Introduction to Compiling -- Compiler Design

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1. Compilers

A compiler is a program that translates a source program written in a high-level programming language (like C, Java) into a target program, often machine code or another lower-level form.

Why are Compilers Important?

• Efficiency: Translates human-readable code to efficient machine code.
• Portability: Enables the same code to run on different machines by recompiling.
• Error Detection: Identifies syntax and semantic errors in programs before execution.

Basic Phases of Compilation:

1. Lexical Analysis (Scanning): Breaks down the source code into tokens.
2. Syntax Analysis (Parsing): Checks the structure according to grammatical rules.
3. Semantic Analysis: Ensures that the syntax is logically correct.
4. Intermediate Code Generation: Produces an intermediate form of the source code.
5. Code Optimization: Improves the intermediate code by making it more efficient.
6. Code Generation: Translates the optimized intermediate code into machine code.
7. Code Linking and Assembly: Links machine code with other code and libraries to form an executable.

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2. Analysis of the Source Program

To understand compilation, you first need to understand how the source program is analyzed. This is divided into two parts:

1. Analysis Phase:

The compiler reads the source program and breaks it down into intermediate representations. This involves:

• Lexical Analysis: Identifying tokens like keywords, identifiers, operators.
• Syntax Analysis: Checking if the token sequence adheres to the rules of the language’s grammar.
• Semantic Analysis: Verifying whether the statements make sense logically, like type checking.

2. Synthesis Phase:

The compiler then generates the target machine code from the intermediate representation. This involves:

• Code Optimization
• Code Generation

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3. The Phases of the Compiler

As a refresher, the main phases of the compiler are:

1. Lexical Analysis: Breaks source code into a sequence of tokens.
2. Syntax Analysis: Builds a syntax tree (or parse tree) based on grammar rules.
3. Semantic Analysis: Performs checks like type checking to ensure correctness.
4. Intermediate Code Generation: Converts code into a platform-independent intermediate code.
5. Code Optimization: Optimizes the intermediate code without changing the output.
6. Code Generation: Generates assembly or machine code.
7. Symbol Table Management: Stores information about variables, functions, etc.
8. Error Handling: Detects and handles various types of errors.

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4. Cousins of the Compiler

These are programs that are closely related to compilers but serve different purposes:

1. Preprocessor: A tool that processes the source code before it is compiled, performing tasks like macro substitution, file inclusion, and conditional compilation.

   • Example: In C, #include and #define are handled by the preprocessor.

2. Assembler: Translates assembly code (low-level human-readable instructions) into machine code (binary). It converts assembly instructions into their corresponding machine instructions.

3. Interpreter: Unlike a compiler, which translates the entire program into machine code before execution, an interpreter translates and executes one statement at a time.

   • Example: Python uses an interpreter.

4. Linker: Combines multiple object files (compiled code) into a single executable program. It links the code with necessary libraries.

5. Loader: Loads the executable into memory and prepares it for execution. It takes care of resolving addresses and allocating memory to the program.

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Summary for Module 1:

1. Compiler: Translates high-level code to machine code.
2. Phases of Compilation:
   • Lexical Analysis, Syntax Analysis, Semantic Analysis, Intermediate Code Generation, Optimization, Code Generation.
3. Analysis of Source Program: Breaks down the source into intermediate forms and checks it for correctness.
4. Cousins of Compilers: Preprocessors, Assemblers, Interpreters, Linkers, Loaders.

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