fidget_core/compiler/

alloc.rs

use crate::compiler::{Lru, RegOp, RegTape, SsaOp};

#[derive(Copy, Clone, Debug)]
enum Allocation {
    Register(u8),
    Memory(u32),
    Unassigned,
}

const UNASSIGNED: u32 = u32::MAX;

/// Cheap and cheerful single-pass register allocation
pub struct RegisterAllocator<const N: usize> {
    /// Map from the index in the original (globally allocated) tape to a
    /// specific register or memory slot.
    ///
    /// Unallocated slots are marked with `UNASSIGNED` (`u32::MAX`); allocated
    /// slots have the value of their register or memory slot (which are both
    /// integers; the dividing point is based on register count).
    allocations: Vec<u32>,

    /// Map from a particular register to the index in the original tape that's
    /// using that register, or `UNASSIGNED` (`u32::MAX`) if the register is
    /// currently unused.
    ///
    /// The inner `u32` here is an index into the original (SSA) tape
    registers: [u32; N],

    /// Stores a least-recently-used list of registers
    ///
    /// Registers are indexed by their value in the output tape
    register_lru: Lru<N>,

    /// Available short registers (index < N)
    ///
    /// The most recently available is at the back
    spare_registers: Vec<u8>,

    /// Available extended registers (index >= N)
    ///
    /// The most recently available is at the back of the `Vec`
    spare_memory: Vec<u32>,

    /// Output slots, assembled in reverse order
    out: RegTape,
}

impl<const N: usize> RegisterAllocator<N> {
    /// Builds a new `RegisterAllocator`.
    pub fn new(size: usize) -> Self {
        assert!(N <= u8::MAX as usize);
        Self {
            allocations: vec![UNASSIGNED; size],

            registers: [UNASSIGNED; N],
            register_lru: Lru::new(),

            spare_registers: (0..N as u8).rev().collect(),
            spare_memory: Vec::with_capacity(1024),

            out: RegTape::empty(),
        }
    }

    /// Build a new empty register allocator
    pub fn empty() -> Self {
        Self {
            allocations: vec![],

            registers: [UNASSIGNED; N],
            register_lru: Lru::new(),

            spare_registers: (0..N as u8).rev().collect(),
            spare_memory: vec![],

            out: RegTape::empty(),
        }
    }

    /// Resets internal state, reusing allocations and the provided tape
    ///
    /// This must be called after the allocator is finalized (removing the
    /// internal [`RegTape`]).
    ///
    /// # Panics
    /// If the internal tape is not empty
    pub fn reset(&mut self, size: usize, tape: RegTape) {
        assert!(self.out.is_empty());
        self.allocations.fill(UNASSIGNED);
        self.allocations.resize(size, UNASSIGNED);
        self.registers.fill(UNASSIGNED);
        self.register_lru = Lru::new();
        self.spare_registers.clear();
        self.spare_registers.extend((0..N as u8).rev());
        self.spare_memory.clear();
        self.out = tape;
        self.out.reset();
    }

    /// Claims the internal [`RegTape`], leaving the allocator empty
    #[inline]
    pub fn finalize(&mut self) -> RegTape {
        std::mem::take(&mut self.out)
    }

    /// Returns an available memory slot.
    ///
    /// Memory is treated as unlimited; if we don't have any spare slots, then
    /// we'll assign a new one (incrementing `self.total_slots`).
    ///
    /// > If there's one thing I love  
    /// > It's an infinite resource  
    /// > If there's one thing worth loving  
    /// > It's a surplus of supplies
    #[inline]
    fn get_memory(&mut self) -> u32 {
        if let Some(p) = self.spare_memory.pop() {
            p
        } else {
            let out = self.out.slot_count;
            self.out.slot_count += 1;
            assert!(out as usize >= N);
            out
        }
    }

    /// Finds the oldest register
    ///
    /// This is useful when deciding which register to evict to make room
    #[inline]
    fn oldest_reg(&mut self) -> u8 {
        self.register_lru.pop()
    }

