[Bug tree-optimization/108306] false-positive -Warray-bounds warning emitted with -fsanitize=shift

[kees at outflux dot net via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108306

--- Comment #6 from Kees Cook <kees at outflux dot net> ---
Sorry, I forgot to include those details fully! Here's how I'm seeing it:

$ gcc --version
gcc (GCC) 13.0.0 20230105 (experimental)
...
$ gcc -O2 -fno-strict-overflow -fsanitize=shift -Warray-bounds -c -o /dev/null
poc.c
enum psi_task_count {
        NR_IOWAIT,
        NR_PSI_TASK_COUNTS = 4,
};

unsigned int tasks[NR_PSI_TASK_COUNTS];

static void psi_group_change(unsigned int set)
{
        unsigned int t;
        unsigned int state_mask = 0;

        for (t = 0; set; set &= ~(1 << t), t++)
                if (set & (1 << t))
                        tasks[t]++;
}

void psi_task_switch(int sleep)
{
        int set = 0;

        if (sleep)
                set |= (1 << NR_IOWAIT);

        psi_group_change(set);
}