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Make RecursivelyDeleteDeadPHINode delete a phi node that has no users and add a

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test for that. With this change, test/CodeGen/X86/codegen-dce.ll no longer finds
any instructions to DCE, so delete the test.

Also renamed J and JP to I and IP in RecursivelyDeleteDeadPHINode.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@126088 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Nick Lewycky
2011-02-20 18:05:56 +00:00
parent cd6c93ec48
commit eff5e69c82
3 changed files with 17 additions and 50 deletions
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19
lib/Transforms/Utils/Local.cpp
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@@ -283,6 +283,11 @@ static bool areAllUsesEqual(Instruction *I) {
/// delete it. If that makes any of its operands trivially dead, delete them
/// too, recursively. Return true if the PHI node is actually deleted.
bool llvm::RecursivelyDeleteDeadPHINode(PHINode *PN) {
if (PN->use_empty()) {
PN->eraseFromParent();
return true;
}
// We can remove a PHI if it is on a cycle in the def-use graph
// where each node in the cycle has degree one, i.e. only one use,
// and is an instruction with no side effects.
@@ -292,16 +297,16 @@ bool llvm::RecursivelyDeleteDeadPHINode(PHINode *PN) {
bool Changed = false;
SmallPtrSet<PHINode *, 4> PHIs;
PHIs.insert(PN);
for (Instruction *J = cast<Instruction>(*PN->use_begin());
areAllUsesEqual(J) && !J->mayHaveSideEffects();
J = cast<Instruction>(*J->use_begin()))
for (Instruction *I = cast<Instruction>(*PN->use_begin());
areAllUsesEqual(I) && !I->mayHaveSideEffects();
I = cast<Instruction>(*I->use_begin()))
// If we find a PHI more than once, we're on a cycle that
// won't prove fruitful.
if (PHINode *JP = dyn_cast<PHINode>(J))
if (!PHIs.insert(JP)) {
if (PHINode *IP = dyn_cast<PHINode>(I))
if (!PHIs.insert(IP)) {
// Break the cycle and delete the PHI and its operands.
JP->replaceAllUsesWith(UndefValue::get(JP->getType()));
(void)RecursivelyDeleteTriviallyDeadInstructions(JP);
IP->replaceAllUsesWith(UndefValue::get(IP->getType()));
(void)RecursivelyDeleteTriviallyDeadInstructions(IP);
Changed = true;
break;
}