On Mon, 18 Oct 2021 at 17:10, Richard Biener <rguent...@suse.de> wrote:
>
> On Mon, 18 Oct 2021, Prathamesh Kulkarni wrote:
>
> > On Mon, 18 Oct 2021 at 16:18, Richard Biener <rguent...@suse.de> wrote:
> > >
> > > On Mon, 18 Oct 2021, Prathamesh Kulkarni wrote:
> > >
> > > > Hi Richard,
> > > > As suggested in PR, I have attached WIP patch that adds two patterns
> > > > to match.pd:
> > > > erfc(x) --> 1 - erf(x) if canonicalize_math_p() and,
> > > > 1 - erf(x) --> erfc(x) if !canonicalize_math_p().
> > > >
> > > > This works to remove call to erfc for the following test:
> > > > double f(double x)
> > > > {
> > > > double g(double, double);
> > > >
> > > > double t1 = __builtin_erf (x);
> > > > double t2 = __builtin_erfc (x);
> > > > return g(t1, t2);
> > > > }
> > > >
> > > > with .optimized dump shows:
> > > > t1_2 = __builtin_erf (x_1(D));
> > > > t2_3 = 1.0e+0 - t1_2;
> > > >
> > > > However, for the following test:
> > > > double f(double x)
> > > > {
> > > > double g(double, double);
> > > >
> > > > double t1 = __builtin_erfc (x);
> > > > return t1;
> > > > }
> > > >
> > > > It canonicalizes erfc(x) to 1 - erf(x), but does not transform 1 -
> > > > erf(x) to erfc(x) again
> > > > post canonicalization.
> > > > -fdump-tree-folding shows that 1 - erf(x) --> erfc(x) gets applied,
> > > > but then it tries to
> > > > resimplify erfc(x), which fails post canonicalization. So we end up
> > > > with erfc(x) transformed to
> > > > 1 - erf(x) in .optimized dump, which I suppose isn't ideal.
> > > > Could you suggest how to proceed ?
> > >
> > > I applied your patch manually and it does the intended
> > > simplifications so I wonder what I am missing?
> > Would it be OK to always fold erfc(x) -> 1 - erf(x) even when there's
> > no erf(x) in the source ?
>
> I do think it's reasonable to expect erfc to be available when erf
> is and vice versa but note both are C99 specified functions (either
> requires -lm).
OK, thanks. Would it be OK to commit the patch after bootstrap+test ?
Thanks,
Prathamesh
>
> Richard.
>
> > So for the following test:
> > double f(double x)
> > {
> > t1 = __builtin_erfc(x)
> > return t1;
> > }
> >
> > .optimized dump shows:
> > double f (double x)
> > {
> > double t1;
> > double _2;
> >
> > <bb 2> [local count: 1073741824]:
> > _2 = __builtin_erf (x_1(D));
> > t1_3 = 1.0e+0 - _2;
> > return t1_3;
> > }
> >
> > while before patch, it has:
> > t1_4 = __builtin_erfc (x_2(D)); [tail call]
> > return t1_4;
> >
> > Thanks,
> > Prathamesh
> >
> > >
> > > Richard.
> > >
> > > > Thanks,
> > > > Prathamesh
> > > >
> > >
> > > --
> > > Richard Biener <rguent...@suse.de>
> > > SUSE Software Solutions Germany GmbH, Maxfeldstrasse 5, 90409 Nuernberg,
> > > Germany; GF: Felix Imendörffer; HRB 36809 (AG Nuernberg)
> >
>
> --
> Richard Biener <rguent...@suse.de>
> SUSE Software Solutions Germany GmbH, Maxfeldstrasse 5, 90409 Nuernberg,
> Germany; GF: Felix Imendörffer; HRB 36809 (AG Nuernberg)
