v_lshl_add_u64 GPU Native ISA AMD Vector

Vector Arithmetic

v_lshl_add_u64

Given a shift count in the second input, calculate the logical shift left of the first input, then add the third input to the intermediate result…

Encoding

Binary Layout (AMD CDNA 5)
NEG
63:61
OMOD
60:59
SRC2
58:50
SRC1
49:41
SRC0
40:32
110101
31:26
1001010010
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 594 in OP rebuilds 0x00000000D6520000, an identifier AMD lists for this encoding. Not the same in every generation: AMD CDNA 4 (opcode 520, field layout), AMD CDNA 3 (opcode 520, field layout).

Format VOP3
Width 64 bits
Opcode 594
Identifier 0x00000000D6520000

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 64-bit integral data. (OPR_SRC, FMT_NUM_U64)
  • SRC1
    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)
  • SRC2
    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

Per-target GFX compatibility has not yet been verified for this instruction.

The design treats unsupported shift counts as a shift of zero.

Related

More in Vector Arithmetic

Reference

AMDGPU / GFX ISA

Description

Given a shift count in the second input, calculate the logical shift left of the first input, then add the third input to the intermediate result, then store the final result into a vector register. For this opcode the shift count must be between 0 and 4, higher shift counts are unsupported.

Semantics

D0.u64 = (S0.u64 << S1.u32[2 : 0].u32) + S2.u64

Example

v_lshl_add_u64 v[2:3], v[4:5], 0, 1

A real instruction accepted by the LLVM assembler, taken verbatim from LLVM's own AMDGPU MC test suite (gfx1250_asm_vop3-fake16.s). Not from an AMD document, and not authored here.

Sources