Better control of AVX kernels

Sometimes it might be desirable that only one of the specifc AVX
kernels (AVX, AVX2, and in the future AVX512) are build, even though the processor
supports all (or several) of these instructions.

The flag --disable-[avx | avx2 | avx512] allows to define which kernels
should NOT be build. The default is: what can be build will be build

configure.ac

@@ -258,19 +258,32 @@ fi
 dnl check whether one can compile with avx - gcc intrinsics
 
 dnl first pass: try with specified CFLAGS and CXXFLAGS
-AC_MSG_CHECKING([whether we can compile AVX intrinsics in C])
-AC_COMPILE_IFELSE([AC_LANG_SOURCE([
- #include <x86intrin.h>
- int main(int argc, char **argv){
- double* q;
- __m256d a1_1 = _mm256_load_pd(q);
- return 0;
- }
- ])],
- [can_compile_avx=yes],
- [can_compile_avx=no]
-)
-AC_MSG_RESULT([${can_compile_avx}])
+
+AC_MSG_CHECKING(whether --enable-avx is specified)
+AC_ARG_ENABLE([avx],
+		AS_HELP_STRING([--enable-avx],
+			       [check whether AVX kernels can be build, default yes]),
+	      [check_avx=no],
+	      [check_avx=yes])
+AC_MSG_RESULT([$check_avx])
+
+if test "${check_avx}" = "yes"; then
+  AC_MSG_CHECKING([whether we can compile AVX intrinsics in C])
+  AC_COMPILE_IFELSE([AC_LANG_SOURCE([
+   #include <x86intrin.h>
+   int main(int argc, char **argv){
+   double* q;
+   __m256d a1_1 = _mm256_load_pd(q);
+   return 0;
+   }
+   ])],
+   [can_compile_avx=yes],
+   [can_compile_avx=no]
+  )
+  AC_MSG_RESULT([${can_compile_avx}])
+else
+  can_compile_avx=no
+fi
 
 dnl if test "${can_compile_avx}" = "yes" ; then
 dnl   AC_MSG_CHECKING([whether we can compile AVX intrinsics in C++])
@@ -293,20 +306,32 @@ dnl     AC_MSG_WARN([Cannot compile C++ with AVX: disabling AVX alltogether])
 dnl   fi
 dnl fi
 
-AC_MSG_CHECKING([whether we can compile AVX2 intrinsics in C])
-AC_COMPILE_IFELSE([AC_LANG_SOURCE([
- #include <x86intrin.h>
- int main(int argc, char **argv){
- double* q;
- __m256d q1 = _mm256_load_pd(q);
- __m256d y1 = _mm256_fmadd_pd(q1, q1, q1);
- return 0;
- }
- ])],
- [can_compile_avx2=yes],
- [can_compile_avx2=no]
-)
-AC_MSG_RESULT([${can_compile_avx2}])
+AC_MSG_CHECKING(whether --enable-avx2 is specified)
+AC_ARG_ENABLE([avx2],
+		AS_HELP_STRING([--enable-avx2],
+			       [check whether AVX2 kernels can be build, default yes]),
+	      [check_avx2=no],
+	      [check_avx2=yes])
+AC_MSG_RESULT([$check_avx2])
+
+if test "${check_avx2}" = "yes"; then
+  AC_MSG_CHECKING([whether we can compile AVX2 intrinsics in C])
+  AC_COMPILE_IFELSE([AC_LANG_SOURCE([
+   #include <x86intrin.h>
+   int main(int argc, char **argv){
+   double* q;
+   __m256d q1 = _mm256_load_pd(q);
+   __m256d y1 = _mm256_fmadd_pd(q1, q1, q1);
+   return 0;
+   }
+   ])],
+   [can_compile_avx2=yes],
+   [can_compile_avx2=no]
+  )
+  AC_MSG_RESULT([${can_compile_avx2}])
+else
+  can_compile_avx2=no
+fi
 
 dnl if test "${can_compile_avx2}" = "yes" ; then
 dnl   AC_MSG_CHECKING([whether we can compile AVX2 intrinsics in C++])