v_lshrrev_b64 GPU Native ISA AMD Vector

Vector Arithmetic

v_lshrrev_b64

Given a shift count in the first vector input, calculate the logical shift right of the second vector input and store the result into a vector…

Encoding

Binary Layout (AMD CDNA 5)
NEG
63:61
OMOD
60:59
SRC2
58:50
SRC1
49:41
SRC0
40:32
110101
31:26
1100111101
25:16
CLAMP
15
OPSEL
14:11
ABS
10:8
VDST
7:0
 

The ENC_VOP3 layout from AMD's machine-readable ISA specification (AMD CDNA 5). Opcode 829 in OP rebuilds 0x00000000D73D0000, an identifier AMD lists for this encoding. Not the same in every generation: AMD CDNA 4 (opcode 656, field layout), AMD CDNA 3 (opcode 656, field layout), AMD CDNA 2 (opcode 656, field layout), AMD CDNA 1 (opcode 656, field layout), AMD RDNA 3.5 (field layout), AMD RDNA 3 (field layout), AMD RDNA 2 (opcode 768, field layout), AMD RDNA 1 (opcode 768, field layout). The same in AMD RDNA 4.

Format VOP3
Width 64 bits
Opcode 829
Identifier 0x00000000D73D0000

Operands

  • VDST
    Written. Operand must be a vector GPR. Uses an 8-bit operand field. Data format: Unsigned 64-bit integral data. (OPR_VGPR, FMT_NUM_U64)
  • SRC0
    Read. All operands. Covers all operands that are allowed as scalar or vector sources. Data format: Unsigned 32-bit integral data. (OPR_SRC, FMT_NUM_U32)
  • SRC1
    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)

In AMD's order, as its machine-readable ISA specification lists them for the ENC_VOP3 encoding (AMD CDNA 5).

GFX Target Compatibility

TargetSupport
gfx1100✅ Supported

Related

More in Vector Arithmetic

Reference

AMDGPU / GFX ISA

Description

Given a shift count in the first vector input, calculate the logical shift right of the second vector input and store the result into a vector register.

Semantics

D0.u64 = (S1.u64 >> S0[5 : 0].u32)

Example

v_lshrrev_b64 v[5:6], -1, -1

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