"Linuxppc-dev"
<linuxppc-dev-bounces+joakim.tjernlund=transmode...@lists.ozlabs.org>
wrote 2013/05/13 12:38:13:
>
> 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:
>
> [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
A bit rusty on the ppc asm but can you not remove the mr completely:
rlwimi 10,4,24,16,23
rlwimi 11,3,24,16,23
mr 4,11
mr 3,10
to
rlwimi 4,4,24,16,23
rlwimi 3,3,24,16,23
Jocke
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