课程名称：编译程式设计 课程性质：必修 课程老师：陈俊良 开课学院：电资学院 开课系所：资工系 考试日期(年月日)：2010.06.22 考试时限(分钟)：120分钟 是否需发放奖励金：是 (如未明确表示，则不予发放) 试题： 1. The followings are the production rules with semantic actions for assi -gnment, if and while statements. P → {S.next = newLabel();} S {gen(Label S.next);} S → assign {gen(Assign...);} S → {S1.next = newLabel();} S {gen(Label S1.next);S2.next = S.next;} S S → if( {B.true = newLabel();B.false = newLabel();} B) {gen(Label B.true);S5.next = S.next;} S {gen(Label B.false)} S → if( {B.true = newLabel();B.flase = newLabel();} B) {gen(Label B.true);S5.next = S.next;} S else {gen(GotoS.next);gen(LabelB.false);S7.nextS.next;} S S → while( {B.true = newLabel();B.false = S.next; S5.next = newLabel();gen(Label S5.next);} B) {gen(Label B.true);} s {gen(Goto S5.next);} Now, you are asked to add a new statement, break statement, as follow： S → break; A break statement ends a shile loop and moves control to the next statement outside the loop. Within nested statements, the break statement ends only the smallest enclosing while statement. (a) Modify/add the semantic actions to implement this new statement. [20%, at most 15 lines] (b) When a break statement isn't enclosed by any while statement, it is illegal. How does your compiler detect this illegality? [10%, at most 3 lines] 2. (a) What is the purpose of a maker nonterminal in a bottom-up parser? [ 5%, at most 3 lines] (b) What is the purpose of a synthesized record in a top-down parser? [ 5%, at most 3 lines] 3. How to compile a field access of a struct? [20%, at most 10 lines] 4. How to do automatic garbaage collections? [20%, at most 10 lines] 5. What's a compiler? Assume that the audiences are CS freshmen. No 全牛 answer. [20%, at most 10 lines] -- 将竭尽心力所追求的 握紧在手掌之间 入世的那刻早已注定 --

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