constant propagation: `a = 1; local = a;` can be replaced by the compiler on`a = 1; local = 1;`跨原子/易失性操作的普通读data_ready=true; //spilling cpu_ram_data_will_read_by_device to RAM, should be memory fence
atomic:以保证易失性操作将是原子的但是,的现代标准C++11 (不是C++0x草案)、C++14和C++17是否保证vol