holey-bytes/hblang/src/son.rs

use {
    crate::{
        ident::Ident,
        instrs,
        lexer::{self, TokenKind},
        log,
        parser::{
            self,
            idfl::{self},
            Expr, ExprRef, FileId, Pos,
        },
        task,
        ty::{self},
        vc::{BitSet, Vc},
        Func, HashMap, IdentityHasher, Offset, OffsetIter, Reloc, Sig, SymKey, TypedReloc, Types,
    },
    alloc::{borrow::ToOwned, string::String, vec::Vec},
    core::{
        assert_matches::debug_assert_matches,
        cell::RefCell,
        convert::identity,
        fmt::{self, Debug, Display, Write},
        format_args as fa,
        hash::{Hash as _, Hasher},
        mem, ops,
    },
    hashbrown::hash_map,
    regalloc2::VReg,
};

const VOID: Nid = 0;
const NEVER: Nid = 1;
const ENTRY: Nid = 2;
const MEM: Nid = 3;

type Nid = u16;

pub mod reg {
    pub const STACK_PTR: Reg = 254;
    pub const ZERO: Reg = 0;
    pub const RET: Reg = 1;
    pub const RET_ADDR: Reg = 31;

    pub type Reg = u8;
}

struct LookupEntry {
    nid: Nid,
    hash: u64,
}

impl core::hash::Hash for LookupEntry {
    fn hash<H: Hasher>(&self, state: &mut H) {
        state.write_u64(self.hash);
    }
}

type Lookup = hashbrown::HashMap<LookupEntry, (), core::hash::BuildHasherDefault<IdentityHasher>>;

struct Nodes {
    values: Vec<Result<Node, Nid>>,
    visited: BitSet,
    free: Nid,
    lookup: Lookup,
}

impl Default for Nodes {
    fn default() -> Self {
        Self {
            values: Default::default(),
            free: Nid::MAX,
            lookup: Default::default(),
            visited: Default::default(),
        }
    }
}

impl Nodes {
    fn trace_mem(&self, mut op: Nid) -> Nid {
        loop {
            op = match self[op].kind {
                Kind::Stre { .. } => self[op].inputs[2],
                Kind::Ptr { .. } | Kind::Load { .. } => self[op].inputs[1],
                _ => break op,
            };
        }
    }

    fn remove_low(&mut self, id: Nid) -> Node {
        let value = mem::replace(&mut self.values[id as usize], Err(self.free)).unwrap();
        self.free = id;
        value
    }

    fn clear(&mut self) {
        self.values.clear();
        self.lookup.clear();
        self.free = Nid::MAX;
    }

    fn new_node_nop(&mut self, ty: impl Into<ty::Id>, kind: Kind, inps: impl Into<Vc>) -> Nid {
        let ty = ty.into();

        let node =
            Node { ralloc_backref: u16::MAX, inputs: inps.into(), kind, ty, ..Default::default() };

        let mut lookup_meta = None;
        if !node.is_lazy_phi() {
            let (raw_entry, hash) = Self::find_node(&mut self.lookup, &self.values, &node);

            let entry = match raw_entry {
                hash_map::RawEntryMut::Occupied(o) => return o.get_key_value().0.nid,
                hash_map::RawEntryMut::Vacant(v) => v,
            };

            lookup_meta = Some((entry, hash));
        }

        if self.free == Nid::MAX {
            self.free = self.values.len() as _;
            self.values.push(Err(Nid::MAX));
        }

        let free = self.free;
        for &d in node.inputs.as_slice() {
            debug_assert_ne!(d, free);
            self.values[d as usize].as_mut().unwrap_or_else(|_| panic!("{d}")).outputs.push(free);
        }
        self.free = mem::replace(&mut self.values[free as usize], Ok(node)).unwrap_err();

        if let Some((entry, hash)) = lookup_meta {
            entry.insert(LookupEntry { nid: free, hash }, ());
        }
        free
    }

    fn find_node<'a>(
        lookup: &'a mut Lookup,
        values: &[Result<Node, Nid>],
        node: &Node,
    ) -> (
        hash_map::RawEntryMut<'a, LookupEntry, (), core::hash::BuildHasherDefault<IdentityHasher>>,
        u64,
    ) {
        let mut hasher = crate::FnvHasher::default();
        node.key().hash(&mut hasher);
        let hash = hasher.finish();
        let entry = lookup
            .raw_entry_mut()
            .from_hash(hash, |n| values[n.nid as usize].as_ref().unwrap().key() == node.key());
        (entry, hash)
    }

    fn remove_node_lookup(&mut self, target: Nid) {
        if !self[target].is_lazy_phi() {
            match Self::find_node(
                &mut self.lookup,
                &self.values,
                self.values[target as usize].as_ref().unwrap(),
            )
            .0
            {
                hash_map::RawEntryMut::Occupied(o) => o.remove(),
                hash_map::RawEntryMut::Vacant(_) => unreachable!(),
            };
        }
    }

    fn new_node_low(
        &mut self,
        ty: impl Into<ty::Id>,
        kind: Kind,
        inps: impl Into<Vc>,
    ) -> (Nid, bool) {
        let id = self.new_node_nop(ty, kind, inps);
        if let Some(opt) = self.peephole(id) {
            debug_assert_ne!(opt, id);
            self.lock(opt);
            self.remove(id);
            self.unlock(opt);
            (opt, true)
        } else {
            (id, false)
        }
    }

    fn new_node(&mut self, ty: impl Into<ty::Id>, kind: Kind, inps: impl Into<Vc>) -> Nid {
        self.new_node_low(ty, kind, inps).0
    }

    fn lock(&mut self, target: Nid) {
        self[target].lock_rc += 1;
    }

    #[track_caller]
    fn unlock(&mut self, target: Nid) {
        self[target].lock_rc -= 1;
    }

    fn remove(&mut self, target: Nid) -> bool {
        if !self[target].is_dangling() {
            return false;
        }

        for i in 0..self[target].inputs.len() {
            let inp = self[target].inputs[i];
            let index = self[inp].outputs.iter().position(|&p| p == target).unwrap();
            self[inp].outputs.swap_remove(index);
            self.remove(inp);
        }

        self.remove_node_lookup(target);
        self.remove_low(target);

        true
    }

    fn peephole(&mut self, target: Nid) -> Option<Nid> {
        use {Kind as K, TokenKind as T};
        match self[target].kind {
            K::BinOp { op } => {
                let &[ctrl, mut lhs, mut rhs] = self[target].inputs.as_slice() else {
                    unreachable!()
                };
                let ty = self[target].ty;

                if let (&K::CInt { value: a }, &K::CInt { value: b }) =
                    (&self[lhs].kind, &self[rhs].kind)
                {
                    return Some(
                        self.new_node(ty, K::CInt { value: op.apply_binop(a, b) }, [ctrl]),
                    );
                }

                if lhs == rhs {
                    match op {
                        T::Sub => return Some(self.new_node(ty, K::CInt { value: 0 }, [ctrl])),
                        T::Add => {
                            let rhs = self.new_node_nop(ty, K::CInt { value: 2 }, [ctrl]);
                            return Some(
                                self.new_node(ty, K::BinOp { op: T::Mul }, [ctrl, lhs, rhs]),
                            );
                        }
                        _ => {}
                    }
                }

                // this is more general the pushing constants to left to help deduplicate expressions more
                let mut changed = false;
                if op.is_comutative() && self[lhs].key() < self[rhs].key() {
                    core::mem::swap(&mut lhs, &mut rhs);
                    changed = true;
                }

                if let K::CInt { value } = self[lhs].kind
                    && op == T::Sub
                {
                    let lhs = self.new_node_nop(ty, K::CInt { value: -value }, [ctrl]);
                    return Some(self.new_node(ty, K::BinOp { op: T::Add }, [ctrl, rhs, lhs]));
                }

                if let K::CInt { value } = self[rhs].kind {
                    match (op, value) {
                        (T::Add | T::Sub | T::Shl, 0) | (T::Mul | T::Div, 1) => return Some(lhs),
                        (T::Mul, 0) => return Some(rhs),
                        _ => {}
                    }
                }

                if op.is_comutative() && self[lhs].kind == (K::BinOp { op }) {
                    let &[_, a, b] = self[lhs].inputs.as_slice() else { unreachable!() };
                    if let K::CInt { value: av } = self[b].kind
                        && let K::CInt { value: bv } = self[rhs].kind
                    {
                        // (a op #b) op #c => a op (#b op #c)
                        let new_rhs =
                            self.new_node_nop(ty, K::CInt { value: op.apply_binop(av, bv) }, [
                                ctrl,
                            ]);
                        return Some(self.new_node(ty, K::BinOp { op }, [ctrl, a, new_rhs]));
                    }

                    if self.is_const(b) {
                        // (a op #b) op c => (a op c) op #b
                        let new_lhs = self.new_node(ty, K::BinOp { op }, [ctrl, a, rhs]);
                        return Some(self.new_node(ty, K::BinOp { op }, [ctrl, new_lhs, b]));
                    }
                }

                if op == T::Add
                    && self[lhs].kind == (K::BinOp { op: T::Mul })
                    && self[lhs].inputs[1] == rhs
                    && let K::CInt { value } = self[self[lhs].inputs[2]].kind
                {
                    // a * #n + a => a * (#n + 1)
                    let new_rhs = self.new_node_nop(ty, K::CInt { value: value + 1 }, [ctrl]);
                    return Some(self.new_node(ty, K::BinOp { op: T::Mul }, [ctrl, rhs, new_rhs]));
                }

                if op == T::Sub && self[lhs].kind == (K::BinOp { op }) {
                    // (a - b) - c => a - (b + c)
                    let &[_, a, b] = self[lhs].inputs.as_slice() else { unreachable!() };
                    let c = rhs;
                    let new_rhs = self.new_node(ty, K::BinOp { op: T::Add }, [ctrl, b, c]);
                    return Some(self.new_node(ty, K::BinOp { op }, [ctrl, a, new_rhs]));
                }

                if changed {
                    return Some(self.new_node(ty, self[target].kind, [ctrl, lhs, rhs]));
                }
            }
            K::UnOp { op } => {
                let &[ctrl, oper] = self[target].inputs.as_slice() else { unreachable!() };
                let ty = self[target].ty;

                if let K::CInt { value } = self[oper].kind {
                    return Some(
                        self.new_node(ty, K::CInt { value: op.apply_unop(value) }, [ctrl]),
                    );
                }
            }
            K::If => {
                let cond = self[target].inputs[1];
                if let K::CInt { value } = self[cond].kind {
                    let ty = if value == 0 { ty::LEFT_UNREACHABLE } else { ty::RIGHT_UNREACHABLE };
                    return Some(self.new_node_nop(ty, K::If, [self[target].inputs[0], cond]));
                }
            }
            K::Phi => {
                if self[target].inputs[1] == self[target].inputs[2] {
                    return Some(self[target].inputs[1]);
                }
            }
            K::Stre { offset } => {
                let parent = self[target].inputs[2];

                if self[parent].kind == (K::Stre { offset }) && self[parent].outputs.len() == 1 {
                    return Some(self.modify_input(parent, 1, self[target].inputs[1]));
                }
            }
            K::Load { offset } => {
                let parent = self[target].inputs[1];

                if self[parent].kind == (K::Stre { offset }) && self[parent].offset != u32::MAX {
                    debug_assert_eq!(self[target].ty, self[parent].ty, "TODO");
                    return Some(self[parent].inputs[1]);
                }

                if self[parent].kind == (K::Load { offset }) && self[parent].offset != u32::MAX {
                    return Some(parent);
                }
            }
            _ => {}
        }

