linux-kernel - Re: optimizing out inline functions

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Message-ID: <20080528200057.GA7300@uranus.ravnborg.org>
Date:	Wed, 28 May 2008 22:00:57 +0200
From:	Sam Ravnborg <sam@...nborg.org>
To:	Steve French <smfrench@...il.com>
Cc:	lkml <linux-kernel@...r.kernel.org>
Subject: Re: optimizing out inline functions

On Wed, May 28, 2008 at 02:51:02PM -0500, Steve French wrote:
> In trying to remove some macros, I ran across another kernel style
> question.  I see two ways that people try to let the compiler optimize
> out unused code and would like to know which is preferred.  The first
> example uses an empty inline function and trusts the compiler will
> optimize it out.
> 
> #ifdef CONFIG_DEBUG_SOMETHING
> static inline void some_debug_function(var1)
> {
>     something = var1;
>     printk(some debug text);
> }
> #else
> static inline void some_debug_function(var1)
> {
>    /* empty function */
> }
> #endif

With reference to a recent thread about kconfig
I would prefer:
static inline void some_debug_function(var1)
{
	if (KCONFIG_DEBUG_SOMETHING) {
		something = var1;
		printk(some debug text);
	}
}


But we do not have KCONFIG_DEBUG_SOMETHING available
so the second best is to use an empty function
to keep the typechecking in place.

IIRC gcc optimize both away.

	Sam
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