flat_atomic_dec GPU Native ISA AMD Vector

Flat Memory

flat_atomic_dec

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

Also written as flat_atomic_dec_u32. AMD's machine-readable ISA specification lists this name for the same instruction.

Encoding

Verified bit-level encoding data is not yet available for this instruction. The instruction-format classification below (FLAT) is well-documented and stable; exact per-target opcode/field bit positions have not yet been imported from a verified source.
Format FLAT

Operands

  • VDST
    Written. N/A Data format: Value can be anything. (OPR_VGPR_OR_ACCVGPR, FMT_ANY)
  • ADDR
    Read. N/A Data format: Value can be anything. (OPR_VGPR, FMT_ANY)
  • DATA
    Read. N/A Data format: Value can be anything. (OPR_VGPR_OR_ACCVGPR, FMT_ANY)

In AMD's order, as its machine-readable ISA specification lists them for the ENC_FLAT encoding (AMD CDNA 4).

GFX Target Compatibility

TargetSupport
gfx1100✅ Supported

Related

More in Flat Memory

Reference

AMDGPU / GFX ISA

Description

Decrement an unsigned 32-bit integer value from a location in the flat aperture with wraparound to a value in the data register if the decrement yields a negative value. Store the original value from flat aperture into a vector register iff the SC0 bit is set.

Semantics

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

Example

flat_atomic_dec v[1:2], 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