[llvm] [LAA] Be more precise on different store sizes (PR #122318)

[Ramkumar Ramachandra via llvm-commits]

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@@ -2091,6 +2089,17 @@ MemoryDepChecker::getDependenceDistanceStrideAndSize(
     return Dependence::Unknown;
   }
 
+  // When the distance is possibly zero, we're reading/writing the same memory
+  // location: if the store sizes are not equal, fail with an unknown
+  // dependence.
+  TypeSize AStoreSz = DL.getTypeStoreSize(ATy);
+  TypeSize BStoreSz = DL.getTypeStoreSize(BTy);
+  if (AStoreSz != BStoreSz && !SE.isKnownNonZero(Dist)) {
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artagnon wrote:

I think `SE.isKnownNon{Positive,Negative}` is equivalent to `!SE.isKnownNonZero`. As @fhahn mentions, isZero is too narrow, and can miss cases when the distance could be zero. Yes, store size is different from alloc size, although one can be computed from the other (see the corresponding functions).

https://github.com/llvm/llvm-project/pull/122318