Evan pointed out that folding sext to zext may not be correct

if the zext is not legal.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@50368 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/lib/CodeGen/SelectionDAG/DAGCombiner.cpp b/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
index dc59006fcfbe54ffd32315add3901b955b83d834..28f32d3d3b967deb4ee38aacc9c7e87669217b7f 100644 (file)
--- a/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
+++ b/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
@@ -2888,7 +2888,8 @@ SDOperand DAGCombiner::visitSIGN_EXTEND(SDNode *N) {
   }
   
   // fold (sext x) -> (zext x) if the sign bit is known zero.
-  if (DAG.SignBitIsZero(N0))
+  if ((!AfterLegalize || TLI.isOperationLegal(ISD::ZERO_EXTEND, VT)) &&
+      DAG.SignBitIsZero(N0))
     return DAG.getNode(ISD::ZERO_EXTEND, VT, N0);
   
   return SDOperand();