Fence and Address Spaces for more details on fencing specific address spaces.

  • s_waitcnt vmcnt(0) must happen after any preceding global/generic load/store/ load atomic/store atomic/ atomicrmw.

  • s_waitcnt lgkmcnt(0) must happen after any preceding local/generic load/load atomic/store/store atomic/atomicrmw.

  • Must happen before any following store atomic/atomicrmw with an equal or wider sync scope and memory ordering stronger than unordered (this is termed the fence-paired-atomic).

  • Ensures that all memory operations have completed before performing the following fence-paired-atomic.

fence

release

  • agent

none

  1. buffer_wbl2 sc1=1

  • If OpenCL and address space is local, omit.

  • Must happen before following s_waitcnt.

  • Performs L2 writeback to ensure previous global/generic store/atomicrmw are visible at agent scope.

  1. s_waitcnt lgkmcnt(0) & vmcnt(0)

  • If TgSplit execution mode, omit lgkmcnt(0).

  • If OpenCL and address space is not generic, omit lgkmcnt(0).

  • If OpenCL and address space is local, omit vmcnt(0).

  • See Fence and Address Spaces for more details on fencing specific address spaces.

  • Could be split into separate s_waitcnt vmcnt(0) and s_waitcnt lgkmcnt(0) to allow them to be independently moved according to the following rules.

  • s_waitcnt vmcnt(0) must happen after any preceding global/generic load/store/load atomic/store atomic/atomicrmw.

  • s_waitcnt lgkmcnt(0) must happen after any preceding local/generic load/store/load atomic/store atomic/atomicrmw.

  • Must happen before any following store atomic/atomicrmw with an equal or wider sync scope and memory ordering stronger than unordered (this is termed the fence-paired-atomic).

  • Ensures that all memory operations have completed before performing the following fence-paired-atomic.

fence

release

  • system

none

  1. buffer_wbl2 sc0=1 sc1=1

  • Must happen before following s_waitcnt.

  • Performs L2 writeback to ensure previous global/generic store/atomicrmw are visible at system scope.

  1. s_waitcnt lgkmcnt(0) & vmcnt(0)

  • If TgSplit execution mode, omit lgkmcnt(0).

  • If OpenCL and address space is not generic, omit lgkmcnt(0).

  • If OpenCL and address space is local, omit vmcnt(0).

  • See Fence and Address Spaces for more details on fencing specific address spaces.

  • Could be split into separate s_waitcnt vmcnt(0) and s_waitcnt lgkmcnt(0) to allow them to be independently moved according to the following rules.

  • s_waitcnt vmcnt(0) must happen after any preceding global/generic load/store/load atomic/store atomic/atomicrmw.

  • s_waitcnt lgkmcnt(0) must happen after any preceding local/generic load/store/load atomic/store atomic/atomicrmw.

  • Must happen before any following store atomic/atomicrmw with an equal or wider sync scope and memory ordering stronger than unordered (this is termed the fence-paired-atomic).

  • Ensures that all memory operations have completed before performing the following fence-paired-atomic.

Acquire-Release Atomic

atomicrmw

acq_rel

  • singlethread

  • wavefront

  • global

  • generic

  1. buffer/global/flat_atomic

atomicrmw

acq_rel

  • singlethread

  • wavefront

  • local

If TgSplit execution mode, local address space cannot be used.

  1. ds_atomic

atomicrmw

acq_rel

  • workgroup

  • global

  1. s_waitcnt lgkm/vmcnt(0)

  • Use lgkmcnt(0) if not TgSplit execution mode and vmcnt(0) if TgSplit execution mode.

  • If OpenCL, omit lgkmcnt(0).

  • Must happen after any preceding local/generic load/store/load atomic/store atomic/atomicrmw.

  • s_waitcnt vmcnt(0) must happen after any preceding global/generic load/store/ load atomic/store atomic/ atomicrmw.

  • s_waitcnt lgkmcnt(0) must happen after any preceding local/generic load/store/load atomic/store atomic/atomicrmw.

  • Must happen before the following atomicrmw.

  • Ensures that all memory operations have completed before performing the atomicrmw that is being released.

  1. buffer/global_atomic

  2. s_waitcnt vmcnt(0)

  • If not TgSplit execution mode, omit.

  • Must happen before the following buffer_inv.

  • Ensures any following global data read is no older than the atomicrmw value being acquired.

  1. buffer_inv sc0=1

  • If not TgSplit execution mode, omit.

  • Ensures that following loads will not see stale data.

atomicrmw

acq_rel

  • workgroup

  • local

If TgSplit execution mode, local address space cannot be used.

  1. ds_atomic

  2. s_waitcnt lgkmcnt(0)

  • If OpenCL, omit.

  • Must happen before any following global/generic load/load atomic/store/store atomic/atomicrmw.

  • Ensures any following global data read is no older than the local load atomic value being acquired.

atomicrmw

acq_rel

  • workgroup

  • generic

  1. s_waitcnt lgkm/vmcnt(0)

  • Use lgkmcnt(0) if not TgSplit execution mode and vmcnt(0) if TgSplit execution mode.

  • If OpenCL, omit lgkmcnt(0).

  • s_waitcnt vmcnt(0) must happen after any preceding global/generic load/store/ load atomic/store atomic/ atomicrmw.

  • s_waitcnt lgkmcnt(0) must happen after any preceding local/generic load/store/load atomic/store atomic/atomicrmw.

  • Must happen before the following atomicrmw.

  • Ensures that all memory operations have completed before performing the atomicrmw that is being released.

  1. flat_atomic

  2. s_waitcnt lgkmcnt(0) & vmcnt(0)

  • If not TgSplit execution mode, omit vmcnt(0).

  • If OpenCL, omit lgkmcnt(0).

  • Must happen before the following buffer_inv and any following global/generic load/load atomic/store/store atomic/atomicrmw.

  • Ensures any following global data read is no older than a local load atomic value being acquired.

  1. buffer_inv sc0=1

  • If not TgSplit execution mode, omit.

  • Ensures that following loads will not see stale data.

atomicrmw

acq_rel

  • agent

  • global

  1. buffer_wbl2 sc1=1

  • Must happen before following s_waitcnt.

  • Performs L2 writeback to ensure previous global/generic store/atomicrmw are visible at agent scope.

  1. s_waitcnt lgkmcnt(0) & vmcnt(0)

  • If TgSplit execution mode, omit lgkmcnt(0).

  • If OpenCL, omit lgkmcnt(0).

  • Could be split into separate s_waitcnt vmcnt(0) and s_waitcnt lgkmcnt(0) to allow them to be independently moved according to the following rules.

  • s_waitcnt vmcnt(0) must happen after any preceding global/generic load/store/load atomic/store atomic/atomicrmw.

  • s_waitcnt lgkmcnt(0) must happen after any preceding local/generic load/store/load atomic/store atomic/atomicrmw.

  • Must happen before the following atomicrmw.

  • Ensures that all memory operations to global have completed before performing the atomicrmw that is being released.

  1. buffer/global_atomic

  2. s_waitcnt vmcnt(0)

  • Must happen before following buffer_inv.

  • Ensures the atomicrmw has completed before invalidating the cache.

  1. buffer_inv sc1=1

  • Must happen before any following global/generic load/load atomic/atomicrmw.

  • Ensures that following loads will not see stale global data.

atomicrmw

acq_rel

  • system

  • global

  1. buffer_wbl2 sc0=1 sc1=1

  • Must happen before following s_waitcnt.

  • Performs L2 writeback to ensure previous global/generic store/atomicrmw are visible at system scope.

  1. s_waitcnt lgkmcnt(0) & vmcnt(0)

  • If TgSplit execution mode, omit lgkmcnt(0).

  • If OpenCL, omit lgkmcnt(0).

  • Could be split into separate s_waitcnt vmcnt(0) and s_waitcnt lgkmcnt(0) to allow them to be independently moved according to the following rules.

  • s_waitcnt vmcnt(0) must happen after any preceding global/generic load/store/load atomic/store atomic/atomicrmw.

  • s_waitcnt lgkmcnt(0) must happen after any preceding local/generic load/store/load atomic/store atomic/atomicrmw.

  • Must happen before the following atomicrmw.

  • Ensures that all memory operations to global and L2 writeback have completed before performing the atomicrmw that is being released.

  1. buffer/global_atomic sc1=1

  2. s_waitcnt vmcnt(0)

  • Must happen before following buffer_inv.

  • Ensures the atomicrmw has completed before invalidating the caches.

  1. buffer_inv sc0=1 sc1=1

  • Must happen before any following global/generic load/load atomic/atomicrmw.

  • Ensures that following loads will not see stale MTYPE NC global data. MTYPE RW and CC memory will never be stale due to the memory probes.

atomicrmw

acq_rel

  • agent

  • generic

  1. buffer_wbl2 sc1=1

  • Must happen before following s_waitcnt.

  • Performs L2 writeback to ensure previous global/generic store/atomicrmw are visible at agent scope.

  1. s_waitcnt lgkmcnt(0) & vmcnt(0)

  • If TgSplit execution mode, omit lgkmcnt(0).

  • If OpenCL, omit lgkmcnt(0).

  • Could be split into separate s_waitcnt vmcnt(0) and s_waitcnt lgkmcnt(0) to allow them to be independently moved according to the following rules.

  • s_waitcnt vmcnt(0) must happen after any preceding global/generic load/store/load atomic/store atomic/atomicrmw.

  • s_waitcnt lgkmcnt(0) must happen after any preceding local/generic load/store/load atomic/store atomic/atomicrmw.

  • Must happen before the following atomicrmw.

  • Ensures that all memory operations to global have completed before performing the atomicrmw that is being released.

  1. flat_atomic

  2. s_waitcnt vmcnt(0) & lgkmcnt(0)

  • If TgSplit execution mode, omit lgkmcnt(0).

  • If OpenCL, omit lgkmcnt(0).

  • Must happen before following buffer_inv.

  • Ensures the atomicrmw has completed before invalidating the cache.

  1. buffer_inv sc1=1

  • Must happen before any following global/generic load/load atomic/atomicrmw.

  • Ensures that following loads will not see stale global data.

atomicrmw

acq_rel

  • system

  • generic

  1. buffer_wbl2 sc0=1 sc1=1

  • Must happen before following s_waitcnt.

  • Performs L2 writeback to ensure previous global/generic store/atomicrmw are visible at system scope.

  1. s_waitcnt lgkmcnt(0) & vmcnt(0)

  • If TgSplit execution mode, omit lgkmcnt(0).

  • If OpenCL, omit lgkmcnt(0).

  • Could be split into separate s_waitcnt vmcnt(0) and s_waitcnt lgkmcnt(0) to allow them to be independently moved according to the following rules.

  • s_waitcnt vmcnt(0) must happen after any preceding global/generic load/store/load atomic/store atomic/atomicrmw.

  • s_waitcnt lgkmcnt(0) must happen after any preceding local/generic load/store/load atomic/store atomic/atomicrmw.

  • Must happen before the following atomicrmw.

  • Ensures that all memory operations to global and L2 writeback have completed before performing the atomicrmw that is being released.

  1. flat_atomic sc1=1

  2. s_waitcnt vmcnt(0) & lgkmcnt(0)

  • If TgSplit execution mode, omit lgkmcnt(0).

  • If OpenCL, omit lgkmcnt(0).

  • Must happen before following buffer_inv.

  • Ensures the atomicrmw has completed before invalidating the caches.

  1. buffer_inv sc0=1 sc1=1

  • Must happen before any following global/generic load/load atomic/atomicrmw.

  • Ensures that following loads will not see stale MTYPE NC global data. MTYPE RW and CC memory will never be stale due to the memory probes.

fence

acq_rel

  • singlethread

  • wavefront

none

none

fence

acq_rel

  • workgroup

none

  1. s_waitcnt lgkm/vmcnt(0)

  • Use lgkmcnt(0) if not TgSplit execution mode and vmcnt(0) if TgSplit execution mode.

  • If OpenCL and address space is not generic, omit lgkmcnt(0).

  • If OpenCL and address space is local, omit vmcnt(0).

  • However, since LLVM currently has no address space on the fence need to conservatively always generate (see comment for previous fence).

  • s_waitcnt vmcnt(0) must happen after any preceding global/generic load/store/ load atomic/store atomic/ atomicrmw.

  • s_waitcnt lgkmcnt(0) must happen after any preceding local/generic load/load atomic/store/store atomic/atomicrmw.

  • Must happen before any following global/generic load/load atomic/store/store atomic/atomicrmw.

  • Ensures that all memory operations have completed before performing any following global memory operations.

  • Ensures that the preceding local/generic load atomic/atomicrmw with an equal or wider sync scope and memory ordering stronger than unordered (this is termed the acquire-fence-paired-atomic) has completed before following global memory operations. This satisfies the requirements of acquire.

  • Ensures that all previous memory operations have completed before a following local/generic store atomic/atomicrmw with an equal or wider sync scope and memory ordering stronger than unordered (this is termed the release-fence-paired-atomic). This satisfies the requirements of release.

  • Must happen before the following buffer_inv.

  • Ensures that the acquire-fence-paired atomic has completed before invalidating the cache. Therefore any following locations read must be no older than the value read by the acquire-fence-paired-atomic.

  1. buffer_inv sc0=1

  • If not TgSplit execution mode, omit.

  • Ensures that following loads will not see stale data.

fence

acq_rel

  • agent

none

  1. buffer_wbl2 sc1=1

  • If OpenCL and address space is local, omit.

  • Must happen before following s_waitcnt.

  • Performs L2 writeback to ensure previous global/generic store/atomicrmw are visible at agent scope.

  1. s_waitcnt lgkmcnt(0) & vmcnt(0)

  • If TgSplit execution mode, omit lgkmcnt(0).

  • If OpenCL and address space is not generic, omit lgkmcnt(0).

  • See Fence and Address Spaces for more details on fencing specific address spaces.

  • Could be split into separate s_waitcnt vmcnt(0) and s_waitcnt lgkmcnt(0) to allow them to be independently moved according to the following rules.

  • s_waitcnt vmcnt(0) must happen after any preceding global/generic load/store/load atomic/store atomic/atomicrmw.

  • s_waitcnt lgkmcnt(0) must happen after any preceding local/generic load/store/load atomic/store atomic/atomicrmw.

  • Must happen before the following buffer_inv.

  • Ensures that the preceding global/local/generic load atomic/atomicrmw with an equal or wider sync scope and memory ordering stronger than unordered (this is termed the acquire-fence-paired-atomic) has completed before invalidating the cache. This satisfies the requirements of acquire.

  • Ensures that all previous memory operations have completed before a following global/local/generic store atomic/atomicrmw with an equal or wider sync scope and memory ordering stronger than unordered (this is termed the release-fence-paired-atomic). This satisfies the requirements of release.

  1. buffer_inv sc1=1

  • Must happen before any following global/generic load/load atomic/store/store atomic/atomicrmw.

  • Ensures that following loads will not see stale global data. This satisfies the requirements of acquire.

fence

acq_rel

  • system

none

  1. buffer_wbl2 sc0=1 sc1=1

  • If OpenCL and address space is local, omit.

  • Must happen before following s_waitcnt.

  • Performs L2 writeback to ensure previous global/generic store/atomicrmw are visible at system scope.

  1. s_waitcnt lgkmcnt(0) & vmcnt(0)

  • If TgSplit execution mode, omit lgkmcnt(0).

  • If OpenCL and address space is not generic, omit lgkmcnt(0).

  • See Fence and Address Spaces for more details on fencing specific address spaces.

