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

[Florian Hahn via llvm-commits]

================
@@ -9478,10 +9486,18 @@ void VPWidenStoreEVLRecipe::execute(VPTransformState &State) {
   CallInst *NewSI = nullptr;
   Value *StoredVal = State.get(StoredValue, 0);
   Value *EVL = State.get(getEVL(), VPIteration(0, 0));
-  // FIXME: Support reverse store after vp_reverse is added.
-  Value *Mask = getMask()
-                    ? State.get(getMask(), 0)
-                    : Builder.CreateVectorSplat(State.VF, Builder.getTrue());
+  if (isReverse())
+    // Use cheap all-true mask for reverse rather than actual mask, it does not
+    // affect the result.
+    StoredVal = createReverseEVL(Builder, StoredVal, EVL, "vp.reverse");
+  Value *Mask = nullptr;
+  if (getMask()) {
----------------
fhahn wrote:

```suggestion
  if (VPValue *VPMask = getMask()) {
      Mask = State.get(VPMask, 0);
```

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