//! 32-bit ARM ISA: binary code emission.

use crate::binemit::{Reloc, StackMap};
use crate::ir::SourceLoc;
use crate::isa::arm32::inst::*;

use core::convert::TryFrom;
use log::debug;

/// Memory addressing mode finalization: convert "special" modes (e.g.,
/// nominal stack offset) into real addressing modes, possibly by
/// emitting some helper instructions that come immediately before the use
/// of this amode.
pub fn mem_finalize(mem: &AMode, state: &EmitState) -> (SmallVec<[Inst; 4]>, AMode) {
    match mem {
        &AMode::RegOffset(_, off)
        | &AMode::SPOffset(off, _)
        | &AMode::FPOffset(off, _)
        | &AMode::NominalSPOffset(off, _) => {
            let basereg = match mem {
                &AMode::RegOffset(reg, _) => reg,
                &AMode::SPOffset(..) | &AMode::NominalSPOffset(..) => sp_reg(),
                &AMode::FPOffset(..) => fp_reg(),
                _ => unreachable!(),
            };
            let adj = match mem {
                &AMode::NominalSPOffset(..) => {
                    debug!(
                        "mem_finalize: nominal SP offset {} + adj {} -> {}",
                        off,
                        state.virtual_sp_offset,
                        off + state.virtual_sp_offset
                    );
                    state.virtual_sp_offset
                }
                _ => 0,
            };
            let off = off + adj;

            assert!(-(1 << 31) <= off && off <= (1 << 32));

            if let Some(off) = UImm12::maybe_from_i64(off) {
                let mem = AMode::RegOffset12(basereg, off);
                (smallvec![], mem)
            } else {
                let tmp = writable_ip_reg();
                let const_insts = Inst::load_constant(tmp, off as u32);
                let mem = AMode::reg_plus_reg(basereg, tmp.to_reg(), 0);
                (const_insts, mem)
            }
        }
        // Just assert immediate is valid here.
        _ => (smallvec![], mem.clone()),
    }
}

//=============================================================================
// Instructions and subcomponents: emission

fn machreg_to_gpr(m: Reg) -> u16 {
    assert_eq!(m.get_class(), RegClass::I32);
    u16::try_from(m.to_real_reg().get_hw_encoding()).unwrap()
}

fn machreg_to_gpr_lo(m: Reg) -> u16 {
    let gpr_lo = machreg_to_gpr(m);
    assert!(gpr_lo < 8);
    gpr_lo
}

fn machreg_is_lo(m: Reg) -> bool {
    machreg_to_gpr(m) < 8
}

fn enc_16_rr(bits_15_6: u16, rd: Reg, rm: Reg) -> u16 {
    (bits_15_6 << 6) | machreg_to_gpr_lo(rd) | (machreg_to_gpr_lo(rm) << 3)
}

fn enc_16_rr_any(bits_15_8: u16, rd: Reg, rm: Reg) -> u16 {
    let rd = machreg_to_gpr(rd);
    (bits_15_8 << 8) | (rd & 0x7) | ((rd >> 3) << 7) | (machreg_to_gpr(rm) << 3)
}

fn enc_16_mov(rd: Writable<Reg>, rm: Reg) -> u16 {
    enc_16_rr_any(0b01000110, rd.to_reg(), rm)
}

fn enc_16_it(cond: Cond, insts: &Vec<CondInst>) -> u16 {
    let cond = cond.bits();
    let mut mask: u16 = 0;
    for inst in insts.iter().skip(1) {
        if inst.then {
            mask |= cond & 0x1;
        } else {
            mask |= (cond & 0x1) ^ 0x1;
        }
        mask <<= 1;
    }
    mask |= 0x1;
    mask <<= 4 - insts.len();
    0b1011_1111_0000_0000 | (cond << 4) | mask
}

