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

[Igor Kirillov via llvm-commits]

================
@@ -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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igogo-x86 wrote:

Before the patch, we could get into this message when:

```
  // Negative distances are not plausible dependencies.
  if (SE.isKnownNonPositive(Dist)) {
    if (SE.isKnownNonNegative(Dist)) {
```

But that's equivalent to `Dist->isZero()`, which has a narrower range and is faster than `!SE.isKnownNonZero(Dist)`

Also, is there a difference between  `TypeSize AStoreSz = DL.getTypeStoreSize(ATy);` and `uint64_t ASz = DL.getTypeAllocSize(ATy);` in our context?


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