Phases of Compiler | Compiler Design

Phases of Compiler

Overview of Compiler Phases

• The video introduces the six phases of a compiler: Lexical Analyzer, Syntax Analyzer, Semantic Analyzer, Intermediate Code Generation, Code Optimization, and Target Code Generation.

• A compiler is defined as a program that converts pure high-level language into assembly language through these six functions.

Detailed Breakdown of Each Phase

Lexical Analyzer

• The first phase is the Lexical Analyzer which takes pure high-level language input (stream of characters) and converts it into a stream of tokens.

• Tokenization is the process where the lexical analyzer transforms the program into tokens for further processing.

Syntax Analyzer

• The Syntax Analyzer constructs a parse tree based on grammar rules. This parse tree serves as an essential structure for subsequent analysis.

Semantic Analyzer

• Following syntax analysis, the Semantic Analyzer creates a semantically verified parse tree to ensure that the syntax adheres to semantic rules.

Intermediate Code Generation

• The output from the semantic analyzer (semantically verified parse tree) is used in Intermediate Code Generation, often represented in three-address code format.

Code Optimization and Target Code Generation

• In this phase, code optimization refines the three-address code into optimized versions before converting it into assembly code during target code generation.

Data Structures and Error Handling

Symbol Table Usage

• Throughout all phases, data structures like symbol tables are utilized to store variable types and values needed during compilation.

Error Reporting Mechanism

• An error handler operates across all phases to report any errors encountered during compilation processes back to users.

Example Program Analysis

Simple Program Breakdown

• A simple example program X = Y + Z * 60 illustrates how each phase processes high-level language input.

Tokenization Process

• The lexical analyzer generates tokens for identifiers (X, Y, Z), operators (+, *), and constants (60), assigning unique identifier numbers for tracking purposes.

Symbol Table Creation

• Tokens are stored in a symbol table with attributes such as identifier number and type (e.g., float for X, Y, Z).

Understanding Compiler Phases and Tokenization

Introduction to Identifiers and Tokenization

• The compiler recognizes operator keywords (e.g., equal to, plus, multiplication) but does not inherently understand identifiers like variable names or function names.

• Variables and function names must be stored in a symbol table for later reference, as the compiler needs to know what these identifiers represent.

Lexical Analysis and Syntax Analysis

• The process of tokenization involves converting code into tokens; for example, "X = Y + Z * 60" is transformed into a series of tokens.

• The output from the lexical analyzer serves as input for the syntax analyzer (parser), which checks the syntactical correctness of the code.

Construction of Parse Trees

• The parser constructs a parse tree based on grammar rules. If successfully constructed, it indicates that the input is syntactically correct.

• Grammar rules are essential for generating parse trees; they define how statements can be structured within the language.

Validating Syntax with Parse Trees

• To validate if a parse tree is correct, each node is checked against its expected value using top-down traversal methods.

• Successful validation confirms that the program's structure adheres to defined grammatical rules.

Semantic Analysis Phase

• The semantic analyzer takes the parse tree as input and outputs a semantically verified version of it, ensuring all variables have appropriate data types.

• Key tasks performed by the semantic analyzer include type checking, undeclared variable detection, and handling multiple declarations.

Type Checking and Type Casting

• Type checking ensures that operations involving variables are valid; mismatched data types lead to errors during compilation.

• Type casting may be necessary when combining different data types (e.g., converting an integer to float).

Importance of Symbol Table in Semantic Analysis

• The symbol table stores information about variables' data types. This information is crucial for semantic analysis but not utilized by lexical analysis directly.

Understanding the Role of Analyzers in Code Compilation

Functions and Their Execution

• The discussion begins with the mention of six different functions within a code set, emphasizing that functions can be called at any time during execution.

• The importance of type matching is highlighted, indicating that a semantic analyzer will store information about declared variables like float X, Y, Z.

Lexical and Semantic Analysis

• An example is provided where an undeclared variable (X) is analyzed. The lexical analyzer converts it into a token but does not verify its declaration.

• When the semantic analyzer checks for undeclared variables, it identifies missing declarations and generates errors accordingly.

Variable Declarations

• Multiple declarations are discussed; for instance, declaring int X and then float X in the same program leads to conflicts.

• The semantic analyzer's role includes identifying these multiple declarations to prevent memory allocation issues.

Type Checking by Semantic Analyzer

• The primary tasks of the semantic analyzer include type checking for undeclared variables and detecting multiple declarations.

• If no issues are found (type mismatches or undeclared variables), the output will be a semantically verified parse tree.

Intermediate Code Generation

• Intermediate code generation produces three-address code, which allows only three maximum variables per operation (e.g., T2 = Y + T1).

• This section also explains how temporary variables are used to store intermediate results before final calculations.

Code Optimization Process

• Code optimization aims to reduce program size or line count. It’s noted as an optional phase since optimized code can sometimes be written directly without additional steps.

Target Code Generation

• Target code generation translates optimized three-address code into assembly language using registers (e.g., storing values in R0 and R1).

Summary of Key Phases in Compilation

• A recap emphasizes the roles of various analyzers:

• Lexical Analyzer: Generates tokens.

• Syntax Analyzer: Constructs parse trees through grammar.

• Semantic Analyzer: Verifies trees semantically while checking for type consistency and variable declarations.

• Intermediate Code Generation: Produces three-address code.

What is Target Code Generation in Compilers?

Overview of Compiler Phases

• The target code generation phase of a compiler is responsible for generating assembly code from the intermediate representation.

• A symbol table is introduced, which serves as a crucial data structure used throughout various phases of the compiler.

• While the semantic analyzer and lexical analyzer primarily utilize the symbol table, it can be accessed by any phase of the compilation process.

• The discussion highlights that understanding these components is essential for grasping how compilers function overall.