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Delete PHI nodes that are not dead but are locked in a cycle of single

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useness.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@19629 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Chris Lattner 2005-01-17 05:10:15 +00:00
parent b352fa5853
commit a3fd1c569c
1 changed files with 26 additions and 0 deletions
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26
lib/Transforms/Scalar/InstructionCombining.cpp
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@ -4051,6 +4051,22 @@ Instruction *InstCombiner::FoldPHIArgOpIntoPHI(PHINode &PN) {
PhiVal, ConstantOp); PhiVal, ConstantOp);
} }
/// DeadPHICycle - Return true if this PHI node is only used by a PHI node cycle
/// that is dead.
static bool DeadPHICycle(PHINode *PN, std::set<PHINode*> &PotentiallyDeadPHIs) {
if (PN->use_empty()) return true;
if (!PN->hasOneUse()) return false;
// Remember this node, and if we find the cycle, return.
if (!PotentiallyDeadPHIs.insert(PN).second)
return true;
if (PHINode *PU = dyn_cast<PHINode>(PN->use_back()))
return DeadPHICycle(PU, PotentiallyDeadPHIs);
return false;
}
// PHINode simplification // PHINode simplification
// //
Instruction *InstCombiner::visitPHINode(PHINode &PN) { Instruction *InstCombiner::visitPHINode(PHINode &PN) {
@ -4109,6 +4125,16 @@ Instruction *InstCombiner::visitPHINode(PHINode &PN) {
if (Instruction *Result = FoldPHIArgOpIntoPHI(PN)) if (Instruction *Result = FoldPHIArgOpIntoPHI(PN))
return Result; return Result;
// 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())) {
std::set<PHINode*> PotentiallyDeadPHIs;
PotentiallyDeadPHIs.insert(&PN);
if (DeadPHICycle(PU, PotentiallyDeadPHIs))
return ReplaceInstUsesWith(PN, UndefValue::get(PN.getType()));
}
return 0; return 0;
} }