Doubt regarding a tail optimized code under ‘gdb’

[Amit Saha <amitsaha.in@gmail.com>]

Hello all,

Out of sheer curiosity, I tried to run a tail optimised code under
'gdb'. Consider a tail recursive factorial implementation in C:

<code>

#include <stdio.h>

unsigned long long factorial(unsigned long long fact_so_far, unsigned
long long count, unsigned long long max_count){

if (max_count==0 || max_count==1 || count >= max_count)
        return fact_so_far;
else
{
        printf("%llu  %p \n", count, &factorial);
        return factorial(fact_so_far * count, ++count, max_count);
}

}

int main(int argc, char **argv)
{
        unsigned long long n;
        scanf("%llu", &n);
        printf("\n Factorial %llu \n",factorial(1,0,n));
        return 0;

}


</code>

I place a breakpoint in 'factorial' and I run the above under 'gdb'.
The breakpoint is never hit. Assuming that its tail call optimised (I
have compiled it using gcc -O2), it should hit the breakpoint, at
least once. I get the final result without hitting any breakpoint. For
eg,

(gdb) b factorial
Breakpoint 1 at 0x8048429: file factorial-tail.c, line 3.
(gdb) run
Starting program: /home/amit/quest/codes/factorial-tail
5
0  0x8048420
1  0x8048420
2  0x8048420
3  0x8048420
4  0x8048420

 Factorial 120

Program exited normally.
(gdb)

Where am I going wrong? Any pointers would be appreciated?  I am using
'gdb-6.8-debian' and gcc-4.3.3.


Best Regards,
Amit

-- 
Journal: http://amitksaha.wordpress.com
IRC: cornucopic on #scheme, #lisp, #math, #linux

"Recursion is the basic iteration mechanism in Scheme"
--- http://c2.com/cgi/wiki?TailRecursion