On Wed, Nov 20, 2024 at 7:16 PM Sam James <s...@gentoo.org> wrote:
>
> Sam James <s...@gentoo.org> writes:
>
> > STAGE1_CFLAGS can be used to accelerate the just-built stage1 compiler
> > which especially improves its performance on some of the large generated
> > files during bootstrap. It defaults to nothing (i.e. -O0).
> >
> > The downside is that if the native compiler is buggy, there's a greater
> > risk of a failed bootstrap. Those with a modern native compiler, ideally
> > a recent version of GCC, should be able to use -O1 or -O2 without issue
> > to get a faster build.
> >
> > PR rtl-optimization/111619
> > * doc/install.texi (Building a native compiler): Discuss
> > STAGE1_CFLAGS.
> > ---
> > This came out of a discussion between mjw and I a little while ago when
> > working on the buildbots. OK?
>
> Ping.
>
> >
> > gcc/doc/install.texi | 6 +++++-
> > 1 file changed, 5 insertions(+), 1 deletion(-)
> >
> > diff --git a/gcc/doc/install.texi b/gcc/doc/install.texi
> > index 705440ffd330..4bd60555af9b 100644
> > --- a/gcc/doc/install.texi
> > +++ b/gcc/doc/install.texi
> > @@ -3017,7 +3017,11 @@ bootstrapped, you can use @code{CFLAGS_FOR_TARGET}
> > to modify their
> > compilation flags, as for non-bootstrapped target libraries.
> > Again, if the native compiler miscompiles the stage1 compiler, you may
> > need to work around this by avoiding non-working parts of the stage1
> > -compiler. Use @code{STAGE1_TFLAGS} to this end.
> > +compiler. Use @code{STAGE1_CFLAGS} and @code{STAGE1_TFLAGS} (for target
> > +libraries) to this end. The default value for @code{STAGE1_CFLAGS} is
> > +@samp{STAGE1_CFLAGS='-O0'} to increase the chances of a successful
> > bootstrap
The default for STAGE1_CFLAGS is '-g', not -O0 (this can make a
difference for non-GCC host
compilers). The default for STAGE1_TFLAGS is '-O2 -g', note the
stage1 target libraries are
built by the stage1 compiler, not the host compiler. I think the
sentence above for a reason
talks about STAGE1_TFLAGS and a better change would be to simply add
'You can use @code{STAGE1_CFLAGS} to set the flags passed to the host compiler
when building the stage1 compiler. The default is to pass
@option{-g}, when the host
compiler is GCC this is results in a non-optimizing build of the
stage1 compiler. You
can speed up the bootstrap by using @samp{STAGE1_CFLAGS='-O2'} at the increased
chance to miscompile the stage1 compiler when the host compiler is buggy.'
Richard.
> > +with a buggy native compiler. Changing this to @code{-O1} or @code{-O2}
> > +can improve bootstrap times, with some greater risk of a failed bootstrap.
> >
> > If you used the flag @option{--enable-languages=@dots{}} to restrict
> > the compilers to be built, only those you've actually enabled will be
> >
> > base-commit: 00448f9b5a123b4b6b3e6f45d2fecf0a5dca66b3
