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Date:      Tue, 22 Jul 2003 16:07:31 -0700
From:      Marcel Moolenaar <marcel@xcllnt.net>
To:        Poul-Henning Kamp <phk@phk.freebsd.dk>
Cc:        cvs-all@FreeBSD.org
Subject:   Re: cvs commit: src/sys/kern init_main.c kern_malloc.c md5c.c subr_autoconf.c subr_mbuf.c subr_prf.c tty_subr.c vfs_cluster.c vfs_subr.c
Message-ID:  <20030722230731.GB61493@athlon.pn.xcllnt.net>
In-Reply-To: <16119.1058914594@critter.freebsd.dk>
References:  <3F1DBD05.A4886D5E@imimic.com> <16119.1058914594@critter.freebsd.dk>

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On Wed, Jul 23, 2003 at 12:56:34AM +0200, Poul-Henning Kamp wrote:
> 
> And the only two criteria I think are trivial to use for proving an
> actual benefit is:
> 	1. less code is generated.
> 	2. it runs faster in tests.

criterium 1 is the worst possible. Only criterium 2 makes sense.

ia64 specifically moves all the hard work to the compiler. It's
not unsurprising that a normal -O yields marginal performance.
Only when one takes advantage of speculation, prefetching and
optimization techniques that increase ILP (which most of the time
imply code expansion -- loop unrolling, inlining, code duplication)
will you see a performance increase.

The old gcc metric of less code is better has been demonstrated
to not work in general nowadays.

-- 
 Marcel Moolenaar	  USPA: A-39004		 marcel@xcllnt.net



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