code_translator.rs

//! This module contains the bulk of the interesting code performing the translation between
//! WebAssembly and Cranelift IR.
//!
//! The translation is done in one pass, opcode by opcode. Two main data structures are used during
//! code translations: the value stack and the control stack. The value stack mimics the execution
//! of the WebAssembly stack machine: each instruction result is pushed onto the stack and
//! instruction arguments are popped off the stack. Similarly, when encountering a control flow
//! block, it is pushed onto the control stack and popped off when encountering the corresponding
//! `End`.
//!
//! Another data structure, the translation state, records information concerning unreachable code
//! status and about if inserting a return at the end of the function is necessary.
//!
//! Some of the WebAssembly instructions need information about the environment for which they
//! are being translated:
//!
//! - the loads and stores need the memory base address;
//! - the `get_global` and `set_global` instructions depend on how the globals are implemented;
//! - `memory.size` and `memory.grow` are runtime functions;
//! - `call_indirect` has to translate the function index into the address of where this
//!    is;
//!
//! That is why `translate_function_body` takes an object having the `WasmRuntime` trait as
//! argument.
//!
//! There is extra complexity associated with translation of 128-bit SIMD instructions.
//! Wasm only considers there to be a single 128-bit vector type.  But CLIF's type system
//! distinguishes different lane configurations, so considers 8X16, 16X8, 32X4 and 64X2 to be
//! different types.  The result is that, in wasm, it's perfectly OK to take the output of (eg)
//! an `add.16x8` and use that as an operand of a `sub.32x4`, without using any cast.  But when
//! translated into CLIF, that will cause a verifier error due to the apparent type mismatch.
//!
//! This file works around that problem by liberally inserting `bitcast` instructions in many
//! places -- mostly, before the use of vector values, either as arguments to CLIF instructions
//! or as block actual parameters.  These are no-op casts which nevertheless have different
//! input and output types, and are used (mostly) to "convert" 16X8, 32X4 and 64X2-typed vectors
//! to the "canonical" type, 8X16.  Hence the functions `optionally_bitcast_vector`,
//! `bitcast_arguments`, `pop*_with_bitcast`, `canonicalise_then_jump`,
//! `canonicalise_then_br{z,nz}`, `is_non_canonical_v128` and `canonicalise_v128_values`.
//! Note that the `bitcast*` functions are occasionally used to convert to some type other than
//! 8X16, but the `canonicalise*` functions always convert to type 8X16.
//!
//! Be careful when adding support for new vector instructions.  And when adding new jumps, even
//! if they are apparently don't have any connection to vectors.  Never generate any kind of
//! (inter-block) jump directly.  Instead use `canonicalise_then_jump` and
//! `canonicalise_then_br{z,nz}`.
//!
//! The use of bitcasts is ugly and inefficient, but currently unavoidable:
//!
//! * they make the logic in this file fragile: miss out a bitcast for any reason, and there is
//!   the risk of the system failing in the verifier.  At least for debug builds.
//!
//! * in the new backends, they potentially interfere with pattern matching on CLIF -- the
//!   patterns need to take into account the presence of bitcast nodes.
//!
//! * in the new backends, they get translated into machine-level vector-register-copy
//!   instructions, none of which are actually necessary.  We then depend on the register
//!   allocator to coalesce them all out.
//!
//! * they increase the total number of CLIF nodes that have to be processed, hence slowing down
//!   the compilation pipeline.  Also, the extra coalescing work generates a slowdown.
//!
//! A better solution which would avoid all four problems would be to remove the 8X16, 16X8,
//! 32X4 and 64X2 types from CLIF and instead have a single V128 type.
//!
//! For further background see also:
//!   <https://github.com/bytecodealliance/wasmtime/issues/1147>
//!     ("Too many raw_bitcasts in SIMD code")
//!   <https://github.com/bytecodealliance/cranelift/pull/1251>
//!     ("Add X128 type to represent WebAssembly's V128 type")
//!   <https://github.com/bytecodealliance/cranelift/pull/1236>
//!     ("Relax verification to allow I8X16 to act as a default vector type")

use crate::Reachability;
use crate::bounds_checks::{BoundsCheck, bounds_check_and_compute_addr};
use crate::func_environ::{Extension, FuncEnvironment};
use crate::translate::TargetEnvironment;
use crate::translate::environ::StructFieldsVec;
use crate::translate::stack::{ControlStackFrame, ElseData};
use crate::translate::translation_utils::{
    block_with_params, blocktype_params_results, f32_translation, f64_translation,
};
use cranelift_codegen::ir::condcodes::{FloatCC, IntCC};
use cranelift_codegen::ir::immediates::Offset32;
use cranelift_codegen::ir::{
    self, AtomicRmwOp, ExceptionTag, InstBuilder, JumpTableData, MemFlags, Value, ValueLabel,
};
use cranelift_codegen::ir::{BlockArg, types::*};
use cranelift_codegen::packed_option::ReservedValue;
use cranelift_frontend::{FunctionBuilder, Variable};
use itertools::Itertools;
use smallvec::{SmallVec, ToSmallVec};
use std::collections::{HashMap, hash_map};
use std::vec::Vec;
use wasmparser::{FuncValidator, MemArg, Operator, WasmModuleResources};
use wasmtime_environ::{
    DataIndex, ElemIndex, FuncIndex, GlobalIndex, MemoryIndex, TableIndex, TagIndex, TypeConvert,
    TypeIndex, WasmHeapType, WasmRefType, WasmResult, WasmValType, wasm_unsupported,
};

/// Given a `Reachability<T>`, unwrap the inner `T` or, when unreachable, set
/// `state.reachable = false` and return.
///
/// Used in combination with calling `prepare_addr` and `prepare_atomic_addr`
/// when we can statically determine that a Wasm access will unconditionally
/// trap.
macro_rules! unwrap_or_return_unreachable_state {
    ($environ:ident, $value:expr) => {
        match $value {
            Reachability::Reachable(x) => x,
            Reachability::Unreachable => {
                $environ.stacks.reachable = false;
                return Ok(());
            }
        }
    };
}

/// Translates wasm operators into Cranelift IR instructions.
pub fn translate_operator(
    validator: &mut FuncValidator<impl WasmModuleResources>,
    op: &Operator,
    operand_types: Option<&[WasmValType]>,
    builder: &mut FunctionBuilder,
    environ: &mut FuncEnvironment<'_>,
) -> WasmResult<()> {
    log::trace!("Translating Wasm opcode: {op:?}");

    if !environ.is_reachable() {
        translate_unreachable_operator(validator, &op, builder, environ)?;
        return Ok(());
    }

    // Given that we believe the current block is reachable, the FunctionBuilder ought to agree.
    debug_assert!(!builder.is_unreachable());
    let srcloc = builder.srcloc();

    let operand_types = operand_types.unwrap_or_else(|| {
        panic!("should always have operand types available for valid, reachable ops; op = {op:?}")
    });

    // This big match treats all Wasm code operators.
    match op {
        /********************************** Locals ****************************************
         *  `get_local` and `set_local` are treated as non-SSA variables and will completely
         *  disappear in the Cranelift Code
         ***********************************************************************************/
        Operator::LocalGet { local_index } => {
            let val = builder.use_var(Variable::from_u32(*local_index));
            environ.stacks.push1(val);
            let label = ValueLabel::from_u32(*local_index);
            builder.set_val_label(val, label);
        }
        Operator::LocalSet { local_index } => {
            let mut val = environ.stacks.pop1();

            // Ensure SIMD values are cast to their default Cranelift type, I8x16.
            let ty = builder.func.dfg.value_type(val);
            if ty.is_vector() {
                val = optionally_bitcast_vector(val, I8X16, builder);
            }

            builder.def_var(Variable::from_u32(*local_index), val);
            let label = ValueLabel::from_u32(*local_index);
            builder.set_val_label(val, label);
            environ.state_slot_local_set(builder, *local_index, val);
        }
        Operator::LocalTee { local_index } => {
            let mut val = environ.stacks.peek1();

            // Ensure SIMD values are cast to their default Cranelift type, I8x16.
            let ty = builder.func.dfg.value_type(val);
            if ty.is_vector() {
                val = optionally_bitcast_vector(val, I8X16, builder);
            }

            builder.def_var(Variable::from_u32(*local_index), val);
            let label = ValueLabel::from_u32(*local_index);
            builder.set_val_label(val, label);
            environ.state_slot_local_set(builder, *local_index, val);
        }
        /********************************** Globals ****************************************
         *  `get_global` and `set_global` are handled by the environment.
         ***********************************************************************************/
        Operator::GlobalGet { global_index } => {
            let global_index = GlobalIndex::from_u32(*global_index);
            let val = environ.translate_global_get(builder, global_index)?;
            environ.stacks.push1(val);
        }
        Operator::GlobalSet { global_index } => {
            let global_index = GlobalIndex::from_u32(*global_index);
            let mut val = environ.stacks.pop1();
            // Ensure SIMD values are cast to their default Cranelift type, I8x16.
            if builder.func.dfg.value_type(val).is_vector() {
                val = optionally_bitcast_vector(val, I8X16, builder);
            }
            environ.translate_global_set(builder, global_index, val)?;
        }
        /********************************* Stack misc ***************************************
         *  `drop`, `nop`, `unreachable` and `select`.
         ***********************************************************************************/
        Operator::Drop => {
            environ.stacks.pop1();
        }
        Operator::Select => {
            let (mut arg1, mut arg2, cond) = environ.stacks.pop3();
            if builder.func.dfg.value_type(arg1).is_vector() {
                arg1 = optionally_bitcast_vector(arg1, I8X16, builder);
            }
            if builder.func.dfg.value_type(arg2).is_vector() {
                arg2 = optionally_bitcast_vector(arg2, I8X16, builder);
            }
            environ.stacks.push1(builder.ins().select(cond, arg1, arg2));
        }
        Operator::TypedSelect { ty: _ } => {
            // We ignore the explicit type parameter as it is only needed for
            // validation, which we require to have been performed before
            // translation.
            let (mut arg1, mut arg2, cond) = environ.stacks.pop3();
            if builder.func.dfg.value_type(arg1).is_vector() {
                arg1 = optionally_bitcast_vector(arg1, I8X16, builder);
            }
            if builder.func.dfg.value_type(arg2).is_vector() {
                arg2 = optionally_bitcast_vector(arg2, I8X16, builder);
            }
            environ.stacks.push1(builder.ins().select(cond, arg1, arg2));
        }
        Operator::Nop => {
            // We do nothing
        }
        Operator::Unreachable => {
            environ.trap(builder, crate::TRAP_UNREACHABLE);
            environ.stacks.reachable = false;
        }
        /***************************** Control flow blocks **********************************
         *  When starting a control flow block, we create a new `Block` that will hold the code
         *  after the block, and we push a frame on the control stack. Depending on the type
         *  of block, we create a new `Block` for the body of the block with an associated
         *  jump instruction.
         *
         *  The `End` instruction pops the last control frame from the control stack, seals
         *  the destination block (since `br` instructions targeting it only appear inside the
         *  block and have already been translated) and modify the value stack to use the
         *  possible `Block`'s arguments values.
         ***********************************************************************************/
        Operator::Block { blockty } => {
            let (params, results) = blocktype_params_results(validator, *blockty)?;
            let next = block_with_params(builder, results.clone(), environ)?;
            environ.stacks.push_block(next, params.len(), results.len());
        }
        Operator::Loop { blockty } => {
            let (params, results) = blocktype_params_results(validator, *blockty)?;
            let loop_body = block_with_params(builder, params.clone(), environ)?;
            let next = block_with_params(builder, results.clone(), environ)?;
            canonicalise_then_jump(builder, loop_body, environ.stacks.peekn(params.len()));
            environ
                .stacks
                .push_loop(loop_body, next, params.len(), results.len());

            // Pop the initial `Block` actuals and replace them with the `Block`'s
            // params since control flow joins at the top of the loop.
            environ.stacks.popn(params.len());
            environ
                .stacks
                .stack
                .extend_from_slice(builder.block_params(loop_body));

            builder.switch_to_block(loop_body);
            environ.translate_loop_header(builder)?;
        }
        Operator::If { blockty } => {
            let val = environ.stacks.pop1();

            let next_block = builder.create_block();
            let (params, results) = blocktype_params_results(validator, *blockty)?;
            let (destination, else_data) = if params.clone().eq(results.clone()) {
                // It is possible there is no `else` block, so we will only
                // allocate a block for it if/when we find the `else`. For now,
                // we if the condition isn't true, then we jump directly to the
                // destination block following the whole `if...end`. If we do end
                // up discovering an `else`, then we will allocate a block for it
                // and go back and patch the jump.
                let destination = block_with_params(builder, results.clone(), environ)?;
                let branch_inst = canonicalise_brif(
                    builder,
                    val,
                    next_block,
                    &[],
                    destination,
                    environ.stacks.peekn(params.len()),
                );
                (
                    destination,
                    ElseData::NoElse {
                        branch_inst,
                        placeholder: destination,
                    },
                )
            } else {
                // The `if` type signature is not valid without an `else` block,
                // so we eagerly allocate the `else` block here.
                let destination = block_with_params(builder, results.clone(), environ)?;
                let else_block = block_with_params(builder, params.clone(), environ)?;
                canonicalise_brif(
                    builder,
                    val,
                    next_block,
                    &[],
                    else_block,
                    environ.stacks.peekn(params.len()),
                );
                builder.seal_block(else_block);
                (destination, ElseData::WithElse { else_block })
            };

            builder.seal_block(next_block); // Only predecessor is the current block.
            builder.switch_to_block(next_block);

            // Here we append an argument to a Block targeted by an argumentless jump instruction
            // But in fact there are two cases:
            // - either the If does not have a Else clause, in that case ty = EmptyBlock
            //   and we add nothing;
            // - either the If have an Else clause, in that case the destination of this jump
            //   instruction will be changed later when we translate the Else operator.
            environ.stacks.push_if(
                destination,
                else_data,
                params.len(),
                results.len(),
                *blockty,
            );
        }
        Operator::Else => {
            let i = environ.stacks.control_stack.len() - 1;
            let reachable = environ.is_reachable();
            match environ.stacks.control_stack[i] {
                ControlStackFrame::If {
                    ref else_data,
                    head_is_reachable,
                    ref mut consequent_ends_reachable,
                    num_return_values,
                    blocktype,
                    destination,
                    ..
                } => {
                    // We finished the consequent, so record its final
                    // reachability state.
                    debug_assert!(consequent_ends_reachable.is_none());
                    *consequent_ends_reachable = Some(reachable);

                    if head_is_reachable {
                        // We have a branch from the head of the `if` to the `else`.
                        environ.stacks.reachable = true;

                        // Ensure we have a block for the `else` block (it may have
                        // already been pre-allocated, see `ElseData` for details).
                        let else_block = match *else_data {
                            ElseData::NoElse {
                                branch_inst,
                                placeholder,
                            } => {
                                let (params, _results) =
                                    blocktype_params_results(validator, blocktype)?;
                                debug_assert_eq!(params.len(), num_return_values);
                                let else_block =
                                    block_with_params(builder, params.clone(), environ)?;
                                canonicalise_then_jump(
                                    builder,
                                    destination,
                                    environ.stacks.peekn(params.len()),
                                );
                                environ.stacks.popn(params.len());

                                builder.change_jump_destination(
                                    branch_inst,
                                    placeholder,
                                    else_block,
                                );
                                builder.seal_block(else_block);
                                else_block
                            }
                            ElseData::WithElse { else_block } => {
                                canonicalise_then_jump(
                                    builder,
                                    destination,
                                    environ.stacks.peekn(num_return_values),
                                );
                                environ.stacks.popn(num_return_values);
                                else_block
                            }
                        };

                        // You might be expecting that we push the parameters for this
                        // `else` block here, something like this:
                        //
                        //     state.pushn(&control_stack_frame.params);
                        //
                        // We don't do that because they are already on the top of the stack
                        // for us: we pushed the parameters twice when we saw the initial
                        // `if` so that we wouldn't have to save the parameters in the
                        // `ControlStackFrame` as another `Vec` allocation.

                        builder.switch_to_block(else_block);

                        // We don't bother updating the control frame's `ElseData`
                        // to `WithElse` because nothing else will read it.
                    }
                }
                _ => unreachable!(),
            }
        }
        Operator::End => {
            let frame = environ.stacks.control_stack.pop().unwrap();
            let next_block = frame.following_code();
            let return_count = frame.num_return_values();
            let return_args = environ.stacks.peekn_mut(return_count);

            canonicalise_then_jump(builder, next_block, return_args);
            // You might expect that if we just finished an `if` block that
            // didn't have a corresponding `else` block, then we would clean
            // up our duplicate set of parameters that we pushed earlier
            // right here. However, we don't have to explicitly do that,
            // since we truncate the stack back to the original height
            // below.

            builder.switch_to_block(next_block);
            builder.seal_block(next_block);

            // If it is a loop we also have to seal the body loop block
            if let ControlStackFrame::Loop { header, .. } = frame {
                builder.seal_block(header)
            }

            frame.restore_catch_handlers(&mut environ.stacks.handlers, builder);

            frame.truncate_value_stack_to_original_size(
                &mut environ.stacks.stack,
                &mut environ.stacks.stack_shape,
            );
            environ
                .stacks
                .stack
                .extend_from_slice(builder.block_params(next_block));
        }
        /**************************** Branch instructions *********************************
         * The branch instructions all have as arguments a target nesting level, which
         * corresponds to how many control stack frames do we have to pop to get the
         * destination `Block`.
         *
         * Once the destination `Block` is found, we sometimes have to declare a certain depth
         * of the stack unreachable, because some branch instructions are terminator.
         *
         * The `br_table` case is much more complicated because Cranelift's `br_table` instruction
         * does not support jump arguments like all the other branch instructions. That is why, in
         * the case where we would use jump arguments for every other branch instruction, we
         * need to split the critical edges leaving the `br_tables` by creating one `Block` per
         * table destination; the `br_table` will point to these newly created `Blocks` and these
         * `Block`s contain only a jump instruction pointing to the final destination, this time with
         * jump arguments.
         *
         * This system is also implemented in Cranelift's SSA construction algorithm, because
         * `use_var` located in a destination `Block` of a `br_table` might trigger the addition
         * of jump arguments in each predecessor branch instruction, one of which might be a
         * `br_table`.
         ***********************************************************************************/
        Operator::Br { relative_depth } => {
            let i = environ.stacks.control_stack.len() - 1 - (*relative_depth as usize);
            let (return_count, br_destination) = {
                let frame = &mut environ.stacks.control_stack[i];
                // We signal that all the code that follows until the next End is unreachable
                frame.set_branched_to_exit();
                let return_count = if frame.is_loop() {
                    frame.num_param_values()
                } else {
                    frame.num_return_values()
                };
                (return_count, frame.br_destination())
            };
            let destination_args = environ.stacks.peekn_mut(return_count);
            canonicalise_then_jump(builder, br_destination, destination_args);
            environ.stacks.popn(return_count);
            environ.stacks.reachable = false;
        }
        Operator::BrIf { relative_depth } => translate_br_if(*relative_depth, builder, environ),
        Operator::BrTable { targets } => {
            let default = targets.default();
            let mut min_depth = default;
            for depth in targets.targets() {
                let depth = depth?;
                if depth < min_depth {
                    min_depth = depth;
                }
            }
            let jump_args_count = {
                let i = environ.stacks.control_stack.len() - 1 - (min_depth as usize);
                let min_depth_frame = &environ.stacks.control_stack[i];
                if min_depth_frame.is_loop() {
                    min_depth_frame.num_param_values()
                } else {
                    min_depth_frame.num_return_values()
                }
            };
            let val = environ.stacks.pop1();
            let mut data = Vec::with_capacity(targets.len() as usize);
            if jump_args_count == 0 {
                // No jump arguments
                for depth in targets.targets() {
                    let depth = depth?;
                    let block = {
                        let i = environ.stacks.control_stack.len() - 1 - (depth as usize);
                        let frame = &mut environ.stacks.control_stack[i];
                        frame.set_branched_to_exit();
                        frame.br_destination()
                    };
                    data.push(builder.func.dfg.block_call(block, &[]));
                }
                let block = {
                    let i = environ.stacks.control_stack.len() - 1 - (default as usize);
                    let frame = &mut environ.stacks.control_stack[i];
                    frame.set_branched_to_exit();
                    frame.br_destination()
                };
                let block = builder.func.dfg.block_call(block, &[]);
                let jt = builder.create_jump_table(JumpTableData::new(block, &data));
                builder.ins().br_table(val, jt);
            } else {
                // Here we have jump arguments, but Cranelift's br_table doesn't support them
                // We then proceed to split the edges going out of the br_table
                let return_count = jump_args_count;
                let mut dest_block_sequence = vec![];
                let mut dest_block_map = HashMap::new();
                for depth in targets.targets() {
                    let depth = depth?;
                    let branch_block = match dest_block_map.entry(depth as usize) {
                        hash_map::Entry::Occupied(entry) => *entry.get(),
                        hash_map::Entry::Vacant(entry) => {
                            let block = builder.create_block();
                            dest_block_sequence.push((depth as usize, block));
                            *entry.insert(block)
                        }
                    };
                    data.push(builder.func.dfg.block_call(branch_block, &[]));
                }
                let default_branch_block = match dest_block_map.entry(default as usize) {
                    hash_map::Entry::Occupied(entry) => *entry.get(),
                    hash_map::Entry::Vacant(entry) => {
                        let block = builder.create_block();
                        dest_block_sequence.push((default as usize, block));
                        *entry.insert(block)
                    }
                };
                let default_branch_block = builder.func.dfg.block_call(default_branch_block, &[]);
                let jt = builder.create_jump_table(JumpTableData::new(default_branch_block, &data));
                builder.ins().br_table(val, jt);
                for (depth, dest_block) in dest_block_sequence {
                    builder.switch_to_block(dest_block);
                    builder.seal_block(dest_block);
                    let real_dest_block = {
                        let i = environ.stacks.control_stack.len() - 1 - depth;
                        let frame = &mut environ.stacks.control_stack[i];
                        frame.set_branched_to_exit();
                        frame.br_destination()
                    };
                    let destination_args = environ.stacks.peekn_mut(return_count);
                    canonicalise_then_jump(builder, real_dest_block, destination_args);
                }
                environ.stacks.popn(return_count);
            }
            environ.stacks.reachable = false;
        }
        Operator::Return => {
            let return_count = {
                let frame = &mut environ.stacks.control_stack[0];
                frame.num_return_values()
            };
            {
                let mut return_args = environ.stacks.peekn(return_count).to_vec();
                environ.handle_before_return(&return_args, builder);
                bitcast_wasm_returns(&mut return_args, builder);
                builder.ins().return_(&return_args);
            }
            environ.stacks.popn(return_count);
            environ.stacks.reachable = false;
        }
        /********************************** Exception handling **********************************/
        Operator::Catch { .. }
        | Operator::Rethrow { .. }
        | Operator::Delegate { .. }
        | Operator::CatchAll => {
            return Err(wasm_unsupported!(
                "legacy exception handling proposal is not supported"
            ));
        }

