use bumpalo::{self, collections::Vec};

use code_builder::Align;
use roc_builtins::bitcode::IntWidth;
use roc_collections::all::MutMap;
use roc_module::ident::Ident;
use roc_module::low_level::{LowLevel, LowLevelWrapperType};
use roc_module::symbol::{Interns, Symbol};
use roc_mono::code_gen_help::{CodeGenHelp, REFCOUNT_MAX};
use roc_mono::ir::{
    BranchInfo, CallType, Expr, JoinPointId, ListLiteralElement, Literal, ModifyRc, Param, Proc,
    ProcLayout, Stmt,
};

use roc_error_macros::internal_error;
use roc_mono::layout::{Builtin, Layout, LayoutIds, TagIdIntType, UnionLayout};

use crate::layout::{CallConv, ReturnMethod, WasmLayout};
use crate::low_level::LowLevelCall;
use crate::storage::{Storage, StoredValue, StoredValueKind};
use crate::wasm_module::linking::{DataSymbol, LinkingSegment, WasmObjectSymbol};
use crate::wasm_module::sections::{DataMode, DataSegment};
use crate::wasm_module::{
    code_builder, CodeBuilder, Export, ExportType, LocalId, Signature, SymInfo, ValueType,
    WasmModule,
};
use crate::{
    copy_memory, round_up_to_alignment, CopyMemoryConfig, Env, DEBUG_LOG_SETTINGS, MEMORY_NAME,
    PTR_SIZE, PTR_TYPE, STACK_POINTER_GLOBAL_ID, STACK_POINTER_NAME, TARGET_INFO,
};

/// The memory address where the constants data will be loaded during module instantiation.
/// We avoid address zero and anywhere near it. They're valid addresses but maybe bug-prone.
/// Follow Emscripten's example by leaving 1kB unused (though 4 bytes would probably do!)
const CONST_SEGMENT_BASE_ADDR: u32 = 1024;

pub struct WasmBackend<'a> {
    pub env: &'a Env<'a>,
    interns: &'a mut Interns,

    // Module-level data
    module: WasmModule<'a>,
    layout_ids: LayoutIds<'a>,
    next_constant_addr: u32,
    fn_index_offset: u32,
    called_preload_fns: Vec<'a, u32>,
    proc_symbols: Vec<'a, (Symbol, u32)>,
    helper_proc_gen: CodeGenHelp<'a>,

    // Function-level data
    pub code_builder: CodeBuilder<'a>,
    pub storage: Storage<'a>,

    /// how many blocks deep are we (used for jumps)
    block_depth: u32,
    joinpoint_label_map: MutMap<JoinPointId, (u32, Vec<'a, StoredValue>)>,
}

impl<'a> WasmBackend<'a> {
    #[allow(clippy::too_many_arguments)]
    pub fn new(
        env: &'a Env<'a>,
        interns: &'a mut Interns,
        layout_ids: LayoutIds<'a>,
        proc_symbols: Vec<'a, (Symbol, u32)>,
        mut module: WasmModule<'a>,
        fn_index_offset: u32,
        helper_proc_gen: CodeGenHelp<'a>,
    ) -> Self {
        module.export.append(Export {
            name: MEMORY_NAME.as_bytes(),
            ty: ExportType::Mem,
            index: 0,
        });
        module.export.append(Export {
            name: STACK_POINTER_NAME.as_bytes(),
            ty: ExportType::Global,
            index: STACK_POINTER_GLOBAL_ID,
        });

        WasmBackend {
            env,
            interns,

            // Module-level data
            module,

            layout_ids,
            next_constant_addr: CONST_SEGMENT_BASE_ADDR,
            fn_index_offset,
            called_preload_fns: Vec::with_capacity_in(2, env.arena),
            proc_symbols,
            helper_proc_gen,

            // Function-level data
            block_depth: 0,
            joinpoint_label_map: MutMap::default(),
            code_builder: CodeBuilder::new(env.arena),
            storage: Storage::new(env.arena),
        }
    }

    pub fn generate_helpers(&mut self) -> Vec<'a, Proc<'a>> {
        self.helper_proc_gen.take_procs()
    }

    fn register_helper_proc(&mut self, new_proc_info: (Symbol, ProcLayout<'a>)) {
        let (new_proc_sym, new_proc_layout) = new_proc_info;
        let wasm_fn_index = self.proc_symbols.len() as u32;
        let linker_sym_index = self.module.linking.symbol_table.len() as u32;

        let name = self
            .layout_ids
            .get_toplevel(new_proc_sym, &new_proc_layout)
            .to_symbol_string(new_proc_sym, self.interns);

        self.proc_symbols.push((new_proc_sym, linker_sym_index));
        let linker_symbol = SymInfo::Function(WasmObjectSymbol::Defined {
            flags: 0,
            index: wasm_fn_index,
            name,
        });
        self.module.linking.symbol_table.push(linker_symbol);
    }

    pub fn finalize(self) -> (WasmModule<'a>, Vec<'a, u32>) {
        (self.module, self.called_preload_fns)
    }

    /// Register the debug names of Symbols in a global lookup table
    /// so that they have meaningful names when you print them.
    /// Particularly useful after generating IR for refcount procedures
    #[cfg(debug_assertions)]
    pub fn register_symbol_debug_names(&self) {
        let module_id = self.env.module_id;
        let ident_ids = self.interns.all_ident_ids.get(&module_id).unwrap();
        self.env.module_id.register_debug_idents(ident_ids);
    }

