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List:       linux-xfs
Subject:    Re: compile errors
From:       "Andi Kleen" <ak () suse ! de>
Date:       2000-04-27 16:55:46
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On Thu, Apr 27, 2000 at 11:46:05AM -0500, Steve Lord wrote:
> The pragmas are still there because I want to find a way to tell gcc that
> this is an infrequently executed code path. If you know how to do that I
> will change them all.

This is only supported in gcc-current (since about two weeks or so) and 
in the latest GnuPRO release from cygnus. You do it via __builtin_expect(),
e.g.:

	ptr = function(); 
	if (__builtin_expect(ptr == NULL, 0)) { 
		/* error path */
	} 

At least for == NULL checks gcc-current (the upcoming gcc 3.0) will default
to not predicted. When you compile with -freorder-blocks it should also
move the error path out of line (in theory, -freorder-blocks seems to be
still rather buggy). I don't know what GnuPro does exactly with 
__builtin_expect, apparently it is a different implementation.

I'm guess it'll be quite some time until gcc 3.0 is released and accepted
generally for Linux kernel development (the later is probably years away)


-Andi

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