// Reference: ELF Application Binary Interface s390x Supplement
// https://github.com/IBM/s390x-abi

use rustc_abi::{BackendRepr, HasDataLayout, TyAbiInterface};

use crate::callconv::{ArgAbi, FnAbi, Reg, RegKind};
use crate::spec::HasTargetSpec;

fn classify_ret<Ty>(ret: &mut ArgAbi<'_, Ty>) {
    let size = ret.layout.size;
    if size.bits() <= 128 && matches!(ret.layout.backend_repr, BackendRepr::SimdVector { .. }) {
        return;
    }
    if !ret.layout.is_aggregate() && size.bits() <= 64 {
        ret.extend_integer_width_to(64);
    } else {
        ret.make_indirect();
    }
}

fn classify_arg<'a, Ty, C>(cx: &C, arg: &mut ArgAbi<'a, Ty>)
where
    Ty: TyAbiInterface<'a, C> + Copy,
    C: HasDataLayout + HasTargetSpec,
{
    if !arg.layout.is_sized() {
        // Not touching this...
        return;
    }
    if arg.is_ignore() {
        // s390x-unknown-linux-{gnu,musl,uclibc} doesn't ignore ZSTs.
        if cx.target_spec().os == "linux"
            && matches!(&*cx.target_spec().env, "gnu" | "musl" | "uclibc")
            && arg.layout.is_zst()
        {
            arg.make_indirect_from_ignore();
        }
        return;
    }

    let size = arg.layout.size;
    if size.bits() <= 128 {
        if let BackendRepr::SimdVector { .. } = arg.layout.backend_repr {
            // pass non-wrapped vector types using `PassMode::Direct`
            return;
        }

        if arg.layout.is_single_vector_element(cx, size) {
            // pass non-transparent wrappers around a vector as `PassMode::Cast`
            arg.cast_to(Reg { kind: RegKind::Vector, size });
            return;
        }
    }
    if !arg.layout.is_aggregate() && size.bits() <= 64 {
        arg.extend_integer_width_to(64);
        return;
    }

    if arg.layout.is_single_fp_element(cx) {
        match size.bytes() {
            4 => arg.cast_to(Reg::f32()),
            8 => arg.cast_to(Reg::f64()),
            _ => arg.make_indirect(),
        }
    } else {
        match size.bytes() {
            1 => arg.cast_to(Reg::i8()),
            2 => arg.cast_to(Reg::i16()),
            4 => arg.cast_to(Reg::i32()),
            8 => arg.cast_to(Reg::i64()),
            _ => arg.make_indirect(),
        }
    }
}

pub(crate) fn compute_abi_info<'a, Ty, C>(cx: &C, fn_abi: &mut FnAbi<'a, Ty>)
where
    Ty: TyAbiInterface<'a, C> + Copy,
    C: HasDataLayout + HasTargetSpec,
{
    if !fn_abi.ret.is_ignore() {
        classify_ret(&mut fn_abi.ret);
    }

    for arg in fn_abi.args.iter_mut() {
        classify_arg(cx, arg);
    }
}