    #[cfg(not(debug_assertions))]
    pub fn register_symbol_debug_names(&self) {}

    /// Create an IR Symbol for an anonymous value (such as ListLiteral)
    fn create_symbol(&mut self, debug_name: &str) -> Symbol {
        let ident_ids = self
            .interns
            .all_ident_ids
            .get_mut(&self.env.module_id)
            .unwrap();

        let ident_id = ident_ids.add(Ident::from(debug_name));
        Symbol::new(self.env.module_id, ident_id)
    }

    /// Reset function-level data
    fn reset(&mut self) {
        // Push the completed CodeBuilder into the module and swap it for a new empty one
        let mut swap_code_builder = CodeBuilder::new(self.env.arena);
        std::mem::swap(&mut swap_code_builder, &mut self.code_builder);
        self.module.code.code_builders.push(swap_code_builder);

        self.storage.clear();
        self.joinpoint_label_map.clear();
        assert_eq!(self.block_depth, 0);
    }

    /**********************************************************

            PROCEDURE

    ***********************************************************/

    pub fn build_proc(&mut self, proc: &Proc<'a>) {
        if DEBUG_LOG_SETTINGS.proc_start_end {
            println!("\ngenerating procedure {:?}\n", proc.name);
        }

        self.start_proc(proc);

        self.stmt(&proc.body);

        self.finalize_proc();
        self.reset();

        if DEBUG_LOG_SETTINGS.proc_start_end {
            println!("\nfinished generating {:?}\n", proc.name);
        }
    }

    fn start_proc(&mut self, proc: &Proc<'a>) {
        let ret_layout = WasmLayout::new(&proc.ret_layout);

        let ret_type = match ret_layout.return_method() {
            ReturnMethod::Primitive(ty) => Some(ty),
            ReturnMethod::NoReturnValue => None,
            ReturnMethod::WriteToPointerArg => {
                self.storage.arg_types.push(PTR_TYPE);
                None
            }
        };

        // Create a block so we can exit the function without skipping stack frame "pop" code.
        // We never use the `return` instruction. Instead, we break from this block.
        self.start_block();

        for (layout, symbol) in proc.args {
            self.storage
                .allocate(*layout, *symbol, StoredValueKind::Parameter);
        }

        if let Some(ty) = ret_type {
            let ret_var = self.storage.create_anonymous_local(ty);
            self.storage.return_var = Some(ret_var);
        }

        self.module.add_function_signature(Signature {
            param_types: self.storage.arg_types.clone(),
            ret_type,
        });
    }

    fn finalize_proc(&mut self) {
        // end the block from start_proc, to ensure all paths pop stack memory (if any)
        self.end_block();

        if let Some(ret_var) = self.storage.return_var {
            self.code_builder.get_local(ret_var);
        }

        // Write local declarations and stack frame push/pop code
        self.code_builder.build_fn_header_and_footer(
            &self.storage.local_types,
            self.storage.stack_frame_size,
            self.storage.stack_frame_pointer,
        );
    }

    /**********************************************************

            STATEMENTS

    ***********************************************************/

    fn stmt(&mut self, stmt: &Stmt<'a>) {
        match stmt {
            Stmt::Let(_, _, _, _) => self.stmt_let(stmt),

            Stmt::Ret(sym) => self.stmt_ret(*sym),

            Stmt::Switch {
                cond_symbol,
                cond_layout,
                branches,
                default_branch,
                ret_layout: _,
            } => self.stmt_switch(*cond_symbol, cond_layout, branches, default_branch),

            Stmt::Join {
                id,
                parameters,
                body,
                remainder,
            } => self.stmt_join(*id, parameters, body, remainder),

            Stmt::Jump(id, arguments) => self.stmt_jump(*id, arguments),

            Stmt::Refcounting(modify, following) => self.stmt_refcounting(modify, following),

            Stmt::RuntimeError(msg) => self.stmt_runtime_error(msg),
        }
    }

    fn start_block(&mut self) {
        // Wasm blocks can have result types, but we don't use them.
        // You need the right type on the stack when you jump from an inner block to an outer one.
        // The rules are confusing, and implementing them would add complexity and slow down code gen.
        // Instead we use local variables to move a value from an inner block to an outer one.
        self.block_depth += 1;
        self.code_builder.block();
    }

    fn start_loop(&mut self) {
        self.block_depth += 1;
        self.code_builder.loop_();
    }

    fn end_block(&mut self) {
        self.block_depth -= 1;
        self.code_builder.end();
    }

    fn stmt_let(&mut self, stmt: &Stmt<'a>) {
        let mut current_stmt = stmt;
        while let Stmt::Let(sym, expr, layout, following) = current_stmt {
            if DEBUG_LOG_SETTINGS.let_stmt_ir {
                println!("let {:?} = {}", sym, expr.to_pretty(200)); // ignore `following`! Too confusing otherwise.
            }

            let kind = match following {
                Stmt::Ret(ret_sym) if *sym == *ret_sym => StoredValueKind::ReturnValue,
                _ => StoredValueKind::Variable,
            };

            self.stmt_let_store_expr(*sym, layout, expr, kind);

            current_stmt = *following;
        }

        self.stmt(current_stmt);
    }

    fn stmt_let_store_expr(
        &mut self,
        sym: Symbol,
        layout: &Layout<'a>,
        expr: &Expr<'a>,
        kind: StoredValueKind,
    ) {
        let sym_storage = self.storage.allocate(*layout, sym, kind);

        self.expr(sym, expr, layout, &sym_storage);

