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References: <20221002123424.3079805-1-aurelien@aurel32.net> <20221002123424.3079805-7-aurelien@aurel32.net>
In-Reply-To: <20221002123424.3079805-7-aurelien@aurel32.net>
From: Noah Goldstein <goldstein.w.n@gmail.com>
Date: Sun, 2 Oct 2022 17:09:06 -0400
Message-ID: <CAFUsyf+tQ4hGXtR4_OGGZBaqk2DEA85ZKsuuwa_bmnPKhjEesQ@mail.gmail.com>
Subject: Re: [PATCH v2 6/6] x86-64: Require BMI2 for AVX2 memrchr implementation
To: Aurelien Jarno <aurelien@aurel32.net>
Cc: libc-alpha@sourceware.org, "H . J . Lu" <hjl.tools@gmail.com>, 
	Sunil K Pandey <skpgkp2@gmail.com>
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On Sun, Oct 2, 2022 at 8:34 AM Aurelien Jarno <aurelien@aurel32.net> wrote:
>
> The AVX2 memrchr implementation use the 'shlxl' instruction, which
> belongs to the BMI2 CPU feature.
>
> Fixes: af5306a735eb ("x86: Optimize memrchr-avx2.S")
> Partially resolves: BZ #29611
> ---
>  sysdeps/x86_64/multiarch/ifunc-impl-list.c | 3 +++
>  1 file changed, 3 insertions(+)
>
> diff --git a/sysdeps/x86_64/multiarch/ifunc-impl-list.c b/sysdeps/x86_64/multiarch/ifunc-impl-list.c
> index 1c8afa229f..00a91123d3 100644
> --- a/sysdeps/x86_64/multiarch/ifunc-impl-list.c
> +++ b/sysdeps/x86_64/multiarch/ifunc-impl-list.c
> @@ -210,14 +210,17 @@ __libc_ifunc_impl_list (const char *name, struct libc_ifunc_impl *array,
>               X86_IFUNC_IMPL_ADD_V4 (array, i, memrchr,
>                                      (CPU_FEATURE_USABLE (AVX512VL)
>                                       && CPU_FEATURE_USABLE (AVX512BW)
> +                                     && CPU_FEATURE_USABLE (BMI2)
>                                       && CPU_FEATURE_USABLE (LZCNT)),
>                                      __memrchr_evex)
>               X86_IFUNC_IMPL_ADD_V3 (array, i, memrchr,
>                                      (CPU_FEATURE_USABLE (AVX2)
> +                                     && CPU_FEATURE_USABLE (BMI2)
>                                       && CPU_FEATURE_USABLE (LZCNT)),
>                                      __memrchr_avx2)
>               X86_IFUNC_IMPL_ADD_V3 (array, i, memrchr,
>                                      (CPU_FEATURE_USABLE (AVX2)
> +                                     && CPU_FEATURE_USABLE (BMI2)
>                                       && CPU_FEATURE_USABLE (LZCNT)
>                                       && CPU_FEATURE_USABLE (RTM)),
>                                      __memrchr_avx2_rtm)
> --
> 2.35.1
>

LGTM.