linux-kernel - optimizing out inline functions

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Message-ID: <524f69650805281251r1b1d99a1tc3223d15e3aeb50c@mail.gmail.com>
Date:	Wed, 28 May 2008 14:51:02 -0500
From:	"Steve French" <smfrench@...il.com>
To:	lkml <linux-kernel@...r.kernel.org>
Subject: optimizing out inline functions

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

alternatively I have seen places where people put a #define of do while 0, e.g.

#ifdef CONFIG_DEBUG_SOMETHING
static inline void some_debug_function(var1)
{
    something = var1;
    printk(some debug text);
}
#else
#define some_debug_function(var) do {} while (0)
#endif

Is one or the other style (with or without #define of empty function)
preferred?  Does the compiler optimize both #else clauses out
properly?  sparse and checkpatch seem to take either

-- 
Thanks,

Steve
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