Function fuel

cranelift/interpreter/src/interpreter.rs:677–715

()

    #[test]
    fn fuel() {
        let code = "function %test() -> i8 {
        block0:
            v0 = iconst.i32 1
            v2 = iconst.i32 1
            v1 = iadd v0, v2
            return v1
        }";

        let func = parse_functions(code).unwrap().into_iter().next().unwrap();
        let mut env = FunctionStore::default();
        env.add(func.name.to_string(), &func);

        // The default interpreter should not enable the fuel mechanism
        let state = InterpreterState::default().with_function_store(env.clone());
        let result = Interpreter::new(state).call_by_name("%test", &[]).unwrap();

        assert_eq!(result, ControlFlow::Return(smallvec![DataValue::I32(2)]));

        // With 3 fuel, we should execute the two iconsts and the iadd, but not the return thus
        // giving a fuel exhausted error
        let state = InterpreterState::default().with_function_store(env.clone());
        let result = Interpreter::new(state)
            .with_fuel(Some(3))
            .call_by_name("%test", &[]);
        match result {
            Err(InterpreterError::FuelExhausted) => {}
            _ => panic!("Expected Err(FuelExhausted), but got {result:?}"),
        }

        // With 4 fuel, we should be able to execute the return instruction, and complete the test
        let state = InterpreterState::default().with_function_store(env.clone());
        let result = Interpreter::new(state)
            .with_fuel(Some(4))
            .call_by_name("%test", &[])
            .unwrap();

        assert_eq!(result, ControlFlow::Return(smallvec![DataValue::I32(2)]));
    }

    // Verifies that writing to the stack on a called function does not overwrite the parents
    // stack slots.