ELVM Compiler Infrastructure
ELVM is similar to LLVM but dedicated to Esoteric Languages. This project consists of two components - frontend and backend. Currently, the only frontend we have is a modified version of 8cc. The modified 8cc translates C code to an internal representation format called ELVM IR (EIR). Unlike LLVM bitcode, EIR is designed to be extremely simple, so there's more chance we can write a translator from EIR to an esoteric language.
Currently, there are 31 backends:
- C++14 constexpr (compile-time) (by @kw-udon)
- C++ Template Metaprogramming (compile-time) (by @kw-udon) (WIP)
- C# (by @masaedw)
- CommonLisp (by @youz)
- Crystal (compile-time) (by @MakeNowJust)
- Emacs Lisp
- F# (by @masaedw)
- Forth (by @dubek)
- Go (by @shogo82148)
- Perl5 (by @mackee)
- PHP (by @zonuexe)
- SQLite3 (by @youz)
- Swift (by @kwakasa)
- TeX (by @hak7a3)
- TensorFlow (WIP)
- Turing machine (by @ND-CSE-30151)
- Unlambda (by @irori)
- Vim script (by @rhysd)
- arm-linux (by @irori)
The above list contains languages which are known to be difficult to program in, but with ELVM, you can create programs in such languages. You can easily create Brainfuck programs by writing C code for example. One of interesting testcases ELVM has is a tiny Lisp interpreter. The all above language backends are passing the test, which means you can run Lisp on the above languages.
Moreover, 8cc and ELVM themselves are written in C. So we can run a C compiler written in the above languages to compile the ELVM's compiler toolchain itself, though such compilation takes long time in some esoteric languages.
A demo site
Example big programs
- 8cc in Brainfuck
- 8cc in Unlambda
- Lisp in Piet
- Lisp in C-INTERCAL
- 8cc in Befunge
- 8cc in Whitespace
- Harvard architecture, not Neumann (allowing self-modifying code is hard)
- 6 registers: A, B, C, D, SP, and BP
- Ops: mov, add, sub, load, store, setcc, jcc, putc, getc, and exit
- Psuedo ops: .text, .data, .long, and .string
- mul/div/mod are implemented by __builtin_*
- No bit operations
- No floating point arithmetic
- sizeof(char) == sizeof(int) == sizeof(void*) == 1
- The word-size is backend dependent, but most backend uses 24bit words
- A single programming counter may contain multiple operations
See ELVM.md for more detail.
shinh/8cc's eir branch is the frontend C compiler.
ir/ directory has a parser and an interpreter of ELVM IR. ELVM IR has
target/ directory has backend implementations. Code in this directory uses the IR parser to generate backend code.
libc/ directory has an incomplete libc implementation which is necessary to run tests.
Notes on language backends
Running a Lisp interpreter on Brainfuck was the first motivation of this project (bflisp). ELVM IR is designed for Brainfuck but it turned out such a simple IR could be suitable for other esoteric languages.
As Brainfuck is slow, this project contains a Brainfuck interpreter/compiler in tools/bfopt.cc. You can also use other optimized Brainfuck implementations such as tritium. Note you need implementations with 8bit cells. For tritium, you need to specify `-b' flag.
This backend is tested with Emil Jeřábek's interpreter. tools/rununl.sh automatically downloads it.
This backend uses 16bit registers and address space, though ELVM's standard is 24bit. Due to the lack of address space, you cannot compile large C programs using 8cc on C-INTERCAL.
This backend won't be tested by default because C-INTERCAL is slow. Use
$ CINT=1 make i
to run them. Note you may need to adjust tools/runi.sh.
You can make faster executables by doing something like
$ cp out/fizzbuzz.c.eir.i fizzbuzz.i && ick fizzbuzz.i $ ./fizzbuzz
But compilation takes much more time as it uses gcc instead of tcc.
This backend also has 16bit address space. There's the same limitation as C-INTERCAL's.
This backend won't be tested by default because npiet is slow. Use
$ PIET=1 make piet
to run them.
BefLisp, which translates LLVM bitcode to Befunge, has very similar code. The interpreter, tools/befunge.cc is mostly Befunge-93, but its address space is extended to make Befunge-93 Turing-complete.
This backend is somewhat more interesting than other non-esoteric backends. You can run a C compiler on Emacs:
- M-x load-file tools/elvm.el
- open test/putchar.c (or write C code without #include)
- M-x 8cc
- Now you'll see ELVM IR. You need to prepend a backend name (`el' for example) as the first line.
- M-x elc
- M-x eval-buffer
- M-x elvm-main
This backend was contributed by @rhysd. You can run a C compiler on Vim:
- Open test/hello.c (or write your C code)
- Now you can see ELVM IR in the buffer
- Please prepend a backend name (
vimfor Vim) to the first line
- You can see Vim script code as the compilation result in current buffer
- You can
:sourceto run the code
You can find more descriptions and released vim script in 8cc.vim.
C++14 constexpr (compile-time)
This backend is very slow so only limited tests run by default. You can run them by
$ FULL=1 make sed
but it could take years to run all tests. I believe C compiler in sed works, but I haven't confirmed it's working yet. You can try Lisp interpreter instead:
$ FULL=1 make out/lisp.c.eir.sed.out.diff $ echo '(+ 4 3)' | time sed -n -f out/lisp.c.eir.sed
This backend should support both GNU sed and BSD sed, so this backend is more portable than sedlisp, though much slower. Also note, due to limitation of BSD sed, programs cannot output non-ASCII characters and NUL.
Thanks to control flow operations such as tf.while_loop and tf.cond, a TensorFlow's graph is Turing complete. This backend translates EIR to a Python code which constructs a graph which is equivalent to the source EIR. This backend is very slow and uses a huge amount of memory. I've never seen 8cc.c.eir.tf works, but lisp.c.eir.tf does work. You can test this backend by
$ TF=1 make tf
TODO: Reduce the size of the graph and run 8cc
I'm interested in
- adding more backends (e.g., WebAssembly, 16bit CPU, Malbolge Unshackled, ...)
- running more programs (e.g., lua.bf or mruby.bf?)
- supporting more C features (e.g., bit operations)
- eliminating unnecessary code in 8cc
Adding a backend shouldn't be extremely difficult. PRs are welcomed!
This project is a sequel of bflisp.
I'd like to thank Rui Ueyama for his easy-to-hack compiler and suggesting the basic idea which made this possible.