AMDGPU Instruction Syntax

Instructions

Syntax

Syntax of Regular Instructions

An instruction has the following syntax:

<opcode mnemonic>    <operand0>, <operand1>,...    <modifier0> <modifier1>...

Operands are normally comma-separated, while modifiers are space-separated.

The order of operands and modifiers is fixed. Most modifiers are optional and may be omitted.

Syntax of VOPD Instructions

VOPDX and VOPDY instructions must be concatenated with the :: operator to form a single VOPD instruction:

<VOPDX instruction>  ::  <VOPDY instruction>

An example:

v_dual_add_f32 v255, v255, v2 :: v_dual_fmaak_f32 v6, v2, v3, 1.0

Note that VOPDX and VOPDY instructions cannot be used as separate opcodes.

Opcode Mnemonic

Opcode mnemonic describes opcode semantics and may include one or more suffices in this order:

• Packing suffix.

• Destination operand type suffix.

• Source operand type suffix.

• Encoding suffix.

Packing Suffix

Most instructions which operate on packed data have a _pk suffix. Unless otherwise noted, these instructions operate on and produce packed data composed of two values. The type of values is indicated by type suffices.

For example, the following instruction sums up two pairs of f16 values and produces a pair of f16 values:

v_pk_add_f16 v1, v2, v3     // Each operand has f16x2 type

Type and Size Suffices

Instructions which operate with data have an implied type of data operands. This data type is specified as a suffix of instruction mnemonic.

There are instructions which have 2 type suffices: the first is the data type of the destination operand, the second is the data type of source data operand(s).

Note that data type specified by an instruction does not apply to other kinds of operands such as addresses, offsets and so on.

The following table enumerates the most frequently used type suffices.

Type Suffices	Packed instruction?	Data Type
_b512, _b256, _b128, _b64, _b32, _b16, _b8	No	Bits.
_u64, _u32, _u16, _u8	No	Unsigned integer.
_i64, _i32, _i16, _i8	No	Signed integer.
_f64, _f32, _f16	No	Floating-point.
_b16, _u16, _i16, _f16	Yes	Packed (b16x2, u16x2, etc).

Instructions which have no type suffices are assumed to operate with typeless data. The size of typeless data is specified by size suffices:

Size Suffix	Implied data type	Required register size in dwords
-	b32	1
x2	b64	2
x3	b96	3
x4	b128	4
x8	b256	8
x16	b512	16
x	b32	1
xy	b64	2
xyz	b96	3
xyzw	b128	4
d16_x	b16	1
d16_xy	b16x2	2 for GFX8.0, 1 for GFX8.1 and GFX9+
d16_xyz	b16x3	3 for GFX8.0, 2 for GFX8.1 and GFX9+
d16_xyzw	b16x4	4 for GFX8.0, 2 for GFX8.1 and GFX9+
d16_format_x	b16	1
d16_format_xy	b16x2	1
d16_format_xyz	b16x3	2
d16_format_xyzw	b16x4	2

Warning

There are exceptions to the rules described above. Operands which have a type different from the type specified by the opcode are tagged in the description.

Examples of instructions with different types of source and destination operands:

s_bcnt0_i32_b64
v_cvt_f32_u32

Examples of instructions with one data type:

v_max3_f32
v_max3_i16

Examples of instructions which operate with packed data:

v_pk_add_u16
v_pk_add_i16
v_pk_add_f16

Examples of typeless instructions which operate on b128 data:

buffer_store_dwordx4
flat_load_dwordx4

Encoding Suffices

Most VOP1, VOP2 and VOPC instructions have several variants: they may also be encoded in VOP3, DPP and SDWA formats.

The assembler selects an optimal encoding automatically based on instruction operands and modifiers, unless a specific encoding is explicitly requested. To force specific encoding, one can add a suffix to the opcode of the instruction:

Encoding	Encoding Suffix
VOP1, VOP2 and VOPC (32-bit) encoding	_e32
VOP3 (64-bit) encoding	_e64
DPP encoding	_dpp
SDWA encoding	_sdwa
VOP3 DPP encoding	_e64_dpp

This reference uses encoding suffices to specify which encoding is implied. When no suffix is specified, native instruction encoding is assumed.

Operands

Syntax

The syntax of generic operands is described in this document.

For detailed information about operands, follow operand links in GPU-specific documents.

Modifiers

Syntax

The syntax of modifiers is described in this document.

Information about modifiers supported for individual instructions may be found in GPU-specific documents.