Proposal: Dropping MSVC support and use clang-cl exclusively on Windows
Hi! Herb here from the MSVC team. It makes total sense to use the right compiler for the job and prune unused configs (and it sounds like no one is relying on building with MSVC, correct?). I just wanted to ask about this part, in case there were things we could do better:
1. MSVC does not support various C++20 features, so it is putting our C++20 adoption much behind (For example, we cannot use concept). By using clang-cl, we can start much newer set of C++20 features, improving code quality, static checks etc.
We’ve had full C++20 including concepts for a couple of years so I wasn’t sure what problem you were running into… are you encountering bugs in those features? or you can’t turn on /std:c++20 for some reason? or are you using an older pre-concepts (pre-VS2022 17.0) compiler? Thanks for any feedback you have time to share. Herb _____ +1 Cheers, Keith
On Apr 30, 2024, at 10:06 AM, Yusuke Suzuki via webkit-dev <webkit-dev at lists.webkit.org <https://lists.webkit.org/mailman/listinfo/webkit-dev> > wrote:
Hello WebKittens!
Right now, MSVC support is putting significant burden on JavaScriptCore. It lacks many features for JSC development,
as a result, we have so many workarounds for MSVC in JavaScriptCore (For example, LLInt CLoop 16-bit opcode is disabled only for MSVC since MSVC cannot compile it reasonably).
I talked with JSC team and Don at Sony, and now I would like to propose dropping MSVC support on Windows port and using clang-cl exclusively on Windows.
There are many motivating factors for this change.
1. Post-commit testing bots (WinCairo) are using clang-cl. So literally, there is zero test coverage on MSVC build right now.
2. On the other hand, EWS is using MSVC for build test. This discrepancy is making maintenance of Windows ports harder and harder.
3. MSVC has various compilation issues which makes JSC lesser quality. Lack of `__builtin_frame_address` support makes JSC bloating JIT code much. CheckedArith has bunch of special code due to lack of overflow-detecting `__builtin_add_overflow` like operations, and so on. (but TBH, given there is zero coverage, we even don't know whether it is working right now!)
4. Major third-parties using Windows WebKit (e.g. Bun.js, praywright etc.) are using clang-cl, not MSVC.
Not only solving existing issues, using clang-cl opens significant code / implementation quality improvements opportunities for Windows.
1. MSVC does not support various C++20 features, so it is putting our C++20 adoption much behind (For example, we cannot use concept). By using clang-cl, we can start much newer set of C++20 features, improving code quality, static checks etc.
2. This paves a way to make Windows JSC implementation super solid. clang-cl offers sysv-abi feature for function attributes. This allows using Linux / macOS amd64 ABI on certain annotated functions. This basically means that we potentially unify our interpreter and JIT implementations completely in Linux / macOS / Windows for x64, (which makes our LLInt / Wasm LLInt on Windows super solid, plus, it paves a way to fully enable all JIT tiers on Windows including FTL).
We already discussed with Don and we agreed on this.
And now I would like to formally propose MSVC deprecation towards more cleaner and solid Windows port.
Best regards,
-Yusuke Suzuki
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Hi
On 2 May 2024, at 10:07 am, Herb Sutter via webkit-dev <webkit-dev@lists.webkit.org> wrote:
We’ve had full C++20 including concepts for a couple of years so I wasn’t sure what problem you were running into… are you encountering bugs in those features? or you can’t turn on /std:c++20 for some reason? or are you using an older pre-concepts (pre-VS2022 17.0) compiler?
Thanks for any feedback you have time to share.
