Trait Backend

Source

pub trait Backend {
    type Output;

    // Required method
    fn compile(&self, func: &Function) -> Result<Self::Output, CodegenError>;
}

Expand description

A code generator: lowers a function in SSA form to a concrete target representation.

This is the abstraction the crate is built around. A backend reads the IR a front-end produced and turns it into the form a particular target consumes. The Bytecode backend shipped here emits a flat Program; a backend layered on a native code generator later — LLVM, Cranelift — produces that generator’s own module type, named by the Output associated type. Drawing the boundary as a trait is what lets a front-end be written against codegen without committing to any one target.

A backend does not own the function and keeps no per-call state, so a single instance compiles many functions and is cheap to pass around and share.

§Implementing a backend

A backend’s compile is responsible for rejecting input it cannot lower. The convention the bytecode backend follows is to call Function::validate first and return CodegenError::InvalidIr on failure, so the lowering proper only ever runs on well-formed SSA.

§Examples

Compile with the shipped backend through the trait:

use codegen_lang::{Backend, Bytecode};
use ir_lang::{Builder, Type};

let mut b = Builder::new("noop", &[], Type::Unit);
b.ret(None);

let program = Bytecode.compile(&b.finish()).expect("noop is well-formed");
assert_eq!(program.name(), "noop");