Awesome

A JITting Brainfuck Interpreter

##What? Brainfuck is a very minimal programming language which models a (limited) Turing Machine. It has a very small set of commmands which makes it an ideal target for a toy compiler project, like this one.

##Why? This was inspired by Erik's post, as well as my interest in building some form of a compiler. This work follows on from the assembler I started building for the early version of Notch's DCPU.

##How?

1. Parse the program
2. Generate code
   1. Pull blocks out of a look-up-table
   2. Construct fixup table
3. Link jumps and printf calls
4. mprotect the code buffer to make it executable
5. Jump to it

Running:

1. Build (with buildjit.sh)
2. Run with a brainfuck program in argv[1], e.g. ./jit '>+++++++++[<++++++++>-]<.>+++++++[<++++>-]<+.+++++++..+++.[-]>++++++++[<++++>-]<.>+++++++++++[<++++++++>-]<-.--------.+++.------.--------.[-]>++++++++[<++++>-]<+.[-]++++++++++.' (From Speedy's implementation over at helloworld.org)

##Issues

• Doesn't support input, yet.
• Handling of invalid commands (AKA comments) is brittle - spaces break it, for instance.
• Isn't doing anything particularly clever. Since the IR is a list with some metadata for loops it's not possible to do any fancy optimisations.
• The lookup-table codegen approach is klunky. Since the code blocks are fixed, smart things like register allocation aren't possible. I guess since block-level info is available it should be feasible to deduce where fragments that repeatedly load & store the same cell could be exchanged for ones that don't waste this time.
• It doesn't bounds-check the pointer, so it's vulnerable to memory corruption attacks.