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Message-ID: <5A1C0434.5000109@foss.arm.com>
Date: Mon, 27 Nov 2017 12:39:00 -0000
From: Kyrill  Tkachov <kyrylo.tkachov@foss.arm.com>
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To: Sudi Das <Sudi.Das@arm.com>,  "gcc-patches@gcc.gnu.org" <gcc-patches@gcc.gnu.org>
CC: nd <nd@arm.com>, Ramana Radhakrishnan <Ramana.Radhakrishnan@arm.com>,  Richard Earnshaw <Richard.Earnshaw@arm.com>
Subject: Re: [PATCH][ARM] Fix wrong code by arm_final_prescan with fp16 move instructions
References: <4db1e5be-24b1-bab7-d351-b00ef5332728@arm.com>
In-Reply-To: <4db1e5be-24b1-bab7-d351-b00ef5332728@arm.com>
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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?

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.