        // If this value is stored in the VM stack, we need code_builder to track it
        // (since every instruction can change the VM stack)
        if let Some(StoredValue::VirtualMachineStack { vm_state, .. }) =
            self.storage.symbol_storage_map.get_mut(&sym)
        {
            *vm_state = self.code_builder.set_top_symbol(sym);
        }
    }

    fn stmt_ret(&mut self, sym: Symbol) {
        use crate::storage::StoredValue::*;

        let storage = self.storage.symbol_storage_map.get(&sym).unwrap();

        match storage {
            StackMemory {
                location,
                size,
                alignment_bytes,
                ..
            } => {
                let (from_ptr, from_offset) =
                    location.local_and_offset(self.storage.stack_frame_pointer);
                copy_memory(
                    &mut self.code_builder,
                    CopyMemoryConfig {
                        from_ptr,
                        from_offset,
                        to_ptr: LocalId(0),
                        to_offset: 0,
                        size: *size,
                        alignment_bytes: *alignment_bytes,
                    },
                );
            }

            _ => {
                self.storage.load_symbols(&mut self.code_builder, &[sym]);

                // If we have a return value, store it to the return variable
                // This avoids complications with block result types when returning from nested blocks
                if let Some(ret_var) = self.storage.return_var {
                    self.code_builder.set_local(ret_var);
                }
            }
        }
        // jump to the "stack frame pop" code at the end of the function
        self.code_builder.br(self.block_depth - 1);
    }

    fn stmt_switch(
        &mut self,
        cond_symbol: Symbol,
        cond_layout: &Layout<'a>,
        branches: &'a [(u64, BranchInfo<'a>, Stmt<'a>)],
        default_branch: &(BranchInfo<'a>, &'a Stmt<'a>),
    ) {
        // NOTE currently implemented as a series of conditional jumps
        // We may be able to improve this in the future with `Select`
        // or `BrTable`

        // Ensure the condition value is not stored only in the VM stack
        // Otherwise we can't reach it from inside the block
        let cond_storage = self.storage.get(&cond_symbol).to_owned();
        self.storage
            .ensure_value_has_local(&mut self.code_builder, cond_symbol, cond_storage);

        // create a block for each branch except the default
        for _ in 0..branches.len() {
            self.start_block()
        }

        let is_bool = matches!(cond_layout, Layout::Builtin(Builtin::Bool));
        let cond_type = WasmLayout::new(cond_layout).arg_types(CallConv::C)[0];

        // then, we jump whenever the value under scrutiny is equal to the value of a branch
        for (i, (value, _, _)) in branches.iter().enumerate() {
            // put the cond_symbol on the top of the stack
            self.storage
                .load_symbols(&mut self.code_builder, &[cond_symbol]);

            if is_bool {
                // We already have a bool, don't need to compare against a const to get one
                if *value == 0 {
                    self.code_builder.i32_eqz();
                }
            } else {
                match cond_type {
                    ValueType::I32 => {
                        self.code_builder.i32_const(*value as i32);
                        self.code_builder.i32_eq();
                    }
                    ValueType::I64 => {
                        self.code_builder.i64_const(*value as i64);
                        self.code_builder.i64_eq();
                    }
                    ValueType::F32 => {
                        self.code_builder.f32_const(f32::from_bits(*value as u32));
                        self.code_builder.f32_eq();
                    }
                    ValueType::F64 => {
                        self.code_builder.f64_const(f64::from_bits(*value as u64));
                        self.code_builder.f64_eq();
                    }
                }
            }

            // "break" out of `i` surrounding blocks
            self.code_builder.br_if(i as u32);
        }

        // if we never jumped because a value matched, we're in the default case
        self.stmt(default_branch.1);

        // now put in the actual body of each branch in order
        // (the first branch would have broken out of 1 block,
        // hence we must generate its code first)
        for (_, _, branch) in branches.iter() {
            self.end_block();

            self.stmt(branch);
        }
    }

    fn stmt_join(
        &mut self,
        id: JoinPointId,
        parameters: &'a [Param<'a>],
        body: &'a Stmt<'a>,
        remainder: &'a Stmt<'a>,
    ) {
        // make locals for join pointer parameters
        let mut jp_param_storages = Vec::with_capacity_in(parameters.len(), self.env.arena);
        for parameter in parameters.iter() {
            let mut param_storage = self.storage.allocate(
                parameter.layout,
                parameter.symbol,
                StoredValueKind::Variable,
            );
            param_storage = self.storage.ensure_value_has_local(
                &mut self.code_builder,
                parameter.symbol,
                param_storage,
            );
            jp_param_storages.push(param_storage);
        }

        self.start_block();

        self.joinpoint_label_map
            .insert(id, (self.block_depth, jp_param_storages));

        self.stmt(remainder);

        self.end_block();
        self.start_loop();

        self.stmt(body);

        // ends the loop
        self.end_block();
    }

    fn stmt_jump(&mut self, id: JoinPointId, arguments: &'a [Symbol]) {
        let (target, param_storages) = self.joinpoint_label_map[&id].clone();

        for (arg_symbol, param_storage) in arguments.iter().zip(param_storages.iter()) {
            let arg_storage = self.storage.get(arg_symbol).clone();
            self.storage.clone_value(
                &mut self.code_builder,
                param_storage,
                &arg_storage,
                *arg_symbol,
            );
        }

