#include <stdio.h>

/*
$ gcc -O0 a.c -o a-O0 && ./a-O0 > o0
$ gcc -O1 a.c -o a-O1 && ./a-O1 > o1
$ diff -U0 o0 o1

-off>>: 7fffffff
+off>>: ffffffff
*/

typedef unsigned int u32;

u32 bug (u32 * result) __attribute__((noinline));
u32 bug (u32 * result)
{
    // non-static and non-volatile to inhibit constant propagation
    volatile u32 ss = 0xFFFFffff;
    volatile u32 d  = 0xEEEEeeee;
    u32 tt = d & 0x00800000;
    u32 r  = tt << 8;

    // rotate
    r = (r >> 31)
      | (r <<  1);

    u32 u = r^ss;
    u32 off = u >> 1;

    // seemingly unrelated but bug-triggering side-effect
    *result = tt;
    return off;
}

int main() {
    u32 l;
    u32 off = bug(&l);
    printf ("off>>: %08x\n", off);
    return 0;
}