Fat Binary - Haswell Detection Bug (and fix)

[John Sully]

That fix is sufficient for our use cases, it looks like we don't exercise
the other code paths.  You would know best as to exactly which features to
detect.

By the way we're really happy with the extra performance in the latest
development builds.  Keep up the good work!


On Thu, Feb 20, 2014 at 12:51 PM, Torbjorn Granlund <tg at gmplib.org> wrote:

> John Sully <john at csquare.ca> writes:
>
>   While testing the latest development code we've discovered that it fails
> on
>   specific Pentium D "Haswell" CPUs.  These CPUs are odd in that they don't
>   have the BMI2 instruction set.  Because of this GMP will crash when it
>   attempts to execute a MULX.  The specific model is: Intel(R) Pentium(R)
> CPU
>   G3420
>
> From Intel's "ARK" pages and from /proc/cpuinfo it seems that AVX is
> also missing.
>
> GMP is not prepared for these instruction omissions.  The AVX problem
> should preclude your system from working also with your patch applied.
>
> Also, fixing fat builds along is not enough.
>
>
> I am glad you spotted this problem before 5.2!
>
> Torbjörn
> Please encrypt, key id 0xC8601622
>