[llvm] [VPlan] Add VPExpressionRecipe, 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  single 'expression' recipe,
+/// which should be considered a single entity for cost-modeling and transforms.
+/// The recipe needs to be 'unbundled', i.e. replaced by its individual
+/// expression recipes before execute. The individual expression recipes are
+/// completely disconnected from the def-use graph of other recipes not part of
+/// the expression. Def-use edges between pairs of expression recipes remain
+/// intact, whereas every edge between an expression recipe and a recipe outside
+/// the expression is elevated to connect the non-expression recipe with the
+/// VPExpressionRecipe itself.
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ayalz wrote:

/// Expression recipes currently supported are of integer types only, and are side-effect free.

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