Re: Optimizing empty functions in C

"Mark Lacey \[MSFT\]" <mlacey@microsoft.com> writes:
>> [What do C++ compilers do? Identical functions in C++ are pretty common
>> when using templates, particularly templates for container classes that
>> don't interpret the data they're containing. -John]
>
>The Microsoft Visual C++ toolset will eliminate duplicated functions
>through a process it calls "identical COMDAT folding" (ICF). By
>specifying -O1 or -O2 for the compilation and -opt:icf as a link
>option, you get this effect. For elimination of (statically)
>unreferenced functions, you again need either -O1 or -O2 on the
>compilation and -opt:ref as a link option. -opt:ref implies -opt:icf
>by default.




/* Does standard C require twice_1 to compare unequal to twice_2? */


#include <stdio.h>


static int twice_1(int x) {return 2*x;}
static int twice_2(int x) {return 2*x;}


int main(void)
{
        printf("twice_1 = %p, twice_2 = %p, %s\n", twice_1, twice_2,
              (twice_1 == twice_2 ? "same" : "different"));


        return 0;
}
--
                Peter-Lawrence.Montgomery@cwi.nl Home: San Rafael, California
                Microsoft Research and CWI
[A footnote in C99 says "There is no linkage between different identifiers."
so I believe the intention is that different functions have different
addresses. -John]

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