Stages of Compilation

• What is Compilation? 

  • Compilation is a process that translates a program written in a high-level programming language into machine code 
  • Only machine code can be executed by a computer 
  • There are four stages involved in this process: 
  • Lexical Analysis 
  • Syntax Analysis 
  • Code Generation 
  • Optimisation 
• Lexical Analysis

  • Lexical analysis means studying the words or vocabulary of a language 
  • This stage involves identifying lexical 'tokens' in the code 

  
• Syntax Analysis #1

  • Now that tokens have been identified, syntax analysis makes sure they all adhere to the syntax rules of the programming language 
  • A symbol, e.g. '$' could be a valid token but not a valid character according to particular programming languages 
  • The dollar symbol would be flagged as breaking the syntax rules 
  • Other syntax errors programmers commonly make include mismatched parentheses or missing semicolons
• Syntax Analysis #2

  • If the code passes the syntax analysis, the compiler can create an Abstract Syntax Tree (AST) 
  • An AST is a graph-based representation of the code being compiled 
  • An AST is an efficient way to represent the code for the next step 
• Example abstract syntax tree 

  
• Code Generation 

  • This step takes the AST and traverses it to generate object code that can be executed by the computer
• Optimisation 

  • This step modifies the code to make it more efficient without changing its functionality 
  • This is important to attempt because it reduces the memory required to run the code, which leads to faster execution 
  • A common optimisation action is removing duplicate code 
  • If an 'add' function is written twice in the source code, a sophisticated compiler will notice this and include it only once in the object code