[LoopUnroll] Don't crash trying to unroll loop with EH pad exit

We do not support splitting cleanuppad or catchswitches.  This is
problematic for passes which assume that a loop is in loop simplify
form (the loop would have a dedicated exit block instead of sharing it).

While it isn't great that we don't support this for cleanups, we still
cannot make loop-simplify form an assertable precondition because
indirectbr will also disable these sorts of CFG cleanups.

This fixes PR28132.

llvm-svn: 272739

1 files changed, 5 insertions, 0 deletions

diff --git a/llvm/lib/Transforms/Scalar/LoopUnrollPass.cpp b/llvm/lib/Transforms/Scalar/LoopUnrollPass.cpp
index 65eab475b69..91af4a1922c 100644
--- a/llvm/lib/Transforms/Scalar/LoopUnrollPass.cpp
+++ b/llvm/lib/Transforms/Scalar/LoopUnrollPass.cpp
@@ -922,6 +922,11 @@ static bool tryToUnrollLoop(Loop *L, DominatorTree &DT, LoopInfo *LI,
     DEBUG(dbgs() << "  Not unrolling loop with inlinable calls.\n");
     return false;
   }
+  if (!L->isLoopSimplifyForm()) {
+    DEBUG(
+        dbgs() << "  Not unrolling loop which is not in loop-simplify form.\n");
+    return false;
+  }
 
   // Find trip count and trip multiple if count is not available
   unsigned TripCount = 0;