Working of __asm__ __volatile__ (“” : : : “memory”)

Question

What basically __asm__ __volatile__ () does and what is significance of \"memory\" for ARM architecture?

Answer 1

static inline unsigned long arch_local_irq_save(void)
{
    unsigned long flags;

    asm volatile(
        "   mrs %0, cpsr    @ arch_local_irq_save\n"
        "   cpsid   i"      //disabled irq
        : "=r" (flags) : : "memory", "cc");
return flags;
}