[llvm] [VPlan] Add VPSingleDefBundleRecipe, replacing extended reduction recipes. (PR #144281)

[via llvm-commits]

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@@ -525,14 +525,13 @@ class VPSingleDefRecipe : public VPRecipeBase, public VPValue {
 
   static inline bool classof(const VPRecipeBase *R) {
     switch (R->getVPDefID()) {
+    case VPRecipeBase::VPBundleSC:
----------------
ayalz wrote:

```suggestion
    case VPRecipeBase::VPSingleDefBundleSC:
```
to be consistent, and place below following lex order.

But would `VPExpressionRecipe` be better - conveying the notion that (a) it produces a single value (b) out of multiple simpler components - which are potentially side-effect-free(?) and potentially (sub)expressions themselves(?). I.e., a bundle recipe can potentially be bundled inside another bundle recipe, unbundle() can be recursive. Worth commenting that this may be possible but that currently bundle recipes are restricted to flat/single-level bundling.

https://github.com/llvm/llvm-project/pull/144281