Add a comment to SelectionDAG::ReplaceAllUsesWith to describe a subtle

iteraction with SelectionDAG CSE.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@62713 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/include/llvm/CodeGen/SelectionDAG.h b/include/llvm/CodeGen/SelectionDAG.h
index d7802d3..f93b620 100644 (file)
--- a/include/llvm/CodeGen/SelectionDAG.h
+++ b/include/llvm/CodeGen/SelectionDAG.h
@@ -680,6 +680,11 @@ public:
   /// informed about nodes that are deleted and modified due to recursive
   /// changes in the dag.
   ///
+  /// These functions only replace all existing uses. It's possible that as
+  /// these replacements are being performed, CSE may cause the From node
+  /// to be given new uses. These new uses of From are left in place, and
+  /// not automatically transfered to To.
+  ///
   void ReplaceAllUsesWith(SDValue From, SDValue Op,
                           DAGUpdateListener *UpdateListener = 0);
   void ReplaceAllUsesWith(SDNode *From, SDNode *To,