        // jump
        let levels = self.block_depth - target;
        self.code_builder.br(levels);
    }

    fn stmt_refcounting(&mut self, modify: &ModifyRc, following: &'a Stmt<'a>) {
        let value = modify.get_symbol();
        let layout = self.storage.symbol_layouts[&value];

        let ident_ids = self
            .interns
            .all_ident_ids
            .get_mut(&self.env.module_id)
            .unwrap();

        let (rc_stmt, new_specializations) = self
            .helper_proc_gen
            .expand_refcount_stmt(ident_ids, layout, modify, following);

        if false {
            self.register_symbol_debug_names();
            println!("## rc_stmt:\n{}\n{:?}", rc_stmt.to_pretty(200), rc_stmt);
        }

        // If any new specializations were created, register their symbol data
        for spec in new_specializations.into_iter() {
            self.register_helper_proc(spec);
        }

        self.stmt(rc_stmt);
    }

    fn stmt_runtime_error(&mut self, msg: &'a str) {
        todo!("RuntimeError {:?}", msg)
    }

    /**********************************************************

            EXPRESSIONS

    ***********************************************************/

    fn expr(&mut self, sym: Symbol, expr: &Expr<'a>, layout: &Layout<'a>, storage: &StoredValue) {
        match expr {
            Expr::Literal(lit) => self.expr_literal(lit, storage, sym, layout),

            Expr::Call(roc_mono::ir::Call {
                call_type,
                arguments,
            }) => self.expr_call(call_type, arguments, sym, layout, storage),

            Expr::Struct(fields) => self.expr_struct(sym, layout, storage, fields),

            Expr::StructAtIndex {
                index,
                field_layouts,
                structure,
            } => self.expr_struct_at_index(sym, storage, *index, field_layouts, *structure),

            Expr::Array { elems, elem_layout } => self.expr_array(sym, storage, elem_layout, elems),

            Expr::EmptyArray => self.expr_empty_array(sym, storage),

            Expr::Tag {
                tag_layout: union_layout,
                tag_id,
                arguments,
                ..
            } => self.expr_tag(union_layout, *tag_id, arguments, sym, storage),

            Expr::GetTagId {
                structure,
                union_layout,
            } => self.expr_get_tag_id(*structure, union_layout, sym, storage),

            Expr::UnionAtIndex {
                structure,
                tag_id,
                union_layout,
                index,
            } => self.expr_union_at_index(*structure, *tag_id, union_layout, *index, sym),

            _ => todo!("Expression `{}`", expr.to_pretty(100)),
        }
    }

    /*******************************************************************
     * Literals
     *******************************************************************/

    fn expr_literal(
        &mut self,
        lit: &Literal<'a>,
        storage: &StoredValue,
        sym: Symbol,
        layout: &Layout<'a>,
    ) {
        let invalid_error =
            || internal_error!("Literal value {:?} has invalid storage {:?}", lit, storage);

        match storage {
            StoredValue::VirtualMachineStack { value_type, .. } => {
                match (lit, value_type) {
                    (Literal::Float(x), ValueType::F64) => self.code_builder.f64_const(*x as f64),
                    (Literal::Float(x), ValueType::F32) => self.code_builder.f32_const(*x as f32),
                    (Literal::Int(x), ValueType::I64) => self.code_builder.i64_const(*x as i64),
                    (Literal::Int(x), ValueType::I32) => self.code_builder.i32_const(*x as i32),
                    (Literal::Bool(x), ValueType::I32) => self.code_builder.i32_const(*x as i32),
                    (Literal::Byte(x), ValueType::I32) => self.code_builder.i32_const(*x as i32),
                    _ => invalid_error(),
                };
            }

            StoredValue::StackMemory { location, .. } => {
                let mut write128 = |lower_bits, upper_bits| {
                    let (local_id, offset) =
                        location.local_and_offset(self.storage.stack_frame_pointer);

                    self.code_builder.get_local(local_id);
                    self.code_builder.i64_const(lower_bits);
                    self.code_builder.i64_store(Align::Bytes8, offset);

                    self.code_builder.get_local(local_id);
                    self.code_builder.i64_const(upper_bits);
                    self.code_builder.i64_store(Align::Bytes8, offset + 8);
                };

                match lit {
                    Literal::Decimal(decimal) => {
                        let lower_bits = (decimal.0 & 0xffff_ffff_ffff_ffff) as i64;
                        let upper_bits = (decimal.0 >> 64) as i64;
                        write128(lower_bits, upper_bits);
                    }
                    Literal::Int(x) => {
                        let lower_bits = (*x & 0xffff_ffff_ffff_ffff) as i64;
                        let upper_bits = (*x >> 64) as i64;
                        write128(lower_bits, upper_bits);
                    }
                    Literal::Float(_) => {
                        // Also not implemented in LLVM backend (nor in Rust!)
                        todo!("f128 type");
                    }
                    Literal::Str(string) => {
                        let (local_id, offset) =
                            location.local_and_offset(self.storage.stack_frame_pointer);

                        let len = string.len();
                        if len < 8 {
                            let mut stack_mem_bytes = [0; 8];
                            stack_mem_bytes[0..len].clone_from_slice(string.as_bytes());
                            stack_mem_bytes[7] = 0x80 | (len as u8);
                            let str_as_int = i64::from_le_bytes(stack_mem_bytes);

                            // Write all 8 bytes at once using an i64
                            // Str is normally two i32's, but in this special case, we can get away with fewer instructions
                            self.code_builder.get_local(local_id);
                            self.code_builder.i64_const(str_as_int);
                            self.code_builder.i64_store(Align::Bytes4, offset);
                        } else {
                            let (linker_sym_index, elements_addr) =
                                self.expr_literal_big_str(string, sym, layout);

