https://gcc.gnu.org/bugzilla/show_bug.cgi?id=118222
Andrew Pinski <pinskia at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Resolution|--- |INVALID
Status|WAITING |RESOLVED
--- Comment #2 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
(In reply to Andrew Pinski from comment #1)
> GCC has an IPA RA.
> So if is_ENOTSUP is local to that file, GCC will see if edx is not clobbered
> by that function, GCC can assume it can be used across the call.
>
> I am suspecting you are seeing that effect.
Yes that is exactly it.
is_ENOTSUP is defined in sys/system.h as:
```
static inline bool
is_ENOTSUP (int err)
{
return err == EOPNOTSUPP || (ENOTSUP != EOPNOTSUPP && err == ENOTSUP);
}
```
So when not inlined, GCC's IPA RA comes into play and knows that is_ENOTSUP
does not clobber edx at all so it knows that specific call is not going to
clobber edx so it can use it as such.
This is 100% valid optimization since the function binds local to the TU and
the call does NOT need to use the full x86_64 ABI here since GCC knows it can't
be changed out.
Aka this is by design, GCC 5 added this IPA optimization.
