AX_EXT: determine if the OS actually supports AVX

AX_EXT checks for different SIMD variants on a CPU. It checks for AVX, but
doesn't 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.

Further details are at <http://savannah.gnu.org/patch/?8084>.

1 files changed, 39 insertions, 14 deletions

diff --git a/m4/ax_ext.m4 b/m4/ax_ext.m4
index 09c7bf2..f660a6a 100644
--- a/m4/ax_ext.m4
+++ b/m4/ax_ext.m4
@@ -10,8 +10,8 @@
 #
 #   Find supported SIMD extensions by requesting cpuid. When an SIMD
 #   extension is found, the -m"simdextensionname" is added to SIMD_FLAGS if
-#   compilator supports it. For example, if "sse2" is available, then
-#   "-msse2" is added to SIMD_FLAGS.
+#   compiler supports it. For example, if "sse2" is available, then "-msse2"
+#   is added to SIMD_FLAGS.
 #
 #   This macro calls:
 #
@@ -24,13 +24,14 @@
 # LICENSE
 #
 #   Copyright (c) 2007 Christophe Tournayre <turn3r@users.sourceforge.net>
+#   Copyright (c) 2013 Michael Petch <mpetch@capp-sysware.com>
 #
 #   Copying and distribution of this file, with or without modification, are
 #   permitted in any medium without royalty provided the copyright notice
 #   and this notice are preserved. This file is offered as-is, without any
 #   warranty.
 
-#serial 11
+#serial 12
 
 AC_DEFUN([AX_EXT],
 [
@@ -57,6 +58,7 @@ AC_DEFUN([AX_EXT],
     i[[3456]]86*|x86_64*|amd64*)
 
       AC_REQUIRE([AX_GCC_X86_CPUID])
+      AC_REQUIRE([AX_GCC_X86_AVX_XGETBV])
 
       AX_GCC_X86_CPUID(0x00000001)
       ecx=`echo $ax_cv_gcc_x86_cpuid_0x00000001 | cut -d ":" -f 3`
@@ -118,21 +120,44 @@ AC_DEFUN([AX_EXT],
         fi
       ])
 
-      AC_CACHE_CHECK([whether avx is supported], [ax_cv_have_avx_ext],
+      AC_CACHE_CHECK([whether avx is supported by processor], [ax_cv_have_avx_cpu_ext],
       [
-        ax_cv_have_avx_ext=no
+        ax_cv_have_avx_cpu_ext=no
         if test "$((0x$ecx>>28&0x01))" = 1; then
-          ax_cv_have_avx_ext=yes
+          ax_cv_have_avx_cpu_ext=yes
         fi
       ])
 
+      if test x"$ax_cv_have_avx_cpu_ext" = x"yes"; then
+        AX_GCC_X86_AVX_XGETBV(0x00000000)
+
+        xgetbv_eax="0"
+        if test x"$ax_cv_gcc_x86_avx_xgetbv_0x00000000" != x"unknown"; then
+          xgetbv_eax=`echo $ax_cv_gcc_x86_avx_xgetbv_0x00000000 | cut -d ":" -f 1`
+        fi
+
+        AC_CACHE_CHECK([whether avx is supported by operating system], [ax_cv_have_avx_ext],
+        [
+          ax_cv_have_avx_ext=no
+
+          if test "$((0x$ecx>>27&0x01))" = 1; then
+            if test "$((0x$xgetbv_eax&0x6))" = 6; then
+              ax_cv_have_avx_ext=yes
+            fi
+          fi
+        ])
+        if test x"$ax_cv_have_avx_ext" = x"no"; then
+          AC_MSG_WARN([Your processor supports AVX, but your operating system doesn't])
+        fi
+      fi
+
       if test "$ax_cv_have_mmx_ext" = yes; then
         AX_CHECK_COMPILE_FLAG(-mmmx, ax_cv_support_mmx_ext=yes, [])
         if test x"$ax_cv_support_mmx_ext" = x"yes"; then
           SIMD_FLAGS="$SIMD_FLAGS -mmmx"
           AC_DEFINE(HAVE_MMX,,[Support mmx instructions])
         else
-          AC_MSG_WARN([Your processor support mmx instructions but not your compilor, can you try another compilor ?])
+          AC_MSG_WARN([Your processor supports mmx instructions but not your compiler, can you try another compiler?])
         fi
       fi
 
