If the phi node was used by an unreachable instruction that ends up using

itself without going via a phi node then we could return false here in
spite of making a change.  Also, tweak the comment because this method
can (and always could) return true without deleting the original phi node.
For example, if the phi node was used by a read-only invoke instruction
which is used by another phi node phi2 which is only used by and only uses
the invoke, then phi2 would be deleted but not the invoke instruction and
not the original phi node.

llvm-svn: 126129

1 files changed, 3 insertions, 2 deletions

diff --git a/llvm/lib/Transforms/Utils/Local.cpp b/llvm/lib/Transforms/Utils/Local.cpp
index 40a56b0c99a..3f789fa8658 100644
--- a/llvm/lib/Transforms/Utils/Local.cpp
+++ b/llvm/lib/Transforms/Utils/Local.cpp
@@ -282,7 +282,7 @@ static bool areAllUsesEqual(Instruction *I) {
 /// dead PHI node, due to being a def-use chain of single-use nodes that
 /// either forms a cycle or is terminated by a trivially dead instruction,
 /// delete it.  If that makes any of its operands trivially dead, delete them
-/// too, recursively.  Return true if the PHI node is actually deleted.
+/// too, recursively.  Return true if a change was made.
 bool llvm::RecursivelyDeleteDeadPHINode(PHINode *PN) {
   SmallPtrSet<Instruction*, 4> Visited;
   for (Instruction *I = PN; areAllUsesEqual(I) && !I->mayHaveSideEffects();
@@ -295,7 +295,8 @@ bool llvm::RecursivelyDeleteDeadPHINode(PHINode *PN) {
     if (!Visited.insert(I)) {
       // Break the cycle and delete the instruction and its operands.
       I->replaceAllUsesWith(UndefValue::get(I->getType()));
-      return RecursivelyDeleteTriviallyDeadInstructions(I);
+      (void)RecursivelyDeleteTriviallyDeadInstructions(I);
+      return true;
     }
   }
   return false;