Re: [eigen] Matrix product crashes when compiled with MSVC 2010 in release

[Hauke Heibel <hauke.heibel@xxxxxxxxxxxxxx>]

I already tried all simple things such as using directly the SSE
intrinsics and introducing temporaries. It is just a nasty
optimization error of MSVC.

- Hauke

On Fri, Aug 13, 2010 at 4:12 PM, Benoit Jacob <jacob.benoit.1@xxxxxxxxx> wrote:
> 2010/8/13 Benoit Jacob <jacob.benoit.1@xxxxxxxxx>:
>> 2010/8/13 Hauke Heibel <hauke.heibel@xxxxxxxxxxxxxx>:
>>> On Fri, Aug 13, 2010 at 4:00 PM, Benoit Jacob <jacob.benoit.1@xxxxxxxxx> wrote:
>>>> 2010/8/13 Hauke Heibel <hauke.heibel@xxxxxxxxxxxxxx>:
>>>> Unfortunately, the patch creates a wrong result:
>>>>
>>>> +#if defined(EIGEN_VECTORIZE) && defined(_MSC_VER) && !defined(_WIN64)
>>>> +    const AccPacket tmp1 = ei_pmul(alpha,c);
>>>> +    const AccPacket tmp2 = ei_pmul(alpha,r);
>>>> +    r = ei_padd(tmp1,tmp2);
>>>> +#else
>>>>     r = ei_pmadd(c,alpha,r);
>>>> +#endif
>>>>
>>>> Here, the current code r=pmadd(c,alpha,r) does (in pseudocode):
>>>>
>>>>    r = alpha*c+r.
>>>>
>>>> But your variant does instead:
>>>>
>>>>    r = alpha*c + alpha*r
>>>
>>> Ups, too hasty.
>>
>> Here's a fun counter-proposal: if the issue is really that MSVC
>> mis-compiles ei_pmadd, how about implementing it with asm volatile?
>
> Ah, something to try first: in this acc() method, try replacing this
> ei_pmadd(x,y,z) by
>
>    ei_padd(ei_pmul(x,y), z)
>
> i.e. just don't use our ei_pmadd function. My suspiscion is that
> ei_pmadd might be mis-compiled because it is defined (in
> genericpacketmath.h) before the ei_padd and ei_pmul receive their
> specializations (under arch/SSE/) i.e. that would again be just a
> problem with templates support in MSVC.
>
> Benoit
>
>>
>> Benoit
>>
>
>
>