Brainfuck LLVM Compiler

Nicholas Ramsay

Transpiles Brainfuck code into LLVM IR, and subsequently, a compiled binary executable. LLVM IR is a standardised representation of code whereby a slew of existing back-end compiler optimizations are already avalaible.

Since Brainfuck syntax comprises exclusively single character tokens, no scanner/tokenizer is needed. Instead the parser LL(1) parses directly over a (subclass of) std::ostream.

The CLI is designed to be identical to that of clang whenever there is overlap. So, if you are familiar with clang's -emit-llvm and the -S/-c options, there is nothing new to learn, the output types are the same.

Additionally, for both input and output file arguments, a "-" denotes stdin and stdout respectively.

Usage

Until executable file output is available, one can use the provided script (which uses llc and clang/lld)

bin/bfc -lS -o output.ll input.bf
sh scripts/make-exe.sh output.ll

chmod +x output
./output

Alternatively, you can simply output an object file, then use clang.

bin/bfc -c -o output.o input.bf
clang -o output output.o

Building

1. Ensure llvm headers are installed
2. Ensure llvm-config is installed (it should be if you have llvm)
3. Simply run make, compiled project is in bin/bfc

Command Line Options

Usage: bfc [--help] [--output VAR] [[--asm]|[--compile]|[--exe]] [--emit-llvm] input

Positional arguments:
  input                       Input file name [default: "-"]

Optional arguments:
  -h, --help                  shows help message and exits 
  -v, --version               prints version information and exits 
  -o, --output                Output executable file name [default: "a.out"]

Stage Selection Options:
  -S, --asm                   LLVM generation and optimization stages and target-specific code generation, producing an assembly file 
  -c, --compile               The above, plus the assembler, generating a target ".o" object file. 
  -e, --exe                   The above, plus linking to produce an executable [default]

Code Generation Options:
  -l, --llvm-ir, --emit-llvm  Emit LLVM IR 

Roadmap

• llvm::Module emitter/code generator via visitor design pattern
• Abstract syntax tree
• LL(1), recursive descent parser
• Command line interface via argument parsing
• Input from stdin or a file
• Output to stdout or a file
• AST debug string representation printing
• Output LLVM IR (.ll)
• Output LLVM Bitcode (.bc)
• Output to assembly (.S)
• Output to object file (.o)
• Output to linked executable
• Source file manager class for tracking cursor position for error reporting
• Error reporter class
• Multiple executable formats besides ELF.
• Customizable LLVM passes
• Customizable target selection
• Add LLVM to project build, so LLVM will be built if not available
• Debug CLI flags, e.g. enable parse tree result debug output
• Make use of environment variables for some flag defaults