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Date: Wed, 10 Jul 2013 17:01:49 -0400
From: Rich Felker <dalias@...ifal.cx>
To: musl@...ts.openwall.com
Subject: Re: Thinking about release
On Thu, Jul 11, 2013 at 08:34:03AM +1200, Andre Renaud wrote:
> >> What also might be worth testing is whether GCC can compete if you
> >> just give it a naive loop (not the fancy pseudo-vectorized stuff
> >> currently in musl) and good CFLAGS. I know on x86 I was able to beat
> >> the fanciest asm strlen I could come up with simply by writing the
> >> naive loop in C and unrolling it a lot.
> >
> >
> > Duff's device!
>
> That was exactly my first idea too, but interestingly it turns out not
> to have really added any performance improvement. Looking at the
> assembler, with -O3, gcc does a pretty good job of unrolling as it is.
For what it's worth, my testing showed the current memcpy code in musl
and the naive "while (n--) *d++=*s++;" version performing
near-identically at -O3, and both got about 20% faster with
-funroll-all-loops. With -O2 or -Os, the naive version was about 5
times slower.
Rich
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