  • Could be split into separate s_waitcnt vmcnt(0) and s_waitcnt lgkmcnt(0) to allow them to be independently moved according to the following rules.

  • s_waitcnt vmcnt(0) must happen after any preceding global/generic load/store/load atomic/store atomic/atomicrmw.

  • s_waitcnt lgkmcnt(0) must happen after any preceding local/generic load/store/load atomic/store atomic/atomicrmw.

  • Must happen before the following buffer_inv.

  • Ensures that the preceding global/local/generic load atomic/atomicrmw with an equal or wider sync scope and memory ordering stronger than unordered (this is termed the acquire-fence-paired-atomic) has completed before invalidating the cache. This satisfies the requirements of acquire.

  • Ensures that all previous memory operations have completed before a following global/local/generic store atomic/atomicrmw with an equal or wider sync scope and memory ordering stronger than unordered (this is termed the release-fence-paired-atomic). This satisfies the requirements of release.

  1. buffer_inv sc0=1 sc1=1

  • Must happen before any following global/generic load/load atomic/store/store atomic/atomicrmw.

  • Ensures that following loads will not see stale MTYPE NC global data. MTYPE RW and CC memory will never be stale due to the memory probes.

Sequential Consistent Atomic

load atomic

seq_cst

  • singlethread

  • wavefront

  • global

  • local

  • generic

Same as corresponding load atomic acquire, except must generate all instructions even for OpenCL.

load atomic

seq_cst

  • workgroup

  • global

  • generic

  1. s_waitcnt lgkm/vmcnt(0)

  • Use lgkmcnt(0) if not TgSplit execution mode and vmcnt(0) if TgSplit execution mode.

  • s_waitcnt lgkmcnt(0) must happen after preceding local/generic load atomic/store atomic/atomicrmw with memory ordering of seq_cst and with equal or wider sync scope. (Note that seq_cst fences have their own s_waitcnt lgkmcnt(0) and so do not need to be considered.)

  • s_waitcnt vmcnt(0) must happen after preceding global/generic load atomic/store atomic/atomicrmw with memory ordering of seq_cst and with equal or wider sync scope. (Note that seq_cst fences have their own s_waitcnt vmcnt(0) and so do not need to be considered.)

  • Ensures any preceding sequential consistent global/local memory instructions have completed before executing this sequentially consistent instruction. This prevents reordering a seq_cst store followed by a seq_cst load. (Note that seq_cst is stronger than acquire/release as the reordering of load acquire followed by a store release is prevented by the s_waitcnt of the release, but there is nothing preventing a store release followed by load acquire from completing out of order. The s_waitcnt could be placed after seq_store or before the seq_load. We choose the load to make the s_waitcnt be as late as possible so that the store may have already completed.)

  1. Following instructions same as corresponding load atomic acquire, except must generate all instructions even for OpenCL.

load atomic

seq_cst

  • workgroup

  • local

If TgSplit execution mode, local address space cannot be used.

Same as corresponding load atomic acquire, except must generate all instructions even for OpenCL.

load atomic

seq_cst

  • agent

  • system

  • global

  • generic

  1. s_waitcnt lgkmcnt(0) & vmcnt(0)

  • If TgSplit execution mode, omit lgkmcnt(0).

  • Could be split into separate s_waitcnt vmcnt(0) and s_waitcnt lgkmcnt(0) to allow them to be independently moved according to the following rules.

  • s_waitcnt lgkmcnt(0) must happen after preceding global/generic load atomic/store atomic/atomicrmw with memory ordering of seq_cst and with equal or wider sync scope. (Note that seq_cst fences have their own s_waitcnt lgkmcnt(0) and so do not need to be considered.)

  • s_waitcnt vmcnt(0) must happen after preceding global/generic load atomic/store atomic/atomicrmw with memory ordering of seq_cst and with equal or wider sync scope. (Note that seq_cst fences have their own s_waitcnt vmcnt(0) and so do not need to be considered.)

  • Ensures any preceding sequential consistent global memory instructions have completed before executing this sequentially consistent instruction. This prevents reordering a seq_cst store followed by a seq_cst load. (Note that seq_cst is stronger than acquire/release as the reordering of load acquire followed by a store release is prevented by the s_waitcnt of the release, but there is nothing preventing a store release followed by load acquire from completing out of order. The s_waitcnt could be placed after seq_store or before the seq_load. We choose the load to make the s_waitcnt be as late as possible so that the store may have already completed.)

  1. Following instructions same as corresponding load atomic acquire, except must generate all instructions even for OpenCL.

store atomic

seq_cst

  • singlethread

  • wavefront

  • workgroup

  • agent

  • system

  • global

  • local

  • generic

Same as corresponding store atomic release, except must generate all instructions even for OpenCL.

atomicrmw

seq_cst

  • singlethread

  • wavefront

  • workgroup

  • agent

  • system

  • global

  • local

  • generic

Same as corresponding atomicrmw acq_rel, except must generate all instructions even for OpenCL.

fence

seq_cst

  • singlethread

  • wavefront

  • workgroup

  • agent

  • system

none

Same as corresponding fence acq_rel, except must generate all instructions even for OpenCL.
Memory Model GFX10-GFX11

For GFX10-GFX11:

  • Each agent has multiple shader arrays (SA).

  • Each SA has multiple work-group processors (WGP).

  • Each WGP has multiple compute units (CU).

  • Each CU has multiple SIMDs that execute wavefronts.

  • The wavefronts for a single work-group are executed in the same WGP. In CU wavefront execution mode the wavefronts may be executed by different SIMDs in the same CU. In WGP wavefront execution mode the wavefronts may be executed by different SIMDs in different CUs in the same WGP.

  • Each WGP has a single LDS memory shared by the wavefronts of the work-groups executing on it.

  • All LDS operations of a WGP are performed as wavefront wide operations in a global order and involve no caching. Completion is reported to a wavefront in execution order.

  • The LDS memory has multiple request queues shared by the SIMDs of a WGP. Therefore, the LDS operations performed by different wavefronts of a work-group can be reordered relative to each other, which can result in reordering the visibility of vector memory operations with respect to LDS operations of other wavefronts in the same work-group. A s_waitcnt lgkmcnt(0) is required to ensure synchronization between LDS operations and vector memory operations between wavefronts of a work-group, but not between operations performed by the same wavefront.

  • The vector memory operations are performed as wavefront wide operations. Completion of load/store/sample operations are reported to a wavefront in execution order of other load/store/sample operations performed by that wavefront.

  • The vector memory operations access a vector L0 cache. There is a single L0 cache per CU. Each SIMD of a CU accesses the same L0 cache. Therefore, no special action is required for coherence between the lanes of a single wavefront. However, a buffer_gl0_inv is required for coherence between wavefronts executing in the same work-group as they may be executing on SIMDs of different CUs that access different L0s. A buffer_gl0_inv is also required for coherence between wavefronts executing in different work-groups as they may be executing on different WGPs.

  • The scalar memory operations access a scalar L0 cache shared by all wavefronts on a WGP. The scalar and vector L0 caches are not coherent. However, scalar operations are used in a restricted way so do not impact the memory model. See Memory Spaces.

  • The vector and scalar memory L0 caches use an L1 cache shared by all WGPs on the same SA. Therefore, no special action is required for coherence between the wavefronts of a single work-group. However, a buffer_gl1_inv is required for coherence between wavefronts executing in different work-groups as they may be executing on different SAs that access different L1s.

  • The L1 caches have independent quadrants to service disjoint ranges of virtual addresses.

  • Each L0 cache has a separate request queue per L1 quadrant. Therefore, the vector and scalar memory operations performed by different wavefronts, whether executing in the same or different work-groups (which may be executing on different CUs accessing different L0s), can be reordered relative to each other. A s_waitcnt vmcnt(0) & vscnt(0) is required to ensure synchronization between vector memory operations of different wavefronts. It ensures a previous vector memory operation has completed before executing a subsequent vector memory or LDS operation and so can be used to meet the requirements of acquire, release and sequential consistency.

  • The L1 caches use an L2 cache shared by all SAs on the same agent.

  • The L2 cache has independent channels to service disjoint ranges of virtual addresses.

  • Each L1 quadrant of a single SA accesses a different L2 channel. Each L1 quadrant has a separate request queue per L2 channel. Therefore, the vector and scalar memory operations performed by wavefronts executing in different work-groups (which may be executing on different SAs) of an agent can be reordered relative to each other. A s_waitcnt vmcnt(0) & vscnt(0) is required to ensure synchronization between vector memory operations of different SAs. It ensures a previous vector memory operation has completed before executing a subsequent vector memory and so can be used to meet the requirements of acquire, release and sequential consistency.

  • The L2 cache can be kept coherent with other agents on some targets, or ranges of virtual addresses can be set up to bypass it to ensure system coherence.

  • On GFX10.3 and GFX11 a memory attached last level (MALL) cache exists for GPU memory. The MALL cache is fully coherent with GPU memory and has no impact on system coherence. All agents (GPU and CPU) access GPU memory through the MALL cache.

Scalar memory operations are only used to access memory that is proven to not change during the execution of the kernel dispatch. This includes constant address space and global address space for program scope const variables. Therefore, the kernel machine code does not have to maintain the scalar cache to ensure it is coherent with the vector caches. The scalar and vector caches are invalidated between kernel dispatches by CP since constant address space data may change between kernel dispatch executions. See Memory Spaces.

The one exception is if scalar writes are used to spill SGPR registers. In this case the AMDGPU backend ensures the memory location used to spill is never accessed by vector memory operations at the same time. If scalar writes are used then a s_dcache_wb is inserted before the s_endpgm and before a function return since the locations may be used for vector memory instructions by a future wavefront that uses the same scratch area, or a function call that creates a frame at the same address, respectively. There is no need for a s_dcache_inv as all scalar writes are write-before-read in the same thread.

For kernarg backing memory:

  • CP invalidates the L0 and L1 caches at the start of each kernel dispatch.

  • On dGPU the kernarg backing memory is accessed as MTYPE UC (uncached) to avoid needing to invalidate the L2 cache.

  • On APU the kernarg backing memory is accessed as MTYPE CC (cache coherent) and so the L2 cache will be coherent with the CPU and other agents.

Scratch backing memory (which is used for the private address space) is accessed with MTYPE NC (non-coherent). Since the private address space is only accessed by a single thread, and is always write-before-read, there is never a need to invalidate these entries from the L0 or L1 caches.

Wavefronts are executed in native mode with in-order reporting of loads and sample instructions. In this mode vmcnt reports completion of load, atomic with return and sample instructions in order, and the vscnt reports the completion of store and atomic without return in order. See MEM_ORDERED field in compute_pgm_rsrc1 for GFX6-GFX12.

Wavefronts can be executed in WGP or CU wavefront execution mode:

  • In WGP wavefront execution mode the wavefronts of a work-group are executed on the SIMDs of both CUs of the WGP. Therefore, explicit management of the per CU L0 caches is required for work-group synchronization. Also accesses to L1 at work-group scope need to be explicitly ordered as the accesses from different CUs are not ordered.

  • In CU wavefront execution mode the wavefronts of a work-group are executed on the SIMDs of a single CU of the WGP. Therefore, all global memory access by the work-group access the same L0 which in turn ensures L1 accesses are ordered and so do not require explicit management of the caches for work-group synchronization.

See WGP_MODE field in compute_pgm_rsrc1 for GFX6-GFX12 and Target Features.

The code sequences used to implement the memory model for GFX10-GFX11 are defined in table AMDHSA Memory Model Code Sequences GFX10-GFX11.

Table 81 AMDHSA Memory Model Code Sequences GFX10-GFX11

LLVM Instr

LLVM Memory Ordering

LLVM Memory Sync Scope

AMDGPU Address Space

AMDGPU Machine Code GFX10-GFX11

Non-Atomic

load

none

none

  • global

  • generic

  • private

  • constant

  • !volatile & !nontemporal

    1. buffer/global/flat_load

  • !volatile & nontemporal

    1. buffer/global/flat_load slc=1 dlc=1

    • If GFX10, omit dlc=1.

  • volatile

    1. buffer/global/flat_load glc=1 dlc=1

    2. s_waitcnt vmcnt(0)

    • Must happen before any following volatile global/generic load/store.

    • Ensures that volatile operations to different addresses will not be reordered by hardware.

load

none

none

  • local

  1. ds_load

store

none

none

  • global

  • generic

  • private

  • constant

  • !volatile & !nontemporal

    1. buffer/global/flat_store

  • !volatile & nontemporal

    1. buffer/global/flat_store glc=1 slc=1 dlc=1

    • If GFX10, omit dlc=1.

  • volatile

    1. buffer/global/flat_store dlc=1

    • If GFX10, omit dlc=1.

    1. s_waitcnt vscnt(0)

    • Must happen before any following volatile global/generic load/store.

    • Ensures that volatile operations to different addresses will not be reordered by hardware.

store

none

none

  • local

  1. ds_store

Unordered Atomic

load atomic

unordered

any

any

Same as non-atomic.

store atomic

unordered

any

any

Same as non-atomic.

atomicrmw

unordered

any

any

Same as monotonic atomic.

Monotonic Atomic

load atomic

monotonic

  • singlethread

  • wavefront

  • global

  • generic

  1. buffer/global/flat_load

load atomic

monotonic

  • workgroup

  • global

  • generic

  1. buffer/global/flat_load glc=1

  • If CU wavefront execution mode, omit glc=1.

load atomic

monotonic

  • singlethread

  • wavefront

  • workgroup

  • local

  1. ds_load

load atomic

monotonic

  • agent

  • system

  • global

  • generic

  1. buffer/global/flat_load glc=1 dlc=1

  • If GFX11, omit dlc=1.

store atomic

monotonic

  • singlethread

  • wavefront

  • workgroup

  • agent

  • system

  • global

  • generic

  1. buffer/global/flat_store

store atomic

monotonic

  • singlethread

  • wavefront

  • workgroup

  • local

  1. ds_store

atomicrmw

monotonic

  • singlethread

  • wavefront

  • workgroup

  • agent

  • system

  • global

  • generic

  1. buffer/global/flat_atomic

atomicrmw

monotonic

  • singlethread

  • wavefront

  • workgroup

  • local

  1. ds_atomic

Acquire Atomic

load atomic

acquire

  • singlethread

  • wavefront

  • global

  • local

  • generic

  1. buffer/global/ds/flat_load

load atomic

acquire

  • workgroup

  • global

  1. buffer/global_load glc=1

  • If CU wavefront execution mode, omit glc=1.

  1. s_waitcnt vmcnt(0)

  • If CU wavefront execution mode, omit.

  • Must happen before the following buffer_gl0_inv and before any following global/generic load/load atomic/store/store atomic/atomicrmw.

  1. buffer_gl0_inv

  • If CU wavefront execution mode, omit.

  • Ensures that following loads will not see stale data.

load atomic

acquire

  • workgroup

  • local

  1. ds_load

  2. s_waitcnt lgkmcnt(0)

  • If OpenCL, omit.

  • Must happen before the following buffer_gl0_inv and before any following global/generic load/load atomic/store/store atomic/atomicrmw.

  • Ensures any following global data read is no older than the local load atomic value being acquired.

  1. buffer_gl0_inv

  • If CU wavefront execution mode, omit.

  • If OpenCL, omit.

  • Ensures that following loads will not see stale data.

load atomic

acquire

  • workgroup

  • generic

  1. flat_load glc=1

  • If CU wavefront execution mode, omit glc=1.

  1. s_waitcnt lgkmcnt(0) & vmcnt(0)

  • If CU wavefront execution mode, omit vmcnt(0).

