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Re: [PATCH, PR59833]: Fix sNaN handling in ARM float to double conversion


On Wed, Jul 20, 2016 at 10:56 AM, Aurelien Jarno <aurelien@aurel32.net> wrote:
> On 2016-07-20 10:10, Ramana Radhakrishnan wrote:
>> On Wed, Jul 20, 2016 at 8:48 AM, Aurelien Jarno <aurelien@aurel32.net> wrote:
>> > On ARM soft-float, the float to double conversion doesn't convert a sNaN
>> > to qNaN as the IEEE Std 754 standard mandates:
>> >
>> > "Under default exception handling, any operation signaling an invalid
>> > operation exception and for which a floating-point result is to be
>> > delivered shall deliver a quiet NaN."
>> >
>> > Given the soft float ARM code ignores exceptions and always provides a
>> > result, a float to double conversion of a signaling NaN should return a
>> > quiet NaN. Fix this in extendsfdf2.
>> >
>> > gcc/ChangeLog:
>> >
>> >         PR target/59833
>> >         * config/arm/ieee754-df.S (extendsfdf2): Convert sNaN to qNaN.
>> >
>> > gcc/testsuite/ChangeLog:
>> >
>> >         * gcc.dg/pr59833.c: New testcase.
>>
>>
>> Ok - assuming this was tested appropriately with no regressions.
>
> Given it only touches arm code, I only tested it on arm and I have seen
> no regression. That said I wouldn't be surprised if the new testcase
> fails on some other architectures.

I was assuming you tested it on ARM :)  In this case given the change
is only in the backend I would have expected this patch to have been
tested for soft-float ARM or an appropriate multilib. Saying what
configuration the patch was tested on is useful for the audit trail.
For e.g. it's no use testing this patch on armhf ( i.e.
--with-float=hard --with-fpu=vfpv3/neon --with-arch=armv7-a) as by
default the test would never generate the call to the library function
but I'm sure you know all that anyway.

I don't know if this would pass or fail on other architectures - if it
fails it indicates a bug in their ports and for them to fix up as
appropriate.


>
> Also I have done the copyright assignment for GCC, but I do not have SVN
> write access. Could someone please commit this for me?

I will take care of it. Thanks again for following up on the patch.

Thanks,
Ramana

>
> Thanks,
> Aurelien
>
> --
> Aurelien Jarno                          GPG: 4096R/1DDD8C9B
> aurelien@aurel32.net                 http://www.aurel32.net


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