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Be more careful when constant-folding PHI nodes.

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llvm-svn: 41998
This commit is contained in:
Owen Anderson 2007-09-16 08:04:16 +00:00
parent 890c3898e0
commit fd6ec5cf82
1 changed files with 16 additions and 1 deletions
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17
lib/Transforms/Scalar/GVN.cpp
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@ -673,6 +673,7 @@ namespace {
void dump(DenseMap<BasicBlock*, Value*>& d);
bool iterateOnFunction(Function &F);
Value* CollapsePhi(PHINode* p);
bool isSafeReplacement(PHINode* p, Instruction* inst);
};
char GVN::ID = 0;
@ -731,7 +732,8 @@ Value* GVN::CollapsePhi(PHINode* p) {
if (constVal) {
if (Instruction* inst = dyn_cast<Instruction>(constVal)) {
if (DT.dominates(inst, p))
return inst;
if (isSafeReplacement(p, inst))
return inst;
} else {
return constVal;
}
@ -740,6 +742,19 @@ Value* GVN::CollapsePhi(PHINode* p) {
return 0;
}
bool GVN::isSafeReplacement(PHINode* p, Instruction* inst) {
if (!isa<PHINode>(inst))
return true;
for (Instruction::use_iterator UI = p->use_begin(), E = p->use_end();
UI != E; ++UI)
if (PHINode* use_phi = dyn_cast<PHINode>(UI))
if (use_phi->getParent() == inst->getParent())
return false;
return true;
}
/// GetValueForBlock - Get the value to use within the specified basic block.
/// available values are in Phis.
Value *GVN::GetValueForBlock(BasicBlock *BB, LoadInst* orig,