《编译原理-龙书》练习第6章
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6.1 语法树的变体
6.1.1 xy+-*/的表达式在纸上构造DAG是比较容易的，如果用LL或LR文法构造，则如第4章，需要先建表，然后分析。
6.1.2 类似6.1.1
6.2 三地址代码
6.2.1 a + -(b+c)
三地址代码
t1 = b + c
t2 = minus t1
t3 = a + b2
四元式
| op | arg1 | arg2 | result |
| + | b | c | t1 |
| minus | t1 | t2 | |
| + | a | t2 | t3 |
三元式
| op | arg1 | arg2 |
| + | b | c |
| minus | (0) | |
| + | a | (1) |
间接三元式
| 35 | (0) | 0 | + | b | c | ||
| 36 | (1) | 1 | minus | (0) | |||
| 37 | (2) | 2 | + | a | (1) | ||
| op | arg1 | arg2 |
6.2.3
6.3 类型和声明
6.3.1 计算相对地址参考图6-17
float x; 类型float，偏移0
record { float x; float y; } p;
x 类型float，偏移0；y类型float，偏移4；p类型record，偏移0
6.4 表达式的翻译
6.4.1
| E -> E1*E2 | E.addr=new Temp() E.code = E1.code E2.code gen(E.adr '=' E1.addr '+' E2.addr |
| E -> +E2 | E.addr = E1.addr E.code = E2.code |
6.4.2
| E -> E1*E2 | E.addr = new Temp() gen(E.addr '=' E1.addr '+' E2.addr) |
| E -> +E2 | E.addr = E1.addr |
6.4.3 类似例6.12，略
6.4.4-6.4.9 按列存储跟行差距不大，略去；计算位置很容易，略去
6.5 类型检查
6.5.1 仿照图6-27即可
x(float) = s(short) + c(char)
t.type = max(short, char) = float
a1 = widen(s.addr, short, float);
a2 = widen(c.addr, char, float);
x.addr = new Temp()
gen(x.addr '=' a1 '+' a2)
6.5.2
6.6 控制流
6.6.1
1) repeat S while B S -> do S1 while B
B.true = newlabel();
B.false = S.next
S1.next = newlabel();
S.code = label(B.true) S.code label(S1.next) B.code
2) for(S1; B; S2) S3 S -> for(S1; B; S2) S3
相当于 S1 while(B) S3;S2
begin = newlabel()
B.true = newlabel
B.false = S.next
S.code = S1.code label(begin) B.code label(B.true) S2.code S3.code gen('goto' begin)
6.6.2 if(B) { repeat S until !(B) } S -> if(B1) { repeat S1 while(B2) }
start = B1.true = B2.true = newlabel()
B1.false = B2.false = S.next
S1.next = newlabel();
S.code = B1.code label(start) S1.code label(S1.next) B2.code
6.6.3 B -> B1 ^ B2
B.code = B1.code B2.code gen('if' B1 '==' B2 'goto' B.false) gen('goto' B.true)
6.6.4 1) if (a==b && c==d || e==f) x==1;
iffalse a==b goto L3
if c==d goto L2
L3: iffalse e==f goto L1
L2: x==1;
L1:
6.6.5 不会
6.6.6 这道题的意思不知道是不是避免冗余的共同，如果是，对于B->B1&&B2有
B1.true = fall
B1.false = if B.false!=fall then B.false else newlabel()
B2.true = B.true
B2.false = B.false
B.code = if B.false!=fall then B1.code B2.code
else B1.code B2.code label(B1.false)
6.6.7
6.7 回填
6.7.1 1) a==b && (c==d || e==f)
100: if(a==b) goto _102
101: goto _false
102: if(c==d) goto _true
103: goto 104
104: if(e==f) goto _true
105: goto _false
6.7.2
E3.false = E4
S2.next = S3
E4.false = S3
S1.next = E3
E2.true = E3
6.7.3
S4.next = E1
S5.next = S3
S6.next = E1
S7.next = E1
S8.next = S.next
6.8 switch语句
6.8.1
switch ( E ) {
case V1: S1 gen S1.code addPair(V1, L1)
case V2: S2 gen S2.code addPair(V2, L2)
...
case Vn-1: Sn-1 gen Sn-1.code addPair(Vn-1, Ln-1)
default: Sn gen Sn.code default Ln