On Mon, Aug 14, 2017 at 6:11 AM, Till Schneidereit < t...@tillschneidereit.net> wrote:
> On Mon, Aug 14, 2017 at 9:27 AM, Julian Seward <jsew...@acm.org> wrote: > > > On 13/08/17 03:40, Ehsan Akhgari wrote: > > > As you may have heard by now, Chromium has started to switch their > > Windows > > > builds to use clang-cl instead of MSVC [1]. This has improved their > > > Speedometer v2 benchmark score on x86 (but not on x86-64) by about 30% > > > according to AWFY [2]. [..] > > > > Do we have any insight into why the Clang version is so much faster? > > 30% strikes me as a large difference for two supposedly mature optimizing > > compilers. And stranger still that it applies only for the 32-bit case. > > So I'm curious to know what's changed. > > > > AFAICT, the real change is about 19%: shortly before the jump to ~103, > their score regressed from 86 to 78. I think using 86 as the baseline makes > much more sense. 19% is obviously still a substantial improvement from a > compiler change. > Google ran a bisect on the regression and improvements. Here is some explanation of the regression: https://bugs.chromium.org/p/chromium/issues/detail?id=749359#c4 The comment suggests that the change would see an improvement in clang since the code would then use class "overflow builtins". Its hard to tell if all of the clang-on-windows improvement is due to this same set of code or not. The bisects were run from this issue: https://bugs.chromium.org/p/chromium/issues/detail?id=750672#c12 Ben _______________________________________________ dev-platform mailing list dev-platform@lists.mozilla.org https://lists.mozilla.org/listinfo/dev-platform
