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Make instcombine not remove Phi nodes when LCSSA is live. 

llvm-svn: 29083
This commit is contained in:
Owen Anderson 2006-07-10 19:03:49 +00:00
parent 7ac78b99e6
commit a6968f83b2
1 changed files with 50 additions and 46 deletions
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96
llvm/lib/Transforms/Scalar/InstructionCombining.cpp
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@ -96,6 +96,7 @@ namespace {
virtual void getAnalysisUsage(AnalysisUsage &AU) const { virtual void getAnalysisUsage(AnalysisUsage &AU) const {
AU.addRequired<TargetData>(); AU.addRequired<TargetData>();
AU.addPreservedID(LCSSAID);
AU.setPreservesCFG(); AU.setPreservesCFG();
} }
@ -6251,56 +6252,59 @@ static bool DeadPHICycle(PHINode *PN, std::set<PHINode*> &PotentiallyDeadPHIs) {
// PHINode simplification // PHINode simplification
// //
Instruction *InstCombiner::visitPHINode(PHINode &PN) { Instruction *InstCombiner::visitPHINode(PHINode &PN) {
if (Value *V = PN.hasConstantValue()) // If LCSSA is around, don't nuke PHIs.
return ReplaceInstUsesWith(PN, V); if (!mustPreserveAnalysisID(LCSSAID)) {
if (Value *V = PN.hasConstantValue())
return ReplaceInstUsesWith(PN, V);
// If the only user of this instruction is a cast instruction, and all of the // If the only user of this instruction is a cast instruction, and all of
// incoming values are constants, change this PHI to merge together the casted //the incoming values are constants, change this PHI to merge together the
// constants. // casted constants.
if (PN.hasOneUse()) if (PN.hasOneUse())
if (CastInst *CI = dyn_cast<CastInst>(PN.use_back())) if (CastInst *CI = dyn_cast<CastInst>(PN.use_back()))
if (CI->getType() != PN.getType()) { // noop casts will be folded if (CI->getType() != PN.getType()) { // noop casts will be folded
bool AllConstant = true; bool AllConstant = true;
for (unsigned i = 0, e = PN.getNumIncomingValues(); i != e; ++i) for (unsigned i = 0, e = PN.getNumIncomingValues(); i != e; ++i)
if (!isa<Constant>(PN.getIncomingValue(i))) { if (!isa<Constant>(PN.getIncomingValue(i))) {
AllConstant = false; AllConstant = false;
break; break;
} }
if (AllConstant) { if (AllConstant) {
// Make a new PHI with all casted values. // Make a new PHI with all casted values.
PHINode *New = new PHINode(CI->getType(), PN.getName(), &PN); PHINode *New = new PHINode(CI->getType(), PN.getName(), &PN);
for (unsigned i = 0, e = PN.getNumIncomingValues(); i != e; ++i) { for (unsigned i = 0, e = PN.getNumIncomingValues(); i != e; ++i) {
Constant *OldArg = cast<Constant>(PN.getIncomingValue(i)); Constant *OldArg = cast<Constant>(PN.getIncomingValue(i));
New->addIncoming(ConstantExpr::getCast(OldArg, New->getType()), New->addIncoming(ConstantExpr::getCast(OldArg, New->getType()),
PN.getIncomingBlock(i)); PN.getIncomingBlock(i));
} }
// Update the cast instruction. // Update the cast instruction.
CI->setOperand(0, New); CI->setOperand(0, New);
WorkList.push_back(CI); // revisit the cast instruction to fold. WorkList.push_back(CI); // revisit the cast instruction to fold.
WorkList.push_back(New); // Make sure to revisit the new Phi WorkList.push_back(New); // Make sure to revisit the new Phi
return &PN; // PN is now dead! return &PN; // PN is now dead!
}
} }
// If all PHI operands are the same operation, pull them through the PHI,
// reducing code size.
if (isa<Instruction>(PN.getIncomingValue(0)) &&
PN.getIncomingValue(0)->hasOneUse())
if (Instruction *Result = FoldPHIArgOpIntoPHI(PN))
return Result;
// If this is a trivial cycle in the PHI node graph, remove it. Basically,
// if this PHI only has a single use (a PHI), and if that PHI only has one
// use (a PHI)... break the cycle.
if (PN.hasOneUse())
if (PHINode *PU = dyn_cast<PHINode>(PN.use_back())) {
std::set<PHINode*> PotentiallyDeadPHIs;
PotentiallyDeadPHIs.insert(&PN);
if (DeadPHICycle(PU, PotentiallyDeadPHIs))
return ReplaceInstUsesWith(PN, UndefValue::get(PN.getType()));
} }
}
// If all PHI operands are the same operation, pull them through the PHI,
// reducing code size.
if (isa<Instruction>(PN.getIncomingValue(0)) &&
PN.getIncomingValue(0)->hasOneUse())
if (Instruction *Result = FoldPHIArgOpIntoPHI(PN))
return Result;
// If this is a trivial cycle in the PHI node graph, remove it. Basically, if
// this PHI only has a single use (a PHI), and if that PHI only has one use (a
// PHI)... break the cycle.
if (PN.hasOneUse())
if (PHINode *PU = dyn_cast<PHINode>(PN.use_back())) {
std::set<PHINode*> PotentiallyDeadPHIs;
PotentiallyDeadPHIs.insert(&PN);
if (DeadPHICycle(PU, PotentiallyDeadPHIs))
return ReplaceInstUsesWith(PN, UndefValue::get(PN.getType()));
}
return 0; return 0;
} }