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Remove terminating_scopes hash set.

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This commit is contained in:
Mara Bos 2025-03-28 15:24:49 +01:00
parent 19f42cb9bb
commit 122d7e1dcd
1 changed files with 95 additions and 164 deletions
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253
compiler/rustc_hir_analysis/src/check/region.rs
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@ -8,7 +8,6 @@
use std::mem;
use rustc_data_structures::fx::FxHashSet;
use rustc_hir as hir;
use rustc_hir::def_id::DefId;
use rustc_hir::intravisit::{self, Visitor};
@ -45,28 +44,6 @@ struct ScopeResolutionVisitor<'tcx> {
scope_tree: ScopeTree,
cx: Context,
/// `terminating_scopes` is a set containing the ids of each
/// statement, or conditional/repeating expression. These scopes
/// are calling "terminating scopes" because, when attempting to
/// find the scope of a temporary, by default we search up the
/// enclosing scopes until we encounter the terminating scope. A
/// conditional/repeating expression is one which is not
/// guaranteed to execute exactly once upon entering the parent
/// scope. This could be because the expression only executes
/// conditionally, such as the expression `b` in `a && b`, or
/// because the expression may execute many times, such as a loop
/// body. The reason that we distinguish such expressions is that,
/// upon exiting the parent scope, we cannot statically know how
/// many times the expression executed, and thus if the expression
/// creates temporaries we cannot know statically how many such
/// temporaries we would have to cleanup. Therefore, we ensure that
/// the temporaries never outlast the conditional/repeating
/// expression, preventing the need for dynamic checks and/or
/// arbitrary amounts of stack space. Terminating scopes end
/// up being contained in a DestructionScope that contains the
/// destructor's execution.
terminating_scopes: FxHashSet<hir::ItemLocalId>,
}
/// Records the lifetime of a local variable as `cx.var_parent`
@ -81,7 +58,11 @@ fn record_var_lifetime(visitor: &mut ScopeResolutionVisitor<'_>, var_id: hir::It
}
}
fn resolve_block<'tcx>(visitor: &mut ScopeResolutionVisitor<'tcx>, blk: &'tcx hir::Block<'tcx>) {
fn resolve_block<'tcx>(
visitor: &mut ScopeResolutionVisitor<'tcx>,
blk: &'tcx hir::Block<'tcx>,
terminating: bool,
) {
debug!("resolve_block(blk.hir_id={:?})", blk.hir_id);
let prev_cx = visitor.cx;
@ -111,7 +92,7 @@ fn resolve_block<'tcx>(visitor: &mut ScopeResolutionVisitor<'tcx>, blk: &'tcx hi
// `other_argument()` has run and also the call to `quux(..)`
// itself has returned.
visitor.enter_node_scope_with_dtor(blk.hir_id.local_id);
visitor.enter_node_scope_with_dtor(blk.hir_id.local_id, terminating);
visitor.cx.var_parent = visitor.cx.parent;
{
@ -140,8 +121,7 @@ fn resolve_block<'tcx>(visitor: &mut ScopeResolutionVisitor<'tcx>, blk: &'tcx hi
// the sequence of visits agree with the order in the default
// `hir::intravisit` visitor.
mem::swap(&mut prev_cx, &mut visitor.cx);
visitor.terminating_scopes.insert(els.hir_id.local_id);
visitor.visit_block(els);
resolve_block(visitor, els, true);
// From now on, we continue normally.
visitor.cx = prev_cx;
}
@ -169,9 +149,9 @@ fn resolve_block<'tcx>(visitor: &mut ScopeResolutionVisitor<'tcx>, blk: &'tcx hi
if let Some(tail_expr) = blk.expr {
let local_id = tail_expr.hir_id.local_id;
let edition = blk.span.edition();
if edition.at_least_rust_2024() {
visitor.terminating_scopes.insert(local_id);
} else if !visitor
let terminating = edition.at_least_rust_2024();
if !terminating
&& !visitor
.tcx
.lints_that_dont_need_to_run(())
.contains(&lint::LintId::of(lint::builtin::TAIL_EXPR_DROP_ORDER))
@ -185,7 +165,7 @@ fn resolve_block<'tcx>(visitor: &mut ScopeResolutionVisitor<'tcx>, blk: &'tcx hi
.backwards_incompatible_scope
.insert(local_id, Scope { local_id, data: ScopeData::Node });
}
visitor.visit_expr(tail_expr);
resolve_expr(visitor, tail_expr, terminating);
}
}
@ -203,18 +183,14 @@ fn resolve_arm<'tcx>(visitor: &mut ScopeResolutionVisitor<'tcx>, arm: &'tcx hir:
let prev_cx = visitor.cx;
visitor.terminating_scopes.insert(arm.hir_id.local_id);
visitor.enter_node_scope_with_dtor(arm.hir_id.local_id);
visitor.enter_node_scope_with_dtor(arm.hir_id.local_id, true);
visitor.cx.var_parent = visitor.cx.parent;
if let Some(expr) = arm.guard
&& !has_let_expr(expr)
{
visitor.terminating_scopes.insert(expr.hir_id.local_id);
resolve_pat(visitor, arm.pat);
if let Some(guard) = arm.guard {
resolve_expr(visitor, guard, !has_let_expr(guard));
}
intravisit::walk_arm(visitor, arm);
resolve_expr(visitor, arm.body, false);
visitor.cx = prev_cx;
}
@ -243,126 +219,24 @@ fn resolve_stmt<'tcx>(visitor: &mut ScopeResolutionVisitor<'tcx>, stmt: &'tcx hi
// associated destruction scope that represents the scope of the
// statement plus its destructors, and thus the scope for which
// regions referenced by the destructors need to survive.
