[PATCH] D32530: [SVE][IR] Scalable Vector IR Type

[Diana Picus via Phabricator via llvm-commits]

rovka added a comment.

In D32530#1453182 <https://reviews.llvm.org/D32530#1453182>, @sebpop wrote:

> In D32530#1452773 <https://reviews.llvm.org/D32530#1452773>, @rovka wrote:
>
> > In D32530#1451505 <https://reviews.llvm.org/D32530#1451505>, @lebedev.ri wrote:
> >
> > > I'd advise caution here, it's really significant/impactful change, and a single sign-off is a bit worrying.
> >
>
>
> There were several people who voted for a scalable vector type in the llvm-dev thread that I referred to
>  http://lists.llvm.org/pipermail/llvm-dev/2019-March/131137.html
>  Maybe those people can also sign-off to accept this change.
>
> I am somewhat against extending the IR with the SV type
>  and I recognize that as we stand today adding the SV type is a good way to get ARM-SVE support in LLVM.


I think this patch is a good start and I don't mind having it merged as is, I was just suggesting a way forward since it seems people are still hesitating. While there seems to be some consensus on moving forward with native types, I'm sure many of the details are still somewhat fuzzy. In my opinion having more patches reviewed would make those details clear, and it would thus make it easier to get more sign-offs on this patch as well.

>> I agree that this is a significant change and I can understand why people are a bit nervous about merging it. Would it help if we had more middle-end patches reviewed before committing, so people could have a better understanding of the impact? Off the top of my head, the rework of D35137 <https://reviews.llvm.org/D35137> would be interesting, and also constant handling.
>> 
>> Can you also tell us what the plan is regarding all the places in the optimizer that may need updating to handle the new vectors?
> 
> A patch series has been posted for review, see section 7. in
>  http://lists.llvm.org/pipermail/llvm-dev/2018-June/123780.html

My understanding is that Graham is reworking some of those. Some were only RFC to begin with, some have been abandoned since, and in any case there has been some back-and-forth on the mailing list since then. I think now would be a good time to rebase/update all the patches that are still relevant so people can see the current version of things.

Also, my question regarding updating the optimizer still stands, I don't think I've seen patches related to updating the existing passes to take the 'scalable' property into account. While in some places it's likely to have no impact, I'd be very surprised if you could pass an IR file with scalable types through the optimizer and not get a soup of fixed-width and scalable vectors out the other end (or the corresponding assertions about mismatched types). I'd be happy to help deal with that churn, by the way :) that's rather why I was asking about the plan.


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