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).
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@126124 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Transforms/Utils/Local.cpp b/lib/Transforms/Utils/Local.cpp
index 20d7989..40a56b0 100644
--- a/lib/Transforms/Utils/Local.cpp
+++ b/lib/Transforms/Utils/Local.cpp
@@ -262,12 +262,13 @@
/// 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 @@
/// 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