                            self.code_builder.get_local(local_id);
                            self.code_builder
                                .i32_const_mem_addr(elements_addr, linker_sym_index);
                            self.code_builder.i32_store(Align::Bytes4, offset);

                            self.code_builder.get_local(local_id);
                            self.code_builder.i32_const(string.len() as i32);
                            self.code_builder.i32_store(Align::Bytes4, offset + 4);
                        };
                    }
                    _ => invalid_error(),
                }
            }

            _ => invalid_error(),
        };
    }

    /// Create a string constant in the module data section
    /// Return the data we need for code gen: linker symbol index and memory address
    fn expr_literal_big_str(
        &mut self,
        string: &'a str,
        sym: Symbol,
        layout: &Layout<'a>,
    ) -> (u32, u32) {
        // Place the segment at a 4-byte aligned offset
        let segment_addr = round_up_to_alignment!(self.next_constant_addr, PTR_SIZE);
        let elements_addr = segment_addr + PTR_SIZE;
        let length_with_refcount = 4 + string.len();
        self.next_constant_addr = segment_addr + length_with_refcount as u32;

        let mut segment = DataSegment {
            mode: DataMode::active_at(segment_addr),
            init: Vec::with_capacity_in(length_with_refcount, self.env.arena),
        };

        // Prefix the string bytes with "infinite" refcount
        let refcount_max_bytes: [u8; 4] = (REFCOUNT_MAX as i32).to_le_bytes();
        segment.init.extend_from_slice(&refcount_max_bytes);
        segment.init.extend_from_slice(string.as_bytes());

        let segment_index = self.module.data.append_segment(segment);

        // Generate linker symbol
        let name = self
            .layout_ids
            .get(sym, layout)
            .to_symbol_string(sym, self.interns);

        let linker_symbol = SymInfo::Data(DataSymbol::Defined {
            flags: 0,
            name: name.clone(),
            segment_index,
            segment_offset: 4,
            size: string.len() as u32,
        });

        // Ensure the linker keeps the segment aligned when relocating it
        self.module.linking.segment_info.push(LinkingSegment {
            name,
            alignment: Align::Bytes4,
            flags: 0,
        });

        let linker_sym_index = self.module.linking.symbol_table.len();
        self.module.linking.symbol_table.push(linker_symbol);

        (linker_sym_index as u32, elements_addr)
    }

    /*******************************************************************
     * Call expressions
     *******************************************************************/

    fn expr_call(
        &mut self,
        call_type: &CallType<'a>,
        arguments: &'a [Symbol],
        ret_sym: Symbol,
        ret_layout: &Layout<'a>,
        ret_storage: &StoredValue,
    ) {
        match call_type {
            CallType::ByName { name: func_sym, .. } => {
                self.expr_call_by_name(*func_sym, arguments, ret_sym, ret_layout, ret_storage)
            }
            CallType::LowLevel { op: lowlevel, .. } => {
                self.expr_call_low_level(*lowlevel, arguments, ret_sym, ret_layout, ret_storage)
            }

            x => todo!("call type {:?}", x),
        }
    }

    fn expr_call_by_name(
        &mut self,
        func_sym: Symbol,
        arguments: &'a [Symbol],
        ret_sym: Symbol,
        ret_layout: &Layout<'a>,
        ret_storage: &StoredValue,
    ) {
        let wasm_layout = WasmLayout::new(ret_layout);

        // If this function is just a lowlevel wrapper, then inline it
        if let LowLevelWrapperType::CanBeReplacedBy(lowlevel) =
            LowLevelWrapperType::from_symbol(func_sym)
        {
            return self.expr_call_low_level(lowlevel, arguments, ret_sym, ret_layout, ret_storage);
        }

        let (param_types, ret_type) = self.storage.load_symbols_for_call(
            self.env.arena,
            &mut self.code_builder,
            arguments,
            ret_sym,
            &wasm_layout,
            CallConv::C,
        );

        for (roc_proc_index, (ir_sym, linker_sym_index)) in self.proc_symbols.iter().enumerate() {
            let wasm_fn_index = self.fn_index_offset + roc_proc_index as u32;
            if *ir_sym == func_sym {
                let num_wasm_args = param_types.len();
                let has_return_val = ret_type.is_some();
                self.code_builder.call(
                    wasm_fn_index,
                    *linker_sym_index,
                    num_wasm_args,
                    has_return_val,
                );
                return;
            }
        }

        internal_error!(
            "Could not find procedure {:?}\nKnown procedures: {:?}",
            func_sym,
            self.proc_symbols
        );
    }

    fn expr_call_low_level(
        &mut self,
        lowlevel: LowLevel,
        arguments: &'a [Symbol],
        ret_symbol: Symbol,
        ret_layout: &Layout<'a>,
        ret_storage: &StoredValue,
    ) {
        let low_level_call = LowLevelCall {
            lowlevel,
            arguments,
            ret_symbol,
            ret_layout: ret_layout.to_owned(),
            ret_storage: ret_storage.to_owned(),
        };
        low_level_call.generate(self);
    }

    /// Generate a call instruction to a Zig builtin function.
    /// And if we haven't seen it before, add an Import and linker data for it.
    /// Zig calls use LLVM's "fast" calling convention rather than our usual C ABI.
    pub fn call_zig_builtin_after_loading_args(
        &mut self,
        name: &'a str,
        num_wasm_args: usize,
        has_return_val: bool,
    ) {
        let fn_index = self.module.names.functions[name.as_bytes()];
        self.called_preload_fns.push(fn_index);
        let linker_symbol_index = u32::MAX;

        self.code_builder
            .call(fn_index, linker_symbol_index, num_wasm_args, has_return_val);
    }