Herb
We’ve had issues where some use of concepts made the latest MSVC compiler crash See https://searchfox.org/wubkat/source/Source/WTF/wtf/TypeTraits.h#145-172 See https://bugs.webkit.org/show_bug.cgi?id=261598 Jean-Yves
Hi Herb If you grep around the WebKit codebase for COMPILER(MSVC) there are a number of workarounds hanging out. Some may have been fixed over time but the workaround wasn’t removed. Biggest issue was around the JIT and some other low level features the JSC folks utilize that isn’t present in MSVC. The lion’s share of JSC development is done using Clang and those working on it don’t have a Windows box handy so we have seen the JIT break on Windows. Yusuke I’m sure has a list of feature requests that would improve the quality of MSVC for people developing VMs. MSVC has definitely caught some issues in the code and compiler mono-culture isn’t great but realistically we don’t have the resources to keep MSVC up and running. Regards, Don From: Jean-Yves Avenard via webkit-dev <webkit-dev@lists.webkit.org> Sent: Wednesday, May 1, 2024 5:10 PM To: Herb Sutter <herb.sutter@gmail.com> Cc: Webkit Development List <webkit-dev@lists.webkit.org> Subject: Re: [webkit-dev] Proposal: Dropping MSVC support and use clang-cl exclusively on Windows Hi On 2 May 2024, at 10:07 am, Herb Sutter via webkit-dev <webkit-dev@lists.webkit.org<mailto:webkit-dev@lists.webkit.org>> wrote: We’ve had full C++20 including concepts for a couple of years so I wasn’t sure what problem you were running into… are you encountering bugs in those features? or you can’t turn on /std:c++20 for some reason? or are you using an older pre-concepts (pre-VS2022 17.0) compiler? Thanks for any feedback you have time to share. Herb We’ve had issues where some use of concepts made the latest MSVC compiler crash See https://searchfox.org/wubkat/source/Source/WTF/wtf/TypeTraits.h#145-172<https://searchfox.org/wubkat/source/Source/WTF/wtf/TypeTraits.h#145-172> See https://bugs.webkit.org/show_bug.cgi?id=261598<https://bugs.webkit.org/show_bug.cgi?id=261598> Jean-Yves
Thank you, Jean-Yves and Don! One followup: I don’t know WebKit well but was surprised that it was being built with MSVC, and Yusuke mentioned Windows projects that build with clang-cl instead. Are there known users/products who are building with WebKit that are important not to break, so that we (Microsoft) should be thinking about doing work so you can keep using MSVC, or is this really an unused configuration that it makes sense to just drop? Herb From: Olmstead, Don <Don.Olmstead@sony.com> Sent: Thursday, May 2, 2024 12:06 PM To: Jean-Yves Avenard <jean-yves.avenard@apple.com>; Herb Sutter <herb.sutter@gmail.com> Cc: WebKit-Dev Development (webkit-dev@lists.webkit.org) <webkit-dev@lists.webkit.org> Subject: RE: [webkit-dev] Proposal: Dropping MSVC support and use clang-cl exclusively on Windows Hi Herb If you grep around the WebKit codebase for COMPILER(MSVC) there are a number of workarounds hanging out. Some may have been fixed over time but the workaround wasn’t removed. Biggest issue was around the JIT and some other low level features the JSC folks utilize that isn’t present in MSVC. The lion’s share of JSC development is done using Clang and those working on it don’t have a Windows box handy so we have seen the JIT break on Windows. Yusuke I’m sure has a list of feature requests that would improve the quality of MSVC for people developing VMs. MSVC has definitely caught some issues in the code and compiler mono-culture isn’t great but realistically we don’t have the resources to keep MSVC up and running. Regards, Don From: Jean-Yves Avenard via webkit-dev <webkit-dev@lists.webkit.org <mailto:webkit-dev@lists.webkit.org> > Sent: Wednesday, May 1, 2024 5:10 PM To: Herb Sutter <herb.sutter@gmail.com <mailto:herb.sutter@gmail.com> > Cc: Webkit Development List <webkit-dev@lists.webkit.org> Subject: Re: [webkit-dev] Proposal: Dropping MSVC support and use clang-cl exclusively on Windows Hi On 2 May 2024, at 10:07 am, Herb Sutter via webkit-dev <webkit-dev@lists.webkit.org <mailto:webkit-dev@lists.webkit.org> > wrote: We’ve had full C++20 including concepts for a couple of years so I wasn’t sure what problem you were running into… are you encountering bugs in those features? or you can’t turn on /std:c++20 for some reason? or are you using an older pre-concepts (pre-VS2022 17.0) compiler? Thanks for any feedback you have time to share. Herb We’ve had issues where some use of concepts made the latest MSVC compiler crash See https://searchfox.org/wubkat/source/Source/WTF/wtf/TypeTraits.h#145-172 See https://bugs.webkit.org/show_bug.cgi?id=261598 Jean-Yves
On Fri, May 3, 2024 at 5:28 AM Herb Sutter via webkit-dev < webkit-dev@lists.webkit.org> wrote:
One followup: I don’t know WebKit well but was surprised that it was being built with MSVC, and Yusuke mentioned Windows projects that build with clang-cl instead. Are there known users/products who are building with WebKit that are important not to break, so that we (Microsoft) should be thinking about doing work so you can keep using MSVC, or is this really an unused configuration that it makes sense to just drop?