        Operator::TryTable { try_table } => {
            // First, create a block on the control stack. This also
            // updates the handler state that is attached to all calls
            // made within this block.
            let body = builder.create_block();
            let (params, results) = blocktype_params_results(validator, try_table.ty)?;
            let next = block_with_params(builder, results.clone(), environ)?;
            builder.ins().jump(body, []);
            builder.seal_block(body);

            // For each catch clause, create a block with the
            // equivalent of `br` to the target (unboxing the exnref
            // into stack values or pushing it directly, depending on
            // the kind of clause).
            let ckpt = environ.stacks.handlers.take_checkpoint();
            let mut catch_blocks = vec![];
            // Process in *reverse* order: see the comment on
            // [`HandlerState`]. In brief, this allows us to unify the
            // left-to-right matching semantics of a single
            // `try_table`'s catch clauses with the inside-out
            // (deepest scope first) semantics of nested `try_table`s.
            for catch in try_table.catches.iter().rev() {
                // This will register the block in `state.handlers`
                // under the appropriate tag.
                catch_blocks.push(create_catch_block(builder, catch, environ)?);
            }

            environ.stacks.push_try_table_block(
                next,
                catch_blocks,
                params.len(),
                results.len(),
                ckpt,
            );

            // Continue codegen into the main body block.
            builder.switch_to_block(body);
        }

        Operator::Throw { tag_index } => {
            let tag_index = TagIndex::from_u32(*tag_index);
            let arity = environ.tag_param_arity(tag_index);
            let args = environ.stacks.peekn(arity).to_vec();
            environ.translate_exn_throw(builder, tag_index, &args)?;
            environ.stacks.popn(arity);
            environ.stacks.reachable = false;
        }

        Operator::ThrowRef => {
            let exnref = environ.stacks.pop1();
            environ.translate_exn_throw_ref(builder, exnref)?;
            environ.stacks.reachable = false;
        }

        /************************************ Calls ****************************************
         * The call instructions pop off their arguments from the stack and append their
         * return values to it. `call_indirect` needs environment support because there is an
         * argument referring to an index in the external functions table of the module.
         ************************************************************************************/
        Operator::Call { function_index } => {
            let function_index = FuncIndex::from_u32(*function_index);
            let ty = environ.module.functions[function_index]
                .signature
                .unwrap_module_type_index();
            let sig_ref = environ.get_or_create_interned_sig_ref(builder.func, ty);
            let num_args = environ.num_params_for_func(function_index);

            // Bitcast any vector arguments to their default type, I8X16, before calling.
            let mut args = environ.stacks.peekn(num_args).to_vec();
            bitcast_wasm_params(environ, sig_ref, &mut args, builder);

            let inst_results =
                environ.translate_call(builder, srcloc, function_index, sig_ref, &args)?;

            debug_assert_eq!(
                inst_results.len(),
                builder.func.dfg.signatures[sig_ref].returns.len(),
                "translate_call results should match the call signature"
            );
            environ.stacks.popn(num_args);
            environ.stacks.pushn(&inst_results);
        }
        Operator::CallIndirect {
            type_index,
            table_index,
        } => {
            // `type_index` is the index of the function's signature and
            // `table_index` is the index of the table to search the function
            // in.
            let type_index = TypeIndex::from_u32(*type_index);
            let sigref = environ.get_or_create_sig_ref(builder.func, type_index);
            let num_args = environ.num_params_for_function_type(type_index);
            let callee = environ.stacks.pop1();

            // Bitcast any vector arguments to their default type, I8X16, before calling.
            let mut args = environ.stacks.peekn(num_args).to_vec();
            bitcast_wasm_params(environ, sigref, &mut args, builder);

            let inst_results = environ.translate_call_indirect(
                builder,
                srcloc,
                validator.features(),
                TableIndex::from_u32(*table_index),
                type_index,
                sigref,
                callee,
                &args,
            )?;
            let inst_results = match inst_results {
                Some(results) => results,
                None => {
                    environ.stacks.reachable = false;
                    return Ok(());
                }
            };

            debug_assert_eq!(
                inst_results.len(),
                builder.func.dfg.signatures[sigref].returns.len(),
                "translate_call_indirect results should match the call signature"
            );
            environ.stacks.popn(num_args);
            environ.stacks.pushn(&inst_results);
        }
        /******************************* Tail Calls ******************************************
         * The tail call instructions pop their arguments from the stack and
         * then permanently transfer control to their callee. The indirect
         * version requires environment support (while the direct version can
         * optionally be hooked but doesn't require it) it interacts with the
         * VM's runtime state via tables.
         ************************************************************************************/
        Operator::ReturnCall { function_index } => {
            let function_index = FuncIndex::from_u32(*function_index);
            let ty = environ.module.functions[function_index]
                .signature
                .unwrap_module_type_index();
            let sig_ref = environ.get_or_create_interned_sig_ref(builder.func, ty);
            let num_args = environ.num_params_for_func(function_index);

            // Bitcast any vector arguments to their default type, I8X16, before calling.
            let mut args = environ.stacks.peekn(num_args).to_vec();
            bitcast_wasm_params(environ, sig_ref, &mut args, builder);

            environ.translate_return_call(builder, srcloc, function_index, sig_ref, &args)?;

            environ.stacks.popn(num_args);
            environ.stacks.reachable = false;
        }
        Operator::ReturnCallIndirect {
            type_index,
            table_index,
        } => {
            // `type_index` is the index of the function's signature and
            // `table_index` is the index of the table to search the function
            // in.
            let type_index = TypeIndex::from_u32(*type_index);
            let sigref = environ.get_or_create_sig_ref(builder.func, type_index);
            let num_args = environ.num_params_for_function_type(type_index);
            let callee = environ.stacks.pop1();

            // Bitcast any vector arguments to their default type, I8X16, before calling.
            let mut args = environ.stacks.peekn(num_args).to_vec();
            bitcast_wasm_params(environ, sigref, &mut args, builder);

            environ.translate_return_call_indirect(
                builder,
                srcloc,
                validator.features(),
                TableIndex::from_u32(*table_index),
                type_index,
                sigref,
                callee,
                &args,
            )?;

            environ.stacks.popn(num_args);
            environ.stacks.reachable = false;
        }
        Operator::ReturnCallRef { type_index } => {
            // Get function signature
            // `index` is the index of the function's signature and `table_index` is the index of
            // the table to search the function in.
            let type_index = TypeIndex::from_u32(*type_index);
            let sigref = environ.get_or_create_sig_ref(builder.func, type_index);
            let num_args = environ.num_params_for_function_type(type_index);
            let callee = environ.stacks.pop1();

            // Bitcast any vector arguments to their default type, I8X16, before calling.
            let mut args = environ.stacks.peekn(num_args).to_vec();
            bitcast_wasm_params(environ, sigref, &mut args, builder);

            environ.translate_return_call_ref(builder, srcloc, sigref, callee, &args)?;

            environ.stacks.popn(num_args);
            environ.stacks.reachable = false;
        }
        /******************************* Memory management ***********************************
         * Memory management is handled by environment. It is usually translated into calls to
         * special functions.
         ************************************************************************************/
        Operator::MemoryGrow { mem } => {
            // The WebAssembly MVP only supports one linear memory, but we expect the reserved
            // argument to be a memory index.
            let mem = MemoryIndex::from_u32(*mem);
            let _heap = environ.get_or_create_heap(builder.func, mem);
            let val = environ.stacks.pop1();
            environ.before_memory_grow(builder, val, mem);
            let result = environ.translate_memory_grow(builder, mem, val)?;
            environ.stacks.push1(result);
        }
        Operator::MemorySize { mem } => {
            let mem = MemoryIndex::from_u32(*mem);
            let _heap = environ.get_or_create_heap(builder.func, mem);
            let result = environ.translate_memory_size(builder.cursor(), mem)?;
            environ.stacks.push1(result);
        }
        /******************************* Load instructions ***********************************
         * Wasm specifies an integer alignment flag but we drop it in Cranelift.
         * The memory base address is provided by the environment.
         ************************************************************************************/
        Operator::I32Load8U { memarg } => {
            unwrap_or_return_unreachable_state!(
                environ,
                translate_load(memarg, ir::Opcode::Uload8, I32, builder, environ)?
            );
        }
        Operator::I32Load16U { memarg } => {
            unwrap_or_return_unreachable_state!(
                environ,
                translate_load(memarg, ir::Opcode::Uload16, I32, builder, environ)?
            );
        }
        Operator::I32Load8S { memarg } => {
            unwrap_or_return_unreachable_state!(
                environ,
                translate_load(memarg, ir::Opcode::Sload8, I32, builder, environ)?
            );
        }
        Operator::I32Load16S { memarg } => {
            unwrap_or_return_unreachable_state!(
                environ,
                translate_load(memarg, ir::Opcode::Sload16, I32, builder, environ)?
            );
        }
        Operator::I64Load8U { memarg } => {
            unwrap_or_return_unreachable_state!(
                environ,
                translate_load(memarg, ir::Opcode::Uload8, I64, builder, environ)?
            );
        }
        Operator::I64Load16U { memarg } => {
            unwrap_or_return_unreachable_state!(
                environ,
                translate_load(memarg, ir::Opcode::Uload16, I64, builder, environ)?
            );
        }
        Operator::I64Load8S { memarg } => {
            unwrap_or_return_unreachable_state!(
                environ,
                translate_load(memarg, ir::Opcode::Sload8, I64, builder, environ)?
            );
        }
        Operator::I64Load16S { memarg } => {
            unwrap_or_return_unreachable_state!(
                environ,
                translate_load(memarg, ir::Opcode::Sload16, I64, builder, environ)?
            );
        }
        Operator::I64Load32S { memarg } => {
            unwrap_or_return_unreachable_state!(
                environ,
                translate_load(memarg, ir::Opcode::Sload32, I64, builder, environ)?
            );
        }
        Operator::I64Load32U { memarg } => {
            unwrap_or_return_unreachable_state!(
                environ,
                translate_load(memarg, ir::Opcode::Uload32, I64, builder, environ)?
            );
        }
        Operator::I32Load { memarg } => {
            unwrap_or_return_unreachable_state!(
                environ,
                translate_load(memarg, ir::Opcode::Load, I32, builder, environ)?
            );
        }
        Operator::F32Load { memarg } => {
            unwrap_or_return_unreachable_state!(
                environ,
                translate_load(memarg, ir::Opcode::Load, F32, builder, environ)?
            );
        }
        Operator::I64Load { memarg } => {
            unwrap_or_return_unreachable_state!(
                environ,
                translate_load(memarg, ir::Opcode::Load, I64, builder, environ)?
            );
        }
        Operator::F64Load { memarg } => {
            unwrap_or_return_unreachable_state!(
                environ,
                translate_load(memarg, ir::Opcode::Load, F64, builder, environ)?
            );
        }
        Operator::V128Load { memarg } => {
            unwrap_or_return_unreachable_state!(
                environ,
                translate_load(memarg, ir::Opcode::Load, I8X16, builder, environ)?
            );
        }
        Operator::V128Load8x8S { memarg } => {
            //TODO(#6829): add before_load() and before_store() hooks for SIMD loads and stores.
            let (flags, _, base) = unwrap_or_return_unreachable_state!(
                environ,
                prepare_addr(memarg, 8, builder, environ)?
            );
            let loaded = builder.ins().sload8x8(flags, base, 0);
            environ.stacks.push1(loaded);
        }
        Operator::V128Load8x8U { memarg } => {
            let (flags, _, base) = unwrap_or_return_unreachable_state!(
                environ,
                prepare_addr(memarg, 8, builder, environ)?
            );
            let loaded = builder.ins().uload8x8(flags, base, 0);
            environ.stacks.push1(loaded);
        }
        Operator::V128Load16x4S { memarg } => {
            let (flags, _, base) = unwrap_or_return_unreachable_state!(
                environ,
                prepare_addr(memarg, 8, builder, environ)?
            );
            let loaded = builder.ins().sload16x4(flags, base, 0);
            environ.stacks.push1(loaded);
        }
        Operator::V128Load16x4U { memarg } => {
            let (flags, _, base) = unwrap_or_return_unreachable_state!(
                environ,
                prepare_addr(memarg, 8, builder, environ)?
            );
            let loaded = builder.ins().uload16x4(flags, base, 0);
            environ.stacks.push1(loaded);
        }
        Operator::V128Load32x2S { memarg } => {
            let (flags, _, base) = unwrap_or_return_unreachable_state!(
                environ,
                prepare_addr(memarg, 8, builder, environ)?
            );
            let loaded = builder.ins().sload32x2(flags, base, 0);
            environ.stacks.push1(loaded);
        }
        Operator::V128Load32x2U { memarg } => {
            let (flags, _, base) = unwrap_or_return_unreachable_state!(
                environ,
                prepare_addr(memarg, 8, builder, environ)?
            );
            let loaded = builder.ins().uload32x2(flags, base, 0);
            environ.stacks.push1(loaded);
        }
        /****************************** Store instructions ***********************************
         * Wasm specifies an integer alignment flag but we drop it in Cranelift.
         * The memory base address is provided by the environment.
         ************************************************************************************/
        Operator::I32Store { memarg }
        | Operator::I64Store { memarg }
        | Operator::F32Store { memarg }
        | Operator::F64Store { memarg } => {
            translate_store(memarg, ir::Opcode::Store, builder, environ)?;
        }
        Operator::I32Store8 { memarg } | Operator::I64Store8 { memarg } => {
            translate_store(memarg, ir::Opcode::Istore8, builder, environ)?;
        }
        Operator::I32Store16 { memarg } | Operator::I64Store16 { memarg } => {
            translate_store(memarg, ir::Opcode::Istore16, builder, environ)?;
        }
        Operator::I64Store32 { memarg } => {
            translate_store(memarg, ir::Opcode::Istore32, builder, environ)?;
        }
        Operator::V128Store { memarg } => {
            translate_store(memarg, ir::Opcode::Store, builder, environ)?;
        }
        /****************************** Nullary Operators ************************************/
        Operator::I32Const { value } => {
            environ
                .stacks
                .push1(builder.ins().iconst(I32, i64::from(value.cast_unsigned())));
        }
        Operator::I64Const { value } => environ.stacks.push1(builder.ins().iconst(I64, *value)),
        Operator::F32Const { value } => {
            environ
                .stacks
                .push1(builder.ins().f32const(f32_translation(*value)));
        }
        Operator::F64Const { value } => {
            environ
                .stacks
                .push1(builder.ins().f64const(f64_translation(*value)));
        }
        /******************************* Unary Operators *************************************/
        Operator::I32Clz | Operator::I64Clz => {
            let arg = environ.stacks.pop1();
            environ.stacks.push1(builder.ins().clz(arg));
        }
        Operator::I32Ctz | Operator::I64Ctz => {
            let arg = environ.stacks.pop1();
            environ.stacks.push1(builder.ins().ctz(arg));
        }
        Operator::I32Popcnt | Operator::I64Popcnt => {
            let arg = environ.stacks.pop1();
            environ.stacks.push1(builder.ins().popcnt(arg));
        }
        Operator::I64ExtendI32S => {
            let val = environ.stacks.pop1();
            environ.stacks.push1(builder.ins().sextend(I64, val));
        }
        Operator::I64ExtendI32U => {
            let val = environ.stacks.pop1();
            environ.stacks.push1(builder.ins().uextend(I64, val));
        }
        Operator::I32WrapI64 => {
            let val = environ.stacks.pop1();
            environ.stacks.push1(builder.ins().ireduce(I32, val));
        }
        Operator::F32Sqrt | Operator::F64Sqrt => {
            let arg = environ.stacks.pop1();
            environ.stacks.push1(builder.ins().sqrt(arg));
        }
        Operator::F32Ceil => {
            let arg = environ.stacks.pop1();
            let result = environ.ceil_f32(builder, arg);
            environ.stacks.push1(result);
        }
        Operator::F64Ceil => {
            let arg = environ.stacks.pop1();
            let result = environ.ceil_f64(builder, arg);
            environ.stacks.push1(result);
        }
        Operator::F32Floor => {
            let arg = environ.stacks.pop1();
            let result = environ.floor_f32(builder, arg);
            environ.stacks.push1(result);
        }
        Operator::F64Floor => {
            let arg = environ.stacks.pop1();
            let result = environ.floor_f64(builder, arg);
            environ.stacks.push1(result);
        }
        Operator::F32Trunc => {
            let arg = environ.stacks.pop1();
            let result = environ.trunc_f32(builder, arg);
            environ.stacks.push1(result);
        }
        Operator::F64Trunc => {
            let arg = environ.stacks.pop1();
            let result = environ.trunc_f64(builder, arg);
            environ.stacks.push1(result);
        }
        Operator::F32Nearest => {
            let arg = environ.stacks.pop1();
            let result = environ.nearest_f32(builder, arg);
            environ.stacks.push1(result);
        }
        Operator::F64Nearest => {
            let arg = environ.stacks.pop1();
            let result = environ.nearest_f64(builder, arg);
            environ.stacks.push1(result);
        }
        Operator::F32Abs | Operator::F64Abs => {
            let val = environ.stacks.pop1();
            environ.stacks.push1(builder.ins().fabs(val));
        }
        Operator::F32Neg | Operator::F64Neg => {
            let arg = environ.stacks.pop1();
            environ.stacks.push1(builder.ins().fneg(arg));
        }
        Operator::F64ConvertI64U | Operator::F64ConvertI32U => {
            let val = environ.stacks.pop1();
            environ.stacks.push1(builder.ins().fcvt_from_uint(F64, val));
        }
        Operator::F64ConvertI64S | Operator::F64ConvertI32S => {
            let val = environ.stacks.pop1();
            environ.stacks.push1(builder.ins().fcvt_from_sint(F64, val));
        }
        Operator::F32ConvertI64S | Operator::F32ConvertI32S => {
            let val = environ.stacks.pop1();
            environ.stacks.push1(builder.ins().fcvt_from_sint(F32, val));
        }
        Operator::F32ConvertI64U | Operator::F32ConvertI32U => {
            let val = environ.stacks.pop1();
            environ.stacks.push1(builder.ins().fcvt_from_uint(F32, val));
        }
        Operator::F64PromoteF32 => {
            let val = environ.stacks.pop1();
            environ.stacks.push1(builder.ins().fpromote(F64, val));
        }
        Operator::F32DemoteF64 => {
            let val = environ.stacks.pop1();
            environ.stacks.push1(builder.ins().fdemote(F32, val));
        }
        Operator::I64TruncF64S | Operator::I64TruncF32S => {
            let val = environ.stacks.pop1();
            let result = environ.translate_fcvt_to_sint(builder, I64, val);
            environ.stacks.push1(result);
        }
        Operator::I32TruncF64S | Operator::I32TruncF32S => {
            let val = environ.stacks.pop1();
            let result = environ.translate_fcvt_to_sint(builder, I32, val);
            environ.stacks.push1(result);
        }
        Operator::I64TruncF64U | Operator::I64TruncF32U => {
            let val = environ.stacks.pop1();
            let result = environ.translate_fcvt_to_uint(builder, I64, val);
            environ.stacks.push1(result);
        }
        Operator::I32TruncF64U | Operator::I32TruncF32U => {
            let val = environ.stacks.pop1();
            let result = environ.translate_fcvt_to_uint(builder, I32, val);
            environ.stacks.push1(result);
        }
        Operator::I64TruncSatF64S | Operator::I64TruncSatF32S => {
            let val = environ.stacks.pop1();
            environ
                .stacks
                .push1(builder.ins().fcvt_to_sint_sat(I64, val));
        }
        Operator::I32TruncSatF64S | Operator::I32TruncSatF32S => {
            let val = environ.stacks.pop1();
            environ
                .stacks
                .push1(builder.ins().fcvt_to_sint_sat(I32, val));
        }
        Operator::I64TruncSatF64U | Operator::I64TruncSatF32U => {
            let val = environ.stacks.pop1();
            environ
                .stacks
                .push1(builder.ins().fcvt_to_uint_sat(I64, val));
        }
        Operator::I32TruncSatF64U | Operator::I32TruncSatF32U => {
            let val = environ.stacks.pop1();
            environ
                .stacks
                .push1(builder.ins().fcvt_to_uint_sat(I32, val));
        }
        Operator::F32ReinterpretI32 => {
            let val = environ.stacks.pop1();
            environ
                .stacks
                .push1(builder.ins().bitcast(F32, MemFlags::new(), val));
        }
        Operator::F64ReinterpretI64 => {
            let val = environ.stacks.pop1();
            environ
                .stacks
                .push1(builder.ins().bitcast(F64, MemFlags::new(), val));
        }
        Operator::I32ReinterpretF32 => {
            let val = environ.stacks.pop1();
            environ
                .stacks
                .push1(builder.ins().bitcast(I32, MemFlags::new(), val));
        }
        Operator::I64ReinterpretF64 => {
            let val = environ.stacks.pop1();
            environ
                .stacks
                .push1(builder.ins().bitcast(I64, MemFlags::new(), val));
        }
        Operator::I32Extend8S => {
            let val = environ.stacks.pop1();
            environ.stacks.push1(builder.ins().ireduce(I8, val));
            let val = environ.stacks.pop1();
            environ.stacks.push1(builder.ins().sextend(I32, val));
        }
        Operator::I32Extend16S => {
            let val = environ.stacks.pop1();
            environ.stacks.push1(builder.ins().ireduce(I16, val));
            let val = environ.stacks.pop1();
            environ.stacks.push1(builder.ins().sextend(I32, val));
        }
        Operator::I64Extend8S => {
            let val = environ.stacks.pop1();
            environ.stacks.push1(builder.ins().ireduce(I8, val));
            let val = environ.stacks.pop1();
            environ.stacks.push1(builder.ins().sextend(I64, val));
        }
        Operator::I64Extend16S => {
            let val = environ.stacks.pop1();
            environ.stacks.push1(builder.ins().ireduce(I16, val));
            let val = environ.stacks.pop1();
            environ.stacks.push1(builder.ins().sextend(I64, val));
        }
        Operator::I64Extend32S => {
            let val = environ.stacks.pop1();
            environ.stacks.push1(builder.ins().ireduce(I32, val));
            let val = environ.stacks.pop1();
            environ.stacks.push1(builder.ins().sextend(I64, val));
        }
        /****************************** Binary Operators ************************************/
        Operator::I32Add | Operator::I64Add => {
            let (arg1, arg2) = environ.stacks.pop2();
            environ.stacks.push1(builder.ins().iadd(arg1, arg2));
        }
        Operator::I32And | Operator::I64And => {
            let (arg1, arg2) = environ.stacks.pop2();
            environ.stacks.push1(builder.ins().band(arg1, arg2));
        }
        Operator::I32Or | Operator::I64Or => {
            let (arg1, arg2) = environ.stacks.pop2();
            environ.stacks.push1(builder.ins().bor(arg1, arg2));
        }
        Operator::I32Xor | Operator::I64Xor => {
            let (arg1, arg2) = environ.stacks.pop2();
            environ.stacks.push1(builder.ins().bxor(arg1, arg2));
        }
        Operator::I32Shl | Operator::I64Shl => {
            let (arg1, arg2) = environ.stacks.pop2();
            environ.stacks.push1(builder.ins().ishl(arg1, arg2));
        }
        Operator::I32ShrS | Operator::I64ShrS => {
            let (arg1, arg2) = environ.stacks.pop2();
            environ.stacks.push1(builder.ins().sshr(arg1, arg2));
        }
        Operator::I32ShrU | Operator::I64ShrU => {
            let (arg1, arg2) = environ.stacks.pop2();
            environ.stacks.push1(builder.ins().ushr(arg1, arg2));
        }
        Operator::I32Rotl | Operator::I64Rotl => {
            let (arg1, arg2) = environ.stacks.pop2();
            environ.stacks.push1(builder.ins().rotl(arg1, arg2));
        }
        Operator::I32Rotr | Operator::I64Rotr => {
            let (arg1, arg2) = environ.stacks.pop2();
            environ.stacks.push1(builder.ins().rotr(arg1, arg2));
        }
        Operator::F32Add | Operator::F64Add => {
            let (arg1, arg2) = environ.stacks.pop2();
            environ.stacks.push1(builder.ins().fadd(arg1, arg2));
        }
        Operator::I32Sub | Operator::I64Sub => {
            let (arg1, arg2) = environ.stacks.pop2();
            environ.stacks.push1(builder.ins().isub(arg1, arg2));
        }
        Operator::F32Sub | Operator::F64Sub => {
            let (arg1, arg2) = environ.stacks.pop2();
            environ.stacks.push1(builder.ins().fsub(arg1, arg2));
        }
        Operator::I32Mul | Operator::I64Mul => {
            let (arg1, arg2) = environ.stacks.pop2();
            environ.stacks.push1(builder.ins().imul(arg1, arg2));
        }
        Operator::F32Mul | Operator::F64Mul => {
            let (arg1, arg2) = environ.stacks.pop2();
            environ.stacks.push1(builder.ins().fmul(arg1, arg2));
        }
        Operator::F32Div | Operator::F64Div => {
            let (arg1, arg2) = environ.stacks.pop2();
            environ.stacks.push1(builder.ins().fdiv(arg1, arg2));
        }
        Operator::I32DivS | Operator::I64DivS => {
            let (arg1, arg2) = environ.stacks.pop2();
            let result = environ.translate_sdiv(builder, arg1, arg2);
            environ.stacks.push1(result);
        }
        Operator::I32DivU | Operator::I64DivU => {
            let (arg1, arg2) = environ.stacks.pop2();
            let result = environ.translate_udiv(builder, arg1, arg2);
            environ.stacks.push1(result);
        }
        Operator::I32RemS | Operator::I64RemS => {
            let (arg1, arg2) = environ.stacks.pop2();
            let result = environ.translate_srem(builder, arg1, arg2);
            environ.stacks.push1(result);
        }
        Operator::I32RemU | Operator::I64RemU => {
            let (arg1, arg2) = environ.stacks.pop2();
            let result = environ.translate_urem(builder, arg1, arg2);
            environ.stacks.push1(result);
        }
        Operator::F32Min | Operator::F64Min => {
            let (arg1, arg2) = environ.stacks.pop2();
            environ.stacks.push1(builder.ins().fmin(arg1, arg2));
        }
        Operator::F32Max | Operator::F64Max => {
            let (arg1, arg2) = environ.stacks.pop2();
            environ.stacks.push1(builder.ins().fmax(arg1, arg2));
        }
        Operator::F32Copysign | Operator::F64Copysign => {
            let (arg1, arg2) = environ.stacks.pop2();
            environ.stacks.push1(builder.ins().fcopysign(arg1, arg2));
        }
        /**************************** Comparison Operators **********************************/
        Operator::I32LtS | Operator::I64LtS => {
            translate_icmp(IntCC::SignedLessThan, builder, environ)
        }
        Operator::I32LtU | Operator::I64LtU => {
            translate_icmp(IntCC::UnsignedLessThan, builder, environ)
        }
        Operator::I32LeS | Operator::I64LeS => {
            translate_icmp(IntCC::SignedLessThanOrEqual, builder, environ)
        }
        Operator::I32LeU | Operator::I64LeU => {
            translate_icmp(IntCC::UnsignedLessThanOrEqual, builder, environ)
        }
        Operator::I32GtS | Operator::I64GtS => {
            translate_icmp(IntCC::SignedGreaterThan, builder, environ)
        }
        Operator::I32GtU | Operator::I64GtU => {
            translate_icmp(IntCC::UnsignedGreaterThan, builder, environ)
        }
        Operator::I32GeS | Operator::I64GeS => {
            translate_icmp(IntCC::SignedGreaterThanOrEqual, builder, environ)
        }
        Operator::I32GeU | Operator::I64GeU => {
            translate_icmp(IntCC::UnsignedGreaterThanOrEqual, builder, environ)
        }
        Operator::I32Eqz | Operator::I64Eqz => {
            let arg = environ.stacks.pop1();
            let val = builder.ins().icmp_imm(IntCC::Equal, arg, 0);
            environ.stacks.push1(builder.ins().uextend(I32, val));
        }
        Operator::I32Eq | Operator::I64Eq => translate_icmp(IntCC::Equal, builder, environ),
        Operator::F32Eq | Operator::F64Eq => translate_fcmp(FloatCC::Equal, builder, environ),
        Operator::I32Ne | Operator::I64Ne => translate_icmp(IntCC::NotEqual, builder, environ),
        Operator::F32Ne | Operator::F64Ne => translate_fcmp(FloatCC::NotEqual, builder, environ),
        Operator::F32Gt | Operator::F64Gt => translate_fcmp(FloatCC::GreaterThan, builder, environ),
        Operator::F32Ge | Operator::F64Ge => {
            translate_fcmp(FloatCC::GreaterThanOrEqual, builder, environ)
        }
        Operator::F32Lt | Operator::F64Lt => translate_fcmp(FloatCC::LessThan, builder, environ),
        Operator::F32Le | Operator::F64Le => {
            translate_fcmp(FloatCC::LessThanOrEqual, builder, environ)
        }
        Operator::RefNull { hty } => {
            let hty = environ.convert_heap_type(*hty)?;
            let result = environ.translate_ref_null(builder.cursor(), hty)?;
            environ.stacks.push1(result);
        }
        Operator::RefIsNull => {
            let value = environ.stacks.pop1();
            let [WasmValType::Ref(ty)] = operand_types else {
                unreachable!("validation")
            };
            let result = environ.translate_ref_is_null(builder.cursor(), value, *ty)?;
            environ.stacks.push1(result);
        }
        Operator::RefFunc { function_index } => {
            let index = FuncIndex::from_u32(*function_index);
            let result = environ.translate_ref_func(builder.cursor(), index)?;
            environ.stacks.push1(result);
        }
        Operator::MemoryAtomicWait32 { memarg } | Operator::MemoryAtomicWait64 { memarg } => {
            // The WebAssembly MVP only supports one linear memory and
            // wasmparser will ensure that the memory indices specified are
            // zero.
            let implied_ty = match op {
                Operator::MemoryAtomicWait64 { .. } => I64,
                Operator::MemoryAtomicWait32 { .. } => I32,
                _ => unreachable!(),
            };
            let memory_index = MemoryIndex::from_u32(memarg.memory);
            let heap = environ.get_or_create_heap(builder.func, memory_index);
            let timeout = environ.stacks.pop1(); // 64 (fixed)
            let expected = environ.stacks.pop1(); // 32 or 64 (per the `Ixx` in `IxxAtomicWait`)
            assert!(builder.func.dfg.value_type(expected) == implied_ty);
            let addr = environ.stacks.pop1();
            let effective_addr = if memarg.offset == 0 {
                addr
            } else {
                let index_type = environ.heaps()[heap].index_type();
                let offset = builder.ins().iconst(index_type, memarg.offset as i64);
                environ.uadd_overflow_trap(builder, addr, offset, ir::TrapCode::HEAP_OUT_OF_BOUNDS)
            };
            // `fn translate_atomic_wait` can inspect the type of `expected` to figure out what
            // code it needs to generate, if it wants.
            let res = environ.translate_atomic_wait(
                builder,
                memory_index,
                heap,
                effective_addr,
                expected,
                timeout,
            )?;
            environ.stacks.push1(res);
        }
        Operator::MemoryAtomicNotify { memarg } => {
            let memory_index = MemoryIndex::from_u32(memarg.memory);
            let heap = environ.get_or_create_heap(builder.func, memory_index);
            let count = environ.stacks.pop1(); // 32 (fixed)
            let addr = environ.stacks.pop1();
            let effective_addr = if memarg.offset == 0 {
                addr
            } else {
                let index_type = environ.heaps()[heap].index_type();
                let offset = builder.ins().iconst(index_type, memarg.offset as i64);
                environ.uadd_overflow_trap(builder, addr, offset, ir::TrapCode::HEAP_OUT_OF_BOUNDS)
            };
            let res = environ.translate_atomic_notify(
                builder,
                memory_index,
                heap,
                effective_addr,
                count,
            )?;
            environ.stacks.push1(res);
        }
        Operator::I32AtomicLoad { memarg } => {
            translate_atomic_load(I32, I32, memarg, builder, environ)?
        }
        Operator::I64AtomicLoad { memarg } => {
            translate_atomic_load(I64, I64, memarg, builder, environ)?
        }
        Operator::I32AtomicLoad8U { memarg } => {
            translate_atomic_load(I32, I8, memarg, builder, environ)?
        }
        Operator::I32AtomicLoad16U { memarg } => {
            translate_atomic_load(I32, I16, memarg, builder, environ)?
        }
        Operator::I64AtomicLoad8U { memarg } => {
            translate_atomic_load(I64, I8, memarg, builder, environ)?
        }
        Operator::I64AtomicLoad16U { memarg } => {
            translate_atomic_load(I64, I16, memarg, builder, environ)?
        }
        Operator::I64AtomicLoad32U { memarg } => {
            translate_atomic_load(I64, I32, memarg, builder, environ)?
        }