  • If OpenCL, omit lgkmcnt(0).

  • Must happen before the following buffer_gl0_inv and any following global/generic load/load atomic/store/store atomic/atomicrmw.

  • Ensures any following global data read is no older than a local load atomic value being acquired.

  1. buffer_gl0_inv

  • If CU wavefront execution mode, omit.

  • Ensures that following loads will not see stale data.

load atomic

acquire

  • agent

  • system

  • global

  1. buffer/global_load glc=1 dlc=1

  • If GFX11, omit dlc=1.

  1. s_waitcnt vmcnt(0)

  • Must happen before following buffer_gl*_inv.

  • Ensures the load has completed before invalidating the caches.

  1. buffer_gl1_inv; buffer_gl0_inv

  • Must happen before any following global/generic load/load atomic/atomicrmw.

  • Ensures that following loads will not see stale global data.

load atomic

acquire

  • agent

  • system

  • generic

  1. flat_load glc=1 dlc=1

  • If GFX11, omit dlc=1.

  1. s_waitcnt vmcnt(0) & lgkmcnt(0)

  • If OpenCL omit lgkmcnt(0).

  • Must happen before following buffer_gl*_invl.

  • Ensures the flat_load has completed before invalidating the caches.

  1. buffer_gl1_inv; buffer_gl0_inv

  • Must happen before any following global/generic load/load atomic/atomicrmw.

  • Ensures that following loads will not see stale global data.

atomicrmw

acquire

  • singlethread

  • wavefront

  • global

  • local

  • generic

  1. buffer/global/ds/flat_atomic

atomicrmw

acquire

  • workgroup

  • global

  1. buffer/global_atomic

  2. s_waitcnt vm/vscnt(0)

  • If CU wavefront execution mode, omit.

  • Use vmcnt(0) if atomic with return and vscnt(0) if atomic with no-return.

  • Must happen before the following buffer_gl0_inv and before any following global/generic load/load atomic/store/store atomic/atomicrmw.

  1. buffer_gl0_inv

  • If CU wavefront execution mode, omit.

  • Ensures that following loads will not see stale data.

atomicrmw

acquire

  • workgroup

  • local

  1. ds_atomic

  2. s_waitcnt lgkmcnt(0)

  • If OpenCL, omit.

  • Must happen before the following buffer_gl0_inv.

  • Ensures any following global data read is no older than the local atomicrmw value being acquired.

  1. buffer_gl0_inv

  • If OpenCL omit.

  • Ensures that following loads will not see stale data.

atomicrmw

acquire

  • workgroup

  • generic

  1. flat_atomic

  2. s_waitcnt lgkmcnt(0) & vm/vscnt(0)

  • If CU wavefront execution mode, omit vm/vscnt(0).

  • If OpenCL, omit lgkmcnt(0).

  • Use vmcnt(0) if atomic with return and vscnt(0) if atomic with no-return.

  • Must happen before the following buffer_gl0_inv.

  • Ensures any following global data read is no older than a local atomicrmw value being acquired.

  1. buffer_gl0_inv

  • If CU wavefront execution mode, omit.

  • Ensures that following loads will not see stale data.

atomicrmw

acquire

  • agent

  • system

  • global

  1. buffer/global_atomic

  2. s_waitcnt vm/vscnt(0)

  • Use vmcnt(0) if atomic with return and vscnt(0) if atomic with no-return.

  • Must happen before following buffer_gl*_inv.

  • Ensures the atomicrmw has completed before invalidating the caches.

  1. buffer_gl1_inv; buffer_gl0_inv

  • Must happen before any following global/generic load/load atomic/atomicrmw.

  • Ensures that following loads will not see stale global data.

atomicrmw

acquire

  • agent

  • system

  • generic

  1. flat_atomic

  2. s_waitcnt vm/vscnt(0) & lgkmcnt(0)

  • If OpenCL, omit lgkmcnt(0).

  • Use vmcnt(0) if atomic with return and vscnt(0) if atomic with no-return.

  • Must happen before following buffer_gl*_inv.

  • Ensures the atomicrmw has completed before invalidating the caches.

  1. buffer_gl1_inv; buffer_gl0_inv

  • Must happen before any following global/generic load/load atomic/atomicrmw.

  • Ensures that following loads will not see stale global data.

fence

acquire

  • singlethread

  • wavefront

none

none

fence

acquire

  • workgroup

none

  1. s_waitcnt lgkmcnt(0) & vmcnt(0) & vscnt(0)

  • If CU wavefront execution mode, omit vmcnt(0) and vscnt(0).

  • If OpenCL and address space is not generic, omit lgkmcnt(0).

  • If OpenCL and address space is local, omit vmcnt(0) and vscnt(0).

  • See Fence and Address Spaces for more details on fencing specific address spaces.

  • Could be split into separate s_waitcnt vmcnt(0), s_waitcnt vscnt(0) and s_waitcnt lgkmcnt(0) to allow them to be independently moved according to the following rules.

  • s_waitcnt vmcnt(0) must happen after any preceding global/generic load atomic/ atomicrmw-with-return-value with an equal or wider sync scope and memory ordering stronger than unordered (this is termed the fence-paired-atomic).

  • s_waitcnt vscnt(0) must happen after any preceding global/generic atomicrmw-no-return-value with an equal or wider sync scope and memory ordering stronger than unordered (this is termed the fence-paired-atomic).

  • s_waitcnt lgkmcnt(0) must happen after any preceding local/generic load atomic/atomicrmw with an equal or wider sync scope and memory ordering stronger than unordered (this is termed the fence-paired-atomic).

  • Must happen before the following buffer_gl0_inv.

  • Ensures that the fence-paired atomic has completed before invalidating the cache. Therefore any following locations read must be no older than the value read by the fence-paired-atomic.

  1. buffer_gl0_inv

  • If CU wavefront execution mode, omit.

  • Ensures that following loads will not see stale data.

fence

acquire

  • agent

  • system

none

  1. s_waitcnt lgkmcnt(0) & vmcnt(0) & vscnt(0)

  • If OpenCL and address space is not generic, omit lgkmcnt(0).

  • If OpenCL and address space is local, omit vmcnt(0) and vscnt(0).

  • See Fence and Address Spaces for more details on fencing specific address spaces.

  • Could be split into separate s_waitcnt vmcnt(0), s_waitcnt vscnt(0) and s_waitcnt lgkmcnt(0) to allow them to be independently moved according to the following rules.

  • s_waitcnt vmcnt(0) must happen after any preceding global/generic load atomic/ atomicrmw-with-return-value with an equal or wider sync scope and memory ordering stronger than unordered (this is termed the fence-paired-atomic).

  • s_waitcnt vscnt(0) must happen after any preceding global/generic atomicrmw-no-return-value with an equal or wider sync scope and memory ordering stronger than unordered (this is termed the fence-paired-atomic).

  • s_waitcnt lgkmcnt(0) must happen after any preceding local/generic load atomic/atomicrmw with an equal or wider sync scope and memory ordering stronger than unordered (this is termed the fence-paired-atomic).

  • Must happen before the following buffer_gl*_inv.

  • Ensures that the fence-paired atomic has completed before invalidating the caches. Therefore any following locations read must be no older than the value read by the fence-paired-atomic.

  1. buffer_gl1_inv; buffer_gl0_inv

  • Must happen before any following global/generic load/load atomic/store/store atomic/atomicrmw.

  • Ensures that following loads will not see stale global data.

Release Atomic

store atomic

release

  • singlethread

  • wavefront

  • global

  • local

  • generic

  1. buffer/global/ds/flat_store

store atomic

release

  • workgroup

  • global

  • generic

  1. s_waitcnt lgkmcnt(0) & vmcnt(0) & vscnt(0)

  • If CU wavefront execution mode, omit vmcnt(0) and vscnt(0).

  • If OpenCL, omit lgkmcnt(0).

  • Could be split into separate s_waitcnt vmcnt(0), s_waitcnt vscnt(0) and s_waitcnt lgkmcnt(0) to allow them to be independently moved according to the following rules.

  • s_waitcnt vmcnt(0) must happen after any preceding global/generic load/load atomic/ atomicrmw-with-return-value.

  • s_waitcnt vscnt(0) must happen after any preceding global/generic store/store atomic/ atomicrmw-no-return-value.

  • s_waitcnt lgkmcnt(0) must happen after any preceding local/generic load/store/load atomic/store atomic/atomicrmw.

  • Must happen before the following store.

  • Ensures that all memory operations have completed before performing the store that is being released.

  1. buffer/global/flat_store

store atomic

release

  • workgroup

  • local

  1. s_waitcnt vmcnt(0) & vscnt(0)

  • If CU wavefront execution mode, omit.

  • If OpenCL, omit.

  • Could be split into separate s_waitcnt vmcnt(0) and s_waitcnt vscnt(0) to allow them to be independently moved according to the following rules.

  • s_waitcnt vmcnt(0) must happen after any preceding global/generic load/load atomic/ atomicrmw-with-return-value.

  • s_waitcnt vscnt(0) must happen after any preceding global/generic store/store atomic/ atomicrmw-no-return-value.

  • Must happen before the following store.

  • Ensures that all global memory operations have completed before performing the store that is being released.

  1. ds_store

store atomic

release

  • agent

  • system

  • global

  • generic

  1. s_waitcnt lgkmcnt(0) & vmcnt(0) & vscnt(0)

  • If OpenCL and address space is not generic, omit lgkmcnt(0).

  • Could be split into separate s_waitcnt vmcnt(0), s_waitcnt vscnt(0) and s_waitcnt lgkmcnt(0) to allow them to be independently moved according to the following rules.

  • s_waitcnt vmcnt(0) must happen after any preceding global/generic load/load atomic/ atomicrmw-with-return-value.

  • s_waitcnt vscnt(0) must happen after any preceding global/generic store/store atomic/ atomicrmw-no-return-value.

  • s_waitcnt lgkmcnt(0) must happen after any preceding local/generic load/store/load atomic/store atomic/atomicrmw.

  • Must happen before the following store.

  • Ensures that all memory operations have completed before performing the store that is being released.

  1. buffer/global/flat_store

atomicrmw

release

  • singlethread

  • wavefront

  • global

  • local

  • generic

  1. buffer/global/ds/flat_atomic

atomicrmw

release

  • workgroup

  • global

  • generic

  1. s_waitcnt lgkmcnt(0) & vmcnt(0) & vscnt(0)

  • If CU wavefront execution mode, omit vmcnt(0) and vscnt(0).

  • If OpenCL, omit lgkmcnt(0).

  • Could be split into separate s_waitcnt vmcnt(0), s_waitcnt vscnt(0) and s_waitcnt lgkmcnt(0) to allow them to be independently moved according to the following rules.

  • s_waitcnt vmcnt(0) must happen after any preceding global/generic load/load atomic/ atomicrmw-with-return-value.

  • s_waitcnt vscnt(0) must happen after any preceding global/generic store/store atomic/ atomicrmw-no-return-value.

  • s_waitcnt lgkmcnt(0) must happen after any preceding local/generic load/store/load atomic/store atomic/atomicrmw.

  • Must happen before the following atomicrmw.

  • Ensures that all memory operations have completed before performing the atomicrmw that is being released.

  1. buffer/global/flat_atomic

atomicrmw

release

  • workgroup

  • local

  1. s_waitcnt vmcnt(0) & vscnt(0)

  • If CU wavefront execution mode, omit.

  • If OpenCL, omit.

  • Could be split into separate s_waitcnt vmcnt(0) and s_waitcnt vscnt(0) to allow them to be independently moved according to the following rules.

  • s_waitcnt vmcnt(0) must happen after any preceding global/generic load/load atomic/ atomicrmw-with-return-value.

  • s_waitcnt vscnt(0) must happen after any preceding global/generic store/store atomic/ atomicrmw-no-return-value.

  • Must happen before the following store.

  • Ensures that all global memory operations have completed before performing the store that is being released.

  1. ds_atomic

atomicrmw

release

  • agent

  • system

  • global

  • generic
  1. s_waitcnt lgkmcnt(0) &

    vmcnt(0) & vscnt(0)

  • If OpenCL, omit lgkmcnt(0).

  • Could be split into separate s_waitcnt vmcnt(0), s_waitcnt vscnt(0) and s_waitcnt lgkmcnt(0) to allow them to be independently moved according to the following rules.

  • s_waitcnt vmcnt(0) must happen after any preceding global/generic load/load atomic/ atomicrmw-with-return-value.

  • s_waitcnt vscnt(0) must happen after any preceding global/generic store/store atomic/ atomicrmw-no-return-value.

  • s_waitcnt lgkmcnt(0) must happen after any preceding local/generic load/store/load atomic/store atomic/atomicrmw.

  • Must happen before the following atomicrmw.

  • Ensures that all memory operations to global and local have completed before performing the atomicrmw that is being released.

  1. buffer/global/flat_atomic

fence

release

  • singlethread

  • wavefront

none

none

fence

release

  • workgroup

none

  1. s_waitcnt lgkmcnt(0) & vmcnt(0) & vscnt(0)

  • If CU wavefront execution mode, omit vmcnt(0) and vscnt(0).

  • If OpenCL and address space is not generic, omit lgkmcnt(0).

  • If OpenCL and address space is local, omit vmcnt(0) and vscnt(0).

  • See Fence and Address Spaces for more details on fencing specific address spaces.

  • Could be split into separate s_waitcnt vmcnt(0), s_waitcnt vscnt(0) and s_waitcnt lgkmcnt(0) to allow them to be independently moved according to the following rules.

  • s_waitcnt vmcnt(0) must happen after any preceding global/generic load/load atomic/ atomicrmw-with-return-value.

  • s_waitcnt vscnt(0) must happen after any preceding global/generic store/store atomic/ atomicrmw-no-return-value.

  • s_waitcnt lgkmcnt(0) must happen after any preceding local/generic load/store/load atomic/store atomic/ atomicrmw.

  • Must happen before any following store atomic/atomicrmw with an equal or wider sync scope and memory ordering stronger than unordered (this is termed the fence-paired-atomic).

  • Ensures that all memory operations have completed before performing the following fence-paired-atomic.

fence

release

  • agent

  • system

none

  1. s_waitcnt lgkmcnt(0) & vmcnt(0) & vscnt(0)

  • If OpenCL and address space is not generic, omit lgkmcnt(0).

  • If OpenCL and address space is local, omit vmcnt(0) and vscnt(0).

  • See Fence and Address Spaces for more details on fencing specific address spaces.

  • Could be split into separate s_waitcnt vmcnt(0), s_waitcnt vscnt(0) and s_waitcnt lgkmcnt(0) to allow them to be independently moved according to the following rules.

  • s_waitcnt vmcnt(0) must happen after any preceding global/generic load/load atomic/ atomicrmw-with-return-value.

  • s_waitcnt vscnt(0) must happen after any preceding global/generic store/store atomic/ atomicrmw-no-return-value.

  • s_waitcnt lgkmcnt(0) must happen after any preceding local/generic load/store/load atomic/store atomic/atomicrmw.

  • Must happen before any following store atomic/atomicrmw with an equal or wider sync scope and memory ordering stronger than unordered (this is termed the fence-paired-atomic).

  • Ensures that all memory operations have completed before performing the following fence-paired-atomic.

Acquire-Release Atomic

atomicrmw

acq_rel

  • singlethread

  • wavefront

  • global

  • local

  • generic

  1. buffer/global/ds/flat_atomic

atomicrmw

acq_rel

  • workgroup

  • global

  1. s_waitcnt lgkmcnt(0) & vmcnt(0) & vscnt(0)

  • If CU wavefront execution mode, omit vmcnt(0) and vscnt(0).

