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 ?
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)
