Index: lib/CodeGen/SelectionDAG/SelectionDAG.cpp
===================================================================
--- lib/CodeGen/SelectionDAG/SelectionDAG.cpp
+++ lib/CodeGen/SelectionDAG/SelectionDAG.cpp
@@ -1912,6 +1912,18 @@
     }
   }
 
+  // InstCombine implements:
+  //
+  // icmp X, X -> true/false
+  // X icmp undef -> true/false.  For example, icmp ugt %X, undef -> false
+  // because X could be 0.
+  //
+  // fcmp pred X, undef -> undef
+  //
+  // Do the same here
+  if (N1 == N2 || N1.getOpcode() == ISD::UNDEF || N1.getOpcode() == ISD::UNDEF)
+    return getConstant(isTrueWhenEqual(Cond), VT);
+
   // Could not fold it.
   return SDValue();
 }