[llvm] [LAA] Pass maximum stride to isSafeDependenceDistance. (PR #90036)

[Michael Kruse via llvm-commits]

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@@ -2046,14 +2046,15 @@ MemoryDepChecker::Dependence::DepType MemoryDepChecker::isDependent(
 
   ScalarEvolution &SE = *PSE.getSE();
   auto &DL = InnermostLoop->getHeader()->getModule()->getDataLayout();
+  uint64_t MaxStride = std::max(StrideA, StrideB);
 
-  // If the distance between the acecsses is larger than their absolute stride
-  // multiplied by the backedge taken count, the accesses are independet, i.e.
-  // they are far enough appart that accesses won't access the same location
-  // across all loop ierations.
-  if (HasSameSize && CommonStride &&
+  // If the distance between the acecsses is larger than their maximum absolute
+  // stride multiplied by the backedge taken count, the accesses are independet,
+  // i.e. they are far enough appart that accesses won't access the same
+  // location across all loop ierations.
+  if (HasSameSize &&
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Meinersbur wrote:

I think StrideA/StrideB are set to 0 if the stride could not be computed (and then indistinguishable from no stride; `getPtrStride` actually returns an `std::optional` but it is lost somewhere). I think we must ensure that neither StrideA nor StrideB are zero.

Or even better: Keep passing on the `std::optional` from `getPtrStride`.

Or even better: Use `StrideA` or `StrideB` depending on whether `Dist` is negative or positive.

https://github.com/llvm/llvm-project/pull/90036