fn enc_32_regs(
    mut inst: u32,
    reg_0: Option<Reg>,
    reg_8: Option<Reg>,
    reg_12: Option<Reg>,
    reg_16: Option<Reg>,
) -> u32 {
    if let Some(reg_0) = reg_0 {
        inst |= u32::from(machreg_to_gpr(reg_0));
    }
    if let Some(reg_8) = reg_8 {
        inst |= u32::from(machreg_to_gpr(reg_8)) << 8;
    }
    if let Some(reg_12) = reg_12 {
        inst |= u32::from(machreg_to_gpr(reg_12)) << 12;
    }
    if let Some(reg_16) = reg_16 {
        inst |= u32::from(machreg_to_gpr(reg_16)) << 16;
    }
    inst
}

fn enc_32_reg_shift(inst: u32, shift: &Option<ShiftOpAndAmt>) -> u32 {
    match shift {
        Some(shift) => {
            let op = u32::from(shift.op().bits());
            let amt = u32::from(shift.amt().value());
            let imm2 = amt & 0x3;
            let imm3 = (amt >> 2) & 0x7;

            inst | (op << 4) | (imm2 << 6) | (imm3 << 12)
        }
        None => inst,
    }
}

fn enc_32_r_imm16(bits_31_20: u32, rd: Reg, imm16: u16) -> u32 {
    let imm16 = u32::from(imm16);
    let imm8 = imm16 & 0xff;
    let imm3 = (imm16 >> 8) & 0x7;
    let i = (imm16 >> 11) & 0x1;
    let imm4 = (imm16 >> 12) & 0xf;

    let inst = ((bits_31_20 << 20) & !(1 << 26)) | imm8 | (imm3 << 12) | (imm4 << 16) | (i << 26);
    enc_32_regs(inst, None, Some(rd), None, None)
}

fn enc_32_rrr(bits_31_20: u32, bits_15_12: u32, bits_7_4: u32, rd: Reg, rm: Reg, rn: Reg) -> u32 {
    let inst = (bits_31_20 << 20) | (bits_15_12 << 12) | (bits_7_4 << 4);
    enc_32_regs(inst, Some(rm), Some(rd), None, Some(rn))
}

fn enc_32_imm12(inst: u32, imm12: UImm12) -> u32 {
    let imm12 = imm12.bits();
    let imm8 = imm12 & 0xff;
    let imm3 = (imm12 >> 8) & 0x7;
    let i = (imm12 >> 11) & 0x1;
    inst | imm8 | (imm3 << 12) | (i << 26)
}

fn enc_32_mem_r(bits_24_20: u32, rt: Reg, rn: Reg, rm: Reg, imm2: u8) -> u32 {
    let imm2 = u32::from(imm2);
    let inst = (imm2 << 4) | (bits_24_20 << 20) | (0b11111 << 27);
    enc_32_regs(inst, Some(rm), None, Some(rt), Some(rn))
}

fn enc_32_mem_off12(bits_24_20: u32, rt: Reg, rn: Reg, off12: UImm12) -> u32 {
    let off12 = off12.bits();
    let inst = off12 | (bits_24_20 << 20) | (0b11111 << 27);
    enc_32_regs(inst, None, None, Some(rt), Some(rn))
}

fn enc_32_jump(target: BranchTarget) -> u32 {
    let off24 = target.as_off24();
    let imm11 = off24 & 0x7ff;
    let imm10 = (off24 >> 11) & 0x3ff;
    let i2 = (off24 >> 21) & 0x1;
    let i1 = (off24 >> 22) & 0x1;
    let s = (off24 >> 23) & 0x1;
    let j1 = (i1 ^ s) ^ 1;
    let j2 = (i2 ^ s) ^ 1;

    0b11110_0_0000000000_10_0_1_0_00000000000
        | imm11
        | (j2 << 11)
        | (j1 << 13)
        | (imm10 << 16)
        | (s << 26)
}

fn enc_32_cond_branch(cond: Cond, target: BranchTarget) -> u32 {
    let cond = u32::from(cond.bits());
    let off20 = target.as_off20();
    let imm11 = off20 & 0x7ff;
    let imm6 = (off20 >> 11) & 0x3f;
    let j1 = (off20 >> 17) & 0x1;
    let j2 = (off20 >> 18) & 0x1;
    let s = (off20 >> 19) & 0x1;

