On Mon, Jan 21, 2019 at 8:43 AM Uros Bizjak <ubiz...@gmail.com> wrote:
>
> On Mon, Jan 21, 2019 at 5:15 PM H.J. Lu <hjl.to...@gmail.com> wrote:
> >
> > TI->SF and TI->DF conversions in libgcc2.c:
> >
> > FSTYPE
> > FUNC (DWtype u)
> > {
> > ...
> > }
> >
> > have no rounding mode support. We should replace __floattisf, __floattidf,
> > __floatuntisf and __floatuntidf in libgcc2.c with these from soft-fp.
> >
> > PR libgcc/88931
> > * config/i386/64/t-softfp-compat (libgcc2-ti-functions): New.
> > (LIB2FUNCS_EXCLUDE): Likewise.
> > (libgcc2-ti-softp): Likewise.
> > (LIB2ADD): Likewise.
> > ---
> > libgcc/config/i386/64/t-softfp-compat | 8 ++++++++
> > 1 file changed, 8 insertions(+)
> >
> > diff --git a/libgcc/config/i386/64/t-softfp-compat
> > b/libgcc/config/i386/64/t-softfp-compat
> > index 0978695c3a4..abb78032bf5 100644
> > --- a/libgcc/config/i386/64/t-softfp-compat
> > +++ b/libgcc/config/i386/64/t-softfp-compat
> > @@ -13,3 +13,11 @@ libgcc2-tf-functions = _divtc3 _multc3 _powitf2
> > LIB2FUNCS_EXCLUDE += $(libgcc2-tf-functions)
> > libgcc2-tf-compats = $(addsuffix .c, $(libgcc2-tf-functions))
> > LIB2ADD += $(addprefix $(srcdir)/config/i386/64/, $(libgcc2-tf-compats))
> > +
> > +# Replace _floatdisf, _floatdidf, _floatundisf and _floatundidf in
> > +# libgcc2.c, which have no rounding mode support, with floattisf.c,
> > +# floattidf.c, floatundisf.c and floatundidf.c from soft-fp.
> > +libgcc2-ti-functions = _floatdisf _floatdidf _floatundisf _floatundidf
> > +LIB2FUNCS_EXCLUDE += $(libgcc2-ti-functions)
> > +libgcc2-ti-softp = floattisf.c floattidf.c floatuntisf.c floatuntidf.c
> > +LIB2ADD += $(addprefix $(srcdir)/soft-fp/, $(libgcc2-ti-softp))
>
> It is not that simple. Please note that libgcc2 functions use FP
> instructions in narrower mode (so, in effect still use FPU), while
> soft-fp functions don't even touch the FPU, and do everything using
> bit twiddling. I think that your change would introduce qoute
> noticeable runtime regressions.
>
By "run-time regressions", did you mean performance or correctness?
--
H.J.