        None
    }

    fn is_const(&self, id: Nid) -> bool {
        matches!(self[id].kind, Kind::CInt { .. })
    }

    fn replace(&mut self, target: Nid, with: Nid) {
        let mut back_press = 0;
        for i in 0..self[target].outputs.len() {
            let out = self[target].outputs[i - back_press];
            let index = self[out].inputs.iter().position(|&p| p == target).unwrap();
            self.lock(target);
            let prev_len = self[target].outputs.len();
            self.modify_input(out, index, with);
            back_press += (self[target].outputs.len() != prev_len) as usize;
            self.unlock(target);
        }

        self.remove(target);
    }

    fn modify_input(&mut self, target: Nid, inp_index: usize, with: Nid) -> Nid {
        self.remove_node_lookup(target);
        debug_assert_ne!(self[target].inputs[inp_index], with);

        let prev = self[target].inputs[inp_index];
        self[target].inputs[inp_index] = with;
        let (entry, hash) = Self::find_node(
            &mut self.lookup,
            &self.values,
            self.values[target as usize].as_ref().unwrap(),
        );
        match entry {
            hash_map::RawEntryMut::Occupied(other) => {
                let rpl = other.get_key_value().0.nid;
                self[target].inputs[inp_index] = prev;
                self.replace(target, rpl);
                rpl
            }
            hash_map::RawEntryMut::Vacant(slot) => {
                slot.insert(LookupEntry { nid: target, hash }, ());
                let index = self[prev].outputs.iter().position(|&o| o == target).unwrap();
                self[prev].outputs.swap_remove(index);
                self[with].outputs.push(target);
                self.remove(prev);

                target
            }
        }
    }

    #[track_caller]
    fn unlock_remove(&mut self, id: Nid) -> bool {
        self[id].lock_rc -= 1;
        self.remove(id)
    }

    fn iter(&self) -> impl DoubleEndedIterator<Item = (Nid, &Node)> {
        self.values.iter().enumerate().filter_map(|(i, s)| Some((i as _, s.as_ref().ok()?)))
    }

    fn graphviz_low(&self, out: &mut String) -> core::fmt::Result {
        use core::fmt::Write;

        for (i, node) in self.iter() {
            let color = if self.is_cfg(i) { "yellow" } else { "white" };
            writeln!(out, "node{i}[label=\"{}\" color={color}]", node.kind)?;
            for (j, &o) in node.outputs.iter().enumerate() {
                let color = if self.is_cfg(i) && self.is_cfg(o) { "red" } else { "lightgray" };
                let index = self[o].inputs.iter().position(|&inp| i == inp).unwrap();
                let style = if index == 0 && !self.is_cfg(o) { "style=dotted" } else { "" };
                writeln!(
                    out,
                    "node{o} -> node{i}[color={color} taillabel={index} headlabel={j} {style}]",
                )?;
            }
        }

        Ok(())
    }

    #[allow(clippy::format_in_format_args)]
    fn basic_blocks_instr(&mut self, out: &mut String, node: Nid) -> core::fmt::Result {
        if self[node].kind != Kind::Loop && self[node].kind != Kind::Region {
            write!(out, "  {node:>2}-c{:>2}: ", self[node].ralloc_backref)?;
        }
        match self[node].kind {
            Kind::Start => unreachable!(),
            Kind::End => unreachable!(),
            Kind::If => write!(out, "  if:      "),
            Kind::Region | Kind::Loop => writeln!(out, "      goto: {node}"),
            Kind::Return => write!(out, " ret:      "),
            Kind::CInt { value } => write!(out, "cint: #{value:<4}"),
            Kind::Phi => write!(out, " phi:      "),
            Kind::Arg { index } => write!(out, " arg: {index:<5}"),
            Kind::BinOp { op } | Kind::UnOp { op } => {
                write!(out, "{:>4}:      ", op.name())
            }
            Kind::Call { func } => {
                write!(out, "call: {func} {}  ", self[node].depth)
            }
            Kind::Entry => write!(out, "ctrl: {:<5}", "entry"),
            Kind::Then => write!(out, "ctrl: {:<5}", "then"),
            Kind::Else => write!(out, "ctrl: {:<5}", "else"),
            Kind::Stck => write!(out, "stck:      "),
            Kind::Load { offset } => write!(out, "load: {offset:<5}"),
            Kind::Stre { offset } => write!(out, "stre: {offset:<5}"),
            _ => unreachable!(),
        }?;

        if self[node].kind != Kind::Loop && self[node].kind != Kind::Region {
            writeln!(
                out,
                " {:<14} {}",
                format!("{:?}", self[node].inputs),
                format!("{:?}", self[node].outputs)
            )?;
        }

        Ok(())
    }

    fn basic_blocks_low(&mut self, out: &mut String, mut node: Nid) -> core::fmt::Result {
        let iter = |nodes: &Nodes, node| nodes[node].outputs.clone().into_iter().rev();
        while self.visited.set(node) {
            match self[node].kind {
                Kind::Start => {
                    writeln!(out, "start: {}", self[node].depth)?;
                    let mut cfg_index = Nid::MAX;
                    for o in iter(self, node) {
                        self.basic_blocks_instr(out, o)?;
                        if self[o].kind.is_cfg() {
                            cfg_index = o;
                        }
                    }
                    node = cfg_index;
                }
                Kind::End => break,
                Kind::If => {
                    self.basic_blocks_low(out, self[node].outputs[0])?;
                    node = self[node].outputs[1];
                }
                Kind::Region => {
                    writeln!(
                        out,
                        "region{node}: {} {} {:?}",
                        self[node].depth, self[node].loop_depth, self[node].inputs
                    )?;
                    let mut cfg_index = Nid::MAX;
                    for o in iter(self, node) {
                        self.basic_blocks_instr(out, o)?;
                        if self.is_cfg(o) {
                            cfg_index = o;
                        }
                    }
                    node = cfg_index;
                }
                Kind::Loop => {
                    writeln!(
                        out,
                        "loop{node}: {} {} {:?}",
                        self[node].depth, self[node].loop_depth, self[node].outputs
                    )?;
                    let mut cfg_index = Nid::MAX;
                    for o in iter(self, node) {
                        self.basic_blocks_instr(out, o)?;
                        if self.is_cfg(o) {
                            cfg_index = o;
                        }
                    }
                    node = cfg_index;
                }
                Kind::Return => {
                    node = self[node].outputs[0];
                }
                Kind::Then | Kind::Else | Kind::Entry => {
                    writeln!(
                        out,
                        "b{node}: {} {} {:?}",
                        self[node].depth, self[node].loop_depth, self[node].outputs
                    )?;
                    let mut cfg_index = Nid::MAX;
                    for o in iter(self, node) {
                        self.basic_blocks_instr(out, o)?;
                        if self.is_cfg(o) {
                            cfg_index = o;
                        }
                    }
                    node = cfg_index;
                }
                Kind::Call { .. } => {
                    let mut cfg_index = Nid::MAX;
                    let mut print_ret = true;
                    for o in iter(self, node) {
                        if self[o].inputs[0] == node
                            && (self[node].outputs[0] != o || core::mem::take(&mut print_ret))
                        {
                            self.basic_blocks_instr(out, o)?;
                        }
                        if self.is_cfg(o) {
                            cfg_index = o;
                        }
                    }
                    node = cfg_index;
                }
                _ => unreachable!(),
            }
        }

        Ok(())
    }

    fn basic_blocks(&mut self) {
        let mut out = String::new();
        self.visited.clear(self.values.len());
        self.basic_blocks_low(&mut out, VOID).unwrap();
        log::inf!("{out}");
    }

    #[allow(dead_code)]
    fn graphviz(&self) {
        let out = &mut String::new();
        _ = self.graphviz_low(out);
        log::inf!("{out}");
    }

    fn is_cfg(&self, o: Nid) -> bool {
        self[o].kind.is_cfg()
    }

    fn check_final_integrity(&self) {
        //let mut failed = false;
        for (_, node) in self.iter() {
            debug_assert_eq!(node.lock_rc, 0, "{:?}", node.kind);
            // if !matches!(node.kind, Kind::Return | Kind::End) && node.outputs.is_empty() {
            //     log::err!("outputs are empry {i} {:?}", node.kind);
            //     failed = true;
            // }

            // let mut allowed_cfgs = 1 + (node.kind == Kind::If) as usize;
            // for &o in node.outputs.iter() {
            //     if self.is_cfg(i) {
            //         if allowed_cfgs == 0 && self.is_cfg(o) {
            //             log::err!(
            //                 "multiple cfg outputs detected: {:?} -> {:?}",
            //                 node.kind,
            //                 self[o].kind
            //             );
            //             failed = true;
            //         } else {
            //             allowed_cfgs += self.is_cfg(o) as usize;
            //         }
            //     }

            //     let other = match &self.values[o as usize] {
            //         Ok(other) => other,
            //         Err(_) => {
            //             log::err!("the edge points to dropped node: {i} {:?} {o}", node.kind,);
            //             failed = true;
            //             continue;
            //         }
            //     };
            //     let occurs = self[o].inputs.iter().filter(|&&el| el == i).count();
            //     let self_occurs = self[i].outputs.iter().filter(|&&el| el == o).count();
            //     if occurs != self_occurs {
            //         log::err!(
            //             "the edge is not bidirectional: {i} {:?} {self_occurs} {o} {:?} {occurs}",
            //             node.kind,
            //             other.kind
            //         );
            //         failed = true;
            //     }
            // }
        }
        //if failed {
        //    panic!()
        //}
    }

    #[expect(dead_code)]
    fn climb_expr(&mut self, from: Nid, mut for_each: impl FnMut(Nid, &Node) -> bool) -> bool {
        fn climb_impl(
            nodes: &mut Nodes,
            from: Nid,
            for_each: &mut impl FnMut(Nid, &Node) -> bool,
        ) -> bool {
            for i in 0..nodes[from].inputs.len() {
                let n = nodes[from].inputs[i];
                if n != Nid::MAX
                    && nodes.visited.set(n)
                    && !nodes.is_cfg(n)
                    && (for_each(n, &nodes[n]) || climb_impl(nodes, n, for_each))
                {
                    return true;
                }
            }
            false
        }
        self.visited.clear(self.values.len());
        climb_impl(self, from, &mut for_each)
    }

    #[expect(dead_code)]
    fn late_peephole(&mut self, target: Nid) -> Nid {
        if let Some(id) = self.peephole(target) {
            self.replace(target, id);
            return id;
        }
        target
    }

    fn load_loop_value(&mut self, index: usize, value: &mut Nid, loops: &mut [Loop]) {
        if *value != 0 {
            return;
        }

        let [loob, loops @ ..] = loops else { unreachable!() };
        let lvalue = &mut loob.scope[index].value;

        self.load_loop_value(index, lvalue, loops);

        if !self[*lvalue].is_lazy_phi() {
            self.unlock(*value);
            let inps = [loob.node, *lvalue, VOID];
            self.unlock(inps[1]);
            let ty = self[inps[1]].ty;
            let phi = self.new_node_nop(ty, Kind::Phi, inps);
            self[phi].lock_rc += 2;
            *value = phi;
            *lvalue = phi;
        } else {
            self.lock(*lvalue);
            self.unlock(*value);
            *value = *lvalue;
        }
    }

    fn check_dominance(&mut self, nd: Nid, min: Nid, check_outputs: bool) {
        let node = self[nd].clone();
        for &i in node.inputs.iter() {
            let dom = idom(self, i);
            debug_assert!(
                self.dominates(dom, min),
                "{dom} {min} {node:?} {:?}",
                self.basic_blocks()
            );
        }
        if check_outputs {
            for &o in node.outputs.iter() {
                let dom = use_block(nd, o, self);
                debug_assert!(
                    self.dominates(min, dom),
                    "{min} {dom} {node:?} {:?}",
                    self.basic_blocks()
                );
            }
        }
    }

    fn dominates(&mut self, dominator: Nid, mut dominated: Nid) -> bool {
        loop {
            if dominator == dominated {
                break true;
            }

            if idepth(self, dominator) > idepth(self, dominated) {
                break false;
            }

            dominated = idom(self, dominated);
        }
    }

    #[expect(dead_code)]
    fn iter_mut(&mut self) -> impl Iterator<Item = &mut Node> {
        self.values.iter_mut().flat_map(Result::as_mut)
    }
}

impl ops::Index<Nid> for Nodes {
    type Output = Node;

    fn index(&self, index: Nid) -> &Self::Output {
        self.values[index as usize].as_ref().unwrap()
    }
}

impl ops::IndexMut<Nid> for Nodes {
    fn index_mut(&mut self, index: Nid) -> &mut Self::Output {
        self.values[index as usize].as_mut().unwrap()
    }
}

