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Implement InstCombine/phi.ll:test7, deletion of trivial value loops for
induction variables. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@33234 91177308-0d34-0410-b5e6-96231b3b80d8
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@ -7595,13 +7595,27 @@ Instruction *InstCombiner::visitPHINode(PHINode &PN) {
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// If this is a trivial cycle in the PHI node graph, remove it. Basically, if
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// this PHI only has a single use (a PHI), and if that PHI only has one use (a
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// PHI)... break the cycle.
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if (PN.hasOneUse())
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if (PHINode *PU = dyn_cast<PHINode>(PN.use_back())) {
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if (PN.hasOneUse()) {
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Instruction *PHIUser = cast<Instruction>(PN.use_back());
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if (PHINode *PU = dyn_cast<PHINode>(PHIUser)) {
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std::set<PHINode*> PotentiallyDeadPHIs;
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PotentiallyDeadPHIs.insert(&PN);
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if (DeadPHICycle(PU, PotentiallyDeadPHIs))
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return ReplaceInstUsesWith(PN, UndefValue::get(PN.getType()));
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}
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// If this phi has a single use, and if that use just computes a value for
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// the next iteration of a loop, delete the phi. This occurs with unused
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// induction variables, e.g. "for (int j = 0; ; ++j);". Detecting this
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// common case here is good because the only other things that catch this
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// are induction variable analysis (sometimes) and ADCE, which is only run
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// late.
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if (PHIUser->hasOneUse() &&
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(isa<BinaryOperator>(PHIUser) || isa<GetElementPtrInst>(PHIUser)) &&
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PHIUser->use_back() == &PN) {
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return ReplaceInstUsesWith(PN, UndefValue::get(PN.getType()));
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}
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}
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return 0;
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}
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