Introduction to Compiler Design

Compiler is a software , converts high level language to low level language .

🔹 Language Levels

• High-Level Language (HLL): Python, Java, C, etc. (easy for humans, independent of machine).
• Low-Level Language: Machine code (binary 0s and 1s, understood by CPU).

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🔹 Language Processing System

When we write a program, it goes through several steps before becoming executable machine code:

High Level Language → Preprocessor → Compiler → Assembler → Linker/Loader → Machine Code

1. Preprocessor

• Handles macros, file inclusion (#include), and conditional compilation.
• Input: High-Level Language (like C source code).
• Output: Modified source code.

2. Compiler

• Converts preprocessed code into Assembly/Intermediate Code.
• Performs analysis + synthesis (phases explained below).

3. Assembler

• Converts assembly code into object code (machine-readable but not yet linked).

4. Linker

• Combines multiple object files and libraries into a single executable file.

5. Loader

• Loads the executable into main memory for execution by CPU.

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🔹 Compiler Phases

A compiler works in two major phases: Analysis (Front-End) and Synthesis (Back-End).

1. Analysis Phase (Front-End)

• Lexical Analyzer (Scanner):

  • Breaks source code into tokens (keywords, identifiers, symbols).
  • Example: int x = 5; → int, x, =, 5, ;

• Syntax Analyzer (Parser):

  • Checks grammar (CFG rules).
  • Example: detects if parentheses/braces are matched.

• Semantic Analyzer:

  • Ensures meaning is correct (type checking, scope rules).
  • Example: int x = "hello"; → error.

• Intermediate Code Generator:

  • Produces intermediate representation (IR), closer to machine code.

2. Synthesis Phase (Back-End)

• Code Optimizer:

  • Improves performance (removes redundancies, optimizes loops).

• Target Code Generator:

  • Converts IR into target machine code.

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🔹 Summary Table

Step	Tool/Phase	Input	Output
1	Preprocessor	HLL Source Code	Modified Source
2	Compiler Front-End	Modified Source	Intermediate Code
3	Compiler Back-End	Intermediate Code	Optimized Code
4	Assembler	Assembly/Intermediate	Object Code
5	Linker	Object Code + Libraries	Executable
6	Loader	Executable	Machine Code in Memory

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Final Flow:
High-Level Language → Preprocessor → Compiler → Assembler → Linker → Loader → Machine Code