#[derive(Clone, Copy, Debug, PartialEq, Eq, Hash, PartialOrd, Ord, Default)]
#[repr(u8)]
pub enum Kind {
    #[default]
    Start,
    // [ctrl]
    Entry,
    Mem,
    // [terms...]
    End,
    // [ctrl, cond]
    If,
    Then,
    Else,
    // [lhs, rhs]
    Region,
    // [entry, back]
    Loop,
    // [ctrl, ?value]
    Return,
    // [ctrl]
    CInt {
        value: i64,
    },
    // [ctrl, lhs, rhs]
    Phi,
    Arg {
        index: u32,
    },
    // [ctrl, oper]
    UnOp {
        op: lexer::TokenKind,
    },
    // [ctrl, lhs, rhs]
    BinOp {
        op: lexer::TokenKind,
    },
    // [ctrl, ...args]
    Call {
        func: ty::Func,
    },
    // [ctrl]
    Stck,
    // [ctrl, memory]
    Ptr {
        offset: Offset,
    },
    // [ctrl, memory]
    Load {
        offset: Offset,
    },
    // [ctrl, value, memory]
    Stre {
        offset: Offset,
    },
}

impl Kind {
    fn is_pinned(&self) -> bool {
        self.is_cfg() || matches!(self, Self::Phi | Self::Mem)
    }

    fn is_cfg(&self) -> bool {
        matches!(
            self,
            Self::Start
                | Self::End
                | Self::Return
                | Self::Entry
                | Self::Then
                | Self::Else
                | Self::Arg { .. }
                | Self::Call { .. }
                | Self::If
                | Self::Region
                | Self::Loop
        )
    }

    fn ends_basic_block(&self) -> bool {
        matches!(self, Self::Return | Self::If | Self::End)
    }
}

impl fmt::Display for Kind {
    fn fmt(&self, f: &mut core::fmt::Formatter<'_>) -> core::fmt::Result {
        match self {
            Kind::CInt { value } => write!(f, "#{value}"),
            Kind::Entry => write!(f, "ctrl[entry]"),
            Kind::Then => write!(f, "ctrl[then]"),
            Kind::Else => write!(f, "ctrl[else]"),
            Kind::BinOp { op } => write!(f, "{op}"),
            Kind::Call { func, .. } => write!(f, "call {func}"),
            slf => write!(f, "{slf:?}"),
        }
    }
}

#[derive(Debug, Default, Clone)]
//#[repr(align(64))]
struct Node {
    kind: Kind,
    inputs: Vc,
    outputs: Vc,
    ty: ty::Id,
    offset: Offset,
    ralloc_backref: RallocBRef,
    depth: IDomDepth,
    lock_rc: LockRc,
    loop_depth: LoopDepth,
}

impl Node {
    fn is_dangling(&self) -> bool {
        self.outputs.len() + self.lock_rc as usize == 0
    }

    fn key(&self) -> (Kind, &[Nid], ty::Id) {
        (self.kind, &self.inputs, self.ty)
    }

    fn is_lazy_phi(&self) -> bool {
        self.kind == Kind::Phi && self.inputs[2] == 0
    }
}

type RallocBRef = u16;
type LoopDepth = u16;
type LockRc = u16;
type IDomDepth = u16;

struct Loop {
    node: Nid,
    ctrl: [Nid; 2],
    ctrl_scope: [Vec<Variable>; 2],
    scope: Vec<Variable>,
}

#[derive(Clone, Copy)]
struct Variable {
    id: Ident,
    value: Nid,
}

#[derive(PartialEq, Eq, Clone, Copy, Debug)]
struct MemKey {
    region: Nid,
    offset: u32,
    node: Nid,
}

#[derive(Default)]
struct ItemCtx {
    file: FileId,
    #[expect(dead_code)]
    id: ty::Id,
    ret: Option<ty::Id>,

    task_base: usize,

    nodes: Nodes,
    ctrl: Nid,

    call_count: u16,
    filled: Vec<Nid>,

    loops: Vec<Loop>,
    vars: Vec<Variable>,
    memories: Vec<MemKey>,
    ret_relocs: Vec<Reloc>,
    relocs: Vec<TypedReloc>,
    jump_relocs: Vec<(Nid, Reloc)>,
    code: Vec<u8>,
}

impl ItemCtx {
    fn emit(&mut self, instr: (usize, [u8; instrs::MAX_SIZE])) {
        crate::emit(&mut self.code, instr);
    }
}

fn write_reloc(doce: &mut [u8], offset: usize, value: i64, size: u16) {
    let value = value.to_ne_bytes();
    doce[offset..offset + size as usize].copy_from_slice(&value[..size as usize]);
}

struct FTask {
    file: FileId,
    id: ty::Func,
}

#[derive(Default, Debug)]
struct Ctx {
    ty: Option<ty::Id>,
}

impl Ctx {
    pub fn with_ty(self, ty: impl Into<ty::Id>) -> Self {
        Self { ty: Some(ty.into()) }
    }
}

#[derive(Default)]
struct Pool {
    cis: Vec<ItemCtx>,
}

struct Regalloc {
    env: regalloc2::MachineEnv,
    ctx: regalloc2::Ctx,
}

impl Default for Regalloc {
    fn default() -> Self {
        Self {
            env: regalloc2::MachineEnv {
                preferred_regs_by_class: [
                    (1..13).map(|i| regalloc2::PReg::new(i, regalloc2::RegClass::Int)).collect(),
                    vec![],
                    vec![],
                ],
                non_preferred_regs_by_class: [
                    (13..64).map(|i| regalloc2::PReg::new(i, regalloc2::RegClass::Int)).collect(),
                    vec![],
                    vec![],
                ],
                scratch_by_class: Default::default(),
                fixed_stack_slots: Default::default(),
            },
            ctx: Default::default(),
        }
    }
}

#[derive(Default)]
pub struct Codegen {
    pub files: Vec<parser::Ast>,
    tasks: Vec<Option<FTask>>,

    tys: Types,
    ci: ItemCtx,
    pool: Pool,
    ralloc: Regalloc,
    errors: RefCell<String>,
}

impl Codegen {
    fn mem_op(
        &mut self,
        mut region: Nid,
        offset: Offset,
        kind: Kind,
        mut ty: ty::Id,
        mut inps: Vc,
    ) -> Nid {
        region = self.ci.nodes.trace_mem(region);

        let size = self.tys.size_of(ty);
        let insert_start = self
            .ci
            .memories
            .binary_search_by_key(&(region, offset), |k| (k.region, k.offset))
            .unwrap_or_else(identity);
        let insert_end = self
            .ci
            .memories
            .binary_search_by(|k| (k.region, k.offset).cmp(&(region, offset + size)))
            .unwrap_or_else(identity);

        for mk in &self.ci.memories[insert_start..insert_end] {
            debug_assert_eq!(mk.region, region);
            debug_assert!(mk.offset >= offset);
            debug_assert!(mk.offset < offset + size);
            inps.push(mk.node);
        }

        if insert_start == insert_end {
            inps.push(region);
        }

        if matches!(kind, Kind::Ptr { .. }) {
            ty = self.tys.make_ptr(ty);
        }

        let (new_op, peeped) = self.ci.nodes.new_node_low(ty, kind, inps);
        if !peeped && !matches!(kind, Kind::Ptr { .. }) {
            for mk in &self.ci.memories[insert_start..insert_end] {
                self.ci.nodes.unlock(mk.node);
            }

            self.ci.memories.splice(
                insert_start..insert_end,
                core::iter::once(MemKey { node: new_op, region, offset }),
            );
            self.ci.nodes.lock(new_op);
        }
        new_op
    }

    fn store_mem(&mut self, region: Nid, offset: Offset, value: Nid) -> Nid {
        self.mem_op(region, offset, Kind::Stre { offset }, self.tof(value), [VOID, value].into())
    }

    fn load_mem(&mut self, region: Nid, offset: Offset, ty: ty::Id) -> Nid {
        self.mem_op(region, offset, Kind::Load { offset }, ty, [VOID].into())
    }

    fn ptr_mem(&mut self, region: Nid, offset: Offset, ty: ty::Id) -> Nid {
        self.mem_op(region, offset, Kind::Ptr { offset }, ty, [VOID].into())
    }

    pub fn generate(&mut self) {
        self.find_or_declare(0, 0, None, "main");
        self.make_func_reachable(0);
        self.complete_call_graph();
    }

    fn make_func_reachable(&mut self, func: ty::Func) {
        let fuc = &mut self.tys.funcs[func as usize];
        if fuc.offset == u32::MAX {
            fuc.offset = task::id(self.tasks.len() as _);
            self.tasks.push(Some(FTask { file: fuc.file, id: func }));
        }
    }

    fn expr(&mut self, expr: &Expr) -> Option<Nid> {
        self.expr_ctx(expr, Ctx::default())
    }

    fn expr_ctx(&mut self, expr: &Expr, ctx: Ctx) -> Option<Nid> {
        let msg = "i know nothing about this name, gal, which is vired \
                  because we parsed succesfully";
        // ordered by complexity of the expression
        match *expr {
            Expr::Comment { .. } => Some(VOID),
            Expr::Ident { pos, id, .. } => {
                let Some(index) = self.ci.vars.iter().position(|v| v.id == id) else {
                    self.report(pos, msg);
                    return Some(NEVER);
                };

                self.ci.nodes.load_loop_value(
                    index,
                    &mut self.ci.vars[index].value,
                    &mut self.ci.loops,
                );

                Some(self.ci.vars[index].value)
            }
            Expr::Number { value, .. } => Some(self.ci.nodes.new_node(
                ctx.ty.filter(|ty| ty.is_integer() || ty.is_pointer()).unwrap_or(ty::Id::INT),
                Kind::CInt { value },
                [VOID],
            )),
            Expr::Return { pos, val } => {
                let value = if let Some(val) = val {
                    self.expr_ctx(val, Ctx { ty: self.ci.ret })?
                } else {
                    VOID
                };

                let mut inps = Vc::from([self.ci.ctrl, value]);
                for m in self.ci.memories.iter() {
                    inps.push(m.node);
                }

                let out = &mut String::new();
                self.report_log_to(pos, "returning here", out);
                self.ci.ctrl = self.ci.nodes.new_node(ty::VOID, Kind::Return, inps);

                self.ci.nodes[NEVER].inputs.push(self.ci.ctrl);
                self.ci.nodes[self.ci.ctrl].outputs.push(NEVER);

                let expected = *self.ci.ret.get_or_insert(self.tof(value));
                _ = self.assert_ty(pos, self.tof(value), expected, true, "return value");

                None
            }
            Expr::Field { target, name, pos } => {
                let vtarget = self.expr(target)?;
                let tty = self.tof(vtarget);

                let ty::Kind::Struct(s) = self.tys.base_of(tty).unwrap_or(tty).expand() else {
                    self.report(
                        pos,
                        fa!(
                            "the '{}' is not a struct, or pointer to one, \
                            but accessing fields is only possible on structs",
                            self.ty_display(tty)
                        ),
                    );
                    return Some(NEVER);
                };

                let Some((ty, offset)) = OffsetIter::offset_of(&self.tys, s, name) else {
                    let field_list = self
                        .tys
                        .struct_fields(s)
                        .iter()
                        .map(|f| self.tys.field_names.ident_str(f.name))
                        .intersperse("', '")
                        .collect::<String>();
                    self.report(
                        pos,
                        fa!(
                            "the '{}' does not have this field, \
                            but it does have '{field_list}'",
                            self.ty_display(tty)
                        ),
                    );
                    return Some(NEVER);
                };

                Some(self.load_mem(vtarget, ty, offset))
            }
            Expr::UnOp { op: TokenKind::Band, val, .. } => {
                let ctx = Ctx { ty: ctx.ty.and_then(|ty| self.tys.base_of(ty)) };

                let mut val = self.expr_ctx(val, ctx)?;
                let ty = self.tof(val);
                if !matches!(self.ci.nodes[val].kind, Kind::Stck) {
                    let stck = self.ci.nodes.new_node_nop(ty, Kind::Stck, [VOID, MEM]);
                    self.store_mem(stck, 0, val);
                    val = stck;
                }