    0b11110_0_0000_000000_10_0_0_0_00000000000
        | imm11
        | (j2 << 11)
        | (j1 << 13)
        | (imm6 << 16)
        | (cond << 22)
        | (s << 26)
}

fn u32_swap_halfwords(x: u32) -> u32 {
    (x >> 16) | (x << 16)
}

fn emit_32(inst: u32, sink: &mut MachBuffer<Inst>) {
    let inst_hi = (inst >> 16) as u16;
    let inst_lo = (inst & 0xffff) as u16;
    sink.put2(inst_hi);
    sink.put2(inst_lo);
}

/// State carried between emissions of a sequence of instructions.
#[derive(Default, Clone, Debug)]
pub struct EmitState {
    /// Addend to convert nominal-SP offsets to real-SP offsets at the current
    /// program point.
    pub(crate) virtual_sp_offset: i64,
    /// Offset of FP from nominal-SP.
    pub(crate) nominal_sp_to_fp: i64,
    /// Safepoint stack map for upcoming instruction, as provided to `pre_safepoint()`.
    stack_map: Option<StackMap>,
    /// Source location of next machine code instruction to be emitted.
    cur_srcloc: SourceLoc,
}

impl MachInstEmitState<Inst> for EmitState {
    fn new(abi: &dyn ABICallee<I = Inst>) -> Self {
        EmitState {
            virtual_sp_offset: 0,
            nominal_sp_to_fp: abi.frame_size() as i64,
            stack_map: None,
            cur_srcloc: SourceLoc::default(),
        }
    }

    fn pre_safepoint(&mut self, stack_map: StackMap) {
        self.stack_map = Some(stack_map);
    }

    fn pre_sourceloc(&mut self, srcloc: SourceLoc) {
        self.cur_srcloc = srcloc;
    }
}

impl EmitState {
    fn take_stack_map(&mut self) -> Option<StackMap> {
        self.stack_map.take()
    }

    fn clear_post_insn(&mut self) {
        self.stack_map = None;
    }

    fn cur_srcloc(&self) -> SourceLoc {
        self.cur_srcloc
    }
}

pub struct EmitInfo {
    flags: settings::Flags,
}

impl EmitInfo {
    pub(crate) fn new(flags: settings::Flags) -> Self {
        EmitInfo { flags }
    }
}

impl MachInstEmitInfo for EmitInfo {
    fn flags(&self) -> &settings::Flags {
        &self.flags
    }
}

impl MachInstEmit for Inst {
    type Info = EmitInfo;
    type State = EmitState;

    fn emit(&self, sink: &mut MachBuffer<Inst>, emit_info: &Self::Info, state: &mut EmitState) {
        let start_off = sink.cur_offset();

