[webkit-dev] Drop x86 (32bit) JIT backend

[Xan]

Hi all,

We at Igalia use the x86 32bit port for testing, prototyping, etc, in our
32bit work. We recently added a JSC EWS x86 instance. That being said only
the LLInt tier is working properly at the moment, and if the maintenance of
the JIT code is a big burden we think it makes sense to remove it.

This already happened during the weekend, so I guess this can count as an
after the fact tacit agreement. In the future we'd appreciate if we could
have at least a full week day (including Europe) to discuss these kinds of
changes though.

Cheers,
Xan (on behalf of Igalia's compilers team)

On Sat, Sep 14, 2019 at 9:32 PM Yusuke Suzuki <ysuzuki at apple.com> wrote:

> Thanks!
>
> I think we are not testing x86 JIT configuration, and nobody is seriously
> using it (Default build option for c86 is no JIT). Removed :D
>
> [1]: https://trac.webkit.org/changeset/249830/webkit
>
> Best regards,
> Yusuke Suzuki
>
> On Sep 13, 2019, at 15:08, Geoffrey Garen <ggaren at apple.com> wrote:
>
> No objection.
>
> Geoff
>
> On Sep 13, 2019, at 1:39 PM, Yusuke Suzuki <ysuzuki at apple.com> wrote:
>
>
> Hello all,
>
>
> Now, Xcode no longer has ability to build 32bit binary.
>
> Fedora starts dropping x86 32bit kernel shipping.
>
> Our x86/x86_64 JIT requires SSE2, so such CPUs can use JIT if they want by
> switching x86 to x86_64.
>
> And these CPUs are modern enough to run CLoop at high speed.
>
>
> x86 32bit JIT backend is very complicated and is being a major maintenance
> burden.
>
> This is due to very few # of registers. Which scatters a lot of isX86 /
> CPU(X86) in Baseline, DFG, and Yarr.
>
> I’m now planning to optimize some part of Yarr, but x86 YarrJIT is being a
> major barrier of such cleanups / optimizations.
>
>
> So, I would like to propose dropping X86 32bit JIT support.
>
>
> -Yusuke
>
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