masm.rs

use super::{
    RegAlloc,
    abi::X64ABI,
    address::Address,
    asm::{Assembler, PatchableAddToReg, VcmpKind, VcvtKind, VroundMode},
    regs::{self, rbp, rsp, scratch_fpr_bitset, scratch_gpr_bitset},
};
use anyhow::{Result, anyhow, bail};

use crate::masm::{
    DivKind, Extend, ExtendKind, ExtractLaneKind, FloatCmpKind, FloatScratch, Imm as I, IntCmpKind,
    IntScratch, LaneSelector, LoadKind, MacroAssembler as Masm, MulWideKind, OperandSize, RegImm,
    RemKind, ReplaceLaneKind, RmwOp, RoundingMode, Scratch, ScratchType, ShiftKind, SplatKind,
    StoreKind, TRUSTED_FLAGS, TrapCode, TruncKind, UNTRUSTED_FLAGS, V128AbsKind, V128AddKind,
    V128ConvertKind, V128ExtAddKind, V128ExtMulKind, V128ExtendKind, V128MaxKind, V128MinKind,
    V128MulKind, V128NarrowKind, V128NegKind, V128SubKind, V128TruncKind, VectorCompareKind,
    VectorEqualityKind, Zero,
};
use crate::{
    abi::{self, LocalSlot, align_to, calculate_frame_adjustment},
    codegen::{CodeGenContext, CodeGenError, Emission, FuncEnv, ptr_type_from_ptr_size},
    stack::{TypedReg, Val},
};
use crate::{
    abi::{ABI, vmctx},
    masm::{SPOffset, StackSlot},
};
use crate::{
    isa::{
        CallingConvention,
        reg::{Reg, RegClass, WritableReg, writable},
    },
    masm::CalleeKind,
};
use cranelift_codegen::{
    Final, MachBufferFinalized, MachLabel,
    binemit::CodeOffset,
    ir::{MemFlags, RelSourceLoc, SourceLoc},
    isa::{
        unwind::UnwindInst,
        x64::{AtomicRmwSeqOp, args::CC, settings as x64_settings},
    },
    settings,
};
use wasmtime_cranelift::TRAP_UNREACHABLE;
use wasmtime_environ::{PtrSize, WasmValType};

// Taken from `cranelift/codegen/src/isa/x64/lower/isle.rs`
// Since x64 doesn't have 8x16 shifts and we must use a 16x8 shift instead, we
// need to fix up the bits that migrate from one half of the lane to the
// other. Each 16-byte mask is indexed by the shift amount: e.g. if we shift
// right by 0 (no movement), we want to retain all the bits so we mask with
// `0xff`; if we shift right by 1, we want to retain all bits except the MSB so
// we mask with `0x7f`; etc.

#[rustfmt::skip] // Preserve 16 bytes (i.e. one mask) per row.
const I8X16_ISHL_MASKS: [u8; 128] = [
    0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
    0xfe, 0xfe, 0xfe, 0xfe, 0xfe, 0xfe, 0xfe, 0xfe, 0xfe, 0xfe, 0xfe, 0xfe, 0xfe, 0xfe, 0xfe, 0xfe,
    0xfc, 0xfc, 0xfc, 0xfc, 0xfc, 0xfc, 0xfc, 0xfc, 0xfc, 0xfc, 0xfc, 0xfc, 0xfc, 0xfc, 0xfc, 0xfc,
    0xf8, 0xf8, 0xf8, 0xf8, 0xf8, 0xf8, 0xf8, 0xf8, 0xf8, 0xf8, 0xf8, 0xf8, 0xf8, 0xf8, 0xf8, 0xf8,
    0xf0, 0xf0, 0xf0, 0xf0, 0xf0, 0xf0, 0xf0, 0xf0, 0xf0, 0xf0, 0xf0, 0xf0, 0xf0, 0xf0, 0xf0, 0xf0,
    0xe0, 0xe0, 0xe0, 0xe0, 0xe0, 0xe0, 0xe0, 0xe0, 0xe0, 0xe0, 0xe0, 0xe0, 0xe0, 0xe0, 0xe0, 0xe0,
    0xc0, 0xc0, 0xc0, 0xc0, 0xc0, 0xc0, 0xc0, 0xc0, 0xc0, 0xc0, 0xc0, 0xc0, 0xc0, 0xc0, 0xc0, 0xc0,
    0x80, 0x80, 0x80, 0x80, 0x80, 0x80, 0x80, 0x80, 0x80, 0x80, 0x80, 0x80, 0x80, 0x80, 0x80, 0x80,
];

#[rustfmt::skip] // Preserve 16 bytes (i.e. one mask) per row.
const I8X16_USHR_MASKS: [u8; 128] = [
    0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
    0x7f, 0x7f, 0x7f, 0x7f, 0x7f, 0x7f, 0x7f, 0x7f, 0x7f, 0x7f, 0x7f, 0x7f, 0x7f, 0x7f, 0x7f, 0x7f,
    0x3f, 0x3f, 0x3f, 0x3f, 0x3f, 0x3f, 0x3f, 0x3f, 0x3f, 0x3f, 0x3f, 0x3f, 0x3f, 0x3f, 0x3f, 0x3f,
    0x1f, 0x1f, 0x1f, 0x1f, 0x1f, 0x1f, 0x1f, 0x1f, 0x1f, 0x1f, 0x1f, 0x1f, 0x1f, 0x1f, 0x1f, 0x1f,
    0x0f, 0x0f, 0x0f, 0x0f, 0x0f, 0x0f, 0x0f, 0x0f, 0x0f, 0x0f, 0x0f, 0x0f, 0x0f, 0x0f, 0x0f, 0x0f,
    0x07, 0x07, 0x07, 0x07, 0x07, 0x07, 0x07, 0x07, 0x07, 0x07, 0x07, 0x07, 0x07, 0x07, 0x07, 0x07,
    0x03, 0x03, 0x03, 0x03, 0x03, 0x03, 0x03, 0x03, 0x03, 0x03, 0x03, 0x03, 0x03, 0x03, 0x03, 0x03,
    0x01, 0x01, 0x01, 0x01, 0x01, 0x01, 0x01, 0x01, 0x01, 0x01, 0x01, 0x01, 0x01, 0x01, 0x01, 0x01,
];

/// x64 MacroAssembler.
pub(crate) struct MacroAssembler {
    /// Stack pointer offset.
    sp_offset: u32,
    /// This value represents the maximum stack size seen while compiling the function. While the
    /// function is still being compiled its value will not be valid (the stack will grow and
    /// shrink as space is reserved and freed during compilation), but once all instructions have
    /// been seen this value will be the maximum stack usage seen.
    sp_max: u32,
    /// Add instructions that are used to add the constant stack max to a register.
    stack_max_use_add: Option<PatchableAddToReg>,
    /// Low level assembler.
    asm: Assembler,
    /// ISA flags.
    flags: x64_settings::Flags,
    /// Shared flags.vmcontext_store_context
    shared_flags: settings::Flags,
    /// The target pointer size.
    ptr_size: OperandSize,
    /// Scratch register scope.
    scratch_scope: RegAlloc,
}

impl Masm for MacroAssembler {
    type Address = Address;
    type Ptr = u8;
    type ABI = X64ABI;

    fn frame_setup(&mut self) -> Result<()> {
        let frame_pointer = rbp();
        let stack_pointer = rsp();

        self.asm.push_r(frame_pointer);

        if self.shared_flags.unwind_info() {
            self.asm.unwind_inst(UnwindInst::PushFrameRegs {
                offset_upward_to_caller_sp: Self::ABI::arg_base_offset().into(),
            })
        }

        self.asm
            .mov_rr(stack_pointer, writable!(frame_pointer), OperandSize::S64);

        Ok(())
    }

    fn check_stack(&mut self, vmctx: Reg) -> Result<()> {
        let ptr_size: u8 = self.ptr_size.bytes().try_into().unwrap();

        self.with_scratch::<IntScratch, _>(|masm, scratch| {
            masm.load_ptr(
                masm.address_at_reg(vmctx, ptr_size.vmcontext_store_context().into())?,
                scratch.writable(),
            )?;

            masm.load_ptr(
                Address::offset(
                    scratch.inner(),
                    ptr_size.vmstore_context_stack_limit().into(),
                ),
                scratch.writable(),
            )?;

            masm.add_stack_max(scratch.inner());

            masm.asm.cmp_rr(scratch.inner(), regs::rsp(), masm.ptr_size);
            masm.asm.trapif(IntCmpKind::GtU, TrapCode::STACK_OVERFLOW);
            anyhow::Ok(())
        })?;

        // Emit unwind info.
        if self.shared_flags.unwind_info() {
            self.asm.unwind_inst(UnwindInst::DefineNewFrame {
                offset_upward_to_caller_sp: Self::ABI::arg_base_offset().into(),

                // The Winch calling convention has no callee-save registers, so nothing will be
                // clobbered.
                offset_downward_to_clobbers: 0,
            })
        }
        Ok(())
    }

    fn push(&mut self, reg: Reg, size: OperandSize) -> Result<StackSlot> {
        let bytes = match (reg.class(), size) {
            (RegClass::Int, OperandSize::S64) => {
                let word_bytes = <Self::ABI as ABI>::word_bytes() as u32;
                self.asm.push_r(reg);
                self.increment_sp(word_bytes);
                word_bytes
            }
            (RegClass::Int, OperandSize::S32) => {
                let bytes = size.bytes();
                self.reserve_stack(bytes)?;
                let sp_offset = SPOffset::from_u32(self.sp_offset);
                self.asm
                    .mov_rm(reg, &self.address_from_sp(sp_offset)?, size, TRUSTED_FLAGS);
                bytes
            }
            (RegClass::Float, _) => {
                let bytes = size.bytes();
                self.reserve_stack(bytes)?;
                let sp_offset = SPOffset::from_u32(self.sp_offset);
                self.asm
                    .xmm_mov_rm(reg, &self.address_from_sp(sp_offset)?, size, TRUSTED_FLAGS);
                bytes
            }
            _ => unreachable!(),
        };

        Ok(StackSlot {
            offset: SPOffset::from_u32(self.sp_offset),
            size: bytes,
        })
    }

    fn reserve_stack(&mut self, bytes: u32) -> Result<()> {
        if bytes == 0 {
            return Ok(());
        }

        self.asm
            .sub_ir(bytes as i32, writable!(rsp()), OperandSize::S64);
        self.increment_sp(bytes);

        Ok(())
    }

    fn free_stack(&mut self, bytes: u32) -> Result<()> {
        if bytes == 0 {
            return Ok(());
        }
        self.asm
            .add_ir(bytes as i32, writable!(rsp()), OperandSize::S64);
        self.decrement_sp(bytes);

        Ok(())
    }

    fn reset_stack_pointer(&mut self, offset: SPOffset) -> Result<()> {
        self.sp_offset = offset.as_u32();

        Ok(())
    }

    fn local_address(&mut self, local: &LocalSlot) -> Result<Address> {
        let (reg, offset) = if local.addressed_from_sp() {
            let offset = self
                .sp_offset
                .checked_sub(local.offset)
                .ok_or_else(|| CodeGenError::invalid_local_offset())?;
            (rsp(), offset)
        } else {
            (rbp(), local.offset)
        };

        Ok(Address::offset(reg, offset))
    }

    fn address_from_sp(&self, offset: SPOffset) -> Result<Self::Address> {
        Ok(Address::offset(
            regs::rsp(),
            self.sp_offset - offset.as_u32(),
        ))
    }

    fn address_at_sp(&self, offset: SPOffset) -> Result<Self::Address> {
        Ok(Address::offset(regs::rsp(), offset.as_u32()))
    }

    fn address_at_vmctx(&self, offset: u32) -> Result<Self::Address> {
        Ok(Address::offset(vmctx!(Self), offset))
    }

    fn store_ptr(&mut self, src: Reg, dst: Self::Address) -> Result<()> {
        self.store(src.into(), dst, self.ptr_size)
    }

    fn store(&mut self, src: RegImm, dst: Address, size: OperandSize) -> Result<()> {
        self.store_impl(src, dst, size, TRUSTED_FLAGS)
    }

    fn wasm_store(&mut self, src: Reg, dst: Self::Address, kind: StoreKind) -> Result<()> {
        match kind {
            StoreKind::Operand(size) => {
                self.store_impl(src.into(), dst, size, UNTRUSTED_FLAGS)?;
            }
            StoreKind::Atomic(size) => {
                if size == OperandSize::S128 {
                    // TODO: we don't support 128-bit atomic store yet.
                    bail!(CodeGenError::unexpected_operand_size());
                }
                // To stay consistent with cranelift, we emit a normal store followed by a mfence,
                // although, we could probably just emit a xchg.
                self.store_impl(src.into(), dst, size, UNTRUSTED_FLAGS)?;
                self.asm.mfence();
            }
            StoreKind::VectorLane(LaneSelector { lane, size }) => {
                self.ensure_has_avx()?;
                self.asm
                    .xmm_vpextr_rm(&dst, src, lane, size, UNTRUSTED_FLAGS);
            }
        }

        Ok(())
    }

    fn pop(&mut self, dst: WritableReg, size: OperandSize) -> Result<()> {
        let current_sp = SPOffset::from_u32(self.sp_offset);
        let _ = match (dst.to_reg().class(), size) {
            (RegClass::Int, OperandSize::S32) => {
                let addr = self.address_from_sp(current_sp)?;
                self.asm.movzx_mr(
                    &addr,
                    dst,
                    size.extend_to::<Zero>(OperandSize::S64),
                    TRUSTED_FLAGS,
                );
                self.free_stack(size.bytes())?;
            }
            (RegClass::Int, OperandSize::S64) => {
                self.asm.pop_r(dst);
                self.decrement_sp(<Self::ABI as ABI>::word_bytes() as u32);
            }
            (RegClass::Float, _) | (RegClass::Vector, _) => {
                let addr = self.address_from_sp(current_sp)?;
                self.asm.xmm_mov_mr(&addr, dst, size, TRUSTED_FLAGS);
                self.free_stack(size.bytes())?;
            }
            _ => bail!(CodeGenError::invalid_operand_combination()),
        };
        Ok(())
    }

    fn with_scratch<T: ScratchType, R>(&mut self, f: impl FnOnce(&mut Self, Scratch) -> R) -> R {
        let r = self
            .scratch_scope
            .reg_for_class(T::reg_class(), &mut |_| Ok(()))
            .expect("Scratch register to be available");

        let ret = f(self, Scratch::new(r));
        self.scratch_scope.free(r);
        ret
    }

    fn call(
        &mut self,
        stack_args_size: u32,
        mut load_callee: impl FnMut(&mut Self) -> Result<(CalleeKind, CallingConvention)>,
    ) -> Result<u32> {
        let alignment: u32 = <Self::ABI as abi::ABI>::call_stack_align().into();
        let addend: u32 = <Self::ABI as abi::ABI>::initial_frame_size().into();
        let delta = calculate_frame_adjustment(self.sp_offset()?.as_u32(), addend, alignment);
        let aligned_args_size = align_to(stack_args_size, alignment);
        let total_stack = delta + aligned_args_size;
        self.reserve_stack(total_stack)?;
        let (callee, cc) = load_callee(self)?;
        match callee {
            CalleeKind::Indirect(reg) => self.asm.call_with_reg(cc, reg),
            CalleeKind::Direct(idx) => self.asm.call_with_name(cc, idx),
        };
        Ok(total_stack)
    }

    fn load_ptr(&mut self, src: Self::Address, dst: WritableReg) -> Result<()> {
        self.load(src, dst, self.ptr_size)
    }

    fn compute_addr(
        &mut self,
        src: Self::Address,
        dst: WritableReg,
        size: OperandSize,
    ) -> Result<()> {
        self.asm.lea(&src, dst, size);
        Ok(())
    }

    fn load(&mut self, src: Address, dst: WritableReg, size: OperandSize) -> Result<()> {
        self.load_impl(src, dst, size, TRUSTED_FLAGS)
    }

    fn wasm_load(&mut self, src: Self::Address, dst: WritableReg, kind: LoadKind) -> Result<()> {
        let size = kind.derive_operand_size();

        match kind {
            LoadKind::ScalarExtend(ext) => match ext {
                ExtendKind::Signed(ext) => {
                    self.asm.movsx_mr(&src, dst, ext, UNTRUSTED_FLAGS);
                }
                ExtendKind::Unsigned(_) => self.load_impl(src, dst, size, UNTRUSTED_FLAGS)?,
            },
            LoadKind::Operand(_) | LoadKind::Atomic(_, _) => {
                // The guarantees of the x86-64 memory model ensure that `SeqCst`
                // loads are equivalent to normal loads.
                if kind.is_atomic() && size == OperandSize::S128 {
                    bail!(CodeGenError::unexpected_operand_size());
                }

                self.load_impl(src, dst, size, UNTRUSTED_FLAGS)?;
            }
            LoadKind::VectorExtend(ext) => {
                self.ensure_has_avx()?;
                self.asm
                    .xmm_vpmov_mr(&src, dst, ext.into(), UNTRUSTED_FLAGS)
            }
            LoadKind::Splat(_) => {
                self.ensure_has_avx()?;

                if size == OperandSize::S64 {
                    self.asm
                        .xmm_mov_mr(&src, dst, OperandSize::S64, UNTRUSTED_FLAGS);
                    self.asm.xmm_vpshuf_rr(
                        dst.to_reg(),
                        dst,
                        Self::vpshuf_mask_for_64_bit_splats(),
                        OperandSize::S32,
                    );
                } else {
                    self.asm
                        .xmm_vpbroadcast_mr(&src, dst, size, UNTRUSTED_FLAGS);
                }
            }
            LoadKind::VectorLane(LaneSelector { lane, size }) => {
                self.ensure_has_avx()?;
                self.with_scratch::<IntScratch, _>(|masm, byte_tmp| {
                    masm.load_impl(src, byte_tmp.writable(), size, UNTRUSTED_FLAGS)?;
                    masm.asm
                        .xmm_vpinsr_rrr(dst, dst.to_reg(), byte_tmp.inner(), lane, size);
                    anyhow::Ok(())
                })?;
            }
            LoadKind::VectorZero(size) => {
                self.ensure_has_avx()?;
                self.with_scratch::<IntScratch, _>(|masm, scratch| {
                    masm.load_impl(src, scratch.writable(), size, UNTRUSTED_FLAGS)?;
                    masm.asm.avx_gpr_to_xmm(scratch.inner(), dst, size);
                    anyhow::Ok(())
                })?;
            }
        }

