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[AMDGPU] Fold into uses of splat REG_SEQUENCEs through COPYs. #145691

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[AMDGPU] Fold into uses of splat REG_SEQUENCEs through COPYs. #145691

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9 changes: 8 additions & 1 deletion llvm/lib/Target/AMDGPU/SIFoldOperands.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -1164,11 +1164,18 @@ void SIFoldOperandsImpl::foldOperand(
// Grab the use operands first
SmallVector<MachineOperand *, 4> UsesToProcess(
llvm::make_pointer_range(MRI->use_nodbg_operands(RegSeqDstReg)));
for (auto *RSUse : UsesToProcess) {
for (unsigned I = 0; I != UsesToProcess.size(); ++I) {
MachineOperand *RSUse = UsesToProcess[I];
MachineInstr *RSUseMI = RSUse->getParent();
unsigned OpNo = RSUseMI->getOperandNo(RSUse);

if (SplatRC) {
if (RSUseMI->isCopy()) {
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I guess this could be isFoldableCopy(), but I hesitate to use it without test coverage.

Register DstReg = RSUseMI->getOperand(0).getReg();
append_range(UsesToProcess,
make_pointer_range(MRI->use_nodbg_operands(DstReg)));
continue;
}
if (tryFoldRegSeqSplat(RSUseMI, OpNo, SplatVal, SplatRC)) {
FoldableDef SplatDef(SplatVal, SplatRC);
appendFoldCandidate(FoldList, RSUseMI, OpNo, SplatDef);
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10 changes: 2 additions & 8 deletions llvm/test/CodeGen/AMDGPU/packed-fp32.ll
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Expand Up @@ -2155,11 +2155,8 @@ define amdgpu_kernel void @fadd_fadd_fsub_0(<2 x float> %arg) {
; GFX90A-GISEL-LABEL: fadd_fadd_fsub_0:
; GFX90A-GISEL: ; %bb.0: ; %bb
; GFX90A-GISEL-NEXT: s_load_dwordx2 s[0:1], s[4:5], 0x24
; GFX90A-GISEL-NEXT: s_mov_b32 s2, 0
; GFX90A-GISEL-NEXT: s_mov_b32 s3, s2
; GFX90A-GISEL-NEXT: v_pk_mov_b32 v[0:1], s[2:3], s[2:3] op_sel:[0,1]
; GFX90A-GISEL-NEXT: s_waitcnt lgkmcnt(0)
; GFX90A-GISEL-NEXT: v_pk_add_f32 v[0:1], s[0:1], v[0:1]
; GFX90A-GISEL-NEXT: v_pk_add_f32 v[0:1], s[0:1], 0
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The only test change is one globalisel case, so that's a hint this is just hiding a missed optimization that should have happened earlier in the pipeline. Do you have another example where this is useful?

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Discussed elsewhere.

; GFX90A-GISEL-NEXT: v_mov_b32_e32 v0, v1
; GFX90A-GISEL-NEXT: v_pk_add_f32 v[0:1], v[0:1], 0
; GFX90A-GISEL-NEXT: v_mov_b32_e32 v2, s0
Expand All @@ -2170,11 +2167,8 @@ define amdgpu_kernel void @fadd_fadd_fsub_0(<2 x float> %arg) {
; GFX942-GISEL-LABEL: fadd_fadd_fsub_0:
; GFX942-GISEL: ; %bb.0: ; %bb
; GFX942-GISEL-NEXT: s_load_dwordx2 s[0:1], s[4:5], 0x24
; GFX942-GISEL-NEXT: s_mov_b32 s2, 0
; GFX942-GISEL-NEXT: s_mov_b32 s3, s2
; GFX942-GISEL-NEXT: v_mov_b64_e32 v[0:1], s[2:3]
; GFX942-GISEL-NEXT: s_waitcnt lgkmcnt(0)
; GFX942-GISEL-NEXT: v_pk_add_f32 v[0:1], s[0:1], v[0:1]
; GFX942-GISEL-NEXT: v_pk_add_f32 v[0:1], s[0:1], 0
; GFX942-GISEL-NEXT: s_nop 0
; GFX942-GISEL-NEXT: v_mov_b32_e32 v0, v1
; GFX942-GISEL-NEXT: v_pk_add_f32 v[0:1], v[0:1], 0
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