On Tue, Mar 13, 2018 at 3:35 PM, Nathan Froyd <nfr...@mozilla.com> wrote: > On Tue, Mar 13, 2018 at 3:10 AM, Henri Sivonen <hsivo...@hsivonen.fi> wrote: >> On Tue, Mar 13, 2018 at 2:56 AM, Nathan Froyd <nfr...@mozilla.com> wrote: >>> (Our release builds use -O2 for Rust code.) >> >> What does cargo bench use by default? >> (https://internals.rust-lang.org/t/default-opt-level-for-release-builds/4581 >> suggests -O3.) > > As mentioned by Alexis, -O3 is indeed what gets used by default. > >> That is, is cargo bench for a crate that's vendored into m-c >> reflective of that crate's performance when included in a Firefox >> release? > > I do not know. I know that folks working on WebRender were finding > that -O3 produces *much* better code for certain things; they filed > bugs for rustc that I can't find right now. I don't know if those > bugs have been addressed. > > When Stylo was getting off the ground a year ago, mbrubeck did some > -O2 vs. -O3 size analysis, which led to some -O2 vs. -O3 performance > analysis in https://bugzilla.mozilla.org/show_bug.cgi?id=1328954. The > conclusion there is that -O3 wasn't worth it and came with a > reasonably large codesize increase. > > I guess the answer is "probably, but you should measure to make sure"?
For encoding_rs, -O2 vs -O3 has pretty big performance effects in both directions. (Didn't measure code size.) I think I'd rather have the -O3 scenario than the -O2 scenario for encoding_rs. Can we make a particular vendored crate (encoding_rs) use -O3 while the default for Rust code remains at -O2? -- Henri Sivonen hsivo...@hsivonen.fi https://hsivonen.fi/ _______________________________________________ dev-platform mailing list dev-platform@lists.mozilla.org https://lists.mozilla.org/listinfo/dev-platform