        match self {
            &Inst::Nop0 | &Inst::EpiloguePlaceholder => {}
            &Inst::Nop2 => {
                sink.put2(0b1011_1111_0000_0000);
            }
            &Inst::AluRRR { alu_op, rd, rn, rm } => {
                let (bits_31_20, bits_15_12, bits_7_4) = match alu_op {
                    ALUOp::Lsl => (0b111110100000, 0b1111, 0b0000),
                    ALUOp::Lsr => (0b111110100010, 0b1111, 0b0000),
                    ALUOp::Asr => (0b111110100100, 0b1111, 0b0000),
                    ALUOp::Ror => (0b111110100110, 0b1111, 0b0000),
                    ALUOp::Qadd => (0b111110101000, 0b1111, 0b1000),
                    ALUOp::Qsub => (0b111110101000, 0b1111, 0b1010),
                    ALUOp::Mul => (0b111110110000, 0b1111, 0b0000),
                    ALUOp::Udiv => (0b111110111011, 0b1111, 0b1111),
                    ALUOp::Sdiv => (0b111110111001, 0b1111, 0b1111),
                    _ => panic!("Invalid ALUOp {:?} in RRR form!", alu_op),
                };
                emit_32(
                    enc_32_rrr(bits_31_20, bits_15_12, bits_7_4, rd.to_reg(), rm, rn),
                    sink,
                );
            }
            &Inst::AluRRRShift {
                alu_op,
                rd,
                rn,
                rm,
                ref shift,
            } => {
                let bits_31_24 = 0b111_0101;
                let bits_24_20 = match alu_op {
                    ALUOp::And => 0b00000,
                    ALUOp::Bic => 0b00010,
                    ALUOp::Orr => 0b00100,
                    ALUOp::Orn => 0b00110,
                    ALUOp::Eor => 0b01000,
                    ALUOp::Add => 0b10000,
                    ALUOp::Adds => 0b10001,
                    ALUOp::Adc => 0b10100,
                    ALUOp::Adcs => 0b10101,
                    ALUOp::Sbc => 0b10110,
                    ALUOp::Sbcs => 0b10111,
                    ALUOp::Sub => 0b11010,
                    ALUOp::Subs => 0b11011,
                    ALUOp::Rsb => 0b11100,
                    _ => panic!("Invalid ALUOp {:?} in RRRShift form!", alu_op),
                };
                let bits_31_20 = (bits_31_24 << 5) | bits_24_20;
                let inst = enc_32_rrr(bits_31_20, 0, 0, rd.to_reg(), rm, rn);
                let inst = enc_32_reg_shift(inst, shift);
                emit_32(inst, sink);
            }
            &Inst::AluRRShift {
                alu_op,
                rd,
                rm,
                ref shift,
            } => {
                let bits_24_21 = match alu_op {
                    ALUOp1::Mvn => 0b0011,
                    ALUOp1::Mov => 0b0010,
                };
                let inst = 0b1110101_0000_0_1111_0_000_0000_00_00_0000 | (bits_24_21 << 21);
                let inst = enc_32_regs(inst, Some(rm), Some(rd.to_reg()), None, None);
                let inst = enc_32_reg_shift(inst, shift);
                emit_32(inst, sink);
            }
            &Inst::AluRRRR {
                alu_op,
                rd_hi,
                rd_lo,
                rn,
                rm,
            } => {
                let (bits_22_20, bits_7_4) = match alu_op {
                    ALUOp::Smull => (0b000, 0b0000),
                    ALUOp::Umull => (0b010, 0b0000),
                    _ => panic!("Invalid ALUOp {:?} in RRRR form!", alu_op),
                };
                let inst = (0b111110111 << 23) | (bits_22_20 << 20) | (bits_7_4 << 4);
                let inst = enc_32_regs(
                    inst,
                    Some(rm),
                    Some(rd_hi.to_reg()),
                    Some(rd_lo.to_reg()),
                    Some(rn),
                );
                emit_32(inst, sink);
            }
            &Inst::AluRRImm12 {
                alu_op,
                rd,
                rn,
                imm12,
            } => {
                let bits_24_20 = match alu_op {
                    ALUOp::Add => 0b00000,
                    ALUOp::Sub => 0b01010,
                    _ => panic!("Invalid ALUOp {:?} in RRImm12 form!", alu_op),
                };
                let inst = (0b11110_0_1 << 25) | (bits_24_20 << 20);
                let inst = enc_32_regs(inst, None, Some(rd.to_reg()), None, Some(rn));
                let inst = enc_32_imm12(inst, imm12);
                emit_32(inst, sink);
            }
            &Inst::AluRRImm8 {
                alu_op,
                rd,
                rn,
                imm8,
            } => {
                let bits_24_20 = match alu_op {
                    ALUOp::And => 0b00000,
                    ALUOp::Bic => 0b00010,
                    ALUOp::Orr => 0b00100,
                    ALUOp::Orn => 0b00110,
                    ALUOp::Eor => 0b01000,
                    ALUOp::Add => 0b10000,
                    ALUOp::Adds => 0b10001,
                    ALUOp::Adc => 0b10100,
                    ALUOp::Adcs => 0b10101,
                    ALUOp::Sbc => 0b10110,
                    ALUOp::Sbcs => 0b10111,
                    ALUOp::Sub => 0b11010,
                    ALUOp::Subs => 0b11011,
                    ALUOp::Rsb => 0b11100,
                    _ => panic!("Invalid ALUOp {:?} in RRImm8 form!", alu_op),
                };
                let imm8 = imm8.bits();
                let inst = 0b11110_0_0_00000_0000_0_000_0000_00000000 | imm8 | (bits_24_20 << 20);
                let inst = enc_32_regs(inst, None, Some(rd.to_reg()), None, Some(rn));
                emit_32(inst, sink);
            }
            &Inst::AluRImm8 { alu_op, rd, imm8 } => {
                let bits_24_20 = match alu_op {
                    ALUOp1::Mvn => 0b00110,
                    ALUOp1::Mov => 0b00100,
                };
                let imm8 = imm8.bits();
