P4Dcc

P4Dcc is a tiny, but self-hosted C compiler. It takes C source code and compiles it to assembly language. For assembling and linking, it deletegates to gcc as-is.

This project was started to prove the hypothesis: "Could a self-hostable C compiler be built in four days, if the feature set is carefully limited?" - "P4D" stands for the ISO 8601 notation meaning "four days." However, I actually completed the project by the morning of the third day.

The code is written following the instructions at https://www.sigbus.info/compilerbook, and several key design decisions were inspired by the book.

Dependencies

• gcc
• just, a general-purpose task runner

Build

$ just build

Test

$ just test
$ just test-all  # test all things, including binary equiality between generations

Design

To meet the four-day goal, many design decisions were made to reduce complexity (ideas directly taken from https://www.sigbus.info/compilerbook are not listed):

• Simplified declaration syntax
  • No support for typedef
    • Structs always begin with struct keyword
  • No support for array types
    • No stack-allocated arrays
    • All arrays are heap-allocated and accessed via pointers
  • No support for function types
  • Type information always precede the variable name
• Minimal syntax sugar
  • No increment/decrement operators
    • Partially implemented after self-hosting
  • No compound assignment operators
    • Implemented after self-hosting
  • No while
    • Implemented after self-hosting
  • No switch
• Limited preprocessor
  • Supports only simple #define that replaces identifiers with single integer or identifier
• No global variables
  • Including stdin, stdout, and stderr
  • Only function/struct definitions/declarations are allowed at the top level
• No variable shadowing
  • All variables are function-scoped

License

See LICENSE.