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

[via llvm-commits]

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@@ -2930,6 +2719,122 @@ class VPBranchOnMaskRecipe : public VPRecipeBase {
   }
 };
 
+/// A recipe to combine multiple recipes into a 'bundle' recipe, which should be
+/// considered a single entity for cost-modeling and transforms. The recipe
+/// needs to be 'unbundled', i.e. replaced by its bundled recipes before
+/// execute. The bundled recipes are completely disconnected from the def-use
+/// graph of other, non-bundled recipes. Def-use edges between pairs of bundled
+/// recipes remain intact, whereas every edge between a bundled and a
+/// non-bundled recipe is elevated to connect the non-bundled recipe with the
+/// VPSingleDefBundleRecipe itself.
+class VPSingleDefBundleRecipe : public VPSingleDefRecipe {
+  /// Recipes bundled together in this VPSingleDefBundleRecipe.
+  SmallVector<VPSingleDefRecipe *> BundledRecipes;
+
+  /// Temporary VPValues used for external operands of the bundle, i.e. operands
+  /// not defined by recipes in the bundle.
+  SmallVector<VPValue *> BundleLiveInPlaceholders;
+
+  enum class BundleTypes {
+    /// Represents an inloop extended reduction operation, performing a
+    /// reduction on a extended vector operand into a scalar value, and adding
+    /// the result to a chain.
+    ExtendedReduction,
+    /// Represent an inloop multiply-accumulate reduction, multiplying the
+    /// extended vector operands, performing a reduction.add on the result, and
+    /// adding the scalar result to a chain.
+    ExtMulAccumulateReduction,
----------------
ayalz wrote:

```suggestion
    ExtMulAccReduction,
```
(also aligning with TTI API)

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