                Some(self.ptr_mem(val, 0, ty))
            }
            Expr::UnOp { op: TokenKind::Mul, val, pos } => {
                let ctx = Ctx { ty: ctx.ty.map(|ty| self.tys.make_ptr(ty)) };
                let val = self.expr_ctx(val, ctx)?;
                let Some(base) = self.get_load_type(val) else {
                    self.report(
                        pos,
                        fa!("the '{}' can not be dereferneced", self.ty_display(self.tof(val))),
                    );
                    return Some(NEVER);
                };
                Some(self.load_mem(val, 0, base))
            }
            Expr::UnOp { pos, op: op @ TokenKind::Sub, val } => {
                let val = self.expr_ctx(val, ctx)?;
                if !self.tof(val).is_integer() {
                    self.report(pos, fa!("cant negate '{}'", self.ty_display(self.tof(val))));
                }
                Some(self.ci.nodes.new_node(self.tof(val), Kind::UnOp { op }, [VOID, val]))
            }
            Expr::BinOp { left: &Expr::Ident { id, .. }, op: TokenKind::Decl, right } => {
                let value = self.expr(right)?;
                self.ci.nodes.lock(value);
                self.ci.vars.push(Variable { id, value });
                Some(VOID)
            }
            Expr::BinOp { left: &Expr::Ident { id, pos, .. }, op: TokenKind::Assign, right } => {
                let value = self.expr(right)?;
                self.ci.nodes.lock(value);

                let Some(var) = self.ci.vars.iter_mut().find(|v| v.id == id) else {
                    self.report(pos, msg);
                    return Some(NEVER);
                };

                let prev = core::mem::replace(&mut var.value, value);
                self.ci.nodes.unlock_remove(prev);
                Some(VOID)
            }
            Expr::BinOp {
                left: &Expr::UnOp { pos, op: TokenKind::Mul, val },
                op: TokenKind::Assign,
                right,
            } => {
                let ctx = Ctx { ty: ctx.ty.map(|ty| self.tys.make_ptr(ty)) };
                let val = self.expr_ctx(val, ctx)?;
                let base = self.get_load_type(val).unwrap_or_else(|| {
                    self.report(
                        pos,
                        fa!("the '{}' can not be dereferneced", self.ty_display(self.tof(val))),
                    );
                    ty::Id::NEVER
                });
                let value = self.expr_ctx(right, Ctx::default().with_ty(base))?;
                _ = self.assert_ty(right.pos(), self.tof(value), base, true, "stored value");
                self.store_mem(val, 0, value);
                Some(VOID)
            }
            Expr::BinOp { left, op, right } if op != TokenKind::Assign => {
                let lhs = self.expr_ctx(left, ctx)?;
                self.ci.nodes.lock(lhs);
                let rhs = self.expr_ctx(right, Ctx::default().with_ty(self.tof(lhs)));
                self.ci.nodes.unlock(lhs);
                let rhs = rhs?;
                let ty = self.assert_ty(
                    left.pos(),
                    self.tof(rhs),
                    self.tof(lhs),
                    false,
                    "right operand",
                );
                let inps = [VOID, lhs, rhs];
                Some(self.ci.nodes.new_node(ty::bin_ret(ty, op), Kind::BinOp { op }, inps))
            }
            Expr::Directive { name: "sizeof", args: [ty], .. } => {
                let ty = self.ty(ty);
                Some(self.ci.nodes.new_node_nop(
                    ty::INT,
                    Kind::CInt { value: self.tys.size_of(ty) as _ },
                    [VOID],
                ))
            }
            Expr::Call { func: &Expr::Ident { pos, id, name, .. }, args, .. } => {
                self.ci.call_count += 1;
                let func = self.find_or_declare(pos, self.ci.file, Some(id), name);
                let ty::Kind::Func(func) = func else {
                    self.report(
                        pos,
                        fa!("compiler cant (yet) call '{}'", self.ty_display(func.compress())),
                    );
                    return Some(NEVER);
                };

                self.make_func_reachable(func);

                let fuc = &self.tys.funcs[func as usize];
                let sig = fuc.sig.expect("TODO: generic functions");
                let ast = self.files[fuc.file as usize].clone();
                let Expr::BinOp { right: &Expr::Closure { args: cargs, .. }, .. } =
                    fuc.expr.get(&ast).unwrap()
                else {
                    unreachable!()
                };

                self.assert_report(
                    args.len() == cargs.len(),
                    pos,
                    fa!(
                        "expected {} function argumenr{}, got {}",
                        cargs.len(),
                        if cargs.len() == 1 { "" } else { "s" },
                        args.len()
                    ),
                );

                let mut inps = Vc::from([self.ci.ctrl]);
                for ((arg, carg), tyx) in args.iter().zip(cargs).zip(sig.args.range()) {
                    let ty = self.tys.args[tyx];
                    if self.tys.size_of(ty) == 0 {
                        continue;
                    }
                    let mut value = self.expr_ctx(arg, Ctx::default().with_ty(ty))?;
                    _ = self.assert_ty(
                        arg.pos(),
                        self.tof(value),
                        ty,
                        true,
                        fa!("argument {}", carg.name),
                    );
                    if ty.is_pointer() {
                        value = self.ci.nodes.trace_mem(value);
                        value = self
                            .ci
                            .memories
                            .binary_search_by_key(&(value, 0), |k| (k.region, k.offset))
                            .map_or(value, |i| self.ci.memories[i].node);
                        // mark the read as clobbed since function can store
                        self.ci.nodes[value].offset = u32::MAX;
                    }
                    inps.push(value);
                }
                self.ci.ctrl = self.ci.nodes.new_node(sig.ret, Kind::Call { func }, inps);

                Some(self.ci.ctrl)
            }
            Expr::Ctor { pos, ty, fields, .. } => {
                let Some(sty) = ty.map(|ty| self.ty(ty)).or(ctx.ty) else {
                    self.report(
                        pos,
                        "the type of struct cannot be inferred from context, \
                        use an explicit type instead: <type>.{ ... }",
                    );
                    return Some(NEVER);
                };

                let ty::Kind::Struct(s) = sty.expand() else {
                    let inferred = if ty.is_some() { "" } else { "inferred " };
                    self.report(
                        pos,
                        fa!(
                            "the {inferred}type of the constructor is `{}`, \
                            but thats not a struct",
                            self.ty_display(sty)
                        ),
                    );
                    return Some(NEVER);
                };

                // TODO: dont allocate
                let mut offs = OffsetIter::new(s, &self.tys)
                    .into_iter(&self.tys)
                    .map(|(f, o)| (f.ty, o))
                    .collect::<Vec<_>>();
                let mem = self.ci.nodes.new_node(sty, Kind::Stck, [VOID, MEM]);
                for field in fields {
                    let Some(index) = self.tys.find_struct_field(s, field.name) else {
                        self.report(
                            field.pos,
                            fa!("struct '{}' does not have this field", self.ty_display(sty)),
                        );
                        continue;
                    };

                    let (ty, offset) =
                        core::mem::replace(&mut offs[index], (ty::Id::UNDECLARED, field.pos));

                    if ty == ty::Id::UNDECLARED {
                        self.report(field.pos, "the struct field is already initialized");
                        self.report(offset, "previous initialization is here");
                        continue;
                    }

                    let value = self.expr_ctx(&field.value, Ctx::default().with_ty(ty))?;
                    self.store_mem(mem, offset, value);
                }

                let field_list = self
                    .tys
                    .struct_fields(s)
                    .iter()
                    .zip(offs)
                    .filter(|&(_, (ty, _))| ty != ty::Id::UNDECLARED)
                    .map(|(f, _)| self.tys.field_names.ident_str(f.name))
                    .intersperse(", ")
                    .collect::<String>();

                if !field_list.is_empty() {
                    self.report(pos, fa!("the struct initializer is missing {field_list}"));
                }

                Some(mem)
            }
            Expr::Block { stmts, .. } => {
                let base = self.ci.vars.len();

                let mut ret = Some(VOID);
                for stmt in stmts {
                    ret = ret.and(self.expr(stmt));
                    if let Some(id) = ret {
                        _ = self.assert_ty(
                            stmt.pos(),
                            self.tof(id),
                            ty::Id::VOID,
                            true,
                            "statement",
                        );
                    } else {
                        break;
                    }
                }

                self.ci.nodes.lock(self.ci.ctrl);
                for var in self.ci.vars.drain(base..) {
                    self.ci.nodes.unlock_remove(var.value);
                }
                self.ci.nodes.unlock(self.ci.ctrl);

                ret
            }
            Expr::Loop { body, .. } => {
                self.ci.ctrl = self.ci.nodes.new_node(ty::VOID, Kind::Loop, [self.ci.ctrl; 2]);
                self.ci.loops.push(Loop {
                    node: self.ci.ctrl,
                    ctrl: [Nid::MAX; 2],
                    ctrl_scope: core::array::from_fn(|_| vec![]),
                    scope: self.ci.vars.clone(),
                });

                for var in &mut self.ci.vars {
                    var.value = VOID;
                }
                self.ci.nodes[VOID].lock_rc += self.ci.vars.len() as LockRc;

                self.expr(body);

                let Loop { node, ctrl: [mut con, bre], ctrl_scope: [mut cons, mut bres], scope } =
                    self.ci.loops.pop().unwrap();

                if con != Nid::MAX {
                    con = self.ci.nodes.new_node(ty::VOID, Kind::Region, [con, self.ci.ctrl]);
                    Self::merge_scopes(
                        &mut self.ci.nodes,
                        &mut self.ci.loops,
                        con,
                        &mut self.ci.vars,
                        &mut cons,
                        true,
                    );
                    self.ci.ctrl = con;
                }

                self.ci.nodes.modify_input(node, 1, self.ci.ctrl);

                let idx = self.ci.nodes[node]
                    .outputs
                    .iter()
                    .position(|&n| self.ci.nodes.is_cfg(n))
                    .unwrap();
                self.ci.nodes[node].outputs.swap(idx, 0);

                if bre == Nid::MAX {
                    self.ci.ctrl = NEVER;
                    return None;
                }
                self.ci.ctrl = bre;

                self.ci.nodes.lock(self.ci.ctrl);

                core::mem::swap(&mut self.ci.vars, &mut bres);

                for ((dest_var, mut scope_var), loop_var) in
                    self.ci.vars.iter_mut().zip(scope).zip(bres)
                {
                    self.ci.nodes.unlock(loop_var.value);

                    if loop_var.value != VOID {
                        self.ci.nodes.unlock(scope_var.value);
                        if loop_var.value != scope_var.value {
                            scope_var.value =
                                self.ci.nodes.modify_input(scope_var.value, 2, loop_var.value);
                            self.ci.nodes.lock(scope_var.value);
                        } else {
                            if dest_var.value == scope_var.value {
                                self.ci.nodes.unlock(dest_var.value);
                                dest_var.value = VOID;
                                self.ci.nodes.lock(dest_var.value);
                            }
                            let phi = &self.ci.nodes[scope_var.value];
                            debug_assert_eq!(phi.kind, Kind::Phi);
                            debug_assert_eq!(phi.inputs[2], VOID);
                            let prev = phi.inputs[1];
                            self.ci.nodes.replace(scope_var.value, prev);
                            scope_var.value = prev;
                            self.ci.nodes.lock(prev);
                        }
                    }

                    if dest_var.value == VOID {
                        self.ci.nodes.unlock(dest_var.value);
                        dest_var.value = scope_var.value;
                        self.ci.nodes.lock(dest_var.value);
                    }

                    debug_assert!(
                        self.ci.nodes[dest_var.value].kind != Kind::Phi
                            || self.ci.nodes[dest_var.value].inputs[2] != 0
                    );

                    self.ci.nodes.unlock_remove(scope_var.value);
                }

                self.ci.nodes.unlock(self.ci.ctrl);

                Some(VOID)
            }
            Expr::Break { pos } => self.jump_to(pos, 1),
            Expr::Continue { pos } => self.jump_to(pos, 0),
            Expr::If { cond, then, else_, .. } => {
                let cond = self.expr_ctx(cond, Ctx::default().with_ty(ty::BOOL))?;

                let if_node = self.ci.nodes.new_node(ty::VOID, Kind::If, [self.ci.ctrl, cond]);

