linux-kernel - Re: [PATCH] x86: Introduce ASM flags to bitops

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Message-ID: <20150727154035.GA18213@gmail.com>
Date:	Mon, 27 Jul 2015 17:40:35 +0200
From:	Ingo Molnar <mingo@...nel.org>
To:	Uros Bizjak <uros_bizjak1@....net>
Cc:	linux-kernel@...r.kernel.org, x86@...nel.org,
	Uros Bizjak <ubizjak@...il.com>
Subject: Re: [PATCH] x86: Introduce ASM flags to bitops


* Uros Bizjak <uros_bizjak1@....net> wrote:

> From: Uros Bizjak <ubizjak@...il.com>
> 
> This patch introduces GCC ASM flags to bitops. Instead of e.g.
> 
>    136d7:	48 0f a3 3d 00 00 00 	bt     %rdi,0x0(%rip)
>    136de:	00
>    136df:	19 ff                	sbb    %edi,%edi
>    136e1:	85 ff                	test   %edi,%edi
>    136e3:	0f 95 c0             	setne  %al
> 
> following code is generated:
> 
>    13767:	48 0f a3 3d 00 00 00 	bt     %rdi,0x0(%rip)
>    1376e:	00
>    1376f:	0f 92 c0             	setb   %al
> 
> Similar improvement can be seen in following code:
> 
>     7a6c:	48 0f a3 11          	bt     %rdx,(%rcx)
>     7a70:	19 d2                	sbb    %edx,%edx
>     7a72:	85 d2                	test   %edx,%edx
>     7a74:	74 eb                	je     7a61
> 
> which becomes:
> 
>     7a8c:	48 0f a3 11          	bt     %rdx,(%rcx)
>     7a90:	73 ef                	jae    7a81
> 
> Signed-off-by: Uros Bizjak <ubizjak@...il.com>
> ---
>  arch/x86/include/asm/bitops.h      | 26 ++++++++++++++++++++++++--
>  arch/x86/include/asm/percpu.h      | 18 +++++++++++++++++-
>  arch/x86/include/asm/signal.h      |  6 ++++++
>  arch/x86/include/asm/sync_bitops.h | 18 ++++++++++++++++++
>  4 files changed, 65 insertions(+), 3 deletions(-)

Nothing in your patch seems to be setting __GCC_ASM_FLAG_OUTPUTS__, and the patch 
does not seem to be mailed as part of a larger series ...

So how is this supposed to work?

Thanks,

	Ingo
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