[llvm] [LV][EVL]Support reversed loads/stores. (PR #88025)

[via llvm-commits]

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@@ -9398,7 +9399,14 @@ void VPWidenLoadEVLRecipe::execute(VPTransformState &State) {
   NewLI->addParamAttr(
       0, Attribute::getWithAlignment(NewLI->getContext(), Alignment));
   State.addMetadata(NewLI, LI);
-  State.set(this, NewLI, 0);
+  Instruction *Res = NewLI;
+  if (isReverse()) {
+    Value *MaskVal =
+        Builder.CreateVectorSplat(DataTy->getElementCount(), Builder.getTrue());
+    Res = Builder.CreateIntrinsic(DataTy, Intrinsic::experimental_vp_reverse,
+                                  {Res, MaskVal, EVL}, nullptr, "vp.reverse");
+  }
----------------
ayalz wrote:

The values were loaded into `Res` under (possibly partial) `Mask`, should they also be reversed under (possibly reversed) Mask, rather than under an all-true mask?

If the latter, can it be reused:
```suggestion
  if (isReverse())
    Res = Builder.CreateIntrinsic(DataTy, Intrinsic::experimental_vp_reverse,
                                  {Res, AllTrueMask, EVL}, nullptr, "vp.reverse");
```

https://github.com/llvm/llvm-project/pull/88025