enhance RecursivelyDeleteTriviallyDeadInstructions to make

PHIs dead if they are single-value.

llvm-svn: 60194

1 files changed, 9 insertions, 0 deletions

diff --git a/llvm/lib/Transforms/Utils/Local.cpp b/llvm/lib/Transforms/Utils/Local.cpp
index 1e1b3869446..cab7f03ab0f 100644
--- a/llvm/lib/Transforms/Utils/Local.cpp
+++ b/llvm/lib/Transforms/Utils/Local.cpp
@@ -190,6 +190,15 @@ void llvm::RecursivelyDeleteTriviallyDeadInstructions(Value *V,
   while (!Insts.empty()) {
     I = *Insts.begin();
     Insts.erase(I);
+    
+    // If this is a PHI node, we may be able to make it dead if we know all the
+    // input values are the same.
+    if (PHINode *PN = dyn_cast<PHINode>(I)) {
+      if (Value *PNV = PN->hasConstantValue())
+        PN->replaceAllUsesWith(PNV);
+    }
+    
+    // Okay, if the instruction is dead, delete it.
     if (!isInstructionTriviallyDead(I))
       continue;