[webkit-dev] Bring back ARMv6 support to JSC

[Filip Pizlo]

The fact that V8Spider is regressed indicates major problems with the JIT on ARMv6. 

I think that it would be better to work on fixing this JIT outside trunk, and then come back with patches once you have a speed up. In the future we shouldn’t allow partially-working JIT ports to land.

-Filip

> On Jul 13, 2017, at 7:47 AM, Caio Lima <ticaiolima at gmail.com> wrote:
> 
> Finally I got the results from the last benchmark run. The results
> shows that the speed-ups are considerable comparing with CLoop
> version, since we get faster results in a big number of tests and
> regress in a minor number of scripts. I would like to get feedback
> from you as well, but IMHO enabling JIT for ARMv6 looks a good
> improvement step and the amount of code we are touching in current
> trunk code to make it possible is small.
> 
> The results are attached and I also uploaded them in
> https://bugs.webkit.org/show_bug.cgi?id=172765.
> 
> PS.: Some test cases (bigswitch-indirect-symbol-or-undefined,
> bigswitch-indirect-symbol, bigswitch, etc) are failing now and I'm
> already investigating the source of problem to fix them.
> 
> Regards,
> Caio.
> 
> 2017-07-05 22:54 GMT-03:00 Filip Pizlo <fpizlo at apple.com>:
>> To be clear, I’m concerned that the 32-bit JIT backends have such bad tuning for these embedded platforms that it’s just pure badness. Until you can prove that you can change this, I think that porting should focus on making the cloop great. Then, we can rip out support for weird CPUs rather than bringing it back.
>> 
>> -Filip
>> 
>>> On Jul 5, 2017, at 6:14 PM, Caio Lima <ticaiolima at gmail.com> wrote:
>>> 
>>> 2017-07-05 18:25 GMT-03:00 Filip Pizlo <fpizlo at apple.com>:
>>>> You need to establish that the JIT is a performance progression over the LLInt on ARMv6. I am opposed to more ARMv6 patches landing until there is some evidence provided that you’re actually getting speed-ups.
>>> 
>>> It makes sense. I can get these numbers related to JIT.
>>> 
>>> BTW, there is a Patch that isn't JIT related
>>> (https://bugs.webkit.org/show_bug.cgi?id=172766).
>>> 
>>> Regards,
>>> Caio.
>>> 
>>>> -Filip
>>>> 
>>>>> On Jun 13, 2017, at 6:48 PM, Caio Lima <ticaiolima at gmail.com> wrote:
>>>>> 
>>>>> Hi All.
>>>>> 
>>>>> Some of you guys might know me through the work I have been doing in
>>>>> JSC. The experience working with WebKit has been great so far, thank
>>>>> you for the reviews!
>>>>> 
>>>>> Since 1st May, we at Igalia have been working on bring back the ARMv6
>>>>> support into JSC. We already have commits into our downstream branch
>>>>> port[2] that fixes some compile/runtime errors when building JSC to
>>>>> ARMv6 and also fixes some bugs. However, this branch is not synced
>>>>> with WebKit upstream tree and I would like to pursue the upstreaming
>>>>> of this ARMv6/JSC support to WebKit.
>>>>> 
>>>>> As a long shot, we are planning to maintain the ARMv6 support and make
>>>>> tests run as green as possible. Also, it's our goal make ARMv6 support
>>>>> not interfere with other ARM versions support code negatively and we
>>>>> will be in charge of implement platform-specific fixes/features for
>>>>> JSC/ARM6, this way no imposing burden to the rest of the community.
>>>>> 
>>>>> To keep track of work to be done, I've create a meta-bug in
>>>>> bugzilla[3] and it's going to be used firstly to organize the commits
>>>>> from our downstream branch, but pretty soon I'm going to create issues
>>>>> related with javascriptcore-test failures and send patches to fix
>>>>> them. We have already submitted 3 patches (they are marked as
>>>>> dependence of [3]) that fixes ARMv6 into LLInt and JIT layers and got
>>>>> a round of review into them.
>>>>> 
>>>>> Best Regards,
>>>>> Caio.
>>>>> 
>>>>> [1] - https://www.igalia.com/about-us/coding-experience
>>>>> [2] - https://github.com/WebPlatformForEmbedded/WPEWebKit
>>>>> [3] - https://bugs.webkit.org/show_bug.cgi?id=172765
>>>>> _______________________________________________
>>>>> webkit-dev mailing list
>>>>> webkit-dev at lists.webkit.org
>>>>> https://lists.webkit.org/mailman/listinfo/webkit-dev
> <baseline_changes_SunSpiderLongSpiderV8SpiderMicrobenchmarksSixSpeed_buildroot_20170712_1029_report.txt>