    /// Returns the slot allocated to the given node
    ///
    /// The input is an SSA assignment (i.e. an assignment in the input
    /// `SsaTape`)
    ///
    /// If the output is a register, then it's poked to update recency
    #[inline]
    fn get_allocation(&mut self, n: u32) -> Allocation {
        match self.allocations[n as usize] {
            i if i < N as u32 => {
                self.register_lru.poke(i as u8);
                Allocation::Register(i as u8)
            }
            UNASSIGNED => Allocation::Unassigned,
            i => Allocation::Memory(i),
        }
    }

    /// Return an unoccupied register, if available
    #[inline]
    fn get_spare_register(&mut self) -> Option<u8> {
        let r = self.spare_registers.pop()?;
        self.out.slot_count = self.out.slot_count.max(r as u32 + 1);
        Some(r)
    }

    #[inline]
    fn get_register(&mut self) -> u8 {
        if let Some(reg) = self.get_spare_register() {
            assert_eq!(self.registers[reg as usize], UNASSIGNED);
            self.register_lru.poke(reg);
            reg
        } else {
            // Slot is in memory, and no spare register is available
            let reg = self.oldest_reg();

            // Here's where it will go:
            let mem = self.get_memory();

            // Whoever was previously using you is in for a surprise
            let prev_node = self.registers[reg as usize];
            self.allocations[prev_node as usize] = mem;

            // This register is now unassigned
            self.registers[reg as usize] = UNASSIGNED;

            self.out.push(RegOp::Load(reg, mem));
            reg
        }
    }

    #[inline]
    fn rebind_register(&mut self, n: u32, reg: u8) {
        assert!(self.allocations[n as usize] >= N as u32);
        assert!(self.registers[reg as usize] != UNASSIGNED);

        let prev_node = self.registers[reg as usize];
        self.allocations[prev_node as usize] = UNASSIGNED;

        // Bind the register, but don't bother poking; whoever got the register
        // for us is responsible for that step.
        self.registers[reg as usize] = n;
        self.allocations[n as usize] = reg as u32;
    }

    #[inline]
    fn bind_register(&mut self, n: u32, reg: u8) {
        assert!(self.allocations[n as usize] >= N as u32);
        assert!(self.registers[reg as usize] == UNASSIGNED);

        // Bind the register, but don't bother poking; whoever got the register
        // for us is responsible for that step.
        self.registers[reg as usize] = n;
        self.allocations[n as usize] = reg as u32;
    }

    /// Release a register back to the pool of spares
    #[inline]
    fn release_reg(&mut self, reg: u8) {
        // Release the output register, so it could be used for inputs
        assert!((reg as usize) < N);

        let node = self.registers[reg as usize];
        assert!(node != UNASSIGNED);

        self.registers[reg as usize] = UNASSIGNED;
        self.spare_registers.push(reg);
        // Modifying self.allocations isn't strictly necessary, but could help
        // us detect logical errors (since it should never be used after this)
        self.allocations[node as usize] = UNASSIGNED;
    }

    #[inline]
    fn release_mem(&mut self, mem: u32) {
        assert!(mem >= N as u32);
        self.spare_memory.push(mem);
        // This leaves self.allocations[...] still pointing to the memory slot,
        // but that's okay, because it should never be used
    }