    /// Call a helper procedure that implements `==` for a data structure (not numbers or Str)
    /// If this is the first call for this Layout, it will generate the IR for the procedure.
    /// Call stack is expr_call_low_level -> LowLevelCall::generate -> call_eq_specialized
    /// It's a bit circuitous, but the alternative is to give low_level.rs `pub` access to
    /// interns, helper_proc_gen, and expr(). That just seemed all wrong.
    pub fn call_eq_specialized(
        &mut self,
        arguments: &'a [Symbol],
        arg_layout: &Layout<'a>,
        ret_symbol: Symbol,
        ret_storage: &StoredValue,
    ) {
        let ident_ids = self
            .interns
            .all_ident_ids
            .get_mut(&self.env.module_id)
            .unwrap();

        // Get an IR expression for the call to the specialized procedure
        let (specialized_call_expr, new_specializations) = self
            .helper_proc_gen
            .call_specialized_equals(ident_ids, arg_layout, arguments);

        // If any new specializations were created, register their symbol data
        for spec in new_specializations.into_iter() {
            self.register_helper_proc(spec);
        }

        // Generate Wasm code for the IR call expression
        self.expr(
            ret_symbol,
            self.env.arena.alloc(specialized_call_expr),
            &Layout::Builtin(Builtin::Bool),
            ret_storage,
        );
    }

    /*******************************************************************
     * Structs
     *******************************************************************/

    fn expr_struct(
        &mut self,
        sym: Symbol,
        layout: &Layout<'a>,
        storage: &StoredValue,
        fields: &'a [Symbol],
    ) {
        if matches!(layout, Layout::Struct(_)) {
            match storage {
                StoredValue::StackMemory { location, size, .. } => {
                    if *size > 0 {
                        let (local_id, struct_offset) =
                            location.local_and_offset(self.storage.stack_frame_pointer);
                        let mut field_offset = struct_offset;
                        for field in fields.iter() {
                            field_offset += self.storage.copy_value_to_memory(
                                &mut self.code_builder,
                                local_id,
                                field_offset,
                                *field,
                            );
                        }
                    } else {
                        // Zero-size struct. No code to emit.
                        // These values are purely conceptual, they only exist internally in the compiler
                    }
                }
                _ => internal_error!("Cannot create struct {:?} with storage {:?}", sym, storage),
            };
        } else {
            // Struct expression but not Struct layout => single element. Copy it.
            let field_storage = self.storage.get(&fields[0]).to_owned();
            self.storage
                .clone_value(&mut self.code_builder, storage, &field_storage, fields[0]);
        }
    }

    fn expr_struct_at_index(
        &mut self,
        sym: Symbol,
        storage: &StoredValue,
        index: u64,
        field_layouts: &'a [Layout<'a>],
        structure: Symbol,
    ) {
        self.storage
            .ensure_value_has_local(&mut self.code_builder, sym, storage.to_owned());
        let (local_id, mut offset) = match self.storage.get(&structure) {
            StoredValue::StackMemory { location, .. } => {
                location.local_and_offset(self.storage.stack_frame_pointer)
            }

            StoredValue::Local {
                value_type,
                local_id,
                ..
            } => {
                debug_assert!(matches!(value_type, ValueType::I32));
                (*local_id, 0)
            }

            StoredValue::VirtualMachineStack { .. } => {
                internal_error!("ensure_value_has_local didn't work")
            }
        };
        for field in field_layouts.iter().take(index as usize) {
            offset += field.stack_size(TARGET_INFO);
        }
        self.storage
            .copy_value_from_memory(&mut self.code_builder, sym, local_id, offset);
    }

    /*******************************************************************
     * Heap allocation
     *******************************************************************/

    /// Allocate heap space and write an initial refcount
    /// If the data size is known at compile time, pass it in comptime_data_size.
    /// If size is only known at runtime, push *data* size to the VM stack first.
    /// Leaves the *data* address on the VM stack
    fn allocate_with_refcount(
        &mut self,
        comptime_data_size: Option<u32>,
        alignment_bytes: u32,
        initial_refcount: u32,
    ) {
        // Add extra bytes for the refcount
        let extra_bytes = alignment_bytes.max(PTR_SIZE);

        if let Some(data_size) = comptime_data_size {
            // Data size known at compile time and passed as an argument
            self.code_builder
                .i32_const((data_size + extra_bytes) as i32);
        } else {
            // Data size known only at runtime and is on top of VM stack
            self.code_builder.i32_const(extra_bytes as i32);
            self.code_builder.i32_add();
        }

        // Provide a constant for the alignment argument
        self.code_builder.i32_const(alignment_bytes as i32);

        // Call the foreign function. (Zig and C calling conventions are the same for this signature)
        self.call_zig_builtin_after_loading_args("roc_alloc", 2, true);

        // Save the allocation address to a temporary local variable
        let local_id = self.storage.create_anonymous_local(ValueType::I32);
        self.code_builder.tee_local(local_id);

        // Write the initial refcount
        let refcount_offset = extra_bytes - PTR_SIZE;
        let encoded_refcount = (initial_refcount as i32) - 1 + i32::MIN;
        self.code_builder.i32_const(encoded_refcount);
        self.code_builder.i32_store(Align::Bytes4, refcount_offset);

        // Put the data address on the VM stack
        self.code_builder.get_local(local_id);
        self.code_builder.i32_const(extra_bytes as i32);
        self.code_builder.i32_add();
    }