        Operator::I32AtomicStore { memarg } => {
            translate_atomic_store(I32, memarg, builder, environ)?
        }
        Operator::I64AtomicStore { memarg } => {
            translate_atomic_store(I64, memarg, builder, environ)?
        }
        Operator::I32AtomicStore8 { memarg } => {
            translate_atomic_store(I8, memarg, builder, environ)?
        }
        Operator::I32AtomicStore16 { memarg } => {
            translate_atomic_store(I16, memarg, builder, environ)?
        }
        Operator::I64AtomicStore8 { memarg } => {
            translate_atomic_store(I8, memarg, builder, environ)?
        }
        Operator::I64AtomicStore16 { memarg } => {
            translate_atomic_store(I16, memarg, builder, environ)?
        }
        Operator::I64AtomicStore32 { memarg } => {
            translate_atomic_store(I32, memarg, builder, environ)?
        }

        Operator::I32AtomicRmwAdd { memarg } => {
            translate_atomic_rmw(I32, I32, AtomicRmwOp::Add, memarg, builder, environ)?
        }
        Operator::I64AtomicRmwAdd { memarg } => {
            translate_atomic_rmw(I64, I64, AtomicRmwOp::Add, memarg, builder, environ)?
        }
        Operator::I32AtomicRmw8AddU { memarg } => {
            translate_atomic_rmw(I32, I8, AtomicRmwOp::Add, memarg, builder, environ)?
        }
        Operator::I32AtomicRmw16AddU { memarg } => {
            translate_atomic_rmw(I32, I16, AtomicRmwOp::Add, memarg, builder, environ)?
        }
        Operator::I64AtomicRmw8AddU { memarg } => {
            translate_atomic_rmw(I64, I8, AtomicRmwOp::Add, memarg, builder, environ)?
        }
        Operator::I64AtomicRmw16AddU { memarg } => {
            translate_atomic_rmw(I64, I16, AtomicRmwOp::Add, memarg, builder, environ)?
        }
        Operator::I64AtomicRmw32AddU { memarg } => {
            translate_atomic_rmw(I64, I32, AtomicRmwOp::Add, memarg, builder, environ)?
        }

        Operator::I32AtomicRmwSub { memarg } => {
            translate_atomic_rmw(I32, I32, AtomicRmwOp::Sub, memarg, builder, environ)?
        }
        Operator::I64AtomicRmwSub { memarg } => {
            translate_atomic_rmw(I64, I64, AtomicRmwOp::Sub, memarg, builder, environ)?
        }
        Operator::I32AtomicRmw8SubU { memarg } => {
            translate_atomic_rmw(I32, I8, AtomicRmwOp::Sub, memarg, builder, environ)?
        }
        Operator::I32AtomicRmw16SubU { memarg } => {
            translate_atomic_rmw(I32, I16, AtomicRmwOp::Sub, memarg, builder, environ)?
        }
        Operator::I64AtomicRmw8SubU { memarg } => {
            translate_atomic_rmw(I64, I8, AtomicRmwOp::Sub, memarg, builder, environ)?
        }
        Operator::I64AtomicRmw16SubU { memarg } => {
            translate_atomic_rmw(I64, I16, AtomicRmwOp::Sub, memarg, builder, environ)?
        }
        Operator::I64AtomicRmw32SubU { memarg } => {
            translate_atomic_rmw(I64, I32, AtomicRmwOp::Sub, memarg, builder, environ)?
        }

        Operator::I32AtomicRmwAnd { memarg } => {
            translate_atomic_rmw(I32, I32, AtomicRmwOp::And, memarg, builder, environ)?
        }
        Operator::I64AtomicRmwAnd { memarg } => {
            translate_atomic_rmw(I64, I64, AtomicRmwOp::And, memarg, builder, environ)?
        }
        Operator::I32AtomicRmw8AndU { memarg } => {
            translate_atomic_rmw(I32, I8, AtomicRmwOp::And, memarg, builder, environ)?
        }
        Operator::I32AtomicRmw16AndU { memarg } => {
            translate_atomic_rmw(I32, I16, AtomicRmwOp::And, memarg, builder, environ)?
        }
        Operator::I64AtomicRmw8AndU { memarg } => {
            translate_atomic_rmw(I64, I8, AtomicRmwOp::And, memarg, builder, environ)?
        }
        Operator::I64AtomicRmw16AndU { memarg } => {
            translate_atomic_rmw(I64, I16, AtomicRmwOp::And, memarg, builder, environ)?
        }
        Operator::I64AtomicRmw32AndU { memarg } => {
            translate_atomic_rmw(I64, I32, AtomicRmwOp::And, memarg, builder, environ)?
        }

        Operator::I32AtomicRmwOr { memarg } => {
            translate_atomic_rmw(I32, I32, AtomicRmwOp::Or, memarg, builder, environ)?
        }
        Operator::I64AtomicRmwOr { memarg } => {
            translate_atomic_rmw(I64, I64, AtomicRmwOp::Or, memarg, builder, environ)?
        }
        Operator::I32AtomicRmw8OrU { memarg } => {
            translate_atomic_rmw(I32, I8, AtomicRmwOp::Or, memarg, builder, environ)?
        }
        Operator::I32AtomicRmw16OrU { memarg } => {
            translate_atomic_rmw(I32, I16, AtomicRmwOp::Or, memarg, builder, environ)?
        }
        Operator::I64AtomicRmw8OrU { memarg } => {
            translate_atomic_rmw(I64, I8, AtomicRmwOp::Or, memarg, builder, environ)?
        }
        Operator::I64AtomicRmw16OrU { memarg } => {
            translate_atomic_rmw(I64, I16, AtomicRmwOp::Or, memarg, builder, environ)?
        }
        Operator::I64AtomicRmw32OrU { memarg } => {
            translate_atomic_rmw(I64, I32, AtomicRmwOp::Or, memarg, builder, environ)?
        }

        Operator::I32AtomicRmwXor { memarg } => {
            translate_atomic_rmw(I32, I32, AtomicRmwOp::Xor, memarg, builder, environ)?
        }
        Operator::I64AtomicRmwXor { memarg } => {
            translate_atomic_rmw(I64, I64, AtomicRmwOp::Xor, memarg, builder, environ)?
        }
        Operator::I32AtomicRmw8XorU { memarg } => {
            translate_atomic_rmw(I32, I8, AtomicRmwOp::Xor, memarg, builder, environ)?
        }
        Operator::I32AtomicRmw16XorU { memarg } => {
            translate_atomic_rmw(I32, I16, AtomicRmwOp::Xor, memarg, builder, environ)?
        }
        Operator::I64AtomicRmw8XorU { memarg } => {
            translate_atomic_rmw(I64, I8, AtomicRmwOp::Xor, memarg, builder, environ)?
        }
        Operator::I64AtomicRmw16XorU { memarg } => {
            translate_atomic_rmw(I64, I16, AtomicRmwOp::Xor, memarg, builder, environ)?
        }
        Operator::I64AtomicRmw32XorU { memarg } => {
            translate_atomic_rmw(I64, I32, AtomicRmwOp::Xor, memarg, builder, environ)?
        }

        Operator::I32AtomicRmwXchg { memarg } => {
            translate_atomic_rmw(I32, I32, AtomicRmwOp::Xchg, memarg, builder, environ)?
        }
        Operator::I64AtomicRmwXchg { memarg } => {
            translate_atomic_rmw(I64, I64, AtomicRmwOp::Xchg, memarg, builder, environ)?
        }
        Operator::I32AtomicRmw8XchgU { memarg } => {
            translate_atomic_rmw(I32, I8, AtomicRmwOp::Xchg, memarg, builder, environ)?
        }
        Operator::I32AtomicRmw16XchgU { memarg } => {
            translate_atomic_rmw(I32, I16, AtomicRmwOp::Xchg, memarg, builder, environ)?
        }
        Operator::I64AtomicRmw8XchgU { memarg } => {
            translate_atomic_rmw(I64, I8, AtomicRmwOp::Xchg, memarg, builder, environ)?
        }
        Operator::I64AtomicRmw16XchgU { memarg } => {
            translate_atomic_rmw(I64, I16, AtomicRmwOp::Xchg, memarg, builder, environ)?
        }
        Operator::I64AtomicRmw32XchgU { memarg } => {
            translate_atomic_rmw(I64, I32, AtomicRmwOp::Xchg, memarg, builder, environ)?
        }

        Operator::I32AtomicRmwCmpxchg { memarg } => {
            translate_atomic_cas(I32, I32, memarg, builder, environ)?
        }
        Operator::I64AtomicRmwCmpxchg { memarg } => {
            translate_atomic_cas(I64, I64, memarg, builder, environ)?
        }
        Operator::I32AtomicRmw8CmpxchgU { memarg } => {
            translate_atomic_cas(I32, I8, memarg, builder, environ)?
        }
        Operator::I32AtomicRmw16CmpxchgU { memarg } => {
            translate_atomic_cas(I32, I16, memarg, builder, environ)?
        }
        Operator::I64AtomicRmw8CmpxchgU { memarg } => {
            translate_atomic_cas(I64, I8, memarg, builder, environ)?
        }
        Operator::I64AtomicRmw16CmpxchgU { memarg } => {
            translate_atomic_cas(I64, I16, memarg, builder, environ)?
        }
        Operator::I64AtomicRmw32CmpxchgU { memarg } => {
            translate_atomic_cas(I64, I32, memarg, builder, environ)?
        }