        Ok(())
    }

    fn sp_offset(&self) -> Result<SPOffset> {
        Ok(SPOffset::from_u32(self.sp_offset))
    }

    fn zero(&mut self, reg: WritableReg) -> Result<()> {
        self.asm.xor_rr(
            reg.to_reg(),
            reg,
            OperandSize::from_bytes(<Self::ABI>::word_bytes()),
        );
        Ok(())
    }

    fn mov(&mut self, dst: WritableReg, src: RegImm, size: OperandSize) -> Result<()> {
        match (src, dst.to_reg()) {
            (RegImm::Reg(src), dst_reg) => match (src.class(), dst_reg.class()) {
                (RegClass::Int, RegClass::Int) => Ok(self.asm.mov_rr(src, dst, size)),
                (RegClass::Float, RegClass::Float) => Ok(self.asm.xmm_mov_rr(src, dst, size)),
                _ => bail!(CodeGenError::invalid_operand_combination()),
            },
            (RegImm::Imm(imm), _) => self.load_constant(&imm, dst, size),
        }
    }

    fn cmov(
        &mut self,
        dst: WritableReg,
        src: Reg,
        cc: IntCmpKind,
        size: OperandSize,
    ) -> Result<()> {
        match (src.class(), dst.to_reg().class()) {
            (RegClass::Int, RegClass::Int) => Ok(self.asm.cmov(src, dst, cc, size)),
            (RegClass::Float, RegClass::Float) => Ok(self.asm.xmm_cmov(src, dst, cc, size)),
            _ => Err(anyhow!(CodeGenError::invalid_operand_combination())),
        }
    }

    fn add(&mut self, dst: WritableReg, lhs: Reg, rhs: RegImm, size: OperandSize) -> Result<()> {
        Self::ensure_two_argument_form(&dst.to_reg(), &lhs)?;
        match (rhs, dst) {
            (RegImm::Imm(imm), _) => {
                if let Some(v) = imm.to_i32() {
                    self.asm.add_ir(v, dst, size);
                } else {
                    self.with_scratch::<IntScratch, _>(|masm, scratch| {
                        masm.load_constant(&imm, scratch.writable(), size)?;
                        masm.asm.add_rr(scratch.inner(), dst, size);
                        anyhow::Ok(())
                    })?;
                }
            }

            (RegImm::Reg(src), dst) => {
                self.asm.add_rr(src, dst, size);
            }
        }

        Ok(())
    }

    fn checked_uadd(
        &mut self,
        dst: WritableReg,
        lhs: Reg,
        rhs: RegImm,
        size: OperandSize,
        trap: TrapCode,
    ) -> Result<()> {
        self.add(dst, lhs, rhs, size)?;
        self.asm.trapif(CC::B, trap);
        Ok(())
    }

    fn sub(&mut self, dst: WritableReg, lhs: Reg, rhs: RegImm, size: OperandSize) -> Result<()> {
        Self::ensure_two_argument_form(&dst.to_reg(), &lhs)?;
        match (rhs, dst) {
            (RegImm::Imm(imm), reg) => {
                if let Some(v) = imm.to_i32() {
                    self.asm.sub_ir(v, reg, size);
                } else {
                    self.with_scratch::<IntScratch, _>(|masm, scratch| {
                        masm.load_constant(&imm, scratch.writable(), size)?;
                        masm.asm.sub_rr(scratch.inner(), reg, size);
                        anyhow::Ok(())
                    })?;
                }
            }

            (RegImm::Reg(src), dst) => {
                self.asm.sub_rr(src, dst, size);
            }
        }

        Ok(())
    }

    fn mul(&mut self, dst: WritableReg, lhs: Reg, rhs: RegImm, size: OperandSize) -> Result<()> {
        Self::ensure_two_argument_form(&dst.to_reg(), &lhs)?;
        match (rhs, dst) {
            (RegImm::Imm(imm), _) => {
                if let Some(v) = imm.to_i32() {
                    self.asm.mul_ir(v, dst, size);
                } else {
                    self.with_scratch::<IntScratch, _>(|masm, scratch| {
                        masm.load_constant(&imm, scratch.writable(), size)?;
                        masm.asm.mul_rr(scratch.inner(), dst, size);
                        anyhow::Ok(())
                    })?;
                }
            }

            (RegImm::Reg(src), dst) => {
                self.asm.mul_rr(src, dst, size);
            }
        }

        Ok(())
    }

    fn float_add(&mut self, dst: WritableReg, lhs: Reg, rhs: Reg, size: OperandSize) -> Result<()> {
        Self::ensure_two_argument_form(&dst.to_reg(), &lhs)?;
        self.asm.xmm_add_rr(rhs, dst, size);
        Ok(())
    }

    fn float_sub(&mut self, dst: WritableReg, lhs: Reg, rhs: Reg, size: OperandSize) -> Result<()> {
        Self::ensure_two_argument_form(&dst.to_reg(), &lhs)?;
        self.asm.xmm_sub_rr(rhs, dst, size);
        Ok(())
    }

    fn float_mul(&mut self, dst: WritableReg, lhs: Reg, rhs: Reg, size: OperandSize) -> Result<()> {
        Self::ensure_two_argument_form(&dst.to_reg(), &lhs)?;
        self.asm.xmm_mul_rr(rhs, dst, size);
        Ok(())
    }

    fn float_div(&mut self, dst: WritableReg, lhs: Reg, rhs: Reg, size: OperandSize) -> Result<()> {
        Self::ensure_two_argument_form(&dst.to_reg(), &lhs)?;
        self.asm.xmm_div_rr(rhs, dst, size);
        Ok(())
    }

    fn float_min(&mut self, dst: WritableReg, lhs: Reg, rhs: Reg, size: OperandSize) -> Result<()> {
        Self::ensure_two_argument_form(&dst.to_reg(), &lhs)?;
        self.asm.xmm_min_seq(rhs, dst, size);
        Ok(())
    }

    fn float_max(&mut self, dst: WritableReg, lhs: Reg, rhs: Reg, size: OperandSize) -> Result<()> {
        Self::ensure_two_argument_form(&dst.to_reg(), &lhs)?;
        self.asm.xmm_max_seq(rhs, dst, size);
        Ok(())
    }

    fn float_copysign(
        &mut self,
        dst: WritableReg,
        lhs: Reg,
        rhs: Reg,
        size: OperandSize,
    ) -> Result<()> {
        Self::ensure_two_argument_form(&dst.to_reg(), &lhs)?;
        let sign_mask = match size {
            OperandSize::S32 => I::I32(0x80000000),
            OperandSize::S64 => I::I64(0x8000000000000000),
            OperandSize::S8 | OperandSize::S16 | OperandSize::S128 => {
                bail!(CodeGenError::unexpected_operand_size())
            }
        };

        self.with_scratch::<IntScratch, _>(|masm, scratch_gpr| {
            masm.with_scratch::<FloatScratch, _>(|masm, scratch_xmm| {
                masm.load_constant(&sign_mask, scratch_gpr.writable(), size)?;
                masm.asm
                    .gpr_to_xmm(scratch_gpr.inner(), scratch_xmm.writable(), size);

                // Clear everything except sign bit in src.
                masm.asm
                    .xmm_and_rr(scratch_xmm.inner(), writable!(rhs), size);

                // Clear sign bit in dst using scratch to store result. Then copy the
                // result back to dst.
                masm.asm
                    .xmm_andn_rr(dst.to_reg(), scratch_xmm.writable(), size);
                masm.asm.xmm_mov_rr(scratch_xmm.inner(), dst, size);

                // Copy sign bit from src to dst.
                masm.asm.xmm_or_rr(rhs, dst, size);
                Ok(())
            })
        })
    }

    fn float_neg(&mut self, dst: WritableReg, size: OperandSize) -> Result<()> {
        debug_assert_eq!(dst.to_reg().class(), RegClass::Float);
        let mask = match size {
            OperandSize::S32 => I::I32(0x80000000),
            OperandSize::S64 => I::I64(0x8000000000000000),
            OperandSize::S8 | OperandSize::S16 | OperandSize::S128 => {
                bail!(CodeGenError::unexpected_operand_size())
            }
        };
        self.with_scratch::<IntScratch, _>(|masm, scratch_gpr| {
            masm.with_scratch::<FloatScratch, _>(|masm, scratch_xmm| {
                masm.load_constant(&mask, scratch_gpr.writable(), size)?;
                masm.asm
                    .gpr_to_xmm(scratch_gpr.inner(), scratch_xmm.writable(), size);
                masm.asm.xmm_xor_rr(scratch_xmm.inner(), dst, size);
                Ok(())
            })
        })
    }

    fn float_abs(&mut self, dst: WritableReg, size: OperandSize) -> Result<()> {
        debug_assert_eq!(dst.to_reg().class(), RegClass::Float);
        let mask = match size {
            OperandSize::S32 => I::I32(0x7fffffff),
            OperandSize::S64 => I::I64(0x7fffffffffffffff),
            OperandSize::S128 | OperandSize::S16 | OperandSize::S8 => {
                bail!(CodeGenError::unexpected_operand_size())
            }
        };

        self.with_scratch::<IntScratch, _>(|masm, scratch_gpr| {
            masm.with_scratch::<FloatScratch, _>(|masm, scratch_xmm| {
                masm.load_constant(&mask, scratch_gpr.writable(), size)?;

                masm.asm
                    .gpr_to_xmm(scratch_gpr.inner(), scratch_xmm.writable(), size);
                masm.asm.xmm_and_rr(scratch_xmm.inner(), dst, size);
                Ok(())
            })
        })
    }

    fn float_round<
        F: FnMut(&mut FuncEnv<Self::Ptr>, &mut CodeGenContext<Emission>, &mut Self) -> Result<()>,
    >(
        &mut self,
        mode: RoundingMode,
        env: &mut FuncEnv<Self::Ptr>,
        context: &mut CodeGenContext<Emission>,
        size: OperandSize,
        mut fallback: F,
    ) -> Result<()> {
        if self.flags.has_sse41() {
            let src = context.pop_to_reg(self, None)?;
            self.asm
                .xmm_rounds_rr(src.into(), writable!(src.into()), mode, size);
            context.stack.push(src.into());
            Ok(())
        } else {
            fallback(env, context, self)
        }
    }

    fn float_sqrt(&mut self, dst: WritableReg, src: Reg, size: OperandSize) -> Result<()> {
        self.asm.sqrt(src, dst, size);
        Ok(())
    }

    fn and(&mut self, dst: WritableReg, lhs: Reg, rhs: RegImm, size: OperandSize) -> Result<()> {
        Self::ensure_two_argument_form(&dst.to_reg(), &lhs)?;
        match (rhs, dst) {
            (RegImm::Imm(imm), _) => {
                if let Some(v) = imm.to_i32() {
                    self.asm.and_ir(v, dst, size);
                } else {
                    self.with_scratch::<IntScratch, _>(|masm, scratch| {
                        masm.load_constant(&imm, scratch.writable(), size)?;
                        masm.asm.and_rr(scratch.inner(), dst, size);
                        anyhow::Ok(())
                    })?;
                }
            }

            (RegImm::Reg(src), dst) => {
                self.asm.and_rr(src, dst, size);
            }
        }

        Ok(())
    }

    fn or(&mut self, dst: WritableReg, lhs: Reg, rhs: RegImm, size: OperandSize) -> Result<()> {
        Self::ensure_two_argument_form(&dst.to_reg(), &lhs)?;
        match (rhs, dst) {
            (RegImm::Imm(imm), _) => {
                if let Some(v) = imm.to_i32() {
                    self.asm.or_ir(v, dst, size);
                } else {
                    self.with_scratch::<IntScratch, _>(|masm, scratch| {
                        masm.load_constant(&imm, scratch.writable(), size)?;
                        masm.asm.or_rr(scratch.inner(), dst, size);
                        anyhow::Ok(())
                    })?;
                }
            }

            (RegImm::Reg(src), dst) => {
                self.asm.or_rr(src, dst, size);
            }
        }

        Ok(())
    }

    fn xor(&mut self, dst: WritableReg, lhs: Reg, rhs: RegImm, size: OperandSize) -> Result<()> {
        Self::ensure_two_argument_form(&dst.to_reg(), &lhs)?;
        match (rhs, dst) {
            (RegImm::Imm(imm), _) => {
                if let Some(v) = imm.to_i32() {
                    self.asm.xor_ir(v, dst, size);
                } else {
                    self.with_scratch::<IntScratch, _>(|masm, scratch| {
                        masm.load_constant(&imm, scratch.writable(), size)?;
                        masm.asm.xor_rr(scratch.inner(), dst, size);
                        anyhow::Ok(())
                    })?;
                }
            }

            (RegImm::Reg(src), _) => {
                self.asm.xor_rr(src, dst, size);
            }
        }

        Ok(())
    }

    fn shift_ir(
        &mut self,
        dst: WritableReg,
        imm: I,
        lhs: Reg,
        kind: ShiftKind,
        size: OperandSize,
    ) -> Result<()> {
        Self::ensure_two_argument_form(&dst.to_reg(), &lhs)?;
        self.asm
            .shift_ir(imm.unwrap_as_u64() as u8, dst, kind, size);
        Ok(())
    }

    fn shift(
        &mut self,
        context: &mut CodeGenContext<Emission>,
        kind: ShiftKind,
        size: OperandSize,
    ) -> Result<()> {
        // Number of bits to shift must be in the CL register.
        let src = context.pop_to_reg(self, Some(regs::rcx()))?;
        let dst = context.pop_to_reg(self, None)?;

        self.asm
            .shift_rr(src.into(), writable!(dst.into()), kind, size);

        context.free_reg(src);
        context.stack.push(dst.into());

        Ok(())
    }

    fn div(
        &mut self,
        context: &mut CodeGenContext<Emission>,
        kind: DivKind,
        size: OperandSize,
    ) -> Result<()> {
        // Allocate rdx:rax.
        let rdx = context.reg(regs::rdx(), self)?;
        let rax = context.reg(regs::rax(), self)?;

        // Allocate the divisor, which can be any gpr.
        let divisor = context.pop_to_reg(self, None)?;

        // Mark rax as allocatable.
        context.free_reg(rax);
        // Move the top value to rax.
        let rax = context.pop_to_reg(self, Some(rax))?;
        self.asm.div(divisor.into(), (rax.into(), rdx), kind, size);

        // Free the divisor and rdx.
        context.free_reg(divisor);
        context.free_reg(rdx);

        // Push the quotient.
        context.stack.push(rax.into());
        Ok(())
    }

    fn rem(
        &mut self,
        context: &mut CodeGenContext<Emission>,
        kind: RemKind,
        size: OperandSize,
    ) -> Result<()> {
        // Allocate rdx:rax.
        let rdx = context.reg(regs::rdx(), self)?;
        let rax = context.reg(regs::rax(), self)?;

        // Allocate the divisor, which can be any gpr.
        let divisor = context.pop_to_reg(self, None)?;

        // Mark rax as allocatable.
        context.free_reg(rax);
        // Move the top value to rax.
        let rax = context.pop_to_reg(self, Some(rax))?;
        self.asm.rem(divisor.reg, (rax.into(), rdx), kind, size);

        // Free the divisor and rax.
        context.free_reg(divisor);
        context.free_reg(rax);

        // Push the remainder.
        context.stack.push(Val::reg(rdx, divisor.ty));

        Ok(())
    }

    fn frame_restore(&mut self) -> Result<()> {
        debug_assert_eq!(self.sp_offset, 0);
        self.asm.pop_r(writable!(rbp()));
        self.asm.ret();
        Ok(())
    }

    fn finalize(mut self, base: Option<SourceLoc>) -> Result<MachBufferFinalized<Final>> {
        if let Some(patch) = self.stack_max_use_add {
            patch.finalize(i32::try_from(self.sp_max).unwrap(), self.asm.buffer_mut());
        }

        Ok(self.asm.finalize(base))
    }

    fn address_at_reg(&self, reg: Reg, offset: u32) -> Result<Self::Address> {
        Ok(Address::offset(reg, offset))
    }

    fn cmp(&mut self, src1: Reg, src2: RegImm, size: OperandSize) -> Result<()> {
        match src2 {
            RegImm::Imm(imm) => {
                if let Some(v) = imm.to_i32() {
                    self.asm.cmp_ir(src1, v, size);
                } else {
                    self.with_scratch::<IntScratch, _>(|masm, scratch| {
                        masm.load_constant(&imm, scratch.writable(), size)?;
                        masm.asm.cmp_rr(src1, scratch.inner(), size);
                        anyhow::Ok(())
                    })?;
                }
            }
            RegImm::Reg(src2) => {
                self.asm.cmp_rr(src1, src2, size);
            }
        }

