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Instcombine PHI's of the form %PN = phi PN, X into X and

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%PN = phi PN, PN, PN into 0 (because the phi must not be reachable)


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@3470 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Chris Lattner 2002-08-22 20:22:01 +00:00
parent 74d8dcc9d2
commit c20e24524f
1 changed files with 13 additions and 4 deletions
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17
lib/Transforms/Scalar/InstructionCombining.cpp
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@ -610,10 +610,19 @@ Instruction *InstCombiner::visitPHINode(PHINode &PN) {
// Otherwise if all of the incoming values are the same for the PHI, replace
// the PHI node with the incoming value.
//
Value *InVal = PN.getIncomingValue(0);
for (unsigned i = 1, e = PN.getNumIncomingValues(); i != e; ++i)
if (PN.getIncomingValue(i) != InVal)
return 0; // Not the same, bail out.
Value *InVal = 0;
for (unsigned i = 0, e = PN.getNumIncomingValues(); i != e; ++i)
if (PN.getIncomingValue(i) != &PN) // Not the PHI node itself...
if (InVal && PN.getIncomingValue(i) != InVal)
return 0; // Not the same, bail out.
else
InVal = PN.getIncomingValue(i);
// The only case that could cause InVal to be null is if we have a PHI node
// that only has entries for itself. In this case, there is no entry into the
// loop, so kill the PHI.
//
if (InVal == 0) InVal = Constant::getNullValue(PN.getType());
// All of the incoming values are the same, replace the PHI node now.
return ReplaceInstUsesWith(PN, InVal);