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//! Reachability walkers used by the DCE pass.
//!
//! The walkers traverse [`crate::ir::ResolvedType`] and [`IrExpr`] values,
//! marking any [`StructId`], [`TraitId`], or [`EnumId`] they encounter as
//! live in the parent [`super::DeadCodeEliminator`].
use crate::ir::IrExpr;
use super::DeadCodeEliminator;
impl DeadCodeEliminator<'_> {
/// Mark structs used in a type.
pub(super) fn mark_used_in_type(&mut self, ty: &crate::ir::ResolvedType) {
use crate::ir::ResolvedType;
match ty {
ResolvedType::Struct(id) => {
self.used_structs.insert(*id);
}
ResolvedType::Trait(id) => {
self.used_traits.insert(*id);
}
ResolvedType::Generic { base, args } => {
match base {
crate::ir::GenericBase::Struct(id) => {
self.used_structs.insert(*id);
}
crate::ir::GenericBase::Enum(id) => {
self.used_enums.insert(*id);
}
crate::ir::GenericBase::Trait(id) => {
self.used_traits.insert(*id);
}
}
for arg in args {
self.mark_used_in_type(arg);
}
}
ResolvedType::Array(inner)
| ResolvedType::Range(inner)
| ResolvedType::Optional(inner) => {
self.mark_used_in_type(inner);
}
ResolvedType::Tuple(fields) => {
for (_, field_ty) in fields {
self.mark_used_in_type(field_ty);
}
}
ResolvedType::Dictionary { key_ty, value_ty } => {
self.mark_used_in_type(key_ty);
self.mark_used_in_type(value_ty);
}
ResolvedType::Closure {
param_tys,
return_ty,
} => {
for (_, pty) in param_tys {
self.mark_used_in_type(pty);
}
self.mark_used_in_type(return_ty);
}
ResolvedType::External { type_args, .. } => {
for arg in type_args {
self.mark_used_in_type(arg);
}
}
ResolvedType::Enum(id) => {
self.used_enums.insert(*id);
}
// Placeholder types do not reference any definition.
ResolvedType::Primitive(_) | ResolvedType::TypeParam(_) | ResolvedType::Error => {}
}
}
/// Mark structs used in an expression.
#[expect(
clippy::too_many_lines,
reason = "exhaustive match over every IrExpr variant; splitting would hide the walk"
)]
pub(super) fn mark_used_in_expr(&mut self, expr: &IrExpr) {
match expr {
IrExpr::StructInst {
struct_id,
fields,
ty,
type_args,
..
} => {
if let Some(id) = struct_id {
self.used_structs.insert(*id);
}
// walk the resolved type and any explicit
// type-arguments so a local struct/enum used as a generic
// arg of an external receiver (e.g. `Box<LocalThing>` from
// an imported module) is marked used.
self.mark_used_in_type(ty);
for arg in type_args {
self.mark_used_in_type(arg);
}
for (_, _, e) in fields {
self.mark_used_in_expr(e);
}
}
IrExpr::BinaryOp { left, right, .. } => {
self.mark_used_in_expr(left);
self.mark_used_in_expr(right);
}
IrExpr::UnaryOp { operand, .. } => self.mark_used_in_expr(operand),
IrExpr::If {
condition,
then_branch,
else_branch,
..
} => {
self.mark_used_in_expr(condition);
self.mark_used_in_expr(then_branch);
if let Some(else_b) = else_branch {
self.mark_used_in_expr(else_b);
}
}
IrExpr::Array { elements, .. } => {
for e in elements {
self.mark_used_in_expr(e);
}
}
IrExpr::EnumInst {
enum_id,
fields,
ty,
..
} => {
if let Some(id) = enum_id {
self.used_enums.insert(*id);
}
// walk the resolved type so a local
// struct/enum used as a generic arg of an external
// enum (e.g. `Result<LocalErr, OK>`) is marked used.
self.mark_used_in_type(ty);
for (_, _, e) in fields {
self.mark_used_in_expr(e);
}
}
IrExpr::Tuple { fields, .. } => {
for (_, e) in fields {
self.mark_used_in_expr(e);
}
}
IrExpr::For {
collection, body, ..
} => {
self.mark_used_in_expr(collection);
self.mark_used_in_expr(body);
}
IrExpr::Match {
scrutinee, arms, ..
} => {
self.mark_used_in_expr(scrutinee);
for arm in arms {
self.mark_used_in_expr(&arm.body);
}
}
IrExpr::FunctionCall { args, .. } => {
for (_, arg) in args {
self.mark_used_in_expr(arg);
}
}
IrExpr::CallClosure {
closure, args, ty, ..
} => {
self.mark_used_in_type(ty);
self.mark_used_in_expr(closure);
for (_, arg) in args {
self.mark_used_in_expr(arg);
}
}
IrExpr::MethodCall {
receiver,
args,
dispatch,
..
} => {
self.mark_used_in_expr(receiver);
for (_, arg) in args {
self.mark_used_in_expr(arg);
}
// Virtual dispatch keeps its trait alive.
if let crate::ir::DispatchKind::Virtual { trait_id, .. } = dispatch {
self.used_traits.insert(*trait_id);
}
// Static dispatch points at an impl whose target struct/enum
// is already reached via the receiver's type.
}
IrExpr::DictLiteral { entries, .. } => {
for (k, v) in entries {
self.mark_used_in_expr(k);
self.mark_used_in_expr(v);
}
}
IrExpr::DictAccess { dict, key, .. } => {
self.mark_used_in_expr(dict);
self.mark_used_in_expr(key);
}
IrExpr::Block {
statements, result, ..
} => {
for stmt in statements {
self.mark_used_in_block_statement(stmt);
}
self.mark_used_in_expr(result);
}
IrExpr::Literal { .. }
| IrExpr::Reference { .. }
| IrExpr::SelfFieldRef { .. }
| IrExpr::LetRef { .. } => {}
IrExpr::FieldAccess { object, .. } => self.mark_used_in_expr(object),
IrExpr::Closure {
params,
captures,
body,
..
} => {
for (_, _, _, ty) in params {
self.mark_used_in_type(ty);
}
for (_, _, _, ty) in captures {
self.mark_used_in_type(ty);
}
self.mark_used_in_expr(body);
}
IrExpr::ClosureRef { env_struct, ty, .. } => {
self.mark_used_in_type(ty);
self.mark_used_in_expr(env_struct);
}
}
}
pub(super) fn mark_used_in_block_statement(&mut self, stmt: &crate::ir::IrBlockStatement) {
use crate::ir::IrBlockStatement;
match stmt {
IrBlockStatement::Let { value, .. } => {
self.mark_used_in_expr(value);
}
IrBlockStatement::Assign { target, value, .. } => {
self.mark_used_in_expr(target);
self.mark_used_in_expr(value);
}
IrBlockStatement::Expr(expr) => {
self.mark_used_in_expr(expr);
}
}
}
}