编译原理及实现技术（郭德贵）Compiler Construction Principles2.pptVIP

Compiler Construction Principles Implementation Techniques Dr. Ying JIN Main Content of Chapter 6 §6. Semantic Analysis 6.1 Overview of Semantic Analysis 6.2 Symbol Table 6.3 Semantic Analysis of Types 6.4 Semantic Analysis of Declaration 6.5 Semantic Analysis of Body 6.6 Attribute Grammar and Action Grammar Role of Semantic Analysis in a Compiler Review the process of Natural Language Translation 6.1 Overview of Semantic Analysis The differences between Syntax and Semantics(区别) The necessity of semantic analysis(必要性) Classification of Semantics for Programming Languages(分类) How to describe semantics of a programming language formally? (如何形式地描述语义) The main task of Semantic Analysis(主要任务) Differences between Syntax Semantics Syntax: （语法） Rules for describing the structure of a well-defined program; Semantics:（语义） The meaning of syntactic structures of a well-defined program; The Necessity of Semantic Analysis A syntactically correct program can not guarantee that it is meaningful! The Semantic errors for programming languages Undeclared identifier (无声明) The type of operands does not match for their operator; (类型不匹配) ….. Classification of Semantics for Programming Languages Static semantics(静态语义) Can be checked during compilation(编译时检查) For instance： Undeclared identifier Dynamic semantics(动态语义) Can only be checked during execution(执行时检查) For instance： divide zero Formal Description of Semantics Formal Semantics for Programming Languages (形式语义) Attribute Grammar (for static semantics)属性文法 Operational Semantics 操作语义 Denotational Semantics 指称语义 Algebra Semantics 代数语义 Axiomatic Semantics 公理语义 Not as mature as Syntax Analysis Master Course: “Formal Semantics for Programming Languages” Semantic Analyzer(语义分析程序) 依据： (静态)语义定义(自然语言/部分形式化) 目标：基于语法分析树（抽象语法树）检查是否有语义错误，为生成代码提供信息； 输入：语法分析树 输出：带属性信息的语法分析树 数据结构： 符号表（各类标识符的属性信息 – 各类标识符的内部表示） Main Task of Semantic Analysis Establish Symbol Table (符号表)from declaration part Store attributes of identifiers (标识符属性)f