[LoopVersioning] Require loop-simplify form for loop versioning.

Summary:
Requiring loop-simplify form for loop versioning ensures that the
runtime check block always dominates the exit block.
    
This patch closes #30958 (https://llvm.org/bugs/show_bug.cgi?id=30958).

Reviewers: silviu.baranga, hfinkel, anemet, ashutosh.nema

Subscribers: ashutosh.nema, mzolotukhin, efriedma, hfinkel, llvm-commits

Differential Revision: https://reviews.llvm.org/D27469

llvm-svn: 290116

1 files changed, 5 insertions, 0 deletions

diff --git a/llvm/lib/Transforms/Scalar/LoopLoadElimination.cpp b/llvm/lib/Transforms/Scalar/LoopLoadElimination.cpp
index 8e83c4700aa..08e7acdaaf7 100644
--- a/llvm/lib/Transforms/Scalar/LoopLoadElimination.cpp
+++ b/llvm/lib/Transforms/Scalar/LoopLoadElimination.cpp
@@ -517,6 +517,11 @@ public:
         return false;
       }
 
+      if (!L->isLoopSimplifyForm()) {
+        DEBUG(dbgs() << "Loop is not is loop-simplify form");
+        return false;
+      }
+
       // Point of no-return, start the transformation.  First, version the loop
       // if necessary.