[llvm-dev] RFC: CfgTraits/CfgInterface design discussion

Sat Oct 31 12:40:36 PDT 2020

On Sat, Oct 31, 2020 at 12:32 PM Chris Lattner via llvm-dev <
llvm-dev at lists.llvm.org> wrote:

> I agree with Eric here.  There is clearly controversy w.r.t. this patch
> and regardless of what the formally written policy is, it seems best to
> revert this and resolve the outstanding issues.  Keeping it in tree will
> cause more things to be built on top of it, and over constrains the
> discussion about getting to the best possible design.
>
> Sean’s point is also excellent: often it is best to pop out of email and
> into a higher bandwidth communication form (voice, video chat, etc) when
> hitting controversy like this.
>

Yep, Nicolai's reverted the patch (see:
http://lists.llvm.org/pipermail/llvm-dev/2020-October/146107.html ) - the
conversation's got a bit fragmented between the review thread, new RFC
thread, and rename of that thread) and Alina, Nicolai, and myself chatted
offline on Thursday - think we came to some pieces of common understanding.
Nicolai's going to work up a new RFC (
https://reviews.llvm.org/D83088#2365320 ,
http://lists.llvm.org/pipermail/llvm-dev/2020-October/146258.html )  we can
hopefully get a few eyes on/clarify some things to make progress.

- Dave

>
> -Chris
>
>
> On Oct 26, 2020, at 4:26 PM, Sean Silva via llvm-dev <
> llvm-dev at lists.llvm.org> wrote:
>
> Also, if this hasn't happened already, I would recommend some 1-on-1 (at
> least over chat, or if possible video call) between Nicolai and Dave. In
> the past, I have found this to fairly quickly come to consensus about
> design direction (though of course please update any relevant threads with
> the takeaways of such private discussions!).
>
> -- Sean Silva
>
> On Mon, Oct 26, 2020 at 1:05 PM Eric Christopher via llvm-dev <
> llvm-dev at lists.llvm.org> wrote:
>
>> Hi Nicolai,
>>
>> I've been watching this and the associated review that +Mehdi AMINI
>> <joker.eph at gmail.com> brought up as far as the process.
>>
>> I think you should revert this patch and anything dependent upon it until
>> the review is complete. Dave has many good points in his review and while
>> you pinged there needs to be resolution before applying. In particular,
>> he's probably the most active reviewer in exactly this space right now and
>> is obviously also the right reviewer for this patch.
>>
>> Please revert immediately and thanks. I'm sorry the patch has gotten
>> contentious, but this is a fairly major overhaul and it does happen
>> sometimes.
>>
>> Thanks.
>>
>> -eric
>>
>>
>>
>> On Mon, Oct 26, 2020 at 2:46 PM Renato Golin via llvm-dev <
>> llvm-dev at lists.llvm.org> wrote:
>>
>>> On Sat, 24 Oct 2020 at 23:13, Nicolai Hähnle via llvm-dev <
>>> llvm-dev at lists.llvm.org> wrote:
>>>
>>>> Maybe David wants to forbid this use of dynamic polymorphism outright.
>>>> I think this is unacceptable, so in that case, it seems we have no
>>>> choice but to start a formal process for resolving contentious
>>>> decisions.
>>>
>>>
>>> If this ends up being the case, then you *must* revert the patch until
>>> the matter can be solved.
>>>
>>> But as I said before, I would have reverted it a long time ago.
>>>
>>> (I would still ask people to _please_ be good citizens and allow us to
>>>> make upstream progress in AMDGPU as we usually do while this is
>>>> happening -- I explain my reasoning a bit more below -- but I'd accept
>>>> it based on the rules that are in effect today. Invoking the formal
>>>> process should give all participants the confidence that the question
>>>> doesn't just end up dropped on the floor, and that the in-tree status
>>>> of the code wouldn't implicitly favor either side of the discussion.)
>>>>
>>>
>>> The AMD backend doesn't trump a high-level CFG design decision that
>>> affects *all* back-ends, front-ends and middle-ends.
>>>
>>> If you progress your AMD work on your current assumption and it turns
>>> out people decide against it you will have to revert *all* of it, which is
>>> a lot more substantial (and a potentially dangerous merge) than just this
>>> CFG change.
>>>
>>> I'd also strongly advise people reviewing the remaining work from
>>> approving the patches until this matter can be resolved. This is not a
>>> trivial issue and can have further consequences than just a simple revert.
>>>
>>> And please, do not assume what being a good citizens is. We can all be
>>> good citizens and still overwhelmingly disagree with each other, as long as
>>> we keep it civil.
>>>
>>> I see no evidence of lack of civility from either David or Mehdi. On the
>>> contrary, they're being extremely kind and patient.
>>>
>>> cheers,
>>> --renato
>>> _______________________________________________
>>> LLVM Developers mailing list
>>> llvm-dev at lists.llvm.org
>>> https://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>>>
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