Index: lib/Transforms/Scalar/SCCP.cpp
===================================================================
--- lib/Transforms/Scalar/SCCP.cpp
+++ lib/Transforms/Scalar/SCCP.cpp
@@ -918,6 +918,15 @@
   // Otherwise, one of our operands is overdefined.  Try to produce something
   // better than overdefined with some tricks.
 
+  // If this is a xor %blah, %blah, it doesn't matter if %blah is overdefined,
+  // we can just mark that constant.
+  if (I.getOpcode() == Instruction::Xor) {
+	  if (I.getOperand(0) == I.getOperand(1)) {
+		  markConstant(IV, &I, Constant::getNullValue(I.getType()));
+		  return;
+	  }
+  }
+
   // If this is an AND or OR with 0 or -1, it doesn't matter that the other
   // operand is overdefined.
   if (I.getOpcode() == Instruction::And || I.getOpcode() == Instruction::Or) {
Index: test/Transforms/SCCP/xor.ll
===================================================================
--- /dev/null
+++ test/Transforms/SCCP/xor.ll
@@ -0,0 +1,10 @@
+; RUN: opt -S -sccp %s | FileCheck %s
+
+define i32 @myxor(i32 %x) {
+  %patatino = xor i32 %x, %x
+  ret i32 %patatino
+}
+
+; CHECK: define i32 @myxor(i32 %x) {
+; CHECK-NEXT:   ret i32 0
+; CHECK-NEXT: }