[llvm] [VPlan] Sink vector loop region recipes in licm (PR #172343)

[Mel Chen via llvm-commits]

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Mel-Chen wrote:

> So I presume this now gets costed in `isOutsideLoopWorkProfitable`. AFAIK the vector preheader isn't costed?

Yes, the preheader isn't costed.

> FWIW we should probably be sinking this recipe where possible to minimize register pressure, but maybe best to look at doing this as a follow up in another PR so we can add your planContainsAdditionalSimplifications check?

hmm, I’m indeed concerned about the user and def being split between the preheader and the middle block, which is why I chose to sink first. So do you mean we should still hoist first and then sink, and open another PR later to change it to sink-first?



https://github.com/llvm/llvm-project/pull/172343