[patch #8084] av_ext's AVX check doesn't determine if OS actually supports AVX

[Michael Petch]

URL:
  <http://savannah.gnu.org/patch/?8084>

                 Summary: av_ext's AVX check doesn't determine if OS actually
supports AVX
                 Project: GNU Autoconf Archive
            Submitted by: mdpetch
            Submitted on: Thu 20 Jun 2013 14:37:24 MDT
                Priority: 5 - Normal
                  Status: None
             Assigned to: None
        Originator Email: 
             Open/Closed: Open
         Discussion Lock: Any

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Details:

Per the Intel documentation (see section 13.8.1):
http://www.intel.com/content/dam/www/public/us/en/documents/manuals/64-ia-32-architectures-software-developer-vol-3a-part-1-manual.pdf
) and http://software.intel.com/en-us/blogs/2011/04/14/is-avx-enabled

ax_ext.m4 checks for different SIMD variants on a CPU. It checks for AVX, but
doesn't (IMHO) go far enough to actually be useful in some cases. It is
possible to be on a CPU with AVX support and the OS doesn't support it. We
should be checking that such support exists. This is via an additional check
of cpuinfo's ECX register bit 27. Then one needs to call xgetbv and if
EAX&0b110 = 0b110 then AVX is supported by the CPU and OS.

Attached is a patch to ax_ext.m4 and a new support file
ax_gcc_x86_avx_xgetbv.m4



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File Attachments:


-------------------------------------------------------
Date: Thu 20 Jun 2013 14:37:24 MDT  Name: ax_ext.patch  Size: 2kB   By:
mdpetch

<http://savannah.gnu.org/patch/download.php?file_id=28365>
-------------------------------------------------------
Date: Thu 20 Jun 2013 14:37:24 MDT  Name: ax_gcc_x86_avx_xgetbv.m4  Size: 3kB 
 By: mdpetch

<http://savannah.gnu.org/patch/download.php?file_id=28366>

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