> On Wed, Sep 13, 2017 at 3:21 AM, Michael Clark <michaeljcl...@mac.com> wrote: > > > >> On 13 Sep 2017, at 1:15 PM, Michael Clark <michaeljcl...@mac.com> wrote: > >> > >> - https://rv8.io/bench#optimisation > >> - https://rv8.io/bench#executable-file-sizes > >> > >> -O2 is 98% perf of -O3 on x86-64 > >> -Os is 81% perf of -O3 on x86-64 > >> > >> -O2 saves 5% space on -O3 on x86-64 > >> -Os saves 8% space on -Os on x86-64 > >> > >> 17% drop in performance for 3% saving in space is not a good trade for a > >> “general” size optimisation. It’s more like executable compression. > > > > Sorry fixed typo: > > > > -O2 is 98% perf of -O3 on x86-64 > > -Os is 81% perf of -O3 on x86-64 > > > > -O2 saves 5% space on -O3 on x86-64 > > -Os saves 8% space on -O3 on x86-64
I am bit surprised you see only 8% of code size difference for -Os and -O3. I look into these numbers occasionally and it is usualy well over two digit number. http://hubicka.blogspot.cz/2014/04/linktime-optimization-in-gcc-2-firefox.html http://hubicka.blogspot.cz/2014/09/linktime-optimization-in-gcc-part-3.html has 42% code segment size reduction for Firefox and 19% for libreoffice Honza