As far as I know, projects publicly distributing Windows WebKit and JavaScriptCore are only Microsoft Playwright and Bun. As Yusuke mentioned, they already switched to clang-cl.
4. Major third-parties using Windows WebKit (e.g. Bun.js, praywright etc.) are using clang-cl, not MSVC.
Other browser engines, Chrome and Firefox, already switched to Clang. You might be interested in their blogs. Clang is now used to build Chrome for Windows - The LLVM Project Blog https://blog.llvm.org/2018/03/clang-is-now-used-to-build-chrome-for.html Building Firefox on Windows with clang-cl | Home Page https://ehsanakhgari.org/blog/2014-06-26/building-firefox-on-windows-with-cl... an unexpected benefit of standardizing on clang-cl | Nathan's Blog https://blog.mozilla.org/nfroyd/2019/04/25/an-unexpected-benefit-of-standard... For someone worrying about compiler monoculture, it seems that some QtWebKit users are using GCC (MinGW) on Windows. https://github.com/qtwebkit/qtwebkit/issues/1102
Hey Herb, Not everyone whose embedding WebKit on Windows announces to us that they’re using it so unsure if someone is still compiling using MSVC. All the documentation we have points to clang-cl being the preferred way. The ones we know of Bun, https://bun.sh/ , and Playwright, https://playwright.dev/ , have switched to clang-cl. I was personally keeping the dream alive and would compile out WebKit with MSVC. WebKit on Windows doesn’t have the highest tier JITs because we don’t have anyone working on it for Windows and the maintenance costs around MSVC are centered around that. If MSVC had the functionality that helps the JSC folks make the VM run fast we wouldn’t be in this situation. If that functionality is added to the roadmap then we’d definitely reconsider at that time. Don From: Herb Sutter <herb.sutter@gmail.com> Sent: Thursday, May 2, 2024 1:28 PM To: Olmstead, Don <Don.Olmstead@sony.com>; 'Jean-Yves Avenard' <jean-yves.avenard@apple.com> Cc: 'WebKit-Dev Development' <webkit-dev@lists.webkit.org> Subject: RE: [webkit-dev] Proposal: Dropping MSVC support and use clang-cl exclusively on Windows Thank you, Jean-Yves and Don! One followup: I don’t know WebKit well but was surprised that it was being built with MSVC, and Yusuke mentioned Windows projects that build with clang-cl instead. Are there known users/products who are building with WebKit that are important not to break, so that we (Microsoft) should be thinking about doing work so you can keep using MSVC, or is this really an unused configuration that it makes sense to just drop? Herb From: Olmstead, Don <Don.Olmstead@sony.com<mailto:Don.Olmstead@sony.com>> Sent: Thursday, May 2, 2024 12:06 PM To: Jean-Yves Avenard <jean-yves.avenard@apple.com<mailto:jean-yves.avenard@apple.com>>; Herb Sutter <herb.sutter@gmail.com<mailto:herb.sutter@gmail.com>> Cc: WebKit-Dev Development (webkit-dev@lists.webkit.org<mailto:webkit-dev@lists.webkit.org>) <webkit-dev@lists.webkit.org<mailto:webkit-dev@lists.webkit.org>> Subject: RE: [webkit-dev] Proposal: Dropping MSVC support and use clang-cl exclusively on Windows Hi Herb If you grep around the WebKit codebase for COMPILER(MSVC) there are a number of workarounds hanging out. Some may have been fixed over time but the workaround wasn’t removed. Biggest issue was around the JIT and some other low level features the JSC