[BasicBlockUtils] Do not move loop metadata if outer loop header.

Fixes a bug preventing moving the loop's metadata to an outer loop's header,
which happens if the loop's exit is also the header of an outer loop.

Adjusts test for above.

Fixes #55416.

Differential Revision: https://reviews.llvm.org/D125574

1 files changed, 5 insertions, 1 deletions

diff --git a/llvm/lib/Transforms/Utils/BasicBlockUtils.cpp b/llvm/lib/Transforms/Utils/BasicBlockUtils.cpp
index fd92a39..e9983ff 100644
--- a/llvm/lib/Transforms/Utils/BasicBlockUtils.cpp
+++ b/llvm/lib/Transforms/Utils/BasicBlockUtils.cpp
@@ -1162,7 +1162,11 @@ SplitBlockPredecessorsImpl(BasicBlock *BB, ArrayRef<BasicBlock *> Preds,
     if (NewLatch != OldLatch) {
       MDNode *MD = OldLatch->getTerminator()->getMetadata("llvm.loop");
       NewLatch->getTerminator()->setMetadata("llvm.loop", MD);
-      OldLatch->getTerminator()->setMetadata("llvm.loop", nullptr);
+      // It's still possible that OldLatch is the latch of another inner loop,
+      // in which case we do not remove the metadata.
+      Loop *IL = LI->getLoopFor(OldLatch);
+      if (IL && IL->getLoopLatch() != OldLatch)
+        OldLatch->getTerminator()->setMetadata("llvm.loop", nullptr);
     }
   }