  • If OpenCL, omit lgkmcnt(0).

  • Must happen after any preceding local/generic load/store/load atomic/store atomic/atomicrmw.

  • Could be split into separate s_waitcnt vmcnt(0), s_waitcnt vscnt(0), and s_waitcnt lgkmcnt(0) to allow them to be independently moved according to the following rules.

  • s_waitcnt vmcnt(0) must happen after any preceding global/generic load/load atomic/ atomicrmw-with-return-value.

  • s_waitcnt vscnt(0) must happen after any preceding global/generic store/store atomic/ atomicrmw-no-return-value.

  • s_waitcnt lgkmcnt(0) must happen after any preceding local/generic load/store/load atomic/store atomic/atomicrmw.

  • Must happen before the following atomicrmw.

  • Ensures that all memory operations have completed before performing the atomicrmw that is being released.

  1. buffer/global_atomic

  2. s_waitcnt vm/vscnt(0)

  • If CU wavefront execution mode, omit.

  • Use vmcnt(0) if atomic with return and vscnt(0) if atomic with no-return.

  • Must happen before the following buffer_gl0_inv.

  • Ensures any following global data read is no older than the atomicrmw value being acquired.

  1. buffer_gl0_inv

  • If CU wavefront execution mode, omit.

  • Ensures that following loads will not see stale data.

atomicrmw

acq_rel

  • workgroup

  • local

  1. s_waitcnt vmcnt(0) & vscnt(0)

  • If CU wavefront execution mode, omit.

  • If OpenCL, omit.

  • Could be split into separate s_waitcnt vmcnt(0) and s_waitcnt vscnt(0) to allow them to be independently moved according to the following rules.

  • s_waitcnt vmcnt(0) must happen after any preceding global/generic load/load atomic/ atomicrmw-with-return-value.

  • s_waitcnt vscnt(0) must happen after any preceding global/generic store/store atomic/ atomicrmw-no-return-value.

  • Must happen before the following store.

  • Ensures that all global memory operations have completed before performing the store that is being released.

  1. ds_atomic

  2. s_waitcnt lgkmcnt(0)

  • If OpenCL, omit.

  • Must happen before the following buffer_gl0_inv.

  • Ensures any following global data read is no older than the local load atomic value being acquired.

  1. buffer_gl0_inv

  • If CU wavefront execution mode, omit.

  • If OpenCL omit.

  • Ensures that following loads will not see stale data.

atomicrmw

acq_rel

  • workgroup

  • generic

  1. s_waitcnt lgkmcnt(0) & vmcnt(0) & vscnt(0)

  • If CU wavefront execution mode, omit vmcnt(0) and vscnt(0).

  • If OpenCL, omit lgkmcnt(0).

  • Could be split into separate s_waitcnt vmcnt(0), s_waitcnt vscnt(0) and s_waitcnt lgkmcnt(0) to allow them to be independently moved according to the following rules.

  • s_waitcnt vmcnt(0) must happen after any preceding global/generic load/load atomic/ atomicrmw-with-return-value.

  • s_waitcnt vscnt(0) must happen after any preceding global/generic store/store atomic/ atomicrmw-no-return-value.

  • s_waitcnt lgkmcnt(0) must happen after any preceding local/generic load/store/load atomic/store atomic/atomicrmw.

  • Must happen before the following atomicrmw.

  • Ensures that all memory operations have completed before performing the atomicrmw that is being released.

  1. flat_atomic

  2. s_waitcnt lgkmcnt(0) & vmcnt(0) & vscnt(0)

  • If CU wavefront execution mode, omit vmcnt(0) and vscnt(0).

  • If OpenCL, omit lgkmcnt(0).

  • Must happen before the following buffer_gl0_inv.

  • Ensures any following global data read is no older than the load atomic value being acquired.

  1. buffer_gl0_inv

  • If CU wavefront execution mode, omit.

  • Ensures that following loads will not see stale data.

atomicrmw

acq_rel

  • agent

  • system

  • global

  1. s_waitcnt lgkmcnt(0) & vmcnt(0) & vscnt(0)

  • If OpenCL, omit lgkmcnt(0).

  • Could be split into separate s_waitcnt vmcnt(0), s_waitcnt vscnt(0) and s_waitcnt lgkmcnt(0) to allow them to be independently moved according to the following rules.

  • s_waitcnt vmcnt(0) must happen after any preceding global/generic load/load atomic/ atomicrmw-with-return-value.

  • s_waitcnt vscnt(0) must happen after any preceding global/generic store/store atomic/ atomicrmw-no-return-value.

  • s_waitcnt lgkmcnt(0) must happen after any preceding local/generic load/store/load atomic/store atomic/atomicrmw.

  • Must happen before the following atomicrmw.

  • Ensures that all memory operations to global have completed before performing the atomicrmw that is being released.

  1. buffer/global_atomic

  2. s_waitcnt vm/vscnt(0)

  • Use vmcnt(0) if atomic with return and vscnt(0) if atomic with no-return.

  • Must happen before following buffer_gl*_inv.

  • Ensures the atomicrmw has completed before invalidating the caches.

  1. buffer_gl1_inv; buffer_gl0_inv

  • Must happen before any following global/generic load/load atomic/atomicrmw.

  • Ensures that following loads will not see stale global data.

atomicrmw

acq_rel

  • agent

  • system

  • generic

  1. s_waitcnt lgkmcnt(0) & vmcnt(0) & vscnt(0)

  • If OpenCL, omit lgkmcnt(0).

  • Could be split into separate s_waitcnt vmcnt(0), s_waitcnt vscnt(0), and s_waitcnt lgkmcnt(0) to allow them to be independently moved according to the following rules.

  • s_waitcnt vmcnt(0) must happen after any preceding global/generic load/load atomic atomicrmw-with-return-value.

  • s_waitcnt vscnt(0) must happen after any preceding global/generic store/store atomic/ atomicrmw-no-return-value.

  • s_waitcnt lgkmcnt(0) must happen after any preceding local/generic load/store/load atomic/store atomic/atomicrmw.

  • Must happen before the following atomicrmw.

  • Ensures that all memory operations have completed before performing the atomicrmw that is being released.

  1. flat_atomic

  2. s_waitcnt vm/vscnt(0) & lgkmcnt(0)

  • If OpenCL, omit lgkmcnt(0).

  • Use vmcnt(0) if atomic with return and vscnt(0) if atomic with no-return.

  • Must happen before following buffer_gl*_inv.

  • Ensures the atomicrmw has completed before invalidating the caches.

  1. buffer_gl1_inv; buffer_gl0_inv

  • Must happen before any following global/generic load/load atomic/atomicrmw.

  • Ensures that following loads will not see stale global data.

fence

acq_rel

  • singlethread

  • wavefront

none

none

fence

acq_rel

  • workgroup

none

  1. s_waitcnt lgkmcnt(0) & vmcnt(0) & vscnt(0)

  • If CU wavefront execution mode, omit vmcnt(0) and vscnt(0).

  • If OpenCL and address space is not generic, omit lgkmcnt(0).

  • If OpenCL and address space is local, omit vmcnt(0) and vscnt(0).

  • However, since LLVM currently has no address space on the fence need to conservatively always generate (see comment for previous fence).

  • Could be split into separate s_waitcnt vmcnt(0), s_waitcnt vscnt(0) and s_waitcnt lgkmcnt(0) to allow them to be independently moved according to the following rules.

  • s_waitcnt vmcnt(0) must happen after any preceding global/generic load/load atomic/ atomicrmw-with-return-value.

  • s_waitcnt vscnt(0) must happen after any preceding global/generic store/store atomic/ atomicrmw-no-return-value.

  • s_waitcnt lgkmcnt(0) must happen after any preceding local/generic load/store/load atomic/store atomic/ atomicrmw.

  • Must happen before any following global/generic load/load atomic/store/store atomic/atomicrmw.

  • Ensures that all memory operations have completed before performing any following global memory operations.

  • Ensures that the preceding local/generic load atomic/atomicrmw with an equal or wider sync scope and memory ordering stronger than unordered (this is termed the acquire-fence-paired-atomic) has completed before following global memory operations. This satisfies the requirements of acquire.

  • Ensures that all previous memory operations have completed before a following local/generic store atomic/atomicrmw with an equal or wider sync scope and memory ordering stronger than unordered (this is termed the release-fence-paired-atomic). This satisfies the requirements of release.

  • Must happen before the following buffer_gl0_inv.

  • Ensures that the acquire-fence-paired atomic has completed before invalidating the cache. Therefore any following locations read must be no older than the value read by the acquire-fence-paired-atomic.

  1. buffer_gl0_inv

  • If CU wavefront execution mode, omit.

  • Ensures that following loads will not see stale data.

fence

acq_rel

  • agent

  • system

none

  1. s_waitcnt lgkmcnt(0) & vmcnt(0) & vscnt(0)

  • If OpenCL and address space is not generic, omit lgkmcnt(0).

  • If OpenCL and address space is local, omit vmcnt(0) and vscnt(0).

  • See Fence and Address Spaces for more details on fencing specific address spaces.

  • Could be split into separate s_waitcnt vmcnt(0), s_waitcnt vscnt(0) and s_waitcnt lgkmcnt(0) to allow them to be independently moved according to the following rules.

  • s_waitcnt vmcnt(0) must happen after any preceding global/generic load/load atomic/ atomicrmw-with-return-value.

  • s_waitcnt vscnt(0) must happen after any preceding global/generic store/store atomic/ atomicrmw-no-return-value.

  • s_waitcnt lgkmcnt(0) must happen after any preceding local/generic load/store/load atomic/store atomic/atomicrmw.

  • Must happen before the following buffer_gl*_inv.

  • Ensures that the preceding global/local/generic load atomic/atomicrmw with an equal or wider sync scope and memory ordering stronger than unordered (this is termed the acquire-fence-paired-atomic) has completed before invalidating the caches. This satisfies the requirements of acquire.

  • Ensures that all previous memory operations have completed before a following global/local/generic store atomic/atomicrmw with an equal or wider sync scope and memory ordering stronger than unordered (this is termed the release-fence-paired-atomic). This satisfies the requirements of release.

  1. buffer_gl1_inv; buffer_gl0_inv

  • Must happen before any following global/generic load/load atomic/store/store atomic/atomicrmw.

  • Ensures that following loads will not see stale global data. This satisfies the requirements of acquire.

Sequential Consistent Atomic

load atomic

seq_cst

  • singlethread

  • wavefront

  • global

  • local

  • generic

Same as corresponding load atomic acquire, except must generate all instructions even for OpenCL.

load atomic

seq_cst

  • workgroup

  • global

  • generic

  1. s_waitcnt lgkmcnt(0) & vmcnt(0) & vscnt(0)

  • If CU wavefront execution mode, omit vmcnt(0) and vscnt(0).

  • Could be split into separate s_waitcnt vmcnt(0), s_waitcnt vscnt(0), and s_waitcnt lgkmcnt(0) to allow them to be independently moved according to the following rules.

  • s_waitcnt lgkmcnt(0) must happen after preceding local/generic load atomic/store atomic/atomicrmw with memory ordering of seq_cst and with equal or wider sync scope. (Note that seq_cst fences have their own s_waitcnt lgkmcnt(0) and so do not need to be considered.)

  • s_waitcnt vmcnt(0) must happen after preceding global/generic load atomic/ atomicrmw-with-return-value with memory ordering of seq_cst and with equal or wider sync scope. (Note that seq_cst fences have their own s_waitcnt vmcnt(0) and so do not need to be considered.)

  • s_waitcnt vscnt(0) Must happen after preceding global/generic store atomic/ atomicrmw-no-return-value with memory ordering of seq_cst and with equal or wider sync scope. (Note that seq_cst fences have their own s_waitcnt vscnt(0) and so do not need to be considered.)

  • Ensures any preceding sequential consistent global/local memory instructions have completed before executing this sequentially consistent instruction. This prevents reordering a seq_cst store followed by a seq_cst load. (Note that seq_cst is stronger than acquire/release as the reordering of load acquire followed by a store release is prevented by the s_waitcnt of the release, but there is nothing preventing a store release followed by load acquire from completing out of order. The s_waitcnt could be placed after seq_store or before the seq_load. We choose the load to make the s_waitcnt be as late as possible so that the store may have already completed.)

  1. Following instructions same as corresponding load atomic acquire, except must generate all instructions even for OpenCL.

load atomic

seq_cst

  • workgroup

  • local

  1. s_waitcnt vmcnt(0) & vscnt(0)

  • If CU wavefront execution mode, omit.

  • Could be split into separate s_waitcnt vmcnt(0) and s_waitcnt vscnt(0) to allow them to be independently moved according to the following rules.

  • s_waitcnt vmcnt(0) Must happen after preceding global/generic load atomic/ atomicrmw-with-return-value with memory ordering of seq_cst and with equal or wider sync scope. (Note that seq_cst fences have their own s_waitcnt vmcnt(0) and so do not need to be considered.)

  • s_waitcnt vscnt(0) Must happen after preceding global/generic store atomic/ atomicrmw-no-return-value with memory ordering of seq_cst and with equal or wider sync scope. (Note that seq_cst fences have their own s_waitcnt vscnt(0) and so do not need to be considered.)

  • Ensures any preceding sequential consistent global memory instructions have completed before executing this sequentially consistent instruction. This prevents reordering a seq_cst store followed by a seq_cst load. (Note that seq_cst is stronger than acquire/release as the reordering of load acquire followed by a store release is prevented by the s_waitcnt of the release, but there is nothing preventing a store release followed by load acquire from completing out of order. The s_waitcnt could be placed after seq_store or before the seq_load. We choose the load to make the s_waitcnt be as late as possible so that the store may have already completed.)

  1. Following instructions same as corresponding load atomic acquire, except must generate all instructions even for OpenCL.

load atomic

seq_cst

  • agent

  • system

  • global

  • generic

  1. s_waitcnt lgkmcnt(0) & vmcnt(0) & vscnt(0)

  • Could be split into separate s_waitcnt vmcnt(0), s_waitcnt vscnt(0) and s_waitcnt lgkmcnt(0) to allow them to be independently moved according to the following rules.

  • s_waitcnt lgkmcnt(0) must happen after preceding local load atomic/store atomic/atomicrmw with memory ordering of seq_cst and with equal or wider sync scope. (Note that seq_cst fences have their own s_waitcnt lgkmcnt(0) and so do not need to be considered.)

  • s_waitcnt vmcnt(0) must happen after preceding global/generic load atomic/ atomicrmw-with-return-value with memory ordering of seq_cst and with equal or wider sync scope. (Note that seq_cst fences have their own s_waitcnt vmcnt(0) and so do not need to be considered.)

  • s_waitcnt vscnt(0) Must happen after preceding global/generic store atomic/ atomicrmw-no-return-value with memory ordering of seq_cst and with equal or wider sync scope. (Note that seq_cst fences have their own s_waitcnt vscnt(0) and so do not need to be considered.)

  • Ensures any preceding sequential consistent global memory instructions have completed before executing this sequentially consistent instruction. This prevents reordering a seq_cst store followed by a seq_cst load. (Note that seq_cst is stronger than acquire/release as the reordering of load acquire followed by a store release is prevented by the s_waitcnt of the release, but there is nothing preventing a store release followed by load acquire from completing out of order. The s_waitcnt could be placed after seq_store or before the seq_load. We choose the load to make the s_waitcnt be as late as possible so that the store may have already completed.)

