AMDGPU Instruction Syntax¶
Instructions¶
Syntax¶
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.
Opcode Mnemonic¶
Opcode mnemonic describes opcode semantics and may include one or more suffices in this order:
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 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+
Warning
There are exceptions from rules described above. Operands which have type different from 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 will automatically use optimal encoding based on instruction operands. 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
These suffices are used in this reference to indicate the assumed encoding. When no suffix is specified, native instruction encoding is implied.