Thanks!

> On Sep 16, 2019, at 4:39 AM, Xan <xan.lo...@gmail.com> wrote:
> 
> 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.

Yes, x86 adds many special logic. You can see the actual diff, which involves 
many “only for x86” logic involving weird stack push/pop.
And it is not well-abstracted. As a result, changes are in all of our JIT tiers 
(except for FTL b/c we are not supporting x86 in FTL) :(
https://trac.webkit.org/changeset/249880/webkit 
<https://trac.webkit.org/changeset/249880/webkit>

YarrJIT has HAVE_INITIAL_START_REG ifdef and separate logic, which is only for 
x86. All the other platforms including ARMv7 do not require this.
If this architecture has enough # of registers (like, MIPS), keeping it would 
be much easier.
But it only has very few registers and this makes x86 special compared to the 
other 32bit architectures.
I also note that x86 JIT is not working for at least 3 months. I found that x86 
callee-save-register definition is broken at some point[1].

[1]: https://trac.webkit.org/changeset/249830/webkit 
<https://trac.webkit.org/changeset/249830/webkit>

> 
> 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.

OK, I see.

-Yusuke

> 
> Cheers,
> Xan (on behalf of Igalia's compilers team)
> 
> On Sat, Sep 14, 2019 at 9:32 PM Yusuke Suzuki <ysuz...@apple.com 
> <mailto:ysuz...@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 
> <https://trac.webkit.org/changeset/249830/webkit>
> 
> Best regards,
> Yusuke Suzuki
> 
>> On Sep 13, 2019, at 15:08, Geoffrey Garen <gga...@apple.com 
>> <mailto:gga...@apple.com>> wrote:
>> 
>> No objection.
>> 
>> Geoff
>> 
>>> On Sep 13, 2019, at 1:39 PM, Yusuke Suzuki <ysuz...@apple.com 
>>> <mailto:ysuz...@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
>>> _______________________________________________
>>> webkit-dev mailing list
>>> webkit-dev@lists.webkit.org <mailto:webkit-dev@lists.webkit.org>
>>> https://lists.webkit.org/mailman/listinfo/webkit-dev 
>>> <https://lists.webkit.org/mailman/listinfo/webkit-dev>
>> 
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