        Operator::AtomicFence { .. } => {
            builder.ins().fence();
        }
        Operator::MemoryCopy { src_mem, dst_mem } => {
            let src_index = MemoryIndex::from_u32(*src_mem);
            let _src_heap = environ.get_or_create_heap(builder.func, src_index);

            let dst_index = MemoryIndex::from_u32(*dst_mem);
            let _dst_heap = environ.get_or_create_heap(builder.func, dst_index);

            let len = environ.stacks.pop1();
            let src_pos = environ.stacks.pop1();
            let dst_pos = environ.stacks.pop1();
            environ.translate_memory_copy(builder, src_index, dst_index, dst_pos, src_pos, len)?;
        }
        Operator::MemoryFill { mem } => {
            let mem = MemoryIndex::from_u32(*mem);
            let _heap = environ.get_or_create_heap(builder.func, mem);
            let len = environ.stacks.pop1();
            let val = environ.stacks.pop1();
            let dest = environ.stacks.pop1();
            environ.translate_memory_fill(builder, mem, dest, val, len)?;
        }
        Operator::MemoryInit { data_index, mem } => {
            let mem = MemoryIndex::from_u32(*mem);
            let _heap = environ.get_or_create_heap(builder.func, mem);
            let len = environ.stacks.pop1();
            let src = environ.stacks.pop1();
            let dest = environ.stacks.pop1();
            environ.translate_memory_init(builder, mem, *data_index, dest, src, len)?;
        }
        Operator::DataDrop { data_index } => {
            environ.translate_data_drop(builder.cursor(), *data_index)?;
        }
        Operator::TableSize { table: index } => {
            let result =
                environ.translate_table_size(builder.cursor(), TableIndex::from_u32(*index))?;
            environ.stacks.push1(result);
        }
        Operator::TableGrow { table: index } => {
            let table_index = TableIndex::from_u32(*index);
            let delta = environ.stacks.pop1();
            let init_value = environ.stacks.pop1();
            let result = environ.translate_table_grow(builder, table_index, delta, init_value)?;
            environ.stacks.push1(result);
        }
        Operator::TableGet { table: index } => {
            let table_index = TableIndex::from_u32(*index);
            let index = environ.stacks.pop1();
            let result = environ.translate_table_get(builder, table_index, index)?;
            environ.stacks.push1(result);
        }
        Operator::TableSet { table: index } => {
            let table_index = TableIndex::from_u32(*index);
            let value = environ.stacks.pop1();
            let index = environ.stacks.pop1();
            environ.translate_table_set(builder, table_index, value, index)?;
        }
        Operator::TableCopy {
            dst_table: dst_table_index,
            src_table: src_table_index,
        } => {
            let len = environ.stacks.pop1();
            let src = environ.stacks.pop1();
            let dest = environ.stacks.pop1();
            environ.translate_table_copy(
                builder,
                TableIndex::from_u32(*dst_table_index),
                TableIndex::from_u32(*src_table_index),
                dest,
                src,
                len,
            )?;
        }
        Operator::TableFill { table } => {
            let table_index = TableIndex::from_u32(*table);
            let len = environ.stacks.pop1();
            let val = environ.stacks.pop1();
            let dest = environ.stacks.pop1();
            environ.translate_table_fill(builder, table_index, dest, val, len)?;
        }
        Operator::TableInit {
            elem_index,
            table: table_index,
        } => {
            let len = environ.stacks.pop1();
            let src = environ.stacks.pop1();
            let dest = environ.stacks.pop1();
            environ.translate_table_init(
                builder,
                *elem_index,
                TableIndex::from_u32(*table_index),
                dest,
                src,
                len,
            )?;
        }
        Operator::ElemDrop { elem_index } => {
            environ.translate_elem_drop(builder.cursor(), *elem_index)?;
        }
        Operator::V128Const { value } => {
            let data = value.bytes().to_vec().into();
            let handle = builder.func.dfg.constants.insert(data);
            let value = builder.ins().vconst(I8X16, handle);
            // the v128.const is typed in CLIF as a I8x16 but bitcast to a different type
            // before use
            environ.stacks.push1(value)
        }
        Operator::I8x16Splat | Operator::I16x8Splat => {
            let reduced = builder
                .ins()
                .ireduce(type_of(op).lane_type(), environ.stacks.pop1());
            let splatted = builder.ins().splat(type_of(op), reduced);
            environ.stacks.push1(splatted)
        }
        Operator::I32x4Splat
        | Operator::I64x2Splat
        | Operator::F32x4Splat
        | Operator::F64x2Splat => {
            let splatted = builder.ins().splat(type_of(op), environ.stacks.pop1());
            environ.stacks.push1(splatted)
        }
        Operator::V128Load8Splat { memarg }
        | Operator::V128Load16Splat { memarg }
        | Operator::V128Load32Splat { memarg }
        | Operator::V128Load64Splat { memarg } => {
            unwrap_or_return_unreachable_state!(
                environ,
                translate_load(
                    memarg,
                    ir::Opcode::Load,
                    type_of(op).lane_type(),
                    builder,
                    environ,
                )?
            );
            let splatted = builder.ins().splat(type_of(op), environ.stacks.pop1());
            environ.stacks.push1(splatted)
        }
        Operator::V128Load32Zero { memarg } | Operator::V128Load64Zero { memarg } => {
            unwrap_or_return_unreachable_state!(
                environ,
                translate_load(
                    memarg,
                    ir::Opcode::Load,
                    type_of(op).lane_type(),
                    builder,
                    environ,
                )?
            );
            let as_vector = builder
                .ins()
                .scalar_to_vector(type_of(op), environ.stacks.pop1());
            environ.stacks.push1(as_vector)
        }
        Operator::V128Load8Lane { memarg, lane }
        | Operator::V128Load16Lane { memarg, lane }
        | Operator::V128Load32Lane { memarg, lane }
        | Operator::V128Load64Lane { memarg, lane } => {
            let vector = pop1_with_bitcast(environ, type_of(op), builder);
            unwrap_or_return_unreachable_state!(
                environ,
                translate_load(
                    memarg,
                    ir::Opcode::Load,
                    type_of(op).lane_type(),
                    builder,
                    environ,
                )?
            );
            let replacement = environ.stacks.pop1();
            environ
                .stacks
                .push1(builder.ins().insertlane(vector, replacement, *lane))
        }
        Operator::V128Store8Lane { memarg, lane }
        | Operator::V128Store16Lane { memarg, lane }
        | Operator::V128Store32Lane { memarg, lane }
        | Operator::V128Store64Lane { memarg, lane } => {
            let vector = pop1_with_bitcast(environ, type_of(op), builder);
            environ
                .stacks
                .push1(builder.ins().extractlane(vector, *lane));
            translate_store(memarg, ir::Opcode::Store, builder, environ)?;
        }
        Operator::I8x16ExtractLaneS { lane } | Operator::I16x8ExtractLaneS { lane } => {
            let vector = pop1_with_bitcast(environ, type_of(op), builder);
            let extracted = builder.ins().extractlane(vector, *lane);
            environ.stacks.push1(builder.ins().sextend(I32, extracted))
        }
        Operator::I8x16ExtractLaneU { lane } | Operator::I16x8ExtractLaneU { lane } => {
            let vector = pop1_with_bitcast(environ, type_of(op), builder);
            let extracted = builder.ins().extractlane(vector, *lane);
            environ.stacks.push1(builder.ins().uextend(I32, extracted));
            // On x86, PEXTRB zeroes the upper bits of the destination register of extractlane so
            // uextend could be elided; for now, uextend is needed for Cranelift's type checks to
            // work.
        }
        Operator::I32x4ExtractLane { lane }
        | Operator::I64x2ExtractLane { lane }
        | Operator::F32x4ExtractLane { lane }
        | Operator::F64x2ExtractLane { lane } => {
            let vector = pop1_with_bitcast(environ, type_of(op), builder);
            environ
                .stacks
                .push1(builder.ins().extractlane(vector, *lane))
        }
        Operator::I8x16ReplaceLane { lane } | Operator::I16x8ReplaceLane { lane } => {
            let (vector, replacement) = environ.stacks.pop2();
            let ty = type_of(op);
            let reduced = builder.ins().ireduce(ty.lane_type(), replacement);
            let vector = optionally_bitcast_vector(vector, ty, builder);
            environ
                .stacks
                .push1(builder.ins().insertlane(vector, reduced, *lane))
        }
        Operator::I32x4ReplaceLane { lane }
        | Operator::I64x2ReplaceLane { lane }
        | Operator::F32x4ReplaceLane { lane }
        | Operator::F64x2ReplaceLane { lane } => {
            let (vector, replacement) = environ.stacks.pop2();
            let vector = optionally_bitcast_vector(vector, type_of(op), builder);
            environ
                .stacks
                .push1(builder.ins().insertlane(vector, replacement, *lane))
        }
        Operator::I8x16Shuffle { lanes, .. } => {
            let (a, b) = pop2_with_bitcast(environ, I8X16, builder);
            let result = environ.i8x16_shuffle(builder, a, b, lanes);
            environ.stacks.push1(result);
            // At this point the original types of a and b are lost; users of this value (i.e. this
            // WASM-to-CLIF translator) may need to bitcast for type-correctness. This is due
            // to WASM using the less specific v128 type for certain operations and more specific
            // types (e.g. i8x16) for others.
        }
        Operator::I8x16Swizzle => {
            let (a, b) = pop2_with_bitcast(environ, I8X16, builder);
            let result = environ.swizzle(builder, a, b);
            environ.stacks.push1(result);
        }
        Operator::I8x16Add | Operator::I16x8Add | Operator::I32x4Add | Operator::I64x2Add => {
            let (a, b) = pop2_with_bitcast(environ, type_of(op), builder);
            environ.stacks.push1(builder.ins().iadd(a, b))
        }
        Operator::I8x16AddSatS | Operator::I16x8AddSatS => {
            let (a, b) = pop2_with_bitcast(environ, type_of(op), builder);
            environ.stacks.push1(builder.ins().sadd_sat(a, b))
        }
        Operator::I8x16AddSatU | Operator::I16x8AddSatU => {
            let (a, b) = pop2_with_bitcast(environ, type_of(op), builder);
            environ.stacks.push1(builder.ins().uadd_sat(a, b))
        }
        Operator::I8x16Sub | Operator::I16x8Sub | Operator::I32x4Sub | Operator::I64x2Sub => {
            let (a, b) = pop2_with_bitcast(environ, type_of(op), builder);
            environ.stacks.push1(builder.ins().isub(a, b))
        }
        Operator::I8x16SubSatS | Operator::I16x8SubSatS => {
            let (a, b) = pop2_with_bitcast(environ, type_of(op), builder);
            environ.stacks.push1(builder.ins().ssub_sat(a, b))
        }
        Operator::I8x16SubSatU | Operator::I16x8SubSatU => {
            let (a, b) = pop2_with_bitcast(environ, type_of(op), builder);
            environ.stacks.push1(builder.ins().usub_sat(a, b))
        }
        Operator::I8x16MinS | Operator::I16x8MinS | Operator::I32x4MinS => {
            let (a, b) = pop2_with_bitcast(environ, type_of(op), builder);
            environ.stacks.push1(builder.ins().smin(a, b))
        }
        Operator::I8x16MinU | Operator::I16x8MinU | Operator::I32x4MinU => {
            let (a, b) = pop2_with_bitcast(environ, type_of(op), builder);
            environ.stacks.push1(builder.ins().umin(a, b))
        }
        Operator::I8x16MaxS | Operator::I16x8MaxS | Operator::I32x4MaxS => {
            let (a, b) = pop2_with_bitcast(environ, type_of(op), builder);
            environ.stacks.push1(builder.ins().smax(a, b))
        }
        Operator::I8x16MaxU | Operator::I16x8MaxU | Operator::I32x4MaxU => {
            let (a, b) = pop2_with_bitcast(environ, type_of(op), builder);
            environ.stacks.push1(builder.ins().umax(a, b))
        }
        Operator::I8x16AvgrU | Operator::I16x8AvgrU => {
            let (a, b) = pop2_with_bitcast(environ, type_of(op), builder);
            environ.stacks.push1(builder.ins().avg_round(a, b))
        }
        Operator::I8x16Neg | Operator::I16x8Neg | Operator::I32x4Neg | Operator::I64x2Neg => {
            let a = pop1_with_bitcast(environ, type_of(op), builder);
            environ.stacks.push1(builder.ins().ineg(a))
        }
        Operator::I8x16Abs | Operator::I16x8Abs | Operator::I32x4Abs | Operator::I64x2Abs => {
            let a = pop1_with_bitcast(environ, type_of(op), builder);
            environ.stacks.push1(builder.ins().iabs(a))
        }
        Operator::I16x8Mul | Operator::I32x4Mul | Operator::I64x2Mul => {
            let (a, b) = pop2_with_bitcast(environ, type_of(op), builder);
            environ.stacks.push1(builder.ins().imul(a, b))
        }
        Operator::V128Or => {
            let (a, b) = pop2_with_bitcast(environ, type_of(op), builder);
            environ.stacks.push1(builder.ins().bor(a, b))
        }
        Operator::V128Xor => {
            let (a, b) = pop2_with_bitcast(environ, type_of(op), builder);
            environ.stacks.push1(builder.ins().bxor(a, b))
        }
        Operator::V128And => {
            let (a, b) = pop2_with_bitcast(environ, type_of(op), builder);
            environ.stacks.push1(builder.ins().band(a, b))
        }
        Operator::V128AndNot => {
            let (a, b) = pop2_with_bitcast(environ, type_of(op), builder);
            environ.stacks.push1(builder.ins().band_not(a, b))
        }
        Operator::V128Not => {
            let a = environ.stacks.pop1();
            environ.stacks.push1(builder.ins().bnot(a));
        }
        Operator::I8x16Shl | Operator::I16x8Shl | Operator::I32x4Shl | Operator::I64x2Shl => {
            let (a, b) = environ.stacks.pop2();
            let bitcast_a = optionally_bitcast_vector(a, type_of(op), builder);
            // The spec expects to shift with `b mod lanewidth`; This is directly compatible
            // with cranelift's instruction.
            environ.stacks.push1(builder.ins().ishl(bitcast_a, b))
        }
        Operator::I8x16ShrU | Operator::I16x8ShrU | Operator::I32x4ShrU | Operator::I64x2ShrU => {
            let (a, b) = environ.stacks.pop2();
            let bitcast_a = optionally_bitcast_vector(a, type_of(op), builder);
            // The spec expects to shift with `b mod lanewidth`; This is directly compatible
            // with cranelift's instruction.
            environ.stacks.push1(builder.ins().ushr(bitcast_a, b))
        }
        Operator::I8x16ShrS | Operator::I16x8ShrS | Operator::I32x4ShrS | Operator::I64x2ShrS => {
            let (a, b) = environ.stacks.pop2();
            let bitcast_a = optionally_bitcast_vector(a, type_of(op), builder);
            // The spec expects to shift with `b mod lanewidth`; This is directly compatible
            // with cranelift's instruction.
            environ.stacks.push1(builder.ins().sshr(bitcast_a, b))
        }
        Operator::V128Bitselect => {
            let (a, b, c) = pop3_with_bitcast(environ, I8X16, builder);
            // The CLIF operand ordering is slightly different and the types of all three
            // operands must match (hence the bitcast).
            environ.stacks.push1(builder.ins().bitselect(c, a, b))
        }
        Operator::V128AnyTrue => {
            let a = pop1_with_bitcast(environ, type_of(op), builder);
            let bool_result = builder.ins().vany_true(a);
            environ
                .stacks
                .push1(builder.ins().uextend(I32, bool_result))
        }
        Operator::I8x16AllTrue
        | Operator::I16x8AllTrue
        | Operator::I32x4AllTrue
        | Operator::I64x2AllTrue => {
            let a = pop1_with_bitcast(environ, type_of(op), builder);
            let bool_result = builder.ins().vall_true(a);
            environ
                .stacks
                .push1(builder.ins().uextend(I32, bool_result))
        }
        Operator::I8x16Bitmask
        | Operator::I16x8Bitmask
        | Operator::I32x4Bitmask
        | Operator::I64x2Bitmask => {
            let a = pop1_with_bitcast(environ, type_of(op), builder);
            environ.stacks.push1(builder.ins().vhigh_bits(I32, a));
        }
        Operator::I8x16Eq | Operator::I16x8Eq | Operator::I32x4Eq | Operator::I64x2Eq => {
            translate_vector_icmp(IntCC::Equal, type_of(op), builder, environ)
        }
        Operator::I8x16Ne | Operator::I16x8Ne | Operator::I32x4Ne | Operator::I64x2Ne => {
            translate_vector_icmp(IntCC::NotEqual, type_of(op), builder, environ)
        }
        Operator::I8x16GtS | Operator::I16x8GtS | Operator::I32x4GtS | Operator::I64x2GtS => {
            translate_vector_icmp(IntCC::SignedGreaterThan, type_of(op), builder, environ)
        }
        Operator::I8x16LtS | Operator::I16x8LtS | Operator::I32x4LtS | Operator::I64x2LtS => {
            translate_vector_icmp(IntCC::SignedLessThan, type_of(op), builder, environ)
        }
        Operator::I8x16GtU | Operator::I16x8GtU | Operator::I32x4GtU => {
            translate_vector_icmp(IntCC::UnsignedGreaterThan, type_of(op), builder, environ)
        }
        Operator::I8x16LtU | Operator::I16x8LtU | Operator::I32x4LtU => {
            translate_vector_icmp(IntCC::UnsignedLessThan, type_of(op), builder, environ)
        }
        Operator::I8x16GeS | Operator::I16x8GeS | Operator::I32x4GeS | Operator::I64x2GeS => {
            translate_vector_icmp(
                IntCC::SignedGreaterThanOrEqual,
                type_of(op),
                builder,
                environ,
            )
        }
        Operator::I8x16LeS | Operator::I16x8LeS | Operator::I32x4LeS | Operator::I64x2LeS => {
            translate_vector_icmp(IntCC::SignedLessThanOrEqual, type_of(op), builder, environ)
        }
        Operator::I8x16GeU | Operator::I16x8GeU | Operator::I32x4GeU => translate_vector_icmp(
            IntCC::UnsignedGreaterThanOrEqual,
            type_of(op),
            builder,
            environ,
        ),
        Operator::I8x16LeU | Operator::I16x8LeU | Operator::I32x4LeU => translate_vector_icmp(
            IntCC::UnsignedLessThanOrEqual,
            type_of(op),
            builder,
            environ,
        ),
        Operator::F32x4Eq | Operator::F64x2Eq => {
            translate_vector_fcmp(FloatCC::Equal, type_of(op), builder, environ)
        }
        Operator::F32x4Ne | Operator::F64x2Ne => {
            translate_vector_fcmp(FloatCC::NotEqual, type_of(op), builder, environ)
        }
        Operator::F32x4Lt | Operator::F64x2Lt => {
            translate_vector_fcmp(FloatCC::LessThan, type_of(op), builder, environ)
        }
        Operator::F32x4Gt | Operator::F64x2Gt => {
            translate_vector_fcmp(FloatCC::GreaterThan, type_of(op), builder, environ)
        }
        Operator::F32x4Le | Operator::F64x2Le => {
            translate_vector_fcmp(FloatCC::LessThanOrEqual, type_of(op), builder, environ)
        }
        Operator::F32x4Ge | Operator::F64x2Ge => {
            translate_vector_fcmp(FloatCC::GreaterThanOrEqual, type_of(op), builder, environ)
        }
        Operator::F32x4Add | Operator::F64x2Add => {
            let (a, b) = pop2_with_bitcast(environ, type_of(op), builder);
            environ.stacks.push1(builder.ins().fadd(a, b))
        }
        Operator::F32x4Sub | Operator::F64x2Sub => {
            let (a, b) = pop2_with_bitcast(environ, type_of(op), builder);
            environ.stacks.push1(builder.ins().fsub(a, b))
        }
        Operator::F32x4Mul | Operator::F64x2Mul => {
            let (a, b) = pop2_with_bitcast(environ, type_of(op), builder);
            environ.stacks.push1(builder.ins().fmul(a, b))
        }
        Operator::F32x4Div | Operator::F64x2Div => {
            let (a, b) = pop2_with_bitcast(environ, type_of(op), builder);
            environ.stacks.push1(builder.ins().fdiv(a, b))
        }
        Operator::F32x4Max | Operator::F64x2Max => {
            let (a, b) = pop2_with_bitcast(environ, type_of(op), builder);
            environ.stacks.push1(builder.ins().fmax(a, b))
        }
        Operator::F32x4Min | Operator::F64x2Min => {
            let (a, b) = pop2_with_bitcast(environ, type_of(op), builder);
            environ.stacks.push1(builder.ins().fmin(a, b))
        }
        Operator::F32x4PMax | Operator::F64x2PMax => {
            // Note the careful ordering here with respect to `fcmp` and
            // `bitselect`. This matches the spec definition of:
            //
            //  fpmax(z1, z2) =
            //      * If z1 is less than z2 then return z2.
            //      * Else return z1.
            let ty = type_of(op);
            let (a, b) = pop2_with_bitcast(environ, ty, builder);
            let cmp = builder.ins().fcmp(FloatCC::LessThan, a, b);
            let cmp = optionally_bitcast_vector(cmp, ty, builder);
            environ.stacks.push1(builder.ins().bitselect(cmp, b, a))
        }
        Operator::F32x4PMin | Operator::F64x2PMin => {
            // Note the careful ordering here which is similar to `pmax` above:
            //
            //  fpmin(z1, z2) =
            //      * If z2 is less than z1 then return z2.
            //      * Else return z1.
            let ty = type_of(op);
            let (a, b) = pop2_with_bitcast(environ, ty, builder);
            let cmp = builder.ins().fcmp(FloatCC::LessThan, b, a);
            let cmp = optionally_bitcast_vector(cmp, ty, builder);
            environ.stacks.push1(builder.ins().bitselect(cmp, b, a))
        }
        Operator::F32x4Sqrt | Operator::F64x2Sqrt => {
            let a = pop1_with_bitcast(environ, type_of(op), builder);
            environ.stacks.push1(builder.ins().sqrt(a))
        }
        Operator::F32x4Neg | Operator::F64x2Neg => {
            let a = pop1_with_bitcast(environ, type_of(op), builder);
            environ.stacks.push1(builder.ins().fneg(a))
        }
        Operator::F32x4Abs | Operator::F64x2Abs => {
            let a = pop1_with_bitcast(environ, type_of(op), builder);
            environ.stacks.push1(builder.ins().fabs(a))
        }
        Operator::F32x4ConvertI32x4S => {
            let a = pop1_with_bitcast(environ, I32X4, builder);
            environ.stacks.push1(builder.ins().fcvt_from_sint(F32X4, a))
        }
        Operator::F32x4ConvertI32x4U => {
            let a = pop1_with_bitcast(environ, I32X4, builder);
            environ.stacks.push1(builder.ins().fcvt_from_uint(F32X4, a))
        }
        Operator::F64x2ConvertLowI32x4S => {
            let a = pop1_with_bitcast(environ, I32X4, builder);
            let widened_a = builder.ins().swiden_low(a);
            environ
                .stacks
                .push1(builder.ins().fcvt_from_sint(F64X2, widened_a));
        }
        Operator::F64x2ConvertLowI32x4U => {
            let a = pop1_with_bitcast(environ, I32X4, builder);
            let widened_a = builder.ins().uwiden_low(a);
            environ
                .stacks
                .push1(builder.ins().fcvt_from_uint(F64X2, widened_a));
        }
        Operator::F64x2PromoteLowF32x4 => {
            let a = pop1_with_bitcast(environ, F32X4, builder);
            environ.stacks.push1(builder.ins().fvpromote_low(a));
        }
        Operator::F32x4DemoteF64x2Zero => {
            let a = pop1_with_bitcast(environ, F64X2, builder);
            environ.stacks.push1(builder.ins().fvdemote(a));
        }
        Operator::I32x4TruncSatF32x4S => {
            let a = pop1_with_bitcast(environ, F32X4, builder);
            environ
                .stacks
                .push1(builder.ins().fcvt_to_sint_sat(I32X4, a))
        }
        Operator::I32x4TruncSatF64x2SZero => {
            let a = pop1_with_bitcast(environ, F64X2, builder);
            let converted_a = builder.ins().fcvt_to_sint_sat(I64X2, a);
            let handle = builder.func.dfg.constants.insert(vec![0u8; 16].into());
            let zero = builder.ins().vconst(I64X2, handle);

            environ
                .stacks
                .push1(builder.ins().snarrow(converted_a, zero));
        }

