From 187db7b950e57e2f1f10b57e7ee2a7f38e8965c0 Mon Sep 17 00:00:00 2001
From: Dan Gohman <gohman@apple.com>
Date: Mon, 28 Apr 2008 18:47:17 +0000
Subject: [PATCH] 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
---
 lib/CodeGen/SelectionDAG/DAGCombiner.cpp | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/lib/CodeGen/SelectionDAG/DAGCombiner.cpp b/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
index dc59006fcfb..28f32d3d3b9 100644
--- 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();