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


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.

> 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!

Aurelien

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


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