        Ok(())
    }

    fn cmp_with_set(
        &mut self,
        dst: WritableReg,
        src: RegImm,
        kind: IntCmpKind,
        size: OperandSize,
    ) -> Result<()> {
        self.cmp(dst.to_reg(), src, size)?;
        self.asm.setcc(kind, dst);
        Ok(())
    }

    fn float_cmp_with_set(
        &mut self,
        dst: WritableReg,
        src1: Reg,
        src2: Reg,
        kind: FloatCmpKind,
        size: OperandSize,
    ) -> Result<()> {
        // Float comparisons needs to be ordered (that is, comparing with a NaN
        // should return 0) except for not equal which needs to be unordered.
        // We use ucomis{s, d} because comis{s, d} has an undefined result if
        // either operand is NaN. Since ucomis{s, d} is unordered, we need to
        // compensate to make the comparison ordered.  Ucomis{s, d} sets the
        // ZF, PF, and CF flags if there is an unordered result.
        let (src1, src2, set_kind) = match kind {
            FloatCmpKind::Eq => (src1, src2, IntCmpKind::Eq),
            FloatCmpKind::Ne => (src1, src2, IntCmpKind::Ne),
            FloatCmpKind::Gt => (src1, src2, IntCmpKind::GtU),
            FloatCmpKind::Ge => (src1, src2, IntCmpKind::GeU),
            // Reversing the operands and using the complementary comparison
            // avoids needing to perform an additional SETNP and AND
            // instruction.
            // SETNB and SETNBE check if the carry flag is unset (i.e., not
            // less than and not unordered) so we get the intended result
            // without having to look at the parity flag.
            FloatCmpKind::Lt => (src2, src1, IntCmpKind::GtU),
            FloatCmpKind::Le => (src2, src1, IntCmpKind::GeU),
        };
        self.asm.ucomis(src1, src2, size);
        self.asm.setcc(set_kind, dst);
        let _ = match kind {
            FloatCmpKind::Eq | FloatCmpKind::Gt | FloatCmpKind::Ge => {
                // Return false if either operand is NaN by ensuring PF is
                // unset.
                self.with_scratch::<IntScratch, _>(|masm, scratch| {
                    masm.asm.setnp(scratch.writable());
                    masm.asm.and_rr(scratch.inner(), dst, size);
                });
            }
            FloatCmpKind::Ne => {
                // Return true if either operand is NaN by checking if PF is
                // set.
                self.with_scratch::<IntScratch, _>(|masm, scratch| {
                    masm.asm.setp(scratch.writable());
                    masm.asm.or_rr(scratch.inner(), dst, size);
                });
            }
            FloatCmpKind::Lt | FloatCmpKind::Le => (),
        };
        Ok(())
    }

    fn clz(&mut self, dst: WritableReg, src: Reg, size: OperandSize) -> Result<()> {
        if self.flags.has_lzcnt() {
            self.asm.lzcnt(src, dst, size);
        } else {
            self.with_scratch::<IntScratch, _>(|masm, scratch| {
                // Use the following approach:
                // dst = size.num_bits() - bsr(src) - is_not_zero
                //     = size.num.bits() + -bsr(src) - is_not_zero.
                masm.asm.bsr(src, dst, size);
                masm.asm.setcc(IntCmpKind::Ne, scratch.writable());
                masm.asm.neg(dst.to_reg(), dst, size);
                masm.asm.add_ir(size.num_bits() as i32, dst, size);
                masm.asm.sub_rr(scratch.inner(), dst, size);
            });
        }

        Ok(())
    }

    fn ctz(&mut self, dst: WritableReg, src: Reg, size: OperandSize) -> Result<()> {
        if self.flags.has_bmi1() {
            self.asm.tzcnt(src, dst, size);
        } else {
            self.with_scratch::<IntScratch, _>(|masm, scratch| {
                // Use the following approach:
                // dst = bsf(src) + (is_zero * size.num_bits())
                //     = bsf(src) + (is_zero << size.log2()).
                // BSF outputs the correct value for every value except 0.
                // When the value is 0, BSF outputs 0, correct output for ctz is
                // the number of bits.
                masm.asm.bsf(src, dst, size);
                masm.asm.setcc(IntCmpKind::Eq, scratch.writable());
                masm.asm
                    .shift_ir(size.log2(), scratch.writable(), ShiftKind::Shl, size);
                masm.asm.add_rr(scratch.inner(), dst, size);
            });
        }

        Ok(())
    }

    fn get_label(&mut self) -> Result<MachLabel> {
        let buffer = self.asm.buffer_mut();
        Ok(buffer.get_label())
    }

    fn bind(&mut self, label: MachLabel) -> Result<()> {
        let buffer = self.asm.buffer_mut();
        buffer.bind_label(label, &mut Default::default());
        Ok(())
    }

    fn branch(
        &mut self,
        kind: IntCmpKind,
        lhs: Reg,
        rhs: RegImm,
        taken: MachLabel,
        size: OperandSize,
    ) -> Result<()> {
        use IntCmpKind::*;

        match &(lhs, rhs) {
            (rlhs, RegImm::Reg(rrhs)) => {
                // If the comparison kind is zero or not zero and both operands
                // are the same register, emit a test instruction. Else we emit
                // a normal comparison.
                if (kind == Eq || kind == Ne) && (rlhs == rrhs) {
                    self.asm.test_rr(*rlhs, *rrhs, size);
                } else {
                    self.cmp(lhs, rhs, size)?;
                }
            }
            _ => self.cmp(lhs, rhs, size)?,
        }
        self.asm.jmp_if(kind, taken);
        Ok(())
    }

    fn jmp(&mut self, target: MachLabel) -> Result<()> {
        self.asm.jmp(target);
        Ok(())
    }

    fn popcnt(&mut self, context: &mut CodeGenContext<Emission>, size: OperandSize) -> Result<()> {
        let src = context.pop_to_reg(self, None)?;
        if self.flags.has_popcnt() && self.flags.has_sse42() {
            self.asm.popcnt(src.into(), writable!(src.into()), size);
            context.stack.push(src.into());
            Ok(())
        } else {
            // The fallback functionality here is based on `MacroAssembler::popcnt64` in:
            // https://searchfox.org/mozilla-central/source/js/src/jit/x64/MacroAssembler-x64-inl.h#495

            let tmp = writable!(context.any_gpr(self)?);
            let dst = writable!(src.into());
            let (masks, shift_amt) = match size {
                OperandSize::S64 => (
                    [
                        0x5555555555555555, // m1
                        0x3333333333333333, // m2
                        0x0f0f0f0f0f0f0f0f, // m4
                        0x0101010101010101, // h01
                    ],
                    56u8,
                ),
                // 32-bit popcount is the same, except the masks are half as
                // wide and we shift by 24 at the end rather than 56
                OperandSize::S32 => (
                    [0x55555555i64, 0x33333333i64, 0x0f0f0f0fi64, 0x01010101i64],
                    24u8,
                ),
                _ => bail!(CodeGenError::unexpected_operand_size()),
            };
            self.asm.mov_rr(src.into(), tmp, size);

            // x -= (x >> 1) & m1;
            self.asm.shift_ir(1u8, dst, ShiftKind::ShrU, size);
            let lhs = dst.to_reg();
            self.and(writable!(lhs), lhs, RegImm::i64(masks[0]), size)?;
            self.asm.sub_rr(dst.to_reg(), tmp, size);

            // x = (x & m2) + ((x >> 2) & m2);
            self.asm.mov_rr(tmp.to_reg(), dst, size);
            // Load `0x3333...` into the scratch reg once, allowing us to use
            // `and_rr` and avoid inadvertently loading it twice as with `and`

            self.with_scratch::<IntScratch, _>(|masm, scratch| {
                masm.load_constant(&I::i64(masks[1]), scratch.writable(), size)?;
                masm.asm.and_rr(scratch.inner(), dst, size);
                masm.asm.shift_ir(2u8, tmp, ShiftKind::ShrU, size);
                masm.asm.and_rr(scratch.inner(), tmp, size);
                anyhow::Ok(())
            })?;
            self.asm.add_rr(dst.to_reg(), tmp, size);

            // x = (x + (x >> 4)) & m4;
            self.asm.mov_rr(tmp.to_reg(), dst, size);
            self.asm.shift_ir(4u8, dst, ShiftKind::ShrU, size);
            self.asm.add_rr(tmp.to_reg(), dst, size);
            let lhs = dst.to_reg();
            self.and(writable!(lhs), lhs, RegImm::i64(masks[2]), size)?;

            // (x * h01) >> shift_amt
            let lhs = dst.to_reg();
            self.mul(writable!(lhs), lhs, RegImm::i64(masks[3]), size)?;
            self.asm.shift_ir(shift_amt, dst, ShiftKind::ShrU, size);

            context.stack.push(src.into());
            context.free_reg(tmp.to_reg());

            Ok(())
        }
    }

    fn wrap(&mut self, dst: WritableReg, src: Reg) -> Result<()> {
        self.asm.mov_rr(src, dst, OperandSize::S32);
        Ok(())
    }

    fn extend(&mut self, dst: WritableReg, src: Reg, kind: ExtendKind) -> Result<()> {
        match kind {
            ExtendKind::Signed(ext) => {
                self.asm.movsx_rr(src, dst, ext);
            }
            ExtendKind::Unsigned(ext) => {
                self.asm.movzx_rr(src, dst, ext);
            }
        }

        Ok(())
    }

    fn signed_truncate(
        &mut self,
        dst: WritableReg,
        src: Reg,
        src_size: OperandSize,
        dst_size: OperandSize,
        kind: TruncKind,
    ) -> Result<()> {
        self.with_scratch::<IntScratch, _>(|masm, gpr_scratch| {
            masm.with_scratch::<FloatScratch, _>(|masm, xmm_scratch| {
                masm.asm.cvt_float_to_sint_seq(
                    src,
                    dst,
                    gpr_scratch.inner(),
                    xmm_scratch.inner(),
                    src_size,
                    dst_size,
                    kind.is_checked(),
                );
                Ok(())
            })
        })
    }

    fn unsigned_truncate(
        &mut self,
        ctx: &mut CodeGenContext<Emission>,
        src_size: OperandSize,
        dst_size: OperandSize,
        kind: TruncKind,
    ) -> Result<()> {
        let dst_ty = match dst_size {
            OperandSize::S32 => WasmValType::I32,
            OperandSize::S64 => WasmValType::I64,
            _ => bail!(CodeGenError::unexpected_operand_size()),
        };

        ctx.convert_op_with_tmp_reg(
            self,
            dst_ty,
            RegClass::Float,
            |masm, dst, src, tmp_fpr, dst_size| {
                masm.with_scratch::<IntScratch, _>(|masm, gpr_scratch| {
                    masm.with_scratch::<FloatScratch, _>(|masm, xmm_scratch| {
                        masm.asm.cvt_float_to_uint_seq(
                            src,
                            writable!(dst),
                            gpr_scratch.inner(),
                            xmm_scratch.inner(),
                            tmp_fpr,
                            src_size,
                            dst_size,
                            kind.is_checked(),
                        );
                        Ok(())
                    })
                })
            },
        )
    }

    fn signed_convert(
        &mut self,
        dst: WritableReg,
        src: Reg,
        src_size: OperandSize,
        dst_size: OperandSize,
    ) -> Result<()> {
        self.asm.cvt_sint_to_float(src, dst, src_size, dst_size);
        Ok(())
    }

    fn unsigned_convert(
        &mut self,
        dst: WritableReg,
        src: Reg,
        tmp_gpr: Reg,
        src_size: OperandSize,
        dst_size: OperandSize,
    ) -> Result<()> {
        // Need to convert unsigned uint32 to uint64 for conversion instruction sequence.
        if let OperandSize::S32 = src_size {
            self.extend(
                writable!(src),
                src,
                ExtendKind::Unsigned(Extend::I64Extend32),
            )?;
        }

        self.with_scratch::<IntScratch, _>(|masm, scratch| {
            masm.asm
                .cvt_uint64_to_float_seq(src, dst, scratch.inner(), tmp_gpr, dst_size);
            Ok(())
        })
    }

    fn reinterpret_float_as_int(
        &mut self,
        dst: WritableReg,
        src: Reg,
        size: OperandSize,
    ) -> Result<()> {
        self.asm.xmm_to_gpr(src, dst, size);
        Ok(())
    }

    fn reinterpret_int_as_float(
        &mut self,
        dst: WritableReg,
        src: Reg,
        size: OperandSize,
    ) -> Result<()> {
        self.asm.gpr_to_xmm(src, dst, size);
        Ok(())
    }

    fn demote(&mut self, dst: WritableReg, src: Reg) -> Result<()> {
        self.asm
            .cvt_float_to_float(src, dst, OperandSize::S64, OperandSize::S32);
        Ok(())
    }

    fn promote(&mut self, dst: WritableReg, src: Reg) -> Result<()> {
        self.asm
            .cvt_float_to_float(src, dst, OperandSize::S32, OperandSize::S64);
        Ok(())
    }

    fn unreachable(&mut self) -> Result<()> {
        self.asm.trap(TRAP_UNREACHABLE);
        Ok(())
    }

    fn trap(&mut self, code: TrapCode) -> Result<()> {
        self.asm.trap(code);
        Ok(())
    }

    fn trapif(&mut self, cc: IntCmpKind, code: TrapCode) -> Result<()> {
        self.asm.trapif(cc, code);
        Ok(())
    }

    fn trapz(&mut self, src: Reg, code: TrapCode) -> Result<()> {
        self.asm.test_rr(src, src, self.ptr_size);
        self.asm.trapif(IntCmpKind::Eq, code);
        Ok(())
    }

    fn jmp_table(&mut self, targets: &[MachLabel], index: Reg, tmp: Reg) -> Result<()> {
        // At least one default target.
        debug_assert!(targets.len() >= 1);
        let default_index = targets.len() - 1;
        // Emit bounds check, by conditionally moving the max cases
        // into the given index reg if the contents of the index reg
        // are greater.
        let max = default_index;
        let size = OperandSize::S32;
        self.asm.mov_ir(max as u64, writable!(tmp), size);
        self.asm.cmp_rr(tmp, index, size);
        self.asm.cmov(tmp, writable!(index), IntCmpKind::LtU, size);

        let default = targets[default_index];
        let rest = &targets[0..default_index];

        self.with_scratch::<IntScratch, _>(|masm, tmp1| {
            masm.asm
                .jmp_table(rest.into(), default, index, tmp1.inner(), tmp);
            Ok(())
        })
    }

    fn start_source_loc(&mut self, loc: RelSourceLoc) -> Result<(CodeOffset, RelSourceLoc)> {
        Ok(self.asm.buffer_mut().start_srcloc(loc))
    }

    fn end_source_loc(&mut self) -> Result<()> {
        self.asm.buffer_mut().end_srcloc();
        Ok(())
    }

    fn current_code_offset(&self) -> Result<CodeOffset> {
        Ok(self.asm.buffer().cur_offset())
    }

    fn add128(
        &mut self,
        dst_lo: WritableReg,
        dst_hi: WritableReg,
        lhs_lo: Reg,
        lhs_hi: Reg,
        rhs_lo: Reg,
        rhs_hi: Reg,
    ) -> Result<()> {
        Self::ensure_two_argument_form(&dst_lo.to_reg(), &lhs_lo)?;
        Self::ensure_two_argument_form(&dst_hi.to_reg(), &lhs_hi)?;
        self.asm.add_rr(rhs_lo, dst_lo, OperandSize::S64);
        self.asm.adc_rr(rhs_hi, dst_hi, OperandSize::S64);
        Ok(())
    }

    fn sub128(
        &mut self,
        dst_lo: WritableReg,
        dst_hi: WritableReg,
        lhs_lo: Reg,
        lhs_hi: Reg,
        rhs_lo: Reg,
        rhs_hi: Reg,
    ) -> Result<()> {
        Self::ensure_two_argument_form(&dst_lo.to_reg(), &lhs_lo)?;
        Self::ensure_two_argument_form(&dst_hi.to_reg(), &lhs_hi)?;
        self.asm.sub_rr(rhs_lo, dst_lo, OperandSize::S64);
        self.asm.sbb_rr(rhs_hi, dst_hi, OperandSize::S64);
        Ok(())
    }

    fn mul_wide(
        &mut self,
        context: &mut CodeGenContext<Emission>,
        kind: MulWideKind,
    ) -> Result<()> {
        // Reserve rax/rdx since they're required by the `mul_wide` instruction
        // being used here.
        let rax = context.reg(regs::rax(), self)?;
        let rdx = context.reg(regs::rdx(), self)?;

        // The rhs of this binop can be in any register
        let rhs = context.pop_to_reg(self, None)?;
        // Mark rax as allocatable. and then force the lhs operand to be placed
        // in `rax`.
        context.free_reg(rax);
        let lhs = context.pop_to_reg(self, Some(rax))?;

        self.asm.mul_wide(
            writable!(rax),
            writable!(rdx),
            lhs.reg,
            rhs.reg,
            kind,
            OperandSize::S64,
        );

        // No longer using the rhs register after the multiplication has been
        // executed.
        context.free_reg(rhs);

        // The low bits of the result are in rax, where `lhs` was allocated to
        context.stack.push(lhs.into());
        // The high bits of the result are in rdx, which we previously reserved.
        context.stack.push(Val::Reg(TypedReg::i64(rdx)));

