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//! Globals within a wasm module.
use crate::emit::{Emit, EmitContext, Section};
use crate::parse::IndicesToIds;
use crate::tombstone_arena::{Id, Tombstone, TombstoneArena};
use crate::{ImportId, InitExpr, Module, Result, ValType};
/// The id of a global.
pub type GlobalId = Id<Global>;
/// A wasm global.
#[derive(Debug)]
pub struct Global {
// NB: Not public so that it can't get out of sync with the arena this is
// contained within.
id: GlobalId,
/// This global's type.
pub ty: ValType,
/// Whether this global is mutable or not.
pub mutable: bool,
/// The kind of global this is
pub kind: GlobalKind,
}
impl Tombstone for Global {}
/// The different kinds of globals a wasm module can have
#[derive(Debug)]
pub enum GlobalKind {
/// An imported global without a known initializer
Import(ImportId),
/// A locally declare global with the specified identifier
Local(InitExpr),
}
impl Global {
/// Get this global's id.
pub fn id(&self) -> GlobalId {
self.id
}
}
impl Emit for Global {
fn emit(&self, cx: &mut EmitContext) {
Emit::emit(&self.ty, cx);
cx.encoder.byte(self.mutable as u8);
}
}
/// The set of globals in each function in this module.
#[derive(Debug, Default)]
pub struct ModuleGlobals {
/// The arena where the globals are stored.
arena: TombstoneArena<Global>,
}
impl ModuleGlobals {
/// Adds a new imported global to this list.
pub fn add_import(&mut self, ty: ValType, mutable: bool, import_id: ImportId) -> GlobalId {
self.arena.alloc_with_id(|id| Global {
id,
ty,
mutable,
kind: GlobalKind::Import(import_id),
})
}
/// Construct a new global, that does not originate from any of the input
/// wasm globals.
pub fn add_local(&mut self, ty: ValType, mutable: bool, init: InitExpr) -> GlobalId {
self.arena.alloc_with_id(|id| Global {
id,
ty,
mutable,
kind: GlobalKind::Local(init),
})
}
/// Gets a reference to a memory given its id
pub fn get(&self, id: GlobalId) -> &Global {
&self.arena[id]
}
/// Gets a reference to a memory given its id
pub fn get_mut(&mut self, id: GlobalId) -> &mut Global {
&mut self.arena[id]
}
/// Removes a global from this module.
///
/// It is up to you to ensure that any potential references to the deleted
/// global are also removed, eg `get_global` expressions.
pub fn delete(&mut self, id: GlobalId) {
self.arena.delete(id);
}
/// Get a shared reference to this module's globals.
pub fn iter(&self) -> impl Iterator<Item = &Global> {
self.arena.iter().map(|(_, f)| f)
}
}
impl Module {
/// Construct a new, empty set of globals for a module.
pub(crate) fn parse_globals(
&mut self,
section: wasmparser::GlobalSectionReader,
ids: &mut IndicesToIds,
) -> Result<()> {
log::debug!("parse global section");
for g in section {
let g = g?;
let id = self.globals.add_local(
ValType::parse(&g.ty.content_type)?,
g.ty.mutable,
InitExpr::eval(&g.init_expr, ids)?,
);
ids.push_global(id);
}
Ok(())
}
}
impl Emit for ModuleGlobals {
fn emit(&self, cx: &mut EmitContext) {
log::debug!("emit global section");
fn get_local(global: &Global) -> Option<(&Global, &InitExpr)> {
match &global.kind {
GlobalKind::Import(_) => None,
GlobalKind::Local(local) => Some((global, local)),
}
}
// All imported globals emitted earlier during the import section, so
// filter those out.
let globals = self.iter().filter_map(get_local).count();
if globals == 0 {
return;
}
let mut cx = cx.start_section(Section::Global);
cx.encoder.usize(globals);
for (global, local) in self.iter().filter_map(get_local) {
cx.indices.push_global(global.id());
global.emit(&mut cx);
local.emit(&mut cx);
}
}
}