> When I run GCC 3.4.3 on this code:
> [...]
> it generates the assembly code (this is i686 assembly)

When doing such test, you shouldn't test it on the function main(),
as it is obviously treated specially.  For example, take this example:

int hello()
{
         return(0);
}

int main()
{
         return(0);
}

And compile it with GCC 3.4.3 on x86.  It gives (simplified):

hello:  pushl   %ebp
         movl    %esp, %ebp
         movl    $0, %eax
         popl    %ebp
         ret

main:   pushl   %ebp
         movl    %esp, %ebp
         subl    $8, %esp
         andl    $-16, %esp
         movl    $0, %eax
         addl    $15, %eax
         addl    $15, %eax
         shrl    $4, %eax
         sall    $4, %eax
         subl    %eax, %esp
         movl    $0, %eax
         leave
         ret

You see the difference.  Note that this was done without any optimization
enabled, the command line was "gcc -c -S a.c"

 > Also, when I just compiled a "return 0;", I would expect that to just
 > generate main and the instruction "ret" (or is it "retn?").

No, because frame pointers aren't omitted by default.  Compile the
above example with the option "-fomit-frame-pointer" and you get what
you want, but only for hello(), not for main().  And that still without
optimization turned on.  To make main() a bit shorter, the option "-O"
is enough.

There probably are many reasons to not omit those additional instructions
from main.  And it's not necessary either, because main() only gets
executed once.

jlh