        Ok(())
    }

    fn splat(&mut self, context: &mut CodeGenContext<Emission>, size: SplatKind) -> Result<()> {
        // Get the source and destination operands set up first.
        let (src, dst) = match size {
            // Floats can use the same register for `src` and `dst`.
            SplatKind::F32x4 | SplatKind::F64x2 => {
                let reg = context.pop_to_reg(self, None)?.reg;
                (RegImm::reg(reg), writable!(reg))
            }
            // For ints, we need to load the operand into a vector register if
            // it's not a constant.
            SplatKind::I8x16 | SplatKind::I16x8 | SplatKind::I32x4 | SplatKind::I64x2 => {
                let dst = writable!(context.any_fpr(self)?);
                let src = if size == SplatKind::I64x2 {
                    context.pop_i64_const().map(RegImm::i64)
                } else {
                    context.pop_i32_const().map(RegImm::i32)
                }
                .map_or_else(
                    || -> Result<RegImm> {
                        let reg = context.pop_to_reg(self, None)?.reg;
                        self.reinterpret_int_as_float(
                            dst,
                            reg,
                            match size {
                                SplatKind::I8x16 | SplatKind::I16x8 | SplatKind::I32x4 => {
                                    OperandSize::S32
                                }
                                SplatKind::I64x2 => OperandSize::S64,
                                SplatKind::F32x4 | SplatKind::F64x2 => unreachable!(),
                            },
                        )?;
                        context.free_reg(reg);
                        Ok(RegImm::Reg(dst.to_reg()))
                    },
                    Ok,
                )?;
                (src, dst)
            }
        };

        // Perform the splat on the operands.
        if size == SplatKind::I64x2 || size == SplatKind::F64x2 {
            self.ensure_has_avx()?;
            let mask = Self::vpshuf_mask_for_64_bit_splats();
            match src {
                RegImm::Reg(src) => self.asm.xmm_vpshuf_rr(src, dst, mask, OperandSize::S32),
                RegImm::Imm(imm) => {
                    let src = self.asm.add_constant(&imm.to_bytes());
                    self.asm
                        .xmm_vpshuf_mr(&src, dst, mask, OperandSize::S32, MemFlags::trusted());
                }
            }
        } else {
            self.ensure_has_avx2()?;

            match src {
                RegImm::Reg(src) => self.asm.xmm_vpbroadcast_rr(src, dst, size.lane_size()),
                RegImm::Imm(imm) => {
                    let src = self.asm.add_constant(&imm.to_bytes());
                    self.asm
                        .xmm_vpbroadcast_mr(&src, dst, size.lane_size(), MemFlags::trusted());
                }
            }
        }

        context
            .stack
            .push(Val::reg(dst.to_reg(), WasmValType::V128));
        Ok(())
    }

    fn shuffle(&mut self, dst: WritableReg, lhs: Reg, rhs: Reg, lanes: [u8; 16]) -> Result<()> {
        self.ensure_has_avx()?;

        // Use `vpshufb` with `lanes` to set the lanes in `lhs` and `rhs`
        // separately to either the selected index or 0.
        // Then use `vpor` to combine `lhs` and `rhs` into `dst`.
        // Setting the most significant bit in the mask's lane to 1 will
        // result in corresponding lane in the destination register being
        // set to 0. 0x80 sets the most significant bit to 1.
        let mut mask_lhs: [u8; 16] = [0x80; 16];
        let mut mask_rhs: [u8; 16] = [0x80; 16];
        for i in 0..lanes.len() {
            if lanes[i] < 16 {
                mask_lhs[i] = lanes[i];
            } else {
                mask_rhs[i] = lanes[i] - 16;
            }
        }
        let mask_lhs = self.asm.add_constant(&mask_lhs);
        let mask_rhs = self.asm.add_constant(&mask_rhs);

        self.asm.xmm_vpshufb_rrm(dst, lhs, &mask_lhs);
        self.with_scratch::<FloatScratch, _>(|masm, scratch| {
            masm.asm.xmm_vpshufb_rrm(scratch.writable(), rhs, &mask_rhs);
            masm.asm.xmm_vpor_rrr(dst, dst.to_reg(), scratch.inner());
            Ok(())
        })
    }

    fn swizzle(&mut self, dst: WritableReg, lhs: Reg, rhs: Reg) -> Result<()> {
        self.ensure_has_avx()?;

        // Clamp rhs to [0, 15 (i.e., 0xF)] and substitute 0 for anything
        // outside that range.
        // Each lane is a signed byte so the maximum value is 0x7F. Adding
        // 0x70 to any value higher than 0xF will saturate resulting in a value
        // of 0xFF (i.e., 0).
        let clamp = self.asm.add_constant(&[0x70; 16]);
        self.asm
            .xmm_vpaddus_rrm(writable!(rhs), rhs, &clamp, OperandSize::S8);

        // Don't need to subtract 0x70 since `vpshufb` uses the least
        // significant 4 bits which are the same after adding 0x70.
        self.asm.xmm_vpshufb_rrr(dst, lhs, rhs);
        Ok(())
    }

    fn atomic_rmw(
        &mut self,
        context: &mut CodeGenContext<Emission>,
        addr: Self::Address,
        size: OperandSize,
        op: RmwOp,
        flags: MemFlags,
        extend: Option<Extend<Zero>>,
    ) -> Result<()> {
        let res = match op {
            RmwOp::Add => {
                let operand = context.pop_to_reg(self, None)?;
                self.asm
                    .lock_xadd(addr, writable!(operand.reg), size, flags);
                operand.reg
            }
            RmwOp::Sub => {
                let operand = context.pop_to_reg(self, None)?;
                self.asm.neg(operand.reg, writable!(operand.reg), size);
                self.asm
                    .lock_xadd(addr, writable!(operand.reg), size, flags);
                operand.reg
            }
            RmwOp::Xchg => {
                let operand = context.pop_to_reg(self, None)?;
                self.asm.xchg(addr, writable!(operand.reg), size, flags);
                operand.reg
            }
            RmwOp::And | RmwOp::Or | RmwOp::Xor => {
                let op = match op {
                    RmwOp::And => AtomicRmwSeqOp::And,
                    RmwOp::Or => AtomicRmwSeqOp::Or,
                    RmwOp::Xor => AtomicRmwSeqOp::Xor,
                    _ => unreachable!(
                        "invalid op for atomic_rmw_seq, should be one of `or`, `and` or `xor`"
                    ),
                };
                let dst = context.reg(regs::rax(), self)?;
                let operand = context.pop_to_reg(self, None)?;

                self.with_scratch::<IntScratch, _>(|masm, scratch| {
                    masm.asm.atomic_rmw_seq(
                        addr,
                        operand.reg,
                        writable!(dst),
                        scratch.writable(),
                        size,
                        flags,
                        op,
                    );
                });

                context.free_reg(operand.reg);
                dst
            }
        };

        let dst_ty = match extend {
            Some(ext) => {
                // We don't need to zero-extend from 32 to 64bits.
                if !(ext.from_bits() == 32 && ext.to_bits() == 64) {
                    self.asm.movzx_rr(res, writable!(res), ext);
                }

                WasmValType::int_from_bits(ext.to_bits())
            }
            None => WasmValType::int_from_bits(size.num_bits()),
        };

        context.stack.push(TypedReg::new(dst_ty, res).into());

        Ok(())
    }

    fn extract_lane(
        &mut self,
        src: Reg,
        dst: WritableReg,
        lane: u8,
        kind: ExtractLaneKind,
    ) -> Result<()> {
        self.ensure_has_avx()?;

        match kind {
            ExtractLaneKind::I8x16S
            | ExtractLaneKind::I8x16U
            | ExtractLaneKind::I16x8S
            | ExtractLaneKind::I16x8U
            | ExtractLaneKind::I32x4
            | ExtractLaneKind::I64x2 => self.asm.xmm_vpextr_rr(dst, src, lane, kind.lane_size()),
            ExtractLaneKind::F32x4 | ExtractLaneKind::F64x2 if lane == 0 => {
                // If the `src` and `dst` registers are the same, then the
                // appropriate value is already in the correct position in
                // the register.
                assert!(src == dst.to_reg());
            }
            ExtractLaneKind::F32x4 => self.asm.xmm_vpshuf_rr(src, dst, lane, kind.lane_size()),
            ExtractLaneKind::F64x2 => {
                // `0b11_10` selects the high and low 32-bits of the second
                // 64-bit, so `0b11_10_11_10` splats the 64-bit value across
                // both lanes. Since we put an `f64` on the stack, we use
                // the splatted value.
                // Double-check `lane == 0` was handled in another branch.
                assert!(lane == 1);
                self.asm
                    .xmm_vpshuf_rr(src, dst, 0b11_10_11_10, OperandSize::S32)
            }
        }

        // Sign-extend to 32-bits for sign extended kinds.
        match kind {
            ExtractLaneKind::I8x16S | ExtractLaneKind::I16x8S => {
                self.asm.movsx_rr(dst.to_reg(), dst, kind.into())
            }
            _ => (),
        }

        Ok(())
    }

    fn replace_lane(
        &mut self,
        src: RegImm,
        dst: WritableReg,
        lane: u8,
        kind: ReplaceLaneKind,
    ) -> Result<()> {
        self.ensure_has_avx()?;

        match kind {
            ReplaceLaneKind::I8x16
            | ReplaceLaneKind::I16x8
            | ReplaceLaneKind::I32x4
            | ReplaceLaneKind::I64x2 => match src {
                RegImm::Reg(reg) => {
                    self.asm
                        .xmm_vpinsr_rrr(dst, dst.to_reg(), reg, lane, kind.lane_size());
                }
                RegImm::Imm(imm) => {
                    let address = self.asm.add_constant(&imm.to_bytes());
                    self.asm
                        .xmm_vpinsr_rrm(dst, dst.to_reg(), &address, lane, kind.lane_size());
                }
            },
            ReplaceLaneKind::F32x4 => {
                // Immediate for `vinsertps` uses first 3 bits to determine
                // which elements of the destination to set to 0. The next 2
                // bits specify which element of the destination will be
                // overwritten.
                let imm = lane << 4;
                match src {
                    RegImm::Reg(reg) => self.asm.xmm_vinsertps_rrr(dst, dst.to_reg(), reg, imm),
                    RegImm::Imm(val) => {
                        let address = self.asm.add_constant(&val.to_bytes());
                        self.asm.xmm_vinsertps_rrm(dst, dst.to_reg(), &address, imm);
                    }
                }
            }
            ReplaceLaneKind::F64x2 => match src {
                RegImm::Reg(reg) => match lane {
                    0 => self.asm.xmm_vmovsd_rrr(dst, dst.to_reg(), reg),
                    1 => self.asm.xmm_vmovlhps_rrr(dst, dst.to_reg(), reg),
                    _ => unreachable!(),
                },
                RegImm::Imm(imm) => {
                    let address = self.asm.add_constant(&imm.to_bytes());
                    match lane {
                        0 => {
                            // Memory load variant of `vmovsd` zeroes the upper
                            // 64 bits of the register so need to load the
                            // immediate to a register to use the register
                            // variant of `vmovsd` to perform the merge.

                            self.with_scratch::<FloatScratch, _>(|masm, scratch| {
                                masm.asm.xmm_vmovsd_rm(scratch.writable(), &address);
                                masm.asm.xmm_vmovsd_rrr(dst, dst.to_reg(), scratch.inner());
                            });
                        }
                        1 => self.asm.xmm_vmovlhps_rrm(dst, dst.to_reg(), &address),
                        _ => unreachable!(),
                    }
                }
            },
        }
        Ok(())
    }

    fn atomic_cas(
        &mut self,
        context: &mut CodeGenContext<Emission>,
        addr: Self::Address,
        size: OperandSize,
        flags: MemFlags,
        extend: Option<Extend<Zero>>,
    ) -> Result<()> {
        // `cmpxchg` expects `expected` to be in the `*a*` register.
        // reserve rax for the expected argument.
        let rax = context.reg(regs::rax(), self)?;

        let replacement = context.pop_to_reg(self, None)?;

        // mark `rax` as allocatable again.
        context.free_reg(rax);
        let expected = context.pop_to_reg(self, Some(regs::rax()))?;

        self.asm
            .cmpxchg(addr, replacement.reg, writable!(expected.reg), size, flags);

        if let Some(extend) = extend {
            // We don't need to zero-extend from 32 to 64bits.
            if !(extend.from_bits() == 32 && extend.to_bits() == 64) {
                self.asm
                    .movzx_rr(expected.reg, writable!(expected.reg), extend);
            }
        }

        context.stack.push(expected.into());
        context.free_reg(replacement);

        Ok(())
    }

    fn v128_eq(
        &mut self,
        dst: WritableReg,
        lhs: Reg,
        rhs: Reg,
        kind: VectorEqualityKind,
    ) -> Result<()> {
        self.ensure_has_avx()?;

        match kind {
            VectorEqualityKind::I8x16
            | VectorEqualityKind::I16x8
            | VectorEqualityKind::I32x4
            | VectorEqualityKind::I64x2 => {
                self.asm.xmm_vpcmpeq_rrr(dst, lhs, rhs, kind.lane_size())
            }
            VectorEqualityKind::F32x4 | VectorEqualityKind::F64x2 => {
                self.asm
                    .xmm_vcmpp_rrr(dst, lhs, rhs, kind.lane_size(), VcmpKind::Eq)
            }
        }
        Ok(())
    }

    fn v128_ne(
        &mut self,
        dst: WritableReg,
        lhs: Reg,
        rhs: Reg,
        kind: VectorEqualityKind,
    ) -> Result<()> {
        self.ensure_has_avx()?;

        match kind {
            VectorEqualityKind::I8x16
            | VectorEqualityKind::I16x8
            | VectorEqualityKind::I32x4
            | VectorEqualityKind::I64x2 => {
                // Check for equality and invert the results.
                self.asm
                    .xmm_vpcmpeq_rrr(writable!(lhs), lhs, rhs, kind.lane_size());
                self.asm
                    .xmm_vpcmpeq_rrr(writable!(rhs), rhs, rhs, kind.lane_size());
                self.asm.xmm_vpxor_rrr(lhs, rhs, dst);
            }
            VectorEqualityKind::F32x4 | VectorEqualityKind::F64x2 => {
                self.asm
                    .xmm_vcmpp_rrr(dst, lhs, rhs, kind.lane_size(), VcmpKind::Ne)
            }
        }
        Ok(())
    }

    fn v128_lt(
        &mut self,
        dst: WritableReg,
        lhs: Reg,
        rhs: Reg,
        kind: VectorCompareKind,
    ) -> Result<()> {
        self.ensure_has_avx()?;

        match kind {
            VectorCompareKind::I8x16S
            | VectorCompareKind::I16x8S
            | VectorCompareKind::I32x4S
            | VectorCompareKind::I64x2S => {
                // Perform a greater than check with reversed parameters.
                self.asm.xmm_vpcmpgt_rrr(dst, rhs, lhs, kind.lane_size())
            }
            VectorCompareKind::I8x16U | VectorCompareKind::I16x8U | VectorCompareKind::I32x4U => {
                // Set `lhs` to min values, check for equality, then invert the
                // result.
                // If `lhs` is smaller, then equality check will fail and result
                // will be inverted to true. Otherwise the equality check will
                // pass and be inverted to false.
                self.asm
                    .xmm_vpminu_rrr(writable!(lhs), lhs, rhs, kind.lane_size());
                self.asm
                    .xmm_vpcmpeq_rrr(writable!(lhs), lhs, rhs, kind.lane_size());
                self.asm
                    .xmm_vpcmpeq_rrr(writable!(rhs), rhs, rhs, kind.lane_size());
                self.asm.xmm_vpxor_rrr(lhs, rhs, dst);
            }
            VectorCompareKind::F32x4 | VectorCompareKind::F64x2 => {
                self.asm
                    .xmm_vcmpp_rrr(dst, lhs, rhs, kind.lane_size(), VcmpKind::Lt)
            }
        }
        Ok(())
    }

    fn v128_le(
        &mut self,
        dst: WritableReg,
        lhs: Reg,
        rhs: Reg,
        kind: VectorCompareKind,
    ) -> Result<()> {
        self.ensure_has_avx()?;

        match kind {
            VectorCompareKind::I8x16S | VectorCompareKind::I16x8S | VectorCompareKind::I32x4S => {
                // Set the `rhs` vector to the signed minimum values and then
                // compare them with `lhs` for equality.
                self.asm
                    .xmm_vpmins_rrr(writable!(rhs), lhs, rhs, kind.lane_size());
                self.asm.xmm_vpcmpeq_rrr(dst, lhs, rhs, kind.lane_size());
            }
            VectorCompareKind::I64x2S => {
                // Do a greater than check and invert the results.
                self.asm
                    .xmm_vpcmpgt_rrr(writable!(lhs), lhs, rhs, kind.lane_size());
                self.asm
                    .xmm_vpcmpeq_rrr(writable!(rhs), rhs, rhs, kind.lane_size());
                self.asm.xmm_vpxor_rrr(lhs, rhs, dst);
            }
            VectorCompareKind::I8x16U | VectorCompareKind::I16x8U | VectorCompareKind::I32x4U => {
                // Set the `rhs` vector to the signed minimum values and then
                // compare them with `lhs` for equality.
                self.asm
                    .xmm_vpminu_rrr(writable!(rhs), lhs, rhs, kind.lane_size());
                self.asm.xmm_vpcmpeq_rrr(dst, lhs, rhs, kind.lane_size());
            }
            VectorCompareKind::F32x4 | VectorCompareKind::F64x2 => {
                self.asm
                    .xmm_vcmpp_rrr(dst, lhs, rhs, kind.lane_size(), VcmpKind::Le)
            }
        }
        Ok(())
    }

    fn v128_gt(
        &mut self,
        dst: WritableReg,
        lhs: Reg,
        rhs: Reg,
        kind: VectorCompareKind,
    ) -> Result<()> {
        self.ensure_has_avx()?;