                'b: {
                    let branch = match self.tof(if_node).expand().inner() {
                        ty::LEFT_UNREACHABLE => else_,
                        ty::RIGHT_UNREACHABLE => Some(then),
                        _ => break 'b,
                    };

                    self.ci.nodes.lock(self.ci.ctrl);
                    self.ci.nodes.remove(if_node);
                    self.ci.nodes.unlock(self.ci.ctrl);

                    if let Some(branch) = branch {
                        return self.expr(branch);
                    } else {
                        return Some(VOID);
                    }
                }

                let mut else_scope = self.ci.vars.clone();
                for &el in &self.ci.vars {
                    self.ci.nodes.lock(el.value);
                }

                self.ci.ctrl = self.ci.nodes.new_node(ty::VOID, Kind::Then, [if_node]);
                let lcntrl = self.expr(then).map_or(Nid::MAX, |_| self.ci.ctrl);

                let mut then_scope = core::mem::replace(&mut self.ci.vars, else_scope);
                self.ci.ctrl = self.ci.nodes.new_node(ty::VOID, Kind::Else, [if_node]);
                let rcntrl = if let Some(else_) = else_ {
                    self.expr(else_).map_or(Nid::MAX, |_| self.ci.ctrl)
                } else {
                    self.ci.ctrl
                };

                if lcntrl == Nid::MAX && rcntrl == Nid::MAX {
                    for then_var in then_scope {
                        self.ci.nodes.unlock_remove(then_var.value);
                    }
                    return None;
                } else if lcntrl == Nid::MAX {
                    for then_var in then_scope {
                        self.ci.nodes.unlock_remove(then_var.value);
                    }
                    return Some(VOID);
                } else if rcntrl == Nid::MAX {
                    for else_var in &self.ci.vars {
                        self.ci.nodes.unlock_remove(else_var.value);
                    }
                    self.ci.vars = then_scope;
                    self.ci.ctrl = lcntrl;
                    return Some(VOID);
                }

                self.ci.ctrl = self.ci.nodes.new_node(ty::VOID, Kind::Region, [lcntrl, rcntrl]);

                else_scope = core::mem::take(&mut self.ci.vars);

                Self::merge_scopes(
                    &mut self.ci.nodes,
                    &mut self.ci.loops,
                    self.ci.ctrl,
                    &mut else_scope,
                    &mut then_scope,
                    true,
                );

                self.ci.vars = else_scope;

                Some(VOID)
            }
            ref e => {
                self.report_unhandled_ast(e, "bruh");
                Some(NEVER)
            }
        }
    }

    fn jump_to(&mut self, pos: Pos, id: usize) -> Option<Nid> {
        let Some(mut loob) = self.ci.loops.last_mut() else {
            self.report(pos, "break outside a loop");
            return None;
        };

        if loob.ctrl[id] == Nid::MAX {
            loob.ctrl[id] = self.ci.ctrl;
            loob.ctrl_scope[id] = self.ci.vars[..loob.scope.len()].to_owned();
            for v in &loob.ctrl_scope[id] {
                self.ci.nodes.lock(v.value)
            }
        } else {
            let reg = self.ci.nodes.new_node(ty::VOID, Kind::Region, [self.ci.ctrl, loob.ctrl[id]]);
            let mut scope = core::mem::take(&mut loob.ctrl_scope[id]);

            Self::merge_scopes(
                &mut self.ci.nodes,
                &mut self.ci.loops,
                reg,
                &mut scope,
                &mut self.ci.vars,
                false,
            );

            loob = self.ci.loops.last_mut().unwrap();
            loob.ctrl_scope[id] = scope;
            loob.ctrl[id] = reg;
        }

        self.ci.ctrl = NEVER;
        None
    }

    fn merge_scopes(
        nodes: &mut Nodes,
        loops: &mut [Loop],
        ctrl: Nid,
        to: &mut [Variable],
        from: &mut [Variable],
        drop_from: bool,
    ) {
        for (i, (else_var, then_var)) in to.iter_mut().zip(from).enumerate() {
            if else_var.value != then_var.value {
                nodes.load_loop_value(i, &mut then_var.value, loops);
                nodes.load_loop_value(i, &mut else_var.value, loops);
                if else_var.value != then_var.value {
                    let ty = nodes[else_var.value].ty;
                    debug_assert_eq!(ty, nodes[then_var.value].ty, "TODO: typecheck properly");

                    let inps = [ctrl, then_var.value, else_var.value];
                    nodes.unlock(else_var.value);
                    else_var.value = nodes.new_node(ty, Kind::Phi, inps);
                    nodes.lock(else_var.value);
                }
            }

            if drop_from {
                nodes.unlock_remove(then_var.value);
            }
        }
    }

    #[inline(always)]
    fn tof(&self, id: Nid) -> ty::Id {
        self.ci.nodes[id].ty
    }

    fn complete_call_graph(&mut self) {
        while self.ci.task_base < self.tasks.len()
            && let Some(task_slot) = self.tasks.pop()
        {
            let Some(task) = task_slot else { continue };
            self.emit_func(task);
        }
    }

    fn emit_func(&mut self, FTask { file, id }: FTask) {
        let func = &mut self.tys.funcs[id as usize];
        func.offset = u32::MAX - 1;
        debug_assert!(func.file == file);
        let sig = func.sig.unwrap();
        let ast = self.files[file as usize].clone();
        let expr = func.expr.get(&ast).unwrap();

        let repl = ItemCtx {
            file,
            id: ty::Kind::Func(id).compress(),
            ret: Some(sig.ret),
            ..self.pool.cis.pop().unwrap_or_default()
        };
        let prev_ci = core::mem::replace(&mut self.ci, repl);

        let start = self.ci.nodes.new_node(ty::VOID, Kind::Start, []);
        debug_assert_eq!(start, VOID);
        let end = self.ci.nodes.new_node(ty::NEVER, Kind::End, []);
        debug_assert_eq!(end, NEVER);
        self.ci.nodes.lock(end);
        self.ci.ctrl = self.ci.nodes.new_node(ty::VOID, Kind::Entry, [VOID]);
        debug_assert_eq!(self.ci.ctrl, ENTRY);
        let mem = self.ci.nodes.new_node(ty::VOID, Kind::Mem, [VOID]);
        debug_assert_eq!(mem, MEM);
        self.ci.nodes.lock(mem);

        let Expr::BinOp {
            left: Expr::Ident { .. },
            op: TokenKind::Decl,
            right: &Expr::Closure { body, args, .. },
        } = expr
        else {
            unreachable!("{}", self.ast_display(expr))
        };

        let mut sig_args = sig.args.range();
        for (arg, index) in args.iter().zip(0u32..) {
            let ty = self.tys.args[sig_args.next().unwrap()];
            let value = self.ci.nodes.new_node(ty, Kind::Arg { index }, [VOID]);
            self.ci.nodes.lock(value);
            let sym = parser::find_symbol(&ast.symbols, arg.id);
            assert!(sym.flags & idfl::COMPTIME == 0, "TODO");
            self.ci.vars.push(Variable { id: arg.id, value });
        }

        let orig_vars = self.ci.vars.clone();

        if self.expr(body).is_some() {
            self.report(body.pos(), "expected all paths in the fucntion to return");
        }

        self.ci.nodes.unlock(end);

        for mem in self.ci.memories.drain(..) {
            if self.ci.nodes[mem.region].kind == Kind::Stck
                && self.ci.nodes[mem.node]
                    .outputs
                    .iter()
                    .all(|&n| self.ci.nodes[n].kind == Kind::Return)
            {
                let outs = core::mem::take(&mut self.ci.nodes[mem.node].outputs);
                for out in outs {
                    let index =
                        self.ci.nodes[out].inputs.iter().rposition(|&o| o == mem.node).unwrap();
                    self.ci.nodes[out].inputs.swap_remove(index);
                }
            }
            self.ci.nodes.unlock_remove(mem.node);
        }
        self.ci.nodes.unlock(mem);

        for var in self.ci.vars.drain(..) {
            self.ci.nodes.unlock(var.value);
        }

        if self.errors.borrow().is_empty() {
            self.ci.nodes.graphviz();
            self.gcm();

            #[cfg(debug_assertions)]
            {
                self.ci.nodes.check_final_integrity();
            }

            '_open_function: {
                self.ci.emit(instrs::addi64(reg::STACK_PTR, reg::STACK_PTR, 0));
                self.ci.emit(instrs::st(reg::RET_ADDR, reg::STACK_PTR, 0, 0));
            }

            //self.ci.nodes.basic_blocks();
            self.ci.nodes.graphviz();

            let mut stack_size = 0;
            '_compute_stack: {
                let mems = core::mem::take(&mut self.ci.nodes[MEM].outputs);
                for &stck in mems.iter() {
                    stack_size += self.tys.size_of(self.ci.nodes[stck].ty);
                    self.ci.nodes[stck].offset = stack_size;
                }
                for &stck in mems.iter() {
                    self.ci.nodes[stck].offset = stack_size - self.ci.nodes[stck].offset;
                }
                self.ci.nodes[mem].outputs = mems;
            }

            self.ci.vars = orig_vars;
            self.ci.nodes.visited.clear(self.ci.nodes.values.len());
            let saved = self.emit_body(sig);
            self.ci.vars.clear();

            if let Some(last_ret) = self.ci.ret_relocs.last()
                && last_ret.offset as usize == self.ci.code.len() - 5
            {
                self.ci.code.truncate(self.ci.code.len() - 5);
                self.ci.ret_relocs.pop();
            }

            // FIXME: maybe do this incrementally
            for (nd, rel) in self.ci.jump_relocs.drain(..) {
                let offset = self.ci.nodes[nd].offset;
                rel.apply_jump(&mut self.ci.code, offset, 0);
            }

            let end = self.ci.code.len();
            for ret_rel in self.ci.ret_relocs.drain(..) {
                ret_rel.apply_jump(&mut self.ci.code, end as _, 0);
            }

            let mut stripped_prelude_size = 0;
            '_close_function: {
                let pushed =
                    (saved as i64 + (core::mem::take(&mut self.ci.call_count) != 0) as i64) * 8;
                let stack = stack_size as i64;

                match (pushed, stack) {
                    (0, 0) => {
                        stripped_prelude_size =
                            instrs::addi64(0, 0, 0).0 + instrs::st(0, 0, 0, 0).0;
                        self.ci.code.drain(0..stripped_prelude_size);
                        break '_close_function;
                    }
                    (0, stack) => {
                        write_reloc(&mut self.ci.code, 3, -stack, 8);
                        stripped_prelude_size = instrs::addi64(0, 0, 0).0;
                        let end = stripped_prelude_size + instrs::st(0, 0, 0, 0).0;
                        self.ci.code.drain(stripped_prelude_size..end);
                        self.ci.emit(instrs::addi64(reg::STACK_PTR, reg::STACK_PTR, stack as _));
                        break '_close_function;
                    }
                    _ => {}
                }

                write_reloc(&mut self.ci.code, 3, -(pushed + stack), 8);
                write_reloc(&mut self.ci.code, 3 + 8 + 3, stack, 8);
                write_reloc(&mut self.ci.code, 3 + 8 + 3 + 8, pushed, 2);

                self.ci.emit(instrs::ld(reg::RET_ADDR, reg::STACK_PTR, stack as _, pushed as _));
                self.ci.emit(instrs::addi64(reg::STACK_PTR, reg::STACK_PTR, (pushed + stack) as _));
            }
            self.ci.relocs.iter_mut().for_each(|r| r.reloc.offset -= stripped_prelude_size as u32);
            self.ci.emit(instrs::jala(reg::ZERO, reg::RET_ADDR, 0));
        }

        self.tys.funcs[id as usize].code.append(&mut self.ci.code);
        self.tys.funcs[id as usize].relocs.append(&mut self.ci.relocs);
        self.ci.nodes.clear();
        self.ci.filled.clear();
        self.pool.cis.push(core::mem::replace(&mut self.ci, prev_ci));
    }

