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).
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)
