An instruction has the following syntax:
<opcode mnemonic> <operand0>, <operand1>,... <modifier0> <modifier1>...
:doc:`Operands<AMDGPUOperandSyntax>` are normally comma-separated, while :doc:`modifiers<AMDGPUModifierSyntax>` are space-separated.
The order of operands and modifiers is fixed. Most modifiers are optional and may be omitted.
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 describes opcode semantics and may include one or more suffices in this order:
- :ref:`Packing suffix<amdgpu_syn_instruction_pk>`.
- :ref:`Destination operand type suffix<amdgpu_syn_instruction_type>`.
- :ref:`Source operand type suffix<amdgpu_syn_instruction_type>`.
- :ref:`Encoding suffix<amdgpu_syn_instruction_enc>`.
Most instructions which operate on packed data have a _pk suffix. Unless otherwise :ref:`noted<amdgpu_syn_instruction_operand_tags>`, these instructions operate on and produce packed data composed of two values. The type of values is indicated by :ref:`type suffices<amdgpu_syn_instruction_type>`.
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
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 :ref:`tagged<amdgpu_syn_instruction_operand_tags>` 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
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.
The syntax of generic operands is described :doc:`in this document<AMDGPUOperandSyntax>`.
For detailed information about operands, follow operand links in GPU-specific documents.
The syntax of modifiers is described :doc:`in this document<AMDGPUModifierSyntax>`.
Information about modifiers supported for individual instructions may be found in GPU-specific documents.