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Re: [PATCH, PR59833]: Fix sNaN handling in ARM float to double conversion
On Wed, Jul 20, 2016 at 1:40 PM, Aurelien Jarno <aurelien@aurel32.net> wrote:
> On 2016-07-20 11:22, Ramana Radhakrishnan wrote:
>> On Wed, Jul 20, 2016 at 11:14 AM, Aurelien Jarno <aurelien@aurel32.net> wrote:
>> > On 2016-07-20 11:04, Ramana Radhakrishnan wrote:
>> >> 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.
>> >
>> > Indeed I should have given more details. I tested it on a Debian armel
>> > machine, and I configured GCC the same way as the Debian package, that
>> > is using --with-arch=armv4t --with-float=soft.
>> >
>> > I built it once with the new test but without the fix and a second time
>> > with both the test and the fix. I have verified that the test fails in
>> > the first case and pass in the second case.
>>
>> Thanks for the info - what about all the other regression tests ? Did
>> you do a full make check and ensure that no other tests regressed in
>> comparison ? Patches need to be tested against the entire regression
>> testsuite and not just what was added.
>
> Yes, I compared the testsuite result between the two runs, and there are
> identical beside this new test (hence my "I have seen no regression" in
> my first answer).
>
Thanks now fixed on trunk.
Ramana
> Aurelien
>
> --
> Aurelien Jarno GPG: 4096R/1DDD8C9B
> aurelien@aurel32.net http://www.aurel32.net