On Fri, Apr 20, 2018 at 10:52:57AM -0500, Segher Boessenkool wrote:
> Hi Mike,
>
> On Thu, Apr 19, 2018 at 12:33:45AM -0400, Michael Meissner wrote:
> > This patch adds __powikf2 to libgcc, and makes GCC use it for
> > __builtin_powil
> > when long double is IEEE 128-bit (-mabi=ieeelongdouble).
> >
> > I tested it on a little endian power8 system with a bootstrap compiler.
> > There
> > were no regresion failures. Can I check this into GCC 8? This does not
> > need
> > to be checked into GCC 7, since -mabi=ieeelongdouble was not fully
> > supported in
> > that release.
>
> > [libgcc]
> > 2018-04-18 Michael Meissner <meiss...@linux.vnet.ibm.com>
> >
> > PR target/85456
> > * config/rs6000/_powikf2.c: New file. Entry point for
> > __builtin_powil when -mabi=ieeelongdouble is in effect.
> > * config/rs6000/float128-ifunc.c (__powikf2_resolve): Add
> > __powikf2 support.
> > (__powikf2): Likewise.
> > * config/rs6000/quad-float128.h (__powikf2_sw): Likewise.
> > (__powikf2_hw): Likewise.
> > (__powikf2): Likewise.
> > * config/rs6000/t-float128 (fp128_ppc_funcs): Likewise.
> > * config/rs6000/t-float128-hw (fp128_hw_func): Likewise.
> > (_powikf2-hw.c): Likewise.
>
> This changelog does not make too much sense ("__powikf2: Add __powikf2
> support." does not really say what it does, for example).
Ok, I will rewrite it.
> Does the leading underscore in the filename have any meaning? The kc
> files have one, too, but everything else does not.
It comes from all of the libgcc2.c functions are compiled into _<op><mode>3,
etc. I kept the same name for consistancy.
> > +#if defined(FLOAT128_HW_INSNS) && !defined(__powikf2)
> > +#define __powikf2 __powikf2_sw
> > +#endif
>
> This could use a comment (it seems the wrong way around if you don't
> see how it is built).
Ok.
> > +TFtype
> > +__powikf2 (TFtype x, SItype_ppc m)
> > +{
> > + unsigned int n = m < 0 ? -m : m;
> > + TFtype y = n % 2 ? x : 1;
> > + while (n >>= 1)
> > + {
> > + x = x * x;
> > + if (n % 2)
> > + y = y * x;
> > + }
> > + return m < 0 ? 1/y : y;
> > +}
>
> This work correctly for the most negative integer. Okay.
It is a copy of the code from libgcc2.c, so it should be correct :-)
For simple code like this and mulkc3/divkc3, it was simpler to just extract the
code from libgcc2, rather than add appropriate KC/KF support to libgcc2.c.
--
Michael Meissner, IBM
IBM, M/S 2506R, 550 King Street, Littleton, MA 01460-6245, USA
email: meiss...@linux.vnet.ibm.com, phone: +1 (978) 899-4797
