[llvm-branch-commits] [llvm] [LV] Mask off possibly aliasing vector lanes (PR #100579)

[Benjamin Maxwell via llvm-branch-commits]

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@@ -3073,6 +3075,56 @@ struct VPWidenStoreEVLRecipe final : public VPWidenMemoryRecipe {
   }
 };
 
+// Given a pointer A that is being stored to, and pointer B that is being
+// read from, both with unknown lengths, create a mask that disables
+// elements which could overlap across a loop iteration. For example, if A
+// is X and B is X + 2 with VF being 4, only the final two elements of the
+// loaded vector can be stored since they don't overlap with the stored
+// vector. %b.vec = load %b ; = [s, t, u, v]
+// [...]
+// store %a, %b.vec ; only u and v can be stored as their addresses don't
+// overlap with %a + (VF - 1)
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MacDue wrote:

This is specifically RAW? Of something like:
```
store A[x]
load A[x + 2] 
```
Perhaps I'm muddled on what "final two elements" means, but isn't the first two elements store that is valid (so it won't overwrite the elements for the load)?



https://github.com/llvm/llvm-project/pull/100579