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

[Mel Chen 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,
----------------
Mel-Chen wrote:

> @fhahn Do we currently have a VPlan-based scalarization transformation? If not, do we need to install one before running `legalizeAndOptimizeInductions`?

Hmm...answered it by myself. Looks like just need some fix in `legalizeAndOptimizeInductions`. I will try to fix it tomorrow:)
```
    // Try to narrow wide and replicating recipes to uniform recipes, based on
    // VPlan analysis.
    // TODO: Apply to all recipes in the future, to replace legacy uniformity
    // analysis.
```


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