Bug 171618 – [Win][Meta] Build WebKit using Clang

• Status: RESOLVED
• Resolution: FIXED
• Component: Tools / Tests

[Don Olmstead]

Tracking bug for supporting Clang builds on Windows.

[Fujii Hironori]

Created attachment 349006 [details]
WIP patch

> perl Tools\Scripts\build-webkit --release --wincairo --ninja --cmakeargs="-DCMAKE_C_COMPILER=clang-cl -DCMAKE_CXX_COMPILER=clang-cl -DCMAKE_C_FLAGS=-m64 -DCMAKE_CXX_FLAGS=-m64"

[Fujii Hironori]

Created attachment 349010 [details]
WIP patch

[Fujii Hironori]

I uploaded build logs showing all compilation errors.
https://gist.github.com/fujii/ea5a60634e44f9c2a84cf3d3de95e2ad
I'm using LLVM-8.0.0-r339319-win64.exe.

[Fujii Hironori]

  LLVM Project Blog: Clang is now used to build Chrome for Windows
  http://blog.llvm.org/2018/03/clang-is-now-used-to-build-chrome-for.html

I believe this is the right direction WinCairo port should follow.

[Fujii Hironori]

Created attachment 349627 [details]
WIP patch

Compiler macro definitions should be rethought.

Current definitions:

WTF_COMPILER_GCC_OR_CLANG 0
WTF_COMPILER_CLANG 1
WTF_COMPILER_MSVC 1

* It is weird WTF_COMPILER_GCC_OR_CLANG is off even though WTF_COMPILER_CLANG is on.
* Should WTF_COMPILER_MSVC be on?

[Fujii Hironori]

Here are the built-in macro definitions of Clang for Windows:

_MSC_VER: 1914
__GNUC__ is not defined
__clang__: 1

clang version 8.0.0 (trunk)
Target: x86_64-pc-windows-msvc

check program: https://gist.github.com/fujii/4547bda099b3568f46ee164674b1f60d

[Fujii Hironori]

Using clang-cl to ship Windows builds - Google Group
https://groups.google.com/forum/m/#!topic/mozilla.dev.platform/wwO48xXFx0A

1443590 - Use clang-cl for Windows builds we ship to users
https://bugzilla.mozilla.org/show_bug.cgi?id=1443590

glandium.org » Blog Archive » Firefox is now built with clang LTO on all* platforms
https://glandium.org/blog/?p=3888

[Fujii Hironori]

Created attachment 350006 [details]
WIP Patch not to define WTF_COMPILER_MSVC

WTF_COMPILER_GCC_OR_CLANG 1
WTF_COMPILER_CLANG 1
WTF_COMPILER_MSVC 0

[Fujii Hironori]

Created attachment 350007 [details]
WIP Patch to define WTF_COMPILER_MSVC

WTF_COMPILER_GCC_OR_CLANG 0
WTF_COMPILER_CLANG 1
WTF_COMPILER_MSVC 1

[Fujii Hironori]

Comment on attachment 350006 [details]
WIP Patch not to define WTF_COMPILER_MSVC

It seems safer that Clang for Windows builds the same code path with MSVC in the transition phase.

[Fujii Hironori]

WinCairo port can be built by Clang for Windows (with zillions of compilation warnings).
https://trac.webkit.org/r236450

I took benchmarks:

ARES-6:

MSVC: 37.24ms
Clang: 35.85ms (faster)

Speedometer:

MSVC: 59.38 (faster)
Clang: 56.9

(I needed some trial for Clang because Clang built executable is unstable and did finish the benchmark.)

Build Time:

Ninja+MSVC: 30min (much faster)
Ninja+Clang+link.exe: 50min

[Fujii Hironori]

(In reply to Fujii Hironori from comment #11)
> (I needed some trial for Clang because Clang built executable is unstable
> and did finish the benchmark.)

did not finish

[Fujii Hironori]

(In reply to Fujii Hironori from comment #12)
> (In reply to Fujii Hironori from comment #11)
> > (I needed some trial for Clang because Clang built executable is unstable
> > and did finish the benchmark.)
> 
> did not finish

I was wrong. MSVC builds are also unstable for the benchmark. This is not Clang builds issue.

[Fujii Hironori]

(In reply to Fujii Hironori from comment #11)
> Build Time:
> 
> Ninja+MSVC: 30min (much faster)
> Ninja+Clang+link.exe: 50min

This slowness is caused by the zillions of compilation warnings.
If I apply the part of Comment 8 patch to suppress the warning,
the build time becomes comparable.

