[Bug other/54692] [4.8 Regression] gcc doesn't build with "-Og -g"

["jakub at gcc dot gnu.org" <gcc-bugzilla at gcc dot gnu dot org>]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=54692

--- Comment #9 from Jakub Jelinek <jakub at gcc dot gnu.org> 2012-09-24 15:04:06 UTC ---
(In reply to comment #8)
> (In reply to comment #6)
> > Guess
> >   *) CFLAGS=`echo $CFLAGS | sed "s/-O[[s0-9]]* *//" `
> >      CXXFLAGS=`echo $CXXFLAGS | sed "s/-O[[s0-9]]* *//" ` ;;
> > needs to be now
> > -O[[s0-9gf]] instead (also for -Ofast).
> > That said, I don't see how it is related to using STAGE1_CFLAGS (note missing
> > XX).
> 
> I wonder why we do the above at all?  I suppose that's for removing
> a configure default, but the toplevel passes STAGE1_CFLAGS as CFLAGS to
> gcc configure (that's why we need to re-specify CFLAGS on the make
> command-line?!).

The intent of this is to make sure that the toplevel Makefile has whatever
fancy
CXXFLAGS/CFLAGS is needed for bootstrapping, and gcc/Makefile has corresponding
CXXFLAGS/CFLAGS without -O2 or similar in it.  Thus, if in --disable-bootstrap
(or cross) gcc you do make in toplevel, you are building an optimized compiler,
while cd gcc; make after you tweak stuff here and there will default to no
optimization and thus hopefully better debugging experience.  If/when -Og is
better than -O0 for debug experience surely we can use there -Og instead.
>From toplevel make just passes down CXXFLAGS/CFLAGS, so the values stored in
gcc/Makefile are ignored.