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Watch out for duplicated PHI instructions.

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git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@90816 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Evan Cheng 2009-12-07 23:11:03 +00:00
parent d8f079c25e
commit 3a41ddb1b9
1 changed files with 37 additions and 3 deletions
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40
lib/CodeGen/MachineSSAUpdater.cpp
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@ -85,6 +85,36 @@ unsigned MachineSSAUpdater::GetValueAtEndOfBlock(MachineBasicBlock *BB) {
return GetValueAtEndOfBlockInternal(BB);
}
static
unsigned LookForIdenticalPHI(MachineBasicBlock *BB,
SmallVector<std::pair<MachineBasicBlock*, unsigned>, 8> &PredValues) {
if (BB->empty())
return 0;
MachineBasicBlock::iterator I = BB->front();
if (I->getOpcode() != TargetInstrInfo::PHI)
return 0;
AvailableValsTy AVals;
for (unsigned i = 0, e = PredValues.size(); i != e; ++i)
AVals[PredValues[i].first] = PredValues[i].second;
while (I != BB->end() && I->getOpcode() == TargetInstrInfo::PHI) {
bool Same = true;
for (unsigned i = 1, e = I->getNumOperands(); i != e; i += 2) {
unsigned SrcReg = I->getOperand(i).getReg();
MachineBasicBlock *SrcBB = I->getOperand(i+1).getMBB();
if (AVals[SrcBB] != SrcReg) {
Same = false;
break;
}
}
if (Same)
return I->getOperand(0).getReg();
++I;
}
return 0;
}
/// InsertNewDef - Insert an empty PHI or IMPLICIT_DEF instruction which define
/// a value of the given register class at the start of the specified basic
/// block. It returns the virtual register defined by the instruction.
@ -97,7 +127,6 @@ MachineInstr *InsertNewDef(unsigned Opcode,
return BuildMI(*BB, I, DebugLoc::getUnknownLoc(), TII->get(Opcode), NewVR);
}
/// GetValueInMiddleOfBlock - Construct SSA form, materializing a value that
/// is live in the middle of the specified block.
///
@ -121,7 +150,7 @@ unsigned MachineSSAUpdater::GetValueInMiddleOfBlock(MachineBasicBlock *BB) {
// If there is no definition of the renamed variable in this block, just use
// GetValueAtEndOfBlock to do our work.
if (!getAvailableVals(AV).count(BB))
return GetValueAtEndOfBlock(BB);
return GetValueAtEndOfBlockInternal(BB);
// If there are no predecessors, just return undef.
if (BB->pred_empty()) {
@ -156,6 +185,11 @@ unsigned MachineSSAUpdater::GetValueInMiddleOfBlock(MachineBasicBlock *BB) {
if (SingularValue != 0)
return SingularValue;
// If an identical PHI is already in BB, just reuse it.
unsigned DupPHI = LookForIdenticalPHI(BB, PredValues);
if (DupPHI)
return DupPHI;
// Otherwise, we do need a PHI: insert one now.
MachineBasicBlock::iterator Loc = BB->empty() ? BB->end() : BB->front();
MachineInstr *InsertedPHI = InsertNewDef(TargetInstrInfo::PHI, BB,
@ -199,7 +233,7 @@ void MachineSSAUpdater::RewriteUse(MachineOperand &U) {
unsigned NewVR = 0;
if (UseMI->getOpcode() == TargetInstrInfo::PHI) {
MachineBasicBlock *SourceBB = findCorrespondingPred(UseMI, &U);
NewVR = GetValueAtEndOfBlock(SourceBB);
NewVR = GetValueAtEndOfBlockInternal(SourceBB);
} else {
NewVR = GetValueInMiddleOfBlock(UseMI->getParent());
}