Optimize QArrayDataOps::compare for primitive types

Change-Id: If726e3ee8a3635dcec2a316f1a829392de298634
Reviewed-by: Simon Hausmann <simon.hausmann@qt.io>

src/corelib/tools/qarraydataops.h

@@ -199,6 +199,11 @@ struct QPodArrayOps
 
     bool compare(const T *begin1, const T *begin2, size_t n) const
     {
+        // only use memcmp for fundamental types or pointers.
+        // Other types could have padding in the data structure or custom comparison
+        // operators that would break the comparison using memcmp
+        if (QArrayDataPointer<T>::pass_parameter_by_value)
+            return ::memcmp(begin1, begin2, n * sizeof(T)) == 0;
         const T *end1 = begin1 + n;
         while (begin1 != end1) {
             if (*begin1 == *begin2)