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If all sources of a PHI node are defined by an implicit_def, just emit an implicit_def instead of a copy.

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git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@50927 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Evan Cheng
2008-05-10 00:17:50 +00:00
parent 637980edce
commit b3e0a6d75c
2 changed files with 36 additions and 7 deletions
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18
lib/CodeGen/PHIElimination.cpp
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@@ -127,11 +127,15 @@ bool PNE::EliminatePHINodes(MachineFunction &MF, MachineBasicBlock &MBB) {
return true;
}
static bool isSourceDefinedByImplicitDef(MachineInstr *MPhi, unsigned SrcIdx,
static bool isSourceDefinedByImplicitDef(MachineInstr *MPhi,
MachineRegisterInfo *MRI) {
unsigned SrcReg = MPhi->getOperand(SrcIdx*2+1).getReg();
MachineInstr *DefMI = MRI->getVRegDef(SrcReg);
return DefMI->getOpcode() == TargetInstrInfo::IMPLICIT_DEF;
for (unsigned i = 1; i != MPhi->getNumOperands(); i += 2) {
unsigned SrcReg = MPhi->getOperand(i).getReg();
MachineInstr *DefMI = MRI->getVRegDef(SrcReg);
if (!DefMI || DefMI->getOpcode() != TargetInstrInfo::IMPLICIT_DEF)
return false;
}
return true;
}
/// LowerAtomicPHINode - Lower the PHI node at the top of the specified block,
@@ -156,9 +160,9 @@ void PNE::LowerAtomicPHINode(MachineBasicBlock &MBB,
// into the phi node destination.
//
const TargetInstrInfo *TII = MF.getTarget().getInstrInfo();
if (NumSrcs == 1 && isSourceDefinedByImplicitDef(MPhi, 0, MRI))
// If the only source of a PHI node is an implicit_def, just emit an
// implicit_def instead of a copy.
if (isSourceDefinedByImplicitDef(MPhi, MRI))
// If all sources of a PHI node are implicit_def, just emit an implicit_def
// instead of a copy.
BuildMI(MBB, AfterPHIsIt, TII->get(TargetInstrInfo::IMPLICIT_DEF), DestReg);
else
TII->copyRegToReg(MBB, AfterPHIsIt, DestReg, IncomingReg, RC, RC);