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

[Ramkumar Ramachandra via llvm-commits]

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@@ -2061,14 +2061,12 @@ MemoryDepChecker::getDependenceDistanceStrideAndSize(
     return MemoryDepChecker::Dependence::Unknown;
   }
 
-  TypeSize AStoreSz = DL.getTypeStoreSize(ATy);
-  TypeSize BStoreSz = DL.getTypeStoreSize(BTy);
-
-  // If store sizes are not the same, set TypeByteSize to zero, so we can check
-  // it in the caller isDependent.
   uint64_t ASz = DL.getTypeAllocSize(ATy);
   uint64_t BSz = DL.getTypeAllocSize(BTy);
-  uint64_t TypeByteSize = (AStoreSz == BStoreSz) ? BSz : 0;
+
+  // The TypeByteSize is used to scale Distance and VF. In these contexts, the
+  // only size that matters is the size of the Sink.
+  uint64_t TypeByteSize = BSz;
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artagnon wrote:

So, TypeByteSize is used in couldPreventStoreLoadForward, and in the MinDistanceNeeded computation in the same way: it is used to scale distance and VF; isn't the size of the sink sufficient? It is also used in areStridedAccessesIndependent, where Distance % TypeByteSize should be zero: isn't the size of the sink sufficient here as well? Not sure why the size of the source should be considered in these cases.

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