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[AMDGPU] SIFoldOperands: eagerly erase dead REG_SEQUENCEs 

This is fairly cheap to implement and means less work for future
passes like MachineDCE.

Reapply with a fix for using InstToErase after it had been erased.

Differential Revision: https://reviews.llvm.org/D100188
This commit is contained in:
Jay Foad 2021-04-09 13:52:35 +01:00
parent f0bc2782f2
commit 323ef0eb45
1 changed files with 22 additions and 2 deletions
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24
llvm/lib/Target/AMDGPU/SIFoldOperands.cpp
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@ -1596,6 +1596,10 @@ bool SIFoldOperands::tryFoldRegSequence(MachineInstr &MI) {
LLVM_DEBUG(dbgs() << "Folded " << *RS << " into " << *UseMI);
// Erase the REG_SEQUENCE eagerly, unless we followed a chain of COPY users,
// in which case we can erase them all later in runOnMachineFunction.
if (MRI->use_nodbg_empty(MI.getOperand(0).getReg()))
MI.eraseFromParentAndMarkDBGValuesForRemoval();
return true;
}
@ -1786,8 +1790,24 @@ bool SIFoldOperands::runOnMachineFunction(MachineFunction &MF) {
// If we managed to fold all uses of this copy then we might as well
// delete it now.
if (MRI->use_nodbg_empty(MI.getOperand(0).getReg()))
MI.eraseFromParentAndMarkDBGValuesForRemoval();
// The only reason we need to follow chains of copies here is that
// tryFoldRegSequence looks forward through copies before folding a
// REG_SEQUENCE into its eventual users.
auto *InstToErase = &MI;
while (MRI->use_nodbg_empty(InstToErase->getOperand(0).getReg())) {
auto &SrcOp = InstToErase->getOperand(1);
auto SrcReg = SrcOp.isReg() ? SrcOp.getReg() : Register();
InstToErase->eraseFromParentAndMarkDBGValuesForRemoval();
InstToErase = nullptr;
if (!SrcReg || SrcReg.isPhysical())
break;
InstToErase = MRI->getVRegDef(SrcReg);
if (!InstToErase || !TII->isFoldableCopy(*InstToErase))
break;
}
if (InstToErase && InstToErase->isRegSequence() &&
MRI->use_nodbg_empty(InstToErase->getOperand(0).getReg()))
InstToErase->eraseFromParentAndMarkDBGValuesForRemoval();
}
}
return true;