On Tue, Aug 08, 2017 at 07:12:13AM +0900, Mike Hommey wrote:
> On Fri, Aug 04, 2017 at 08:45:14AM +0300, Henri Sivonen wrote:
> > I guess I buried my questions in too long a post, so extracting them:
> > 
> > On Mon, Jul 31, 2017 at 1:02 PM, Henri Sivonen <hsivo...@hsivonen.fi> wrote:
> > > Naïvely, one would think that it should be possible to do that with
> > > clang producing "object files" holding LLVM IR and rustc producing
> > > "object files" holding LLVM IR and the "link" step involving mashing
> > > those together, running LLVM optimizations again and then producing
> > > machine code from a massive collection of mashed-together LLVM IR.
> > ...
> > > If we were compiling C++ using clang on all platforms, how far off
> > > would such cross-language inlining be?
> > >
> > > If we could have the cross-language inlining benefit from compiling
> > > C++ using clang on all platforms, how far off would we be from being
> > > able to switch to clang on all platforms?
> 
> Here's a bunch of data why "let's switch compilers" is not necessarily
> easy (I happen to have gathered that recently):
> 
> Windows MSVC (PGO) vs. clang-cl:
> https://treeherder.mozilla.org/perf.html#/compare?originalProject=try&originalRevision=581eab2aa162&newProject=try&newRevision=c963d0cd6565&framework=1&showOnlyImportant=0
> 
> Windows MSVC (PGO) vs. clang-cl -O2 (the build system currently uses -O1 for
> msvc builds, which flags we use for clang-cl builds):
> https://treeherder.mozilla.org/perf.html#/compare?originalProject=try&originalRevision=581eab2aa162&newProject=try&newRevision=c963d0cd6565&framework=1&showOnlyImportant=0

It was pointed to me that both urls were the same. The second is
actually:
https://treeherder.mozilla.org/perf.html#/compare?originalProject=try&originalRevision=581eab2aa162&newProject=try&newRevision=232f977d9739&framework=1&showOnlyImportant=0

Mike
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