[LoopInterchange] Do not change LI for BBs in child loops.

If a loop with child loops becomes our new inner loop after
interchanging, we only need to update LoopInfo for the blocks defined in
the old outer loop. BBs in child loops will stay there.

Reviewers: efriedma, karthikthecool, mcrosier

Reviewed By: efriedma

Differential Revision: https://reviews.llvm.org/D45970

llvm-svn: 330653

1 files changed, 3 insertions, 0 deletions

diff --git a/llvm/lib/Transforms/Scalar/LoopInterchange.cpp b/llvm/lib/Transforms/Scalar/LoopInterchange.cpp
index cab6acce771..a641afeda03 100644
--- a/llvm/lib/Transforms/Scalar/LoopInterchange.cpp
+++ b/llvm/lib/Transforms/Scalar/LoopInterchange.cpp
@@ -1220,6 +1220,9 @@ void LoopInterchangeTransform::restructureLoops(
   BasicBlock *OuterHeader = NewOuter->getHeader();
   BasicBlock *OuterLatch = NewOuter->getLoopLatch();
   for (BasicBlock *BB : OrigInnerBBs) {
+    // Nothing will change for BBs in child loops.
+    if (LI->getLoopFor(BB) != NewOuter)
+      continue;
     // Remove the new outer loop header and latch from the new inner loop.
     if (BB == OuterHeader || BB == OuterLatch)
       NewInner->removeBlockFromLoop(BB);