A delay() is dead in AC6, but OK in AC5, help!

Hi guys:

here is my code ,it works in AC5, but when I change to AC6, it is dead in delay_1ms(), I have no idea why it happened:

struct bsl_data_t{
    uint32_t tick_1ms;
};
static struct bsl_data_t g_bsl;

void TIMER16_IRQHandler(void)
{
    if(SET == timer_interrupt_flag_get(TIMER16, TIMER_INT_UP)){

        /* clear channel 0 interrupt bit */
        timer_interrupt_flag_clear(TIMER16, TIMER_INT_UP);

        /* toggle selected led */
        g_bsl.tick_1ms++;
    }
}

uint32_t get_timer_tick(void)
{
    return g_bsl.tick_1ms;
}

/* x1ms */
#define GET_DIFF_TICK(last_tick) ( (0x100000+get_timer_tick()-last_tick)&0xFFFFF )
#define SET_TICK(var1) var1=get_timer_tick()

void delay_1ms(uint32_t xms)
{
    volatile uint32_t tick,diff=xms;

    SET_TICK(tick);
    while(GET_DIFF_TICK(tick) < diff){}  // dead in here, never come out in AC6.
}

here some picture maybe help:

AC5:

AC6: