Constant exprs are not efficiently negatable in practice. This disables

turning X - (constantexpr) into X + (-constantexpr) among other things.

llvm-svn: 18935

1 files changed, 3 insertions, 4 deletions

diff --git a/llvm/lib/Transforms/Scalar/InstructionCombining.cpp b/llvm/lib/Transforms/Scalar/InstructionCombining.cpp
index 807653b56d1..f78a14d4273 100644
--- a/llvm/lib/Transforms/Scalar/InstructionCombining.cpp
+++ b/llvm/lib/Transforms/Scalar/InstructionCombining.cpp
@@ -309,10 +309,9 @@ static inline Value *dyn_castNegVal(Value *V) {
   if (BinaryOperator::isNeg(V))
     return BinaryOperator::getNegArgument(cast<BinaryOperator>(V));
 
-  // Constants can be considered to be negated values if they can be folded...
-  if (Constant *C = dyn_cast<Constant>(V))
-    if (!isa<UndefValue>(C))
-      return ConstantExpr::getNeg(C);
+  // Constants can be considered to be negated values if they can be folded.
+  if (ConstantInt *C = dyn_cast<ConstantInt>(V))
+    return ConstantExpr::getNeg(C);
   return 0;
 }