[AMDGPU] Fold into uses of splat REG_SEQUENCEs through COPYs. #145691
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@llvm/pr-subscribers-backend-amdgpu Author: Ivan Kosarev (kosarev) ChangesFull diff: https://github.com/llvm/llvm-project/pull/145691.diff 2 Files Affected:
diff --git a/llvm/lib/Target/AMDGPU/SIFoldOperands.cpp b/llvm/lib/Target/AMDGPU/SIFoldOperands.cpp
index 8299c0dce1870..2d6afcbfb9447 100644
--- a/llvm/lib/Target/AMDGPU/SIFoldOperands.cpp
+++ b/llvm/lib/Target/AMDGPU/SIFoldOperands.cpp
@@ -1036,11 +1036,18 @@ 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 (SplatVal) {
+ if (RSUseMI->isCopy()) {
+ Register DstReg = RSUseMI->getOperand(0).getReg();
+ append_range(UsesToProcess,
+ make_pointer_range(MRI->use_nodbg_operands(DstReg)));
+ continue;
+ }
if (MachineOperand *Foldable =
tryFoldRegSeqSplat(RSUseMI, OpNo, SplatVal, SplatRC)) {
appendFoldCandidate(FoldList, RSUseMI, OpNo, Foldable);
diff --git a/llvm/test/CodeGen/AMDGPU/packed-fp32.ll b/llvm/test/CodeGen/AMDGPU/packed-fp32.ll
index bef38c1a65ef8..4db3f2189bfc3 100644
--- a/llvm/test/CodeGen/AMDGPU/packed-fp32.ll
+++ b/llvm/test/CodeGen/AMDGPU/packed-fp32.ll
@@ -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
; 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
@@ -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
|
kosarev
changed the title
arsenm
reviewed
Jun 26, 2025
| ; 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.
kosarev
commented
Jun 27, 2025
| MachineInstr *RSUseMI = RSUse->getParent(); | ||
| unsigned OpNo = RSUseMI->getOperandNo(RSUse); | ||
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| if (SplatRC) { | ||
| if (RSUseMI->isCopy()) { |
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I guess this could be isFoldableCopy(), but I hesitate to use it without test coverage.
| ; 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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