[cfe-dev] error: unknown argument: '-ffoo' => reason ?

[Joerg Sonnenberger]

On Tue, Jan 21, 2014 at 10:27:08PM -0500, Rafael Espíndola wrote:
> >> We do try to ignore GCC options that are safe to ignore, so a patch
> >> ignoring the ones that are causing you trouble is probably fine.
> >>
> > OK. Thanks for the information.
> >
> > There are quite some items with their occurrences:
> >       2 '-falign-jumps=2'
> >       2 '-fcheck-new'
> >      33 '-fexcess-precision=standard'
> >       2 '-fforce-addr'
> >       2 '-ffriend-injection'
> >       2 '-fgcse-after-reload'
> >       6 '-finline-limit='
> >       2 '-finput-charset=UTF-8'
> >       6 '-fno-check-new'
> >      40 '-fno-defer-pop'
> >       4 '-fno-delete-null-pointer-checks'
> >       1 '-fno-implement-inlines'
> >       1 '-fno-tree-ter'
> >      11 '-fno-tree-vrp'
> >       4 '-frename-registers'
> >       2 '-frerun-loop-opt'
> >       2 '-fsingle-precision-constant'
> >       2 '-fstack-check'
> >       2 '-fuse-linker-plugin'
> >       2 '-fvar-tracking'
> >       7 '-gnatea'
> >       2 '-gnatec=foo'
> >       2 '-malign-double'
> >       2 '-malign-jumps=1'
> >       4 '-print-multiarch'
> >       4 '-z'
> >
> > Do you think I should ignore (all/most) them?
> 
> At least all the ones that just enable or disable a pass. Things like
> -malign-double would probably turn a build error into a miscompilation
> if ignored, so probably not.

I disagree that we should be adding random "disable pass" options. It
just doesn't make sense and most of them shouldn't have been applied
unconditionally in first place as they are workarounds for optimizer
bugs in specific gcc versions. From the list:
-  -fexcess-precision must not be dropped silently,
-  -fno-check-new / -fcheck-new was discussed before, language lawyers
   can comment
-  -finput-charset=UTF-8 would be safe to drop as it is the default
-  -fsingle-precision-constant potentially changes behavior
-  -fno-defer-pop was typically used without good reason, but custom asm
   parsers might depend on it, so no.
-  -z should likely be fixed to be -Wl,-z

I would not change anything except maybe -finput-charset=UTF-8.

Joerg