  1. Following instructions same as corresponding load atomic acquire, except must generate all instructions even for OpenCL.

store atomic

seq_cst

  • singlethread

  • wavefront

  • workgroup

  • agent

  • system

  • global

  • local

  • generic

Same as corresponding store atomic release, except must generate all instructions even for OpenCL.

atomicrmw

seq_cst

  • singlethread

  • wavefront

  • workgroup

  • agent

  • system

  • global

  • local

  • generic

Same as corresponding atomicrmw acq_rel, except must generate all instructions even for OpenCL.

fence

seq_cst

  • singlethread

  • wavefront

  • workgroup

  • agent

  • system

none

Same as corresponding fence acq_rel, except must generate all instructions even for OpenCL.

Trap Handler ABI

For code objects generated by the AMDGPU backend for HSA [HSA] compatible runtimes (see AMDGPU Operating Systems), the runtime installs a trap handler that supports the s_trap instruction. For usage see:

  • AMDGPU Trap Handler for AMDHSA OS Code Object V2

  • AMDGPU Trap Handler for AMDHSA OS Code Object V3

  • AMDGPU Trap Handler for AMDHSA OS Code Object V4 and Above

    Table 82 AMDGPU Trap Handler for AMDHSA OS Code Object V2

    Usage

    Code Sequence

    Trap Handler Inputs

    Description

    reserved

    s_trap 0x00

    Reserved by hardware.

    debugtrap(arg)

    s_trap 0x01
    SGPR0-1:

    queue_ptr

    VGPR0:

    arg

    Reserved for Finalizer HSA debugtrap intrinsic (not implemented).

    llvm.trap

    s_trap 0x02
    SGPR0-1:

    queue_ptr

    Causes wave to be halted with the PC at the trap instruction. The associated queue is signalled to put it into the error state. When the queue is put in the error state, the waves executing dispatches on the queue will be terminated.

    llvm.debugtrap

    s_trap 0x03

    none

    • If debugger not enabled then behaves as a no-operation. The trap handler is entered and immediately returns to continue execution of the wavefront.

    • If the debugger is enabled, causes the debug trap to be reported by the debugger and the wavefront is put in the halt state with the PC at the instruction. The debugger must increment the PC and resume the wave.

    reserved

    s_trap 0x04

    Reserved.

    reserved

    s_trap 0x05

    Reserved.

    reserved

    s_trap 0x06

    Reserved.

    reserved

    s_trap 0x07

    Reserved.

    reserved

    s_trap 0x08

    Reserved.

    reserved

    s_trap 0xfe

    Reserved.

    reserved

    s_trap 0xff

    Reserved.
Table 83 AMDGPU Trap Handler for AMDHSA OS Code Object V3

Usage

Code Sequence

Trap Handler Inputs

Description

reserved

s_trap 0x00

Reserved by hardware.

debugger breakpoint

s_trap 0x01

none

Reserved for debugger to use for breakpoints. Causes wave to be halted with the PC at the trap instruction. The debugger is responsible to resume the wave, including the instruction that the breakpoint overwrote.

llvm.trap

s_trap 0x02
SGPR0-1:

queue_ptr

Causes wave to be halted with the PC at the trap instruction. The associated queue is signalled to put it into the error state. When the queue is put in the error state, the waves executing dispatches on the queue will be terminated.

llvm.debugtrap

s_trap 0x03

none

  • If debugger not enabled then behaves as a no-operation. The trap handler is entered and immediately returns to continue execution of the wavefront.

  • If the debugger is enabled, causes the debug trap to be reported by the debugger and the wavefront is put in the halt state with the PC at the instruction. The debugger must increment the PC and resume the wave.

reserved

s_trap 0x04

Reserved.

reserved

s_trap 0x05

Reserved.

reserved

s_trap 0x06

Reserved.

reserved

s_trap 0x07

Reserved.

reserved

s_trap 0x08

Reserved.

reserved

s_trap 0xfe

Reserved.

reserved

s_trap 0xff

Reserved.
Table 84 AMDGPU Trap Handler for AMDHSA OS Code Object V4 and Above

Usage

Code Sequence

GFX6-GFX8 Inputs

GFX9-GFX11 Inputs

Description

reserved

s_trap 0x00

Reserved by hardware.

debugger breakpoint

s_trap 0x01

none

none

Reserved for debugger to use for breakpoints. Causes wave to be halted with the PC at the trap instruction. The debugger is responsible to resume the wave, including the instruction that the breakpoint overwrote.

llvm.trap

s_trap 0x02
SGPR0-1:

queue_ptr

none

Causes wave to be halted with the PC at the trap instruction. The associated queue is signalled to put it into the error state. When the queue is put in the error state, the waves executing dispatches on the queue will be terminated.

llvm.debugtrap

s_trap 0x03

none

none

  • If debugger not enabled then behaves as a no-operation. The trap handler is entered and immediately returns to continue execution of the wavefront.

  • If the debugger is enabled, causes the debug trap to be reported by the debugger and the wavefront is put in the halt state with the PC at the instruction. The debugger must increment the PC and resume the wave.

reserved

s_trap 0x04

Reserved.

reserved

s_trap 0x05

Reserved.

reserved

s_trap 0x06

Reserved.

reserved

s_trap 0x07

Reserved.

reserved

s_trap 0x08

Reserved.

reserved

s_trap 0xfe

Reserved.

reserved

s_trap 0xff

Reserved.

Call Convention

Note

This section is currently incomplete and has inaccuracies. It is WIP that will be updated as information is determined.

See Address Space Identifier for information on swizzled addresses. Unswizzled addresses are normal linear addresses.

Kernel Functions

This section describes the call convention ABI for the outer kernel function.

See Initial Kernel Execution State for the kernel call convention.

The following is not part of the AMDGPU kernel calling convention but describes how the AMDGPU implements function calls:

  1. Clang decides the kernarg layout to match the HSA Programmer’s Language Reference [HSA].

    • All structs are passed directly.

    • Lambda values are passed TBA.

  1. The kernel performs certain setup in its prolog, as described in Kernel Prolog.

Non-Kernel Functions

This section describes the call convention ABI for functions other than the outer kernel function.

If a kernel has function calls then scratch is always allocated and used for the call stack which grows from low address to high address using the swizzled scratch address space.

On entry to a function:

  1. SGPR0-3 contain a V# with the following properties (see Private Segment Buffer):

    • Base address pointing to the beginning of the wavefront scratch backing memory.

    • Swizzled with dword element size and stride of wavefront size elements.

  2. The FLAT_SCRATCH register pair is setup. See Flat Scratch.

  3. GFX6-GFX8: M0 register set to the size of LDS in bytes. See M0.

  4. The EXEC register is set to the lanes active on entry to the function.

  5. MODE register: TBD

  6. VGPR0-31 and SGPR4-29 are used to pass function input arguments as described below.

  7. SGPR30-31 return address (RA). The code address that the function must return to when it completes. The value is undefined if the function is no return.

  8. SGPR32 is used for the stack pointer (SP). It is an unswizzled scratch offset relative to the beginning of the wavefront scratch backing memory.

    The unswizzled SP can be used with buffer instructions as an unswizzled SGPR offset with the scratch V# in SGPR0-3 to access the stack in a swizzled manner.

    The unswizzled SP value can be converted into the swizzled SP value by:

    swizzled SP = unswizzled SP / wavefront size

    This may be used to obtain the private address space address of stack objects and to convert this address to a flat address by adding the flat scratch aperture base address.

    The swizzled SP value is always 4 bytes aligned for the r600 architecture and 16 byte aligned for the amdgcn architecture.

    Note

    The amdgcn value is selected to avoid dynamic stack alignment for the OpenCL language which has the largest base type defined as 16 bytes.

    On entry, the swizzled SP value is the address of the first function argument passed on the stack. Other stack passed arguments are positive offsets from the entry swizzled SP value.

    The function may use positive offsets beyond the last stack passed argument for stack allocated local variables and register spill slots. If necessary, the function may align these to greater alignment than 16 bytes. After these the function may dynamically allocate space for such things as runtime sized alloca local allocations.

    If the function calls another function, it will place any stack allocated arguments after the last local allocation and adjust SGPR32 to the address after the last local allocation.

  9. All other registers are unspecified.

  10. Any necessary s_waitcnt has been performed to ensure memory is available to the function.

  11. Use pass-by-reference (byref) in stead of pass-by-value (byval) for struct arguments in C ABI. Callee is responsible for allocating stack memory and copying the value of the struct if modified. Note that the backend still supports byval for struct arguments.

On exit from a function:

  1. VGPR0-31 and SGPR4-29 are used to pass function result arguments as described below. Any registers used are considered clobbered registers.

  2. The following registers are preserved and have the same value as on entry:

    • FLAT_SCRATCH

    • EXEC

    • GFX6-GFX8: M0

    • All SGPR registers except the clobbered registers of SGPR4-31.

    • VGPR40-47

    • VGPR56-63

    • VGPR72-79

    • VGPR88-95

    • VGPR104-111

    • VGPR120-127

    • VGPR136-143

    • VGPR152-159

    • VGPR168-175

    • VGPR184-191

    • VGPR200-207

    • VGPR216-223

    • VGPR232-239

    • VGPR248-255

      Note

      Except the argument registers, the VGPRs clobbered and the preserved registers are intermixed at regular intervals in order to keep a similar ratio independent of the number of allocated VGPRs.

    • GFX90A: All AGPR registers except the clobbered registers AGPR0-31.

    • Lanes of all VGPRs that are inactive at the call site.

      For the AMDGPU backend, an inter-procedural register allocation (IPRA) optimization may mark some of clobbered SGPR and VGPR registers as preserved if it can be determined that the called function does not change their value.

  1. The PC is set to the RA provided on entry.

  2. MODE register: TBD.

  3. All other registers are clobbered.

  4. Any necessary s_waitcnt has been performed to ensure memory accessed by function is available to the caller.

The function input arguments are made up of the formal arguments explicitly declared by the source language function plus the implicit input arguments used by the implementation.

The source language input arguments are:

  1. Any source language implicit this or self argument comes first as a pointer type.

  2. Followed by the function formal arguments in left to right source order.

The source language result arguments are:

  1. The function result argument.

The source language input or result struct type arguments that are less than or equal to 16 bytes, are decomposed recursively into their base type fields, and each field is passed as if a separate argument. For input arguments, if the called function requires the struct to be in memory, for example because its address is taken, then the function body is responsible for allocating a stack location and copying the field arguments into it. Clang terms this direct struct.

The source language input struct type arguments that are greater than 16 bytes, are passed by reference. The caller is responsible for allocating a stack location to make a copy of the struct value and pass the address as the input argument. The called function is responsible to perform the dereference when accessing the input argument. Clang terms this by-value struct.

A source language result struct type argument that is greater than 16 bytes, is returned by reference. The caller is responsible for allocating a stack location to hold the result value and passes the address as the last input argument (before the implicit input arguments). In this case there are no result arguments. The called function is responsible to perform the dereference when storing the result value. Clang terms this structured return (sret).

TODO: correct the ``sret`` definition.

Lambda argument types are treated as struct types with an implementation defined set of fields.

For AMDGPU backend all source language arguments (including the decomposed struct type arguments) are passed in VGPRs unless marked inreg in which case they are passed in SGPRs.

The AMDGPU backend walks the function call graph from the leaves to determine which implicit input arguments are used, propagating to each caller of the function. The used implicit arguments are appended to the function arguments after the source language arguments in the following order:

  1. Work-Item ID (1 VGPR)

    The X, Y and Z work-item ID are packed into a single VGRP with the following layout. Only fields actually used by the function are set. The other bits are undefined.

    The values come from the initial kernel execution state. See Initial Kernel Execution State.

    Table 85 Work-item implicit argument layout

    Bits

    Size

    Field Name

    9:0

    10 bits

    X Work-Item ID

    19:10

    10 bits

    Y Work-Item ID

    29:20

    10 bits

    Z Work-Item ID

    31:30

    2 bits

    Unused

  2. Dispatch Ptr (2 SGPRs)

    The value comes from the initial kernel execution state. See SGPR Register Set Up Order.

  3. Queue Ptr (2 SGPRs)

    The value comes from the initial kernel execution state. See SGPR Register Set Up Order.

  4. Kernarg Segment Ptr (2 SGPRs)

    The value comes from the initial kernel execution state. See SGPR Register Set Up Order.

  5. Dispatch id (2 SGPRs)

    The value comes from the initial kernel execution state. See SGPR Register Set Up Order.

  6. Work-Group ID X (1 SGPR)

    The value comes from the initial kernel execution state. See SGPR Register Set Up Order.

  7. Work-Group ID Y (1 SGPR)

    The value comes from the initial kernel execution state. See SGPR Register Set Up Order.

  8. Work-Group ID Z (1 SGPR)

    The value comes from the initial kernel execution state. See SGPR Register Set Up Order.

  9. Implicit Argument Ptr (2 SGPRs)

    The value is computed by adding an offset to Kernarg Segment Ptr to get the global address space pointer to the first kernarg implicit argument.

The input and result arguments are assigned in order in the following manner:

Note

There are likely some errors and omissions in the following description that need correction.

  • VGPR arguments are assigned to consecutive VGPRs starting at VGPR0 up to VGPR31.

    If there are more arguments than will fit in these registers, the remaining arguments are allocated on the stack in order on naturally aligned addresses.

  • SGPR arguments are assigned to consecutive SGPRs starting at SGPR0 up to SGPR29.

    If there are more arguments than will fit in these registers, the remaining arguments are allocated on the stack in order on naturally aligned addresses.

Note that decomposed struct type arguments may have some fields passed in registers and some in memory.

The following is not part of the AMDGPU function calling convention but describes how the AMDGPU implements function calls:

  1. SGPR33 is used as a frame pointer (FP) if necessary. Like the SP it is an unswizzled scratch address. It is only needed if runtime sized alloca are used, or for the reasons defined in SIFrameLowering.

  2. Runtime stack alignment is supported. SGPR34 is used as a base pointer (BP) to access the incoming stack arguments in the function. The BP is needed only when the function requires the runtime stack alignment.

  3. Allocating SGPR arguments on the stack are not supported.

  4. No CFI is currently generated. See A.6.4 Call Frame Information.

    Note

    CFI will be generated that defines the CFA as the unswizzled address relative to the wave scratch base in the unswizzled private address space of the lowest address stack allocated local variable.

    DW_AT_frame_base will be defined as the swizzled address in the swizzled private address space by dividing the CFA by the wavefront size (since CFA is always at least dword aligned which matches the scratch swizzle element size).

    If no dynamic stack alignment was performed, the stack allocated arguments are accessed as negative offsets relative to DW_AT_frame_base, and the local variables and register spill slots are accessed as positive offsets relative to DW_AT_frame_base.

  5. Function argument passing is implemented by copying the input physical registers to virtual registers on entry. The register allocator can spill if necessary. These are copied back to physical registers at call sites. The net effect is that each function call can have these values in entirely distinct locations. The IPRA can help avoid shuffling argument registers.

  6. Call sites are implemented by setting up the arguments at positive offsets from SP. Then SP is incremented to account for the known frame size before the call and decremented after the call.

    Note

    The CFI will reflect the changed calculation needed to compute the CFA from SP.

  7. 4 byte spill slots are used in the stack frame. One slot is allocated for an emergency spill slot. Buffer instructions are used for stack accesses and not the flat_scratch instruction.

AMDPAL

This section provides code conventions used when the target triple OS is amdpal (see Target Triples).

Code Object Metadata

Note

The metadata is currently in development and is subject to major changes. Only the current version is supported. When this document was generated the version was 2.6.

Code object metadata is specified by the NT_AMDGPU_METADATA note record (see Code Object V3 and Above Note Records).

