Compiler Design and Implementation
Compiler Overview
A compiler translates a program written in one programming language into another. The target language is typically machine language, but it can also be another high-level language or even text. This translation process is called compilation.
Compilers allow developers to write programs in languages closer to human thought processes. These high-level programs are then compiled into a form more readily understood and executed by computers.
The Compilation Process
Compilation translates instructions from a programming language into machine language. Creating an executable program often requires additional tools beyond the compiler itself.
A source program can be divided into modules stored in separate files. A preprocessor often handles the assembly of the source program. It may also expand abbreviations, macro calls, and other source language statements.
Creating an executable typically involves two steps: compilation and linking. Compilation translates source code into low-level code (often object code). Linking combines the generated code from all compiled files, adds library functions, and produces the final executable.
These steps can be performed separately, with object files stored and linked later, or combined into a single process.
Programs can be written in multiple languages (e.g., C, C++, Assembly), compiled separately, and then linked into a single executable.
Compilation Stages
The compilation process involves multiple stages, each performing a specific logical operation. While conceptually distinct, these stages are often integrated in practice.
Analysis Phase
Lexical Analysis
Lexical analysis is the first stage. The source code is read and grouped into tokens—meaningful sequences of characters. Whitespace, comments, and other unnecessary information are removed. The spelling of language symbols (keywords, operators, etc.) is also checked.
Lexical analyzers utilize pattern matching techniques like regular expressions and finite automata. Efficiency is crucial in this stage due to the volume of input processed.
Parsing
Parsing groups tokens hierarchically into grammatical phrases, forming a parse tree. This stage verifies the syntactic correctness of the code according to the language’s grammar. Recursive rules are commonly used to define the hierarchical structure.
The distinction between lexical analysis and parsing is somewhat arbitrary, often based on whether recursion is required. Lexical constructs are typically non-recursive, while syntactic structures often are.
Semantic Analysis
Semantic analysis checks for semantic errors and gathers type information. It uses the parse tree to identify operators and operands. Type checking is a key component, ensuring that operators have compatible operands according to language specifications.
Synthesis Phase
This phase generates object code equivalent to the source program, assuming no errors were found in the analysis phase. The object code can be relocatable machine code or assembly code.
Intermediate Code Generation
Some compilers generate an intermediate representation of the source program. This intermediate form simplifies code generation and optimization. Three-address code is a common intermediate form resembling assembly language.
Code Optimization
Code optimization improves the intermediate code to generate faster-running machine code. Optimizing compilers dedicate significant time to this phase. Even simple optimizations can yield substantial performance improvements.
Key Data Structures
The algorithms and data structures used in each compilation phase are closely intertwined. Efficiency is paramount.
Lexical Tokens
Lexical analyzers typically represent tokens using enumerated data types. Additional information, such as identifier names or numeric values, may also be stored.
Syntax Tree
Syntax trees are usually dynamically allocated pointer-based structures. Each node stores information collected during parsing and semantic analysis, such as data types.
Symbol Table
The symbol table stores information about identifiers, functions, variables, constants, and data types. It is used throughout the compilation process. Efficient insertion, deletion, and lookup operations are essential.
Literal Table
The literal table stores constants and strings, enabling reuse and reducing program size. Fast lookup and insertion are crucial, but deletions are not necessary.
Intermediate Code
Intermediate code can be stored in various formats, such as arrays of strings, temporary files, or linked structures. The choice of representation impacts the efficiency of code optimization.
Temporary Files
While less common due to increased memory capacity, temporary files can still be used to store intermediate results, especially for large programs or when memory is limited.