GCC bug work around in 5.0 through 6.2 inclusive.

configure.ac

@@ -28,11 +28,7 @@ AC_DEFINE_UNQUOTED([GXX_VERSION],["$GXX_VERSION"],
       [version of g++ that will compile the code])
 
 CXXFLAGS="-O3 $CXXFLAGS"
-case ${GXX_VERSION} in
-     6.0.0|6.1.0|6.2.0|5.4.1|5.4.0|5.3.0|5.2.0|5.1.0|5.0.0)
-     CXXFLAGS="-O3 $CXXFLAGS"
-        ;;
-esac
+
 ############### Checks for typedefs, structures, and compiler characteristics
 AC_TYPE_SIZE_T
 AC_TYPE_UINT32_T

lib/simd/Grid_vector_types.h

@@ -327,6 +327,10 @@ class Grid_simd {
   // provides support
   ///////////////////////////////////////
 
+#if (__GNUC__ == 5 ) || ( ( __GNUC__ == 6 ) && __GNUC_MINOR__ < 3 )
+#pragma GCC push_options 
+#pragma GCC optimize ("O0") 
+#endif
   template <class functor>
   friend inline Grid_simd SimdApply(const functor &func, const Grid_simd &v) {
     Grid_simd ret;
@@ -355,7 +359,9 @@ class Grid_simd {
     ret.v = cx.v;
     return ret;
   }
-
+#if (__GNUC__ == 5 ) || ( ( __GNUC__ == 6 ) && __GNUC_MINOR__ < 3 )
+#pragma GCC pop_options
+#endif
   ///////////////////////
   // Exchange 
   // Al Ah , Bl Bh -> Al Bl Ah,Bh