Warning[Pa082]: undefined behavior: the order of volatile accesses is undefined in this statement

IAR 警告：Warning[Pa082]: undefined behavior: the order of volatile accesses is undefined in this statement

这个警告在运算符两边都有volatile修饰的变量时出现，volatile修饰的变量一般不用于计算

如：

void test_volatile(void)

{

volatile unsigned char a;
volatile unsigned char b;

unsigned char x,y;

x = a;
y = b;

return (x * y);

}