[llvm] [VPlan] Compute cost for most opcodes in VPWidenRecipe (NFCI). (PR #98764)

[Shih-Po Hung via llvm-commits]

arcbbb wrote:

> @arcbbb what do you think about porting over the implementations from #67647, in particular the memory-op cost ones?

I just spoke with @ElvisWang123 about the recent changes on the VPlan. We’re planning to provide some initial implementations soon.

https://github.com/llvm/llvm-project/pull/98764