- implemented instcombine of phi (X, X, X) -> X

llvm-svn: 3397

1 files changed, 12 insertions, 1 deletions

diff --git a/llvm/lib/Transforms/Scalar/InstructionCombining.cpp b/llvm/lib/Transforms/Scalar/InstructionCombining.cpp
index 088a758c7f5..71c2cc6e3f5 100644
--- a/llvm/lib/Transforms/Scalar/InstructionCombining.cpp
+++ b/llvm/lib/Transforms/Scalar/InstructionCombining.cpp
@@ -594,10 +594,21 @@ Instruction *InstCombiner::visitCastInst(CastInst &CI) {
 //
 Instruction *InstCombiner::visitPHINode(PHINode &PN) {
   // If the PHI node only has one incoming value, eliminate the PHI node...
+  if (PN.getNumIncomingValues() == 0)
+    return ReplaceInstUsesWith(PN, Constant::getNullValue(PN.getType()));
   if (PN.getNumIncomingValues() == 1)
     return ReplaceInstUsesWith(PN, PN.getIncomingValue(0));
+  
+  // Otherwise if all of the incoming values are the same for the PHI, replace
+  // the PHI node with the incoming value.
+  //
+  Value *InVal = PN.getIncomingValue(0);
+  for (unsigned i = 1, e = PN.getNumIncomingValues(); i != e; ++i)
+    if (PN.getIncomingValue(i) != InVal)
+      return 0;  // Not the same, bail out.
 
-  return 0;
+  // All of the incoming values are the same, replace the PHI node now.
+  return ReplaceInstUsesWith(PN, InVal);
 }