On 06/25/2012 07:04 PM, Jason Garrett-Glaser wrote:
> On Mon, Jun 25, 2012 at 4:00 PM, Loren Merritt <[email protected]>
> wrote:
>> On Mon, 25 Jun 2012, Jason Garrett-Glaser wrote:
>>
>>>> + packssdw m0, m3 ; m0 = 0, 6, 12, 18, 3, 9, 15, 21
>>>> + packssdw m1, m4 ; m1 = 1, 7, 13, 19, 4, 10, 16, 22
>>>> + packssdw m2, m5 ; m2 = 2, 8, 14, 20, 5, 11, 17, 23
>>>> + ; unpack words:
>>>> + movhlps m3, m0 ; m3 = 3, 9, 15, 21, x, x, x, x
>>>> + punpcklwd m0, m1 ; m0 = 0, 1, 6, 7, 12, 13, 18, 19
>>>> + punpckhwd m1, m2 ; m1 = 4, 5, 10, 11, 16, 17, 22, 23
>>>> + punpcklwd m2, m3 ; m2 = 2, 3, 8, 9, 14, 15, 20, 21
>>>> + ; unpack dwords:
>>>> + punpckhdq m3, m0, m2 ; m3 = 12, 13, 14, 15, 18, 19, 20, 21
>>
>> If you swap the inputs here
>>
>>>> + punpckldq m2, m1 ; m2 = 2, 3, 4, 5, 8, 9, 10, 11
>>>> + ; shuffle qwords:
>>>> + movhlps m4, m2 ; m4 = 8, 9, 10, 11, x, x, x, x
>>>> + movlhps m4, m3 ; m4 = 8, 9, 10, 11, 12, 13, 14, 15
>>>> (final)
>>
>> then you can get away with one less op here
>>
>>>> + movlhps m2, m0 ; m2 = 2, 3, 4, 5, 0, 1, 6, 7
>>>> + movhlps m3, m1 ; m3 = 16, 17, 22, 23, 18, 19, 20, 21
>>
>> at the cost of changing this to shufps or pblendw or vpperm.
>> Which should be a good tradeoff on nehalem+ and k10+, but bad on
>> conroe/penryn/k8.
>>
>>>> + ; shuffle dwords:
>>>> + pshufd m2, m2, q3102 ; m2 = 0, 1, 2, 3, 4, 5, 6, 7
>>>> (final)
>>>> + pshufd m3, m3, q1320 ; m3 = 16, 17, 18, 19, 20, 21, 22, 23
>>>> (final)
>>>
>>> Could some shuffps be used here instead?
>>
>> No, shufps has the constraint that the bottom half must come from one
>> source reg and the top half from the other. vpperm would work.
>
> I meant in place of some of the previous movhlps/movlhps stuff as
> well, not merely the pshufd.
I've been trying to figure out what you mean here, but I can't come up
anything significant. The only thing I could find was
changing:
movhlps m4, m2
movlhps m4, m3
to:
shufps m4, m2, m3, q1032
-Justin
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