        match kind {
            VectorCompareKind::I8x16S
            | VectorCompareKind::I16x8S
            | VectorCompareKind::I32x4S
            | VectorCompareKind::I64x2S => {
                self.asm.xmm_vpcmpgt_rrr(dst, lhs, rhs, kind.lane_size())
            }
            VectorCompareKind::I8x16U | VectorCompareKind::I16x8U | VectorCompareKind::I32x4U => {
                // Set `lhs` to max values, check for equality, then invert the
                // result.
                // If `lhs` is larger, then equality check will fail and result
                // will be inverted to true. Otherwise the equality check will
                // pass and be inverted to false.
                self.asm
                    .xmm_vpmaxu_rrr(writable!(lhs), lhs, rhs, kind.lane_size());
                self.asm
                    .xmm_vpcmpeq_rrr(writable!(lhs), lhs, rhs, kind.lane_size());
                self.asm
                    .xmm_vpcmpeq_rrr(writable!(rhs), rhs, rhs, kind.lane_size());
                self.asm.xmm_vpxor_rrr(lhs, rhs, dst);
            }
            VectorCompareKind::F32x4 | VectorCompareKind::F64x2 => {
                // Do a less than comparison with the operands swapped.
                self.asm
                    .xmm_vcmpp_rrr(dst, rhs, lhs, kind.lane_size(), VcmpKind::Lt)
            }
        }
        Ok(())
    }

    fn v128_ge(
        &mut self,
        dst: WritableReg,
        lhs: Reg,
        rhs: Reg,
        kind: VectorCompareKind,
    ) -> Result<()> {
        self.ensure_has_avx()?;

        match kind {
            VectorCompareKind::I8x16S | VectorCompareKind::I16x8S | VectorCompareKind::I32x4S => {
                // Set each lane to maximum value and then compare for equality.
                self.asm
                    .xmm_vpmaxs_rrr(writable!(rhs), lhs, rhs, kind.lane_size());
                self.asm.xmm_vpcmpeq_rrr(dst, lhs, rhs, kind.lane_size());
            }
            VectorCompareKind::I64x2S => {
                // Perform a greater than comparison with operands swapped,
                // then invert the results.
                self.asm
                    .xmm_vpcmpgt_rrr(writable!(rhs), rhs, lhs, kind.lane_size());
                self.asm.xmm_vpcmpeq_rrr(dst, lhs, lhs, kind.lane_size());
                self.asm.xmm_vpxor_rrr(dst.to_reg(), rhs, dst);
            }
            VectorCompareKind::I8x16U | VectorCompareKind::I16x8U | VectorCompareKind::I32x4U => {
                // Set lanes to maximum values and compare them for equality.
                self.asm
                    .xmm_vpmaxu_rrr(writable!(rhs), lhs, rhs, kind.lane_size());
                self.asm.xmm_vpcmpeq_rrr(dst, lhs, rhs, kind.lane_size());
            }
            VectorCompareKind::F32x4 | VectorCompareKind::F64x2 => {
                // Perform a less than or equal comparison on swapped operands.
                self.asm
                    .xmm_vcmpp_rrr(dst, rhs, lhs, kind.lane_size(), VcmpKind::Le)
            }
        }

        Ok(())
    }

    fn fence(&mut self) -> Result<()> {
        self.asm.mfence();
        Ok(())
    }

    fn v128_not(&mut self, dst: WritableReg) -> Result<()> {
        self.ensure_has_avx()?;

        self.with_scratch::<FloatScratch, _>(|masm, tmp| {
            // First, we initialize `tmp` with all ones by comparing it with
            // itself.
            masm.asm
                .xmm_vpcmpeq_rrr(tmp.writable(), tmp.inner(), tmp.inner(), OperandSize::S32);
            // Then we `xor` tmp and `dst` together, yielding `!dst`.
            masm.asm.xmm_vpxor_rrr(tmp.inner(), dst.to_reg(), dst);
            Ok(())
        })
    }

    fn v128_and(&mut self, src1: Reg, src2: Reg, dst: WritableReg) -> Result<()> {
        self.ensure_has_avx()?;
        self.asm.xmm_vpand_rrr(src1, src2, dst);
        Ok(())
    }

    fn v128_and_not(&mut self, src1: Reg, src2: Reg, dst: WritableReg) -> Result<()> {
        self.ensure_has_avx()?;
        self.asm.xmm_vpandn_rrr(src1, src2, dst);
        Ok(())
    }

    fn v128_or(&mut self, src1: Reg, src2: Reg, dst: WritableReg) -> Result<()> {
        self.ensure_has_avx()?;
        self.asm.xmm_vpor_rrr(dst, src1, src2);
        Ok(())
    }

    fn v128_xor(&mut self, src1: Reg, src2: Reg, dst: WritableReg) -> Result<()> {
        self.ensure_has_avx()?;
        self.asm.xmm_vpxor_rrr(src1, src2, dst);
        Ok(())
    }

    fn v128_bitselect(&mut self, src1: Reg, src2: Reg, mask: Reg, dst: WritableReg) -> Result<()> {
        self.ensure_has_avx()?;

        self.with_scratch::<FloatScratch, _>(|masm, tmp| {
            masm.v128_and(src1, mask, tmp.writable())?;
            masm.v128_and_not(mask, src2, dst)?;
            masm.v128_or(dst.to_reg(), tmp.inner(), dst)?;
            Ok(())
        })
    }

    fn v128_any_true(&mut self, src: Reg, dst: WritableReg) -> Result<()> {
        self.ensure_has_avx()?;
        self.asm.xmm_vptest(src, src);
        self.asm.setcc(IntCmpKind::Ne, dst);
        Ok(())
    }

    fn v128_convert(&mut self, src: Reg, dst: WritableReg, kind: V128ConvertKind) -> Result<()> {
        self.ensure_has_avx()?;
        match kind {
            V128ConvertKind::I32x4S => self.asm.xmm_vcvt_rr(src, dst, VcvtKind::I32ToF32),
            V128ConvertKind::I32x4LowS => self.asm.xmm_vcvt_rr(src, dst, VcvtKind::I32ToF64),
            V128ConvertKind::I32x4U => {
                self.with_scratch::<FloatScratch, _>(|masm, scratch| {
                    // Split each 32-bit integer into 16-bit parts.
                    // `scratch` will contain the low bits and `dst` will contain
                    // the high bits.
                    masm.asm
                        .xmm_vpsll_rri(src, scratch.writable(), 0x10, kind.src_lane_size());
                    masm.asm.xmm_vpsrl_rri(
                        scratch.inner(),
                        scratch.writable(),
                        0x10,
                        kind.src_lane_size(),
                    );
                    masm.asm
                        .xmm_vpsub_rrr(src, scratch.inner(), dst, kind.src_lane_size());

                    // Convert the low bits in `scratch` to floating point numbers.
                    masm.asm
                        .xmm_vcvt_rr(scratch.inner(), scratch.writable(), VcvtKind::I32ToF32);

                    // Prevent overflow by right shifting high bits.
                    masm.asm
                        .xmm_vpsrl_rri(dst.to_reg(), dst, 1, kind.src_lane_size());
                    // Convert high bits in `dst` to floating point numbers.
                    masm.asm.xmm_vcvt_rr(dst.to_reg(), dst, VcvtKind::I32ToF32);
                    // Double high bits in `dst` to reverse right shift.
                    masm.asm
                        .xmm_vaddp_rrr(dst.to_reg(), dst.to_reg(), dst, kind.src_lane_size());
                    // Add high bits in `dst` to low bits in `scratch`.
                    masm.asm.xmm_vaddp_rrr(
                        dst.to_reg(),
                        scratch.inner(),
                        dst,
                        kind.src_lane_size(),
                    );
                });
            }
            V128ConvertKind::I32x4LowU => {
                // See
                // https://github.com/bytecodealliance/wasmtime/blob/bb886ffc3c81a476d8ba06311ff2dede15a6f7e1/cranelift/codegen/src/isa/x64/lower.isle#L3668
                // for details on the Cranelift AVX implementation.
                // Use `vunpcklp` to create doubles from the integers.
                // Interleaving 0x1.0p52 (i.e., 0x43300000) with the integers
                // creates a byte array for a double that sets the mantissa
                // bits to the original integer value.
                let conversion_constant = self
                    .asm
                    .add_constant(&[0x00, 0x00, 0x30, 0x43, 0x00, 0x00, 0x30, 0x43]);
                self.asm
                    .xmm_vunpcklp_rrm(src, &conversion_constant, dst, kind.src_lane_size());
                // Subtract the 0x1.0p52 added above.
                let conversion_constant = self.asm.add_constant(&[
                    0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x30, 0x43, 0x00, 0x00, 0x00, 0x00, 0x00,
                    0x00, 0x30, 0x43,
                ]);
                self.asm.xmm_vsub_rrm(
                    dst.to_reg(),
                    &conversion_constant,
                    dst,
                    kind.dst_lane_size(),
                );
            }
        }
        Ok(())
    }

    fn v128_narrow(
        &mut self,
        src1: Reg,
        src2: Reg,
        dst: WritableReg,
        kind: V128NarrowKind,
    ) -> Result<()> {
        self.ensure_has_avx()?;
        match kind {
            V128NarrowKind::I16x8S | V128NarrowKind::I32x4S => {
                self.asm
                    .xmm_vpackss_rrr(src1, src2, dst, kind.dst_lane_size())
            }
            V128NarrowKind::I16x8U | V128NarrowKind::I32x4U => {
                self.asm
                    .xmm_vpackus_rrr(src1, src2, dst, kind.dst_lane_size())
            }
        }
        Ok(())
    }

    fn v128_demote(&mut self, src: Reg, dst: WritableReg) -> Result<()> {
        self.ensure_has_avx()?;
        self.asm.xmm_vcvt_rr(src, dst, VcvtKind::F64ToF32);
        Ok(())
    }

    fn v128_promote(&mut self, src: Reg, dst: WritableReg) -> Result<()> {
        self.ensure_has_avx()?;
        self.asm.xmm_vcvt_rr(src, dst, VcvtKind::F32ToF64);
        Ok(())
    }

    fn v128_extend(&mut self, src: Reg, dst: WritableReg, kind: V128ExtendKind) -> Result<()> {
        self.ensure_has_avx()?;
        match kind {
            V128ExtendKind::LowI8x16S
            | V128ExtendKind::LowI8x16U
            | V128ExtendKind::LowI16x8S
            | V128ExtendKind::LowI16x8U
            | V128ExtendKind::LowI32x4S
            | V128ExtendKind::LowI32x4U => self.asm.xmm_vpmov_rr(src, dst, kind.into()),
            V128ExtendKind::HighI8x16S | V128ExtendKind::HighI16x8S => {
                self.asm.xmm_vpalignr_rrr(src, src, dst, 0x8);
                self.asm.xmm_vpmov_rr(dst.to_reg(), dst, kind.into());
            }
            V128ExtendKind::HighI8x16U | V128ExtendKind::HighI16x8U => {
                self.with_scratch::<FloatScratch, _>(|masm, scratch| {
                    masm.asm
                        .xmm_vpxor_rrr(scratch.inner(), scratch.inner(), scratch.writable());
                    masm.asm
                        .xmm_vpunpckh_rrr(src, scratch.inner(), dst, kind.src_lane_size());
                });
            }
            V128ExtendKind::HighI32x4S => {
                // Move the 3rd element (i.e., 0b10) to the 1st (rightmost)
                // position and the 4th element (i.e., 0b11) to the 2nd (second
                // from the right) position and then perform the extend.
                self.asm
                    .xmm_vpshuf_rr(src, dst, 0b11_10_11_10, kind.src_lane_size());
                self.asm.xmm_vpmov_rr(dst.to_reg(), dst, kind.into());
            }
            V128ExtendKind::HighI32x4U => {
                self.with_scratch::<FloatScratch, _>(|masm, scratch| {
                    // Set `scratch` to a vector 0s.
                    masm.asm.xmm_vxorp_rrr(
                        scratch.inner(),
                        scratch.inner(),
                        scratch.writable(),
                        kind.src_lane_size(),
                    );
                    // Interleave the 0 bits into the two 32-bit integers to zero extend them.
                    masm.asm
                        .xmm_vunpckhp_rrr(src, scratch.inner(), dst, kind.src_lane_size());
                });
            }
        }
        Ok(())
    }

    fn v128_add(&mut self, lhs: Reg, rhs: Reg, dst: WritableReg, kind: V128AddKind) -> Result<()> {
        self.ensure_has_avx()?;
        match kind {
            V128AddKind::F32x4 => self.asm.xmm_vaddp_rrr(lhs, rhs, dst, OperandSize::S32),
            V128AddKind::F64x2 => self.asm.xmm_vaddp_rrr(lhs, rhs, dst, OperandSize::S64),
            V128AddKind::I8x16 => self.asm.xmm_vpadd_rrr(lhs, rhs, dst, OperandSize::S8),
            V128AddKind::I8x16SatS => self.asm.xmm_vpadds_rrr(dst, lhs, rhs, OperandSize::S8),
            V128AddKind::I8x16SatU => self.asm.xmm_vpaddus_rrr(dst, lhs, rhs, OperandSize::S8),
            V128AddKind::I16x8 => self.asm.xmm_vpadd_rrr(lhs, rhs, dst, OperandSize::S16),
            V128AddKind::I16x8SatS => self.asm.xmm_vpadds_rrr(dst, lhs, rhs, OperandSize::S16),
            V128AddKind::I16x8SatU => self.asm.xmm_vpaddus_rrr(dst, lhs, rhs, OperandSize::S16),
            V128AddKind::I32x4 => self.asm.xmm_vpadd_rrr(lhs, rhs, dst, OperandSize::S32),
            V128AddKind::I64x2 => self.asm.xmm_vpadd_rrr(lhs, rhs, dst, OperandSize::S64),
        };
        Ok(())
    }

    fn v128_sub(&mut self, lhs: Reg, rhs: Reg, dst: WritableReg, kind: V128SubKind) -> Result<()> {
        self.ensure_has_avx()?;
        match kind {
            V128SubKind::F32x4 => self.asm.xmm_vsubp_rrr(lhs, rhs, dst, OperandSize::S32),
            V128SubKind::F64x2 => self.asm.xmm_vsubp_rrr(lhs, rhs, dst, OperandSize::S64),
            V128SubKind::I8x16 => self.asm.xmm_vpsub_rrr(lhs, rhs, dst, OperandSize::S8),
            V128SubKind::I8x16SatS => self.asm.xmm_vpsubs_rrr(dst, lhs, rhs, OperandSize::S8),
            V128SubKind::I8x16SatU => self.asm.xmm_vpsubus_rrr(dst, lhs, rhs, OperandSize::S8),
            V128SubKind::I16x8 => self.asm.xmm_vpsub_rrr(lhs, rhs, dst, OperandSize::S16),
            V128SubKind::I16x8SatS => self.asm.xmm_vpsubs_rrr(dst, lhs, rhs, OperandSize::S16),
            V128SubKind::I16x8SatU => self.asm.xmm_vpsubus_rrr(dst, lhs, rhs, OperandSize::S16),
            V128SubKind::I32x4 => self.asm.xmm_vpsub_rrr(lhs, rhs, dst, OperandSize::S32),
            V128SubKind::I64x2 => self.asm.xmm_vpsub_rrr(lhs, rhs, dst, OperandSize::S64),
        };
        Ok(())
    }

    fn v128_mul(
        &mut self,
        context: &mut CodeGenContext<Emission>,
        kind: V128MulKind,
    ) -> Result<()> {
        self.ensure_has_avx()?;

        let rhs = context.pop_to_reg(self, None)?;
        let lhs = context.pop_to_reg(self, None)?;

        let mul_i64x2_avx512 = |this: &mut Self| {
            this.asm.vpmullq(lhs.reg, rhs.reg, writable!(lhs.reg));
        };

        let mul_i64x2_fallback = |this: &mut Self,
                                  context: &mut CodeGenContext<Emission>|
         -> Result<()> {
            // Standard AVX doesn't have an instruction for i64x2 multiplication, instead, we have to fallback
            // to an instruction sequence using 32bits multiplication (taken from cranelift
            // implementation, in `isa/x64/lower.isle`):
            //
            // > Otherwise, for i64x2 multiplication we describe a lane A as being composed of
            // > a 32-bit upper half "Ah" and a 32-bit lower half "Al". The 32-bit long hand
            // > multiplication can then be written as:
            //
            // >    Ah Al
            // > *  Bh Bl
            // >    -----
            // >    Al * Bl
            // > + (Ah * Bl) << 32
            // > + (Al * Bh) << 32
            //
            // > So for each lane we will compute:
            //
            // >   A * B  = (Al * Bl) + ((Ah * Bl) + (Al * Bh)) << 32
            //
            // > Note, the algorithm will use `pmuludq` which operates directly on the lower
            // > 32-bit (`Al` or `Bl`) of a lane and writes the result to the full 64-bits of
            // > the lane of the destination. For this reason we don't need shifts to isolate
            // > the lower 32-bits, however, we will need to use shifts to isolate the high
            // > 32-bits when doing calculations, i.e., `Ah == A >> 32`.

            let tmp2 = context.any_fpr(this)?;
            this.with_scratch::<FloatScratch, _>(|this, tmp1| {
                // tmp1 = lhs_hi = (lhs >> 32)
                this.asm
                    .xmm_vpsrl_rri(lhs.reg, tmp1.writable(), 32, OperandSize::S64);

                // tmp2 = lhs_hi * rhs_low = tmp1 * rhs
                this.asm
                    .xmm_vpmuldq_rrr(tmp1.inner(), rhs.reg, writable!(tmp2));

                // tmp1 = rhs_hi = rhs >> 32
                this.asm
                    .xmm_vpsrl_rri(rhs.reg, tmp1.writable(), 32, OperandSize::S64);