                let inst = 0b11110_0_0_00000_1111_0_000_0000_00000000 | imm8 | (bits_24_20 << 20);
                let inst = enc_32_regs(inst, None, Some(rd.to_reg()), None, None);
                emit_32(inst, sink);
            }
            &Inst::BitOpRR { bit_op, rd, rm } => {
                let (bits_22_20, bits_7_4) = match bit_op {
                    BitOp::Rbit => (0b001, 0b1010),
                    BitOp::Rev => (0b001, 0b1000),
                    BitOp::Clz => (0b011, 0b1000),
                };
                let inst =
                    0b111110101_000_0000_1111_0000_0000_0000 | (bits_22_20 << 20) | (bits_7_4 << 4);
                let inst = enc_32_regs(inst, Some(rm), Some(rd.to_reg()), None, Some(rm));
                emit_32(inst, sink);
            }
            &Inst::Mov { rd, rm } => {
                sink.put2(enc_16_mov(rd, rm));
            }
            &Inst::MovImm16 { rd, imm16 } => {
                emit_32(enc_32_r_imm16(0b11110_0_100100, rd.to_reg(), imm16), sink);
            }
            &Inst::Movt { rd, imm16 } => {
                emit_32(enc_32_r_imm16(0b11110_0_101100, rd.to_reg(), imm16), sink);
            }
            &Inst::Cmp { rn, rm } => {
                // Check which 16-bit encoding is allowed.
                if machreg_is_lo(rn) && machreg_is_lo(rm) {
                    sink.put2(enc_16_rr(0b0100001010, rn, rm));
                } else {
                    sink.put2(enc_16_rr_any(0b01000101, rn, rm));
                }
            }
            &Inst::CmpImm8 { rn, imm8 } => {
                let inst = 0b11110_0_011011_0000_0_000_1111_00000000 | u32::from(imm8);
                let inst = enc_32_regs(inst, None, None, None, Some(rn));
                emit_32(inst, sink);
            }
            &Inst::Store { rt, ref mem, bits } => {
                let (mem_insts, mem) = mem_finalize(mem, state);
                for inst in mem_insts.into_iter() {
                    inst.emit(sink, emit_info, state);
                }
                let srcloc = state.cur_srcloc();
                if srcloc != SourceLoc::default() {
                    // Register the offset at which the store instruction starts.
                    sink.add_trap(srcloc, TrapCode::HeapOutOfBounds);
                }
                match mem {
                    AMode::RegReg(rn, rm, imm2) => {
                        let bits_24_20 = match bits {
                            32 => 0b00100,
                            16 => 0b00010,
                            8 => 0b00000,
                            _ => panic!("Unsupported store case {:?}", self),
                        };
                        emit_32(enc_32_mem_r(bits_24_20, rt, rn, rm, imm2), sink);
                    }
                    AMode::RegOffset12(rn, off12) => {
                        let bits_24_20 = match bits {
                            32 => 0b01100,
                            16 => 0b01010,
                            8 => 0b01000,
                            _ => panic!("Unsupported store case {:?}", self),
                        };
                        emit_32(enc_32_mem_off12(bits_24_20, rt, rn, off12), sink);
                    }
                    AMode::PCRel(_) => panic!("Unsupported store case {:?}", self),
                    _ => unreachable!(),
                }
            }
            &Inst::Load {
                rt,
                ref mem,
                bits,
                sign_extend,
            } => {
                let (mem_insts, mem) = mem_finalize(mem, state);
                for inst in mem_insts.into_iter() {
                    inst.emit(sink, emit_info, state);
                }
                let srcloc = state.cur_srcloc();
                if srcloc != SourceLoc::default() {
                    // Register the offset at which the load instruction starts.
                    sink.add_trap(srcloc, TrapCode::HeapOutOfBounds);
                }
                match mem {
                    AMode::RegReg(rn, rm, imm2) => {
                        let bits_24_20 = match (bits, sign_extend) {
                            (32, _) => 0b00101,
                            (16, true) => 0b10011,
                            (16, false) => 0b00011,
                            (8, true) => 0b10001,
                            (8, false) => 0b00001,
                            _ => panic!("Unsupported load case {:?}", self),
                        };
                        emit_32(enc_32_mem_r(bits_24_20, rt.to_reg(), rn, rm, imm2), sink);
                    }
                    AMode::RegOffset12(rn, off12) => {
                        let bits_24_20 = match (bits, sign_extend) {
                            (32, _) => 0b01101,
                            (16, true) => 0b11011,
                            (16, false) => 0b01011,
                            (8, true) => 0b11001,
                            (8, false) => 0b01001,
                            _ => panic!("Unsupported load case {:?}", self),
                        };
                        emit_32(enc_32_mem_off12(bits_24_20, rt.to_reg(), rn, off12), sink);
                    }
                    AMode::PCRel(off12) => {
                        let mut bits_24_20 = match (bits, sign_extend) {
                            (32, _) => 0b00101,
                            (16, true) => 0b10011,
                            (16, false) => 0b00011,
                            (8, true) => 0b10001,
                            (8, false) => 0b00001,
                            _ => panic!("Unsupported load case {:?}", self),
                        };
                        let (u, off12) = if off12 > 0 { (1, off12) } else { (0, -off12) };
                        let off12 = UImm12::maybe_from_i64(i64::from(off12)).unwrap();
                        bits_24_20 |= u << 3;

