On Tue, Nov 03, 2020 at 02:27:52PM +0100, Richard Biener wrote:
> On Fri, Oct 23, 2020 at 1:47 PM Martin Liška <mli...@suse.cz> wrote:
> > This is a follow-up of the discussion that happened in thread about
> > no_stack_protector
> > attribute: https://gcc.gnu.org/pipermail/gcc-patches/2020-May/545916.html
> >
> > The current optimize attribute works in the following way:
> > - 1) we take current global_options as base
> > - 2) maybe_default_options is called for the currently selected
> > optimization level, which
> > means all rules in default_options_table are executed
> > - 3) attribute values are applied (via decode_options)
> >
> > So the step 2) is problematic: in case of -O2 -fno-omit-frame-pointer and
> > __attribute__((optimize("-fno-stack-protector")))
> > ends basically with -O2 -fno-stack-protector because
> > -fno-omit-frame-pointer is default:
> > /* -O1 and -Og optimizations. */
> > { OPT_LEVELS_1_PLUS, OPT_fomit_frame_pointer, NULL, 1 },
> >
> > My patch handled and the current optimize attribute really behaves that
> > same as appending attribute value
> > to the command line. So far so good. We should also reflect that in
> > documentation entry which is quite
> > vague right now:
> >
> > """
> > The optimize attribute is used to specify that a function is to be compiled
> > with different optimization options than specified on the command line.
> > """
> >
> > and we may want to handle -Ox in the attribute in a special way. I guess
> > many macro/pragma users expect that
> >
> > -O2 -ftree-vectorize and __attribute__((optimize(1))) will end with -O1 and
> > not
> > with -ftree-vectorize -O1 ?
>
> Hmm. I guess the only two reasonable options are to append to the active set
> and thus end up with -ftree-vectorize -O1 or to start from an empty set and
> thus
> end up with -O1.
I'd say we always want to append, but only take into account explicit
options.
So basically get the effect of
take the command line, append to that options from the optimize/target
pragmas in effect and append to that options from optimize/target
attributes and only from that figure out the implicit options.
Jakub