    /*******************************************************************
     * Arrays
     *******************************************************************/

    fn expr_array(
        &mut self,
        sym: Symbol,
        storage: &StoredValue,
        elem_layout: &Layout<'a>,
        elems: &'a [ListLiteralElement<'a>],
    ) {
        if let StoredValue::StackMemory { location, .. } = storage {
            let size = elem_layout.stack_size(TARGET_INFO) * (elems.len() as u32);

            // Allocate heap space and store its address in a local variable
            let heap_local_id = self.storage.create_anonymous_local(PTR_TYPE);
            let heap_alignment = elem_layout.alignment_bytes(TARGET_INFO);
            self.allocate_with_refcount(Some(size), heap_alignment, 1);
            self.code_builder.set_local(heap_local_id);

            let (stack_local_id, stack_offset) =
                location.local_and_offset(self.storage.stack_frame_pointer);

            // elements pointer
            self.code_builder.get_local(stack_local_id);
            self.code_builder.get_local(heap_local_id);
            self.code_builder.i32_store(Align::Bytes4, stack_offset);

            // length of the list
            self.code_builder.get_local(stack_local_id);
            self.code_builder.i32_const(elems.len() as i32);
            self.code_builder.i32_store(Align::Bytes4, stack_offset + 4);

            let mut elem_offset = 0;

            for (i, elem) in elems.iter().enumerate() {
                let elem_sym = match elem {
                    ListLiteralElement::Literal(lit) => {
                        // This has no Symbol but our storage methods expect one.
                        // Let's just pretend it was defined in a `Let`.
                        let debug_name = format!("{:?}_{}", sym, i);
                        let elem_sym = self.create_symbol(&debug_name);
                        let expr = Expr::Literal(*lit);

                        self.stmt_let_store_expr(
                            elem_sym,
                            elem_layout,
                            &expr,
                            StoredValueKind::Variable,
                        );

                        elem_sym
                    }

                    ListLiteralElement::Symbol(elem_sym) => *elem_sym,
                };

                elem_offset += self.storage.copy_value_to_memory(
                    &mut self.code_builder,
                    heap_local_id,
                    elem_offset,
                    elem_sym,
                );
            }
        } else {
            internal_error!("Unexpected storage for Array {:?}: {:?}", sym, storage)
        }
    }

    fn expr_empty_array(&mut self, sym: Symbol, storage: &StoredValue) {
        if let StoredValue::StackMemory { location, .. } = storage {
            let (local_id, offset) = location.local_and_offset(self.storage.stack_frame_pointer);

            // This is a minor cheat.
            // What we want to write to stack memory is { elements: null, length: 0 }
            // But instead of two 32-bit stores, we can do a single 64-bit store.
            self.code_builder.get_local(local_id);
            self.code_builder.i64_const(0);
            self.code_builder.i64_store(Align::Bytes4, offset);
        } else {
            internal_error!("Unexpected storage for {:?}", sym)
        }
    }

    /*******************************************************************
     * Tag Unions
     *******************************************************************/

    fn expr_tag(
        &mut self,
        union_layout: &UnionLayout<'a>,
        tag_id: TagIdIntType,
        arguments: &'a [Symbol],
        symbol: Symbol,
        stored: &StoredValue,
    ) {
        if union_layout.tag_is_null(tag_id) {
            self.code_builder.i32_const(0);
            return;
        }

        let stores_tag_id_as_data = union_layout.stores_tag_id_as_data(TARGET_INFO);
        let stores_tag_id_in_pointer = union_layout.stores_tag_id_in_pointer(TARGET_INFO);
        let (data_size, data_alignment) = union_layout.data_size_and_alignment(TARGET_INFO);

        // We're going to use the pointer many times, so put it in a local variable
        let stored_with_local =
            self.storage
                .ensure_value_has_local(&mut self.code_builder, symbol, stored.to_owned());

        let (local_id, data_offset) = match stored_with_local {
            StoredValue::StackMemory { location, .. } => {
                location.local_and_offset(self.storage.stack_frame_pointer)
            }
            StoredValue::Local { local_id, .. } => {
                // Tag is stored as a pointer to the heap. Call the allocator to get a memory address.
                self.allocate_with_refcount(Some(data_size), data_alignment, 1);
                self.code_builder.set_local(local_id);
                (local_id, 0)
            }
            StoredValue::VirtualMachineStack { .. } => {
                internal_error!("{:?} should have a local variable", symbol)
            }
        };

        // Write the field values to memory
        let mut field_offset = data_offset;
        for field_symbol in arguments.iter() {
            field_offset += self.storage.copy_value_to_memory(
                &mut self.code_builder,
                local_id,
                field_offset,
                *field_symbol,
            );
        }

        // Store the tag ID (if any)
        if stores_tag_id_as_data {
            let id_offset = data_offset + data_size - data_alignment;

            let id_align = union_layout.tag_id_builtin().alignment_bytes(TARGET_INFO);
            let id_align = Align::from(id_align);

            self.code_builder.get_local(local_id);

            match id_align {
                Align::Bytes1 => {
                    self.code_builder.i32_const(tag_id as i32);
                    self.code_builder.i32_store8(id_align, id_offset);
                }
                Align::Bytes2 => {
                    self.code_builder.i32_const(tag_id as i32);
                    self.code_builder.i32_store16(id_align, id_offset);
                }
                Align::Bytes4 => {
                    self.code_builder.i32_const(tag_id as i32);
                    self.code_builder.i32_store(id_align, id_offset);
                }
                Align::Bytes8 => {
                    self.code_builder.i64_const(tag_id as i64);
                    self.code_builder.i64_store(id_align, id_offset);
                }
            }
        } else if stores_tag_id_in_pointer {
            self.code_builder.get_local(local_id);
            self.code_builder.i32_const(tag_id as i32);
            self.code_builder.i32_or();
            self.code_builder.set_local(local_id);
        }
    }