folks utilize that isn’t present in MSVC. The lion’s share of JSC development is done using Clang and those working on it don’t have a Windows box handy so we have seen the JIT break on Windows. Yusuke I’m sure has a list of feature requests that would improve the quality of MSVC for people developing VMs. MSVC has definitely caught some issues in the code and compiler mono-culture isn’t great but realistically we don’t have the resources to keep MSVC up and running. Regards, Don From: Jean-Yves Avenard via webkit-dev <webkit-dev@lists.webkit.org<mailto:webkit-dev@lists.webkit.org>> Sent: Wednesday, May 1, 2024 5:10 PM To: Herb Sutter <herb.sutter@gmail.com<mailto:herb.sutter@gmail.com>> Cc: Webkit Development List <webkit-dev@lists.webkit.org<mailto:webkit-dev@lists.webkit.org>> Subject: Re: [webkit-dev] Proposal: Dropping MSVC support and use clang-cl exclusively on Windows Hi On 2 May 2024, at 10:07 am, Herb Sutter via webkit-dev <webkit-dev@lists.webkit.org<mailto:webkit-dev@lists.webkit.org>> wrote: We’ve had full C++20 including concepts for a couple of years so I wasn’t sure what problem you were running into… are you encountering bugs in those features? or you can’t turn on /std:c++20 for some reason? or are you using an older pre-concepts (pre-VS2022 17.0) compiler? Thanks for any feedback you have time to share. Herb We’ve had issues where some use of concepts made the latest MSVC compiler crash See https://searchfox.org/wubkat/source/Source/WTF/wtf/TypeTraits.h#145-172<https://searchfox.org/wubkat/source/Source/WTF/wtf/TypeTraits.h#145-172> See https://bugs.webkit.org/show_bug.cgi?id=261598<https://bugs.webkit.org/show_bug.cgi?id=261598> Jean-Yves
Herb, if you run “git log --grep MSVC” in a git checkout of WebKit, you’ll find many quirks we’ve done in our code to get it to compile with MSVC. Here are some of the most recent ones: https://commits.webkit.org/272595@main https://commits.webkit.org/271031@main Some warning differences in https://commits.webkit.org/276799@main and https://commits.webkit.org/277563@main The COMPILER(MSVC) addition necessary in https://commits.webkit.org/265366@main puzzled me a lot for a while, but I stopped looking into it. And many more. I don’t have a strong opinion about WebKit’s use of MSVC, but WebKit is certainly a wealth of real-world code that has worked around compiler differences over the last few decades that could be analyzed by the MSVC team if you’re interested.
On May 2, 2024, at 3:49 PM, Olmstead, Don via webkit-dev <webkit-dev@lists.webkit.org> wrote:
Hey Herb,
Not everyone whose embedding WebKit on Windows announces to us that they’re using it so unsure if someone is still compiling using MSVC. All the documentation we have points to clang-cl being the preferred way. The ones we know of Bun, https://bun.sh/ , and Playwright, https://playwright.dev/ , have switched to clang-cl.
I was personally keeping the dream alive and would compile out WebKit with MSVC. WebKit on Windows doesn’t have the highest tier JITs because we don’t have anyone working on it for Windows and the maintenance costs around MSVC are centered around that. If MSVC had the functionality that helps the JSC folks make the VM run fast we wouldn’t be in this situation. If that functionality is added to the roadmap then we’d definitely reconsider at that time.
