v_cmp_gt_u64 GPU Native ISA AMD Vector

Comparison

v_cmp_gt_u64

Set the per-lane condition code to 1 iff the first input is greater than the second input. Store the result into VCC or a scalar register.

Encoding

Binary Layout (AMD CDNA 5)
0111110
31:25
01011100
24:17
VSRC1
16:9
SRC0
8:0
 

The ENC_VOPC layout from AMD's machine-readable ISA specification (AMD CDNA 5). Opcode 92 in OP rebuilds 0x7CB80000, an identifier AMD lists for this encoding. Not the same in every generation: AMD CDNA 4 (opcode 236), AMD CDNA 3 (opcode 236), AMD CDNA 2 (opcode 236), AMD CDNA 1 (opcode 236), AMD RDNA 2 (opcode 228), AMD RDNA 1 (opcode 228). The same in AMD RDNA 4, AMD RDNA 3.5, AMD RDNA 3.

Format VOPC
Width 32 bits
Opcode 92
Identifier 0x7CB80000

Operands

  • vcc
    Written. Written in the assembly; this encoding has no field for it. 64-bit vector condition code. Data format: 64-bit mask value, read or written to a consecutive run of GPRs. The first GPR contains the least significant dword of the data. This format is generally used for lane masks and may be truncated to 32 bits when running in wave32 mode. Scalar operands with the M64 format do not have an alignment restriction when running in wave32 mode. (OPR_VCC, FMT_NUM_M64)
  • SRC0
    Read. All operands. Covers all operands that are allowed as scalar or vector sources. Data format: Unsigned 64-bit integral data. (OPR_SRC, FMT_NUM_U64)
  • VSRC1
    Read. Operand must be a vector GPR. Uses an 8-bit operand field. Data format: Unsigned 64-bit integral data. (OPR_VGPR, FMT_NUM_U64)

In AMD's order, as its machine-readable ISA specification lists them for the ENC_VOPC encoding (AMD CDNA 5).

GFX Target Compatibility

TargetSupport
gfx1100✅ Supported

Related

More in Comparison

Reference

AMDGPU / GFX ISA

Semantics

D0.u64[laneId] = S0.u64 > S1.u64; // D0 = VCC in VOPC encoding.

Example

v_cmp_gt_u64 vcc, -1, v[2:3]

A real instruction accepted by the LLVM assembler, taken verbatim from LLVM's own AMDGPU MC test suite. Not from an AMD document, and not authored here.

Sources