https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110622
--- Comment #15 from Xi Ruoyao <xry111 at gcc dot gnu.org> ---
(In reply to Mathieu Malaterre from comment #14)
> (In reply to Andrew Pinski from comment #13)
> > (In reply to Mathieu Malaterre from comment #12)
> > > I am seeing a difference in result (log1p computation) in the range:
> > >
> > > 4318952042648305665 - 0x1.0000000000001p-64
> > > 4368493837572636672 - 0x1.002p-53
> > >
> > > the other values seems to match expectation of log1p computation.
> >
> > But you used excess-precision=fast
> >
> > *** This bug has been marked as a duplicate of bug 323 ***
>
> AFAIK bug #323 does not mention my trick:
>
> asm volatile("" : "+r"(y.raw[0]) : : "memory");
>
> That simple line totally changed the optimizer code generation.
Because in x87 the excessive precision only exists in x87 stack-like registers.
The "memory" clobber forces a store and reload for all non-register variables,
thus the value is truncated into a normal double value and the excessive
precision is lost.
There are infinite ways to work around an issue, but it does not mean PR 323
must mention all of them.