        // FIXME(#5913): the relaxed instructions here are translated the same
        // as the saturating instructions, even when the code generator
        // configuration allow for different semantics across hosts. On x86,
        // however, it's theoretically possible to have a slightly more optimal
        // lowering which accounts for NaN differently, although the lowering is
        // still not trivial (e.g. one instruction). At this time the
        // more-optimal-but-still-large lowering for x86 is not implemented so
        // the relaxed instructions are listed here instead of down below with
        // the other relaxed instructions. An x86-specific implementation (or
        // perhaps for other backends too) should be added and the codegen for
        // the relaxed instruction should conditionally be different.
        Operator::I32x4RelaxedTruncF32x4U | Operator::I32x4TruncSatF32x4U => {
            let a = pop1_with_bitcast(environ, F32X4, builder);
            environ
                .stacks
                .push1(builder.ins().fcvt_to_uint_sat(I32X4, a))
        }
        Operator::I32x4RelaxedTruncF64x2UZero | Operator::I32x4TruncSatF64x2UZero => {
            let a = pop1_with_bitcast(environ, F64X2, builder);
            let zero_constant = builder.func.dfg.constants.insert(vec![0u8; 16].into());
            let result = if environ.is_x86() && !environ.isa().has_round() {
                // On x86 the vector lowering for `fcvt_to_uint_sat` requires
                // SSE4.1 `round` instructions. If SSE4.1 isn't available it
                // falls back to a libcall which we don't want in Wasmtime.
                // Handle this by falling back to the scalar implementation
                // which does not require SSE4.1 instructions.
                let lane0 = builder.ins().extractlane(a, 0);
                let lane1 = builder.ins().extractlane(a, 1);
                let lane0_rounded = builder.ins().fcvt_to_uint_sat(I32, lane0);
                let lane1_rounded = builder.ins().fcvt_to_uint_sat(I32, lane1);
                let result = builder.ins().vconst(I32X4, zero_constant);
                let result = builder.ins().insertlane(result, lane0_rounded, 0);
                builder.ins().insertlane(result, lane1_rounded, 1)
            } else {
                let converted_a = builder.ins().fcvt_to_uint_sat(I64X2, a);
                let zero = builder.ins().vconst(I64X2, zero_constant);
                builder.ins().uunarrow(converted_a, zero)
            };
            environ.stacks.push1(result);
        }

        Operator::I8x16NarrowI16x8S => {
            let (a, b) = pop2_with_bitcast(environ, I16X8, builder);
            environ.stacks.push1(builder.ins().snarrow(a, b))
        }
        Operator::I16x8NarrowI32x4S => {
            let (a, b) = pop2_with_bitcast(environ, I32X4, builder);
            environ.stacks.push1(builder.ins().snarrow(a, b))
        }
        Operator::I8x16NarrowI16x8U => {
            let (a, b) = pop2_with_bitcast(environ, I16X8, builder);
            environ.stacks.push1(builder.ins().unarrow(a, b))
        }
        Operator::I16x8NarrowI32x4U => {
            let (a, b) = pop2_with_bitcast(environ, I32X4, builder);
            environ.stacks.push1(builder.ins().unarrow(a, b))
        }
        Operator::I16x8ExtendLowI8x16S => {
            let a = pop1_with_bitcast(environ, I8X16, builder);
            environ.stacks.push1(builder.ins().swiden_low(a))
        }
        Operator::I16x8ExtendHighI8x16S => {
            let a = pop1_with_bitcast(environ, I8X16, builder);
            environ.stacks.push1(builder.ins().swiden_high(a))
        }
        Operator::I16x8ExtendLowI8x16U => {
            let a = pop1_with_bitcast(environ, I8X16, builder);
            environ.stacks.push1(builder.ins().uwiden_low(a))
        }
        Operator::I16x8ExtendHighI8x16U => {
            let a = pop1_with_bitcast(environ, I8X16, builder);
            environ.stacks.push1(builder.ins().uwiden_high(a))
        }
        Operator::I32x4ExtendLowI16x8S => {
            let a = pop1_with_bitcast(environ, I16X8, builder);
            environ.stacks.push1(builder.ins().swiden_low(a))
        }
        Operator::I32x4ExtendHighI16x8S => {
            let a = pop1_with_bitcast(environ, I16X8, builder);
            environ.stacks.push1(builder.ins().swiden_high(a))
        }
        Operator::I32x4ExtendLowI16x8U => {
            let a = pop1_with_bitcast(environ, I16X8, builder);
            environ.stacks.push1(builder.ins().uwiden_low(a))
        }
        Operator::I32x4ExtendHighI16x8U => {
            let a = pop1_with_bitcast(environ, I16X8, builder);
            environ.stacks.push1(builder.ins().uwiden_high(a))
        }
        Operator::I64x2ExtendLowI32x4S => {
            let a = pop1_with_bitcast(environ, I32X4, builder);
            environ.stacks.push1(builder.ins().swiden_low(a))
        }
        Operator::I64x2ExtendHighI32x4S => {
            let a = pop1_with_bitcast(environ, I32X4, builder);
            environ.stacks.push1(builder.ins().swiden_high(a))
        }
        Operator::I64x2ExtendLowI32x4U => {
            let a = pop1_with_bitcast(environ, I32X4, builder);
            environ.stacks.push1(builder.ins().uwiden_low(a))
        }
        Operator::I64x2ExtendHighI32x4U => {
            let a = pop1_with_bitcast(environ, I32X4, builder);
            environ.stacks.push1(builder.ins().uwiden_high(a))
        }
        Operator::I16x8ExtAddPairwiseI8x16S => {
            let a = pop1_with_bitcast(environ, I8X16, builder);
            let widen_low = builder.ins().swiden_low(a);
            let widen_high = builder.ins().swiden_high(a);
            environ
                .stacks
                .push1(builder.ins().iadd_pairwise(widen_low, widen_high));
        }
        Operator::I32x4ExtAddPairwiseI16x8S => {
            let a = pop1_with_bitcast(environ, I16X8, builder);
            let widen_low = builder.ins().swiden_low(a);
            let widen_high = builder.ins().swiden_high(a);
            environ
                .stacks
                .push1(builder.ins().iadd_pairwise(widen_low, widen_high));
        }
        Operator::I16x8ExtAddPairwiseI8x16U => {
            let a = pop1_with_bitcast(environ, I8X16, builder);
            let widen_low = builder.ins().uwiden_low(a);
            let widen_high = builder.ins().uwiden_high(a);
            environ
                .stacks
                .push1(builder.ins().iadd_pairwise(widen_low, widen_high));
        }
        Operator::I32x4ExtAddPairwiseI16x8U => {
            let a = pop1_with_bitcast(environ, I16X8, builder);
            let widen_low = builder.ins().uwiden_low(a);
            let widen_high = builder.ins().uwiden_high(a);
            environ
                .stacks
                .push1(builder.ins().iadd_pairwise(widen_low, widen_high));
        }
        Operator::F32x4Ceil => {
            let arg = pop1_with_bitcast(environ, F32X4, builder);
            let result = environ.ceil_f32x4(builder, arg);
            environ.stacks.push1(result);
        }
        Operator::F64x2Ceil => {
            let arg = pop1_with_bitcast(environ, F64X2, builder);
            let result = environ.ceil_f64x2(builder, arg);
            environ.stacks.push1(result);
        }
        Operator::F32x4Floor => {
            let arg = pop1_with_bitcast(environ, F32X4, builder);
            let result = environ.floor_f32x4(builder, arg);
            environ.stacks.push1(result);
        }
        Operator::F64x2Floor => {
            let arg = pop1_with_bitcast(environ, F64X2, builder);
            let result = environ.floor_f64x2(builder, arg);
            environ.stacks.push1(result);
        }
        Operator::F32x4Trunc => {
            let arg = pop1_with_bitcast(environ, F32X4, builder);
            let result = environ.trunc_f32x4(builder, arg);
            environ.stacks.push1(result);
        }
        Operator::F64x2Trunc => {
            let arg = pop1_with_bitcast(environ, F64X2, builder);
            let result = environ.trunc_f64x2(builder, arg);
            environ.stacks.push1(result);
        }
        Operator::F32x4Nearest => {
            let arg = pop1_with_bitcast(environ, F32X4, builder);
            let result = environ.nearest_f32x4(builder, arg);
            environ.stacks.push1(result);
        }
        Operator::F64x2Nearest => {
            let arg = pop1_with_bitcast(environ, F64X2, builder);
            let result = environ.nearest_f64x2(builder, arg);
            environ.stacks.push1(result);
        }
        Operator::I32x4DotI16x8S => {
            let (a, b) = pop2_with_bitcast(environ, I16X8, builder);
            let alow = builder.ins().swiden_low(a);
            let blow = builder.ins().swiden_low(b);
            let low = builder.ins().imul(alow, blow);
            let ahigh = builder.ins().swiden_high(a);
            let bhigh = builder.ins().swiden_high(b);
            let high = builder.ins().imul(ahigh, bhigh);
            environ.stacks.push1(builder.ins().iadd_pairwise(low, high));
        }
        Operator::I8x16Popcnt => {
            let arg = pop1_with_bitcast(environ, type_of(op), builder);
            environ.stacks.push1(builder.ins().popcnt(arg));
        }
        Operator::I16x8Q15MulrSatS => {
            let (a, b) = pop2_with_bitcast(environ, I16X8, builder);
            environ.stacks.push1(builder.ins().sqmul_round_sat(a, b))
        }
        Operator::I16x8ExtMulLowI8x16S => {
            let (a, b) = pop2_with_bitcast(environ, I8X16, builder);
            let a_low = builder.ins().swiden_low(a);
            let b_low = builder.ins().swiden_low(b);
            environ.stacks.push1(builder.ins().imul(a_low, b_low));
        }
        Operator::I16x8ExtMulHighI8x16S => {
            let (a, b) = pop2_with_bitcast(environ, I8X16, builder);
            let a_high = builder.ins().swiden_high(a);
            let b_high = builder.ins().swiden_high(b);
            environ.stacks.push1(builder.ins().imul(a_high, b_high));
        }
        Operator::I16x8ExtMulLowI8x16U => {
            let (a, b) = pop2_with_bitcast(environ, I8X16, builder);
            let a_low = builder.ins().uwiden_low(a);
            let b_low = builder.ins().uwiden_low(b);
            environ.stacks.push1(builder.ins().imul(a_low, b_low));
        }
        Operator::I16x8ExtMulHighI8x16U => {
            let (a, b) = pop2_with_bitcast(environ, I8X16, builder);
            let a_high = builder.ins().uwiden_high(a);
            let b_high = builder.ins().uwiden_high(b);
            environ.stacks.push1(builder.ins().imul(a_high, b_high));
        }
        Operator::I32x4ExtMulLowI16x8S => {
            let (a, b) = pop2_with_bitcast(environ, I16X8, builder);
            let a_low = builder.ins().swiden_low(a);
            let b_low = builder.ins().swiden_low(b);
            environ.stacks.push1(builder.ins().imul(a_low, b_low));
        }
        Operator::I32x4ExtMulHighI16x8S => {
            let (a, b) = pop2_with_bitcast(environ, I16X8, builder);
            let a_high = builder.ins().swiden_high(a);
            let b_high = builder.ins().swiden_high(b);
            environ.stacks.push1(builder.ins().imul(a_high, b_high));
        }
        Operator::I32x4ExtMulLowI16x8U => {
            let (a, b) = pop2_with_bitcast(environ, I16X8, builder);
            let a_low = builder.ins().uwiden_low(a);
            let b_low = builder.ins().uwiden_low(b);
            environ.stacks.push1(builder.ins().imul(a_low, b_low));
        }
        Operator::I32x4ExtMulHighI16x8U => {
            let (a, b) = pop2_with_bitcast(environ, I16X8, builder);
            let a_high = builder.ins().uwiden_high(a);
            let b_high = builder.ins().uwiden_high(b);
            environ.stacks.push1(builder.ins().imul(a_high, b_high));
        }
        Operator::I64x2ExtMulLowI32x4S => {
            let (a, b) = pop2_with_bitcast(environ, I32X4, builder);
            let a_low = builder.ins().swiden_low(a);
            let b_low = builder.ins().swiden_low(b);
            environ.stacks.push1(builder.ins().imul(a_low, b_low));
        }
        Operator::I64x2ExtMulHighI32x4S => {
            let (a, b) = pop2_with_bitcast(environ, I32X4, builder);
            let a_high = builder.ins().swiden_high(a);
            let b_high = builder.ins().swiden_high(b);
            environ.stacks.push1(builder.ins().imul(a_high, b_high));
        }
        Operator::I64x2ExtMulLowI32x4U => {
            let (a, b) = pop2_with_bitcast(environ, I32X4, builder);
            let a_low = builder.ins().uwiden_low(a);
            let b_low = builder.ins().uwiden_low(b);
            environ.stacks.push1(builder.ins().imul(a_low, b_low));
        }
        Operator::I64x2ExtMulHighI32x4U => {
            let (a, b) = pop2_with_bitcast(environ, I32X4, builder);
            let a_high = builder.ins().uwiden_high(a);
            let b_high = builder.ins().uwiden_high(b);
            environ.stacks.push1(builder.ins().imul(a_high, b_high));
        }
        Operator::MemoryDiscard { .. } => {
            return Err(wasm_unsupported!(
                "proposed memory-control operator {:?}",
                op
            ));
        }

        Operator::F32x4RelaxedMax | Operator::F64x2RelaxedMax => {
            let ty = type_of(op);
            let (a, b) = pop2_with_bitcast(environ, ty, builder);
            environ.stacks.push1(
                if environ.relaxed_simd_deterministic() || !environ.is_x86() {
                    // Deterministic semantics match the `fmax` instruction, or
                    // the `fAAxBB.max` wasm instruction.
                    builder.ins().fmax(a, b)
                } else {
                    // Note that this matches the `pmax` translation which has
                    // careful ordering of its operands to trigger
                    // pattern-matches in the x86 backend.
                    let cmp = builder.ins().fcmp(FloatCC::LessThan, a, b);
                    let cmp = optionally_bitcast_vector(cmp, ty, builder);
                    builder.ins().bitselect(cmp, b, a)
                },
            )
        }

        Operator::F32x4RelaxedMin | Operator::F64x2RelaxedMin => {
            let ty = type_of(op);
            let (a, b) = pop2_with_bitcast(environ, ty, builder);
            environ.stacks.push1(
                if environ.relaxed_simd_deterministic() || !environ.is_x86() {
                    // Deterministic semantics match the `fmin` instruction, or
                    // the `fAAxBB.min` wasm instruction.
                    builder.ins().fmin(a, b)
                } else {
                    // Note that this matches the `pmin` translation which has
                    // careful ordering of its operands to trigger
                    // pattern-matches in the x86 backend.
                    let cmp = builder.ins().fcmp(FloatCC::LessThan, b, a);
                    let cmp = optionally_bitcast_vector(cmp, ty, builder);
                    builder.ins().bitselect(cmp, b, a)
                },
            );
        }

        Operator::I8x16RelaxedSwizzle => {
            let (a, b) = pop2_with_bitcast(environ, I8X16, builder);
            let result = environ.relaxed_swizzle(builder, a, b);
            environ.stacks.push1(result);
        }

        Operator::F32x4RelaxedMadd => {
            let (a, b, c) = pop3_with_bitcast(environ, type_of(op), builder);
            let result = environ.fma_f32x4(builder, a, b, c);
            environ.stacks.push1(result);
        }
        Operator::F64x2RelaxedMadd => {
            let (a, b, c) = pop3_with_bitcast(environ, type_of(op), builder);
            let result = environ.fma_f64x2(builder, a, b, c);
            environ.stacks.push1(result);
        }
        Operator::F32x4RelaxedNmadd => {
            let (a, b, c) = pop3_with_bitcast(environ, type_of(op), builder);
            let a = builder.ins().fneg(a);
            let result = environ.fma_f32x4(builder, a, b, c);
            environ.stacks.push1(result);
        }
        Operator::F64x2RelaxedNmadd => {
            let (a, b, c) = pop3_with_bitcast(environ, type_of(op), builder);
            let a = builder.ins().fneg(a);
            let result = environ.fma_f64x2(builder, a, b, c);
            environ.stacks.push1(result);
        }

        Operator::I8x16RelaxedLaneselect
        | Operator::I16x8RelaxedLaneselect
        | Operator::I32x4RelaxedLaneselect
        | Operator::I64x2RelaxedLaneselect => {
            let ty = type_of(op);
            let (a, b, c) = pop3_with_bitcast(environ, ty, builder);
            // Note that the variable swaps here are intentional due to
            // the difference of the order of the wasm op and the clif
            // op.
            environ.stacks.push1(
                if environ.relaxed_simd_deterministic()
                    || !environ.use_blendv_for_relaxed_laneselect(ty)
                {
                    // Deterministic semantics are a `bitselect` along the lines
                    // of the wasm `v128.bitselect` instruction.
                    builder.ins().bitselect(c, a, b)
                } else {
                    builder.ins().blendv(c, a, b)
                },
            );
        }

        Operator::I32x4RelaxedTruncF32x4S => {
            let a = pop1_with_bitcast(environ, F32X4, builder);
            environ.stacks.push1(
                if environ.relaxed_simd_deterministic() || !environ.is_x86() {
                    // Deterministic semantics are to match the
                    // `i32x4.trunc_sat_f32x4_s` instruction.
                    builder.ins().fcvt_to_sint_sat(I32X4, a)
                } else {
                    builder.ins().x86_cvtt2dq(I32X4, a)
                },
            )
        }
        Operator::I32x4RelaxedTruncF64x2SZero => {
            let a = pop1_with_bitcast(environ, F64X2, builder);
            let converted_a = if environ.relaxed_simd_deterministic() || !environ.is_x86() {
                // Deterministic semantics are to match the
                // `i32x4.trunc_sat_f64x2_s_zero` instruction.
                builder.ins().fcvt_to_sint_sat(I64X2, a)
            } else {
                builder.ins().x86_cvtt2dq(I64X2, a)
            };
            let handle = builder.func.dfg.constants.insert(vec![0u8; 16].into());
            let zero = builder.ins().vconst(I64X2, handle);

            environ
                .stacks
                .push1(builder.ins().snarrow(converted_a, zero));
        }
        Operator::I16x8RelaxedQ15mulrS => {
            let (a, b) = pop2_with_bitcast(environ, I16X8, builder);
            environ.stacks.push1(
                if environ.relaxed_simd_deterministic()
                    || !environ.use_x86_pmulhrsw_for_relaxed_q15mul()
                {
                    // Deterministic semantics are to match the
                    // `i16x8.q15mulr_sat_s` instruction.
                    builder.ins().sqmul_round_sat(a, b)
                } else {
                    builder.ins().x86_pmulhrsw(a, b)
                },
            );
        }
        Operator::I16x8RelaxedDotI8x16I7x16S => {
            let (a, b) = pop2_with_bitcast(environ, I8X16, builder);
            environ.stacks.push1(
                if environ.relaxed_simd_deterministic() || !environ.use_x86_pmaddubsw_for_dot() {
                    // Deterministic semantics are to treat both operands as
                    // signed integers and perform the dot product.
                    let alo = builder.ins().swiden_low(a);
                    let blo = builder.ins().swiden_low(b);
                    let lo = builder.ins().imul(alo, blo);
                    let ahi = builder.ins().swiden_high(a);
                    let bhi = builder.ins().swiden_high(b);
                    let hi = builder.ins().imul(ahi, bhi);
                    builder.ins().iadd_pairwise(lo, hi)
                } else {
                    builder.ins().x86_pmaddubsw(a, b)
                },
            );
        }

        Operator::I32x4RelaxedDotI8x16I7x16AddS => {
            let c = pop1_with_bitcast(environ, I32X4, builder);
            let (a, b) = pop2_with_bitcast(environ, I8X16, builder);
            let dot =
                if environ.relaxed_simd_deterministic() || !environ.use_x86_pmaddubsw_for_dot() {
                    // Deterministic semantics are to treat both operands as
                    // signed integers and perform the dot product.
                    let alo = builder.ins().swiden_low(a);
                    let blo = builder.ins().swiden_low(b);
                    let lo = builder.ins().imul(alo, blo);
                    let ahi = builder.ins().swiden_high(a);
                    let bhi = builder.ins().swiden_high(b);
                    let hi = builder.ins().imul(ahi, bhi);
                    builder.ins().iadd_pairwise(lo, hi)
                } else {
                    builder.ins().x86_pmaddubsw(a, b)
                };
            let dotlo = builder.ins().swiden_low(dot);
            let dothi = builder.ins().swiden_high(dot);
            let dot32 = builder.ins().iadd_pairwise(dotlo, dothi);
            environ.stacks.push1(builder.ins().iadd(dot32, c));
        }

        Operator::BrOnNull { relative_depth } => {
            let r = environ.stacks.pop1();
            let &[.., WasmValType::Ref(r_ty)] = operand_types else {
                unreachable!("validation")
            };
            let is_null = environ.translate_ref_is_null(builder.cursor(), r, r_ty)?;
            let (br_destination, inputs) = translate_br_if_args(*relative_depth, environ);
            let else_block = builder.create_block();
            canonicalise_brif(builder, is_null, br_destination, inputs, else_block, &[]);

            builder.seal_block(else_block); // The only predecessor is the current block.
            builder.switch_to_block(else_block);
            environ.stacks.push1(r);
        }
        Operator::BrOnNonNull { relative_depth } => {
            // We write this a bit differently from the spec to avoid an extra
            // block/branch and the typed accounting thereof. Instead of the
            // spec's approach, it's described as such:
            // Peek the value val from the stack.
            // If val is ref.null ht, then: pop the value val from the stack.
            // Else: Execute the instruction (br relative_depth).
            let r = environ.stacks.peek1();
            let [.., WasmValType::Ref(r_ty)] = operand_types else {
                unreachable!("validation")
            };
            let r_ty = *r_ty;
            let (br_destination, inputs) = translate_br_if_args(*relative_depth, environ);
            let inputs = inputs.to_vec();
            let is_null = environ.translate_ref_is_null(builder.cursor(), r, r_ty)?;
            let else_block = builder.create_block();
            canonicalise_brif(builder, is_null, else_block, &[], br_destination, &inputs);

            // In the null case, pop the ref
            environ.stacks.pop1();

            builder.seal_block(else_block); // The only predecessor is the current block.

