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A register def can be partially dead when the whole register has use(s) but a subreg does not.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@31760 91177308-0d34-0410-b5e6-96231b3b80d8
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@ -575,7 +575,6 @@ void LiveIntervals::handlePhysicalRegisterDef(MachineBasicBlock *MBB,
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// A physical register cannot be live across basic block, so its
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// lifetime must end somewhere in its defining basic block.
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DEBUG(std::cerr << "\t\tregister: "; printRegName(interval.reg));
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typedef LiveVariables::killed_iterator KillIter;
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unsigned baseIndex = MIIdx;
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unsigned start = getDefIndex(baseIndex);
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@ -599,6 +598,14 @@ void LiveIntervals::handlePhysicalRegisterDef(MachineBasicBlock *MBB,
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DEBUG(std::cerr << " killed");
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end = getUseIndex(baseIndex) + 1;
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goto exit;
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} else if (lv_->ModifiesRegister(mi, interval.reg)) {
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// Another instruction redefines the register before it is ever read.
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// Then the register is essentially dead at the instruction that defines
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// it. Hence its interval is:
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// [defSlot(def), defSlot(def)+1)
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DEBUG(std::cerr << " dead");
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end = getDefIndex(start) + 1;
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goto exit;
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}
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}
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