[llvm] [LV] Support strided load with a stride of -1 (PR #128718)

[Alexey Bataev via llvm-commits]

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@@ -1115,6 +1115,7 @@ class LoopVectorizationCostModel {
     CM_Widen_Reverse, // For consecutive accesses with stride -1.
     CM_Interleave,
     CM_GatherScatter,
+    CM_Strided,
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alexey-bataev wrote:

Possible in its current state, but not sure it is possible in general. Some (potential) strided memory recipes are currently represented as masked gathers, which require widened pointers. Strided/interleaved mem accesses do not require widened (vector) pointers, so it may affect the cost significantly. I think we need to teach the whole loop vectorizer the strided mem accesses pattern (no matter if the stride is constant, as it is right now, or runtime defined)

https://github.com/llvm/llvm-project/pull/128718