                // tmp1 = lhs_low * rhs_high = tmp1 * lhs
                this.asm
                    .xmm_vpmuludq_rrr(tmp1.inner(), lhs.reg, tmp1.writable());

                // tmp1 = ((lhs_hi * rhs_low) + (lhs_lo * rhs_hi)) = tmp1 + tmp2
                this.asm
                    .xmm_vpadd_rrr(tmp1.inner(), tmp2, tmp1.writable(), OperandSize::S64);

                //tmp1 = tmp1 << 32
                this.asm
                    .xmm_vpsll_rri(tmp1.inner(), tmp1.writable(), 32, OperandSize::S64);

                // tmp2 = lhs_lo + rhs_lo
                this.asm.xmm_vpmuludq_rrr(lhs.reg, rhs.reg, writable!(tmp2));

                // finally, with `lhs` as destination:
                // lhs = (lhs_low * rhs_low) + ((lhs_hi * rhs_low) + (lhs_lo * rhs_hi)) = tmp1 + tmp2
                this.asm
                    .xmm_vpadd_rrr(tmp1.inner(), tmp2, writable!(lhs.reg), OperandSize::S64);
            });

            context.free_reg(tmp2);

            Ok(())
        };

        match kind {
            V128MulKind::F32x4 => {
                self.asm
                    .xmm_vmulp_rrr(lhs.reg, rhs.reg, writable!(lhs.reg), OperandSize::S32)
            }
            V128MulKind::F64x2 => {
                self.asm
                    .xmm_vmulp_rrr(lhs.reg, rhs.reg, writable!(lhs.reg), OperandSize::S64)
            }
            V128MulKind::I16x8 => {
                self.asm
                    .xmm_vpmull_rrr(lhs.reg, rhs.reg, writable!(lhs.reg), OperandSize::S16)
            }
            V128MulKind::I32x4 => {
                self.asm
                    .xmm_vpmull_rrr(lhs.reg, rhs.reg, writable!(lhs.reg), OperandSize::S32)
            }
            // This is the fast path when AVX512 is available.
            V128MulKind::I64x2
                if self.ensure_has_avx512vl().is_ok() && self.ensure_has_avx512dq().is_ok() =>
            {
                mul_i64x2_avx512(self)
            }
            // Otherwise, we emit AVX fallback sequence.
            V128MulKind::I64x2 => mul_i64x2_fallback(self, context)?,
        }

        context.stack.push(lhs.into());
        context.free_reg(rhs);

        Ok(())
    }

    fn v128_abs(&mut self, src: Reg, dst: WritableReg, kind: V128AbsKind) -> Result<()> {
        self.ensure_has_avx()?;

        match kind {
            V128AbsKind::I8x16 | V128AbsKind::I16x8 | V128AbsKind::I32x4 => {
                self.asm.xmm_vpabs_rr(src, dst, kind.lane_size())
            }
            V128AbsKind::I64x2 => {
                self.with_scratch::<FloatScratch, _>(|masm, scratch| {
                    // Perform an arithmetic right shift of 31 bits. If the number
                    // is positive, this will result in all zeroes in the upper
                    // 32-bits. If the number is negative, this will result in all
                    // ones in the upper 32-bits.
                    masm.asm
                        .xmm_vpsra_rri(src, scratch.writable(), 0x1f, OperandSize::S32);
                    // Copy the ones and zeroes in the high bits of each 64-bit
                    // lane to the low bits of each 64-bit lane.
                    masm.asm.xmm_vpshuf_rr(
                        scratch.inner(),
                        scratch.writable(),
                        0b11_11_01_01,
                        OperandSize::S32,
                    );
                    // Flip the bits in lanes that were negative in `src` and leave
                    // the positive lanes as they are. Positive lanes will have a
                    // zero mask in `scratch` so xor doesn't affect them.
                    masm.asm.xmm_vpxor_rrr(src, scratch.inner(), dst);
                    // Subtract the mask from the results of xor which will
                    // complete the two's complement for lanes which were negative.
                    masm.asm
                        .xmm_vpsub_rrr(dst.to_reg(), scratch.inner(), dst, kind.lane_size());
                });
            }
            V128AbsKind::F32x4 | V128AbsKind::F64x2 => {
                self.with_scratch::<FloatScratch, _>(|masm, scratch| {
                    // Create a mask of all ones.
                    masm.asm.xmm_vpcmpeq_rrr(
                        scratch.writable(),
                        scratch.inner(),
                        scratch.inner(),
                        kind.lane_size(),
                    );
                    // Right shift the mask so each lane is a single zero followed
                    // by all ones.
                    masm.asm.xmm_vpsrl_rri(
                        scratch.inner(),
                        scratch.writable(),
                        0x1,
                        kind.lane_size(),
                    );
                    // Use the mask to zero the sign bit in each lane which will
                    // make the float value positive.
                    masm.asm
                        .xmm_vandp_rrr(src, scratch.inner(), dst, kind.lane_size());
                });
            }
        }
        Ok(())
    }

    fn v128_neg(&mut self, op: WritableReg, kind: V128NegKind) -> Result<()> {
        self.ensure_has_avx()?;

        match kind {
            V128NegKind::I8x16 | V128NegKind::I16x8 | V128NegKind::I32x4 | V128NegKind::I64x2 => {
                self.with_scratch::<FloatScratch, _>(|masm, tmp| {
                    masm.v128_xor(tmp.inner(), tmp.inner(), tmp.writable())?;
                    masm.v128_sub(tmp.inner(), op.to_reg(), op, kind.into())?;
                    anyhow::Ok(())
                })?;
            }
            V128NegKind::F32x4 | V128NegKind::F64x2 => {
                self.with_scratch::<FloatScratch, _>(|masm, tmp| {
                    // Create a mask of all 1s.
                    masm.asm.xmm_vpcmpeq_rrr(
                        tmp.writable(),
                        tmp.inner(),
                        tmp.inner(),
                        kind.lane_size(),
                    );
                    // Left shift the lanes in the mask so only the sign bit in the
                    // mask is set to 1.
                    masm.asm.xmm_vpsll_rri(
                        tmp.inner(),
                        tmp.writable(),
                        (kind.lane_size().num_bits() - 1) as u32,
                        kind.lane_size(),
                    );
                    // Use the mask to flip the sign bit.
                    masm.asm
                        .xmm_vxorp_rrr(op.to_reg(), tmp.inner(), op, kind.lane_size());
                });
            }
        }
        Ok(())
    }

    fn v128_shift(
        &mut self,
        context: &mut CodeGenContext<Emission>,
        lane_width: OperandSize,
        kind: ShiftKind,
    ) -> Result<()> {
        self.ensure_has_avx()?;
        let shift_amount = context.pop_to_reg(self, None)?.reg;
        let operand = context.pop_to_reg(self, None)?.reg;
        let amount_mask = lane_width.num_bits() - 1;

        self.and(
            writable!(shift_amount),
            shift_amount,
            RegImm::i32(amount_mask as i32),
            OperandSize::S32,
        )?;

        self.with_scratch::<IntScratch, _>(|masm, tmp| {
            masm.with_scratch::<FloatScratch, _>(|masm, tmp_xmm| {
                let move_to_tmp_xmm = |this: &mut Self| {
                    this.asm
                        .avx_gpr_to_xmm(shift_amount, tmp_xmm.writable(), OperandSize::S32);
                };

                // A helper for deciding between `vpsllw` and `vpsrlw` in
                // `shift_i8x16`.
                enum Direction {
                    Left,
                    Right,
                }

                let shift_i8x16 = |this: &mut Self, masks: &'static [u8], direction: Direction| {
                    // The case for i8x16 is a little bit trickier because x64 doesn't provide a 8bit
                    // shift instruction. Instead, we shift as 16bits, and then mask the bits in the
                    // 8bits lane, for example (with 2 8bits lanes):
                    // - Before shifting:
                    // 01001101 11101110
                    // - shifting by 2 left:
                    // 00110111 10111000
                    //       ^^_ these bits come from the previous byte, and need to be masked.
                    // - The mask:
                    // 11111100 11111111
                    // - After masking:
                    // 00110100 10111000
                    //
                    // The mask is loaded from a well known memory, depending on the shift amount.

                    this.asm
                        .avx_gpr_to_xmm(shift_amount, tmp_xmm.writable(), OperandSize::S32);

                    // Perform the 16-bit shift.
                    match direction {
                        Direction::Left => this.asm.xmm_vpsll_rrr(
                            operand,
                            tmp_xmm.inner(),
                            writable!(operand),
                            OperandSize::S16,
                        ),
                        Direction::Right => this.asm.xmm_vpsrl_rrr(
                            operand,
                            tmp_xmm.inner(),
                            writable!(operand),
                            OperandSize::S16,
                        ),
                    }

                    // Get a handle to the masks array constant.
                    let masks_addr = this.asm.add_constant(masks);

                    // Load the masks array effective address into the tmp register.
                    this.asm.lea(&masks_addr, tmp.writable(), OperandSize::S64);

                    // Compute the offset of the mask that we need to use. This is shift_amount * 16 ==
                    // shift_amount << 4.
                    this.asm
                        .shift_ir(4, writable!(shift_amount), ShiftKind::Shl, OperandSize::S32);

                    // Load the mask to tmp_xmm.
                    this.asm.xmm_vmovdqu_mr(
                        &Address::ImmRegRegShift {
                            simm32: 0,
                            base: tmp.inner(),
                            index: shift_amount,
                            shift: 0,
                        },
                        tmp_xmm.writable(),
                        MemFlags::trusted(),
                    );

                    // Mask unwanted bits from operand.
                    this.asm
                        .xmm_vpand_rrr(tmp_xmm.inner(), operand, writable!(operand));
                };

                let i64x2_shr_s = |this: &mut Self,
                                   context: &mut CodeGenContext<Emission>|
                 -> Result<()> {
                    const SIGN_MASK: u128 = 0x8000000000000000_8000000000000000;

                    // AVX doesn't have an instruction for i64x2 signed right shift. Instead we use the
                    // following formula (from hacker's delight 2-7), where x is the value and n the shift
                    // amount, for each lane:
                    // t = (1 << 63) >> n; ((x >> n) ^ t) - t

                    // We need an extra scratch register:
                    let tmp_xmm2 = context.any_fpr(this)?;

                    this.asm
                        .avx_gpr_to_xmm(shift_amount, tmp_xmm.writable(), OperandSize::S32);

                    let cst = this.asm.add_constant(&SIGN_MASK.to_le_bytes());

                    this.asm
                        .xmm_vmovdqu_mr(&cst, writable!(tmp_xmm2), MemFlags::trusted());
                    this.asm.xmm_vpsrl_rrr(
                        tmp_xmm2,
                        tmp_xmm.inner(),
                        writable!(tmp_xmm2),
                        OperandSize::S64,
                    );
                    this.asm.xmm_vpsrl_rrr(
                        operand,
                        tmp_xmm.inner(),
                        writable!(operand),
                        OperandSize::S64,
                    );
                    this.asm
                        .xmm_vpxor_rrr(operand, tmp_xmm2, writable!(operand));
                    this.asm
                        .xmm_vpsub_rrr(operand, tmp_xmm2, writable!(operand), OperandSize::S64);

                    context.free_reg(tmp_xmm2);

                    Ok(())
                };

                let i8x16_shr_s = |this: &mut Self,
                                   context: &mut CodeGenContext<Emission>|
                 -> Result<()> {
                    // Since the x86 instruction set does not have an 8x16 shift instruction and the
                    // approach used for `ishl` and `ushr` cannot be easily used (the masks do not
                    // preserve the sign), we use a different approach here: separate the low and
                    // high lanes, shift them separately, and merge them into the final result.
                    //
                    // Visually, this looks like the following, where `src.i8x16 = [s0, s1, ...,
                    // s15]:
                    //
                    //   lo.i16x8 = [(s0, s0), (s1, s1), ..., (s7, s7)]
                    //   shifted_lo.i16x8 = shift each lane of `low`
                    //   hi.i16x8 = [(s8, s8), (s9, s9), ..., (s15, s15)]
                    //   shifted_hi.i16x8 = shift each lane of `high`
                    //   result = [s0'', s1'', ..., s15'']

                    // In order for `packsswb` later to only use the high byte of each
                    // 16x8 lane, we shift right an extra 8 bits, relying on `psraw` to
                    // fill in the upper bits appropriately.
                    this.asm
                        .add_ir(8, writable!(shift_amount), OperandSize::S32);
                    this.asm
                        .avx_gpr_to_xmm(shift_amount, tmp_xmm.writable(), OperandSize::S32);

                    let tmp_lo = context.any_fpr(this)?;
                    let tmp_hi = context.any_fpr(this)?;

                    // Extract lower and upper bytes.
                    this.asm
                        .xmm_vpunpckl_rrr(operand, operand, writable!(tmp_lo), OperandSize::S8);
                    this.asm
                        .xmm_vpunpckh_rrr(operand, operand, writable!(tmp_hi), OperandSize::S8);

                    // Perform 16bit right shift of upper and lower bytes.
                    this.asm.xmm_vpsra_rrr(
                        tmp_lo,
                        tmp_xmm.inner(),
                        writable!(tmp_lo),
                        OperandSize::S16,
                    );
                    this.asm.xmm_vpsra_rrr(
                        tmp_hi,
                        tmp_xmm.inner(),
                        writable!(tmp_hi),
                        OperandSize::S16,
                    );

                    // Merge lower and upper bytes back.
                    this.asm
                        .xmm_vpackss_rrr(tmp_lo, tmp_hi, writable!(operand), OperandSize::S8);

                    context.free_reg(tmp_lo);
                    context.free_reg(tmp_hi);

                    Ok(())
                };

                match (lane_width, kind) {
                    // shl
                    (OperandSize::S8, ShiftKind::Shl) => {
                        shift_i8x16(masm, &I8X16_ISHL_MASKS, Direction::Left)
                    }
                    (OperandSize::S16, ShiftKind::Shl) => {
                        move_to_tmp_xmm(masm);
                        masm.asm.xmm_vpsll_rrr(
                            operand,
                            tmp_xmm.inner(),
                            writable!(operand),
                            OperandSize::S16,
                        );
                    }
                    (OperandSize::S32, ShiftKind::Shl) => {
                        move_to_tmp_xmm(masm);
                        masm.asm.xmm_vpsll_rrr(
                            operand,
                            tmp_xmm.inner(),
                            writable!(operand),
                            OperandSize::S32,
                        );
                    }
                    (OperandSize::S64, ShiftKind::Shl) => {
                        move_to_tmp_xmm(masm);
                        masm.asm.xmm_vpsll_rrr(
                            operand,
                            tmp_xmm.inner(),
                            writable!(operand),
                            OperandSize::S64,
                        );
                    }
                    // shr_u
                    (OperandSize::S8, ShiftKind::ShrU) => {
                        shift_i8x16(masm, &I8X16_USHR_MASKS, Direction::Right)
                    }
                    (OperandSize::S16, ShiftKind::ShrU) => {
                        move_to_tmp_xmm(masm);
                        masm.asm.xmm_vpsrl_rrr(
                            operand,
                            tmp_xmm.inner(),
                            writable!(operand),
                            OperandSize::S16,
                        );
                    }
                    (OperandSize::S32, ShiftKind::ShrU) => {
                        move_to_tmp_xmm(masm);
                        masm.asm.xmm_vpsrl_rrr(
                            operand,
                            tmp_xmm.inner(),
                            writable!(operand),
                            OperandSize::S32,
                        );
                    }
                    (OperandSize::S64, ShiftKind::ShrU) => {
                        move_to_tmp_xmm(masm);
                        masm.asm.xmm_vpsrl_rrr(
                            operand,
                            tmp_xmm.inner(),
                            writable!(operand),
                            OperandSize::S64,
                        );
                    }
                    // shr_s
                    (OperandSize::S8, ShiftKind::ShrS) => i8x16_shr_s(masm, context)?,
                    (OperandSize::S16, ShiftKind::ShrS) => {
                        move_to_tmp_xmm(masm);
                        masm.asm.xmm_vpsra_rrr(
                            operand,
                            tmp_xmm.inner(),
                            writable!(operand),
                            OperandSize::S16,
                        );
                    }
                    (OperandSize::S32, ShiftKind::ShrS) => {
                        move_to_tmp_xmm(masm);
                        masm.asm.xmm_vpsra_rrr(
                            operand,
                            tmp_xmm.inner(),
                            writable!(operand),
                            OperandSize::S32,
                        );
                    }
                    (OperandSize::S64, ShiftKind::ShrS) => i64x2_shr_s(masm, context)?,

                    _ => bail!(CodeGenError::invalid_operand_combination()),
                }

                Ok(())
            })
        })?;

        context.free_reg(shift_amount);
        context
            .stack
            .push(TypedReg::new(WasmValType::V128, operand).into());
        Ok(())
    }

    fn v128_q15mulr_sat_s(
        &mut self,
        lhs: Reg,
        rhs: Reg,
        dst: WritableReg,
        size: OperandSize,
    ) -> Result<()> {
        self.ensure_has_avx()?;

        self.asm.xmm_vpmulhrs_rrr(lhs, rhs, dst, size);

