第8章语法制导翻译和中间代码[8学时].ppt

* E?not E1 { E.true := E1.false; E.codebegin := E1.codebegin; E.false := E1.true; } (2) E?E1 and E2 { backpatch(E1.true, E2.codebegin); E.codebegin := E1.codebegin; E.true := E2.true; E.false := merge(E1.false, E2.false); } (3) E?E1 or E2 { backpatch(E1.false, E2.codebegin); E.codebegin := E1.codebegin; E.true := merge(E1.true, E2.true); E.false := E2.false; } 布尔表达式译为四元式的语义描述： Evaluation only. Created with Aspose.Slides for .NET 3.5 Client Profile 5.2.0.0. Copyright 2004-2011 Aspose Pty Ltd. (4) E?(E1) { E.true := E1.true; E.codebegin := E1.codebegin; E.false := E1.false; } (5) E?id1 rop id2 { E.true := nextstat; E.codebegin := nextstat; E.false := nextstat + 1; emit(‘if’,id1.place,‘rop’,id2.place,‘goto’,–); emit(‘goto’,-); } (6) E?id { E.true := nextstat; E.codebegin := nextstat; E.false := nextstat + 1; emit(‘if’,id1.place,‘goto’,–); emit(‘goto’,-); } Evaluation only. Created with Aspose.Slides for .NET 3.5 Client Profile 5.2.0.0. Copyright 2004-2011 Aspose Pty Ltd. 控制语句 S ? if E then S1 else S2 E.false E 的代码 E .true E .false: S 2 的代码 goto out E.true: S 1 的代码 out: 控制语句中布尔表达式的翻译 Evaluation only. Created with Aspose.Slides for .NET 3.5 Client Profile 5.2.0.0. Copyright 2004-2011 Aspose Pty Ltd. 举例 将下列控制语句翻译成四元式 if ab or cd and ef then S1 else S2 控制语句中布尔表达式的翻译 if ab goto (i+1) //i+1是S1的入口 if cd goto (4) goto (6) if ef goto (i+1) [关于S2的四元式] ┋ (i) goto (n) //n是S1的出口 (i+1) [关于S1的四元式] ┋ (n) Evaluation only. Created with Aspose.Slides for .NET 3.5 Client Profile 5.2.0.0. Copyright 2004-2011 Aspose Pty Ltd. 例 for I:=1 step 1 until N do M:=M+I 对应的四元式 For循环语句的翻译 I:=1 goto (4) I:=I+1 if I=N goto (6) goto (9) T:=M+I M:=T goto (3) …… Evaluation only. Created with Aspose.Slides for .NET 3.5 Client Profile 5.2.0.0. Copyright 2004-2011 Aspose Pty Ltd. 课堂练习 1(1)(2)(5)(6)(7) 2 [逆波兰式、三元式、四元式序