Using clang-cl to ship Windows builds

Stuart Philp sphilp at mozilla.com
Tue Aug 21 22:15:04 UTC 2018


That is fantastic, lots of nice wins!

On Tue, Aug 21, 2018 at 6:02 PM, David Major <dmajor at mozilla.com> wrote:

> A quick update about performance: ThinLTO and PGO were enabled for our
> clang-cl builds over the last few weeks. These optimizations have
> cancelled the previous regressions and brought clang well ahead of
> MSVC: https://treeherder.mozilla.org/perf.html#/compare?
> originalProject=try&originalRevision=2adb3cb404ad&
> newProject=try&newRevision=5336df94a9ce&framework=1
> To call out a few: Speedometer scores increased by 6% on Win64 and 12%
> on Win32, and the most dramatic improvement was displaylist_mutate at
> 27%!
>
> As far as I'm aware, no blockers have come up and clang-cl is still
> looking good for the 63 train.
>
> On Tue, Jul 10, 2018 at 4:29 PM David Major <dmajor at mozilla.com> wrote:
> >
> > Bug 1443590 is switching our official Windows builds to use clang-cl
> > as the compiler.
> >
> > Please keep an eye out for regressions and file a blocking bug for
> > anything that might be fallout from this change. I'm especially
> > interested in hearing about the quality of the debugging experience.
> >
> > It's possible that the patch may bounce and we'll go back and forth to
> > MSVC for a while. You can check your build's compiler at
> > `about:buildconfig`. Treeherder is running an additional set of MSVC
> > jobs on mozilla-central to make sure we can fall back to a green MSVC
> > if needed.
> >
> > Watch for more toolchain changes to come. The next steps after this
> > will be to switch to lld-link and enable ThinLTO. That will open the
> > door to a cross-language LTO that could inline calls between Rust and
> > C++. In the longer term we can look into cross-compiling from Linux.
> >
> > But for now, shipping our most-used platform with an open-source
> > compiler is a huge milestone in and of itself. Big thanks to everyone
> > who has contributed to this effort on the Mozilla side, and also big
> > thanks to the developers of LLVM and Chromium who helped make clang on
> > Windows a realistic possibility.
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