On Mon, 5 Nov 2018 at 15:10, Richard Biener <[email protected]> wrote:
>
> On Fri, Nov 2, 2018 at 10:37 AM Prathamesh Kulkarni
> <[email protected]> wrote:
> >
> > Hi,
> > This patch adds two transforms to match.pd to CSE erf/erfc pair.
> > erfc(x) is canonicalized to 1 - erf(x) and is then reversed to 1 -
> > erf(x) when canonicalization is disabled and result of erf(x) has
> > single use within 1 - erf(x).
> >
> > The patch regressed builtin-nonneg-1.c. The following test-case
> > reproduces the issue with patch:
> >
> > void test(double d1) {
> > if (signbit(erfc(d1)))
> > link_failure_erfc();
> > }
> >
> > ssa dump:
> >
> > <bb 2> :
> > _5 = __builtin_erf (d1_4(D));
> > _1 = 1.0e+0 - _5;
> > _6 = _1 < 0.0;
> > _2 = (int) _6;
> > if (_2 != 0)
> > goto <bb 3>; [INV]
> > else
> > goto <bb 4>; [INV]
> >
> > <bb 3> :
> > link_failure_erfc ();
> >
> > <bb 4> :
> > return;
> >
> > As can be seen, erfc(d1) is folded to 1 - erf(d1).
> > forwprop then transforms the if condition from _2 != 0
> > to _5 > 1.0e+0 and that defeats DCE thus resulting in link failure
> > in undefined reference to link_failure_erfc().
> >
> > So, the patch adds another transform erf(x) > 1 -> 0.
>
> Ick.
>
> Why not canonicalize erf (x) to 1-erfc(x) instead?
Sorry I didn't quite follow, won't this cause similar issue with erf ?
I changed the pattern to canonicalize erf(x) -> 1 - erfc(x)
and 1 - erfc(x) -> erf(x) after canonicalization is disabled.
This caused undefined reference to link_failure_erf() in following test-case:
extern int signbit(double);
extern void link_failure_erf(void);
extern double erf(double);
void test(double d1) {
if (signbit(erf(d1)))
link_failure_erf();
}
forwprop1 shows:
<bb 2> :
_5 = __builtin_erfc (d1_4(D));
_1 = 1.0e+0 - _5;
_6 = _5 > 1.0e+0;
_2 = (int) _6;
if (_5 > 1.0e+0)
goto <bb 3>; [INV]
else
goto <bb 4>; [INV]
<bb 3> :
link_failure_erf ();
<bb 4> :
return;
which defeats DCE to remove call to link_failure_erf.
Thanks,
Prathamesh
>
> > which resolves the regression.
> >
> > Bootstrapped+tested on x86_64-unknown-linux-gnu.
> > Cross-testing on arm and aarch64 variants in progress.
> > OK for trunk if passes ?
> >
> > Thanks,
> > Prathamesh
