roc/crates/compiler/gen_wasm/src/lib.rs

mod backend;
mod layout;
mod low_level;
mod storage;
pub mod wasm_module;

// Helpers for interfacing to a Wasm module from outside
pub mod wasm32_result;
pub mod wasm32_sized;

use bitvec::prelude::BitVec;
use bumpalo::collections::Vec;
use bumpalo::{self, Bump};

use roc_collections::all::{MutMap, MutSet};
use roc_module::low_level::LowLevelWrapperType;
use roc_module::symbol::{Interns, ModuleId, Symbol};
use roc_mono::code_gen_help::CodeGenHelp;
use roc_mono::ir::{Proc, ProcLayout};
use roc_mono::layout::LayoutIds;
use roc_target::TargetInfo;
use wasm_module::parse::ParseError;

use crate::backend::{ProcLookupData, ProcSource, WasmBackend};
use crate::wasm_module::{Align, CodeBuilder, LocalId, ValueType, WasmModule};

const TARGET_INFO: TargetInfo = TargetInfo::default_wasm32();
const PTR_SIZE: u32 = {
    let value = TARGET_INFO.ptr_width() as u32;

    // const assert that our pointer width is actually 4
    // the code relies on the pointer width being exactly 4
    assert!(value == 4);

    value
};
const PTR_TYPE: ValueType = ValueType::I32;

pub const STACK_POINTER_GLOBAL_ID: u32 = 0;
pub const FRAME_ALIGNMENT_BYTES: i32 = 16;
pub const MEMORY_NAME: &str = "memory";
pub const BUILTINS_IMPORT_MODULE_NAME: &str = "env";
pub const STACK_POINTER_NAME: &str = "__stack_pointer";

pub struct Env<'a> {
    pub arena: &'a Bump,
    pub module_id: ModuleId,
    pub exposed_to_host: MutSet<Symbol>,
}

/// Parse the preprocessed host binary
/// If successful, the module can be passed to build_app_binary
pub fn parse_host<'a>(arena: &'a Bump, host_bytes: &[u8]) -> Result<WasmModule<'a>, ParseError> {
    WasmModule::preload(arena, host_bytes)
}

/// Generate a Wasm module in binary form, ready to write to a file. Entry point from roc_build.
///   env            environment data from previous compiler stages
///   interns        names of functions and variables (as memory-efficient interned strings)
///   host_module    parsed module from a Wasm object file containing all of the non-Roc code
///   procedures     Roc code in monomorphized intermediate representation
pub fn build_app_binary<'a>(
    env: &'a Env<'a>,
    interns: &'a mut Interns,
    host_module: WasmModule<'a>,
    procedures: MutMap<(Symbol, ProcLayout<'a>), Proc<'a>>,
) -> std::vec::Vec<u8> {
    let (mut wasm_module, called_preload_fns, _) =
        build_app_module(env, interns, host_module, procedures);

    wasm_module.eliminate_dead_code(env.arena, called_preload_fns);

    let mut buffer = std::vec::Vec::with_capacity(wasm_module.size());
    wasm_module.serialize(&mut buffer);
    buffer
}

/// Generate an unserialized Wasm module
/// Shared by all consumers of gen_wasm: roc_build, roc_repl_wasm, and test_gen
/// (roc_repl_wasm and test_gen will add more generated code for a wrapper function
/// that defines a common interface to `main`, independent of return type.)
pub fn build_app_module<'a>(
    env: &'a Env<'a>,
    interns: &'a mut Interns,
    host_module: WasmModule<'a>,
    procedures: MutMap<(Symbol, ProcLayout<'a>), Proc<'a>>,
) -> (WasmModule<'a>, BitVec<usize>, u32) {
    let mut layout_ids = LayoutIds::default();
    let mut procs = Vec::with_capacity_in(procedures.len(), env.arena);
    let mut proc_lookup = Vec::with_capacity_in(procedures.len() * 2, env.arena);
    let mut host_to_app_map = Vec::with_capacity_in(env.exposed_to_host.len(), env.arena);
    let mut maybe_main_fn_index = None;

    // Adjust Wasm function indices to account for functions from the object file
    let fn_index_offset: u32 =
        host_module.import.function_count() as u32 + host_module.code.preloaded_count;

    // Pre-pass over the procedure names & layouts
    // Filter out procs we're going to inline & gather some data for lookups
    let mut fn_index: u32 = fn_index_offset;
    for ((sym, proc_layout), proc) in procedures.into_iter() {
        if matches!(
            LowLevelWrapperType::from_symbol(sym),
            LowLevelWrapperType::CanBeReplacedBy(_)
        ) {
            continue;
        }
        procs.push(proc);

        if env.exposed_to_host.contains(&sym) {
            maybe_main_fn_index = Some(fn_index);

            let exposed_name = layout_ids
                .get_toplevel(sym, &proc_layout)
                .to_exposed_symbol_string(sym, interns);

            let exposed_name_bump: &'a str = env.arena.alloc_str(&exposed_name);

            host_to_app_map.push((exposed_name_bump, fn_index));
        }

        proc_lookup.push(ProcLookupData {
            name: sym,
            layout: proc_layout,
            source: ProcSource::Roc,
        });

        fn_index += 1;
    }

    let mut backend = WasmBackend::new(
        env,
        interns,
        layout_ids,
        proc_lookup,
        host_to_app_map,
        host_module,
        fn_index_offset,
        CodeGenHelp::new(env.arena, TargetInfo::default_wasm32(), env.module_id),
    );

    if DEBUG_SETTINGS.user_procs_ir {
        println!("## procs");
        for proc in procs.iter() {
            println!("{}", proc.to_pretty(200));
            // println!("{:?}", proc);
        }
    }

