diff --git a/llvm/include/llvm/Analysis/MemorySSA.h b/llvm/include/llvm/Analysis/MemorySSA.h
index f119316129b32c..fa333001156b0a 100644
--- a/llvm/include/llvm/Analysis/MemorySSA.h
+++ b/llvm/include/llvm/Analysis/MemorySSA.h
@@ -346,6 +346,9 @@ class MemoryUse final : public MemoryUseOrDef {
     setOperand(0, DMA);
   }
 
+  /// The defining access of a MemoryUses are always optimized if queried from
+  /// outside MSSA construction itself.  This result is only useful inside
+  /// the MSSA implementation.
   bool isOptimized() const {
     return getDefiningAccess() && OptimizedID == getDefiningAccess()->getID();
   }