[LV] Prevent interleaving if computeMaxVF returned None.

As discussed in D57382, interleaving should be avoided if computeMaxVF
returns None, same as we currently do for vectorization.

Fixes https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=6477

Reviewers: Ayal, dcaballe, hsaito, mkuper, rengolin

Reviewed By: Ayal

Differential Revision: https://reviews.llvm.org/D57837

llvm-svn: 353461

1 files changed, 6 insertions, 2 deletions

diff --git a/llvm/lib/Transforms/Vectorize/LoopVectorizationPlanner.h b/llvm/lib/Transforms/Vectorize/LoopVectorizationPlanner.h
index 7e9fee85fc8..7264eb97e1b 100644
--- a/llvm/lib/Transforms/Vectorize/LoopVectorizationPlanner.h
+++ b/llvm/lib/Transforms/Vectorize/LoopVectorizationPlanner.h
@@ -171,6 +171,9 @@ struct VectorizationFactor {
   unsigned Width;
   // Cost of the loop with that width
   unsigned Cost;
+
+  // Width 1 means no vectorization, cost 0 means uncomputed cost.
+  static VectorizationFactor Disabled() { return {1, 0}; }
 };
 
 /// Planner drives the vectorization process after having passed
@@ -221,8 +224,9 @@ public:
                            LoopVectorizationCostModel &CM)
       : OrigLoop(L), LI(LI), TLI(TLI), TTI(TTI), Legal(Legal), CM(CM) {}
 
-  /// Plan how to best vectorize, return the best VF and its cost.
-  VectorizationFactor plan(bool OptForSize, unsigned UserVF);
+  /// Plan how to best vectorize, return the best VF and its cost, or None if
+  /// vectorization and interleaving should be avoided up front.
+  Optional<VectorizationFactor> plan(bool OptForSize, unsigned UserVF);
 
   /// Use the VPlan-native path to plan how to best vectorize, return the best
   /// VF and its cost.