[NFC] Add clarification comment
llvm-svn: 330677
diff --git a/llvm/lib/Transforms/Utils/LoopRotationUtils.cpp b/llvm/lib/Transforms/Utils/LoopRotationUtils.cpp
index d2a2e40..a7dc34f 100644
--- a/llvm/lib/Transforms/Utils/LoopRotationUtils.cpp
+++ b/llvm/lib/Transforms/Utils/LoopRotationUtils.cpp
@@ -259,8 +259,10 @@
return false;
// Anything ScalarEvolution may know about this loop or the PHI nodes
- // in its header will soon be invalidated, and it can also affect its parent
- // loops as well.
+ // in its header will soon be invalidated. We should also invalidate
+ // all outer loops because insertion and deletion of blocks that happens
+ // during the rotation may violate invariants related to backedge taken
+ // infos in them.
if (SE)
SE->forgetTopmostLoop(L);