[llvm] [VPlan][NFC] Add cost for `VPWidenMemoryRecipe`. (PR #105614)

[Elvis Wang via llvm-commits]

ElvisWang123 wrote:

> > > > With the change it should also be possible to remove `VPWidenMemoryRecipe` from `getInstructionForCost` in `VPlan.cpp`
> > > 
> > > 
> > > Still missing?
> > 
> > 
> > Remove `VPWidenMemoryRecipe` from `getInstructionForCost` will cause a test fail due to different VF between legacy model. Maybe leave a TODO behind to revisit it when we don't need to compare to the legacy model?
> 
> yes that would be great, together with an explanation that VPWidenMemoryRecipe case in getInstructionForCost still being needed for force-target-instruction handling.

Done, thanks!

https://github.com/llvm/llvm-project/pull/105614