    fn emit_body(&mut self, sig: Sig) -> usize {
        let mut nodes = core::mem::take(&mut self.ci.nodes);

        let func = Function::new(&mut nodes, &self.tys, sig);
        if self.ci.call_count != 0 {
            core::mem::swap(
                &mut self.ralloc.env.preferred_regs_by_class,
                &mut self.ralloc.env.non_preferred_regs_by_class,
            );
        };

        let options = regalloc2::RegallocOptions {
            verbose_log: false,
            validate_ssa: false,
            algorithm: regalloc2::Algorithm::Ion,
        };
        regalloc2::run_with_ctx(&func, &self.ralloc.env, &options, &mut self.ralloc.ctx)
            .unwrap_or_else(|err| panic!("{err}"));

        if self.ci.call_count != 0 {
            core::mem::swap(
                &mut self.ralloc.env.preferred_regs_by_class,
                &mut self.ralloc.env.non_preferred_regs_by_class,
            );
        };

        let mut saved_regs = HashMap::<u8, u8>::default();
        let mut atr = |allc: regalloc2::Allocation| {
            debug_assert!(allc.is_reg());
            let hvenc = regalloc2::PReg::from_index(allc.index()).hw_enc() as u8;
            if hvenc <= 12 {
                return hvenc;
            }
            let would_insert = saved_regs.len() as u8 + reg::RET_ADDR + 1;
            *saved_regs.entry(hvenc).or_insert(would_insert)
        };

        for (i, block) in func.blocks.iter().enumerate() {
            let blk = regalloc2::Block(i as _);
            func.nodes[block.nid].offset = self.ci.code.len() as _;
            for instr_or_edit in self.ralloc.ctx.output.block_insts_and_edits(&func, blk) {
                let inst = match instr_or_edit {
                    regalloc2::InstOrEdit::Inst(inst) => inst,
                    regalloc2::InstOrEdit::Edit(&regalloc2::Edit::Move { from, to }) => {
                        self.ci.emit(instrs::cp(atr(to), atr(from)));
                        continue;
                    }
                };

                let nid = func.instrs[inst.index()].nid;
                if nid == NEVER {
                    continue;
                };
                let allocs = self.ralloc.ctx.output.inst_allocs(inst);
                let node = &func.nodes[nid];
                match node.kind {
                    Kind::If => {
                        let &[_, cond] = node.inputs.as_slice() else { unreachable!() };
                        if let Kind::BinOp { op } = func.nodes[cond].kind
                            && let Some((op, swapped)) = op.cond_op(node.ty.is_signed())
                        {
                            let rel = Reloc::new(self.ci.code.len(), 3, 2);
                            self.ci.jump_relocs.push((node.outputs[!swapped as usize], rel));
                            let &[lhs, rhs] = allocs else { unreachable!() };
                            self.ci.emit(op(atr(lhs), atr(rhs), 0));
                        } else {
                            todo!()
                        }
                    }
                    Kind::Loop | Kind::Region => {
                        if node.ralloc_backref as usize != i + 1 {
                            let rel = Reloc::new(self.ci.code.len(), 1, 4);
                            self.ci.jump_relocs.push((nid, rel));
                            self.ci.emit(instrs::jmp(0));
                        }
                    }
                    Kind::Return => {
                        if i != func.blocks.len() - 1 {
                            let rel = Reloc::new(self.ci.code.len(), 1, 4);
                            self.ci.ret_relocs.push(rel);
                            self.ci.emit(instrs::jmp(0));
                        }
                    }
                    Kind::CInt { value } => {
                        self.ci.emit(instrs::li64(atr(allocs[0]), value as _));
                    }
                    Kind::UnOp { op } => {
                        let op = op.unop().expect("TODO: unary operator not supported");
                        let &[dst, oper] = allocs else { unreachable!() };
                        self.ci.emit(op(atr(dst), atr(oper)));
                    }
                    Kind::BinOp { op } => {
                        let &[.., rhs] = node.inputs.as_slice() else { unreachable!() };

                        if let Kind::CInt { value } = func.nodes[rhs].kind
                            && let Some(op) =
                                op.imm_binop(node.ty.is_signed(), func.tys.size_of(node.ty))
                        {
                            let &[dst, lhs] = allocs else { unreachable!() };
                            self.ci.emit(op(atr(dst), atr(lhs), value as _));
                        } else if let Some(op) =
                            op.binop(node.ty.is_signed(), func.tys.size_of(node.ty))
                        {
                            let &[dst, lhs, rhs] = allocs else { unreachable!() };
                            self.ci.emit(op(atr(dst), atr(lhs), atr(rhs)));
                        } else if op.cond_op(node.ty.is_signed()).is_some() {
                        } else {
                            todo!()
                        }
                    }
                    Kind::Call { func } => {
                        self.ci.relocs.push(TypedReloc {
                            target: ty::Kind::Func(func).compress(),
                            reloc: Reloc::new(self.ci.code.len(), 3, 4),
                        });
                        self.ci.emit(instrs::jal(reg::RET_ADDR, reg::ZERO, 0));
                    }
                    Kind::Stck => {
                        let base = reg::STACK_PTR;
                        let offset = func.nodes[nid].offset;
                        self.ci.emit(instrs::addi64(atr(allocs[0]), base, offset as _));
                    }
                    Kind::Ptr { offset } => {
                        let region = func.nodes.trace_mem(node.inputs[1]);
                        let base = reg::STACK_PTR;
                        let offset = func.nodes[region].offset + offset;
                        self.ci.emit(instrs::addi64(atr(allocs[0]), base, offset as _));
                    }
                    Kind::Load { offset } => {
                        let region = func.nodes.trace_mem(node.inputs[1]);
                        let size = self.tys.size_of(node.ty);
                        debug_assert_eq!(size, 8, "TODO");
                        let (base, offset) = match func.nodes[region].kind {
                            Kind::Stck => (reg::STACK_PTR, func.nodes[region].offset + offset),
                            k => unreachable!("{k:?}"),
                        };
                        let &[dst] = allocs else { unreachable!() };
                        self.ci.emit(instrs::ld(atr(dst), base, offset as _, size as _));
                    }
                    Kind::Stre { offset } => {
                        let region = func.nodes.trace_mem(node.inputs[2]);
                        let size = self.tys.size_of(node.ty);
                        debug_assert_eq!(size, 8, "TODO");
                        let nd = &func.nodes[region];
                        let (base, offset, src) = match nd.kind {
                            Kind::Stck => (reg::STACK_PTR, nd.offset + offset, allocs[0]),
                            Kind::Arg { .. } => (atr(allocs[0]), offset, allocs[1]),
                            k => unreachable!("{k:?}"),
                        };
                        self.ci.emit(instrs::st(atr(src), base, offset as _, size as _));
                    }
                    _ => unreachable!(),
                }
            }
        }

        self.ci.nodes = nodes;

        saved_regs.len()
    }

    fn ty(&mut self, expr: &Expr) -> ty::Id {
        if let Some(ty) = self.tys.ty(self.ci.file, expr, &self.files) {
            return ty;
        }

        self.report_unhandled_ast(expr, "type");
        ty::Id::NEVER
    }

    fn find_or_declare(
        &mut self,
        pos: Pos,
        file: FileId,
        name: Option<Ident>,
        lit_name: &str,
    ) -> ty::Kind {
        log::trc!("find_or_declare: {lit_name} {file}");

        let f = self.files[file as usize].clone();
        let Some((expr, ident)) = f.find_decl(name.ok_or(lit_name)) else {
            match name.ok_or(lit_name) {
                Ok(name) => {
                    let name = self.cfile().ident_str(name);
                    self.report(pos, fa!("idk indentifier: {name}"))
                }
                Err("main") => self.report(
                    pos,
                    fa!(
                        "missing main function in '{}', compiler can't \
                        emmit libraries since such concept is not defined",
                        f.path
                    ),
                ),
                Err(name) => self.report(pos, fa!("idk indentifier: {name}")),
            }
            return ty::Kind::Builtin(ty::NEVER);
        };

        if let Some(existing) = self.tys.syms.get(&SymKey { file, ident }) {
            if let ty::Kind::Func(id) = existing.expand()
                && let func = &mut self.tys.funcs[id as usize]
                && let Err(idx) = task::unpack(func.offset)
                && idx < self.tasks.len()
            {
                func.offset = task::id(self.tasks.len());
                let task = self.tasks[idx].take();
                self.tasks.push(task);
            }
            return existing.expand();
        }

        let prev_file = core::mem::replace(&mut self.ci.file, file);
        let sym = match expr {
            Expr::BinOp {
                left: Expr::Ident { .. },
                op: TokenKind::Decl,
                right: &Expr::Closure { pos, args, ret, .. },
            } => {
                let func = Func {
                    file,
                    sig: '_b: {
                        let arg_base = self.tys.args.len();
                        for arg in args {
                            let sym = parser::find_symbol(&f.symbols, arg.id);
                            assert!(sym.flags & idfl::COMPTIME == 0, "TODO");
                            let ty = self.ty(&arg.ty);
                            self.tys.args.push(ty);
                        }

                        let Some(args) = self.pack_args(arg_base) else {
                            self.fatal_report(
                                pos,
                                "you cant be serious, using more the 31 arguments in a function",
                            );
                        };
                        let ret = self.ty(ret);

                        Some(Sig { args, ret })
                    },
                    expr: {
                        let refr = ExprRef::new(expr);
                        debug_assert!(refr.get(&f).is_some());
                        refr
                    },
                    ..Default::default()
                };

                let id = self.tys.funcs.len() as _;
                self.tys.funcs.push(func);

                ty::Kind::Func(id)
            }
            Expr::BinOp {
                left: Expr::Ident { .. },
                op: TokenKind::Decl,
                right: right @ Expr::Struct { .. },
            } => self.ty(right).expand(),
            e => unimplemented!("{e:#?}"),
        };
        self.ci.file = prev_file;
        self.tys.syms.insert(SymKey { ident, file }, sym.compress());
        sym
    }

    fn ty_display(&self, ty: ty::Id) -> ty::Display {
        ty::Display::new(&self.tys, &self.files, ty)
    }

    fn ast_display(&self, ast: &Expr) -> String {
        let mut s = String::new();
        parser::Formatter::new(&self.cfile().file).fmt(ast, &mut s).unwrap();
        s
    }

    #[must_use]
    #[track_caller]
    fn assert_ty(
        &self,
        pos: Pos,
        ty: ty::Id,
        expected: ty::Id,
        preserve_expected: bool,
        hint: impl fmt::Display,
    ) -> ty::Id {
        if let Some(res) = ty.try_upcast(expected)
            && (!preserve_expected || res == expected)
        {
            res
        } else {
            let ty = self.ty_display(ty);
            let expected = self.ty_display(expected);
            self.report(pos, fa!("expected {hint} to be of type {expected}, got {ty}"));
            ty::Id::NEVER
        }
    }

    fn report_log(&self, pos: Pos, msg: impl core::fmt::Display) {
        let mut buf = self.errors.borrow_mut();
        self.report_log_to(pos, msg, &mut *buf);
    }

    fn report_log_to(
        &self,
        pos: Pos,
        msg: impl core::fmt::Display,
        out: &mut impl core::fmt::Write,
    ) {
        self.cfile().report_to(pos, msg, out);
    }

    #[track_caller]
    fn assert_report(&self, cond: bool, pos: Pos, msg: impl core::fmt::Display) {
        if !cond {
            self.report(pos, msg);
        }
    }

    #[track_caller]
    fn report(&self, pos: Pos, msg: impl core::fmt::Display) {
        self.report_log(pos, msg);
    }