    /// Lowers an operation that uses a single register into an
    /// [`RegOp`], pushing it to the internal tape.
    ///
    /// This may also push `Load` or `Store` instructions to the internal tape,
    /// if there aren't enough spare registers.
    #[inline(always)]
    fn op_reg(&mut self, op: SsaOp) {
        let (out, arg, op): (u32, u32, fn(u8, u8) -> RegOp) = match op {
            SsaOp::NegReg(out, arg) => (out, arg, RegOp::NegReg),
            SsaOp::AbsReg(out, arg) => (out, arg, RegOp::AbsReg),
            SsaOp::RecipReg(out, arg) => (out, arg, RegOp::RecipReg),
            SsaOp::SqrtReg(out, arg) => (out, arg, RegOp::SqrtReg),
            SsaOp::SquareReg(out, arg) => (out, arg, RegOp::SquareReg),
            SsaOp::FloorReg(out, arg) => (out, arg, RegOp::FloorReg),
            SsaOp::CeilReg(out, arg) => (out, arg, RegOp::CeilReg),
            SsaOp::RoundReg(out, arg) => (out, arg, RegOp::RoundReg),
            SsaOp::SinReg(out, arg) => (out, arg, RegOp::SinReg),
            SsaOp::CosReg(out, arg) => (out, arg, RegOp::CosReg),
            SsaOp::TanReg(out, arg) => (out, arg, RegOp::TanReg),
            SsaOp::AsinReg(out, arg) => (out, arg, RegOp::AsinReg),
            SsaOp::AcosReg(out, arg) => (out, arg, RegOp::AcosReg),
            SsaOp::AtanReg(out, arg) => (out, arg, RegOp::AtanReg),
            SsaOp::ExpReg(out, arg) => (out, arg, RegOp::ExpReg),
            SsaOp::LnReg(out, arg) => (out, arg, RegOp::LnReg),
            SsaOp::NotReg(out, arg) => (out, arg, RegOp::NotReg),
            SsaOp::CopyReg(out, arg) => (out, arg, RegOp::CopyReg),
            _ => panic!("Bad opcode: {op:?}"),
        };
        self.op_reg_fn(out, arg, op);
    }

    /// Allocates the next operation in the tape
    #[inline(always)]
    pub fn op(&mut self, op: SsaOp) {
        match op {
            SsaOp::Output(reg, i) => self.op_output(reg, i),
            SsaOp::Input(out, i) => self.op_input(out, i),
            SsaOp::CopyImm(out, imm) => self.op_copy_imm(out, imm),

            SsaOp::NegReg(..)
            | SsaOp::AbsReg(..)
            | SsaOp::RecipReg(..)
            | SsaOp::SqrtReg(..)
            | SsaOp::SquareReg(..)
            | SsaOp::FloorReg(..)
            | SsaOp::CeilReg(..)
            | SsaOp::RoundReg(..)
            | SsaOp::CopyReg(..)
            | SsaOp::SinReg(..)
            | SsaOp::CosReg(..)
            | SsaOp::TanReg(..)
            | SsaOp::AsinReg(..)
            | SsaOp::AcosReg(..)
            | SsaOp::AtanReg(..)
            | SsaOp::ExpReg(..)
            | SsaOp::LnReg(..)
            | SsaOp::NotReg(..) => self.op_reg(op),

            SsaOp::AddRegImm(..)
            | SsaOp::SubRegImm(..)
            | SsaOp::SubImmReg(..)
            | SsaOp::MulRegImm(..)
            | SsaOp::DivRegImm(..)
            | SsaOp::DivImmReg(..)
            | SsaOp::AtanImmReg(..)
            | SsaOp::AtanRegImm(..)
            | SsaOp::MinRegImm(..)
            | SsaOp::MaxRegImm(..)
            | SsaOp::CompareRegImm(..)
            | SsaOp::CompareImmReg(..)
            | SsaOp::ModRegImm(..)
            | SsaOp::ModImmReg(..)
            | SsaOp::AndRegImm(..)
            | SsaOp::OrRegImm(..) => self.op_reg_imm(op),

            SsaOp::AddRegReg(..)
            | SsaOp::SubRegReg(..)
            | SsaOp::MulRegReg(..)
            | SsaOp::DivRegReg(..)
            | SsaOp::AtanRegReg(..)
            | SsaOp::MinRegReg(..)
            | SsaOp::MaxRegReg(..)
            | SsaOp::CompareRegReg(..)
            | SsaOp::ModRegReg(..)
            | SsaOp::AndRegReg(..)
            | SsaOp::OrRegReg(..) => self.op_reg_reg(op),
        }
    }

    fn push_store(&mut self, reg: u8, mem: u32) {
        self.out.push(RegOp::Store(reg, mem));
        self.release_mem(mem);
    }

