linux-kernel - Re: ASM flags in general

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Message-ID: <55B69F2D.3070603@zytor.com>
Date:	Mon, 27 Jul 2015 14:14:21 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Uros Bizjak <ubizjak@...il.com>
CC:	Uros Bizjak <uros_bizjak1@....net>, linux-kernel@...r.kernel.org,
	"x86@...nel.org" <x86@...nel.org>, Ingo Molnar <mingo@...nel.org>
Subject: Re: ASM flags in general

On 07/27/2015 01:01 PM, Uros Bizjak wrote:
> On Mon, Jul 27, 2015 at 9:04 PM, H. Peter Anvin <hpa@...or.com> wrote:
> 
>> I wonder if using "set" would be a performance regression over "sbb" for
>> the existing bitops, in which case it would slot quite nicely into this
>> scheme.
> 
> As far as I have looked into the compiled code, following sequence was
> produced when the value was directly used as bool
> 
  [...]
> 
> vs. new sequence:
> 

You misunderstood me: I was referring to *old* versions of gcc (≤ 5); in
order words: can we use the macros I proposed instead of #ifdef?  For
gcc 6+ we obviously want to use the flags output.

	-hpa

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