The metadata is represented as Message Pack formatted binary data (see [MsgPack]). The top level is a Message Pack map that includes the keys defined in table AMDPAL Code Object Metadata Map and referenced tables.

Additional information can be added to the maps. To avoid conflicts, any key names should be prefixed by “vendor-name.” where vendor-name can be the name of the vendor and specific vendor tool that generates the information. The prefix is abbreviated to simply “.” when it appears within a map that has been added by the same vendor-name.

Table 86 AMDPAL Code Object Metadata Map

String Key

Value Type

Required?

Description

“amdpal.version”

sequence of 2 integers

Required

PAL code object metadata (major, minor) version. The current values are defined by Util::Abi::PipelineMetadata(Major|Minor)Version.

“amdpal.pipelines”

sequence of map

Required

Per-pipeline metadata. See AMDPAL Code Object Pipeline Metadata Map for the definition of the keys included in that map.
Table 87 AMDPAL Code Object Pipeline Metadata Map

String Key

Value Type

Required?

Description

“.name”

string

Source name of the pipeline.

“.type”

string

Pipeline type, e.g. VsPs. Values include:

  • “VsPs”

  • “Gs”

  • “Cs”

  • “Ngg”

  • “Tess”

  • “GsTess”

  • “NggTess”

“.internal_pipeline_hash”

sequence of 2 integers

Required

Internal compiler hash for this pipeline. Lower 64 bits is the “stable” portion of the hash, used for e.g. shader replacement lookup. Upper 64 bits is the “unique” portion of the hash, used for e.g. pipeline cache lookup. The value is implementation defined, and can not be relied on between different builds of the compiler.

“.shaders”

map

Per-API shader metadata. See AMDPAL Code Object Shader Map for the definition of the keys included in that map.

“.hardware_stages”

map

Per-hardware stage metadata. See AMDPAL Code Object Hardware Stage Map for the definition of the keys included in that map.

“.shader_functions”

map

Per-shader function metadata. See AMDPAL Code Object Shader Function Map for the definition of the keys included in that map.

“.registers”

map

Required

Hardware register configuration. See AMDPAL Code Object Register Map for the definition of the keys included in that map.

“.user_data_limit”

integer

Number of user data entries accessed by this pipeline.

“.spill_threshold”

integer

The user data spill threshold. 0xFFFF for NoUserDataSpilling.

“.uses_viewport_array_index”

boolean

Indicates whether or not the pipeline uses the viewport array index feature. Pipelines which use this feature can render into all 16 viewports, whereas pipelines which do not use it are restricted to viewport #0.

“.es_gs_lds_size”

integer

Size in bytes of LDS space used internally for handling data-passing between the ES and GS shader stages. This can be zero if the data is passed using off-chip buffers. This value should be used to program all user-SGPRs which have been marked with “UserDataMapping::EsGsLdsSize” (typically only the GS and VS HW stages will ever have a user-SGPR so marked).

“.nggSubgroupSize”

integer

Explicit maximum subgroup size for NGG shaders (maximum number of threads in a subgroup).

“.num_interpolants”

integer

Graphics only. Number of PS interpolants.

“.mesh_scratch_memory_size”

integer

Max mesh shader scratch memory used.

“.api”

string

Name of the client graphics API.

“.api_create_info”

binary

Graphics API shader create info binary blob. Can be defined by the driver using the compiler if they want to be able to correlate API-specific information used during creation at a later time.
Table 88 AMDPAL Code Object Shader Map

String Key

Value Type

Description

  • “.compute”

  • “.vertex”

  • “.hull”

  • “.domain”

  • “.geometry”

  • “.pixel”

map

See AMDPAL Code Object API Shader Metadata Map for the definition of the keys included in that map.
Table 89 AMDPAL Code Object API Shader Metadata Map

String Key

Value Type

Required?

Description

“.api_shader_hash”

sequence of 2 integers

Required

Input shader hash, typically passed in from the client. The value is implementation defined, and can not be relied on between different builds of the compiler.

“.hardware_mapping”

sequence of string

Required

Flags indicating the HW stages this API shader maps to. Values include:

  • “.ls”

  • “.hs”

  • “.es”

  • “.gs”

  • “.vs”

  • “.ps”

  • “.cs”
Table 90 AMDPAL Code Object Hardware Stage Map

String Key

Value Type

Description

  • “.ls”

  • “.hs”

  • “.es”

  • “.gs”

  • “.vs”

  • “.ps”

  • “.cs”

map

See AMDPAL Code Object Hardware Stage Metadata Map for the definition of the keys included in that map.
Table 91 AMDPAL Code Object Hardware Stage Metadata Map

String Key

Value Type

Required?

Description

“.entry_point”

string

The ELF symbol pointing to this pipeline’s stage entry point.

“.scratch_memory_size”

integer

Scratch memory size in bytes.

“.lds_size”

integer

Local Data Share size in bytes.

“.perf_data_buffer_size”

integer

Performance data buffer size in bytes.

“.vgpr_count”

integer

Number of VGPRs used.

“.agpr_count”

integer

Number of AGPRs used.

“.sgpr_count”

integer

Number of SGPRs used.

“.vgpr_limit”

integer

If non-zero, indicates the shader was compiled with a directive to instruct the compiler to limit the VGPR usage to be less than or equal to the specified value (only set if different from HW default).

“.sgpr_limit”

integer

SGPR count upper limit (only set if different from HW default).

“.threadgroup_dimensions”

sequence of 3 integers

Thread-group X/Y/Z dimensions (Compute only).

“.wavefront_size”

integer

Wavefront size (only set if different from HW default).

“.uses_uavs”

boolean

The shader reads or writes UAVs.

“.uses_rovs”

boolean

The shader reads or writes ROVs.

“.writes_uavs”

boolean

The shader writes to one or more UAVs.

“.writes_depth”

boolean

The shader writes out a depth value.

“.uses_append_consume”

boolean

The shader uses append and/or consume operations, either memory or GDS.

“.uses_prim_id”

boolean

The shader uses PrimID.
Table 92 AMDPAL Code Object Shader Function Map

String Key

Value Type

Description

symbol name

map

symbol name is the ELF symbol name of the shader function code entry address. The value is the function’s metadata. See AMDPAL Code Object Shader Function Metadata Map.
Table 93 AMDPAL Code Object Shader Function Metadata Map

String Key

Value Type

Description

“.api_shader_hash”

sequence of 2 integers

Input shader hash, typically passed in from the client. The value is implementation defined, and can not be relied on between different builds of the compiler.

“.scratch_memory_size”

integer

Size in bytes of scratch memory used by the shader.

“.lds_size”

integer

Size in bytes of LDS memory.

“.vgpr_count”

integer

Number of VGPRs used by the shader.

“.sgpr_count”

integer

Number of SGPRs used by the shader.

“.stack_frame_size_in_bytes”

integer

Amount of stack size used by the shader.

“.shader_subtype”

string

Shader subtype/kind. Values include:

  • “Unknown”
Table 94 AMDPAL Code Object Register Map

32-bit Integer Key

Value Type

Description

reg offset

32-bit integer

reg offset is the dword offset into the GFXIP register space of a GRBM register (i.e., driver accessible GPU register number, not shader GPR register number). The driver is required to program each specified register to the corresponding specified value when executing this pipeline. Typically, the reg offsets are the uint16_t offsets to each register as defined by the hardware chip headers. The register is set to the provided value. However, a reg offset that specifies a user data register (e.g., COMPUTE_USER_DATA_0) needs special treatment. See User Data section for more information.
User Data

Each hardware stage has a set of 32-bit physical SPI user data registers (either 16 or 32 based on graphics IP and the stage) which can be written from a command buffer and then loaded into SGPRs when waves are launched via a subsequent dispatch or draw operation. This is the way most arguments are passed from the application/runtime to a hardware shader.

PAL abstracts this functionality by exposing a set of 128 user data entries per pipeline a client can use to pass arguments from a command buffer to one or more shaders in that pipeline. The ELF code object must specify a mapping from virtualized user data entries to physical user data registers, and PAL is responsible for implementing that mapping, including spilling overflow user data entries to memory if needed.

Since the user data registers are GRBM-accessible SPI registers, this mapping is actually embedded in the .registers metadata entry. For most registers, the value in that map is a literal 32-bit value that should be written to the register by the driver. However, when the register is a user data register (any USER_DATA register e.g., SPI_SHADER_USER_DATA_PS_5), the value is instead an encoding that tells the driver to write either a user data entry value or one of several driver-internal values to the register. This encoding is described in the following table:

Note

Currently, user data registers 0 and 1 (e.g., SPI_SHADER_USER_DATA_PS_0, and SPI_SHADER_USER_DATA_PS_1) are reserved. User data register 0 must always be programmed to the address of the GlobalTable, and user data register 1 must always be programmed to the address of the PerShaderTable.

Table 95 AMDPAL User Data Mapping

Value

Name

Description

0..127

User Data Entry

32-bit value of user_data_entry[N] as specified via CmdSetUserData()

0x10000000

GlobalTable

32-bit pointer to GPU memory containing the global internal table (should always point to user data register 0).

0x10000001

PerShaderTable

32-bit pointer to GPU memory containing the per-shader internal table. See Per-Shader Table for more detail (should always point to user data register 1).

0x10000002

SpillTable

32-bit pointer to GPU memory containing the user data spill table. See Spill Table for more detail.

0x10000003

BaseVertex

Vertex offset (32-bit unsigned integer). Not needed if the pipeline doesn’t reference the draw index in the vertex shader. Only supported by the first stage in a graphics pipeline.

0x10000004

BaseInstance

Instance offset (32-bit unsigned integer). Only supported by the first stage in a graphics pipeline.

0x10000005

DrawIndex

Draw index (32-bit unsigned integer). Only supported by the first stage in a graphics pipeline.

0x10000006

Workgroup

Thread group count (32-bit unsigned integer). Low half of a 64-bit address of a buffer containing the grid dimensions for a Compute dispatch operation. The high half of the address is stored in the next sequential user-SGPR. Only supported by compute pipelines.

0x1000000A

EsGsLdsSize

Indicates that PAL will program this user-SGPR to contain the amount of LDS space used for the ES/GS pseudo-ring-buffer for passing data between shader stages.

0x1000000B

ViewId

View id (32-bit unsigned integer) identifies a view of graphic pipeline instancing.

0x1000000C

StreamOutTable

32-bit pointer to GPU memory containing the stream out target SRD table. This can only appear for one shader stage per pipeline.

0x1000000D

PerShaderPerfData

32-bit pointer to GPU memory containing the per-shader performance data buffer.

0x1000000F

VertexBufferTable

32-bit pointer to GPU memory containing the vertex buffer SRD table. This can only appear for one shader stage per pipeline.

0x10000010

UavExportTable

32-bit pointer to GPU memory containing the UAV export SRD table. This can only appear for one shader stage per pipeline (PS). These replace color targets and are completely separate from any UAVs used by the shader. This is optional, and only used by the PS when UAV exports are used to replace color-target exports to optimize specific shaders.

0x10000011

NggCullingData

64-bit pointer to GPU memory containing the hardware register data needed by some NGG pipelines to perform culling. This value contains the address of the first of two consecutive registers which provide the full GPU address.

0x10000015

FetchShaderPtr

64-bit pointer to GPU memory containing the fetch shader subroutine.
Per-Shader Table

Low 32 bits of the GPU address for an optional buffer in the .data section of the ELF. The high 32 bits of the address match the high 32 bits of the shader’s program counter.

The buffer can be anything the shader compiler needs it for, and allows each shader to have its own region of the .data section. Typically, this could be a table of buffer SRD’s and the data pointed to by the buffer SRD’s, but it could be a flat-address region of memory as well. Its layout and usage are defined by the shader compiler.

Each shader’s table in the .data section is referenced by the symbol _amdgpu_xs_shdr_intrl_data where xs corresponds with the hardware shader stage the data is for. E.g., _amdgpu_cs_shdr_intrl_data for the compute shader hardware stage.

Spill Table

It is possible for a hardware shader to need access to more user data entries than there are slots available in user data registers for one or more hardware shader stages. In that case, the PAL runtime expects the necessary user data entries to be spilled to GPU memory and use one user data register to point to the spilled user data memory. The value of the user data entry must then represent the location where a shader expects to read the low 32-bits of the table’s GPU virtual address. The spill table itself represents a set of 32-bit values managed by the PAL runtime in GPU-accessible memory that can be made indirectly accessible to a hardware shader.

Unspecified OS

This section provides code conventions used when the target triple OS is empty (see Target Triples).

Trap Handler ABI

For code objects generated by AMDGPU backend for non-amdhsa OS, the runtime does not install a trap handler. The llvm.trap and llvm.debugtrap instructions are handled as follows:

Table 96 AMDGPU Trap Handler for Non-AMDHSA OS

Usage

Code Sequence

Description

llvm.trap

s_endpgm

Causes wavefront to be terminated.

llvm.debugtrap

none

Compiler warning given that there is no trap handler installed.

Source Languages

OpenCL

When the language is OpenCL the following differences occur:

  1. The OpenCL memory model is used (see Memory Model).

  2. The AMDGPU backend appends additional arguments to the kernel’s explicit arguments for the AMDHSA OS (see OpenCL kernel implicit arguments appended for AMDHSA OS).

  3. Additional metadata is generated (see Code Object Metadata).

Table 97 OpenCL kernel implicit arguments appended for AMDHSA OS

Position

Byte Size

Byte Alignment

Description

1

8

8

OpenCL Global Offset X

2

8

8

OpenCL Global Offset Y

3

8

8

OpenCL Global Offset Z

4

8

8

OpenCL address of printf buffer

5

8

8

OpenCL address of virtual queue used by enqueue_kernel.

6

8

8

OpenCL address of AqlWrap struct used by enqueue_kernel.

7

8

8

Pointer argument used for Multi-gird synchronization.

HCC

When the language is HCC the following differences occur:

  1. The HSA memory model is used (see Memory Model).

Assembler

AMDGPU backend has LLVM-MC based assembler which is currently in development. It supports AMDGCN GFX6-GFX11.

This section describes general syntax for instructions and operands.

Instructions

An instruction has the following syntax:

<opcode> <operand0>, <operand1>,... <modifier0> <modifier1>...

Operands are comma-separated while modifiers are space-separated.

The order of operands and modifiers is fixed. Most modifiers are optional and may be omitted.

Links to detailed instruction syntax description may be found in the following table. Note that features under development are not included in this description.

Architecture

Core ISA

ISA Variants and Extensions

GCN 2

GFX7

-

GCN 3, GCN 4

GFX8

-

GCN 5

GFX9

gfx900

gfx902

gfx904

gfx906

gfx909

gfx90c

CDNA 1

GFX9

gfx908

CDNA 2

GFX9

gfx90a

CDNA 3

GFX9

gfx940

gfx941

gfx942

RDNA 1

GFX10 RDNA1

gfx1010

gfx1011

gfx1012

gfx1013

RDNA 2

GFX10 RDNA2

gfx1030

gfx1031

gfx1032

gfx1033

gfx1034

gfx1035

gfx1036

RDNA 3

GFX11

gfx1100

gfx1101

gfx1102

gfx1103

For more information about instructions, their semantics and supported combinations of operands, refer to one of instruction set architecture manuals [AMD-GCN-GFX6], [AMD-GCN-GFX7], [AMD-GCN-GFX8], [AMD-GCN-GFX900-GFX904-VEGA], [AMD-GCN-GFX906-VEGA7NM], [AMD-GCN-GFX908-CDNA1], [AMD-GCN-GFX90A-CDNA2], [AMD-GCN-GFX940-GFX942-CDNA3], [AMD-GCN-GFX10-RDNA1], [AMD-GCN-GFX10-RDNA2] and [AMD-GCN-GFX11-RDNA3].

