[webkit-dev] Proposal on retiring JIT on Windows

[Yusuke Suzuki]

> How about LLInt? LLInt has some Windows specific code.
> Can I revert the change if the JSC team breaks Windows port even though we have no EWS nor maintainers?

I think, ultimately, we cannot guarantee that it is working given that there is no EWS bots running tests on Windows, it means it is not debuggable to us.
Frequency of breakage on LLInt would be smaller than breakage on JIT. But if it happens, then I think reverting is not OK since nothing is doable to JSC team.

@Brent @Mark What is your thought and plan?

-Yusuke

> On Mar 25, 2023, at 3:02 PM, Fujii Hironori <fujii.hironori at gmail.com> wrote:
> 
> It sounds reasonable. I don't object to removing Windows JIT support.
> 
> How about LLInt? LLInt has some Windows specific code.
> Can I revert the change if the JSC team breaks Windows port even though we have no EWS nor maintainers?
> 
> On Sun, Mar 26, 2023 at 6:52 AM Yusuke Suzuki via webkit-dev <webkit-dev at lists.webkit.org <mailto:webkit-dev at lists.webkit.org>> wrote:
>> Hello,
>> 
>> I would like to propose retiring JIT on Windows JavaScriptCore.
>> Recently, Apple Windows EWS bots get removed. As a result, there is no test-running EWS bots on Windows.
>> 
>> This can work for the other part of WebKit since other ports EWS bots are running tests. However this does not work well for JSC.
>> Compile-tests is not sufficient for JIT since JIT is dynamically generated. And JIT is very architecture and platform specific.
>> Windows has different ABI, different calling convention, and register usage. JIT on Windows has very specific things.
>> 
>> Now, because there is no running EWS bots on Windows, it is not possible to catch Windows specific JIT related issues before landing.
>> Recently, JSC DFG patch has been reverted because Windows gets broken[1]. But this puts high burden to JSC maintenance since
>> there is no way to test it before landing, and it makes DFG changes very hard due to Windows.
>> 
>> So, given that there is no active maintainers of Windows JSC JIT and no EWS bots running tests, I propose retiring JIT on Windows.
>> 
>> [1]: https://github.com/WebKit/WebKit/commit/58f0d9e4a395e0173e4d3f59888bf0e761cf6ce3
>> 
>> -Yusuke
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