    /// Returns a register that is bound to the given SSA input
    ///
    /// If the given SSA input is not already bound to a register, then we
    /// evict the oldest register using `Self::get_register`, with the
    /// appropriate set of LOAD/STORE operations.
    #[inline]
    fn get_out_reg(&mut self, out: u32) -> u8 {
        match self.get_allocation(out) {
            Allocation::Register(r_x) => r_x,
            Allocation::Memory(m_x) => {
                // TODO: this could be more efficient with a Swap instruction,
                // since we know that we're about to free a memory slot.
                let r_a = self.get_register();

                self.push_store(r_a, m_x);
                self.bind_register(out, r_a);
                r_a
            }
            Allocation::Unassigned => panic!("Cannot have unassigned output"),
        }
    }

    #[inline(always)]
    fn op_reg_fn(&mut self, out: u32, arg: u32, op: impl Fn(u8, u8) -> RegOp) {
        // When we enter this function, the output can be assigned to either a
        // register or memory, and the input can be a register, memory, or
        // unassigned.  This gives us six unique situations.
        //
        //   out | arg | what do?
        //  ================================================================
        //   r_x | r_y | r_x = op r_y
        //       |     |
        //       |     | Afterwards, r_x is free
        //  -----|-----|----------------------------------------------------
        //   r_x | m_y | r_x = op r_a
        //       |     | store r_a -> m_y
        //       |     | [load r_a <- m_a]
        //       |     |
        //       |     | Afterward, r_x is free and r_a points to the former m_y
        //  -----|-----|----------------------------------------------------
        //   r_x |  U  | r_x = op r_x
        //       |     |
        //       |     | Afterward, r_x points to the arg
        //  -----|-----|----------------------------------------------------
        //
        //  Cases with the output in memory (m_x) are identical except that they
        //  include a trailing
        //
        //      store r_a -> m_x
        //      [load r_a <- m_a]
        //
        // i.e. storing the value in the assigned memory slot, and then
        // restoring the previous register value if present (when read forward).
        let r_x = self.get_out_reg(out);
        match self.get_allocation(arg) {
            Allocation::Register(r_y) => {
                assert!(r_x != r_y);
                self.out.push(op(r_x, r_y));
                self.release_reg(r_x);
            }
            Allocation::Memory(m_y) => {
                let r_a = self.get_register();
                self.push_store(r_a, m_y);
                self.out.push(op(r_x, r_a));
                self.release_reg(r_x);
                self.bind_register(arg, r_a);
            }
            Allocation::Unassigned => {
                self.out.push(op(r_x, r_x));
                self.rebind_register(arg, r_x);
            }
        }
    }