    // Generate procs from user code
    for proc in procs.iter() {
        backend.build_proc(proc);
    }

    // Generate specialized helpers for refcounting & equality
    let helper_procs = backend.get_helpers();

    backend.register_symbol_debug_names();

    if DEBUG_SETTINGS.helper_procs_ir {
        println!("## helper_procs");
        for proc in helper_procs.iter() {
            println!("{}", proc.to_pretty(200));
            // println!("{:#?}", proc);
        }
    }

    // Generate Wasm for helpers and Zig/Roc wrappers
    let sources = Vec::from_iter_in(
        backend
            .proc_lookup
            .iter()
            .map(|ProcLookupData { source, .. }| *source),
        env.arena,
    );
    let mut helper_iter = helper_procs.iter();
    for (idx, source) in sources.iter().enumerate() {
        use ProcSource::*;
        match source {
            Roc => { /* already generated */ }
            Helper => backend.build_proc(helper_iter.next().unwrap()),
            HigherOrderWrapper(inner_idx) => backend.build_higher_order_wrapper(idx, *inner_idx),
        }
    }

    let (module, called_preload_fns) = backend.finalize();
    let main_function_index =
        maybe_main_fn_index.expect("The app must expose at least one value to the host");

    (module, called_preload_fns, main_function_index)
}

pub struct CopyMemoryConfig {
    from_ptr: LocalId,
    from_offset: u32,
    to_ptr: LocalId,
    to_offset: u32,
    size: u32,
    alignment_bytes: u32,
}

pub fn copy_memory(code_builder: &mut CodeBuilder, config: CopyMemoryConfig) {
    if config.from_ptr == config.to_ptr && config.from_offset == config.to_offset {
        return;
    }
    if config.size == 0 {
        return;
    }

    let alignment = Align::from(config.alignment_bytes);
    let mut i = 0;
    while config.size - i >= 8 {
        code_builder.get_local(config.to_ptr);
        code_builder.get_local(config.from_ptr);
        code_builder.i64_load(alignment, i + config.from_offset);
        code_builder.i64_store(alignment, i + config.to_offset);
        i += 8;
    }
    if config.size - i >= 4 {
        code_builder.get_local(config.to_ptr);
        code_builder.get_local(config.from_ptr);
        code_builder.i32_load(alignment, i + config.from_offset);
        code_builder.i32_store(alignment, i + config.to_offset);
        i += 4;
    }
    while config.size - i > 0 {
        code_builder.get_local(config.to_ptr);
        code_builder.get_local(config.from_ptr);
        code_builder.i32_load8_u(alignment, i + config.from_offset);
        code_builder.i32_store8(alignment, i + config.to_offset);
        i += 1;
    }
}

/// Round up to alignment_bytes (which must be a power of 2)
#[macro_export]
macro_rules! round_up_to_alignment {
    ($unaligned: expr, $alignment_bytes: expr) => {
        if $alignment_bytes <= 1 {
            $unaligned
        } else if $alignment_bytes.count_ones() != 1 {
            internal_error!(
                "Cannot align to {} bytes. Not a power of 2.",
                $alignment_bytes
            );
        } else {
            let mut aligned = $unaligned;
            aligned += $alignment_bytes - 1; // if lower bits are non-zero, push it over the next boundary
            aligned &= !$alignment_bytes + 1; // mask with a flag that has upper bits 1, lower bits 0
            aligned
        }
    };
}

pub struct WasmDebugSettings {
    proc_start_end: bool,
    user_procs_ir: bool,
    helper_procs_ir: bool,
    let_stmt_ir: bool,
    instructions: bool,
    storage_map: bool,
    pub keep_test_binary: bool,
    pub skip_dead_code_elim: bool,
}

pub const DEBUG_SETTINGS: WasmDebugSettings = WasmDebugSettings {
    proc_start_end: false && cfg!(debug_assertions),
    user_procs_ir: false && cfg!(debug_assertions), // Note: we also have `ROC_PRINT_IR_AFTER_SPECIALIZATION=1 cargo test-gen-wasm`
    helper_procs_ir: false && cfg!(debug_assertions),
    let_stmt_ir: false && cfg!(debug_assertions),
    instructions: false && cfg!(debug_assertions),
    storage_map: false && cfg!(debug_assertions),
    keep_test_binary: false && cfg!(debug_assertions),
    skip_dead_code_elim: false && cfg!(debug_assertions),
};