测试AND（1）

L1:     A = true
L3:     iffalse A goto L4
iffalse A goto L4
t1 = true
goto L5
L4:     t1 = false
L5:     A = t1
L2:
测试AND(2)

L1:     A = false
L3:     iffalse A goto L4
iffalse A goto L4
t1 = true
goto L5
L4:     t1 = false
L5:     A = t1
L2:

从上面两个例子可以看出AND的思路是：expr1 AND expr2
的结果和expr1和expr2的false结果一样，即如果两个expr有一个为false就转到AND结果的false入口，当两个都为true时才会转到AND结果的true
测试AND(3)

L1:     A = false
L3:     B = false
L4:     iffalse A goto L5
iffalse B goto L5
t1 = true
goto L6
L5:     t1 = false
L6:     A = t1
L2:

从测试AND(2)可以得出结论