commit 8f0ad582e81e24f2ab35f9e9d2308339c8e8cbeb
author Dan Gohman <gohman@apple.com> Mon Apr 28 16:58:24 2008 +0000
committer Dan Gohman <gohman@apple.com> Mon Apr 28 16:58:24 2008 +0000
tree 0ce6f47a7471f58f537749c16168b76f2dfb2731
parent beb4d8293d5311c4581fd3d914f865e358af53a5

Teach DAGCombine to convert (sext x) to (zext x) when the
sign-bit of x is known to be zero.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@50357 91177308-0d34-0410-b5e6-96231b3b80d8

lib/CodeGen/SelectionDAG/DAGCombiner.cpp

diff --git a/lib/CodeGen/SelectionDAG/DAGCombiner.cpp b/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
index 6ac549b..dc59006 100644
--- a/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
+++ b/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
@@ -2887,6 +2887,10 @@
     if (SCC.Val) return SCC;
   }
   
+  // fold (sext x) -> (zext x) if the sign bit is known zero.
+  if (DAG.SignBitIsZero(N0))
+    return DAG.getNode(ISD::ZERO_EXTEND, VT, N0);
+  
   return SDOperand();
 }