[PATCH] D102568: [Driver] Delete -mimplicit-it=

Wed May 19 12:20:05 PDT 2021

dblaikie added a comment.

In D102568#2769395 <https://reviews.llvm.org/D102568#2769395>, @MaskRay wrote:

> In D102568#2769389 <https://reviews.llvm.org/D102568#2769389>, @dblaikie wrote:
>
>> In D102568#2769341 <https://reviews.llvm.org/D102568#2769341>, @MaskRay wrote:
>>
>>> I think libvpx's ASFLAGS usage is about GNU as, not the driver option.
>>>
>>> In D102568#2769296 <https://reviews.llvm.org/D102568#2769296>, @dblaikie wrote:
>>>
>>>>> I think "waiting for a few releases" is too much and doesn't improve things (they will notice issues until you remove the option). I can accept "waiting for one major release".
>>>>
>>>> Having fairly broad windows of not breaking backwards compatibility is a fairly reasonable request. Take LLVM itself, for instance - which supports building with Clang back as far as 3.5. (not suggesting we need to have a window that large for every feature/piece of surface area - but that there is scope for fairly wide windows)
>>>
>>> I understand the broad Windows and I also strive for this portability.
>>>
>>> However, reverting this patch is now a trade-off. It would make x264/openh264's mingw build happy but break musl's arm build (2018-09 ~ ).
>>> There can be other projects doing detection on both -mimplicit-it and -Wa,-mimplicit-it and will be broken by reverting this patch.
>>
>> Not sure I follow - presumably musl's arm build wasn't working with clang before this patch? Or something changed there after this patch landed?
>
> musl's arm build has always been working with clang. It stopped working after the driver option -mimplicit-it= was added earlier this year.
> This patch dropped the driver option/fixed the musl build but broke some mingw arm projects.

Ah, thanks for the history. Yeah, still not sure those bugs are on equal footing - if the patch had been in for a few months before musl was fixed (If they're interested in building from LLVM head - wonder why it took so long & if they aren't, then it doesn't seem like we need to rush to fix this/keep the fix in tree if backing it out and considering how to support both new-ish (self-imposed due to the -mimplicit-it= change) and existing (mingw arm) use cases can be handled gracefully and have it in the next LLVM release or the like).

But sounds like there's some possible both-use-cases-work path forward, which is good to see.

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https://reviews.llvm.org/D102568