[Bug libstdc++/50661] New: std::equal should use more efficient version for arrays of pointers

[emil at wojak dot eu]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=50661

             Bug #: 50661
           Summary: std::equal should use more efficient version for
                    arrays of pointers
    Classification: Unclassified
           Product: gcc
           Version: 4.4.5
            Status: UNCONFIRMED
          Severity: enhancement
          Priority: P3
         Component: libstdc++
        AssignedTo: unassig...@gcc.gnu.org
        ReportedBy: e...@wojak.eu


The following program uses the generic comparison algorithm in
bits/stl_algobase.h, while it could use the template specialization using
__builtin_memcmp instead.

#include <iostream>
#include <boost/array.hpp>

int main() {
        boost::array<void*, 888> a, b; 

        bool res = std::equal(a.begin(), a.begin() + 50, b.begin());

        return 0;
}

I checked with gcc-4.4.5, but I saw it's the same in SVN trunk.
The following patch solves this issue.

--- /usr/lib/gcc/i686-pc-linux-gnu/4.4.5/include/g++-v4/bits/stl_algobase.h    
2011-09-07 16:34:35.581681814 +0200
+++ /usr/lib/gcc/i686-pc-linux-gnu/4.4.5/include/g++-v4/bits/stl_algobase.h    
 2011-10-08 01:09:44.987380358 +0200
@@ -823,7 +823,7 @@
     {
       typedef typename iterator_traits<_II1>::value_type _ValueType1;
       typedef typename iterator_traits<_II2>::value_type _ValueType2;
-      const bool __simple = (__is_integer<_ValueType1>::__value
+      const bool __simple = ((__is_integer<_ValueType1>::__value ||
__is_pointer<_ValueType1>::__value)
                             && __is_pointer<_II1>::__value
                             && __is_pointer<_II2>::__value
                             && __are_same<_ValueType1, _ValueType2>::__value);