Don
From: Herb Sutter <herb.sutter@gmail.com> Sent: Thursday, May 2, 2024 1:28 PM To: Olmstead, Don <Don.Olmstead@sony.com>; 'Jean-Yves Avenard' <jean-yves.avenard@apple.com> Cc: 'WebKit-Dev Development' <webkit-dev@lists.webkit.org> Subject: RE: [webkit-dev] Proposal: Dropping MSVC support and use clang-cl exclusively on Windows
Thank you, Jean-Yves and Don!
One followup: I don’t know WebKit well but was surprised that it was being built with MSVC, and Yusuke mentioned Windows projects that build with clang-cl instead. Are there known users/products who are building with WebKit that are important not to break, so that we (Microsoft) should be thinking about doing work so you can keep using MSVC, or is this really an unused configuration that it makes sense to just drop?
Herb
From: Olmstead, Don <Don.Olmstead@sony.com <mailto:Don.Olmstead@sony.com>> Sent: Thursday, May 2, 2024 12:06 PM To: Jean-Yves Avenard <jean-yves.avenard@apple.com <mailto:jean-yves.avenard@apple.com>>; Herb Sutter <herb.sutter@gmail.com <mailto:herb.sutter@gmail.com>> Cc: WebKit-Dev Development (webkit-dev@lists.webkit.org <mailto:webkit-dev@lists.webkit.org>) <webkit-dev@lists.webkit.org <mailto:webkit-dev@lists.webkit.org>> Subject: RE: [webkit-dev] Proposal: Dropping MSVC support and use clang-cl exclusively on Windows
Hi Herb
If you grep around the WebKit codebase for COMPILER(MSVC) there are a number of workarounds hanging out. Some may have been fixed over time but the workaround wasn’t removed.
Biggest issue was around the JIT and some other low level features the JSC folks utilize that isn’t present in MSVC. The lion’s share of JSC development is done using Clang and those working on it don’t have a Windows box handy so we have seen the JIT break on Windows. Yusuke I’m sure has a list of feature requests that would improve the quality of MSVC for people developing VMs.
MSVC has definitely caught some issues in the code and compiler mono-culture isn’t great but realistically we don’t have the resources to keep MSVC up and running.
Regards, Don
From: Jean-Yves Avenard via webkit-dev <webkit-dev@lists.webkit.org <mailto:webkit-dev@lists.webkit.org>> Sent: Wednesday, May 1, 2024 5:10 PM To: Herb Sutter <herb.sutter@gmail.com <mailto:herb.sutter@gmail.com>> Cc: Webkit Development List <webkit-dev@lists.webkit.org <mailto:webkit-dev@lists.webkit.org>> Subject: Re: [webkit-dev] Proposal: Dropping MSVC support and use clang-cl exclusively on Windows
Hi
On 2 May 2024, at 10:07 am, Herb Sutter via webkit-dev <webkit-dev@lists.webkit.org <mailto:webkit-dev@lists.webkit.org>> wrote:
We’ve had full C++20 including concepts for a couple of years so I wasn’t sure what problem you were running into… are you encountering bugs in those features? or you can’t turn on /std:c++20 for some reason? or are you using an older pre-concepts (pre-VS2022 17.0) compiler?
Thanks for any feedback you have time to share.
Herb
We’ve had issues where some use of concepts made the latest MSVC compiler crash See https://searchfox.org/wubkat/source/Source/WTF/wtf/TypeTraits.h#145-172
See https://bugs.webkit.org/show_bug.cgi?id=261598
Jean-Yves _______________________________________________ webkit-dev mailing list webkit-dev@lists.webkit.org https://lists.webkit.org/mailman/listinfo/webkit-dev
participants (5)
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Alex Christensen
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Fujii Hironori
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Herb Sutter
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Jean-Yves Avenard
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Olmstead, Don