    #[track_caller]
    fn report_unhandled_ast(&self, ast: &Expr, hint: &str) {
        self.report(
            ast.pos(),
            fa!(
                "compiler does not (yet) know how to handle ({hint}):\n\
                {:}\n\
                info for weak people:\n\
                {ast:#?}",
                self.ast_display(ast)
            ),
        );
    }

    fn cfile(&self) -> &parser::Ast {
        &self.files[self.ci.file as usize]
    }

    fn pack_args(&mut self, arg_base: usize) -> Option<ty::Tuple> {
        let needle = &self.tys.args[arg_base..];
        if needle.is_empty() {
            return Some(ty::Tuple::empty());
        }
        let len = needle.len();
        // FIXME: maybe later when this becomes a bottleneck we use more
        // efficient search (SIMD?, indexing?)
        let sp = self.tys.args.windows(needle.len()).position(|val| val == needle).unwrap();
        self.tys.args.truncate((sp + needle.len()).max(arg_base));
        ty::Tuple::new(sp, len)
    }

    fn fatal_report(&self, pos: Pos, msg: impl Display) -> ! {
        self.report(pos, msg);
        panic!("{}", self.errors.borrow());
    }

    fn gcm(&mut self) {
        self.ci.nodes.visited.clear(self.ci.nodes.values.len());
        push_up(&mut self.ci.nodes, NEVER);
        // TODO: handle infinte loops
        self.ci.nodes.visited.clear(self.ci.nodes.values.len());
        push_down(&mut self.ci.nodes, VOID);
    }

    fn get_load_type(&self, val: Nid) -> Option<ty::Id> {
        Some(match self.ci.nodes[val].kind {
            Kind::Stre { .. } | Kind::Load { .. } | Kind::Stck | Kind::Arg { .. } => {
                self.ci.nodes[val].ty
            }
            Kind::Ptr { .. } => self.tys.base_of(self.ci.nodes[val].ty).unwrap(),
            _ => return None,
        })
    }
}

// FIXME: make this more efficient (allocated with arena)

#[derive(Debug)]
struct Block {
    nid: Nid,
    preds: Vec<regalloc2::Block>,
    succs: Vec<regalloc2::Block>,
    instrs: regalloc2::InstRange,
    params: Vec<regalloc2::VReg>,
    branch_blockparams: Vec<regalloc2::VReg>,
}

#[derive(Debug)]
struct Instr {
    nid: Nid,
    ops: Vec<regalloc2::Operand>,
}

struct Function<'a> {
    sig: Sig,
    nodes: &'a mut Nodes,
    tys: &'a Types,
    blocks: Vec<Block>,
    instrs: Vec<Instr>,
}

impl Debug for Function<'_> {
    fn fmt(&self, f: &mut core::fmt::Formatter<'_>) -> core::fmt::Result {
        for (i, block) in self.blocks.iter().enumerate() {
            writeln!(f, "sb{i}{:?}-{:?}:", block.params, block.preds)?;

            for inst in block.instrs.iter() {
                let instr = &self.instrs[inst.index()];
                writeln!(f, "{}: i{:?}:{:?}", inst.index(), self.nodes[instr.nid].kind, instr.ops)?;
            }

            writeln!(f, "eb{i}{:?}-{:?}:", block.branch_blockparams, block.succs)?;
        }
        Ok(())
    }
}

impl<'a> Function<'a> {
    fn new(nodes: &'a mut Nodes, tys: &'a Types, sig: Sig) -> Self {
        let mut s =
            Self { nodes, tys, sig, blocks: Default::default(), instrs: Default::default() };
        s.nodes.visited.clear(s.nodes.values.len());
        s.emit_node(VOID, VOID);
        s.add_block(0);
        s.blocks.pop();
        s
    }

    fn add_block(&mut self, nid: Nid) -> RallocBRef {
        if let Some(prev) = self.blocks.last_mut() {
            prev.instrs = regalloc2::InstRange::new(
                prev.instrs.first(),
                regalloc2::Inst::new(self.instrs.len()),
            );
        }

        self.blocks.push(Block {
            nid,
            preds: Default::default(),
            succs: Default::default(),
            instrs: regalloc2::InstRange::new(
                regalloc2::Inst::new(self.instrs.len()),
                regalloc2::Inst::new(self.instrs.len() + 1),
            ),
            params: Default::default(),
            branch_blockparams: Default::default(),
        });
        self.blocks.len() as RallocBRef - 1
    }

    fn add_instr(&mut self, nid: Nid, ops: Vec<regalloc2::Operand>) {
        self.instrs.push(Instr { nid, ops });
    }

    fn urg(&mut self, nid: Nid) -> regalloc2::Operand {
        regalloc2::Operand::reg_use(self.rg(nid))
    }

    fn def_nid(&mut self, _nid: Nid) {}

    fn drg(&mut self, nid: Nid) -> regalloc2::Operand {
        self.def_nid(nid);
        regalloc2::Operand::reg_def(self.rg(nid))
    }

    fn rg(&self, nid: Nid) -> VReg {
        regalloc2::VReg::new(nid as _, regalloc2::RegClass::Int)
    }

    fn emit_node(&mut self, nid: Nid, prev: Nid) {
        if matches!(self.nodes[nid].kind, Kind::Region | Kind::Loop) {
            let prev_bref = self.nodes[prev].ralloc_backref;
            let node = self.nodes[nid].clone();

            let idx = 1 + node.inputs.iter().position(|&i| i == prev).unwrap();

            for ph in node.outputs {
                if self.nodes[ph].kind != Kind::Phi {
                    continue;
                }

                let rg = self.rg(self.nodes[ph].inputs[idx]);
                self.blocks[prev_bref as usize].branch_blockparams.push(rg);
            }

            self.add_instr(nid, vec![]);

            match (self.nodes[nid].kind, self.nodes.visited.set(nid)) {
                (Kind::Loop, false) => {
                    for i in node.inputs {
                        self.bridge(i, nid);
                    }
                    return;
                }
                (Kind::Region, true) => return,
                _ => {}
            }
        } else if !self.nodes.visited.set(nid) {
            return;
        }

        let node = self.nodes[nid].clone();
        match node.kind {
            Kind::Start => {
                debug_assert_matches!(self.nodes[node.outputs[0]].kind, Kind::Entry);
                self.emit_node(node.outputs[0], VOID)
            }
            Kind::End => {}
            Kind::If => {
                self.nodes[nid].ralloc_backref = self.nodes[prev].ralloc_backref;

                let &[_, cond] = node.inputs.as_slice() else { unreachable!() };
                let &[mut then, mut else_] = node.outputs.as_slice() else { unreachable!() };

                if let Kind::BinOp { op } = self.nodes[cond].kind
                    && let Some((_, swapped)) = op.cond_op(node.ty.is_signed())
                {
                    if swapped {
                        core::mem::swap(&mut then, &mut else_);
                    }
                    let &[_, lhs, rhs] = self.nodes[cond].inputs.as_slice() else { unreachable!() };
                    let ops = vec![self.urg(lhs), self.urg(rhs)];
                    self.add_instr(nid, ops);
                } else {
                    todo!()
                }

                self.emit_node(then, nid);
                self.emit_node(else_, nid);
            }
            Kind::Region | Kind::Loop => {
                self.nodes[nid].ralloc_backref = self.add_block(nid);
                if node.kind == Kind::Region {
                    for i in node.inputs {
                        self.bridge(i, nid);
                    }
                }
                let mut block = vec![];
                for ph in node.outputs.clone() {
                    if self.nodes[ph].kind != Kind::Phi {
                        continue;
                    }
                    self.def_nid(ph);
                    block.push(self.rg(ph));
                }
                self.blocks[self.nodes[nid].ralloc_backref as usize].params = block;
                for o in node.outputs.into_iter().rev() {
                    self.emit_node(o, nid);
                }
            }
            Kind::Return => {
                let ops = if node.inputs[1] != VOID {
                    vec![regalloc2::Operand::reg_fixed_use(
                        self.rg(node.inputs[1]),
                        regalloc2::PReg::new(1, regalloc2::RegClass::Int),
                    )]
                } else {
                    vec![]
                };
                self.add_instr(nid, ops);
                self.emit_node(node.outputs[0], nid);
            }
            Kind::CInt { .. } => {
                let unused = node.outputs.into_iter().all(|o| {
                    let ond = &self.nodes[o];
                    matches!(ond.kind, Kind::BinOp { op }
                        if op.imm_binop(ond.ty.is_signed(), 8).is_some()
                            && self.nodes.is_const(ond.inputs[2])
                            && op.cond_op(ond.ty.is_signed()).is_none())
                });

                if !unused {
                    let ops = vec![self.drg(nid)];
                    self.add_instr(nid, ops);
                }
            }
            Kind::Entry => {
                self.nodes[nid].ralloc_backref = self.add_block(nid);

                let mut parama = self.tys.parama(self.sig.ret);
                for (arg, ti) in
                    self.nodes[VOID].clone().outputs.into_iter().skip(2).zip(self.sig.args.range())
                {
                    let ty = self.tys.args[ti];
                    match self.tys.size_of(ty) {
                        0 => continue,
                        1..=8 => {
                            self.def_nid(arg);
                            self.add_instr(NEVER, vec![regalloc2::Operand::reg_fixed_def(
                                self.rg(arg),
                                regalloc2::PReg::new(parama.next() as _, regalloc2::RegClass::Int),
                            )]);
                        }
                        _ => todo!(),
                    }
                }

                for o in node.outputs.into_iter().rev() {
                    self.emit_node(o, nid);
                }
            }
            Kind::Then | Kind::Else => {
                self.nodes[nid].ralloc_backref = self.add_block(nid);
                self.bridge(prev, nid);
                for o in node.outputs.into_iter().rev() {
                    self.emit_node(o, nid);
                }
            }
            Kind::BinOp { op } => {
                let &[_, lhs, rhs] = node.inputs.as_slice() else { unreachable!() };

                let ops = if let Kind::CInt { .. } = self.nodes[rhs].kind
                    && op.imm_binop(node.ty.is_signed(), 8).is_some()
                {
                    vec![self.drg(nid), self.urg(lhs)]
                } else if op.binop(node.ty.is_signed(), 8).is_some() {
                    vec![self.drg(nid), self.urg(lhs), self.urg(rhs)]
                } else if op.cond_op(node.ty.is_signed()).is_some() {
                    return;
                } else {
                    todo!("{op}")
                };
                self.add_instr(nid, ops);
            }
            Kind::UnOp { .. } => {
                let ops = vec![self.drg(nid), self.urg(node.inputs[1])];
                self.add_instr(nid, ops);
            }
            Kind::Call { func } => {
                self.nodes[nid].ralloc_backref = self.nodes[prev].ralloc_backref;
                let mut ops = vec![];

                let fuc = self.tys.funcs[func as usize].sig.unwrap();
                if self.tys.size_of(fuc.ret) != 0 {
                    self.def_nid(nid);
                    ops.push(regalloc2::Operand::reg_fixed_def(
                        self.rg(nid),
                        regalloc2::PReg::new(1, regalloc2::RegClass::Int),
                    ));
                }

                let mut parama = self.tys.parama(fuc.ret);
                for (&(mut i), ti) in node.inputs[1..].iter().zip(fuc.args.range()) {
                    let ty = self.tys.args[ti];
                    loop {
                        match self.nodes[i].kind {
                            Kind::Stre { .. } => i = self.nodes[i].inputs[2],
                            Kind::Load { .. } => i = self.nodes[i].inputs[1],
                            _ => break,
                        }
                    }
                    match self.tys.size_of(ty) {
                        0 => continue,
                        1..=8 => {
                            ops.push(regalloc2::Operand::reg_fixed_use(
                                self.rg(i),
                                regalloc2::PReg::new(parama.next() as _, regalloc2::RegClass::Int),
                            ));
                        }
                        _ => todo!(),
                    }
                }

                self.add_instr(nid, ops);

                for o in node.outputs.into_iter().rev() {
                    if self.nodes[o].inputs[0] == nid {
                        self.emit_node(o, nid);
                    }
                }
            }
            Kind::Phi | Kind::Arg { .. } | Kind::Mem => {}
            Kind::Stck => {
                let ops = vec![self.drg(nid)];
                self.add_instr(nid, ops);
            }
            Kind::Ptr { .. } => {
                let region = self.nodes.trace_mem(node.inputs[1]);
                let ops = match self.nodes[region].kind {
                    Kind::Stck => vec![self.drg(nid)],
                    k => unreachable!("{k:?}"),
                };
                self.add_instr(nid, ops);
            }
            Kind::Load { .. } => {
                let region = self.nodes.trace_mem(node.inputs[1]);
                let ops = match self.nodes[region].kind {
                    Kind::Stck => vec![self.drg(nid)],
                    k => unreachable!("{k:?}"),
                };
                self.add_instr(nid, ops);
            }
            Kind::Stre { .. } => {
                let region = self.nodes.trace_mem(node.inputs[2]);
                let ops = match self.nodes[region].kind {
                    Kind::Stck => vec![self.urg(node.inputs[1])],
                    Kind::Arg { .. } => vec![self.urg(region), self.urg(node.inputs[1])],
                    k => unreachable!("{k:?}"),
                };
                self.add_instr(nid, ops);
            }
        }
    }

