Re: [PATCH] powerpc: provide __bswapdi2

[David Woodhouse <dwmw2@infradead.org>]

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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




-- 
David Woodhouse                            Open Source Technology Centre
David.Woodhouse@intel.com                              Intel Corporation

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