gistfile1.c

/* If you compile with -O2 the code will print "Wrong behavior", compiling
 * with -O0 the code will print "Correct behavior".
 *
 * Tested with:
 * Apple clang version 2.1 (tags/Apple/clang-163.7.1) (based on LLVM 3.0svn)
 * Target: x86_64-apple-darwin11.3.0
 * Thread model: posix
 */

#include <stdio.h>

int getValue(long long *l) {
    *l = -9223372036854775484LL;
    return 1;
}

void bug(void) {
    long long value, incr, oldvalue;

    incr = -1000;
    if (getValue(&value) != 1) return;

    oldvalue = value;
    value += incr;
    if ((incr < 0 && value > oldvalue) || (incr > 0 && value < oldvalue)) {
        printf("Correct behavior\n");
    } else {
        printf("Wrong behavior\n");
    }
}

int main(void) {
    bug();
}

I'm turning the old code into this one:

    oldvalue = value;
    if ((incr < 0 && oldvalue < 0 && incr < (LLONG_MIN-oldvalue)) ||
        (incr > 0 && oldvalue > 0 && incr > (LLONG_MAX-oldvalue))) {
        printf("Correct behavior\n");
    } else {
        printf("Wrong behavior\n");
    }
    value += incr;

Should be safe since it is guaranteed that all the parts never overflow.
LLONG_MIN-oldvalue can't overflow because oldvalue is guaranteed to be < 0
LLONG_MAX-oldvalue can't overflow because oldvalue is guaranteed to be > 0

Now trying it in practice :)