        // Need to handle edge case of multiplying -1 by -1 (0x8000 in Q15
        // format) because of how `vpmulhrs` handles rounding. `vpmulhrs`
        // produces 0x8000 in that case when the correct result is 0x7FFF (that
        // is, +1) so need to check if the result is 0x8000 and flip the bits
        // of the result if it is.
        let address = self.asm.add_constant(&[
            0x00, 0x80, 0x00, 0x80, 0x00, 0x80, 0x00, 0x80, 0x00, 0x80, 0x00, 0x80, 0x00, 0x80,
            0x00, 0x80,
        ]);
        self.asm
            .xmm_vpcmpeq_rrm(writable!(rhs), dst.to_reg(), &address, size);
        self.asm.xmm_vpxor_rrr(dst.to_reg(), rhs, dst);
        Ok(())
    }

    fn v128_all_true(&mut self, src: Reg, dst: WritableReg, size: OperandSize) -> Result<()> {
        self.ensure_has_avx()?;

        self.with_scratch::<FloatScratch, _>(|masm, scratch| {
            // Create a mask of all 0s.
            masm.asm
                .xmm_vpxor_rrr(scratch.inner(), scratch.inner(), scratch.writable());
            // Sets lane in `dst` to not zero if `src` lane was zero, and lane in
            // `dst` to zero if `src` lane was not zero.
            masm.asm
                .xmm_vpcmpeq_rrr(writable!(src), src, scratch.inner(), size);
            // Sets ZF if all values are zero (i.e., if all original values were not zero).
            masm.asm.xmm_vptest(src, src);
            // Set byte if ZF=1.
        });
        self.asm.setcc(IntCmpKind::Eq, dst);
        Ok(())
    }

    fn v128_bitmask(&mut self, src: Reg, dst: WritableReg, size: OperandSize) -> Result<()> {
        self.ensure_has_avx()?;

        match size {
            OperandSize::S8 => self.asm.xmm_vpmovmsk_rr(src, dst, size, OperandSize::S32),
            OperandSize::S16 => {
                // Signed conversion of 16-bit integers to 8-bit integers.
                self.asm
                    .xmm_vpackss_rrr(src, src, writable!(src), OperandSize::S8);
                // Creates a mask from each byte in `src`.
                self.asm
                    .xmm_vpmovmsk_rr(src, dst, OperandSize::S8, OperandSize::S32);
                // Removes 8 bits added as a result of the `vpackss` step.
                self.asm
                    .shift_ir(0x8, dst, ShiftKind::ShrU, OperandSize::S32);
            }
            OperandSize::S32 | OperandSize::S64 => {
                self.asm.xmm_vmovskp_rr(src, dst, size, OperandSize::S32)
            }
            _ => unimplemented!(),
        }

        Ok(())
    }

    fn v128_trunc(
        &mut self,
        context: &mut CodeGenContext<Emission>,
        kind: V128TruncKind,
    ) -> Result<()> {
        self.ensure_has_avx()?;

        let reg = writable!(context.pop_to_reg(self, None)?.reg);
        match kind {
            V128TruncKind::F32x4 | V128TruncKind::F64x2 => self.asm.xmm_vroundp_rri(
                reg.to_reg(),
                reg,
                VroundMode::TowardZero,
                kind.dst_lane_size(),
            ),
            V128TruncKind::I32x4FromF32x4S => {
                self.v128_trunc_sat_f32x4_s(reg, kind.src_lane_size(), kind.dst_lane_size())?;
            }
            V128TruncKind::I32x4FromF32x4U => {
                let temp_reg = writable!(context.any_fpr(self)?);
                self.v128_trunc_sat_f32x4_u(
                    reg,
                    temp_reg,
                    kind.src_lane_size(),
                    kind.dst_lane_size(),
                )?;
                context.free_reg(temp_reg.to_reg());
            }
            V128TruncKind::I32x4FromF64x2SZero => {
                self.v128_trunc_sat_f64x2_s_zero(reg, kind.src_lane_size())?;
            }
            V128TruncKind::I32x4FromF64x2UZero => {
                self.v128_trunc_sat_f64x2_u_zero(reg, kind.src_lane_size(), kind.dst_lane_size())?;
            }
        }

        context.stack.push(TypedReg::v128(reg.to_reg()).into());
        Ok(())
    }

    fn v128_min(
        &mut self,
        src1: Reg,
        src2: Reg,
        dst: WritableReg,
        kind: V128MinKind,
    ) -> Result<()> {
        self.ensure_has_avx()?;

        match kind {
            V128MinKind::I8x16S
            | V128MinKind::I8x16U
            | V128MinKind::I16x8S
            | V128MinKind::I16x8U
            | V128MinKind::I32x4S
            | V128MinKind::I32x4U => {
                match kind {
                    V128MinKind::I8x16S => {
                        self.asm.xmm_vpmins_rrr(dst, src1, src2, OperandSize::S8)
                    }
                    V128MinKind::I8x16U => {
                        self.asm.xmm_vpminu_rrr(dst, src1, src2, OperandSize::S8)
                    }
                    V128MinKind::I16x8S => {
                        self.asm.xmm_vpmins_rrr(dst, src1, src2, OperandSize::S16)
                    }
                    V128MinKind::I16x8U => {
                        self.asm.xmm_vpminu_rrr(dst, src1, src2, OperandSize::S16)
                    }
                    V128MinKind::I32x4S => {
                        self.asm.xmm_vpmins_rrr(dst, src1, src2, OperandSize::S32)
                    }
                    V128MinKind::I32x4U => {
                        self.asm.xmm_vpminu_rrr(dst, src1, src2, OperandSize::S32)
                    }
                    _ => unreachable!(),
                };
            }
            V128MinKind::F32x4 | V128MinKind::F64x2 => {
                self.with_scratch::<FloatScratch, _>(|masm, scratch| {
                    // Handling +0 and -0 as well as NaN values are not commutative
                    // when using `vminp` so we have to compensate.
                    // Perform two comparison operations with the operands swapped
                    // and OR the result to propagate 0 (positive and negative) and
                    // NaN.
                    masm.asm
                        .xmm_vminp_rrr(src1, src2, scratch.writable(), kind.lane_size());
                    masm.asm.xmm_vminp_rrr(src2, src1, dst, kind.lane_size());
                    // Use a single OR instruction to set the sign bit if either
                    // result has the sign bit set to correctly propagate -0.
                    masm.asm
                        .xmm_vorp_rrr(dst.to_reg(), scratch.inner(), dst, kind.lane_size());
                });
                // Set lanes with NaN to all 1s.
                self.asm.xmm_vcmpp_rrr(
                    writable!(src2),
                    src2,
                    dst.to_reg(),
                    kind.lane_size(),
                    VcmpKind::Unord,
                );
                // Doesn't change non-NaN values. For NaN values, sets all bits.
                self.asm
                    .xmm_vorp_rrr(src2, dst.to_reg(), dst, kind.lane_size());
                self.canonicalize_nans(writable!(src2), dst, kind.lane_size());
            }
        }

        Ok(())
    }

    fn v128_max(
        &mut self,
        src1: Reg,
        src2: Reg,
        dst: WritableReg,
        kind: V128MaxKind,
    ) -> Result<()> {
        self.ensure_has_avx()?;

        match kind {
            V128MaxKind::I8x16S
            | V128MaxKind::I8x16U
            | V128MaxKind::I16x8S
            | V128MaxKind::I16x8U
            | V128MaxKind::I32x4S
            | V128MaxKind::I32x4U => {
                match kind {
                    V128MaxKind::I8x16S => {
                        self.asm.xmm_vpmaxs_rrr(dst, src1, src2, OperandSize::S8)
                    }
                    V128MaxKind::I8x16U => {
                        self.asm.xmm_vpmaxu_rrr(dst, src1, src2, OperandSize::S8)
                    }
                    V128MaxKind::I16x8S => {
                        self.asm.xmm_vpmaxs_rrr(dst, src1, src2, OperandSize::S16)
                    }
                    V128MaxKind::I16x8U => {
                        self.asm.xmm_vpmaxu_rrr(dst, src1, src2, OperandSize::S16)
                    }
                    V128MaxKind::I32x4S => {
                        self.asm.xmm_vpmaxs_rrr(dst, src1, src2, OperandSize::S32)
                    }
                    V128MaxKind::I32x4U => {
                        self.asm.xmm_vpmaxu_rrr(dst, src1, src2, OperandSize::S32)
                    }
                    _ => unreachable!(),
                };
            }
            V128MaxKind::F32x4 | V128MaxKind::F64x2 => {
                self.with_scratch::<FloatScratch, _>(|masm, scratch| {
                    // Handling +0 and -0 as well as NaN values are not commutative
                    // when using `vmaxp` so we have to compensate.
                    // Perform two comparison operations with the operands swapped
                    // so we can propagate 0 (positive and negative) and NaNs
                    // correctly.

                    masm.asm
                        .xmm_vmaxp_rrr(src1, src2, scratch.writable(), kind.lane_size());
                    masm.asm.xmm_vmaxp_rrr(src2, src1, dst, kind.lane_size());
                    // This combination of XOR, OR, and SUB will set the sign bit
                    // on a 0 result to the correct value for a max operation.
                    masm.asm
                        .xmm_vxorp_rrr(dst.to_reg(), scratch.inner(), dst, kind.lane_size());
                    masm.asm.xmm_vorp_rrr(
                        dst.to_reg(),
                        scratch.inner(),
                        writable!(src2),
                        kind.lane_size(),
                    );
                });
                self.asm
                    .xmm_vsub_rrr(src2, dst.to_reg(), dst, kind.lane_size());
                // Set lanes of NaN values to 1.
                self.asm.xmm_vcmpp_rrr(
                    writable!(src2),
                    src2,
                    src2,
                    kind.lane_size(),
                    VcmpKind::Unord,
                );
                self.canonicalize_nans(writable!(src2), dst, kind.lane_size());
            }
        }
        Ok(())
    }

    fn v128_extmul(
        &mut self,
        context: &mut CodeGenContext<Emission>,
        kind: V128ExtMulKind,
    ) -> Result<()> {
        self.ensure_has_avx()?;

        // The implementation for extmul is not optimized; for simplicity's sake, we simply perform
        // an extension followed by a multiplication using already implemented primitives.

        let src1 = context.pop_to_reg(self, None)?;
        let src2 = context.pop_to_reg(self, None)?;

        let ext_kind = kind.into();
        self.v128_extend(src1.reg, writable!(src1.reg), ext_kind)?;
        self.v128_extend(src2.reg, writable!(src2.reg), ext_kind)?;

        context.stack.push(src2.into());
        context.stack.push(src1.into());

        self.v128_mul(context, kind.into())
    }

    fn v128_extadd_pairwise(
        &mut self,
        src: Reg,
        dst: WritableReg,
        kind: V128ExtAddKind,
    ) -> Result<()> {
        self.ensure_has_avx()?;

        match kind {
            V128ExtAddKind::I8x16S => {
                self.with_scratch::<FloatScratch, _>(|masm, scratch| {
                    // Use `vpmaddubsw` with a vector of 16 8-bit 1's which will
                    // sign extend `src` to 16 bits and add adjacent words.
                    // Need to supply constant as first operand since first operand
                    // is treated as unsigned and the second operand is signed.
                    let mask = masm.asm.add_constant(&[1; 16]);
                    masm.asm.xmm_mov_mr(
                        &mask,
                        scratch.writable(),
                        OperandSize::S128,
                        MemFlags::trusted(),
                    );
                    masm.asm.xmm_vpmaddubsw_rrr(scratch.inner(), src, dst);
                });
            }
            V128ExtAddKind::I8x16U => {
                // Same approach as the signed variant but treat `src` as
                // unsigned instead of signed by passing it as the first
                // operand.
                let mask = self.asm.add_constant(&[1; 16]);
                self.asm.xmm_vpmaddubsw_rmr(src, &mask, dst);
            }
            V128ExtAddKind::I16x8S => {
                // Similar approach to the two variants above. The vector is 8
                // lanes of 16-bit 1's and `vpmaddwd` treats both operands as
                // signed.
                let mask = self
                    .asm
                    .add_constant(&[1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0]);
                self.asm.xmm_vpmaddwd_rmr(src, &mask, dst);
            }
            V128ExtAddKind::I16x8U => {
                // Similar approach as the signed variant.
                // `vpmaddwd` operates on signed integers and the operand is
                // unsigned so the operand needs to be converted to a signed
                // format and than that process needs to be reversed after
                // `vpmaddwd`.
                // Flip the sign bit for 8 16-bit lanes.
                let xor_mask = self.asm.add_constant(&[
                    0x00, 0x80, 0x00, 0x80, 0x00, 0x80, 0x00, 0x80, 0x00, 0x80, 0x00, 0x80, 0x00,
                    0x80, 0x00, 0x80,
                ]);
                self.asm.xmm_vpxor_rmr(src, &xor_mask, dst);

                let madd_mask = self
                    .asm
                    .add_constant(&[1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0]);
                self.asm.xmm_vpmaddwd_rmr(dst.to_reg(), &madd_mask, dst);

                // Reverse the XOR. The XOR effectively subtracts 32,768 from
                // both pairs that are added together so 65,536 (0x10000)
                // needs to be added to 4 lanes of 32-bit values.
                let add_mask = self
                    .asm
                    .add_constant(&[0, 0, 1, 0, 0, 0, 1, 0, 0, 0, 1, 0, 0, 0, 1, 0]);
                self.asm
                    .xmm_vpadd_rmr(dst.to_reg(), &add_mask, dst, OperandSize::S32);
            }
        }
        Ok(())
    }

    fn v128_dot(&mut self, lhs: Reg, rhs: Reg, dst: WritableReg) -> Result<()> {
        self.ensure_has_avx()?;
        self.asm.xmm_vpmaddwd_rrr(lhs, rhs, dst);
        Ok(())
    }

    fn v128_popcnt(&mut self, context: &mut CodeGenContext<Emission>) -> Result<()> {
        self.ensure_has_avx()?;

        let reg = writable!(context.pop_to_reg(self, None)?.reg);

        // This works by using a lookup table to determine the count of bits
        // set in the upper 4 bits and lower 4 bits separately and then adding
        // the counts.

        // A mask to zero out the upper 4 bits in each lane.
        let address = self.asm.add_constant(&[
            0x0F, 0x0F, 0x0F, 0x0F, 0x0F, 0x0F, 0x0F, 0x0F, 0x0F, 0x0F, 0x0F, 0x0F, 0x0F, 0x0F,
            0x0F, 0x0F,
        ]);

        self.with_scratch::<FloatScratch, _>(|masm, scratch| {
            // Zero out the upper 4 bits of each lane.
            masm.asm
                .xmm_vpand_rrm(reg.to_reg(), &address, scratch.writable());
            // Right shift bytes in input by 4 bits to put the upper 4 bits in the
            // lower 4 bits.
            masm.asm
                .xmm_vpsrl_rri(reg.to_reg(), reg, 0x4, OperandSize::S16);
            // Zero out the upper 4 bits of each shifted lane.
            masm.asm.xmm_vpand_rrm(reg.to_reg(), &address, reg);

            // Write a lookup table of 4 bit values to number of bits set to a
            // register so we only perform the memory read once.
            // Index (hex) | Value (binary) | Population Count
            // 0x0         | 0000          | 0
            // 0x1         | 0001          | 1
            // 0x2         | 0010          | 1
            // 0x3         | 0011          | 2
            // 0x4         | 0100          | 1
            // 0x5         | 0101          | 2
            // 0x6         | 0110          | 2
            // 0x7         | 0111          | 3
            // 0x8         | 1000          | 1
            // 0x9         | 1001          | 2
            // 0xA         | 1010          | 2
            // 0xB         | 1011          | 3
            // 0xC         | 1100          | 2
            // 0xD         | 1101          | 3
            // 0xE         | 1110          | 3
            // 0xF         | 1111          | 4
            let address = masm.asm.add_constant(&[
                0x0, 0x1, 0x1, 0x2, 0x1, 0x2, 0x2, 0x3, 0x1, 0x2, 0x2, 0x3, 0x2, 0x3, 0x3, 0x4,
            ]);
            let reg2 = writable!(context.any_fpr(masm)?);
            masm.asm
                .xmm_mov_mr(&address, reg2, OperandSize::S128, MemFlags::trusted());
            // Use the upper 4 bits as an index into the lookup table.
            masm.asm.xmm_vpshufb_rrr(reg, reg2.to_reg(), reg.to_reg());
            // Use the lower 4 bits as an index into the lookup table.
            masm.asm
                .xmm_vpshufb_rrr(scratch.writable(), reg2.to_reg(), scratch.inner());
            context.free_reg(reg2.to_reg());

