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

[Mel Chen via llvm-commits]

Mel-Chen wrote:

Got warning 
```
llvm-project/llvm/lib/Transforms/Vectorize/VPlanRecipes.cpp: In member function ‘virtual llvm::InstructionCost llvm::VPExpressionRecipe::computeCost(llvm::ElementCount, llvm::VPCostContext&) const’:
llvm-project/llvm/lib/Transforms/Vectorize/VPlanRecipes.cpp:2667:1: warning: control reaches end of non-void function [-Wreturn-type]
 }
 ^
 ```

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