The new value comparison operators will report an error if either operand in the comparison contains more than one value, so using them expedites detection of the error.
Since y is specified in the output operand section, the updated value in %edx is stored in -8(%ebp), the location of y on stack.
因为 y 是在输出操作数部分中指定的，所以 %edx 中更新的值存储在 -8(%ebp)，堆栈上 y 的位置中。
3
If the size of the operand is not specified in the instruction, that means either that the size doesn't matter (as in logical instructions, for instance) or that it is using a 32-bit value size.