diff --git a/lib/Analysis/InstructionSimplify.cpp b/lib/Analysis/InstructionSimplify.cpp
index cfff9c0..89e55a4 100644
--- a/lib/Analysis/InstructionSimplify.cpp
+++ b/lib/Analysis/InstructionSimplify.cpp
@@ -1348,6 +1348,11 @@
     std::swap(Op0, Op1);
   }
 
+  // A ^ A = 0
+  // Do this first so that we catch the undef ^ undef "idiom".
+  if (Op0 == Op1)
+    return Constant::getNullValue(Op0->getType());
+
   // A ^ undef -> undef
   if (match(Op1, m_Undef()))
     return Op1;
@@ -1356,10 +1361,6 @@
   if (match(Op1, m_Zero()))
     return Op0;
 
-  // A ^ A = 0
-  if (Op0 == Op1)
-    return Constant::getNullValue(Op0->getType());
-
   // A ^ ~A  =  ~A ^ A  =  -1
   if (match(Op0, m_Not(m_Specific(Op1))) ||
       match(Op1, m_Not(m_Specific(Op0))))