    /// Lowers a two-register operation into an [`RegOp`], pushing it to the
    /// internal tape.
    ///
    /// Inputs are SSA registers from a [`SsaTape`](crate::compiler::SsaTape),
    /// i.e. globally addressed.
    ///
    /// If there aren't enough spare registers, this may also push `Load` or
    /// `Store` instructions to the internal tape.  It's trickier than it
    /// sounds; look at the source code for a table showing all 18 (!) possible
    /// configurations.
    #[inline(always)]
    fn op_reg_reg(&mut self, op: SsaOp) {
        // Looking at this horrific table, you may be tempted to think "surely
        // there's a clean abstraction that wraps this up in a few functions".
        // You may be right, but I spent a few days chasing down terrible memory
        // load/store ordering bugs, and decided that the brute-force approach
        // was the right one.
        //
        //   out | lhs  | rhs  | what do?
        //  ================================================================
        //  r_x  | r_y  | r_z  | r_x = op r_y r_z
        //       |      |      |
        //       |      |      | Afterwards, r_x is free
        //  -----|------|------|----------------------------------------------
        //  r_x  | m_y  | r_z  | r_x = op r_a r_z
        //       |      |      | store r_a -> m_y
        //       |      |      | [load r_a <- m_a]
        //       |      |      |
        //       |      |      | Afterwards, r_x is free, r_a points to the
        //       |      |      | former m_y, and m_y is free
        //  -----|------|------|----------------------------------------------
        //  r_x  | r_y  | m_z  | ibid
        //  -----|------|------|----------------------------------------------
        //  r_x  | m_y  | m_z  | r_x = op r_a r_b
        //       |      |      | store r_b -> m_z
        //       |      |      | [load r_b <- m_b]
        //       |      |      | store r_a -> m_y
        //       |      |      | [load r_a <- m_a]
        //       |      |      |
        //       |      |      | Afterwards, r_x points to the former m_y, r_a
        //       |      |      | points to the former m_z, m_y and m_z are free,
        //       |      |      | [and m_a points to the former r_a]
        //  -----|------|------|----------------------------------------------
        //  r_x  | U    | r_z  | r_x = op r_x r_z
        //       |      |      |
        //       |      |      | Afterward, r_x points to the lhs
        //  -----|------|------|----------------------------------------------
        //  r_x  | r_y  | U    | ibid
        //  -----|------|------|----------------------------------------------
        //  r_x  | U    | U    | rx = op r_x r_a
        //       |      |      | [load r_a <- m_a]
        //       |      |      |
        //       |      |      | Afterward, r_x points to the lhs, r_a points to
        //       |      |      | rhs, [and m_a points to the former r_a]
        //  -----|------|------|----------------------------------------------
        //  r_x  | U    | m_z  | r_x = op r_x r_a
        //       |      |      | store r_a -> m_z
        //       |      |      | [load r_a <- m_a]
        //       |      |      |
        //       |      |      | Afterward, r_x points to the lhs, r_a points to
        //       |      |      | rhs, m_z is free, [and m_a points to the former
        //       |      |      | r_a]
        //  -----|------|------|----------------------------------------------
        //  r_x  | m_y  | U    | ibid
        //  =====|======|======|==============================================
        //
        //  The operations with the output in the memory slot are identical,
        //  except that they end with
        //      store r_o -> m_o
        //      [load r_o <- m_o]
        //  (i.e. moving the register to memory immediately, and optionally
        //  restoring the previous value.  Here's an example:
        //
        //  -----|------|------|----------------------------------------------
        //   m_x | r_y  | r_z  | r_a = op r_y r_z
        //       |      |      | store r_a -> m_x
        //       |      |      | [load r_a <- m_a]
        //       |      |      |
        //       |      |      | Afterwards, r_a and m_x are free, [m_a points
        //       |      |      | to the former r_a}
        //  -----|------|------|----------------------------------------------
        let (out, lhs, rhs, op): (_, _, _, fn(u8, u8, u8) -> RegOp) = match op {
            SsaOp::AddRegReg(out, lhs, rhs) => {
                (out, lhs, rhs, RegOp::AddRegReg)
            }
            SsaOp::SubRegReg(out, lhs, rhs) => {
                (out, lhs, rhs, RegOp::SubRegReg)
            }
            SsaOp::MulRegReg(out, lhs, rhs) => {
                (out, lhs, rhs, RegOp::MulRegReg)
            }
            SsaOp::DivRegReg(out, lhs, rhs) => {
                (out, lhs, rhs, RegOp::DivRegReg)
            }
            SsaOp::AtanRegReg(out, lhs, rhs) => {
                (out, lhs, rhs, RegOp::AtanRegReg)
            }
            SsaOp::MinRegReg(out, lhs, rhs) => {
                (out, lhs, rhs, RegOp::MinRegReg)
            }
            SsaOp::MaxRegReg(out, lhs, rhs) => {
                (out, lhs, rhs, RegOp::MaxRegReg)
            }
            SsaOp::CompareRegReg(out, lhs, rhs) => {
                (out, lhs, rhs, RegOp::CompareRegReg)
            }
            SsaOp::ModRegReg(out, lhs, rhs) => {
                (out, lhs, rhs, RegOp::ModRegReg)
            }
            SsaOp::AndRegReg(out, lhs, rhs) => {
                (out, lhs, rhs, RegOp::AndRegReg)
            }
            SsaOp::OrRegReg(out, lhs, rhs) => (out, lhs, rhs, RegOp::OrRegReg),
            _ => panic!("Bad opcode: {op:?}"),
        };
        let r_x = self.get_out_reg(out);
        match (self.get_allocation(lhs), self.get_allocation(rhs)) {
            (Allocation::Register(r_y), Allocation::Register(r_z)) => {
                self.out.push(op(r_x, r_y, r_z));
                self.release_reg(r_x);
            }
            (Allocation::Memory(m_y), Allocation::Register(r_z)) => {
                let r_a = self.get_register();
                self.push_store(r_a, m_y);
                self.out.push(op(r_x, r_a, r_z));
                self.release_reg(r_x);
                self.bind_register(lhs, r_a);
            }
            (Allocation::Register(r_y), Allocation::Memory(m_z)) => {
                let r_a = self.get_register();
                self.push_store(r_a, m_z);
                self.out.push(op(r_x, r_y, r_a));
                self.release_reg(r_x);
                self.bind_register(rhs, r_a);
            }
            (Allocation::Memory(m_y), Allocation::Memory(..)) if lhs == rhs => {
                let r_a = self.get_register();
                self.push_store(r_a, m_y);
                self.out.push(op(r_x, r_a, r_a));
                self.release_reg(r_x);
                self.bind_register(lhs, r_a);
            }
            (Allocation::Memory(m_y), Allocation::Memory(m_z)) => {
                let r_a = self.get_register();
                let r_b = self.get_register();