            // The rest of the translation operates on our is null case, which is
            // currently an empty block
            builder.switch_to_block(else_block);
        }
        Operator::CallRef { type_index } => {
            // Get function signature
            // `index` is the index of the function's signature and `table_index` is the index of
            // the table to search the function in.
            let type_index = TypeIndex::from_u32(*type_index);
            let sigref = environ.get_or_create_sig_ref(builder.func, type_index);
            let num_args = environ.num_params_for_function_type(type_index);
            let callee = environ.stacks.pop1();

            // Bitcast any vector arguments to their default type, I8X16, before calling.
            let mut args = environ.stacks.peekn(num_args).to_vec();
            bitcast_wasm_params(environ, sigref, &mut args, builder);

            let inst_results =
                environ.translate_call_ref(builder, srcloc, sigref, callee, &args)?;

            debug_assert_eq!(
                inst_results.len(),
                builder.func.dfg.signatures[sigref].returns.len(),
                "translate_call_ref results should match the call signature"
            );
            environ.stacks.popn(num_args);
            environ.stacks.pushn(&inst_results);
        }
        Operator::RefAsNonNull => {
            let r = environ.stacks.pop1();
            let [.., WasmValType::Ref(r_ty)] = operand_types else {
                unreachable!("validation")
            };
            let is_null = environ.translate_ref_is_null(builder.cursor(), r, *r_ty)?;
            environ.trapnz(builder, is_null, crate::TRAP_NULL_REFERENCE);
            environ.stacks.push1(r);
        }

        Operator::RefI31 => {
            let val = environ.stacks.pop1();
            let i31ref = environ.translate_ref_i31(builder.cursor(), val)?;
            environ.stacks.push1(i31ref);
        }
        Operator::I31GetS => {
            let i31ref = environ.stacks.pop1();
            let val = environ.translate_i31_get_s(builder, i31ref)?;
            environ.stacks.push1(val);
        }
        Operator::I31GetU => {
            let i31ref = environ.stacks.pop1();
            let val = environ.translate_i31_get_u(builder, i31ref)?;
            environ.stacks.push1(val);
        }

        Operator::StructNew { struct_type_index } => {
            let struct_type_index = TypeIndex::from_u32(*struct_type_index);
            let arity = environ.struct_fields_len(struct_type_index)?;
            let fields: StructFieldsVec = environ.stacks.peekn(arity).iter().copied().collect();
            environ.stacks.popn(arity);
            let struct_ref = environ.translate_struct_new(builder, struct_type_index, fields)?;
            environ.stacks.push1(struct_ref);
        }

        Operator::StructNewDefault { struct_type_index } => {
            let struct_type_index = TypeIndex::from_u32(*struct_type_index);
            let struct_ref = environ.translate_struct_new_default(builder, struct_type_index)?;
            environ.stacks.push1(struct_ref);
        }

        Operator::StructSet {
            struct_type_index,
            field_index,
        } => {
            let struct_type_index = TypeIndex::from_u32(*struct_type_index);
            let val = environ.stacks.pop1();
            let struct_ref = environ.stacks.pop1();
            environ.translate_struct_set(
                builder,
                struct_type_index,
                *field_index,
                struct_ref,
                val,
            )?;
        }

        Operator::StructGetS {
            struct_type_index,
            field_index,
        } => {
            let struct_type_index = TypeIndex::from_u32(*struct_type_index);
            let struct_ref = environ.stacks.pop1();
            let val = environ.translate_struct_get(
                builder,
                struct_type_index,
                *field_index,
                struct_ref,
                Some(Extension::Sign),
            )?;
            environ.stacks.push1(val);
        }

        Operator::StructGetU {
            struct_type_index,
            field_index,
        } => {
            let struct_type_index = TypeIndex::from_u32(*struct_type_index);
            let struct_ref = environ.stacks.pop1();
            let val = environ.translate_struct_get(
                builder,
                struct_type_index,
                *field_index,
                struct_ref,
                Some(Extension::Zero),
            )?;
            environ.stacks.push1(val);
        }

        Operator::StructGet {
            struct_type_index,
            field_index,
        } => {
            let struct_type_index = TypeIndex::from_u32(*struct_type_index);
            let struct_ref = environ.stacks.pop1();
            let val = environ.translate_struct_get(
                builder,
                struct_type_index,
                *field_index,
                struct_ref,
                None,
            )?;
            environ.stacks.push1(val);
        }

        Operator::ArrayNew { array_type_index } => {
            let array_type_index = TypeIndex::from_u32(*array_type_index);
            let (elem, len) = environ.stacks.pop2();
            let array_ref = environ.translate_array_new(builder, array_type_index, elem, len)?;
            environ.stacks.push1(array_ref);
        }
        Operator::ArrayNewDefault { array_type_index } => {
            let array_type_index = TypeIndex::from_u32(*array_type_index);
            let len = environ.stacks.pop1();
            let array_ref = environ.translate_array_new_default(builder, array_type_index, len)?;
            environ.stacks.push1(array_ref);
        }
        Operator::ArrayNewFixed {
            array_type_index,
            array_size,
        } => {
            let array_type_index = TypeIndex::from_u32(*array_type_index);
            let array_size = usize::try_from(*array_size).unwrap();
            let elems = environ.stacks.peekn(array_size).to_vec();
            let array_ref = environ.translate_array_new_fixed(builder, array_type_index, &elems)?;
            environ.stacks.popn(array_size);
            environ.stacks.push1(array_ref);
        }
        Operator::ArrayNewData {
            array_type_index,
            array_data_index,
        } => {
            let array_type_index = TypeIndex::from_u32(*array_type_index);
            let array_data_index = DataIndex::from_u32(*array_data_index);
            let (data_offset, len) = environ.stacks.pop2();
            let array_ref = environ.translate_array_new_data(
                builder,
                array_type_index,
                array_data_index,
                data_offset,
                len,
            )?;
            environ.stacks.push1(array_ref);
        }
        Operator::ArrayNewElem {
            array_type_index,
            array_elem_index,
        } => {
            let array_type_index = TypeIndex::from_u32(*array_type_index);
            let array_elem_index = ElemIndex::from_u32(*array_elem_index);
            let (elem_offset, len) = environ.stacks.pop2();
            let array_ref = environ.translate_array_new_elem(
                builder,
                array_type_index,
                array_elem_index,
                elem_offset,
                len,
            )?;
            environ.stacks.push1(array_ref);
        }
        Operator::ArrayCopy {
            array_type_index_dst,
            array_type_index_src,
        } => {
            let array_type_index_dst = TypeIndex::from_u32(*array_type_index_dst);
            let array_type_index_src = TypeIndex::from_u32(*array_type_index_src);
            let (dst_array, dst_index, src_array, src_index, len) = environ.stacks.pop5();
            environ.translate_array_copy(
                builder,
                array_type_index_dst,
                dst_array,
                dst_index,
                array_type_index_src,
                src_array,
                src_index,
                len,
            )?;
        }
        Operator::ArrayFill { array_type_index } => {
            let array_type_index = TypeIndex::from_u32(*array_type_index);
            let (array, index, val, len) = environ.stacks.pop4();
            environ.translate_array_fill(builder, array_type_index, array, index, val, len)?;
        }
        Operator::ArrayInitData {
            array_type_index,
            array_data_index,
        } => {
            let array_type_index = TypeIndex::from_u32(*array_type_index);
            let array_data_index = DataIndex::from_u32(*array_data_index);
            let (array, dst_index, src_index, len) = environ.stacks.pop4();
            environ.translate_array_init_data(
                builder,
                array_type_index,
                array,
                dst_index,
                array_data_index,
                src_index,
                len,
            )?;
        }
        Operator::ArrayInitElem {
            array_type_index,
            array_elem_index,
        } => {
            let array_type_index = TypeIndex::from_u32(*array_type_index);
            let array_elem_index = ElemIndex::from_u32(*array_elem_index);
            let (array, dst_index, src_index, len) = environ.stacks.pop4();
            environ.translate_array_init_elem(
                builder,
                array_type_index,
                array,
                dst_index,
                array_elem_index,
                src_index,
                len,
            )?;
        }
        Operator::ArrayLen => {
            let array = environ.stacks.pop1();
            let len = environ.translate_array_len(builder, array)?;
            environ.stacks.push1(len);
        }
        Operator::ArrayGet { array_type_index } => {
            let array_type_index = TypeIndex::from_u32(*array_type_index);
            let (array, index) = environ.stacks.pop2();
            let elem =
                environ.translate_array_get(builder, array_type_index, array, index, None)?;
            environ.stacks.push1(elem);
        }
        Operator::ArrayGetS { array_type_index } => {
            let array_type_index = TypeIndex::from_u32(*array_type_index);
            let (array, index) = environ.stacks.pop2();
            let elem = environ.translate_array_get(
                builder,
                array_type_index,
                array,
                index,
                Some(Extension::Sign),
            )?;
            environ.stacks.push1(elem);
        }
        Operator::ArrayGetU { array_type_index } => {
            let array_type_index = TypeIndex::from_u32(*array_type_index);
            let (array, index) = environ.stacks.pop2();
            let elem = environ.translate_array_get(
                builder,
                array_type_index,
                array,
                index,
                Some(Extension::Zero),
            )?;
            environ.stacks.push1(elem);
        }
        Operator::ArraySet { array_type_index } => {
            let array_type_index = TypeIndex::from_u32(*array_type_index);
            let (array, index, elem) = environ.stacks.pop3();
            environ.translate_array_set(builder, array_type_index, array, index, elem)?;
        }
        Operator::RefEq => {
            let (r1, r2) = environ.stacks.pop2();
            let eq = builder.ins().icmp(ir::condcodes::IntCC::Equal, r1, r2);
            let eq = builder.ins().uextend(ir::types::I32, eq);
            environ.stacks.push1(eq);
        }
        Operator::RefTestNonNull { hty } => {
            let r = environ.stacks.pop1();
            let [.., WasmValType::Ref(r_ty)] = operand_types else {
                unreachable!("validation")
            };
            let heap_type = environ.convert_heap_type(*hty)?;
            let result = environ.translate_ref_test(
                builder,
                WasmRefType {
                    heap_type,
                    nullable: false,
                },
                r,
                *r_ty,
            )?;
            environ.stacks.push1(result);
        }
        Operator::RefTestNullable { hty } => {
            let r = environ.stacks.pop1();
            let [.., WasmValType::Ref(r_ty)] = operand_types else {
                unreachable!("validation")
            };
            let heap_type = environ.convert_heap_type(*hty)?;
            let result = environ.translate_ref_test(
                builder,
                WasmRefType {
                    heap_type,
                    nullable: true,
                },
                r,
                *r_ty,
            )?;
            environ.stacks.push1(result);
        }
        Operator::RefCastNonNull { hty } => {
            let r = environ.stacks.pop1();
            let [.., WasmValType::Ref(r_ty)] = operand_types else {
                unreachable!("validation")
            };
            let heap_type = environ.convert_heap_type(*hty)?;
            let cast_okay = environ.translate_ref_test(
                builder,
                WasmRefType {
                    heap_type,
                    nullable: false,
                },
                r,
                *r_ty,
            )?;
            environ.trapz(builder, cast_okay, crate::TRAP_CAST_FAILURE);
            environ.stacks.push1(r);
        }
        Operator::RefCastNullable { hty } => {
            let r = environ.stacks.pop1();
            let [.., WasmValType::Ref(r_ty)] = operand_types else {
                unreachable!("validation")
            };
            let heap_type = environ.convert_heap_type(*hty)?;
            let cast_okay = environ.translate_ref_test(
                builder,
                WasmRefType {
                    heap_type,
                    nullable: true,
                },
                r,
                *r_ty,
            )?;
            environ.trapz(builder, cast_okay, crate::TRAP_CAST_FAILURE);
            environ.stacks.push1(r);
        }
        Operator::BrOnCast {
            relative_depth,
            to_ref_type,
            from_ref_type: _,
        } => {
            let r = environ.stacks.peek1();
            let [.., WasmValType::Ref(r_ty)] = operand_types else {
                unreachable!("validation")
            };

            let to_ref_type = environ.convert_ref_type(*to_ref_type)?;
            let cast_is_okay = environ.translate_ref_test(builder, to_ref_type, r, *r_ty)?;

            let (cast_succeeds_block, inputs) = translate_br_if_args(*relative_depth, environ);
            let cast_fails_block = builder.create_block();
            canonicalise_brif(
                builder,
                cast_is_okay,
                cast_succeeds_block,
                inputs,
                cast_fails_block,
                &[
                    // NB: the `cast_fails_block` is dominated by the current
                    // block, and therefore doesn't need any block params.
                ],
            );

            // The only predecessor is the current block.
            builder.seal_block(cast_fails_block);

            // The next Wasm instruction is executed when the cast failed and we
            // did not branch away.
            builder.switch_to_block(cast_fails_block);
        }
        Operator::BrOnCastFail {
            relative_depth,
            to_ref_type,
            from_ref_type: _,
        } => {
            let r = environ.stacks.peek1();
            let [.., WasmValType::Ref(r_ty)] = operand_types else {
                unreachable!("validation")
            };

            let to_ref_type = environ.convert_ref_type(*to_ref_type)?;
            let cast_is_okay = environ.translate_ref_test(builder, to_ref_type, r, *r_ty)?;

            let (cast_fails_block, inputs) = translate_br_if_args(*relative_depth, environ);
            let cast_succeeds_block = builder.create_block();
            canonicalise_brif(
                builder,
                cast_is_okay,
                cast_succeeds_block,
                &[
                    // NB: the `cast_succeeds_block` is dominated by the current
                    // block, and therefore doesn't need any block params.
                ],
                cast_fails_block,
                inputs,
            );

            // The only predecessor is the current block.
            builder.seal_block(cast_succeeds_block);

            // The next Wasm instruction is executed when the cast succeeded and
            // we did not branch away.
            builder.switch_to_block(cast_succeeds_block);
        }

        Operator::AnyConvertExtern => {
            // Pop an `externref`, push an `anyref`. But they have the same
            // representation, so we don't actually need to do anything.
        }
        Operator::ExternConvertAny => {
            // Pop an `anyref`, push an `externref`. But they have the same
            // representation, so we don't actually need to do anything.
        }

        Operator::ContNew { cont_type_index } => {
            let cont_type_index = TypeIndex::from_u32(*cont_type_index);
            let arg_types: SmallVec<[_; 8]> = environ
                .continuation_arguments(cont_type_index)
                .to_smallvec();
            let result_types: SmallVec<[_; 8]> =
                environ.continuation_returns(cont_type_index).to_smallvec();
            let r = environ.stacks.pop1();
            let contobj = environ.translate_cont_new(builder, r, &arg_types, &result_types)?;
            environ.stacks.push1(contobj);
        }
        Operator::ContBind {
            argument_index,
            result_index,
        } => {
            let src_types = environ.continuation_arguments(TypeIndex::from_u32(*argument_index));
            let dst_arity = environ
                .continuation_arguments(TypeIndex::from_u32(*result_index))
                .len();
            let arg_count = src_types.len() - dst_arity;

            let arg_types = &src_types[0..arg_count];
            for arg_type in arg_types {
                // We can't bind GC objects using cont.bind at the moment: We
                // don't have the necessary infrastructure to traverse the
                // buffers used by cont.bind when looking for GC roots. Thus,
                // this crude check ensures that these buffers can never contain
                // GC roots to begin with.
                if arg_type.is_vmgcref_type_and_not_i31() {
                    return Err(wasmtime_environ::WasmError::Unsupported(
                        "cont.bind does not support GC types at the moment".into(),
                    ));
                }
            }

            let (original_contobj, args) =
                environ.stacks.peekn(arg_count + 1).split_last().unwrap();
            let original_contobj = *original_contobj;
            let args = args.to_vec();

            let new_contobj = environ.translate_cont_bind(builder, original_contobj, &args);

            environ.stacks.popn(arg_count + 1);
            environ.stacks.push1(new_contobj);
        }
        Operator::Suspend { tag_index } => {
            let tag_index = TagIndex::from_u32(*tag_index);
            let param_types = environ.tag_params(tag_index).to_vec();
            let return_types: SmallVec<[_; 8]> = environ
                .tag_returns(tag_index)
                .iter()
                .map(|ty| crate::value_type(environ.isa(), *ty))
                .collect();

            let params = environ.stacks.peekn(param_types.len()).to_vec();
            let param_count = params.len();

            let return_values =
                environ.translate_suspend(builder, tag_index.as_u32(), &params, &return_types);

            environ.stacks.popn(param_count);
            environ.stacks.pushn(&return_values);
        }
        Operator::Resume {
            cont_type_index,
            resume_table: wasm_resume_table,
        } => {
            // We translate the block indices in the wasm resume_table to actual Blocks.
            let mut clif_resume_table = vec![];
            for handle in &wasm_resume_table.handlers {
                match handle {
                    wasmparser::Handle::OnLabel { tag, label } => {
                        let i = environ.stacks.control_stack.len() - 1 - (*label as usize);
                        let frame = &mut environ.stacks.control_stack[i];
                        // This is side-effecting!
                        frame.set_branched_to_exit();
                        clif_resume_table.push((*tag, Some(frame.br_destination())));
                    }
                    wasmparser::Handle::OnSwitch { tag } => {
                        clif_resume_table.push((*tag, None));
                    }
                }
            }

            let cont_type_index = TypeIndex::from_u32(*cont_type_index);
            let arity = environ.continuation_arguments(cont_type_index).len();
            let (contobj, call_args) = environ.stacks.peekn(arity + 1).split_last().unwrap();
            let contobj = *contobj;
            let call_args = call_args.to_vec();

            let cont_return_vals = environ.translate_resume(
                builder,
                cont_type_index.as_u32(),
                contobj,
                &call_args,
                &clif_resume_table,
            )?;

            environ.stacks.popn(arity + 1); // arguments + continuation
            environ.stacks.pushn(&cont_return_vals);
        }
        Operator::ResumeThrow {
            cont_type_index: _,
            tag_index: _,
            resume_table: _,
        } => {
            // TODO(10248) This depends on exception handling
            return Err(wasmtime_environ::WasmError::Unsupported(
                "resume.throw instructions not supported, yet".to_string(),
            ));
        }
        Operator::Switch {
            cont_type_index,
            tag_index,
        } => {
            // Arguments of the continuation we are going to switch to
            let continuation_argument_types: SmallVec<[_; 8]> = environ
                .continuation_arguments(TypeIndex::from_u32(*cont_type_index))
                .to_smallvec();
            // Arity includes the continuation argument
            let arity = continuation_argument_types.len();
            let (contobj, switch_args) = environ.stacks.peekn(arity).split_last().unwrap();
            let contobj = *contobj;
            let switch_args = switch_args.to_vec();

            // Type of the continuation we are going to create by suspending the
            // currently running stack
            let current_continuation_type = continuation_argument_types.last().unwrap();
            let current_continuation_type = current_continuation_type.unwrap_ref_type();

            // Argument types of current_continuation_type. These will in turn
            // be the types of the arguments we receive when someone switches
            // back to this switch instruction
            let current_continuation_arg_types: SmallVec<[_; 8]> =
                match current_continuation_type.heap_type {
                    WasmHeapType::ConcreteCont(index) => {
                        let mti = index
                            .as_module_type_index()
                            .expect("Only supporting module type indices on switch for now");

                        environ
                            .continuation_arguments(TypeIndex::from_u32(mti.as_u32()))
                            .iter()
                            .map(|ty| crate::value_type(environ.isa(), *ty))
                            .collect()
                    }
                    _ => panic!("Invalid type on switch"),
                };

            let switch_return_values = environ.translate_switch(
                builder,
                *tag_index,
                contobj,
                &switch_args,
                &current_continuation_arg_types,
            )?;

            environ.stacks.popn(arity);
            environ.stacks.pushn(&switch_return_values)
        }

        Operator::GlobalAtomicGet { .. }
        | Operator::GlobalAtomicSet { .. }
        | Operator::GlobalAtomicRmwAdd { .. }
        | Operator::GlobalAtomicRmwSub { .. }
        | Operator::GlobalAtomicRmwOr { .. }
        | Operator::GlobalAtomicRmwXor { .. }
        | Operator::GlobalAtomicRmwAnd { .. }
        | Operator::GlobalAtomicRmwXchg { .. }
        | Operator::GlobalAtomicRmwCmpxchg { .. }
        | Operator::TableAtomicGet { .. }
        | Operator::TableAtomicSet { .. }
        | Operator::TableAtomicRmwXchg { .. }
        | Operator::TableAtomicRmwCmpxchg { .. }
        | Operator::StructAtomicGet { .. }
        | Operator::StructAtomicGetS { .. }
        | Operator::StructAtomicGetU { .. }
        | Operator::StructAtomicSet { .. }
        | Operator::StructAtomicRmwAdd { .. }
        | Operator::StructAtomicRmwSub { .. }
        | Operator::StructAtomicRmwOr { .. }
        | Operator::StructAtomicRmwXor { .. }
        | Operator::StructAtomicRmwAnd { .. }
        | Operator::StructAtomicRmwXchg { .. }
        | Operator::StructAtomicRmwCmpxchg { .. }
        | Operator::ArrayAtomicGet { .. }
        | Operator::ArrayAtomicGetS { .. }
        | Operator::ArrayAtomicGetU { .. }
        | Operator::ArrayAtomicSet { .. }
        | Operator::ArrayAtomicRmwAdd { .. }
        | Operator::ArrayAtomicRmwSub { .. }
        | Operator::ArrayAtomicRmwOr { .. }
        | Operator::ArrayAtomicRmwXor { .. }
        | Operator::ArrayAtomicRmwAnd { .. }
        | Operator::ArrayAtomicRmwXchg { .. }
        | Operator::ArrayAtomicRmwCmpxchg { .. }
        | Operator::RefI31Shared { .. } => {
            return Err(wasm_unsupported!(
                "shared-everything-threads operators are not yet implemented"
            ));
        }