                        emit_32(
                            enc_32_mem_off12(bits_24_20, rt.to_reg(), pc_reg(), off12),
                            sink,
                        );
                    }
                    _ => unreachable!(),
                }
            }
            &Inst::LoadAddr { rd, ref mem } => {
                let (mem_insts, mem) = mem_finalize(mem, state);
                for inst in mem_insts.into_iter() {
                    inst.emit(sink, emit_info, state);
                }
                let inst = match mem {
                    AMode::RegReg(reg1, reg2, shift) => {
                        let shift = u32::from(shift);
                        let shift_amt = ShiftOpShiftImm::maybe_from_shift(shift).unwrap();
                        let shift = ShiftOpAndAmt::new(ShiftOp::LSL, shift_amt);
                        Inst::AluRRRShift {
                            alu_op: ALUOp::Add,
                            rd,
                            rn: reg1,
                            rm: reg2,
                            shift: Some(shift),
                        }
                    }
                    AMode::RegOffset12(reg, imm12) => Inst::AluRRImm12 {
                        alu_op: ALUOp::Add,
                        rd,
                        rn: reg,
                        imm12,
                    },
                    AMode::PCRel(off12) => {
                        let (off12, alu_op) = if off12 > 0 {
                            (off12, ALUOp::Add)
                        } else {
                            (-off12, ALUOp::Sub)
                        };
                        let imm12 = UImm12::maybe_from_i64(i64::from(off12)).unwrap();
                        Inst::AluRRImm12 {
                            alu_op,
                            rd,
                            rn: pc_reg(),
                            imm12,
                        }
                    }
                    _ => unreachable!(),
                };
                inst.emit(sink, emit_info, state);
            }
            &Inst::Extend {
                rd,
                rm,
                from_bits,
                signed,
            } if from_bits >= 8 => {
                let rd = rd.to_reg();
                if machreg_is_lo(rd) && machreg_is_lo(rm) {
                    let bits_15_9 = match (from_bits, signed) {
                        (16, true) => 0b1011001000,
                        (16, false) => 0b1011001010,
                        (8, true) => 0b1011001001,
                        (8, false) => 0b1011001011,
                        _ => panic!("Unsupported Extend case: {:?}", self),
                    };
                    sink.put2(enc_16_rr(bits_15_9, rd, rm));
                } else {
                    let bits_22_20 = match (from_bits, signed) {
                        (16, true) => 0b000,
                        (16, false) => 0b001,
                        (8, true) => 0b100,
                        (8, false) => 0b101,
                        _ => panic!("Unsupported Extend case: {:?}", self),
                    };
                    let inst = 0b111110100_000_11111111_0000_1000_0000 | (bits_22_20 << 20);
                    let inst = enc_32_regs(inst, Some(rm), Some(rd), None, None);
                    emit_32(inst, sink);
                }
            }
            &Inst::Extend {
                rd,
                rm,
                from_bits,
                signed,
            } if from_bits == 1 => {
                let inst = Inst::AluRRImm8 {
                    alu_op: ALUOp::And,
                    rd,
                    rn: rm,
                    imm8: UImm8::maybe_from_i64(1).unwrap(),
                };
                inst.emit(sink, emit_info, state);

