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[AMDGPU] Skip debug instructions when eliminating S_SET_GPR_IDX_ON/OFF #160715

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Merged
jayfoad merged 4 commits into from
Nov 4, 2025
Merged

[AMDGPU] Skip debug instructions when eliminating S_SET_GPR_IDX_ON/OFF #160715

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f8311a3
[AMDGPU] Skip debug instructions when eliminating S_SET_GPR_IDX_ON/OFF
jayfoad Sep 25, 2025
31e1d02
Skip all meta instructions
jayfoad Sep 25, 2025
574f561
Test KILL
jayfoad Sep 25, 2025
a9177fe
Test IMPLICIT_DEF. Revert special handling for meta instructions.
jayfoad Sep 26, 2025
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2 changes: 1 addition & 1 deletion llvm/lib/Target/AMDGPU/SIPreEmitPeephole.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -299,7 +299,7 @@ bool SIPreEmitPeephole::optimizeSetGPR(MachineInstr &First,
for (MachineBasicBlock::instr_iterator I = std::next(First.getIterator()),
E = MI.getIterator();
I != E; ++I) {
if (I->isBundle())
if (I->isBundle() || I->isDebugInstr())
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@arsenm arsenm Sep 25, 2025

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Probably should be all meta instructions

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@arsenm arsenm Sep 25, 2025

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If you're doing that, also test KILL and IMPLICIT_DEF?

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@jayfoad jayfoad Sep 25, 2025

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Done for KILL. This is post-RA so I don't think we'll see IMPLICIT_DEF.

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@arsenm arsenm Sep 26, 2025

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IMPLICIT_DEF often survives RA, it is needed to maintain liveness across blocks

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@jayfoad jayfoad Sep 26, 2025

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You're right, I was confused. Added a test for IMPLICIT_DEF.

However, on reflection, I don't think explicitly skipping all meta instructions here is a good idea. Irrelevant instructions are already skipped below based on their operands, and I'm testing that this works for some meta instructions. Explicitly skipping all meta instructions seems unnecessary and possibly wrong.

continue;
switch (I->getOpcode()) {
case AMDGPU::S_SET_GPR_IDX_MODE:
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1 change: 1 addition & 0 deletions llvm/test/CodeGen/AMDGPU/set-gpr-idx-peephole.mir
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@@ -1,5 +1,6 @@
# NOTE: Assertions have been autogenerated by utils/update_mir_test_checks.py
# RUN: llc -mtriple=amdgcn -mcpu=gfx900 -run-pass si-pre-emit-peephole -verify-machineinstrs -o - %s | FileCheck -check-prefix=GCN %s -implicit-check-not=S_SET_GPR_IDX
# RUN: llc -mtriple=amdgcn -mcpu=gfx900 -run-pass si-pre-emit-peephole -verify-machineinstrs -o - %s -debugify-and-strip-all-safe | FileCheck -check-prefix=GCN %s -implicit-check-not=S_SET_GPR_IDX
# RUN: llc -mtriple=amdgcn -mcpu=gfx900 -passes si-pre-emit-peephole -o - %s | FileCheck -check-prefix=GCN %s -implicit-check-not=S_SET_GPR_IDX

---
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