Fix a corner case in updating LoopInfo after fully unrolling an outer loop.

The loop tree's inclusive block lists are painful and expensive to
update. (I have no idea why they're inclusive). The design was
supposed to handle this case but the implementation missed it and my
unit tests weren't thorough enough.

Fixes PR11335: loop unroll update.

llvm-svn: 144970

1 files changed, 9 insertions, 11 deletions

diff --git a/llvm/lib/Analysis/LoopInfo.cpp b/llvm/lib/Analysis/LoopInfo.cpp
index 85aaccaefc3..c7833bf7bb6 100644
--- a/llvm/lib/Analysis/LoopInfo.cpp
+++ b/llvm/lib/Analysis/LoopInfo.cpp
@@ -477,21 +477,19 @@ void UnloopUpdater::updateBlockParents() {
 /// removeBlocksFromAncestors - Remove unloop's blocks from all ancestors below
 /// their new parents.
 void UnloopUpdater::removeBlocksFromAncestors() {
-  // Remove unloop's blocks from all ancestors below their new parents.
+  // Remove all unloop's blocks (including those in nested subloops) from
+  // ancestors below the new parent loop.
   for (Loop::block_iterator BI = Unloop->block_begin(),
          BE = Unloop->block_end(); BI != BE; ++BI) {
-    Loop *NewParent = LI->getLoopFor(*BI);
-    // If this block is an immediate subloop, remove all blocks (including
-    // nested subloops) from ancestors below the new parent loop.
-    // Otherwise, if this block is in a nested subloop, skip it.
-    if (SubloopParents.count(NewParent))
-      NewParent = SubloopParents[NewParent];
-    else if (Unloop->contains(NewParent))
-      continue;
-
+    Loop *OuterParent = LI->getLoopFor(*BI);
+    if (Unloop->contains(OuterParent)) {
+      while (OuterParent->getParentLoop() != Unloop)
+        OuterParent = OuterParent->getParentLoop();
+      OuterParent = SubloopParents[OuterParent];
+    }
     // Remove blocks from former Ancestors except Unloop itself which will be
     // deleted.
-    for (Loop *OldParent = Unloop->getParentLoop(); OldParent != NewParent;
+    for (Loop *OldParent = Unloop->getParentLoop(); OldParent != OuterParent;
          OldParent = OldParent->getParentLoop()) {
       assert(OldParent && "new loop is not an ancestor of the original");
       OldParent->removeBlockFromLoop(*BI);