                self.push_store(r_a, m_y);
                self.push_store(r_b, m_z);
                self.out.push(op(r_x, r_a, r_b));
                self.release_reg(r_x);
                self.bind_register(lhs, r_a);
                self.bind_register(rhs, r_b);
            }
            (Allocation::Unassigned, Allocation::Register(r_z)) => {
                self.out.push(op(r_x, r_x, r_z));
                self.rebind_register(lhs, r_x);
            }
            (Allocation::Register(r_y), Allocation::Unassigned) => {
                self.out.push(op(r_x, r_y, r_x));
                self.rebind_register(rhs, r_x);
            }
            (Allocation::Unassigned, Allocation::Unassigned) if lhs == rhs => {
                self.out.push(op(r_x, r_x, r_x));
                self.rebind_register(lhs, r_x);
            }
            (Allocation::Unassigned, Allocation::Unassigned) => {
                let r_a = self.get_register();

                self.out.push(op(r_x, r_x, r_a));
                self.rebind_register(lhs, r_x);
                self.bind_register(rhs, r_a);
            }
            (Allocation::Unassigned, Allocation::Memory(m_z)) => {
                let r_a = self.get_register();
                assert!(r_a != r_x);
                assert!(lhs != rhs);

                self.push_store(r_a, m_z);
                self.out.push(op(r_x, r_x, r_a));
                self.rebind_register(lhs, r_x);
                self.bind_register(rhs, r_a);
            }
            (Allocation::Memory(m_y), Allocation::Unassigned) => {
                let r_a = self.get_register();
                assert!(r_a != r_x);
                assert!(lhs != rhs);

                self.push_store(r_a, m_y);
                self.out.push(op(r_x, r_a, r_x));
                self.bind_register(lhs, r_a);
                self.rebind_register(rhs, r_x);
            }
        }
    }