Operands

Detailed description of operands may be found here.

Modifiers

Detailed description of modifiers may be found here.

Instruction Examples

DS
ds_add_u32 v2, v4 offset:16
ds_write_src2_b64 v2 offset0:4 offset1:8
ds_cmpst_f32 v2, v4, v6
ds_min_rtn_f64 v[8:9], v2, v[4:5]

For full list of supported instructions, refer to “LDS/GDS instructions” in ISA Manual.

FLAT
flat_load_dword v1, v[3:4]
flat_store_dwordx3 v[3:4], v[5:7]
flat_atomic_swap v1, v[3:4], v5 glc
flat_atomic_cmpswap v1, v[3:4], v[5:6] glc slc
flat_atomic_fmax_x2 v[1:2], v[3:4], v[5:6] glc

For full list of supported instructions, refer to “FLAT instructions” in ISA Manual.

MUBUF
buffer_load_dword v1, off, s[4:7], s1
buffer_store_dwordx4 v[1:4], v2, ttmp[4:7], s1 offen offset:4 glc tfe
buffer_store_format_xy v[1:2], off, s[4:7], s1
buffer_wbinvl1
buffer_atomic_inc v1, v2, s[8:11], s4 idxen offset:4 slc

For full list of supported instructions, refer to “MUBUF Instructions” in ISA Manual.

SMRD/SMEM
s_load_dword s1, s[2:3], 0xfc
s_load_dwordx8 s[8:15], s[2:3], s4
s_load_dwordx16 s[88:103], s[2:3], s4
s_dcache_inv_vol
s_memtime s[4:5]

For full list of supported instructions, refer to “Scalar Memory Operations” in ISA Manual.

SOP1
s_mov_b32 s1, s2
s_mov_b64 s[0:1], 0x80000000
s_cmov_b32 s1, 200
s_wqm_b64 s[2:3], s[4:5]
s_bcnt0_i32_b64 s1, s[2:3]
s_swappc_b64 s[2:3], s[4:5]
s_cbranch_join s[4:5]

For full list of supported instructions, refer to “SOP1 Instructions” in ISA Manual.

SOP2
s_add_u32 s1, s2, s3
s_and_b64 s[2:3], s[4:5], s[6:7]
s_cselect_b32 s1, s2, s3
s_andn2_b32 s2, s4, s6
s_lshr_b64 s[2:3], s[4:5], s6
s_ashr_i32 s2, s4, s6
s_bfm_b64 s[2:3], s4, s6
s_bfe_i64 s[2:3], s[4:5], s6
s_cbranch_g_fork s[4:5], s[6:7]

For full list of supported instructions, refer to “SOP2 Instructions” in ISA Manual.

SOPC
s_cmp_eq_i32 s1, s2
s_bitcmp1_b32 s1, s2
s_bitcmp0_b64 s[2:3], s4
s_setvskip s3, s5

For full list of supported instructions, refer to “SOPC Instructions” in ISA Manual.

SOPP
s_barrier
s_nop 2
s_endpgm
s_waitcnt 0 ; Wait for all counters to be 0
s_waitcnt vmcnt(0) & expcnt(0) & lgkmcnt(0) ; Equivalent to above
s_waitcnt vmcnt(1) ; Wait for vmcnt counter to be 1.
s_sethalt 9
s_sleep 10
s_sendmsg 0x1
s_sendmsg sendmsg(MSG_INTERRUPT)
s_trap 1

For full list of supported instructions, refer to “SOPP Instructions” in ISA Manual.

Unless otherwise mentioned, little verification is performed on the operands of SOPP Instructions, so it is up to the programmer to be familiar with the range or acceptable values.

VALU

For vector ALU instruction opcodes (VOP1, VOP2, VOP3, VOPC, VOP_DPP, VOP_SDWA), the assembler will automatically use optimal encoding based on its operands. To force specific encoding, one can add a suffix to the opcode of the instruction:

  • _e32 for 32-bit VOP1/VOP2/VOPC

  • _e64 for 64-bit VOP3

  • _dpp for VOP_DPP

  • _e64_dpp for VOP3 with DPP

  • _sdwa for VOP_SDWA

VOP1/VOP2/VOP3/VOPC examples:

v_mov_b32 v1, v2
v_mov_b32_e32 v1, v2
v_nop
v_cvt_f64_i32_e32 v[1:2], v2
v_floor_f32_e32 v1, v2
v_bfrev_b32_e32 v1, v2
v_add_f32_e32 v1, v2, v3
v_mul_i32_i24_e64 v1, v2, 3
v_mul_i32_i24_e32 v1, -3, v3
v_mul_i32_i24_e32 v1, -100, v3
v_addc_u32 v1, s[0:1], v2, v3, s[2:3]
v_max_f16_e32 v1, v2, v3

VOP_DPP examples:

v_mov_b32 v0, v0 quad_perm:[0,2,1,1]
v_sin_f32 v0, v0 row_shl:1 row_mask:0xa bank_mask:0x1 bound_ctrl:0
v_mov_b32 v0, v0 wave_shl:1
v_mov_b32 v0, v0 row_mirror
v_mov_b32 v0, v0 row_bcast:31
v_mov_b32 v0, v0 quad_perm:[1,3,0,1] row_mask:0xa bank_mask:0x1 bound_ctrl:0
v_add_f32 v0, v0, |v0| row_shl:1 row_mask:0xa bank_mask:0x1 bound_ctrl:0
v_max_f16 v1, v2, v3 row_shl:1 row_mask:0xa bank_mask:0x1 bound_ctrl:0

VOP3_DPP examples (Available on GFX11+):

v_add_f32_e64_dpp v0, v1, v2 dpp8:[0,1,2,3,4,5,6,7]
v_sqrt_f32_e64_dpp v0, v1 row_shl:1 row_mask:0xa bank_mask:0x1 bound_ctrl:0
v_ldexp_f32 v0, v1, v2 dpp8:[0,1,2,3,4,5,6,7]

VOP_SDWA examples:

v_mov_b32 v1, v2 dst_sel:BYTE_0 dst_unused:UNUSED_PRESERVE src0_sel:DWORD
v_min_u32 v200, v200, v1 dst_sel:WORD_1 dst_unused:UNUSED_PAD src0_sel:BYTE_1 src1_sel:DWORD
v_sin_f32 v0, v0 dst_unused:UNUSED_PAD src0_sel:WORD_1
v_fract_f32 v0, |v0| dst_sel:DWORD dst_unused:UNUSED_PAD src0_sel:WORD_1
v_cmpx_le_u32 vcc, v1, v2 src0_sel:BYTE_2 src1_sel:WORD_0

For full list of supported instructions, refer to “Vector ALU instructions”.

Code Object V2 Predefined Symbols

Warning

Code object V2 generation is no longer supported by this version of LLVM.

The AMDGPU assembler defines and updates some symbols automatically. These symbols do not affect code generation.

.option.machine_version_major

Set to the GFX major generation number of the target being assembled for. For example, when assembling for a “GFX9” target this will be set to the integer value “9”. The possible GFX major generation numbers are presented in Processors.

.option.machine_version_minor

Set to the GFX minor generation number of the target being assembled for. For example, when assembling for a “GFX810” target this will be set to the integer value “1”. The possible GFX minor generation numbers are presented in Processors.

.option.machine_version_stepping

Set to the GFX stepping generation number of the target being assembled for. For example, when assembling for a “GFX704” target this will be set to the integer value “4”. The possible GFX stepping generation numbers are presented in Processors.

.kernel.vgpr_count

Set to zero each time a .amdgpu_hsa_kernel (name) directive is encountered. At each instruction, if the current value of this symbol is less than or equal to the maximum VGPR number explicitly referenced within that instruction then the symbol value is updated to equal that VGPR number plus one.

.kernel.sgpr_count

Set to zero each time a .amdgpu_hsa_kernel (name) directive is encountered. At each instruction, if the current value of this symbol is less than or equal to the maximum VGPR number explicitly referenced within that instruction then the symbol value is updated to equal that SGPR number plus one.

Code Object V2 Directives

Warning

Code object V2 generation is no longer supported by this version of LLVM.

AMDGPU ABI defines auxiliary data in output code object. In assembly source, one can specify them with assembler directives.

.hsa_code_object_version major, minor

major and minor are integers that specify the version of the HSA code object that will be generated by the assembler.

.hsa_code_object_isa [major, minor, stepping, vendor, arch]

major, minor, and stepping are all integers that describe the instruction set architecture (ISA) version of the assembly program.

vendor and arch are quoted strings. vendor should always be equal to “AMD” and arch should always be equal to “AMDGPU”.

By default, the assembler will derive the ISA version, vendor, and arch from the value of the -mcpu option that is passed to the assembler.

.amdgpu_hsa_kernel (name)

This directives specifies that the symbol with given name is a kernel entry point (label) and the object should contain corresponding symbol of type STT_AMDGPU_HSA_KERNEL.

.amd_kernel_code_t

This directive marks the beginning of a list of key / value pairs that are used to specify the amd_kernel_code_t object that will be emitted by the assembler. The list must be terminated by the .end_amd_kernel_code_t directive. For any amd_kernel_code_t values that are unspecified a default value will be used. The default value for all keys is 0, with the following exceptions:

  • amd_code_version_major defaults to 1.

  • amd_kernel_code_version_minor defaults to 2.

  • amd_machine_kind defaults to 1.

  • amd_machine_version_major, machine_version_minor, and amd_machine_version_stepping are derived from the value of the -mcpu option that is passed to the assembler.

  • kernel_code_entry_byte_offset defaults to 256.

  • wavefront_size defaults 6 for all targets before GFX10. For GFX10 onwards defaults to 6 if target feature wavefrontsize64 is enabled, otherwise 5. Note that wavefront size is specified as a power of two, so a value of n means a size of 2^ n.

  • call_convention defaults to -1.

  • kernarg_segment_alignment, group_segment_alignment, and private_segment_alignment default to 4. Note that alignments are specified as a power of 2, so a value of n means an alignment of 2^ n.

  • enable_tg_split defaults to 1 if target feature tgsplit is enabled for GFX90A onwards.

  • enable_wgp_mode defaults to 1 if target feature cumode is disabled for GFX10 onwards.

  • enable_mem_ordered defaults to 1 for GFX10 onwards.

The .amd_kernel_code_t directive must be placed immediately after the function label and before any instructions.

For a full list of amd_kernel_code_t keys, refer to AMDGPU ABI document, comments in lib/Target/AMDGPU/AmdKernelCodeT.h and test/CodeGen/AMDGPU/hsa.s.

Code Object V2 Example Source Code

Warning

Code object V2 generation is no longer supported by this version of LLVM.

Here is an example of a minimal assembly source file, defining one HSA kernel:

 1.hsa_code_object_version 1,0
 2.hsa_code_object_isa
 3
 4.hsatext
 5.globl  hello_world
 6.p2align 8
 7.amdgpu_hsa_kernel hello_world
 8
 9hello_world:
10
11   .amd_kernel_code_t
12      enable_sgpr_kernarg_segment_ptr = 1
13      is_ptr64 = 1
14      compute_pgm_rsrc1_vgprs = 0
15      compute_pgm_rsrc1_sgprs = 0
16      compute_pgm_rsrc2_user_sgpr = 2
17      compute_pgm_rsrc1_wgp_mode = 0
18      compute_pgm_rsrc1_mem_ordered = 0
19      compute_pgm_rsrc1_fwd_progress = 1
20  .end_amd_kernel_code_t
21
22  s_load_dwordx2 s[0:1], s[0:1] 0x0
23  v_mov_b32 v0, 3.14159
24  s_waitcnt lgkmcnt(0)
25  v_mov_b32 v1, s0
26  v_mov_b32 v2, s1
27  flat_store_dword v[1:2], v0
28  s_endpgm
29.Lfunc_end0:
30     .size   hello_world, .Lfunc_end0-hello_world

Code Object V3 and Above Predefined Symbols

The AMDGPU assembler defines and updates some symbols automatically. These symbols do not affect code generation.

.amdgcn.gfx_generation_number

Set to the GFX major generation number of the target being assembled for. For example, when assembling for a “GFX9” target this will be set to the integer value “9”. The possible GFX major generation numbers are presented in Processors.

.amdgcn.gfx_generation_minor

Set to the GFX minor generation number of the target being assembled for. For example, when assembling for a “GFX810” target this will be set to the integer value “1”. The possible GFX minor generation numbers are presented in Processors.

.amdgcn.gfx_generation_stepping

Set to the GFX stepping generation number of the target being assembled for. For example, when assembling for a “GFX704” target this will be set to the integer value “4”. The possible GFX stepping generation numbers are presented in Processors.

.amdgcn.next_free_vgpr

Set to zero before assembly begins. At each instruction, if the current value of this symbol is less than or equal to the maximum VGPR number explicitly referenced within that instruction then the symbol value is updated to equal that VGPR number plus one.

May be used to set the .amdhsa_next_free_vgpr directive in AMDHSA Kernel Assembler Directives.

May be set at any time, e.g. manually set to zero at the start of each kernel.

.amdgcn.next_free_sgpr

Set to zero before assembly begins. At each instruction, if the current value of this symbol is less than or equal the maximum SGPR number explicitly referenced within that instruction then the symbol value is updated to equal that SGPR number plus one.

May be used to set the .amdhsa_next_free_spgr directive in AMDHSA Kernel Assembler Directives.

May be set at any time, e.g. manually set to zero at the start of each kernel.

Code Object V3 and Above Directives

Directives which begin with .amdgcn are valid for all amdgcn architecture processors, and are not OS-specific. Directives which begin with .amdhsa are specific to amdgcn architecture processors when the amdhsa OS is specified. See Target Triples and Processors.

.amdgcn_target <target-triple> “-” <target-id>

Optional directive which declares the <target-triple>-<target-id> supported by the containing assembler source file. Used by the assembler to validate command-line options such as -triple, -mcpu, and --offload-arch=<target-id>. A non-canonical target ID is allowed. See Target Triples and Target ID.

Note

The target ID syntax used for code object V2 to V3 for this directive differs from that used elsewhere. See Code Object V2 to V3 Target ID.

.amdhsa_code_object_version <version>

Optional directive which declares the code object version to be generated by the assembler. If not present, a default value will be used.

.amdhsa_kernel <name>

Creates a correctly aligned AMDHSA kernel descriptor and a symbol, <name>.kd, in the current location of the current section. Only valid when the OS is amdhsa. <name> must be a symbol that labels the first instruction to execute, and does not need to be previously defined.

Marks the beginning of a list of directives used to generate the bytes of a kernel descriptor, as described in Kernel Descriptor. Directives which may appear in this list are described in AMDHSA Kernel Assembler Directives. Directives may appear in any order, must be valid for the target being assembled for, and cannot be repeated. Directives support the range of values specified by the field they reference in Kernel Descriptor. If a directive is not specified, it is assumed to have its default value, unless it is marked as “Required”, in which case it is an error to omit the directive. This list of directives is terminated by an .end_amdhsa_kernel directive.

Table 98 AMDHSA Kernel Assembler Directives

Directive

Default

Supported On

Description

.amdhsa_group_segment_fixed_size

0

GFX6-GFX12

Controls GROUP_SEGMENT_FIXED_SIZE in Code Object V3 Kernel Descriptor.

