[LAA] Make sure MaxVF for Store-Load forward safe dep distances is pow2.

MaxVF computed in couldPreventStoreLoadFowrard may not be a power of 2,
as CommonStride may not be a power-of-2.

This can cause crashes after 78777a20. Use bit_floor to make sure it is
a suitable power-of-2.

Fixes https://github.com/llvm/llvm-project/issues/134696.

1 files changed, 2 insertions, 1 deletions

diff --git a/llvm/lib/Analysis/LoopAccessAnalysis.cpp b/llvm/lib/Analysis/LoopAccessAnalysis.cpp
index a37ed5c..0cb1332 100644
--- a/llvm/lib/Analysis/LoopAccessAnalysis.cpp
+++ b/llvm/lib/Analysis/LoopAccessAnalysis.cpp
@@ -1781,7 +1781,8 @@ bool MemoryDepChecker::couldPreventStoreLoadForward(uint64_t Distance,
           MaxStoreLoadForwardSafeDistanceInBits &&
       MaxVFWithoutSLForwardIssuesPowerOf2 !=
           VectorizerParams::MaxVectorWidth * TypeByteSize) {
-    uint64_t MaxVF = MaxVFWithoutSLForwardIssuesPowerOf2 / CommonStride;
+    uint64_t MaxVF =
+        bit_floor(MaxVFWithoutSLForwardIssuesPowerOf2 / CommonStride);
     uint64_t MaxVFInBits = MaxVF * TypeByteSize * 8;
     MaxStoreLoadForwardSafeDistanceInBits =
         std::min(MaxStoreLoadForwardSafeDistanceInBits, MaxVFInBits);