https://gcc.gnu.org/bugzilla/show_bug.cgi?id=90500
--- Comment #15 from Guobing Chen <neochen.life at aliyun dot com> ---
(In reply to Martin Liška from comment #14)
> (In reply to Guobing Chen from comment #13)
> > (In reply to Martin Liška from comment #12)
> > > > The background is that, we want to try optimize libm with avx2/avx512,
> > > > and
> > > > found that not all the libm math functions will have benefit when we
> > > > generally use 'arch=haswell' or 'arch=skylake-avx512' to compile libm.
> > > > So we
> > > > picked those 'good' libm math functions to add FMV attribute like
> > > > target_clone("default", "arch=haswell", "arch=skylake-avx512") to get
> > > > performance benefit. The alias is used in libm code by default. I have
> > > > no
> > > > idea why these two are conflicting that not allowed by GCC9.
> > >
> > > That makes sense. Based on the test-case you provided, you just want:
> > >
> > > __attribute__((target_clones("default", "arch=haswell",
> > > "arch=skylake-avx512")))
> > > double
> > > __tanh (double x)
> > > {
> > > double t, z;
> > > int32_t jx, ix, lx;
> > >
> > >
> > > do { ieee_double_shape_type ew_u; ew_u.value = (x); (jx) =
> > > ew_u.parts.msw;
> > > (lx) = ew_u.parts.lsw; } while (0);
> > > ix = jx & 0x7fffffff;
> > > ...
> > > }
> > >
> > > extern __typeof (__tanh) tanh __attribute__ ((weak, alias ("__tanh"))); //
> > > __attribute__ ((__copy__ (__tanh)));
> > >
> > > You don't want to use __copy__ attribute because it's responsible for
> > > copying of target_clone attribute to the alias.
> > > And it does not make sense to create clones of an alias.
> >
> > The copy is from alias used by libm by default (Below I paste the src code),
> > I cannot remove this copy seems. How can I then to use FMV for this
> > function?
> >
>
> Then you'll have to make one libm_alias_double_no_copy that will do the same
> except setting the copy attribute.
I am not quite familiar with libm, will this change the its bevhavior or other
side effect?
