rust/src/librustc_target/abi/call/wasm32_bindgen_compat.rs

// This is not and has never been a correct C ABI for WebAssembly, but
// for a long time this was the C ABI that Rust used. wasm-bindgen
// depends on ABI details for this ABI and is incompatible with the
// correct C ABI, so this ABI is being kept around until wasm-bindgen
// can be fixed to work with the correct ABI. See #63649 for further
// discussion.

use crate::abi::call::{FnType, ArgType};

fn classify_ret_ty<Ty>(ret: &mut ArgType<'_, Ty>) {
    ret.extend_integer_width_to(32);
}

fn classify_arg_ty<Ty>(arg: &mut ArgType<'_, Ty>) {
    arg.extend_integer_width_to(32);
}

pub fn compute_abi_info<Ty>(fty: &mut FnType<'_, Ty>) {
    if !fty.ret.is_ignore() {
        classify_ret_ty(&mut fty.ret);
    }

    for arg in &mut fty.args {
        if arg.is_ignore() { continue; }
        classify_arg_ty(arg);
    }
}