    /// Lowers a function taking one register and one immediate into an
    /// [`RegOp`], pushing it to the internal tape.
    #[inline(always)]
    fn op_reg_imm(&mut self, op: SsaOp) {
        let (out, arg, imm, op): (_, _, _, fn(u8, u8, f32) -> RegOp) = match op
        {
            SsaOp::AddRegImm(out, arg, imm) => {
                (out, arg, imm, RegOp::AddRegImm)
            }
            SsaOp::SubRegImm(out, arg, imm) => {
                (out, arg, imm, RegOp::SubRegImm)
            }
            SsaOp::SubImmReg(out, arg, imm) => {
                (out, arg, imm, RegOp::SubImmReg)
            }
            SsaOp::MulRegImm(out, arg, imm) => {
                (out, arg, imm, RegOp::MulRegImm)
            }
            SsaOp::DivRegImm(out, arg, imm) => {
                (out, arg, imm, RegOp::DivRegImm)
            }
            SsaOp::DivImmReg(out, arg, imm) => {
                (out, arg, imm, RegOp::DivImmReg)
            }
            SsaOp::AtanRegImm(out, arg, imm) => {
                (out, arg, imm, RegOp::AtanRegImm)
            }
            SsaOp::AtanImmReg(out, arg, imm) => {
                (out, arg, imm, RegOp::AtanImmReg)
            }
            SsaOp::MinRegImm(out, arg, imm) => {
                (out, arg, imm, RegOp::MinRegImm)
            }
            SsaOp::MaxRegImm(out, arg, imm) => {
                (out, arg, imm, RegOp::MaxRegImm)
            }
            SsaOp::CompareRegImm(out, arg, imm) => {
                (out, arg, imm, RegOp::CompareRegImm)
            }
            SsaOp::CompareImmReg(out, arg, imm) => {
                (out, arg, imm, RegOp::CompareImmReg)
            }
            SsaOp::ModRegImm(out, arg, imm) => {
                (out, arg, imm, RegOp::ModRegImm)
            }
            SsaOp::ModImmReg(out, arg, imm) => {
                (out, arg, imm, RegOp::ModImmReg)
            }
            SsaOp::AndRegImm(out, arg, imm) => {
                (out, arg, imm, RegOp::AndRegImm)
            }
            SsaOp::OrRegImm(out, arg, imm) => (out, arg, imm, RegOp::OrRegImm),
            _ => panic!("Bad opcode: {op:?}"),
        };
        self.op_reg_fn(out, arg, |out, arg| op(out, arg, imm));
    }

    #[inline(always)]
    fn op_out_only(&mut self, out: u32, op: impl Fn(u8) -> RegOp) {
        let r_x = self.get_out_reg(out);
        self.out.push(op(r_x));
        self.release_reg(r_x);
    }

    /// Pushes a [`CopyImm`](crate::compiler::RegOp::CopyImm) operation to the
    /// tape
    #[inline(always)]
    fn op_copy_imm(&mut self, out: u32, imm: f32) {
        self.op_out_only(out, |out| RegOp::CopyImm(out, imm));
    }

    /// Pushes an [`Input`](crate::compiler::RegOp::Input) operation to the tape
    #[inline(always)]
    fn op_input(&mut self, out: u32, i: u32) {
        self.op_out_only(out, |out| RegOp::Input(out, i));
    }

    /// Pushes an [`Output`](crate::compiler::RegOp::Output) operation to the
    /// tape
    #[inline(always)]
    fn op_output(&mut self, arg: u32, i: u32) {
        match self.get_allocation(arg) {
            Allocation::Register(r_y) => self.out.push(RegOp::Output(r_y, i)),
            Allocation::Memory(m_y) => {
                let r_a = self.get_register();
                self.push_store(r_a, m_y);
                self.out.push(RegOp::Output(r_a, i));
                self.bind_register(arg, r_a);
            }
            Allocation::Unassigned => {
                let r_a = self.get_register();
                self.out.push(RegOp::Output(r_a, i));
                self.bind_register(arg, r_a);
            }
        }
    }
}