Compilers

Notes

• The compiler is a program that takes your human-readable source code, analyses it, and produces a computer-readable binary code

• The steps of processing involved in compilng are:

  • Preprocessing: reads the input file and substitutes specific macros, symbols and directives with their definitions;

  • Lexical analysis (or tokenization): split the input up character by character, and group them together to form words, identifiers, symbols, and more - these groups are called tokens;

  • Parsing: take the tokens, attempt to see if they're in certain patterns (usually defined by a grammar), then associate those patterns with expressions like calling functions, recalling variables, or math operations; the output of the parser is the abstract syntax tree (AST);

  • Optimisation: take the AST and try to evaluate constant expressions, remove unused variables or unreachable code, unroll loops if possible, etc.;

  • Generating code: take the AST and emit the equivalent in the assembly language in an object file (or other high-level programming languages in the case of a transpiler)

  • Linking: take all the object files and make an executable, a shared library, or a static library

• The front end is responsible for taking in the source code and turning it into an intermediate representation.

• The middle end is responsible for performing various optimizations on the intermediate representation.

  • these optimisations are independent of the target platform, so they are going to speed up the code regardless of what the back end does

  • some examples of optimisations are constant folding, reachability analysis and dead code elimination

• The back end is responsible for taking the optimised intermediate representation and generating the machine code for the specific CPU architecture or generating bytecode.

Resources

Articles

• Writing a C Compiler - Nora Sandler

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