linux-kernel - Re: [PATCH 1/4] compiler.h: introduce unused

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Message-ID: <4F97E5F7.9030305@openvz.org>
Date:	Wed, 25 Apr 2012 15:54:31 +0400
From:	Konstantin Khlebnikov <khlebnikov@...nvz.org>
To:	Cong Wang <xiyou.wangcong@...il.com>
CC:	Linus Torvalds <torvalds@...ux-foundation.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-arch@...r.kernel.org" <linux-arch@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH 1/4] compiler.h: introduce unused_expression() macro

Cong Wang wrote:
> On 04/25/2012 07:26 PM, Konstantin Khlebnikov wrote:
>> Sometimes we want to check some expressions correctness in compile-time without
>> generating extra code. "(void)(e)" does not work if expression has side-effects.
>> This patch introduces macro unused_expression() which helps in this situation.
>>
>
> Interesting, I am wondering why gcc doesn't eliminate the code as we
> pass either -O2 or -Os to it.

It cannot do this if expression has some side-effects, for example if it contains BUG().
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