Re: [PATCH] Optimize sin(atan(x)) and cos(atan(x)), take 3 (PR tree-optimization/86829)

[Christophe Lyon <christophe dot lyon at linaro dot org>]

On Fri, 12 Oct 2018 at 13:27, Richard Biener <richard.guenther@gmail.com> wrote:
>
> On Fri, Oct 12, 2018 at 10:08 AM Christophe Lyon
> <christophe.lyon@linaro.org> wrote:
> >
> > On Thu, 11 Oct 2018 at 23:07, Jeff Law <law@redhat.com> wrote:
> > >
> > > On 10/9/18 5:29 PM, Giuliano Augusto Faulin Belinassi wrote:
> > > > Fixed all issues pointed in the previous iteration.
> > > > There is now a significant change regarding how the sin(atan(x))
> > > > constant is calculated, as now it checks for which values such that
> > > > computing 1 + x*x won't overflow. There are two reasons for this
> > > > change: (1) Avoid an intermediate infinity value when optimizing
> > > > cos(atan(x)), and (2) avoid the requirement of separate constants for
> > > > sin(atan(x)) and cos(atan(x)), thus making easier to maintain the
> > > > code.
> > > >
> > > > gcc/ChangeLog
> > > >
> > > > 2018-10-09  Giuliano Belinassi  <giuliano.belinassi@usp.br>
> > > >
> > > >     PR tree-optimization/86829
> > > >     * match.pd: Added sin(atan(x)) and cos(atan(x)) simplification rules.
> > > >     * real.c (build_sinatan_real): New function to build a constant equal to the
> > > >     largest value c such that 1 + c*c will not overflow.
> > > >     * real.h (build_sinatan_real): Allows this function to be called externally.
> > > >
> > > > gcc/testsuite/gcc.dg/ChangeLog
> > > >
> > > > 2018-10-09  Giuliano Belinassi  <giuliano.belinassi@usp.br>
> > > >
> > > >     PR tree-optimization/86829
> > > >     * gcc.dg/sinatan-1.c: New test.
> > > >     * gcc.dg/sinatan-2.c: New test.
> > > >     * gcc.dg/sinatan-3.c: New test.
> > > >
> > > > There are no tests broken in trunk that seems related to this PR.
> > > THanks.  I've installed this onto the trunk.  It's right at the
> > > borderline of what would require a copyright assignment.  So if you're
> > > going to do further work on GCC you should go ahead and start the
> > > copyright assignment process.
> > >
> > > Jeff
> >
> > Hi!
> >
> > The new sinatan-1.c test fails to link against newlib on aarch64-elf:
> > /tmp/ccmp5fP4.o: In function `sinatanl':
> > sinatan-1.c:(.text+0x68): undefined reference to `atanl'
> > sinatan-1.c:(.text+0x70): undefined reference to `sinl'
> > /tmp/ccmp5fP4.o: In function `cosatanl':
> > sinatan-1.c:(.text+0x80): undefined reference to `atanl'
> > sinatan-1.c:(.text+0x88): undefined reference to `cosl'
> > collect2: error: ld returned 1 exit status
> >
> > I'm not familiar enough with newlib to know if it's a newlib bug, or
> > if we should skip the test?
> >
> > On arm-eabi, the same test fails at runtime, but I haven't yet taken
> > the time to reproduce it manually.
>
> target_c99_math might do the trick
>

Yes, if we want to skip the test, but I'm not sure about that?
On arm-eabi, adding some traces in the test indicates that the outputs
of cosatanf, cosatan and cosatanl are wrong.

> > Christophe