Fix a fixme in CondPropagate.cpp by moving a PhiNode optimization into

BasicBlock's removePredecessor routine.  This requires shuffling around
the definition and implementation of hasContantValue from Utils.h,cpp into
Instructions.h,cpp

llvm-svn: 22664

1 files changed, 9 insertions, 1 deletions

diff --git a/llvm/lib/VMCore/BasicBlock.cpp b/llvm/lib/VMCore/BasicBlock.cpp
index 98d12d8f138..407080cf68b 100644
--- a/llvm/lib/VMCore/BasicBlock.cpp
+++ b/llvm/lib/VMCore/BasicBlock.cpp
@@ -189,8 +189,16 @@ void BasicBlock::removePredecessor(BasicBlock *Pred,
     // Okay, now we know that we need to remove predecessor #pred_idx from all
     // PHI nodes.  Iterate over each PHI node fixing them up
     PHINode *PN;
-    for (iterator II = begin(); (PN = dyn_cast<PHINode>(II)); ++II)
+    for (iterator II = begin(); (PN = dyn_cast<PHINode>(II)); ++II) {
       PN->removeIncomingValue(Pred, false);
+      // If all incoming values to the Phi are the same, we can replace the Phi
+      // with that value.
+      if (Value *PNV = PN->hasConstantValue())
+        if (!isa<Instruction>(PNV)) {
+          PN->replaceAllUsesWith(PNV);
+          PN->eraseFromParent();
+        }
+    }
   }
 }