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

[Benoit Jacob <jacob.benoit.1@xxxxxxxxx>]

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
>