    fn expr_get_tag_id(
        &mut self,
        structure: Symbol,
        union_layout: &UnionLayout<'a>,
        tag_id_symbol: Symbol,
        stored_value: &StoredValue,
    ) {
        use UnionLayout::*;

        let block_result_id = match union_layout {
            NonRecursive(_) => None,
            Recursive(_) => None,
            NonNullableUnwrapped(_) => {
                self.code_builder.i32_const(0);
                return;
            }
            NullableWrapped { nullable_id, .. } => {
                let stored_with_local = self.storage.ensure_value_has_local(
                    &mut self.code_builder,
                    tag_id_symbol,
                    stored_value.to_owned(),
                );
                let local_id = match stored_with_local {
                    StoredValue::Local { local_id, .. } => local_id,
                    _ => internal_error!("ensure_value_has_local didn't work"),
                };

                // load pointer
                self.storage
                    .load_symbols(&mut self.code_builder, &[structure]);

                // null check
                self.code_builder.i32_eqz();
                self.code_builder.if_();
                self.code_builder.i32_const(*nullable_id as i32);
                self.code_builder.set_local(local_id);
                self.code_builder.else_();
                Some(local_id)
            }
            NullableUnwrapped { nullable_id, .. } => {
                self.code_builder.i32_const(!(*nullable_id) as i32);
                self.code_builder.i32_const(*nullable_id as i32);
                self.storage
                    .load_symbols(&mut self.code_builder, &[structure]);
                self.code_builder.select();
                None
            }
        };

        if union_layout.stores_tag_id_as_data(TARGET_INFO) {
            let (data_size, data_alignment) = union_layout.data_size_and_alignment(TARGET_INFO);
            let id_offset = data_size - data_alignment;

            let id_align = union_layout.tag_id_builtin().alignment_bytes(TARGET_INFO);
            let id_align = Align::from(id_align);

            self.storage
                .load_symbols(&mut self.code_builder, &[structure]);

            match union_layout.tag_id_builtin() {
                Builtin::Bool | Builtin::Int(IntWidth::U8) => {
                    self.code_builder.i32_load8_u(id_align, id_offset)
                }
                Builtin::Int(IntWidth::U16) => self.code_builder.i32_load16_u(id_align, id_offset),
                Builtin::Int(IntWidth::U32) => self.code_builder.i32_load(id_align, id_offset),
                Builtin::Int(IntWidth::U64) => self.code_builder.i64_load(id_align, id_offset),
                x => internal_error!("Unexpected layout for tag union id {:?}", x),
            }
        } else if union_layout.stores_tag_id_in_pointer(TARGET_INFO) {
            self.storage
                .load_symbols(&mut self.code_builder, &[structure]);
            self.code_builder.i32_const(3);
            self.code_builder.i32_and();
        }

        if let Some(local_id) = block_result_id {
            self.code_builder.set_local(local_id);
            self.code_builder.end();
        }
    }

    fn expr_union_at_index(
        &mut self,
        structure: Symbol,
        tag_id: TagIdIntType,
        union_layout: &UnionLayout<'a>,
        index: u64,
        symbol: Symbol,
    ) {
        use UnionLayout::*;

        debug_assert!(!union_layout.tag_is_null(tag_id));

        let tag_index = tag_id as usize;
        let field_layouts = match union_layout {
            NonRecursive(tags) => tags[tag_index],
            Recursive(tags) => tags[tag_index],
            NonNullableUnwrapped(layouts) => *layouts,
            NullableWrapped {
                other_tags,
                nullable_id,
            } => {
                let index = if tag_index > *nullable_id as usize {
                    tag_index - 1
                } else {
                    tag_index
                };
                other_tags[index]
            }
            NullableUnwrapped { other_fields, .. } => *other_fields,
        };

        let field_offset: u32 = field_layouts
            .iter()
            .take(index as usize)
            .map(|field_layout| field_layout.stack_size(TARGET_INFO))
            .sum();

        // Get pointer and offset to the tag's data
        let structure_storage = self.storage.get(&structure).to_owned();
        let stored_with_local = self.storage.ensure_value_has_local(
            &mut self.code_builder,
            structure,
            structure_storage,
        );
        let (tag_local_id, tag_offset) = match stored_with_local {
            StoredValue::StackMemory { location, .. } => {
                location.local_and_offset(self.storage.stack_frame_pointer)
            }
            StoredValue::Local { local_id, .. } => (local_id, 0),
            StoredValue::VirtualMachineStack { .. } => {
                internal_error!("{:?} should have a local variable", structure)
            }
        };

        let stores_tag_id_in_pointer = union_layout.stores_tag_id_in_pointer(TARGET_INFO);

        let from_ptr = if stores_tag_id_in_pointer {
            let ptr = self.storage.create_anonymous_local(ValueType::I32);
            self.code_builder.get_local(tag_local_id);
            self.code_builder.i32_const(-4); // 11111111...1100
            self.code_builder.i32_and();
            self.code_builder.set_local(ptr);
            ptr
        } else {
            tag_local_id
        };

        let from_offset = tag_offset + field_offset;
        self.storage
            .copy_value_from_memory(&mut self.code_builder, symbol, from_ptr, from_offset);
    }
}