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Implement InstCombine/phi.ll:test7, deletion of trivial value loops for

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induction variables.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@33234 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Chris Lattner 2007-01-15 07:30:06 +00:00
parent 151becec7e
commit ff9f13a4b2
1 changed files with 16 additions and 2 deletions
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18
lib/Transforms/Scalar/InstructionCombining.cpp
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@ -7595,14 +7595,28 @@ Instruction *InstCombiner::visitPHINode(PHINode &PN) {
// 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())) {
if (PN.hasOneUse()) {
Instruction *PHIUser = cast<Instruction>(PN.use_back());
if (PHINode *PU = dyn_cast<PHINode>(PHIUser)) {
std::set<PHINode*> PotentiallyDeadPHIs;
PotentiallyDeadPHIs.insert(&PN);
if (DeadPHICycle(PU, PotentiallyDeadPHIs))
return ReplaceInstUsesWith(PN, UndefValue::get(PN.getType()));
}
// If this phi has a single use, and if that use just computes a value for
// the next iteration of a loop, delete the phi. This occurs with unused
// induction variables, e.g. "for (int j = 0; ; ++j);". Detecting this
// common case here is good because the only other things that catch this
// are induction variable analysis (sometimes) and ADCE, which is only run
// late.
if (PHIUser->hasOneUse() &&
(isa<BinaryOperator>(PHIUser) || isa<GetElementPtrInst>(PHIUser)) &&
PHIUser->use_back() == &PN) {
return ReplaceInstUsesWith(PN, UndefValue::get(PN.getType()));
}
}
return 0;
}