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From: Kyle Moffett <mrmacman_g4@mac.com>
Subject: Re: [PATCH] likely cleanup: remove unlikely for kfree(NULL)
Date: Wed, 26 Apr 2006 15:07:28 -0400
To: Bart Hartgers <bart@etpmod.phys.tue.nl>
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Here's code that I've found works as well as can be expected under  
both GCC 3 and GCC 4.  If xp is a known-NULL constant the whole  
function will be optimized out completely.  If xp is known-not-NULL,  
then it will optimize to a kfree function without the null check.   
Otherwise it optimizes to call the out-of-line version.

Cheers,
Kyle Moffett

static inline void kfree(void *ptr)
{
	if (__builtin_constant_p((ptr == NULL))) {
		if (ptr)
			kfree_nonnull(ptr);
	} else {
		kfree_unknown(ptr);
	}
}

void kfree_nonnull(void *ptr)
{
	/* kfree code here, no null check */
}

void kfree_unknown(void *ptr)
{
	if (ptr)
		kfree_nonnull(ptr);
}