Math-JIT

Math-JIT is a limited-scope implementation of a JIT compiler using cranelift. It compiles arithmetic expressions for the host architecture and exposes a function pointer to the result.

Functionality

The expression parsing is implemented in meval. The common arithmetic operations supported by the compiler are:

• Binary:
  • Addition
  • Subtraction
  • Multiplication
  • Division
  • Powers
• Unary:
  • Negation
• Functions:
  • Sine, cosine, tangent
  • Absolute value
  • Square root

The expressions can utilize 8 variables, values of which are supplied by the caller: x, y, a, b, c, d, _1 and _2. _1 and _2 are in-out variables -- they can be overriden by calling special functions _1(..) and _2(..), which set the values of the two signals to that of their arguments. All reads of the signals observe the value before any writes, and the ordering of writes is unspecified.

Extendability

New 1+ argument functions can be added. Operators and syntax cannot be extended, and 0-argument functions don't work due to a bug in the parser.

What for

Walking the AST or evaluating RPN manually is slow. I'm working on a real-time modular software synthesiser, Modal, which requires 44100 executions per second for multiple modules. Interpreters are sufficient in such cases, but greatly lower the margin of safety.

Other than that, I found the toy language example in cranelift to be quite unapproachable for a complete beginner like myself. This project may prove more useful as introductory material for the codegen-related part of compilers.

Optimizations

After translating expressions to RPN, simple constant folding is performed and variable liveliness is minimized. Functions from the library will be called during constant folding under the assumption that they're pure.

Code please

use math_jit::{Program, Compiler, Library};

let program = Program::parse_from_infix("x * 2 + _1(y)").unwrap();
let mut compiler = Compiler::new(&Library::default()).unwrap();

let func = compiler.compile(&program).unwrap();
let mut sig1 = 0.0;
let mut sig2 = 0.0;
let result = func(3.0, 1.0, 0.0, 0.0, 0.0, 0.0, &mut sig1, &mut sig2);

assert_eq!(result, 7.0);
assert_eq!(sig1, 1.0);
assert_eq!(sig2, 0.0);