[llvm] [NVPTX] Preserve v16i8 vector loads when legalizing (PR #67322)

[Pierre-Andre Saulais via llvm-commits]

pasaulais wrote:

> > whether the general improvement in v4i8 lowering would be sufficient to address this particular scenario, too.
> 
> Well, that brought less benefit than I hoped for. Making v4i8 a legal type helps to avoid issues in other areas but does not help much with this particular case. Your changes are still useful and needed.
> 
> > Is it worth separating out the `i8` extraction part from these changes and only keep the `v16i8` load part for now? I have not updated this PR with your suggestions yet as it may need reworking anyway after your `v4i8` work
> 
> Considering that these improvements are independent, it may indeed be a good idea to split them into separate patches.

Thanks. I have integrated your suggestions into the first commit (preserving `v16i8` loads) and removed the second commit from this PR. I'll create a new PR for the `i8` extraction DAG combine when this one is merged.

https://github.com/llvm/llvm-project/pull/67322