> ====================================================================
>  WebKit is now built (32m:13s).
> ====================================================================

[Fujii Hironori]

How to: Debug an Executable Not Part of a Visual Studio Solution | Microsoft Docs
https://docs.microsoft.com/en-us/previous-versions/dotnet/netframework-3.0/0bxe8ytt(v=vs.85)

[Fujii Hironori]

* Set up

http://releases.llvm.org/download.html#7.0.0
LLVM-7.0.0-win64.exe

Add path to clang-cl and ninja

* Build

set CC=clang-cl
set CXX=clang-cl
perl Tools\Scripts\build-webkit --release --wincairo --ninja

* Remaining Tasks

- Create a Docker image with clang-cl
- Fix more compilation warnings

[Fujii Hironori]

This is a blocker for Clang 9.
  Bug 201759 – [Win][Clang 9][MiniBrowser] comip.h(174,16): error: conflicting types for '_com_ptr_t'

Keep you clang-cl 8.0.1 at the moment.

[Fujii Hironori]

New blocker: Bug 204831 – [Win] lld-link: error: /manifestdependency: is not allowed in .drectve

[Don Olmstead]

Can we close this now?

[Fujii Hironori]

There are still remaining compilation warnings.
And, I'm maintaining internal WinCairo clang-cl Jenkins jobs, but there is no public bots using clang-cl. So, I'm using this ticket to let anyone know the current status. https://trac.webkit.org/wiki/BuildingCairoOnWindows#CompileWinCairowithClang

When will WinCairo bots switch to Clang? The MSVC lambda bug is annoying. (Bug 209358)

[Fujii Hironori]

LLVM 12.0.0 was released. I upgraded it for all internal Jenkins workers.

[Fujii Hironori]

I upgraded the internal Jenkins workers to Clang 13.0.0.

[Fujii Hironori]

The latest WinCairo can't compile with Clang.
Bug 234696 – [Clang][Win] NotificationData.h(47,5): error: reference to 'UUID' is ambiguous

[Fujii Hironori]

Build time:
> perl .\Tools\Scripts\build-webkit --debug --skip-library-update --no-fatal-warnings
263045@main

MSVC:  22m:13s
Clang: 25m:16s

Size of WebKitBuild directory:
$ du -hs WebKitBuild/Debug

MSVC:  14G
Clang: 7.5G

[Ian Grunert]

This blocks FTL on windows (bug 145366) - the generated AirOpcodeGenerated.h contains code that builds on clang but warns on MSVC.

Could fix the generator to stop spitting out switch statements with a default case and no case labels, but it might be easier to wait till the switch to clang happens?

[Ian Grunert]

Went ahead and fixed those switch statements in bug 259429

[Fujii Hironori]

Created attachment 467870 [details]
"-T ClangCL" patch

It's possible to use CMake Visual Studio generator and clang-cl extension.
However, there are two problems at the moment.
1. You have to apply a patch to set "-T ClangCL" CMake switch.
2. CMake Visual Studio generator ignores some compiler warning disabling switches like /wd4100.
   It reports compiler warnings. You have to give --no-fatal-warnings switches.

How to build WebKit Windows port with Visual Studio and clang-cl

1. Install LLVM extension.
  https://learn.microsoft.com/en-us/cpp/build/clang-support-msbuild
2. Apply the "-T ClangCL" patch
3. Invoke "perl .\Tools\Scripts\build-webkit --no-ninja --no-fatal-warnings" in WebKit command prompt.

Or, you can open the solution file:

3. Invoke "perl .\Tools\Scripts\build-webkit --no-ninja --no-fatal-warnings --generate-project-only" in WebKit command prompt.
4. Invoke "devenv WebKitBuild\Release\WebKit.sln" in WebKit command prompt.

[Fujii Hironori]

We don't need the patch. 

> perl .\Tools\Scripts\build-webkit --debug --no-fatal-warnings --no-ninja --cmakeargs="-T ClangCL"

[Fujii Hironori]

The build instruction has been updated.
https://github.com/WebKit/Documentation/commit/739ce4449adb3de8e272a4221b67468b404644e2
No remaining tasks. Closed.

[Radar WebKit Bug Importer]

<rdar://problem/116439320>