Re: [PATCH][ARM] Fix wrong code by arm_final_prescan with fp16 move instructions

[Sudakshina Das <sudi dot das at arm dot com>]

Hi Kyrill

On 27/11/17 12:25, Kyrill Tkachov wrote:
> Hi Sudi,
>
> On 24/11/17 14:57, Sudi Das wrote:
> > Hi
> >
> > For the following test case:
> > __fp16
> > test_select (__fp16 a, __fp16 b, __fp16 c)
> > {
> >    return (a < b) ? b : c;
> > }
> >
> > when compiled with -mfpu=fp-armv8 -march=armv8.2-a+fp16 -marm
> > -mfloat-abi=hard trunk generates wrong code:
> >
> > test_select:
> >          @ args = 0, pretend = 0, frame = 0
> >          @ frame_needed = 0, uses_anonymous_args = 0
> >          @ link register save eliminated.
> >          vcvtb.f32.f16   s0, s0
> >          vcvtb.f32.f16   s15, s1
> >          vcmpe.f32       s0, s15
> >          vmrs    APSR_nzcv, FPSCR
> >          // <------ No conditional branch!
> >          vmov    s1, s2  @ __fp16
> > .L2:
> >          vmov    s0, s1  @ __fp16
> >          bx      lr
> >
> > There should have been a conditional branch there to skip one of the
> > VMOVs.
> > This patch fixes this problem by making *movhf_vfp_fp16 unconditional
> > wherever needed.
> >
> > Testing done: Add a new test case and checked for regressions
> > arm-none-linux-gnueabihf.
> >
> > Is this ok for trunk?
>
> This is ok after assuming a bootstrap on arm-none-linux-gnueabihf passes
> as well.
> Does this bug appear on the GCC 7 branch?
> If so, could you please test this patch on that branch as well if so?

I have tested the patch and also sent a new patch request for gcc-7
https://gcc.gnu.org/ml/gcc-patches/2017-11/msg02577.html

Thanks
Sudi

> Thanks,
> Kyrill
>
> > Sudi
> >
> > ChangeLog entry are as follow:
> >
> > *** gcc/ChangeLog ***
> >
> > 2017-11-24  Sudakshina Das  <sudi.das@arm.com>
> >
> >         * config/arm/vfp.md (*movhf_vfp_fp16): Add conds attribute.
> >
> > *** gcc/testsuite/ChangeLog ***
> >
> > 2017-11-24  Sudakshina Das  <sudi.das@arm.com>
> >
> >         * gcc.target/arm/armv8_2-fp16-move-2.c: New test.