        Operator::I64MulWideS => {
            let (arg1, arg2) = environ.stacks.pop2();
            let arg1 = builder.ins().sextend(I128, arg1);
            let arg2 = builder.ins().sextend(I128, arg2);
            let result = builder.ins().imul(arg1, arg2);
            let (lo, hi) = builder.ins().isplit(result);
            environ.stacks.push2(lo, hi);
        }
        Operator::I64MulWideU => {
            let (arg1, arg2) = environ.stacks.pop2();
            let arg1 = builder.ins().uextend(I128, arg1);
            let arg2 = builder.ins().uextend(I128, arg2);
            let result = builder.ins().imul(arg1, arg2);
            let (lo, hi) = builder.ins().isplit(result);
            environ.stacks.push2(lo, hi);
        }
        Operator::I64Add128 => {
            let (arg1, arg2, arg3, arg4) = environ.stacks.pop4();
            let arg1 = builder.ins().iconcat(arg1, arg2);
            let arg2 = builder.ins().iconcat(arg3, arg4);
            let result = builder.ins().iadd(arg1, arg2);
            let (res1, res2) = builder.ins().isplit(result);
            environ.stacks.push2(res1, res2);
        }
        Operator::I64Sub128 => {
            let (arg1, arg2, arg3, arg4) = environ.stacks.pop4();
            let arg1 = builder.ins().iconcat(arg1, arg2);
            let arg2 = builder.ins().iconcat(arg3, arg4);
            let result = builder.ins().isub(arg1, arg2);
            let (res1, res2) = builder.ins().isplit(result);
            environ.stacks.push2(res1, res2);
        }

        // catch-all as `Operator` is `#[non_exhaustive]`
        op => return Err(wasm_unsupported!("operator {op:?}")),
    };
    Ok(())
}

/// Deals with a Wasm instruction located in an unreachable portion of the code. Most of them
/// are dropped but special ones like `End` or `Else` signal the potential end of the unreachable
/// portion so the translation state must be updated accordingly.
fn translate_unreachable_operator(
    validator: &FuncValidator<impl WasmModuleResources>,
    op: &Operator,
    builder: &mut FunctionBuilder,
    environ: &mut FuncEnvironment<'_>,
) -> WasmResult<()> {
    debug_assert!(!environ.is_reachable());
    match *op {
        Operator::If { blockty } => {
            // Push a placeholder control stack entry. The if isn't reachable,
            // so we don't have any branches anywhere.
            environ.stacks.push_if(
                ir::Block::reserved_value(),
                ElseData::NoElse {
                    branch_inst: ir::Inst::reserved_value(),
                    placeholder: ir::Block::reserved_value(),
                },
                0,
                0,
                blockty,
            );
        }
        Operator::Loop { blockty: _ }
        | Operator::Block { blockty: _ }
        | Operator::TryTable { try_table: _ } => {
            environ.stacks.push_block(ir::Block::reserved_value(), 0, 0);
        }
        Operator::Else => {
            let i = environ.stacks.control_stack.len() - 1;
            let reachable = environ.is_reachable();
            match environ.stacks.control_stack[i] {
                ControlStackFrame::If {
                    ref else_data,
                    head_is_reachable,
                    ref mut consequent_ends_reachable,
                    blocktype,
                    ..
                } => {
                    debug_assert!(consequent_ends_reachable.is_none());
                    *consequent_ends_reachable = Some(reachable);

                    if head_is_reachable {
                        // We have a branch from the head of the `if` to the `else`.
                        environ.stacks.reachable = true;

                        let else_block = match *else_data {
                            ElseData::NoElse {
                                branch_inst,
                                placeholder,
                            } => {
                                let (params, _results) =
                                    blocktype_params_results(validator, blocktype)?;
                                let else_block = block_with_params(builder, params, environ)?;
                                let frame = environ.stacks.control_stack.last().unwrap();
                                frame.truncate_value_stack_to_else_params(
                                    &mut environ.stacks.stack,
                                    &mut environ.stacks.stack_shape,
                                );

                                // We change the target of the branch instruction.
                                builder.change_jump_destination(
                                    branch_inst,
                                    placeholder,
                                    else_block,
                                );
                                builder.seal_block(else_block);
                                else_block
                            }
                            ElseData::WithElse { else_block } => {
                                let frame = environ.stacks.control_stack.last().unwrap();
                                frame.truncate_value_stack_to_else_params(
                                    &mut environ.stacks.stack,
                                    &mut environ.stacks.stack_shape,
                                );
                                else_block
                            }
                        };

                        builder.switch_to_block(else_block);

                        // Again, no need to push the parameters for the `else`,
                        // since we already did when we saw the original `if`. See
                        // the comment for translating `Operator::Else` in
                        // `translate_operator` for details.
                    }
                }
                _ => unreachable!(),
            }
        }
        Operator::End => {
            let value_stack = &mut environ.stacks.stack;
            let stack_shape = &mut environ.stacks.stack_shape;
            let control_stack = &mut environ.stacks.control_stack;
            let frame = control_stack.pop().unwrap();

            frame.restore_catch_handlers(&mut environ.stacks.handlers, builder);

            // Pop unused parameters from stack.
            frame.truncate_value_stack_to_original_size(value_stack, stack_shape);

            let reachable_anyway = match frame {
                // If it is a loop we also have to seal the body loop block
                ControlStackFrame::Loop { header, .. } => {
                    builder.seal_block(header);
                    // And loops can't have branches to the end.
                    false
                }
                // If we never set `consequent_ends_reachable` then that means
                // we are finishing the consequent now, and there was no
                // `else`. Whether the following block is reachable depends only
                // on if the head was reachable.
                ControlStackFrame::If {
                    head_is_reachable,
                    consequent_ends_reachable: None,
                    ..
                } => head_is_reachable,
                // Since we are only in this function when in unreachable code,
                // we know that the alternative just ended unreachable. Whether
                // the following block is reachable depends on if the consequent
                // ended reachable or not.
                ControlStackFrame::If {
                    head_is_reachable,
                    consequent_ends_reachable: Some(consequent_ends_reachable),
                    ..
                } => head_is_reachable && consequent_ends_reachable,
                // All other control constructs are already handled.
                _ => false,
            };

            if frame.exit_is_branched_to() || reachable_anyway {
                builder.switch_to_block(frame.following_code());
                builder.seal_block(frame.following_code());

                // And add the return values of the block but only if the next block is reachable
                // (which corresponds to testing if the stack depth is 1)
                value_stack.extend_from_slice(builder.block_params(frame.following_code()));
                environ.stacks.reachable = true;
            }
        }
        _ => {
            // We don't translate because this is unreachable code
        }
    }

    Ok(())
}

/// This function is a generalized helper for validating that a wasm-supplied
/// heap address is in-bounds.
///
/// This function takes a litany of parameters and requires that the *Wasm*
/// address to be verified is at the top of the stack in `state`. This will
/// generate necessary IR to validate that the heap address is correctly
/// in-bounds, and various parameters are returned describing the valid *native*
/// heap address if execution reaches that point.
///
/// Returns `None` when the Wasm access will unconditionally trap.
///
/// Returns `(flags, wasm_addr, native_addr)`.
fn prepare_addr(
    memarg: &MemArg,
    access_size: u8,
    builder: &mut FunctionBuilder,
    environ: &mut FuncEnvironment<'_>,
) -> WasmResult<Reachability<(MemFlags, Value, Value)>> {
    let index = environ.stacks.pop1();

    let memory_index = MemoryIndex::from_u32(memarg.memory);
    let heap = environ.get_or_create_heap(builder.func, memory_index);

    // How exactly the bounds check is performed here and what it's performed
    // on is a bit tricky. Generally we want to rely on access violations (e.g.
    // segfaults) to generate traps since that means we don't have to bounds
    // check anything explicitly.
    //
    // (1) If we don't have a guard page of unmapped memory, though, then we
    // can't rely on this trapping behavior through segfaults. Instead we need
    // to bounds-check the entire memory access here which is everything from
    // `addr32 + offset` to `addr32 + offset + width` (not inclusive). In this
    // scenario our adjusted offset that we're checking is `memarg.offset +
    // access_size`. Note that we do saturating arithmetic here to avoid
    // overflow. The addition here is in the 64-bit space, which means that
    // we'll never overflow for 32-bit wasm but for 64-bit this is an issue. If
    // our effective offset is u64::MAX though then it's impossible for for
    // that to actually be a valid offset because otherwise the wasm linear
    // memory would take all of the host memory!
    //
    // (2) If we have a guard page, however, then we can perform a further
    // optimization of the generated code by only checking multiples of the
    // offset-guard size to be more CSE-friendly. Knowing that we have at least
    // 1 page of a guard page we're then able to disregard the `width` since we
    // know it's always less than one page. Our bounds check will be for the
    // first byte which will either succeed and be guaranteed to fault if it's
    // actually out of bounds, or the bounds check itself will fail. In any case
    // we assert that the width is reasonably small for now so this assumption
    // can be adjusted in the future if we get larger widths.
    //
    // Put another way we can say, where `y < offset_guard_size`:
    //
    //      n * offset_guard_size + y = offset
    //
    // We'll then pass `n * offset_guard_size` as the bounds check value. If
    // this traps then our `offset` would have trapped anyway. If this check
    // passes we know
    //
    //      addr32 + n * offset_guard_size < bound
    //
    // which means
    //
    //      addr32 + n * offset_guard_size + y < bound + offset_guard_size
    //
    // because `y < offset_guard_size`, which then means:
    //
    //      addr32 + offset < bound + offset_guard_size
    //
    // Since we know that that guard size bytes are all unmapped we're
    // guaranteed that `offset` and the `width` bytes after it are either
    // in-bounds or will hit the guard page, meaning we'll get the desired
    // semantics we want.
    //
    // ---
    //
    // With all that in mind remember that the goal is to bounds check as few
    // things as possible. To facilitate this the "fast path" is expected to be
    // hit like so:
    //
    // * For wasm32, wasmtime defaults to 4gb "static" memories with 2gb guard
    //   regions. This means that for all offsets <=2gb, we hit the optimized
    //   case for `heap_addr` on static memories 4gb in size in cranelift's
    //   legalization of `heap_addr`, eliding the bounds check entirely.
    //
    // * For wasm64 offsets <=2gb will generate a single `heap_addr`
    //   instruction, but at this time all heaps are "dynamic" which means that
    //   a single bounds check is forced. Ideally we'd do better here, but
    //   that's the current state of affairs.
    //
    // Basically we assume that most configurations have a guard page and most
    // offsets in `memarg` are <=2gb, which means we get the fast path of one
    // `heap_addr` instruction plus a hardcoded i32-offset in memory-related
    // instructions.
    let heap = environ.heaps()[heap].clone();
    let addr = match u32::try_from(memarg.offset) {
        // If our offset fits within a u32, then we can place the it into the
        // offset immediate of the `heap_addr` instruction.
        Ok(offset) => bounds_check_and_compute_addr(
            builder,
            environ,
            &heap,
            index,
            BoundsCheck::StaticOffset {
                offset,
                access_size,
            },
            ir::TrapCode::HEAP_OUT_OF_BOUNDS,
        ),

        // If the offset doesn't fit within a u32, then we can't pass it
        // directly into `heap_addr`.
        //
        // One reasonable question you might ask is "why not?". There's no
        // fundamental reason why `heap_addr` *must* take a 32-bit offset. The
        // reason this isn't done, though, is that blindly changing the offset
        // to a 64-bit offset increases the size of the `InstructionData` enum
        // in cranelift by 8 bytes (16 to 24). This can have significant
        // performance implications so the conclusion when this was written was
        // that we shouldn't do that.
        //
        // Without the ability to put the whole offset into the `heap_addr`
        // instruction we need to fold the offset into the address itself with
        // an unsigned addition. In doing so though we need to check for
        // overflow because that would mean the address is out-of-bounds (wasm
        // bounds checks happen on the effective 33 or 65 bit address once the
        // offset is factored in).
        //
        // Once we have the effective address, offset already folded in, then
        // `heap_addr` is used to verify that the address is indeed in-bounds.
        //
        // Note that this is generating what's likely to be at least two
        // branches, one for the overflow and one for the bounds check itself.
        // For now though that should hopefully be ok since 4gb+ offsets are
        // relatively odd/rare. In the future if needed we can look into
        // optimizing this more.
        Err(_) => {
            let offset = builder
                .ins()
                .iconst(heap.index_type(), memarg.offset.cast_signed());
            let adjusted_index = environ.uadd_overflow_trap(
                builder,
                index,
                offset,
                ir::TrapCode::HEAP_OUT_OF_BOUNDS,
            );
            bounds_check_and_compute_addr(
                builder,
                environ,
                &heap,
                adjusted_index,
                BoundsCheck::StaticOffset {
                    offset: 0,
                    access_size,
                },
                ir::TrapCode::HEAP_OUT_OF_BOUNDS,
            )
        }
    };
    let addr = match addr {
        Reachability::Unreachable => return Ok(Reachability::Unreachable),
        Reachability::Reachable(a) => a,
    };

    // Note that we don't set `is_aligned` here, even if the load instruction's
    // alignment immediate may says it's aligned, because WebAssembly's
    // immediate field is just a hint, while Cranelift's aligned flag needs a
    // guarantee. WebAssembly memory accesses are always little-endian.
    let mut flags = MemFlags::new();
    flags.set_endianness(ir::Endianness::Little);

    if heap.pcc_memory_type.is_some() {
        // Proof-carrying code is enabled; check this memory access.
        flags.set_checked();
    }

    // The access occurs to the `heap` disjoint category of abstract
    // state. This may allow alias analysis to merge redundant loads,
    // etc. when heap accesses occur interleaved with other (table,
    // vmctx, stack) accesses.
    flags.set_alias_region(Some(ir::AliasRegion::Heap));

    Ok(Reachability::Reachable((flags, index, addr)))
}

fn align_atomic_addr(
    memarg: &MemArg,
    loaded_bytes: u8,
    builder: &mut FunctionBuilder,
    environ: &mut FuncEnvironment<'_>,
) {
    // Atomic addresses must all be aligned correctly, and for now we check
    // alignment before we check out-of-bounds-ness. The order of this check may
    // need to be updated depending on the outcome of the official threads
    // proposal itself.
    //
    // Note that with an offset>0 we generate an `iadd_imm` where the result is
    // thrown away after the offset check. This may truncate the offset and the
    // result may overflow as well, but those conditions won't affect the
    // alignment check itself. This can probably be optimized better and we
    // should do so in the future as well.
    if loaded_bytes > 1 {
        let addr = environ.stacks.pop1(); // "peek" via pop then push
        environ.stacks.push1(addr);
        let effective_addr = if memarg.offset == 0 {
            addr
        } else {
            builder.ins().iadd_imm(addr, memarg.offset.cast_signed())
        };
        debug_assert!(loaded_bytes.is_power_of_two());
        let misalignment = builder
            .ins()
            .band_imm(effective_addr, i64::from(loaded_bytes - 1));
        let f = builder.ins().icmp_imm(IntCC::NotEqual, misalignment, 0);
        environ.trapnz(builder, f, crate::TRAP_HEAP_MISALIGNED);
    }
}

/// Like `prepare_addr` but for atomic accesses.
///
/// Returns `None` when the Wasm access will unconditionally trap.
fn prepare_atomic_addr(
    memarg: &MemArg,
    loaded_bytes: u8,
    builder: &mut FunctionBuilder,
    environ: &mut FuncEnvironment<'_>,
) -> WasmResult<Reachability<(MemFlags, Value, Value)>> {
    align_atomic_addr(memarg, loaded_bytes, builder, environ);
    prepare_addr(memarg, loaded_bytes, builder, environ)
}

/// Translate a load instruction.
///
/// Returns the execution state's reachability after the load is translated.
fn translate_load(
    memarg: &MemArg,
    opcode: ir::Opcode,
    result_ty: Type,
    builder: &mut FunctionBuilder,
    environ: &mut FuncEnvironment<'_>,
) -> WasmResult<Reachability<()>> {
    let mem_op_size = mem_op_size(opcode, result_ty);
    let (flags, wasm_index, base) = match prepare_addr(memarg, mem_op_size, builder, environ)? {
        Reachability::Unreachable => return Ok(Reachability::Unreachable),
        Reachability::Reachable((f, i, b)) => (f, i, b),
    };

    environ.before_load(builder, mem_op_size, wasm_index, memarg.offset);

    let (load, dfg) = builder
        .ins()
        .Load(opcode, result_ty, flags, Offset32::new(0), base);
    environ.stacks.push1(dfg.first_result(load));
    Ok(Reachability::Reachable(()))
}

/// Translate a store instruction.
fn translate_store(
    memarg: &MemArg,
    opcode: ir::Opcode,
    builder: &mut FunctionBuilder,
    environ: &mut FuncEnvironment<'_>,
) -> WasmResult<()> {
    let val = environ.stacks.pop1();
    let val_ty = builder.func.dfg.value_type(val);
    let mem_op_size = mem_op_size(opcode, val_ty);

    let (flags, wasm_index, base) = unwrap_or_return_unreachable_state!(
        environ,
        prepare_addr(memarg, mem_op_size, builder, environ)?
    );

    environ.before_store(builder, mem_op_size, wasm_index, memarg.offset);

    builder
        .ins()
        .Store(opcode, val_ty, flags, Offset32::new(0), val, base);
    Ok(())
}

fn mem_op_size(opcode: ir::Opcode, ty: Type) -> u8 {
    match opcode {
        ir::Opcode::Istore8 | ir::Opcode::Sload8 | ir::Opcode::Uload8 => 1,
        ir::Opcode::Istore16 | ir::Opcode::Sload16 | ir::Opcode::Uload16 => 2,
        ir::Opcode::Istore32 | ir::Opcode::Sload32 | ir::Opcode::Uload32 => 4,
        ir::Opcode::Store | ir::Opcode::Load => u8::try_from(ty.bytes()).unwrap(),
        _ => panic!("unknown size of mem op for {opcode:?}"),
    }
}

fn translate_icmp(cc: IntCC, builder: &mut FunctionBuilder, environ: &mut FuncEnvironment<'_>) {
    let (arg0, arg1) = environ.stacks.pop2();
    let val = builder.ins().icmp(cc, arg0, arg1);
    environ.stacks.push1(builder.ins().uextend(I32, val));
}

fn translate_atomic_rmw(
    widened_ty: Type,
    access_ty: Type,
    op: AtomicRmwOp,
    memarg: &MemArg,
    builder: &mut FunctionBuilder,
    environ: &mut FuncEnvironment<'_>,
) -> WasmResult<()> {
    let mut arg2 = environ.stacks.pop1();
    let arg2_ty = builder.func.dfg.value_type(arg2);

    // The operation is performed at type `access_ty`, and the old value is zero-extended
    // to type `widened_ty`.
    match access_ty {
        I8 | I16 | I32 | I64 => {}
        _ => {
            return Err(wasm_unsupported!(
                "atomic_rmw: unsupported access type {:?}",
                access_ty
            ));
        }
    };
    let w_ty_ok = match widened_ty {
        I32 | I64 => true,
        _ => false,
    };
    assert!(w_ty_ok && widened_ty.bytes() >= access_ty.bytes());

    assert!(arg2_ty.bytes() >= access_ty.bytes());
    if arg2_ty.bytes() > access_ty.bytes() {
        arg2 = builder.ins().ireduce(access_ty, arg2);
    }

    let (flags, _, addr) = unwrap_or_return_unreachable_state!(
        environ,
        prepare_atomic_addr(
            memarg,
            u8::try_from(access_ty.bytes()).unwrap(),
            builder,
            environ,
        )?
    );

    let mut res = builder.ins().atomic_rmw(access_ty, flags, op, addr, arg2);
    if access_ty != widened_ty {
        res = builder.ins().uextend(widened_ty, res);
    }
    environ.stacks.push1(res);
    Ok(())
}

fn translate_atomic_cas(
    widened_ty: Type,
    access_ty: Type,
    memarg: &MemArg,
    builder: &mut FunctionBuilder,
    environ: &mut FuncEnvironment<'_>,
) -> WasmResult<()> {
    let (mut expected, mut replacement) = environ.stacks.pop2();
    let expected_ty = builder.func.dfg.value_type(expected);
    let replacement_ty = builder.func.dfg.value_type(replacement);

    // The compare-and-swap is performed at type `access_ty`, and the old value is zero-extended
    // to type `widened_ty`.
    match access_ty {
        I8 | I16 | I32 | I64 => {}
        _ => {
            return Err(wasm_unsupported!(
                "atomic_cas: unsupported access type {:?}",
                access_ty
            ));
        }
    };
    let w_ty_ok = match widened_ty {
        I32 | I64 => true,
        _ => false,
    };
    assert!(w_ty_ok && widened_ty.bytes() >= access_ty.bytes());

    assert!(expected_ty.bytes() >= access_ty.bytes());
    if expected_ty.bytes() > access_ty.bytes() {
        expected = builder.ins().ireduce(access_ty, expected);
    }
    assert!(replacement_ty.bytes() >= access_ty.bytes());
    if replacement_ty.bytes() > access_ty.bytes() {
        replacement = builder.ins().ireduce(access_ty, replacement);
    }

    let (flags, _, addr) = unwrap_or_return_unreachable_state!(
        environ,
        prepare_atomic_addr(
            memarg,
            u8::try_from(access_ty.bytes()).unwrap(),
            builder,
            environ,
        )?
    );
    let mut res = builder.ins().atomic_cas(flags, addr, expected, replacement);
    if access_ty != widened_ty {
        res = builder.ins().uextend(widened_ty, res);
    }
    environ.stacks.push1(res);
    Ok(())
}

fn translate_atomic_load(
    widened_ty: Type,
    access_ty: Type,
    memarg: &MemArg,
    builder: &mut FunctionBuilder,
    environ: &mut FuncEnvironment<'_>,
) -> WasmResult<()> {
    // The load is performed at type `access_ty`, and the loaded value is zero extended
    // to `widened_ty`.
    match access_ty {
        I8 | I16 | I32 | I64 => {}
        _ => {
            return Err(wasm_unsupported!(
                "atomic_load: unsupported access type {:?}",
                access_ty
            ));
        }
    };
    let w_ty_ok = match widened_ty {
        I32 | I64 => true,
        _ => false,
    };
    assert!(w_ty_ok && widened_ty.bytes() >= access_ty.bytes());

    let (flags, _, addr) = unwrap_or_return_unreachable_state!(
        environ,
        prepare_atomic_addr(
            memarg,
            u8::try_from(access_ty.bytes()).unwrap(),
            builder,
            environ,
        )?
    );
    let mut res = builder.ins().atomic_load(access_ty, flags, addr);
    if access_ty != widened_ty {
        res = builder.ins().uextend(widened_ty, res);
    }
    environ.stacks.push1(res);
    Ok(())
}

fn translate_atomic_store(
    access_ty: Type,
    memarg: &MemArg,
    builder: &mut FunctionBuilder,
    environ: &mut FuncEnvironment<'_>,
) -> WasmResult<()> {
    let mut data = environ.stacks.pop1();
    let data_ty = builder.func.dfg.value_type(data);