    fn bridge(&mut self, pred: u16, succ: u16) {
        if self.nodes[pred].ralloc_backref == u16::MAX
            || self.nodes[succ].ralloc_backref == u16::MAX
        {
            return;
        }
        self.blocks[self.nodes[pred].ralloc_backref as usize]
            .succs
            .push(regalloc2::Block::new(self.nodes[succ].ralloc_backref as usize));
        self.blocks[self.nodes[succ].ralloc_backref as usize]
            .preds
            .push(regalloc2::Block::new(self.nodes[pred].ralloc_backref as usize));
    }
}

impl<'a> regalloc2::Function for Function<'a> {
    fn num_insts(&self) -> usize {
        self.instrs.len()
    }

    fn num_blocks(&self) -> usize {
        self.blocks.len()
    }

    fn entry_block(&self) -> regalloc2::Block {
        regalloc2::Block(0)
    }

    fn block_insns(&self, block: regalloc2::Block) -> regalloc2::InstRange {
        self.blocks[block.index()].instrs
    }

    fn block_succs(&self, block: regalloc2::Block) -> &[regalloc2::Block] {
        &self.blocks[block.index()].succs
    }

    fn block_preds(&self, block: regalloc2::Block) -> &[regalloc2::Block] {
        &self.blocks[block.index()].preds
    }

    fn block_params(&self, block: regalloc2::Block) -> &[regalloc2::VReg] {
        &self.blocks[block.index()].params
    }

    fn is_ret(&self, insn: regalloc2::Inst) -> bool {
        self.nodes[self.instrs[insn.index()].nid].kind == Kind::Return
    }

    fn is_branch(&self, insn: regalloc2::Inst) -> bool {
        matches!(
            self.nodes[self.instrs[insn.index()].nid].kind,
            Kind::If | Kind::Then | Kind::Else | Kind::Entry | Kind::Loop | Kind::Region
        )
    }

    fn branch_blockparams(
        &self,
        block: regalloc2::Block,
        _insn: regalloc2::Inst,
        _succ_idx: usize,
    ) -> &[regalloc2::VReg] {
        debug_assert!(
            self.blocks[block.index()].succs.len() == 1
                || self.blocks[block.index()].branch_blockparams.is_empty()
        );

        &self.blocks[block.index()].branch_blockparams
    }

    fn inst_operands(&self, insn: regalloc2::Inst) -> &[regalloc2::Operand] {
        &self.instrs[insn.index()].ops
    }

    fn inst_clobbers(&self, insn: regalloc2::Inst) -> regalloc2::PRegSet {
        if matches!(self.nodes[self.instrs[insn.index()].nid].kind, Kind::Call { .. }) {
            let mut set = regalloc2::PRegSet::default();
            for i in 2..13 {
                set.add(regalloc2::PReg::new(i, regalloc2::RegClass::Int));
            }
            set
        } else {
            regalloc2::PRegSet::default()
        }
    }

    fn num_vregs(&self) -> usize {
        self.nodes.values.len()
    }

    fn spillslot_size(&self, regclass: regalloc2::RegClass) -> usize {
        match regclass {
            regalloc2::RegClass::Int => 1,
            regalloc2::RegClass::Float => unreachable!(),
            regalloc2::RegClass::Vector => unreachable!(),
        }
    }
}

fn loop_depth(target: Nid, nodes: &mut Nodes) -> LoopDepth {
    if nodes[target].loop_depth != 0 {
        return nodes[target].loop_depth;
    }

    nodes[target].loop_depth = match nodes[target].kind {
        Kind::Entry | Kind::Then | Kind::Else | Kind::Call { .. } | Kind::Return | Kind::If => {
            let dpth = loop_depth(nodes[target].inputs[0], nodes);
            if nodes[target].loop_depth != 0 {
                return nodes[target].loop_depth;
            }
            dpth
        }
        Kind::Region => {
            let l = loop_depth(nodes[target].inputs[0], nodes);
            let r = loop_depth(nodes[target].inputs[1], nodes);
            debug_assert_eq!(l, r);
            l
        }
        Kind::Loop => {
            let depth = loop_depth(nodes[target].inputs[0], nodes) + 1;
            nodes[target].loop_depth = depth;
            let mut cursor = nodes[target].inputs[1];
            while cursor != target {
                nodes[cursor].loop_depth = depth;
                let next = if nodes[cursor].kind == Kind::Region {
                    loop_depth(nodes[cursor].inputs[0], nodes);
                    nodes[cursor].inputs[1]
                } else {
                    idom(nodes, cursor)
                };
                debug_assert_ne!(next, VOID);
                if matches!(nodes[cursor].kind, Kind::Then | Kind::Else) {
                    let other = *nodes[next]
                        .outputs
                        .iter()
                        .find(|&&n| nodes[n].kind != nodes[cursor].kind)
                        .unwrap();
                    if nodes[other].loop_depth == 0 {
                        nodes[other].loop_depth = depth - 1;
                    }
                }
                cursor = next;
            }
            depth
        }
        Kind::Start | Kind::End => 1,
        _ => unreachable!(),
    };

    nodes[target].loop_depth
}

fn better(nodes: &mut Nodes, is: Nid, then: Nid) -> bool {
    loop_depth(is, nodes) < loop_depth(then, nodes)
        || idepth(nodes, is) > idepth(nodes, then)
        || nodes[then].kind == Kind::If
}

fn idepth(nodes: &mut Nodes, target: Nid) -> IDomDepth {
    if target == VOID {
        return 0;
    }
    if nodes[target].depth == 0 {
        nodes[target].depth = match nodes[target].kind {
            Kind::End | Kind::Start => unreachable!(),
            Kind::Region => {
                idepth(nodes, nodes[target].inputs[0]).max(idepth(nodes, nodes[target].inputs[1]))
            }
            _ => idepth(nodes, nodes[target].inputs[0]),
        } + 1;
    }
    nodes[target].depth
}

fn push_up(nodes: &mut Nodes, node: Nid) {
    if !nodes.visited.set(node) {
        return;
    }

    if nodes[node].kind.is_pinned() {
        for i in 0..nodes[node].inputs.len() {
            let i = nodes[node].inputs[i];
            push_up(nodes, i);
        }
    } else {
        let mut max = VOID;
        for i in 0..nodes[node].inputs.len() {
            let i = nodes[node].inputs[i];
            let is_call = matches!(nodes[i].kind, Kind::Call { .. });
            if nodes.is_cfg(i) && !is_call {
                continue;
            }
            push_up(nodes, i);
            if idepth(nodes, i) > idepth(nodes, max) {
                max = if is_call { i } else { idom(nodes, i) };
            }
        }

        #[cfg(debug_assertions)]
        {
            nodes.check_dominance(node, max, false);
        }

        if max == VOID {
            return;
        }

        let index = nodes[0].outputs.iter().position(|&p| p == node).unwrap();
        nodes[0].outputs.remove(index);
        nodes[node].inputs[0] = max;
        debug_assert!(
            !nodes[max].outputs.contains(&node) || matches!(nodes[max].kind, Kind::Call { .. }),
            "{node} {:?} {max} {:?}",
            nodes[node],
            nodes[max]
        );
        nodes[max].outputs.push(node);
    }
}

fn push_down(nodes: &mut Nodes, node: Nid) {
    if !nodes.visited.set(node) {
        return;
    }

    // TODO: handle memory nodes first

    if nodes[node].kind.is_pinned() {
        // TODO: use buffer to avoid allocation or better yet queue the location changes
        for i in nodes[node].outputs.clone() {
            push_down(nodes, i);
        }
    } else {
        let mut min = None::<Nid>;
        for i in 0..nodes[node].outputs.len() {
            let i = nodes[node].outputs[i];
            push_down(nodes, i);
            let i = use_block(node, i, nodes);
            min = min.map(|m| common_dom(i, m, nodes)).or(Some(i));
        }
        let mut min = min.unwrap();

        debug_assert!(nodes.dominates(nodes[node].inputs[0], min));

        let mut cursor = min;
        loop {
            if better(nodes, cursor, min) {
                min = cursor;
            }
            if cursor == nodes[node].inputs[0] {
                break;
            }
            cursor = idom(nodes, cursor);
        }

        if nodes[min].kind.ends_basic_block() {
            min = idom(nodes, min);
        }

        #[cfg(debug_assertions)]
        {
            nodes.check_dominance(node, min, true);
        }

        let prev = nodes[node].inputs[0];
        if min != prev {
            debug_assert!(idepth(nodes, min) > idepth(nodes, prev));
            let index = nodes[prev].outputs.iter().position(|&p| p == node).unwrap();
            nodes[prev].outputs.remove(index);
            nodes[node].inputs[0] = min;
            nodes[min].outputs.push(node);
        }
    }
}

fn use_block(target: Nid, from: Nid, nodes: &mut Nodes) -> Nid {
    if nodes[from].kind != Kind::Phi {
        return idom(nodes, from);
    }

    let index = nodes[from].inputs.iter().position(|&n| n == target).unwrap();
    nodes[nodes[from].inputs[0]].inputs[index - 1]
}

fn idom(nodes: &mut Nodes, target: Nid) -> Nid {
    match nodes[target].kind {
        Kind::Start => VOID,
        Kind::End => unreachable!(),
        Kind::Region => {
            let &[lcfg, rcfg] = nodes[target].inputs.as_slice() else { unreachable!() };
            common_dom(lcfg, rcfg, nodes)
        }
        _ => nodes[target].inputs[0],
    }
}

fn common_dom(mut a: Nid, mut b: Nid, nodes: &mut Nodes) -> Nid {
    while a != b {
        let [ldepth, rdepth] = [idepth(nodes, a), idepth(nodes, b)];
        if ldepth >= rdepth {
            a = idom(nodes, a);
        }
        if ldepth <= rdepth {
            b = idom(nodes, b);
        }
    }
    a
}

#[cfg(test)]
mod tests {
    use {
        alloc::{string::String, vec::Vec},
        core::fmt::Write,
    };

    fn generate(ident: &'static str, input: &'static str, output: &mut String) {
        _ = env_logger::builder().is_test(true).try_init();

        let mut codegen =
            super::Codegen { files: crate::test_parse_files(ident, input), ..Default::default() };

        codegen.generate();

        {
            let errors = codegen.errors.borrow();
            if !errors.is_empty() {
                output.push_str(&errors);
                return;
            }
        }

        let mut out = Vec::new();
        codegen.tys.assemble(&mut out);

        let err = codegen.tys.disasm(&out, &codegen.files, output, |_| {});
        if let Err(e) = err {
            writeln!(output, "!!! asm is invalid: {e}").unwrap();
            return;
        }

        //println!("{output}");

        crate::test_run_vm(&out, output);
    }

    crate::run_tests! { generate:
        arithmetic;
        variables;
        functions;
        comments;
        if_statements;
        loops;
        fb_driver;
        pointers;
        structs;
        //different_types;
        //struct_operators;
        //directives;
        //global_variables;
        //generic_types;
        //generic_functions;
        //c_strings;
        //struct_patterns;
        //arrays;
        //struct_return_from_module_function;
        ////comptime_pointers;
        //sort_something_viredly;
        hex_octal_binary_literals;
        //comptime_min_reg_leak;
        ////structs_in_registers;
        //comptime_function_from_another_file;
        //inline;
        //inline_test;
        const_folding_with_arg;
        branch_assignments;
        exhaustive_loop_testing;
        //idk;
        //comptime_min_reg_leak;
        //some_generic_code;
        //integer_inference_issues;
        //writing_into_string;
        //request_page;
        //tests_ptr_to_ptr_copy;
        //wide_ret;
        pointer_opts;
    }
}