Hi Sam, On Mon, 2024-11-11 at 07:54 +0000, Sam James wrote: > 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?
I cannot approve, but the text does look OK to me. builder.sourceware.org has been using STAGE1_CFLAGS="-O2" for all bootstrap builds. https://sourceware.org/cgit/builder/tree/builder/master.cfg#n4250 BTW. I think I would flip the default to that. It seems having a bootstrap compiler which miscompiles at -O2 is very rare. Keep the env var, but make people set it who don't trust their compiler to behave. Cheers, Mark > 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 > +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
