BF Just-in-Time Compiler

A very over-engineered BrainFuck interpreter/optimizing JIT compiler written in rust.

Usage

  fucker [--int] <program>
  fucker (-d | --debug) <program>
  fucker (-h | --help)

Options:
  -h --help     Show this screen.
  -d --debug    Display intermediate language.
  --int         Use an interpreter instead of the JIT compiler.

What is BrainFuck?

BrainFuck is an esoteric programming language designed to be both turing complete and easy to compile. The environment provides the programmer with an a 30,000 cell array of unsigned bytes and a data pointer. There are only 8 single character commands:

• + : Increment the current memory cell by 1 (with wrapping overflow)
• - : Decrememt the current memory cell by 1 (with wrapping underflow)
• > : Shift the data pointer to the next memory cell
• < : Shift the data pointer to the previous memory cell
• . : Output the current memory cell as an ASCII character
• , : Read one ASCII character from stdin
• [ : Jump to the matching ] if the current memory cell is 0
• ] : Jump to the matching [ if the current memory cell is not 0

Implementation

Optimization

The lowest hanging fruit here is to perform run-length encoding on the instructions. Sequential +, -, > and < commands can be combined before they are executed. Internally this is done by compiling to an intermediate language - which is stored as a vector of Instrs:

pub struct Program {
    pub data: Vec<Instr>,
}

pub enum Instr {
    Incr(u8),
    Decr(u8),
    Next(usize),
    Prev(usize),
    Print,
    Read,
    BeginLoop(usize),
    EndLoop(usize),
}

Without any other optimizations performed (unless you count stripping out comments before execution) this alone results in a ~3x speedup when benchmarked against a BrainFuck Mandelbrot set renderer.

What's next? The more complicated BrainFuck programs are generated from a high level macro language. Decompiling from BrainFuck back to this language could allow me to do more intelligent code execution.

JIT Compiling

While impossible to read BrainFuck code itself, BrainFuck is probably the simplest turing-complete language. This makes it an ideal candidate for exploring JIT compilation.

The first six of our instructions defined in Instr are pretty straitforward to implement in x86-64.

+:

add    BYTE PTR [r10],n

Where:

• r10 is used as the data pointer
• n is the same value that is held by Incr in the Instr enum

-, > and < are equally simple.

Print and Read are slightly more complex but don't require us to do any control flow ourselves.

Benchmarks

Ran on mandelbrot.bf.

Tested with a Intel Core i5-3230M.