[g++] make_pair inlining failure?

[John Doe <m8rph at hotmail dot com>]

Hi!

Currently I am participating in a project where a large number of 
objects are inserted into a std::map. Recently someone replaced all calls of
   map_instance.insert( std::make_pair(key, value) );
with
   map_instance.insert( MapType::value_type(key, value) );
claiming it would be faster.

I called it a pseudo optimization because I assumed g++ was able to 
inline std::make_pair with optimizations enabled. I tried to prove it 
using a simple example (see below) and comparing the resulting 
executables. When using empty constructors the executables were 
identical. They were different when having non-empty constructors.

Now I have two questions:
1. Is the g++ recognizing that std::make_pair can and *should* be inlined?
2. Why do the executables differ (especially if 1. is true)?

Note that I refrained from printing something. I was not sure whether 
optimizing would have changed the "observable behavior" in this case (as 
defined in the C++ standard).


Version:
$ g++ --version
g++ (Gentoo 4.4.5 p1.3, pie-0.4.5) 4.4.5


Comparison:

g++ -O3 -s -finline-limit=1000000 code-0.cpp -o a.out-0
hexdump -C a.out-0 > 0.txt
# repeat with other file
diff 0.txt 1.txt | less


Code:

#include <iostream>
#include <map>
#include <cstring>

using namespace std;

struct A
{
     static const size_t SIZE = 1024 * 1024;

     A() : x_(new size_t[SIZE])
     {
         memset(x_, 0, SIZE * sizeof(size_t));
     }

     A(const A& rhs)
     :    x_(new size_t[SIZE])
     {
         memcpy(x_, rhs.x_, SIZE * sizeof(size_t));
     }

     ~A() { delete [] x_; }

     size_t* x_;
};

int main()
{
     std::map<int, A> test;

     // non-optimized case
     test.insert( std::make_pair(1,A()) );
     // optimized case
     //test.insert( std::map<int, A>::value_type(1,A()) );
}