branch prediction confusion

branch-predict.c

#include <stdint.h>
#include <stdio.h>
#include <inttypes.h>
#include <string.h>

__attribute__((noinline)) int footest0();
__attribute__((noinline)) int footest1();

int (*ppfootest[1])() = {&footest0};
int foo;

__attribute__((noinline))
int footest0()
{
    ppfootest[0] = footest1;
    return foo++;
}

__attribute__((noinline))
int footest1()
{
    ppfootest[0] = footest0;
    return foo--;
}

int main(int argc, char** argv)
{
    (void)argc;

    int sum = 0;
    switch (argv[1][0])
    {
    case '1': {
        for (int i = 0; i < 100000000; i++) {
            sum += (i & 1) == 0 ? footest0() : footest1();
        }
        break;
              }

    case '2': {
        for (int i = 0; i < 100000000; i++) {
            sum += ppfootest[0]();
        }
        break;
              }
    
    case '3': {
        for (int i = 0; i < 100000000; i++) {
            int (*pfootest)() = (i & 1) == 1 ? &footest0 : &footest1;
            sum += pfootest();
        }
        break;
              }

    case '8': { // WARNING: don't use a lower number :P
        for (int i = 0; i < 100000000; i++) {
            sum += footest0();
        }
        break;
              }

    default:
        printf("bad input\n");
    }
    return sum;
}