Add comment that MDNode::getFunction() is not to be used by performance-critical code (currently only used by AsmWriter)

llvm-svn: 93802

llvm/include/llvm/Metadata.h

@@ -154,7 +154,8 @@ public:
   
   // getFunction - If this metadata is function-local and recursively has a
   // function-local operand, return the first such operand's parent function.
-  // Otherwise, return null. 
+  // Otherwise, return null. getFunction() should not be used for performance-
+  // critical code because it recursively visits all the MDNode's operands.  
   Function *getFunction() const;
 
   // destroy - Delete this node.  Only when there are no uses.

llvm/lib/VMCore/Metadata.cpp

@@ -154,7 +154,8 @@ static Function *assertLocalFunction(const MDNode *N) {
 
 // getFunction - If this metadata is function-local and recursively has a
 // function-local operand, return the first such operand's parent function.
-// Otherwise, return null. 
+// Otherwise, return null. getFunction() should not be used for performance-
+// critical code because it recursively visits all the MDNode's operands.  
 Function *MDNode::getFunction() const {
 #ifndef NDEBUG
   return assertLocalFunction(this);