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

[Jeff Law <law at redhat dot com>]

On 10/12/18 8:11 AM, Christophe Lyon wrote:
> 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.
I think skipping on the newlib targets is fine.  I'm much more concerned
about the execution tests -- even if it's the library implementation
that is wrong, it's going to be painful to manage the xfails over time.

jeff