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emit.rs
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emit.rs
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//! Traits and code for emitting high-level structures as low-level, raw wasm
//! structures. E.g. translating from globally unique identifiers down to the
//! raw wasm structure's index spaces.
use crate::encode::{Encoder, MAX_U32_LENGTH};
use crate::ir::Local;
use crate::map::{IdHashMap, IdHashSet};
use crate::{Data, DataId, Element, ElementId, Function, FunctionId};
use crate::{Global, GlobalId, Memory, MemoryId, Module, Table, TableId};
use crate::{Type, TypeId};
use std::ops::{Deref, DerefMut};
pub struct EmitContext<'a> {
pub module: &'a Module,
pub indices: &'a mut IdsToIndices,
pub encoder: Encoder<'a>,
pub locals: IdHashMap<Function, IdHashSet<Local>>,
pub code_transform: Vec<(usize, usize)>,
}
pub struct SubContext<'a, 'cx> {
cx: &'cx mut EmitContext<'a>,
write_size_to: usize,
}
/// Anything that can be lowered to raw wasm structures.
pub trait Emit {
/// Emit `self` into the given context.
fn emit(&self, cx: &mut EmitContext);
}
impl<'a, T: ?Sized + Emit> Emit for &'a T {
fn emit(&self, cx: &mut EmitContext) {
T::emit(self, cx)
}
}
/// Maps our high-level identifiers to the raw indices they end up emitted at.
///
/// As we lower to raw wasm structures, we cement various constructs' locations
/// in their respective index spaces. For example, a type with some id `A` ends
/// up being the `i^th` type emitted in the raw wasm type section. When a
/// function references that type, it needs to reference it by its `i` index
/// since the identifier `A` doesn't exist at the raw wasm level.
#[derive(Debug, Default)]
pub struct IdsToIndices {
tables: IdHashMap<Table, u32>,
types: IdHashMap<Type, u32>,
funcs: IdHashMap<Function, u32>,
globals: IdHashMap<Global, u32>,
memories: IdHashMap<Memory, u32>,
elements: IdHashMap<Element, u32>,
data: IdHashMap<Data, u32>,
pub locals: IdHashMap<Function, IdHashMap<Local, u32>>,
}
macro_rules! define_get_index {
( $get_name:ident, $id_ty:ty, $member:ident ) => {
impl IdsToIndices {
/// Get the index for the given identifier.
#[inline]
#[allow(dead_code)] // not everything is used just yet
pub fn $get_name(&self, id: $id_ty) -> u32 {
self.$member.get(&id).cloned().expect(
"Should never try and get the index for an identifier that has not already had \
its index set. This means that either we are attempting to get the index of \
an unused identifier, or that we are emitting sections in the wrong order."
)
}
}
};
}
macro_rules! define_get_push_index {
( $get_name:ident, $push_name:ident, $id_ty:ty, $member:ident ) => {
define_get_index!($get_name, $id_ty, $member);
impl IdsToIndices {
/// Adds the given identifier to this set, assigning it the next
/// available index.
#[inline]
pub fn $push_name(&mut self, id: $id_ty) {
let idx = self.$member.len() as u32;
self.$member.insert(id, idx);
}
}
};
}
define_get_push_index!(get_table_index, push_table, TableId, tables);
define_get_push_index!(get_type_index, push_type, TypeId, types);
define_get_push_index!(get_func_index, push_func, FunctionId, funcs);
define_get_push_index!(get_global_index, push_global, GlobalId, globals);
define_get_push_index!(get_memory_index, push_memory, MemoryId, memories);
define_get_push_index!(get_element_index, push_element, ElementId, elements);
define_get_index!(get_data_index, DataId, data);
impl IdsToIndices {
/// Sets the data index to the specified value
pub fn set_data_index(&mut self, id: DataId, idx: u32) {
self.data.insert(id, idx);
}
}
impl<'a> EmitContext<'a> {
pub fn start_section<'b>(&'b mut self, id: Section) -> SubContext<'a, 'b> {
self.subsection(id as u8)
}
pub fn subsection<'b>(&'b mut self, id: u8) -> SubContext<'a, 'b> {
self.encoder.byte(id);
let start = self.encoder.reserve_u32();
SubContext {
cx: self,
write_size_to: start,
}
}
pub fn custom_section<'b>(&'b mut self, name: &str) -> SubContext<'a, 'b> {
let mut cx = self.start_section(Section::Custom);
cx.encoder.str(name);
return cx;
}
pub fn list<T>(&mut self, list: T)
where
T: IntoIterator,
T::IntoIter: ExactSizeIterator,
T::Item: Emit,
{
let list = list.into_iter();
self.encoder.usize(list.len());
for item in list {
item.emit(self);
}
}
}
impl<'a> Deref for SubContext<'a, '_> {
type Target = EmitContext<'a>;
fn deref(&self) -> &EmitContext<'a> {
&self.cx
}
}
impl<'a> DerefMut for SubContext<'a, '_> {
fn deref_mut(&mut self) -> &mut EmitContext<'a> {
&mut self.cx
}
}
impl Drop for SubContext<'_, '_> {
fn drop(&mut self) {
let amt = self.cx.encoder.pos() - self.write_size_to - MAX_U32_LENGTH;
assert!(amt <= u32::max_value() as usize);
self.cx.encoder.u32_at(self.write_size_to, amt as u32);
}
}
pub enum Section {
Custom = 0,
Type = 1,
Import = 2,
Function = 3,
Table = 4,
Memory = 5,
Global = 6,
Export = 7,
Start = 8,
Element = 9,
Code = 10,
Data = 11,
DataCount = 12,
}