Mark hasConstantValue as a const method

llvm-svn: 22666
diff --git a/llvm/lib/VMCore/Instructions.cpp b/llvm/lib/VMCore/Instructions.cpp
index 035edb3..a3bd468 100644
--- a/llvm/lib/VMCore/Instructions.cpp
+++ b/llvm/lib/VMCore/Instructions.cpp
@@ -135,7 +135,7 @@
 /// hasConstantValue - If the specified PHI node always merges together the same
 /// value, return the value, otherwise return null.
 ///
-Value *PHINode::hasConstantValue(bool AllowNonDominatingInstruction) {
+Value *PHINode::hasConstantValue(bool AllowNonDominatingInstruction) const {
   // If the PHI node only has one incoming value, eliminate the PHI node...
   if (getNumIncomingValues() == 1)
     return getIncomingValue(0);