.amdhsa_private_segment_fixed_size

0

GFX6-GFX12

Controls PRIVATE_SEGMENT_FIXED_SIZE in Code Object V3 Kernel Descriptor.

.amdhsa_kernarg_size

0

GFX6-GFX12

Controls KERNARG_SIZE in Code Object V3 Kernel Descriptor.

.amdhsa_user_sgpr_count

0

GFX6-GFX12

Controls USER_SGPR_COUNT in COMPUTE_PGM_RSRC2 compute_pgm_rsrc2 for GFX6-GFX12

.amdhsa_user_sgpr_private_segment_buffer

0

GFX6-GFX10 (except GFX940)

Controls ENABLE_SGPR_PRIVATE_SEGMENT_BUFFER in Code Object V3 Kernel Descriptor.

.amdhsa_user_sgpr_dispatch_ptr

0

GFX6-GFX12

Controls ENABLE_SGPR_DISPATCH_PTR in Code Object V3 Kernel Descriptor.

.amdhsa_user_sgpr_queue_ptr

0

GFX6-GFX12

Controls ENABLE_SGPR_QUEUE_PTR in Code Object V3 Kernel Descriptor.

.amdhsa_user_sgpr_kernarg_segment_ptr

0

GFX6-GFX12

Controls ENABLE_SGPR_KERNARG_SEGMENT_PTR in Code Object V3 Kernel Descriptor.

.amdhsa_user_sgpr_dispatch_id

0

GFX6-GFX12

Controls ENABLE_SGPR_DISPATCH_ID in Code Object V3 Kernel Descriptor.

.amdhsa_user_sgpr_flat_scratch_init

0

GFX6-GFX10 (except GFX940)

Controls ENABLE_SGPR_FLAT_SCRATCH_INIT in Code Object V3 Kernel Descriptor.

.amdhsa_user_sgpr_private_segment_size

0

GFX6-GFX12

Controls ENABLE_SGPR_PRIVATE_SEGMENT_SIZE in Code Object V3 Kernel Descriptor.

.amdhsa_wavefront_size32

Target Feature Specific (wavefrontsize64)

GFX10-GFX12

Controls ENABLE_WAVEFRONT_SIZE32 in Code Object V3 Kernel Descriptor.

.amdhsa_uses_dynamic_stack

0

GFX6-GFX12

Controls USES_DYNAMIC_STACK in Code Object V3 Kernel Descriptor.

.amdhsa_system_sgpr_private_segment_wavefront_offset

0

GFX6-GFX10 (except GFX940)

Controls ENABLE_PRIVATE_SEGMENT in compute_pgm_rsrc2 for GFX6-GFX12.

.amdhsa_enable_private_segment

0

GFX940, GFX11-GFX12

Controls ENABLE_PRIVATE_SEGMENT in compute_pgm_rsrc2 for GFX6-GFX12.

.amdhsa_system_sgpr_workgroup_id_x

1

GFX6-GFX12

Controls ENABLE_SGPR_WORKGROUP_ID_X in compute_pgm_rsrc2 for GFX6-GFX12.

.amdhsa_system_sgpr_workgroup_id_y

0

GFX6-GFX12

Controls ENABLE_SGPR_WORKGROUP_ID_Y in compute_pgm_rsrc2 for GFX6-GFX12.

.amdhsa_system_sgpr_workgroup_id_z

0

GFX6-GFX12

Controls ENABLE_SGPR_WORKGROUP_ID_Z in compute_pgm_rsrc2 for GFX6-GFX12.

.amdhsa_system_sgpr_workgroup_info

0

GFX6-GFX12

Controls ENABLE_SGPR_WORKGROUP_INFO in compute_pgm_rsrc2 for GFX6-GFX12.

.amdhsa_system_vgpr_workitem_id

0

GFX6-GFX12

Controls ENABLE_VGPR_WORKITEM_ID in compute_pgm_rsrc2 for GFX6-GFX12. Possible values are defined in System VGPR Work-Item ID Enumeration Values.

.amdhsa_next_free_vgpr

Required

GFX6-GFX12

Maximum VGPR number explicitly referenced, plus one. Used to calculate GRANULATED_WORKITEM_VGPR_COUNT in compute_pgm_rsrc1 for GFX6-GFX12.

.amdhsa_next_free_sgpr

Required

GFX6-GFX12

Maximum SGPR number explicitly referenced, plus one. Used to calculate GRANULATED_WAVEFRONT_SGPR_COUNT in compute_pgm_rsrc1 for GFX6-GFX12.

.amdhsa_accum_offset

Required

GFX90A, GFX940

Offset of a first AccVGPR in the unified register file. Used to calculate ACCUM_OFFSET in compute_pgm_rsrc3 for GFX90A, GFX940.

.amdhsa_reserve_vcc

1

GFX6-GFX12

Whether the kernel may use the special VCC SGPR. Used to calculate GRANULATED_WAVEFRONT_SGPR_COUNT in compute_pgm_rsrc1 for GFX6-GFX12.

.amdhsa_reserve_flat_scratch

1

GFX7-GFX10 (except GFX940)

Whether the kernel may use flat instructions to access scratch memory. Used to calculate GRANULATED_WAVEFRONT_SGPR_COUNT in compute_pgm_rsrc1 for GFX6-GFX12.

.amdhsa_reserve_xnack_mask

Target Feature Specific (xnack)

GFX8-GFX10

Whether the kernel may trigger XNACK replay. Used to calculate GRANULATED_WAVEFRONT_SGPR_COUNT in compute_pgm_rsrc1 for GFX6-GFX12.

.amdhsa_float_round_mode_32

0

GFX6-GFX12

Controls FLOAT_ROUND_MODE_32 in compute_pgm_rsrc1 for GFX6-GFX12. Possible values are defined in Floating Point Rounding Mode Enumeration Values.

.amdhsa_float_round_mode_16_64

0

GFX6-GFX12

Controls FLOAT_ROUND_MODE_16_64 in compute_pgm_rsrc1 for GFX6-GFX12. Possible values are defined in Floating Point Rounding Mode Enumeration Values.

.amdhsa_float_denorm_mode_32

0

GFX6-GFX12

Controls FLOAT_DENORM_MODE_32 in compute_pgm_rsrc1 for GFX6-GFX12. Possible values are defined in Floating Point Denorm Mode Enumeration Values.

.amdhsa_float_denorm_mode_16_64

3

GFX6-GFX12

Controls FLOAT_DENORM_MODE_16_64 in compute_pgm_rsrc1 for GFX6-GFX12. Possible values are defined in Floating Point Denorm Mode Enumeration Values.

.amdhsa_dx10_clamp

1

GFX6-GFX11

Controls ENABLE_DX10_CLAMP in compute_pgm_rsrc1 for GFX6-GFX12.

.amdhsa_ieee_mode

1

GFX6-GFX11

Controls ENABLE_IEEE_MODE in compute_pgm_rsrc1 for GFX6-GFX12.

.amdhsa_round_robin_scheduling

0

GFX12

Controls ENABLE_WG_RR_EN in compute_pgm_rsrc1 for GFX6-GFX12.

.amdhsa_fp16_overflow

0

GFX9-GFX12

Controls FP16_OVFL in compute_pgm_rsrc1 for GFX6-GFX12.

.amdhsa_tg_split

Target Feature Specific (tgsplit)

GFX90A, GFX940, GFX11-GFX12

Controls TG_SPLIT in compute_pgm_rsrc3 for GFX90A, GFX940.

.amdhsa_workgroup_processor_mode

Target Feature Specific (cumode)

GFX10-GFX12

Controls ENABLE_WGP_MODE in Code Object V3 Kernel Descriptor.

.amdhsa_memory_ordered

1

GFX10-GFX12

Controls MEM_ORDERED in compute_pgm_rsrc1 for GFX6-GFX12.

.amdhsa_forward_progress

0

GFX10-GFX12

Controls FWD_PROGRESS in compute_pgm_rsrc1 for GFX6-GFX12.

.amdhsa_shared_vgpr_count

0

GFX10-GFX11

Controls SHARED_VGPR_COUNT in compute_pgm_rsrc3 for GFX10-GFX11.

.amdhsa_exception_fp_ieee_invalid_op

0

GFX6-GFX12

Controls ENABLE_EXCEPTION_IEEE_754_FP_INVALID_OPERATION in compute_pgm_rsrc2 for GFX6-GFX12.

.amdhsa_exception_fp_denorm_src

0

GFX6-GFX12

Controls ENABLE_EXCEPTION_FP_DENORMAL_SOURCE in compute_pgm_rsrc2 for GFX6-GFX12.

.amdhsa_exception_fp_ieee_div_zero

0

GFX6-GFX12

Controls ENABLE_EXCEPTION_IEEE_754_FP_DIVISION_BY_ZERO in compute_pgm_rsrc2 for GFX6-GFX12.

.amdhsa_exception_fp_ieee_overflow

0

GFX6-GFX12

Controls ENABLE_EXCEPTION_IEEE_754_FP_OVERFLOW in compute_pgm_rsrc2 for GFX6-GFX12.

.amdhsa_exception_fp_ieee_underflow

0

GFX6-GFX12

Controls ENABLE_EXCEPTION_IEEE_754_FP_UNDERFLOW in compute_pgm_rsrc2 for GFX6-GFX12.

.amdhsa_exception_fp_ieee_inexact

0

GFX6-GFX12

Controls ENABLE_EXCEPTION_IEEE_754_FP_INEXACT in compute_pgm_rsrc2 for GFX6-GFX12.

.amdhsa_exception_int_div_zero

0

GFX6-GFX12

Controls ENABLE_EXCEPTION_INT_DIVIDE_BY_ZERO in compute_pgm_rsrc2 for GFX6-GFX12.

.amdhsa_user_sgpr_kernarg_preload_length

0

GFX90A, GFX940

Controls KERNARG_PRELOAD_SPEC_LENGTH in Code Object V3 Kernel Descriptor.

.amdhsa_user_sgpr_kernarg_preload_offset

0

GFX90A, GFX940

Controls KERNARG_PRELOAD_SPEC_OFFSET in Code Object V3 Kernel Descriptor.
.amdgpu_metadata

Optional directive which declares the contents of the NT_AMDGPU_METADATA note record (see AMDGPU Code Object V3 and Above ELF Note Records).

The contents must be in the [YAML] markup format, with the same structure and semantics described in Code Object V3 Metadata, Code Object V4 Metadata or Code Object V5 Metadata.

This directive is terminated by an .end_amdgpu_metadata directive.

Code Object V3 and Above Example Source Code

Here is an example of a minimal assembly source file, defining one HSA kernel:

 1.amdgcn_target "amdgcn-amd-amdhsa--gfx900+xnack" // optional
 2
 3.text
 4.globl hello_world
 5.p2align 8
 6.type hello_world,@function
 7hello_world:
 8  s_load_dwordx2 s[0:1], s[0:1] 0x0
 9  v_mov_b32 v0, 3.14159
10  s_waitcnt lgkmcnt(0)
11  v_mov_b32 v1, s0
12  v_mov_b32 v2, s1
13  flat_store_dword v[1:2], v0
14  s_endpgm
15.Lfunc_end0:
16  .size   hello_world, .Lfunc_end0-hello_world
17
18.rodata
19.p2align 6
20.amdhsa_kernel hello_world
21  .amdhsa_user_sgpr_kernarg_segment_ptr 1
22  .amdhsa_next_free_vgpr .amdgcn.next_free_vgpr
23  .amdhsa_next_free_sgpr .amdgcn.next_free_sgpr
24.end_amdhsa_kernel
25
26.amdgpu_metadata
27---
28amdhsa.version:
29  - 1
30  - 0
31amdhsa.kernels:
32  - .name: hello_world
33    .symbol: hello_world.kd
34    .kernarg_segment_size: 48
35    .group_segment_fixed_size: 0
36    .private_segment_fixed_size: 0
37    .kernarg_segment_align: 4
38    .wavefront_size: 64
39    .sgpr_count: 2
40    .vgpr_count: 3
41    .max_flat_workgroup_size: 256
42    .args:
43      - .size: 8
44        .offset: 0
45        .value_kind: global_buffer
46        .address_space: global
47        .actual_access: write_only
48//...
49.end_amdgpu_metadata

This kernel is equivalent to the following HIP program:

1__global__ void hello_world(float *p) {
2    *p = 3.14159f;
3}

If an assembly source file contains multiple kernels and/or functions, the .amdgcn.next_free_vgpr and .amdgcn.next_free_sgpr symbols may be reset using the .set <symbol>, <expression> directive. For example, in the case of two kernels, where function1 is only called from kernel1 it is sufficient to group the function with the kernel that calls it and reset the symbols between the two connected components:

 1.amdgcn_target "amdgcn-amd-amdhsa--gfx900+xnack" // optional
 2
 3// gpr tracking symbols are implicitly set to zero
 4
 5.text
 6.globl kern0
 7.p2align 8
 8.type kern0,@function
 9kern0:
10  // ...
11  s_endpgm
12.Lkern0_end:
13  .size   kern0, .Lkern0_end-kern0
14
15.rodata
16.p2align 6
17.amdhsa_kernel kern0
18  // ...
19  .amdhsa_next_free_vgpr .amdgcn.next_free_vgpr
20  .amdhsa_next_free_sgpr .amdgcn.next_free_sgpr
21.end_amdhsa_kernel
22
23// reset symbols to begin tracking usage in func1 and kern1
24.set .amdgcn.next_free_vgpr, 0
25.set .amdgcn.next_free_sgpr, 0
26
27.text
28.hidden func1
29.global func1
30.p2align 2
31.type func1,@function
32func1:
33  // ...
34  s_setpc_b64 s[30:31]
35.Lfunc1_end:
36.size func1, .Lfunc1_end-func1
37
38.globl kern1
39.p2align 8
40.type kern1,@function
41kern1:
42  // ...
43  s_getpc_b64 s[4:5]
44  s_add_u32 s4, s4, func1@rel32@lo+4
45  s_addc_u32 s5, s5, func1@rel32@lo+4
46  s_swappc_b64 s[30:31], s[4:5]
47  // ...
48  s_endpgm
49.Lkern1_end:
50  .size   kern1, .Lkern1_end-kern1
51
52.rodata
53.p2align 6
54.amdhsa_kernel kern1
55  // ...
56  .amdhsa_next_free_vgpr .amdgcn.next_free_vgpr
57  .amdhsa_next_free_sgpr .amdgcn.next_free_sgpr
58.end_amdhsa_kernel

These symbols cannot identify connected components in order to automatically track the usage for each kernel. However, in some cases careful organization of the kernels and functions in the source file means there is minimal additional effort required to accurately calculate GPR usage.

Additional Documentation

[AMD-GCN-GFX7] (1,2)

AMD Sea Islands Series ISA

[AMD-GCN-GFX900-GFX904-VEGA] (1,2)

AMD Vega Instruction Set Architecture

[AMD-GCN-GFX906-VEGA7NM] (1,2)

AMD Vega 7nm Instruction Set Architecture

[AMD-GCN-GFX940-GFX942-CDNA3] (1,2)

AMD Instinct MI300 Instruction Set Architecture

[AMD-GCN-GFX10-RDNA2] (1,2)

AMD RDNA 2 Instruction Set Architecture

[AMD-GCN-GFX11-RDNA3] (1,2)

AMD RDNA 3 Instruction Set Architecture

[AMD-ROCm-github] (1,2)

AMD ROCm™ github

[CLANG-ATTR] (1,2,3,4,5)

Attributes in Clang

[MsgPack] (1,2,3,4)

Message Pack

[SEMVER] (1,2,3)

Semantic Versioning