Re: [webkit-dev] Proposal on retiring JIT on Windows

[Kirsling, Ross via webkit-dev]

This seems unfortunate and unexpected to me—I thought having a singular Windows 
port was supposed to mean reduced maintenance burden, since we don't have to 
divide the number of Windows maintainers into two.

Although reconciling FTL with Windows' calling convention is a challenge that 
no one's ever had the time to prioritize, we've had a fully working DFG on 
Windows for so many years. If we turn that off, I can't imagine it ever being 
revived again.

How come the discussion here is immediately about getting rid of such a large 
swath of functionality instead of starting with consideration of the EWS 
situation itself?

Ross

From: Yusuke Suzuki via webkit-dev 
Sent: Sunday, March 26, 2023 7:23:04 AM
To: Fujii Hironori ; Brent Fulgham 
; Mark Lam 
Cc: WebKit Development 
Subject: Re: [webkit-dev] Proposal on retiring JIT on Windows

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  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 
mailto:webkit-dev@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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Re: [webkit-dev] Proposal on retiring JIT on Windows

[Yusuke Suzuki via webkit-dev]

> 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  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 
> mailto:webkit-dev@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
>> ___
>> webkit-dev mailing list
>> webkit-dev@lists.webkit.org 
>> https://lists.webkit.org/mailman/listinfo/webkit-dev

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Re: [webkit-dev] Proposal on retiring JIT on Windows

[Fujii Hironori via webkit-dev]

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@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
> ___
> webkit-dev mailing list
> webkit-dev@lists.webkit.org
> https://lists.webkit.org/mailman/listinfo/webkit-dev
>
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[webkit-dev] Proposal on retiring JIT on Windows

[Yusuke Suzuki via webkit-dev]

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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