            // Add the counts of the upper 4 bits and the lower 4 bits to get the
            // total number of bits set.
            masm.asm
                .xmm_vpadd_rrr(reg.to_reg(), scratch.inner(), reg, OperandSize::S8);
            anyhow::Ok(())
        })?;

        context.stack.push(TypedReg::v128(reg.to_reg()).into());
        Ok(())
    }

    fn v128_avgr(&mut self, lhs: Reg, rhs: Reg, dst: WritableReg, size: OperandSize) -> Result<()> {
        self.ensure_has_avx()?;
        self.asm.xmm_vpavg_rrr(lhs, rhs, dst, size);
        Ok(())
    }

    fn v128_div(&mut self, lhs: Reg, rhs: Reg, dst: WritableReg, size: OperandSize) -> Result<()> {
        self.ensure_has_avx()?;
        self.asm.xmm_vdivp_rrr(lhs, rhs, dst, size);
        Ok(())
    }

    fn v128_sqrt(&mut self, src: Reg, dst: WritableReg, size: OperandSize) -> Result<()> {
        self.ensure_has_avx()?;
        self.asm.xmm_vsqrtp_rr(src, dst, size);
        Ok(())
    }

    fn v128_ceil(&mut self, src: Reg, dst: WritableReg, size: OperandSize) -> Result<()> {
        self.ensure_has_avx()?;
        self.asm
            .xmm_vroundp_rri(src, dst, VroundMode::TowardPositiveInfinity, size);
        Ok(())
    }

    fn v128_floor(&mut self, src: Reg, dst: WritableReg, size: OperandSize) -> Result<()> {
        self.ensure_has_avx()?;
        self.asm
            .xmm_vroundp_rri(src, dst, VroundMode::TowardNegativeInfinity, size);
        Ok(())
    }

    fn v128_nearest(&mut self, src: Reg, dst: WritableReg, size: OperandSize) -> Result<()> {
        self.ensure_has_avx()?;
        self.asm
            .xmm_vroundp_rri(src, dst, VroundMode::TowardNearest, size);
        Ok(())
    }

    fn v128_pmin(&mut self, lhs: Reg, rhs: Reg, dst: WritableReg, size: OperandSize) -> Result<()> {
        self.ensure_has_avx()?;
        // Reverse operands since Wasm specifies returning the first operand if
        // either operand is NaN while x86 returns the second operand.
        self.asm.xmm_vminp_rrr(rhs, lhs, dst, size);
        Ok(())
    }

    fn v128_pmax(&mut self, lhs: Reg, rhs: Reg, dst: WritableReg, size: OperandSize) -> Result<()> {
        self.ensure_has_avx()?;
        // Reverse operands since Wasm specifies returning the first operand if
        // either operand is NaN while x86 returns the second operand.
        self.asm.xmm_vmaxp_rrr(rhs, lhs, dst, size);
        Ok(())
    }
}

impl MacroAssembler {
    /// Create an x64 MacroAssembler.
    pub fn new(
        ptr_size: impl PtrSize,
        shared_flags: settings::Flags,
        isa_flags: x64_settings::Flags,
    ) -> Result<Self> {
        let ptr_type: WasmValType = ptr_type_from_ptr_size(ptr_size.size());

        Ok(Self {
            sp_offset: 0,
            sp_max: 0,
            stack_max_use_add: None,
            asm: Assembler::new(shared_flags.clone(), isa_flags.clone()),
            flags: isa_flags,
            shared_flags,
            ptr_size: ptr_type.try_into()?,
            scratch_scope: RegAlloc::from(scratch_gpr_bitset(), scratch_fpr_bitset()),
        })
    }

    /// Add the maximum stack used to a register, recording an obligation to update the
    /// add-with-immediate instruction emitted to use the real stack max when the masm is being
    /// finalized.
    fn add_stack_max(&mut self, reg: Reg) {
        assert!(self.stack_max_use_add.is_none());
        let patch = PatchableAddToReg::new(reg, OperandSize::S64, &mut self.asm);
        self.stack_max_use_add.replace(patch);
    }

    fn ensure_has_avx(&self) -> Result<()> {
        anyhow::ensure!(self.flags.has_avx(), CodeGenError::UnimplementedForNoAvx);
        Ok(())
    }

    fn ensure_has_avx2(&self) -> Result<()> {
        anyhow::ensure!(self.flags.has_avx2(), CodeGenError::UnimplementedForNoAvx2);
        Ok(())
    }

    fn ensure_has_avx512vl(&self) -> Result<()> {
        anyhow::ensure!(
            self.flags.has_avx512vl(),
            CodeGenError::UnimplementedForNoAvx512VL
        );
        Ok(())
    }

    fn ensure_has_avx512dq(&self) -> Result<()> {
        anyhow::ensure!(
            self.flags.has_avx512dq(),
            CodeGenError::UnimplementedForNoAvx512DQ
        );
        Ok(())
    }

    fn increment_sp(&mut self, bytes: u32) {
        self.sp_offset += bytes;

        // NOTE: we use `max` here to track the largest stack allocation in `sp_max`. Once we have
        // seen the entire function, this value will represent the maximum size for the stack
        // frame.
        self.sp_max = self.sp_max.max(self.sp_offset);
    }

    fn decrement_sp(&mut self, bytes: u32) {
        assert!(
            self.sp_offset >= bytes,
            "sp offset = {}; bytes = {}",
            self.sp_offset,
            bytes
        );
        self.sp_offset -= bytes;
    }

    fn load_constant(&mut self, constant: &I, dst: WritableReg, size: OperandSize) -> Result<()> {
        match constant {
            I::I32(v) => Ok(self.asm.mov_ir(*v as u64, dst, size)),
            I::I64(v) => Ok(self.asm.mov_ir(*v, dst, size)),
            I::F32(_) => Ok(self.asm.load_fp_const(dst, &constant.to_bytes(), size)),
            I::F64(_) => Ok(self.asm.load_fp_const(dst, &constant.to_bytes(), size)),
            I::V128(_) => Ok(self.asm.load_fp_const(dst, &constant.to_bytes(), size)),
        }
    }

    /// A common implementation for zero-extend stack loads.
    fn load_impl(
        &mut self,
        src: Address,
        dst: WritableReg,
        size: OperandSize,
        flags: MemFlags,
    ) -> Result<()> {
        if dst.to_reg().is_int() {
            let ext = size.extend_to::<Zero>(OperandSize::S64);
            self.asm.movzx_mr(&src, dst, ext, flags);
        } else {
            self.asm.xmm_mov_mr(&src, dst, size, flags);
        }

        Ok(())
    }

    /// A common implementation for stack stores.
    fn store_impl(
        &mut self,
        src: RegImm,
        dst: Address,
        size: OperandSize,
        flags: MemFlags,
    ) -> Result<()> {
        let _ = match src {
            RegImm::Imm(imm) => match imm {
                I::I32(v) => self.asm.mov_im(v as i32, &dst, size, flags),
                I::I64(v) => match v.try_into() {
                    Ok(v) => self.asm.mov_im(v, &dst, size, flags),
                    Err(_) => {
                        // If the immediate doesn't sign extend, use a scratch
                        // register.
                        self.with_scratch::<IntScratch, _>(|masm, scratch| {
                            masm.asm.mov_ir(v, scratch.writable(), size);
                            masm.asm.mov_rm(scratch.inner(), &dst, size, flags);
                        });
                    }
                },
                I::F32(v) => {
                    let addr = self.asm.add_constant(v.to_le_bytes().as_slice());
                    self.with_scratch::<FloatScratch, _>(|masm, float_scratch| {
                        // Always trusted, since we are loading the constant from
                        // the constant pool.
                        masm.asm.xmm_mov_mr(
                            &addr,
                            float_scratch.writable(),
                            size,
                            MemFlags::trusted(),
                        );
                        masm.asm
                            .xmm_mov_rm(float_scratch.inner(), &dst, size, flags);
                    });
                }
                I::F64(v) => {
                    let addr = self.asm.add_constant(v.to_le_bytes().as_slice());

                    self.with_scratch::<FloatScratch, _>(|masm, float_scratch| {
                        // Similar to above, always trusted since we are loading the
                        // constant from the constant pool.
                        masm.asm.xmm_mov_mr(
                            &addr,
                            float_scratch.writable(),
                            size,
                            MemFlags::trusted(),
                        );
                        masm.asm
                            .xmm_mov_rm(float_scratch.inner(), &dst, size, flags);
                    });
                }
                I::V128(v) => {
                    let addr = self.asm.add_constant(v.to_le_bytes().as_slice());
                    self.with_scratch::<FloatScratch, _>(|masm, vector_scratch| {
                        // Always trusted, since we are loading the constant from
                        // the constant pool.
                        masm.asm.xmm_mov_mr(
                            &addr,
                            vector_scratch.writable(),
                            size,
                            MemFlags::trusted(),
                        );
                        masm.asm
                            .xmm_mov_rm(vector_scratch.inner(), &dst, size, flags);
                    });
                }
            },
            RegImm::Reg(reg) => {
                if reg.is_int() {
                    self.asm.mov_rm(reg, &dst, size, flags);
                } else {
                    self.asm.xmm_mov_rm(reg, &dst, size, flags);
                }
            }
        };
        Ok(())
    }

    fn ensure_two_argument_form(dst: &Reg, lhs: &Reg) -> Result<()> {
        if dst != lhs {
            Err(anyhow!(CodeGenError::invalid_two_arg_form()))
        } else {
            Ok(())
        }
    }

    /// The mask to use when performing a `vpshuf` operation for a 64-bit splat.
    fn vpshuf_mask_for_64_bit_splats() -> u8 {
        // Results in the first 4 bytes and second 4 bytes being
        // swapped and then the swapped bytes being copied.
        // [d0, d1, d2, d3, d4, d5, d6, d7, ...] yields
        // [d4, d5, d6, d7, d0, d1, d2, d3, d4, d5, d6, d7, d0, d1, d2, d3].
        0b01_00_01_00
    }

    fn v128_trunc_sat_f32x4_s(
        &mut self,
        reg: WritableReg,
        src_lane_size: OperandSize,
        dst_lane_size: OperandSize,
    ) -> Result<()> {
        self.with_scratch::<FloatScratch, _>(|masm, scratch| {
            // Create a mask to handle NaN values (1 for not NaN, 0 for
            // NaN).
            masm.asm.xmm_vcmpp_rrr(
                scratch.writable(),
                reg.to_reg(),
                reg.to_reg(),
                src_lane_size,
                VcmpKind::Eq,
            );
            // Zero out any NaN values.
            masm.asm
                .xmm_vandp_rrr(reg.to_reg(), scratch.inner(), reg, src_lane_size);
            // Create a mask for the sign bits.
            masm.asm
                .xmm_vpxor_rrr(scratch.inner(), reg.to_reg(), scratch.writable());
            // Convert floats to integers.
            masm.asm.xmm_vcvt_rr(reg.to_reg(), reg, VcvtKind::F32ToI32);
            // Apply sign mask to the converted integers.
            masm.asm
                .xmm_vpand_rrr(reg.to_reg(), scratch.inner(), scratch.writable());
            // Create a saturation mask of all 1s for negative numbers,
            // all 0s for positive numbers. The arithmetic shift will cop
            // the sign bit.
            masm.asm
                .xmm_vpsra_rri(scratch.inner(), scratch.writable(), 0x1F, dst_lane_size);
            // Combine converted integers with saturation mask.
            masm.asm.xmm_vpxor_rrr(reg.to_reg(), scratch.inner(), reg);
            Ok(())
        })
    }

    fn v128_trunc_sat_f32x4_u(
        &mut self,
        reg: WritableReg,
        temp_reg: WritableReg,
        src_lane_size: OperandSize,
        dst_lane_size: OperandSize,
    ) -> Result<()> {
        self.with_scratch::<FloatScratch, _>(|masm, scratch| {
            // Set scratch to all zeros.
            masm.asm.xmm_vxorp_rrr(
                reg.to_reg(),
                reg.to_reg(),
                scratch.writable(),
                src_lane_size,
            );
            // Clamp negative numbers to 0.
            masm.asm
                .xmm_vmaxp_rrr(reg.to_reg(), scratch.inner(), reg, src_lane_size);
            // Create a vector of all 1s.
            masm.asm.xmm_vpcmpeq_rrr(
                scratch.writable(),
                scratch.inner(),
                scratch.inner(),
                src_lane_size,
            );
            // Set scratch to 0x7FFFFFFF (max signed 32-bit integer) by
            // performing a logical shift right.
            masm.asm
                .xmm_vpsrl_rri(scratch.inner(), scratch.writable(), 0x1, src_lane_size);
            // Convert max signed int to float as a reference point for saturation.
            masm.asm
                .xmm_vcvt_rr(scratch.inner(), scratch.writable(), VcvtKind::I32ToF32);
            // Convert the floats to integers and put the results in `reg2`.
            // This is signed and not unsigned so we need to handle the
            // value for the high bit in each lane.
            masm.asm
                .xmm_vcvt_rr(reg.to_reg(), temp_reg, VcvtKind::F32ToI32);
            // Set `reg` lanes to the amount that the value in the lane
            // exceeds the maximum signed 32-bit integer.
            masm.asm
                .xmm_vsub_rrr(reg.to_reg(), scratch.inner(), reg, dst_lane_size);
            // Create mask in `scratch` for numbers that are larger than
            // the maximum signed 32-bit integer. Lanes that don't fit
            // in 32-bits ints will be 1.
            masm.asm.xmm_vcmpp_rrr(
                scratch.writable(),
                scratch.inner(),
                reg.to_reg(),
                dst_lane_size,
                VcmpKind::Le,
            );
            // Convert the excess over signed 32-bits from floats to integers.
            masm.asm.xmm_vcvt_rr(reg.to_reg(), reg, VcvtKind::F32ToI32);
            // Apply large number mask to excess values which will flip the
            // bits in any lanes that exceed signed 32-bits. Adding this
            // flipped value to the signed value will set the high bit and
            // the carry behavior will update the other bits correctly.
            masm.asm
                .xmm_vpxor_rrr(reg.to_reg(), scratch.inner(), scratch.writable());
            // Set `reg` to all 0s.
            masm.asm.xmm_vpxor_rrr(reg.to_reg(), reg.to_reg(), reg);
            // Ensure excess values are not negative by taking max b/w
            // excess values and zero.
            masm.asm
                .xmm_vpmaxs_rrr(reg, scratch.inner(), reg.to_reg(), dst_lane_size);
        });
        // Perform the addition between the signed conversion value (in
        // `reg2`) and the flipped excess value (in `reg`) to get the
        // unsigned value.
        self.asm
            .xmm_vpadd_rrr(reg.to_reg(), temp_reg.to_reg(), reg, dst_lane_size);
        Ok(())
    }

    fn v128_trunc_sat_f64x2_s_zero(
        &mut self,
        reg: WritableReg,
        src_lane_size: OperandSize,
    ) -> Result<()> {
        self.with_scratch::<FloatScratch, _>(|masm, scratch| {
            // Create a NaN mask (1s for non-NaN, 0s for NaN).
            masm.asm.xmm_vcmpp_rrr(
                scratch.writable(),
                reg.to_reg(),
                reg.to_reg(),
                src_lane_size,
                VcmpKind::Eq,
            );
            // Clamp NaN values to maximum 64-bit float that can be
            // converted to an i32.
            let address = masm.asm.add_constant(&[
                0x00, 0x00, 0xC0, 0xFF, 0xFF, 0xFF, 0xDF, 0x41, 0x00, 0x00, 0xC0, 0xFF, 0xFF, 0xFF,
                0xDF, 0x41,
            ]);
            masm.asm
                .xmm_vandp_rrm(scratch.inner(), &address, scratch.writable(), src_lane_size);
            // Handle the saturation for values too large to fit in an i32.
            masm.asm
                .xmm_vminp_rrr(reg.to_reg(), scratch.inner(), reg, src_lane_size);
            // Convert the floats to integers.
            masm.asm.xmm_vcvt_rr(reg.to_reg(), reg, VcvtKind::F64ToI32);

            Ok(())
        })
    }

    fn v128_trunc_sat_f64x2_u_zero(
        &mut self,
        reg: WritableReg,
        src_lane_size: OperandSize,
        dst_lane_size: OperandSize,
    ) -> Result<()> {
        self.with_scratch::<FloatScratch, _>(|masm, scratch| {
            // Zero out the scratch register.
            masm.asm.xmm_vxorp_rrr(
                scratch.inner(),
                scratch.inner(),
                scratch.writable(),
                src_lane_size,
            );
            // Clamp negative values to zero.
            masm.asm
                .xmm_vmaxp_rrr(reg.to_reg(), scratch.inner(), reg, src_lane_size);
            // Clamp value to maximum unsigned 32-bit integer value
            // (0x41F0000000000000).
            let address = masm.asm.add_constant(&[
                0x00, 0x00, 0xE0, 0xFF, 0xFF, 0xFF, 0xEF, 0x41, 0x00, 0x00, 0xE0, 0xFF, 0xFF, 0xFF,
                0xEF, 0x41,
            ]);
            masm.asm
                .xmm_vminp_rrm(reg.to_reg(), &address, reg, src_lane_size);
            // Truncate floating point values.
            masm.asm
                .xmm_vroundp_rri(reg.to_reg(), reg, VroundMode::TowardZero, src_lane_size);
            // Add 2^52 (doubles store 52 bits in their mantissa) to each
            // lane causing values in the lower bits to be shifted into
            // position for integer conversion.
            let address = masm.asm.add_constant(&[
                0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x30, 0x43, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
                0x30, 0x43,
            ]);
            masm.asm
                .xmm_vaddp_rrm(reg.to_reg(), &address, reg, src_lane_size);
            // Takes lanes 0 and 2 from `reg` (converted values) and lanes
            // 0 and 2 from `scratch` (zeroes) to put the converted ints in
            // the lower lanes and zeroes in the upper lanes.
            masm.asm.xmm_vshufp_rrri(
                reg.to_reg(),
                scratch.inner(),
                reg,
                0b10_00_10_00,
                dst_lane_size,
            );
            Ok(())
        })
    }

    /// Given a vector of floats where lanes with NaN values are set to all 1s
    /// in `reg` and a vector register `dst` with a mix of non-NaN values and
    /// possibly non-canonical NaN values, this canonicalize any NaNs in `dst`.
    fn canonicalize_nans(&mut self, mask: WritableReg, dst: WritableReg, size: OperandSize) {
        // Canonical NaNs do not preserve the sign bit, have the exponent bits
        // all set, and have only the high bit of the mantissa set so shift by
        // that number.
        // The mask we're producing in this step will be inverted in the next
        // step.
        let amount_to_shift = 1 + size.mantissa_bits() + 1;
        self.asm
            .xmm_vpsrl_rri(mask.to_reg(), mask, amount_to_shift as u32, size);
        // The mask will be inverted by the ANDN so non-NaN values will be all
        // 1s and NaN values will set the sign bit, exponent bits, and zero out
        // almost all of the mantissa.
        self.asm
            .xmm_vandnp_rrr(mask.to_reg(), dst.to_reg(), dst, size);
    }
}