On Fri, Apr 5, 2019 at 12:42 PM Martin Liška <mli...@suse.cz> wrote:
>
> Hi.
>
> The patch adds a new config that makes LTO+PGO bootstrap faster by
> using LTO only in stage4. In stage3, generators are build with LTO
> in order to collect a reasonable profile for LTO FE.
>
> Ready for trunk?
I wonder if you need the
+AC_SUBST(GENERATOR_CFLAGS)
at all, can't you just use
+BUILD_CFLAGS= @BUILD_CFLAGS@ $(GENERATOR_CFLAGS) -DGENERATOR_FILE
+BUILD_CXXFLAGS = @BUILD_CXXFLAGS@ $(GENERATOR_CFLAGS) -DGENERATOR_FILE
?
Please mention in both bootstrap-lto-lean.mk and the documentation
that the intended make target for this config is profiledbootstrap
since for non-profiledbootstrap it ends up not using LTO at all. A "lean"
mode for non-profiledbootstrap would need to set up things to
use LTO only for stage3 which means not doing a bootstrap comparison
which means we could "skip" stage2 as well here. So partial support
for that would be to have
STAGE2_CFLAGS += -frandom-seed=1
STAGE3_CFLAGS += -flto=jobserver -frandom-seed=1
...
do-compare = true
So if this works for non-profiledbootstrap the docs could be
changed to say "but is intended for faster build by only
using LTO in the final bootstrap stage. With @samp{...}
the LTO frontend is trained only on generator files."
(why do we need -frandom-seed=1? IIRC that was only for the
comparison step which is elided in all cases for -lean.mk).
Richard.
> Thanks,
> Martin
>
> ChangeLog:
>
> 2019-04-05 Martin Liska <mli...@suse.cz>
>
> * Makefile.in: Regenerate.
> * Makefile.tpl: Pass GENERATOR_CFLAGS
> in all stages.
>
> config/ChangeLog:
>
> 2019-04-05 Martin Liska <mli...@suse.cz>
>
> * bootstrap-lto-lean.mk: New file.
>
> gcc/ChangeLog:
>
> 2019-04-05 Martin Liska <mli...@suse.cz>
>
> * Makefile.in: Use GENERATOR_CFLAGS for all generators.
> * configure: Regenerate.
> * configure.ac: Pass GENERATOR_CFLAGS.
> * doc/install.texi: Document the new config.
> ---
> Makefile.in | 207 +++++++++++++++++++++++++++++++++++
> Makefile.tpl | 2 +
> config/bootstrap-lto-lean.mk | 19 ++++
> gcc/Makefile.in | 4 +-
> gcc/configure | 6 +-
> gcc/configure.ac | 1 +
> gcc/doc/install.texi | 6 +
> 7 files changed, 241 insertions(+), 4 deletions(-)
> create mode 100644 config/bootstrap-lto-lean.mk
>
>
