From 56b092e4cd2679d5d2dc892c722fa912e0dccbf9 Mon Sep 17 00:00:00 2001
From: Dan Gohman <gohman@apple.com>
Date: Mon, 30 Aug 2010 21:18:41 +0000
Subject: [PATCH] Add comments explaining why it's not necessary to include the
 is-function-local flag in metadata uniquing bits.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@112528 91177308-0d34-0410-b5e6-96231b3b80d8
---
 lib/VMCore/Metadata.cpp | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/lib/VMCore/Metadata.cpp b/lib/VMCore/Metadata.cpp
index 17e0bc28da0..b9f97dbf603 100644
--- a/lib/VMCore/Metadata.cpp
+++ b/lib/VMCore/Metadata.cpp
@@ -190,6 +190,8 @@ MDNode *MDNode::getMDNode(LLVMContext &Context, Value *const *Vals,
 
   // Add all the operand pointers. Note that we don't have to add the
   // isFunctionLocal bit because that's implied by the operands.
+  // Note that if the operands are later nulled out, the node will be
+  // removed from the uniquing map.
   FoldingSetNodeID ID;
   for (unsigned i = 0; i != NumVals; ++i)
     ID.AddPointer(Vals[i]);
@@ -276,6 +278,8 @@ Value *MDNode::getOperand(unsigned i) const {
 void MDNode::Profile(FoldingSetNodeID &ID) const {
   // Add all the operand pointers. Note that we don't have to add the
   // isFunctionLocal bit because that's implied by the operands.
+  // Note that if the operands are later nulled out, the node will be
+  // removed from the uniquing map.
   for (unsigned i = 0, e = getNumOperands(); i != e; ++i)
     ID.AddPointer(getOperand(i));
 }
@@ -326,7 +330,8 @@ void MDNode::replaceOperand(MDNodeOperand *Op, Value *To) {
 
   // If we are dropping an argument to null, we choose to not unique the MDNode
   // anymore.  This commonly occurs during destruction, and uniquing these
-  // brings little reuse.
+  // brings little reuse.  Also, this means we don't need to include
+  // isFunctionLocal bits in FoldingSetNodeIDs for MDNodes.
   if (To == 0) {
     setIsNotUniqued();
     return;