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Fold PHI nodes of constants which are only used by a single cast. This implements

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phi.ll:test4


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@11494 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Chris Lattner 2004-02-16 05:07:08 +00:00
parent d8bed768ab
commit 7059f2e76b
1 changed files with 29 additions and 0 deletions
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29
lib/Transforms/Scalar/InstructionCombining.cpp
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@ -1968,6 +1968,35 @@ bool InstCombiner::transformConstExprCastCall(CallSite CS) {
Instruction *InstCombiner::visitPHINode(PHINode &PN) {
if (Value *V = hasConstantValue(&PN))
return ReplaceInstUsesWith(PN, V);
// If the only user of this instruction is a cast instruction, and all of the
// incoming values are constants, change this PHI to merge together the casted
// constants.
if (PN.hasOneUse())
if (CastInst *CI = dyn_cast<CastInst>(PN.use_back()))
if (CI->getType() != PN.getType()) { // noop casts will be folded
bool AllConstant = true;
for (unsigned i = 0, e = PN.getNumIncomingValues(); i != e; ++i)
if (!isa<Constant>(PN.getIncomingValue(i))) {
AllConstant = false;
break;
}
if (AllConstant) {
// Make a new PHI with all casted values.
PHINode *New = new PHINode(CI->getType(), PN.getName(), &PN);
for (unsigned i = 0, e = PN.getNumIncomingValues(); i != e; ++i) {
Constant *OldArg = cast<Constant>(PN.getIncomingValue(i));
New->addIncoming(ConstantExpr::getCast(OldArg, New->getType()),
PN.getIncomingBlock(i));
}
// Update the cast instruction.
CI->setOperand(0, New);
WorkList.push_back(CI); // revisit the cast instruction to fold.
WorkList.push_back(New); // Make sure to revisit the new Phi
return &PN; // PN is now dead!
}
}
return 0;
}