On Mon, 6 May 2019, Martin Liška wrote: > On 5/2/19 9:04 PM, Richard Biener wrote: > > On May 2, 2019 8:14:46 PM GMT+02:00, Segher Boessenkool > > <seg...@kernel.crashing.org> wrote: > >> On Thu, May 02, 2019 at 07:41:18PM +0200, Richard Biener wrote: > >>> On May 2, 2019 7:00:16 PM GMT+02:00, Segher Boessenkool > >> <seg...@kernel.crashing.org> wrote: > >>>> On Thu, May 02, 2019 at 03:18:00PM +0200, Richard Biener wrote: > >>>>> Somewhen earlier this year I've done the experiment with using > >>>>> a compile with -flto -fno-fat-lto-objects and a link > >>>>> via -flto -r -flinker-output=rel into the object file. This cut > >>>>> compile-time more than in half with less maintainance overhead. > >>>>> > >>>>> Adding other files to this handling looks trivial as well, as well > >>>>> as conditionalizing it (I'd probably not want this for devel > >> builds). > >>>> > >>>> But we want devel builds to be a lot faster than they are now :-/ > >>> > >>> My devel build is -O0 non-bootstrapped and building the files after > >> dependency changes is fast enough. It's the bootstraps that matter, no? > >> > >> > >> Yes, I bootstrap most of the time. For development. It catches a > >> *lot* > >> of problems progressive builds do not. (Those are plenty fast already > >> of > >> course, -O0 or not). > > > > So we'd catch it there but disable by default for stage 1 since we probably > > do not want to rely on the host compiler. > > > > Richard. > > > >> > >> Segher > > > > I'm interested in 2 scenarios: > > 1) fast non-bootstrap development build with -O2; typically I want to run a > fraction of test-suite or > I want to install the compiler and run-time binaries; building the compiler > with -O0 will result in terribly > slow build of run-time libraries
That's already overall "fast", mostly dominated by runtime library build. > 2) faster bootstrap on a massively parallel machine (64+ cores) I guess for this we can also try to do LTO bootstap and LTO-link libbackend itself. LTO bootstrap is only slow because we build everything 12 times. I'm most interested in faster bootstrap on low-core machines (4 to 6 physical cores), since that's what I am doing most of the time. This is dominated by testing time, not bootstrap time. Richard.
