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Avoid eraseing copies from a reserved register unless the definition can be
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
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@ -83,6 +83,25 @@ MachineCopyPropagation::SourceNoLongerAvailable(unsigned Reg,
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}
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}
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}
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}
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static bool NoInterveningSideEffect(const MachineInstr *CopyMI,
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const MachineInstr *MI) {
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const MachineBasicBlock *MBB = CopyMI->getParent();
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if (MI->getParent() != MBB)
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return false;
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MachineBasicBlock::const_iterator I = CopyMI;
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MachineBasicBlock::const_iterator E = MBB->end();
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MachineBasicBlock::const_iterator E2 = MI;
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++I;
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while (I != E && I != E2) {
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if (I->hasUnmodeledSideEffects() || I->isCall() ||
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I->isTerminator())
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return false;
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++I;
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}
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return true;
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}
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bool MachineCopyPropagation::CopyPropagateBlock(MachineBasicBlock &MBB) {
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bool MachineCopyPropagation::CopyPropagateBlock(MachineBasicBlock &MBB) {
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SmallSetVector<MachineInstr*, 8> MaybeDeadCopies; // Candidates for deletion
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SmallSetVector<MachineInstr*, 8> MaybeDeadCopies; // Candidates for deletion
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DenseMap<unsigned, MachineInstr*> AvailCopyMap; // Def -> available copies map
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DenseMap<unsigned, MachineInstr*> AvailCopyMap; // Def -> available copies map
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@ -108,6 +127,7 @@ bool MachineCopyPropagation::CopyPropagateBlock(MachineBasicBlock &MBB) {
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MachineInstr *CopyMI = CI->second;
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MachineInstr *CopyMI = CI->second;
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unsigned SrcSrc = CopyMI->getOperand(1).getReg();
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unsigned SrcSrc = CopyMI->getOperand(1).getReg();
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if (!ReservedRegs.test(Def) &&
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if (!ReservedRegs.test(Def) &&
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(!ReservedRegs.test(Src) || NoInterveningSideEffect(CopyMI, MI)) &&
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(SrcSrc == Def || TRI->isSubRegister(SrcSrc, Def))) {
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(SrcSrc == Def || TRI->isSubRegister(SrcSrc, Def))) {
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// The two copies cancel out and the source of the first copy
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// The two copies cancel out and the source of the first copy
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// hasn't been overridden, eliminate the second one. e.g.
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// hasn't been overridden, eliminate the second one. e.g.
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@ -116,6 +136,12 @@ bool MachineCopyPropagation::CopyPropagateBlock(MachineBasicBlock &MBB) {
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// %EAX<def> = COPY %ECX
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// %EAX<def> = COPY %ECX
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// =>
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// =>
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// %ECX<def> = COPY %EAX
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// %ECX<def> = COPY %EAX
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//
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// Also avoid eliminating a copy from reserved registers unless the
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// definition is proven not clobbered. e.g.
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// %RSP<def> = COPY %RAX
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// CALL
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// %RAX<def> = COPY %RSP
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CopyMI->getOperand(1).setIsKill(false);
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CopyMI->getOperand(1).setIsKill(false);
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MI->eraseFromParent();
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MI->eraseFromParent();
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Changed = true;
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Changed = true;
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