                if signed {
                    let inst = Inst::AluRRImm8 {
                        alu_op: ALUOp::Rsb,
                        rd,
                        rn: rd.to_reg(),
                        imm8: UImm8::maybe_from_i64(1).unwrap(),
                    };
                    inst.emit(sink, emit_info, state);
                }
            }
            &Inst::Extend { .. } => {
                panic!("Unsupported extend variant");
            }
            &Inst::It { cond, ref insts } => {
                assert!(1 <= insts.len() && insts.len() <= 4);
                assert!(insts[0].then);

                sink.put2(enc_16_it(cond, insts));
                for inst in insts.iter() {
                    inst.inst.emit(sink, emit_info, state);
                }
            }
            &Inst::Push { ref reg_list } => match reg_list.len() {
                0 => panic!("Unsupported Push case: {:?}", self),
                1 => {
                    let reg = u32::from(machreg_to_gpr(reg_list[0]));
                    let inst: u32 = 0b1111100001001101_0000_110100000100 | (reg << 12);
                    emit_32(inst, sink);
                }
                _ => {
                    let mut inst: u32 = 0b1110100100101101 << 16;
                    for reg in reg_list {
                        inst |= 1 << machreg_to_gpr(*reg);
                    }
                    if inst & ((1 << 13) | (1 << 15)) != 0 {
                        panic!("Unsupported Push case: {:?}", self);
                    }
                    emit_32(inst, sink);
                }
            },
            &Inst::Pop { ref reg_list } => match reg_list.len() {
                0 => panic!("Unsupported Pop case: {:?}", self),
                1 => {
                    let reg = u32::from(machreg_to_gpr(reg_list[0].to_reg()));
                    let inst: u32 = 0b1111100001011101_0000_101100000100 | (reg << 12);
                    emit_32(inst, sink);
                }
                _ => {
                    let mut inst: u32 = 0b1110100010111101 << 16;
                    for reg in reg_list {
                        inst |= 1 << machreg_to_gpr(reg.to_reg());
                    }
                    if (inst & (1 << 14) != 0) && (inst & (1 << 15) != 0) {
                        panic!("Unsupported Pop case: {:?}", self);
                    }
                    emit_32(inst, sink);
                }
            },
            &Inst::Call { ref info } => {
                let srcloc = state.cur_srcloc();
                sink.add_reloc(srcloc, Reloc::Arm32Call, &info.dest, 0);
                emit_32(0b11110_0_0000000000_11_0_1_0_00000000000, sink);
                if info.opcode.is_call() {
                    sink.add_call_site(srcloc, info.opcode);
                }
            }
            &Inst::CallInd { ref info } => {
                let srcloc = state.cur_srcloc();
                sink.put2(0b01000111_1_0000_000 | (machreg_to_gpr(info.rm) << 3));
                if info.opcode.is_call() {
                    sink.add_call_site(srcloc, info.opcode);
                }
            }
            &Inst::LoadExtName {
                rt,
                ref name,
                offset,
            } => {
                //  maybe nop2          (0|2) bytes (pc is now 4-aligned)
                //  ldr rt, [pc, #4]    4 bytes
                //  b continue          4 bytes
                //  addr                4 bytes
                // continue:
                //
                if start_off & 0x3 != 0 {
                    Inst::Nop2.emit(sink, emit_info, state);
                }
                assert_eq!(sink.cur_offset() & 0x3, 0);

