linux-kernel - Re: [PATCH for 3.12] mutex: Avoid gcc version dependent __builtin_constant

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Message-ID: <20131017105243.GM2675@laptop.programming.kicks-ass.net>
Date:	Thu, 17 Oct 2013 12:52:43 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
Cc:	mingo@...nel.org, maarten.lankhorst@...onical.com,
	imirkin@...m.mit.edu, linux-kernel@...r.kernel.org,
	daniel.vetter@...ll.ch, robdclark@...il.com
Subject: Re: [PATCH for 3.12] mutex: Avoid gcc version dependent
 __builtin_constant_p() usage.

On Thu, Oct 17, 2013 at 07:45:29PM +0900, Tetsuo Handa wrote:
> Commit 040a0a37 "mutex: Add support for wound/wait style locks" used
> "!__builtin_constant_p(p == NULL)" but gcc 3.x cannot handle such expression
> correctly, leading to boot failure when built with CONFIG_DEBUG_MUTEXES=y.

So I completely forgot all about this, but wouldn't something like:

 !(__builtin_constant_p(p) && p == NULL)

Not also work and generate the same code?
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