From: Gabriel Paubert <paubert@iram.es>
To: David Woodhouse <dwmw2@infradead.org>
Cc: linuxppc-dev@ozlabs.org, Michael Neuling <mikey@neuling.org>,
viro@zeniv.linux.org.uk
Subject: Re: [PATCH] powerpc: provide __bswapdi2
Date: Mon, 13 May 2013 15:12:37 +0200 [thread overview]
Message-ID: <20130513131237.GA16647@visitor2.iram.es> (raw)
In-Reply-To: <1368441493.24723.41.camel@i7.infradead.org>
On Mon, May 13, 2013 at 11:38:13AM +0100, David Woodhouse wrote:
> On Mon, 2013-05-13 at 11:33 +0100, David Woodhouse wrote:
> >
> > On Mon, 2013-05-13 at 09:33 +0200, Gabriel Paubert wrote:
> > > Actually, I'd swap the two mr instructions to never
> > > have an instruction that uses the result from the
> > > previous one.
> >
> > Bad GCC. No biscuit.
> >
> > Should we file a PR?
>
> Maybe not. If you tell it to tune for an in-order machine like Cell, it
> swaps them round. Although now I'm confused about which of POWER[567]
> were in-order:
It was Power6 IIRC. On this kind of fine point, don't rely too much
on what GCC produces.
>
> [dwmw2@i7 ~]$ powerpc64-linux-gnu-gcc -O2 -S -o- bswapdi2.c -m32 | grep -B1 mr
> rlwimi 11,3,24,16,23
> mr 4,11
> mr 3,10
> [dwmw2@i7 ~]$ powerpc64-linux-gnu-gcc -O2 -S -o- bswapdi2.c -m32 -mtune=cell | grep -B1 mr
> rlwimi 11,3,24,16,23
> mr 3,10
> mr 4,11
> [dwmw2@i7 ~]$ powerpc64-linux-gnu-gcc -O2 -S -o- bswapdi2.c -m32 -mtune=power5 | grep -B1 mr
> rlwimi 11,3,24,16,23
> mr 3,10
> mr 4,11
> [dwmw2@i7 ~]$ powerpc64-linux-gnu-gcc -O2 -S -o- bswapdi2.c -m32 -mtune=power6 | grep -B1 mr
> rlwimi 11,3,24,16,23
> mr 4,11
> mr 3,10
> [dwmw2@i7 ~]$ powerpc64-linux-gnu-gcc -O2 -S -o- bswapdi2.c -m32 -mtune=power7 | grep -B1 mr
> rlwimi 11,3,24,16,23
> mr 4,11
> mr 3,10
I don't know of any processor in which putting the mr 3,10 first can cause stalls, so
even a generic tuning should put it first.
Gabriel
next prev parent reply other threads:[~2013-05-13 13:13 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-05-10 21:18 [PATCH] powerpc: provide __bswapdi2 David Woodhouse
2013-05-13 6:48 ` Anton Blanchard
2013-05-13 7:20 ` Alan Modra
2013-05-13 10:27 ` David Woodhouse
2013-05-13 16:47 ` Segher Boessenkool
2013-05-13 7:09 ` Michael Neuling
2013-05-13 7:20 ` [PATCH v2] " Michael Neuling
2013-05-13 7:33 ` [PATCH] " Gabriel Paubert
2013-05-13 10:23 ` [PATCH v3] " Michael Neuling
2013-05-13 10:33 ` [PATCH] " David Woodhouse
2013-05-13 10:38 ` David Woodhouse
2013-05-13 10:51 ` Joakim Tjernlund
2013-05-13 11:12 ` Joakim Tjernlund
2013-05-13 13:12 ` Gabriel Paubert [this message]
2013-05-13 16:55 ` Segher Boessenkool
2013-05-14 1:09 ` Stephen Rothwell
2013-05-14 1:25 ` Michael Neuling
2013-05-14 6:59 ` David Woodhouse
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