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Simplify RecursivelyDeleteDeadPHINode. The only functionality change 

should be that if the phi is used by a side-effect free instruction with
no uses then the phi and the instruction now get zapped (checked by the
unittest).

llvm-svn: 126124
This commit is contained in:
Duncan Sands 2011-02-21 16:27:36 +00:00
parent 5decec97e5
commit 6dcd49bc2b
2 changed files with 22 additions and 28 deletions
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44
llvm/lib/Transforms/Utils/Local.cpp
View File

@ -262,12 +262,13 @@ bool llvm::RecursivelyDeleteTriviallyDeadInstructions(Value *V) {
/// areAllUsesEqual - Check whether the uses of a value are all the same.
/// This is similar to Instruction::hasOneUse() except this will also return
/// true when there are multiple uses that all refer to the same value.
/// true when there are no uses or multiple uses that all refer to the same
/// value.
static bool areAllUsesEqual(Instruction *I) {
Value::use_iterator UI = I->use_begin();
Value::use_iterator UE = I->use_end();
if (UI == UE)
return false;
return true;
User *TheUse = *UI;
for (++UI; UI != UE; ++UI) {
@ -283,34 +284,21 @@ 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;
}
SmallPtrSet<Instruction*, 4> Visited;
for (Instruction *I = PN; areAllUsesEqual(I) && !I->mayHaveSideEffects();
I = cast<Instruction>(*I->use_begin())) {
if (I->use_empty())
return RecursivelyDeleteTriviallyDeadInstructions(I);
// 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.
if (!areAllUsesEqual(PN))
return false;
bool Changed = false;
SmallPtrSet<PHINode *, 4> PHIs;
PHIs.insert(PN);
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
// If we find an instruction more than once, we're on a cycle that
// won't prove fruitful.
if (PHINode *IP = dyn_cast<PHINode>(I))
if (!PHIs.insert(IP)) {
// Break the cycle and delete the PHI and its operands.
IP->replaceAllUsesWith(UndefValue::get(IP->getType()));
(void)RecursivelyDeleteTriviallyDeadInstructions(IP);
Changed = true;
break;
}
return Changed;
if (!Visited.insert(I)) {
// Break the cycle and delete the instruction and its operands.
I->replaceAllUsesWith(UndefValue::get(I->getType()));
return RecursivelyDeleteTriviallyDeadInstructions(I);
}
}
return false;
}
/// SimplifyInstructionsInBlock - Scan the specified basic block and try to

6
llvm/unittests/Transforms/Utils/Local.cpp
View File

@ -47,6 +47,12 @@ TEST(Local, RecursivelyDeleteDeadPHINodes) {
EXPECT_TRUE(RecursivelyDeleteDeadPHINode(phi));
builder.SetInsertPoint(bb0);
phi = builder.CreatePHI(Type::getInt32Ty(C));
builder.CreateAdd(phi, phi);
EXPECT_TRUE(RecursivelyDeleteDeadPHINode(phi));
bb0->dropAllReferences();
bb1->dropAllReferences();
delete bb0;