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Avoid eraseing copies from a reserved register unless the definition can be

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safely proven not to have been clobbered. No small test case possible.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@147751 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Evan Cheng 2012-01-08 19:52:28 +00:00
parent dfb806f6ba
commit e811d0dd30
1 changed files with 26 additions and 0 deletions
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26
lib/CodeGen/MachineCopyPropagation.cpp
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@ -83,6 +83,25 @@ MachineCopyPropagation::SourceNoLongerAvailable(unsigned Reg,
}
}
static bool NoInterveningSideEffect(const MachineInstr *CopyMI,
const MachineInstr *MI) {
const MachineBasicBlock *MBB = CopyMI->getParent();
if (MI->getParent() != MBB)
return false;
MachineBasicBlock::const_iterator I = CopyMI;
MachineBasicBlock::const_iterator E = MBB->end();
MachineBasicBlock::const_iterator E2 = MI;
++I;
while (I != E && I != E2) {
if (I->hasUnmodeledSideEffects() || I->isCall() ||
I->isTerminator())
return false;
++I;
}
return true;
}
bool MachineCopyPropagation::CopyPropagateBlock(MachineBasicBlock &MBB) {
SmallSetVector<MachineInstr*, 8> MaybeDeadCopies; // Candidates for deletion
DenseMap<unsigned, MachineInstr*> AvailCopyMap; // Def -> available copies map
@ -108,6 +127,7 @@ bool MachineCopyPropagation::CopyPropagateBlock(MachineBasicBlock &MBB) {
MachineInstr *CopyMI = CI->second;
unsigned SrcSrc = CopyMI->getOperand(1).getReg();
if (!ReservedRegs.test(Def) &&
(!ReservedRegs.test(Src) || NoInterveningSideEffect(CopyMI, MI)) &&
(SrcSrc == Def || TRI->isSubRegister(SrcSrc, Def))) {
// The two copies cancel out and the source of the first copy
// hasn't been overridden, eliminate the second one. e.g.
@ -116,6 +136,12 @@ bool MachineCopyPropagation::CopyPropagateBlock(MachineBasicBlock &MBB) {
// %EAX<def> = COPY %ECX
// =>
// %ECX<def> = COPY %EAX
//
// Also avoid eliminating a copy from reserved registers unless the
// definition is proven not clobbered. e.g.
// %RSP<def> = COPY %RAX
// CALL
// %RAX<def> = COPY %RSP
CopyMI->getOperand(1).setIsKill(false);
MI->eraseFromParent();
Changed = true;