Some code that can get rekt by integer overflow undefined behavior

integer_overflow.c

// Adapated from some code at
// http://stackoverflow.com/questions/3948479/integer-overflow-and-undefined-behavior

#include <stdio.h>
#include <stdlib.h>

// gcc starts optimizing the branch out at -O2; clang never does
void f(int a, int b) {
    if (a > 0 && b > 0) {
        if (a + b <= 0) {
            // this branch may be optimized out by compiler
            printf("<= 0\n");
        } else {
            // this branch might always run
            printf("> 0\n");
        }
    }
}

// gcc starts optimizing the branch out at -O2; clang at -O1
void g(int a) {
    if (a > 0) {
        if (a * 2 <= 0) {
            // this branch may be optimized out by compiler
            printf("<= 0\n");
        } else {
            // this branch might always run
            printf("> 0\n");
        }
    }
}


int main(int argc, char **argv) {
    f(atoi(argv[1]), atoi(argv[2]));
    g(atoi(argv[1]));
    return 0;
}