ds_dec_rtn_u32 GPU Native ISA AMD Vector

LDS / Data Share

ds_dec_rtn_u32

Decrement an unsigned 32-bit integer value from a location in a data share with wraparound to a value in the data register if the decrement yields a…

Encoding

Binary Layout (AMD CDNA 5)
VDST
63:56
DATA1
55:48
DATA0
47:40
ADDR
39:32
110110
31:26
00100100
25:18
unassigned
17:16
OFFSET1
15:8
OFFSET0
7:0
 

The ENC_VDS layout from AMD's machine-readable ISA specification (AMD CDNA 5). Opcode 36 in OP rebuilds 0x00000000D8900000, an identifier AMD lists for this encoding. Bits marked unassigned have no field in the specification. Not the same in every generation: AMD CDNA 4 (encoding ENC_DS, field layout), AMD CDNA 3 (encoding ENC_DS, field layout), AMD CDNA 2 (encoding ENC_DS, field layout), AMD CDNA 1 (encoding ENC_DS, field layout), AMD RDNA 3.5 (encoding ENC_DS, field layout), AMD RDNA 3 (encoding ENC_DS, field layout), AMD RDNA 2 (encoding ENC_DS, field layout), AMD RDNA 1 (encoding ENC_DS, field layout). The same in AMD RDNA 4.

Format DS
Width 64 bits
Opcode 36
Identifier 0x00000000D8900000

Operands

  • VDST
    Written. Operand must be a vector GPR. Uses an 8-bit operand field. Data format: Unsigned 32-bit integral data. (OPR_VGPR, FMT_NUM_U32)
  • ADDR
    Read. Operand must be a vector GPR. Uses an 8-bit operand field. Data format: 32 bits of arbitrary data. (OPR_VGPR, FMT_NUM_B32)
  • DATA0
    Read. Operand must be a vector GPR. Uses an 8-bit operand field. Data format: Unsigned 32-bit integral data. (OPR_VGPR, FMT_NUM_U32)

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

GFX Target Compatibility

TargetSupport
gfx1100✅ Supported

Related

More in LDS / Data Share

Reference

AMDGPU / GFX ISA

Description

Decrement an unsigned 32-bit integer value from a location in a data share with wraparound to a value in the data register if the decrement yields a negative value. Store the original value from data share into a vector register.

Semantics

addr = CalcDsAddr(ADDR.b32, OFFSET0.b32, OFFSET1.b32); tmp = MEM[addr].u32; src = DATA.u32; MEM[addr].u32 = ((tmp == 0U) || (tmp > src)) ? src : tmp - 1U; RETURN_DATA.u32 = tmp

Example

ds_dec_rtn_u32 v5, v1, v2

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