    // The operation is performed at type `access_ty`, and the data to be stored may first
    // need to be narrowed accordingly.
    match access_ty {
        I8 | I16 | I32 | I64 => {}
        _ => {
            return Err(wasm_unsupported!(
                "atomic_store: unsupported access type {:?}",
                access_ty
            ));
        }
    };
    let d_ty_ok = match data_ty {
        I32 | I64 => true,
        _ => false,
    };
    assert!(d_ty_ok && data_ty.bytes() >= access_ty.bytes());

    if data_ty.bytes() > access_ty.bytes() {
        data = builder.ins().ireduce(access_ty, data);
    }

    let (flags, _, addr) = unwrap_or_return_unreachable_state!(
        environ,
        prepare_atomic_addr(
            memarg,
            u8::try_from(access_ty.bytes()).unwrap(),
            builder,
            environ,
        )?
    );
    builder.ins().atomic_store(flags, data, addr);
    Ok(())
}

fn translate_vector_icmp(
    cc: IntCC,
    needed_type: Type,
    builder: &mut FunctionBuilder,
    env: &mut FuncEnvironment<'_>,
) {
    let (a, b) = env.stacks.pop2();
    let bitcast_a = optionally_bitcast_vector(a, needed_type, builder);
    let bitcast_b = optionally_bitcast_vector(b, needed_type, builder);
    env.stacks
        .push1(builder.ins().icmp(cc, bitcast_a, bitcast_b))
}

fn translate_fcmp(cc: FloatCC, builder: &mut FunctionBuilder, env: &mut FuncEnvironment<'_>) {
    let (arg0, arg1) = env.stacks.pop2();
    let val = builder.ins().fcmp(cc, arg0, arg1);
    env.stacks.push1(builder.ins().uextend(I32, val));
}

fn translate_vector_fcmp(
    cc: FloatCC,
    needed_type: Type,
    builder: &mut FunctionBuilder,
    env: &mut FuncEnvironment<'_>,
) {
    let (a, b) = env.stacks.pop2();
    let bitcast_a = optionally_bitcast_vector(a, needed_type, builder);
    let bitcast_b = optionally_bitcast_vector(b, needed_type, builder);
    env.stacks
        .push1(builder.ins().fcmp(cc, bitcast_a, bitcast_b))
}

fn translate_br_if(
    relative_depth: u32,
    builder: &mut FunctionBuilder,
    env: &mut FuncEnvironment<'_>,
) {
    let val = env.stacks.pop1();
    let (br_destination, inputs) = translate_br_if_args(relative_depth, env);
    let next_block = builder.create_block();
    canonicalise_brif(builder, val, br_destination, inputs, next_block, &[]);

    builder.seal_block(next_block); // The only predecessor is the current block.
    builder.switch_to_block(next_block);
}

fn translate_br_if_args<'a>(
    relative_depth: u32,
    env: &'a mut FuncEnvironment<'_>,
) -> (ir::Block, &'a mut [ir::Value]) {
    let i = env.stacks.control_stack.len() - 1 - (relative_depth as usize);
    let (return_count, br_destination) = {
        let frame = &mut env.stacks.control_stack[i];
        // The values returned by the branch are still available for the reachable
        // code that comes after it
        frame.set_branched_to_exit();
        let return_count = if frame.is_loop() {
            frame.num_param_values()
        } else {
            frame.num_return_values()
        };
        (return_count, frame.br_destination())
    };
    let inputs = env.stacks.peekn_mut(return_count);
    (br_destination, inputs)
}

/// Determine the returned value type of a WebAssembly operator
fn type_of(operator: &Operator) -> Type {
    match operator {
        Operator::V128Load { .. }
        | Operator::V128Store { .. }
        | Operator::V128Const { .. }
        | Operator::V128Not
        | Operator::V128And
        | Operator::V128AndNot
        | Operator::V128Or
        | Operator::V128Xor
        | Operator::V128AnyTrue
        | Operator::V128Bitselect => I8X16, // default type representing V128

        Operator::I8x16Shuffle { .. }
        | Operator::I8x16Splat
        | Operator::V128Load8Splat { .. }
        | Operator::V128Load8Lane { .. }
        | Operator::V128Store8Lane { .. }
        | Operator::I8x16ExtractLaneS { .. }
        | Operator::I8x16ExtractLaneU { .. }
        | Operator::I8x16ReplaceLane { .. }
        | Operator::I8x16Eq
        | Operator::I8x16Ne
        | Operator::I8x16LtS
        | Operator::I8x16LtU
        | Operator::I8x16GtS
        | Operator::I8x16GtU
        | Operator::I8x16LeS
        | Operator::I8x16LeU
        | Operator::I8x16GeS
        | Operator::I8x16GeU
        | Operator::I8x16Neg
        | Operator::I8x16Abs
        | Operator::I8x16AllTrue
        | Operator::I8x16Shl
        | Operator::I8x16ShrS
        | Operator::I8x16ShrU
        | Operator::I8x16Add
        | Operator::I8x16AddSatS
        | Operator::I8x16AddSatU
        | Operator::I8x16Sub
        | Operator::I8x16SubSatS
        | Operator::I8x16SubSatU
        | Operator::I8x16MinS
        | Operator::I8x16MinU
        | Operator::I8x16MaxS
        | Operator::I8x16MaxU
        | Operator::I8x16AvgrU
        | Operator::I8x16Bitmask
        | Operator::I8x16Popcnt
        | Operator::I8x16RelaxedLaneselect => I8X16,

        Operator::I16x8Splat
        | Operator::V128Load16Splat { .. }
        | Operator::V128Load16Lane { .. }
        | Operator::V128Store16Lane { .. }
        | Operator::I16x8ExtractLaneS { .. }
        | Operator::I16x8ExtractLaneU { .. }
        | Operator::I16x8ReplaceLane { .. }
        | Operator::I16x8Eq
        | Operator::I16x8Ne
        | Operator::I16x8LtS
        | Operator::I16x8LtU
        | Operator::I16x8GtS
        | Operator::I16x8GtU
        | Operator::I16x8LeS
        | Operator::I16x8LeU
        | Operator::I16x8GeS
        | Operator::I16x8GeU
        | Operator::I16x8Neg
        | Operator::I16x8Abs
        | Operator::I16x8AllTrue
        | Operator::I16x8Shl
        | Operator::I16x8ShrS
        | Operator::I16x8ShrU
        | Operator::I16x8Add
        | Operator::I16x8AddSatS
        | Operator::I16x8AddSatU
        | Operator::I16x8Sub
        | Operator::I16x8SubSatS
        | Operator::I16x8SubSatU
        | Operator::I16x8MinS
        | Operator::I16x8MinU
        | Operator::I16x8MaxS
        | Operator::I16x8MaxU
        | Operator::I16x8AvgrU
        | Operator::I16x8Mul
        | Operator::I16x8Bitmask
        | Operator::I16x8RelaxedLaneselect => I16X8,

        Operator::I32x4Splat
        | Operator::V128Load32Splat { .. }
        | Operator::V128Load32Lane { .. }
        | Operator::V128Store32Lane { .. }
        | Operator::I32x4ExtractLane { .. }
        | Operator::I32x4ReplaceLane { .. }
        | Operator::I32x4Eq
        | Operator::I32x4Ne
        | Operator::I32x4LtS
        | Operator::I32x4LtU
        | Operator::I32x4GtS
        | Operator::I32x4GtU
        | Operator::I32x4LeS
        | Operator::I32x4LeU
        | Operator::I32x4GeS
        | Operator::I32x4GeU
        | Operator::I32x4Neg
        | Operator::I32x4Abs
        | Operator::I32x4AllTrue
        | Operator::I32x4Shl
        | Operator::I32x4ShrS
        | Operator::I32x4ShrU
        | Operator::I32x4Add
        | Operator::I32x4Sub
        | Operator::I32x4Mul
        | Operator::I32x4MinS
        | Operator::I32x4MinU
        | Operator::I32x4MaxS
        | Operator::I32x4MaxU
        | Operator::I32x4Bitmask
        | Operator::I32x4TruncSatF32x4S
        | Operator::I32x4TruncSatF32x4U
        | Operator::I32x4RelaxedLaneselect
        | Operator::V128Load32Zero { .. } => I32X4,

        Operator::I64x2Splat
        | Operator::V128Load64Splat { .. }
        | Operator::V128Load64Lane { .. }
        | Operator::V128Store64Lane { .. }
        | Operator::I64x2ExtractLane { .. }
        | Operator::I64x2ReplaceLane { .. }
        | Operator::I64x2Eq
        | Operator::I64x2Ne
        | Operator::I64x2LtS
        | Operator::I64x2GtS
        | Operator::I64x2LeS
        | Operator::I64x2GeS
        | Operator::I64x2Neg
        | Operator::I64x2Abs
        | Operator::I64x2AllTrue
        | Operator::I64x2Shl
        | Operator::I64x2ShrS
        | Operator::I64x2ShrU
        | Operator::I64x2Add
        | Operator::I64x2Sub
        | Operator::I64x2Mul
        | Operator::I64x2Bitmask
        | Operator::I64x2RelaxedLaneselect
        | Operator::V128Load64Zero { .. } => I64X2,

        Operator::F32x4Splat
        | Operator::F32x4ExtractLane { .. }
        | Operator::F32x4ReplaceLane { .. }
        | Operator::F32x4Eq
        | Operator::F32x4Ne
        | Operator::F32x4Lt
        | Operator::F32x4Gt
        | Operator::F32x4Le
        | Operator::F32x4Ge
        | Operator::F32x4Abs
        | Operator::F32x4Neg
        | Operator::F32x4Sqrt
        | Operator::F32x4Add
        | Operator::F32x4Sub
        | Operator::F32x4Mul
        | Operator::F32x4Div
        | Operator::F32x4Min
        | Operator::F32x4Max
        | Operator::F32x4PMin
        | Operator::F32x4PMax
        | Operator::F32x4ConvertI32x4S
        | Operator::F32x4ConvertI32x4U
        | Operator::F32x4Ceil
        | Operator::F32x4Floor
        | Operator::F32x4Trunc
        | Operator::F32x4Nearest
        | Operator::F32x4RelaxedMax
        | Operator::F32x4RelaxedMin
        | Operator::F32x4RelaxedMadd
        | Operator::F32x4RelaxedNmadd => F32X4,

        Operator::F64x2Splat
        | Operator::F64x2ExtractLane { .. }
        | Operator::F64x2ReplaceLane { .. }
        | Operator::F64x2Eq
        | Operator::F64x2Ne
        | Operator::F64x2Lt
        | Operator::F64x2Gt
        | Operator::F64x2Le
        | Operator::F64x2Ge
        | Operator::F64x2Abs
        | Operator::F64x2Neg
        | Operator::F64x2Sqrt
        | Operator::F64x2Add
        | Operator::F64x2Sub
        | Operator::F64x2Mul
        | Operator::F64x2Div
        | Operator::F64x2Min
        | Operator::F64x2Max
        | Operator::F64x2PMin
        | Operator::F64x2PMax
        | Operator::F64x2Ceil
        | Operator::F64x2Floor
        | Operator::F64x2Trunc
        | Operator::F64x2Nearest
        | Operator::F64x2RelaxedMax
        | Operator::F64x2RelaxedMin
        | Operator::F64x2RelaxedMadd
        | Operator::F64x2RelaxedNmadd => F64X2,

        _ => unimplemented!(
            "Currently only SIMD instructions are mapped to their return type; the \
             following instruction is not mapped: {:?}",
            operator
        ),
    }
}

/// Some SIMD operations only operate on I8X16 in CLIF; this will convert them to that type by
/// adding a bitcast if necessary.
fn optionally_bitcast_vector(
    value: Value,
    needed_type: Type,
    builder: &mut FunctionBuilder,
) -> Value {
    if builder.func.dfg.value_type(value) != needed_type {
        let mut flags = MemFlags::new();
        flags.set_endianness(ir::Endianness::Little);
        builder.ins().bitcast(needed_type, flags, value)
    } else {
        value
    }
}

#[inline(always)]
fn is_non_canonical_v128(ty: ir::Type) -> bool {
    match ty {
        I64X2 | I32X4 | I16X8 | F32X4 | F64X2 => true,
        _ => false,
    }
}

/// Cast to I8X16, any vector values in `values` that are of "non-canonical" type (meaning, not
/// I8X16), and return them in a slice.  A pre-scan is made to determine whether any casts are
/// actually necessary, and if not, the original slice is returned.  Otherwise the cast values
/// are returned in a slice that belongs to the caller-supplied `SmallVec`.
fn canonicalise_v128_values<'a>(
    tmp_canonicalised: &'a mut SmallVec<[BlockArg; 16]>,
    builder: &mut FunctionBuilder,
    values: &'a [ir::Value],
) -> &'a [BlockArg] {
    debug_assert!(tmp_canonicalised.is_empty());
    // Cast, and push the resulting `Value`s into `canonicalised`.
    for v in values {
        let value = if is_non_canonical_v128(builder.func.dfg.value_type(*v)) {
            let mut flags = MemFlags::new();
            flags.set_endianness(ir::Endianness::Little);
            builder.ins().bitcast(I8X16, flags, *v)
        } else {
            *v
        };
        tmp_canonicalised.push(BlockArg::from(value));
    }
    tmp_canonicalised.as_slice()
}

/// Generate a `jump` instruction, but first cast all 128-bit vector values to I8X16 if they
/// don't have that type.  This is done in somewhat roundabout way so as to ensure that we
/// almost never have to do any heap allocation.
fn canonicalise_then_jump(
    builder: &mut FunctionBuilder,
    destination: ir::Block,
    params: &[ir::Value],
) -> ir::Inst {
    let mut tmp_canonicalised = SmallVec::<[_; 16]>::new();
    let canonicalised = canonicalise_v128_values(&mut tmp_canonicalised, builder, params);
    builder.ins().jump(destination, canonicalised)
}

/// The same but for a `brif` instruction.
fn canonicalise_brif(
    builder: &mut FunctionBuilder,
    cond: ir::Value,
    block_then: ir::Block,
    params_then: &[ir::Value],
    block_else: ir::Block,
    params_else: &[ir::Value],
) -> ir::Inst {
    let mut tmp_canonicalised_then = SmallVec::<[_; 16]>::new();
    let canonicalised_then =
        canonicalise_v128_values(&mut tmp_canonicalised_then, builder, params_then);
    let mut tmp_canonicalised_else = SmallVec::<[_; 16]>::new();
    let canonicalised_else =
        canonicalise_v128_values(&mut tmp_canonicalised_else, builder, params_else);
    builder.ins().brif(
        cond,
        block_then,
        canonicalised_then,
        block_else,
        canonicalised_else,
    )
}

/// A helper for popping and bitcasting a single value; since SIMD values can lose their type by
/// using v128 (i.e. CLIF's I8x16) we must re-type the values using a bitcast to avoid CLIF
/// typing issues.
fn pop1_with_bitcast(
    env: &mut FuncEnvironment<'_>,
    needed_type: Type,
    builder: &mut FunctionBuilder,
) -> Value {
    optionally_bitcast_vector(env.stacks.pop1(), needed_type, builder)
}

/// A helper for popping and bitcasting two values; since SIMD values can lose their type by
/// using v128 (i.e. CLIF's I8x16) we must re-type the values using a bitcast to avoid CLIF
/// typing issues.
fn pop2_with_bitcast(
    env: &mut FuncEnvironment<'_>,
    needed_type: Type,
    builder: &mut FunctionBuilder,
) -> (Value, Value) {
    let (a, b) = env.stacks.pop2();
    let bitcast_a = optionally_bitcast_vector(a, needed_type, builder);
    let bitcast_b = optionally_bitcast_vector(b, needed_type, builder);
    (bitcast_a, bitcast_b)
}

fn pop3_with_bitcast(
    env: &mut FuncEnvironment<'_>,
    needed_type: Type,
    builder: &mut FunctionBuilder,
) -> (Value, Value, Value) {
    let (a, b, c) = env.stacks.pop3();
    let bitcast_a = optionally_bitcast_vector(a, needed_type, builder);
    let bitcast_b = optionally_bitcast_vector(b, needed_type, builder);
    let bitcast_c = optionally_bitcast_vector(c, needed_type, builder);
    (bitcast_a, bitcast_b, bitcast_c)
}

fn bitcast_arguments<'a>(
    builder: &FunctionBuilder,
    arguments: &'a mut [Value],
    params: &[ir::AbiParam],
    param_predicate: impl Fn(usize) -> bool,
) -> Vec<(Type, &'a mut Value)> {
    let filtered_param_types = params
        .iter()
        .enumerate()
        .filter(|(i, _)| param_predicate(*i))
        .map(|(_, param)| param.value_type);

    // zip_eq, from the itertools::Itertools trait, is like Iterator::zip but panics if one
    // iterator ends before the other. The `param_predicate` is required to select exactly as many
    // elements of `params` as there are elements in `arguments`.
    let pairs = filtered_param_types.zip_eq(arguments.iter_mut());

    // The arguments which need to be bitcasted are those which have some vector type but the type
    // expected by the parameter is not the same vector type as that of the provided argument.
    pairs
        .filter(|(param_type, _)| param_type.is_vector())
        .filter(|(param_type, arg)| {
            let arg_type = builder.func.dfg.value_type(**arg);
            assert!(
                arg_type.is_vector(),
                "unexpected type mismatch: expected {}, argument {} was actually of type {}",
                param_type,
                *arg,
                arg_type
            );

            // This is the same check that would be done by `optionally_bitcast_vector`, except we
            // can't take a mutable borrow of the FunctionBuilder here, so we defer inserting the
            // bitcast instruction to the caller.
            arg_type != *param_type
        })
        .collect()
}

/// A helper for bitcasting a sequence of return values for the function currently being built. If
/// a value is a vector type that does not match its expected type, this will modify the value in
/// place to point to the result of a `bitcast`. This conversion is necessary to translate Wasm
/// code that uses `V128` as function parameters (or implicitly in block parameters) and still use
/// specific CLIF types (e.g. `I32X4`) in the function body.
pub fn bitcast_wasm_returns(arguments: &mut [Value], builder: &mut FunctionBuilder) {
    let changes = bitcast_arguments(builder, arguments, &builder.func.signature.returns, |i| {
        builder.func.signature.returns[i].purpose == ir::ArgumentPurpose::Normal
    });
    for (t, arg) in changes {
        let mut flags = MemFlags::new();
        flags.set_endianness(ir::Endianness::Little);
        *arg = builder.ins().bitcast(t, flags, *arg);
    }
}

/// Like `bitcast_wasm_returns`, but for the parameters being passed to a specified callee.
fn bitcast_wasm_params(
    environ: &mut FuncEnvironment<'_>,
    callee_signature: ir::SigRef,
    arguments: &mut [Value],
    builder: &mut FunctionBuilder,
) {
    let callee_signature = &builder.func.dfg.signatures[callee_signature];
    let changes = bitcast_arguments(builder, arguments, &callee_signature.params, |i| {
        environ.is_wasm_parameter(i)
    });
    for (t, arg) in changes {
        let mut flags = MemFlags::new();
        flags.set_endianness(ir::Endianness::Little);
        *arg = builder.ins().bitcast(t, flags, *arg);
    }
}

fn create_catch_block(
    builder: &mut FunctionBuilder,
    catch: &wasmparser::Catch,
    environ: &mut FuncEnvironment<'_>,
) -> WasmResult<ir::Block> {
    let (is_ref, tag, label) = match catch {
        wasmparser::Catch::One { tag, label } => (false, Some(*tag), *label),
        wasmparser::Catch::OneRef { tag, label } => (true, Some(*tag), *label),
        wasmparser::Catch::All { label } => (false, None, *label),
        wasmparser::Catch::AllRef { label } => (true, None, *label),
    };

    // We always create a handler block with one blockparam for the
    // one exception payload value that we use (`exn0` block-call
    // argument). This one payload value is the `exnref`. Note,
    // however, that we carry it in a native host-pointer-sized
    // payload (because this is what the exception ABI in Cranelift
    // requires). We then generate the args for the actual branch to
    // the handler block: we add unboxing code to load each value in
    // the exception signature if a specific tag is expected (hence
    // signature is known), and then append the `exnref` itself if we
    // are compiling a `*Ref` variant.

    let (exn_ref_ty, needs_stack_map) = environ.reference_type(WasmHeapType::Exn);
    let (exn_payload_wasm_ty, exn_payload_ty) = match environ.pointer_type().bits() {
        32 => (wasmparser::ValType::I32, I32),
        64 => (wasmparser::ValType::I64, I64),
        _ => panic!("Unsupported pointer width"),
    };
    let block = block_with_params(builder, [exn_payload_wasm_ty], environ)?;
    builder.switch_to_block(block);
    let exn_ref = builder.func.dfg.block_params(block)[0];
    debug_assert!(exn_ref_ty.bits() <= exn_payload_ty.bits());
    let exn_ref = if exn_ref_ty.bits() < exn_payload_ty.bits() {
        builder.ins().ireduce(exn_ref_ty, exn_ref)
    } else {
        exn_ref
    };

    if needs_stack_map {
        builder.declare_value_needs_stack_map(exn_ref);
    }

    // We encode tag indices from the module directly as Cranelift
    // `ExceptionTag`s. We will translate those to (instance,
    // defined-tag-index) pairs during the unwind walk -- necessarily
    // dynamic because tag imports are provided only at instantiation
    // time.
    let clif_tag = tag.map(|t| ExceptionTag::from_u32(t));

    environ.stacks.handlers.add_handler(clif_tag, block);

    let mut params = vec![];

    if let Some(tag) = tag {
        let tag = TagIndex::from_u32(tag);
        params.extend(environ.translate_exn_unbox(builder, tag, exn_ref)?);
    }
    if is_ref {
        params.push(exn_ref);
    }

    // Generate the branch itself.
    let i = environ.stacks.control_stack.len() - 1 - (label as usize);
    let frame = &mut environ.stacks.control_stack[i];
    frame.set_branched_to_exit();
    canonicalise_then_jump(builder, frame.br_destination(), &params);

    Ok(block)
}