                let mem = AMode::PCRel(4);
                let inst = Inst::Load {
                    rt,
                    mem,
                    bits: 32,
                    sign_extend: false,
                };
                inst.emit(sink, emit_info, state);

                let inst = Inst::Jump {
                    dest: BranchTarget::ResolvedOffset(4),
                };
                inst.emit(sink, emit_info, state);

                let srcloc = state.cur_srcloc();
                sink.add_reloc(srcloc, Reloc::Abs4, name, offset.into());
                sink.put4(0);
            }
            &Inst::Ret => {
                sink.put2(0b010001110_1110_000); // bx lr
            }
            &Inst::Jump { dest } => {
                let off = sink.cur_offset();
                // Indicate that the jump uses a label, if so, so that a fixup can occur later.
                if let Some(l) = dest.as_label() {
                    sink.use_label_at_offset(off, l, LabelUse::Branch24);
                    sink.add_uncond_branch(off, off + 4, l);
                }
                emit_32(enc_32_jump(dest), sink);
            }
            &Inst::CondBr {
                taken,
                not_taken,
                cond,
            } => {
                // Conditional part first.
                let cond_off = sink.cur_offset();
                if let Some(l) = taken.as_label() {
                    let label_use = LabelUse::Branch20;
                    sink.use_label_at_offset(cond_off, l, label_use);
                    let inverted = enc_32_cond_branch(cond.invert(), taken);
                    let inverted = u32_swap_halfwords(inverted).to_le_bytes();
                    sink.add_cond_branch(cond_off, cond_off + 4, l, &inverted[..]);
                }
                emit_32(enc_32_cond_branch(cond, taken), sink);

                // Unconditional part.
                let uncond_off = sink.cur_offset();
                if let Some(l) = not_taken.as_label() {
                    sink.use_label_at_offset(uncond_off, l, LabelUse::Branch24);
                    sink.add_uncond_branch(uncond_off, uncond_off + 4, l);
                }
                emit_32(enc_32_jump(not_taken), sink);
            }
            &Inst::IndirectBr { rm, .. } => {
                let inst = 0b010001110_0000_000 | (machreg_to_gpr(rm) << 3);
                sink.put2(inst);
            }
            &Inst::Udf { trap_info } => {
                let srcloc = state.cur_srcloc();
                let code = trap_info;
                sink.add_trap(srcloc, code);
                sink.put2(0b11011110_00000000);
            }
            &Inst::Bkpt => {
                sink.put2(0b10111110_00000000);
            }
            &Inst::TrapIf { cond, trap_info } => {
                let cond = cond.invert();
                let dest = BranchTarget::ResolvedOffset(2);
                emit_32(enc_32_cond_branch(cond, dest), sink);

                let trap = Inst::Udf { trap_info };
                trap.emit(sink, emit_info, state);
            }
            &Inst::VirtualSPOffsetAdj { offset } => {
                debug!(
                    "virtual sp offset adjusted by {} -> {}",
                    offset,
                    state.virtual_sp_offset + offset,
                );
                state.virtual_sp_offset += offset;
            }
        }

        let end_off = sink.cur_offset();
        debug_assert!((end_off - start_off) <= Inst::worst_case_size());
    }

    fn pretty_print(&self, mb_rru: Option<&RealRegUniverse>, state: &mut EmitState) -> String {
        self.print_with_state(mb_rru, state)
    }
}