@@ -142,7 +167,7 @@ AC_DEFUN([AX_EXT],
           SIMD_FLAGS="$SIMD_FLAGS -msse"
           AC_DEFINE(HAVE_SSE,,[Support SSE (Streaming SIMD Extensions) instructions])
         else
-          AC_MSG_WARN([Your processor support sse instructions but not your compilor, can you try another compilor ?])
+          AC_MSG_WARN([Your processor supports sse instructions but not your compiler, can you try another compiler?])
         fi
       fi
 
@@ -152,7 +177,7 @@ AC_DEFUN([AX_EXT],
           SIMD_FLAGS="$SIMD_FLAGS -msse2"
           AC_DEFINE(HAVE_SSE2,,[Support SSE2 (Streaming SIMD Extensions 2) instructions])
         else
-          AC_MSG_WARN([Your processor support sse2 instructions but not your compilor, can you try another compilor ?])
+          AC_MSG_WARN([Your processor supports sse2 instructions but not your compiler, can you try another compiler?])
         fi
       fi
 
@@ -162,7 +187,7 @@ AC_DEFUN([AX_EXT],
           SIMD_FLAGS="$SIMD_FLAGS -msse3"
           AC_DEFINE(HAVE_SSE3,,[Support SSE3 (Streaming SIMD Extensions 3) instructions])
         else
-          AC_MSG_WARN([Your processor support sse3 instructions but not your compilor, can you try another compilor ?])
+          AC_MSG_WARN([Your processor supports sse3 instructions but not your compiler, can you try another compiler?])
         fi
       fi
 
@@ -172,7 +197,7 @@ AC_DEFUN([AX_EXT],
           SIMD_FLAGS="$SIMD_FLAGS -mssse3"
           AC_DEFINE(HAVE_SSSE3,,[Support SSSE3 (Supplemental Streaming SIMD Extensions 3) instructions])
         else
-          AC_MSG_WARN([Your processor support ssse3 instructions but not your compilor, can you try another compilor ?])
+          AC_MSG_WARN([Your processor supports ssse3 instructions but not your compiler, can you try another compiler?])
         fi
       fi
 
@@ -182,7 +207,7 @@ AC_DEFUN([AX_EXT],
           SIMD_FLAGS="$SIMD_FLAGS -msse4.1"
           AC_DEFINE(HAVE_SSE4_1,,[Support SSSE4.1 (Streaming SIMD Extensions 4.1) instructions])
         else
-          AC_MSG_WARN([Your processor support sse4.1 instructions but not your compilor, can you try another compilor ?])
+          AC_MSG_WARN([Your processor supports sse4.1 instructions but not your compiler, can you try another compiler?])
         fi
       fi
 
@@ -192,7 +217,7 @@ AC_DEFUN([AX_EXT],
           SIMD_FLAGS="$SIMD_FLAGS -msse4.2"
           AC_DEFINE(HAVE_SSE4_2,,[Support SSSE4.2 (Streaming SIMD Extensions 4.2) instructions])
         else
-          AC_MSG_WARN([Your processor support sse4.2 instructions but not your compilor, can you try another compilor ?])
+          AC_MSG_WARN([Your processor supports sse4.2 instructions but not your compiler, can you try another compiler?])
         fi
       fi
 
@@ -202,7 +227,7 @@ AC_DEFUN([AX_EXT],
           SIMD_FLAGS="$SIMD_FLAGS -mavx"
           AC_DEFINE(HAVE_AVX,,[Support AVX (Advanced Vector Extensions) instructions])
         else
-          AC_MSG_WARN([Your processor support avx instructions but not your compilor, can you try another compilor ?])
+          AC_MSG_WARN([Your processor supports avx instructions but not your compiler, can you try another compiler?])
         fi
       fi