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From: Jeremy Linton <jeremy.linton@arm.com>
To: Liao Chang <liaochang1@huawei.com>,
	catalin.marinas@arm.com, will@kernel.org, broonie@kernel.org,
	mark.rutland@arm.com, maz@kernel.org, joey.gouly@arm.com,
	kristina.martsenko@arm.com, ryan.roberts@arm.com
Cc: linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] arm64: cpufeatures: Clean up temporary variable to simplify code
Date: Fri, 1 Mar 2024 13:46:36 -0600	[thread overview]
Message-ID: <e364b4f9-ce92-43a9-ab06-a0391c5dcc5f@arm.com> (raw)
In-Reply-To: <20240229105208.456704-1-liaochang1@huawei.com>

Hi,

On 2/29/24 04:52, Liao Chang wrote:
> Clean up one temporary variable to simplifiy code in capability
> detection.
> 
> Signed-off-by: Liao Chang <liaochang1@huawei.com>
> ---
>   arch/arm64/kernel/cpufeature.c | 8 ++------
>   1 file changed, 2 insertions(+), 6 deletions(-)
> 
> diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
> index 8d1a634a403e..0e900b23f7ab 100644
> --- a/arch/arm64/kernel/cpufeature.c
> +++ b/arch/arm64/kernel/cpufeature.c
> @@ -3052,13 +3052,9 @@ static void __init enable_cpu_capabilities(u16 scope_mask)
>   	boot_scope = !!(scope_mask & SCOPE_BOOT_CPU);
>   
>   	for (i = 0; i < ARM64_NCAPS; i++) {
> -		unsigned int num;
> -
>   		caps = cpucap_ptrs[i];
> -		if (!caps || !(caps->type & scope_mask))
> -			continue;
> -		num = caps->capability;
> -		if (!cpus_have_cap(num))
> +		if (!caps || !(caps->type & scope_mask) ||
> +		    !cpus_have_cap(caps->capability))
>   			continue;
>   
>   		if (boot_scope && caps->cpu_enable)

Looks functionality equivalent to me, and just to see if it makes a 
binary difference I compiled both variations (gcc 14.0.1) and they do 
result in the same instruction sequence. Meaning gcc is smart enough to 
drop the tmp, its also smart enough equate/apply de Morgan's law. The 
latter might make it more readable too, but I guess its all a matter of 
taste.


Reviewed-by: Jeremy Linton <jeremy.linton@arm.com>



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WARNING: multiple messages have this Message-ID (diff)
From: Jeremy Linton <jeremy.linton@arm.com>
To: Liao Chang <liaochang1@huawei.com>,
	catalin.marinas@arm.com, will@kernel.org, broonie@kernel.org,
	mark.rutland@arm.com, maz@kernel.org, joey.gouly@arm.com,
	kristina.martsenko@arm.com, ryan.roberts@arm.com
Cc: linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] arm64: cpufeatures: Clean up temporary variable to simplify code
Date: Fri, 1 Mar 2024 13:46:36 -0600	[thread overview]
Message-ID: <e364b4f9-ce92-43a9-ab06-a0391c5dcc5f@arm.com> (raw)
In-Reply-To: <20240229105208.456704-1-liaochang1@huawei.com>

Hi,

On 2/29/24 04:52, Liao Chang wrote:
> Clean up one temporary variable to simplifiy code in capability
> detection.
> 
> Signed-off-by: Liao Chang <liaochang1@huawei.com>
> ---
>   arch/arm64/kernel/cpufeature.c | 8 ++------
>   1 file changed, 2 insertions(+), 6 deletions(-)
> 
> diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
> index 8d1a634a403e..0e900b23f7ab 100644
> --- a/arch/arm64/kernel/cpufeature.c
> +++ b/arch/arm64/kernel/cpufeature.c
> @@ -3052,13 +3052,9 @@ static void __init enable_cpu_capabilities(u16 scope_mask)
>   	boot_scope = !!(scope_mask & SCOPE_BOOT_CPU);
>   
>   	for (i = 0; i < ARM64_NCAPS; i++) {
> -		unsigned int num;
> -
>   		caps = cpucap_ptrs[i];
> -		if (!caps || !(caps->type & scope_mask))
> -			continue;
> -		num = caps->capability;
> -		if (!cpus_have_cap(num))
> +		if (!caps || !(caps->type & scope_mask) ||
> +		    !cpus_have_cap(caps->capability))
>   			continue;
>   
>   		if (boot_scope && caps->cpu_enable)

Looks functionality equivalent to me, and just to see if it makes a 
binary difference I compiled both variations (gcc 14.0.1) and they do 
result in the same instruction sequence. Meaning gcc is smart enough to 
drop the tmp, its also smart enough equate/apply de Morgan's law. The 
latter might make it more readable too, but I guess its all a matter of 
taste.


Reviewed-by: Jeremy Linton <jeremy.linton@arm.com>



  parent reply	other threads:[~2024-03-01 19:47 UTC|newest]

Thread overview: 8+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2024-02-29 10:52 [PATCH] arm64: cpufeatures: Clean up temporary variable to simplify code Liao Chang
2024-02-29 10:52 ` Liao Chang
2024-02-29 11:10 ` Mark Rutland
2024-02-29 11:10   ` Mark Rutland
2024-03-01 18:29 ` Catalin Marinas
2024-03-01 18:29   ` Catalin Marinas
2024-03-01 19:46 ` Jeremy Linton [this message]
2024-03-01 19:46   ` Jeremy Linton

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