visitor.terminating_scopes.insert(stmt_id);
let prev_parent = visitor.cx.parent;
visitor.enter_node_scope_with_dtor(stmt_id);
visitor.enter_node_scope_with_dtor(stmt_id, true);
intravisit::walk_stmt(visitor, stmt);
visitor.cx.parent = prev_parent;
}
fn resolve_expr<'tcx>(visitor: &mut ScopeResolutionVisitor<'tcx>, expr: &'tcx hir::Expr<'tcx>) {
fn resolve_expr<'tcx>(
visitor: &mut ScopeResolutionVisitor<'tcx>,
expr: &'tcx hir::Expr<'tcx>,
terminating: bool,
) {
debug!("resolve_expr - pre-increment {} expr = {:?}", visitor.expr_and_pat_count, expr);
let prev_cx = visitor.cx;
visitor.enter_node_scope_with_dtor(expr.hir_id.local_id);
{
let terminating_scopes = &mut visitor.terminating_scopes;
let mut terminating = |id: hir::ItemLocalId| {
terminating_scopes.insert(id);
};
match expr.kind {
// Conditional or repeating scopes are always terminating
// scopes, meaning that temporaries cannot outlive them.
// This ensures fixed size stacks.
hir::ExprKind::Binary(
source_map::Spanned { node: hir::BinOpKind::And | hir::BinOpKind::Or, .. },
l,
r,
) => {
// expr is a short circuiting operator (|| or &&). As its
// functionality can't be overridden by traits, it always
// processes bool sub-expressions. bools are Copy and thus we
// can drop any temporaries in evaluation (read) order
// (with the exception of potentially failing let expressions).
// We achieve this by enclosing the operands in a terminating
// scope, both the LHS and the RHS.
// We optimize this a little in the presence of chains.
// Chains like a && b && c get lowered to AND(AND(a, b), c).
// In here, b and c are RHS, while a is the only LHS operand in
// that chain. This holds true for longer chains as well: the
// leading operand is always the only LHS operand that is not a
// binop itself. Putting a binop like AND(a, b) into a
// terminating scope is not useful, thus we only put the LHS
// into a terminating scope if it is not a binop.
let terminate_lhs = match l.kind {
// let expressions can create temporaries that live on
hir::ExprKind::Let(_) => false,
// binops already drop their temporaries, so there is no
// need to put them into a terminating scope.
// This is purely an optimization to reduce the number of
// terminating scopes.
hir::ExprKind::Binary(
source_map::Spanned {
node: hir::BinOpKind::And | hir::BinOpKind::Or, ..
},
..,
) => false,
// otherwise: mark it as terminating
_ => true,
};
if terminate_lhs {
terminating(l.hir_id.local_id);
}
// `Let` expressions (in a let-chain) shouldn't be terminating, as their temporaries
// should live beyond the immediate expression
if !matches!(r.kind, hir::ExprKind::Let(_)) {
terminating(r.hir_id.local_id);
}
}
hir::ExprKind::If(_, then, Some(otherwise)) => {
terminating(then.hir_id.local_id);
terminating(otherwise.hir_id.local_id);
}
hir::ExprKind::If(_, then, None) => {
terminating(then.hir_id.local_id);
}
hir::ExprKind::Loop(body, _, _, _) => {
terminating(body.hir_id.local_id);
}
hir::ExprKind::DropTemps(expr) => {
// `DropTemps(expr)` does not denote a conditional scope.
// Rather, we want to achieve the same behavior as `{ let _t = expr; _t }`.
terminating(expr.hir_id.local_id);
}
hir::ExprKind::AssignOp(..)
| hir::ExprKind::Index(..)
| hir::ExprKind::Unary(..)
| hir::ExprKind::Call(..)
| hir::ExprKind::MethodCall(..) => {
// FIXME(https://github.com/rust-lang/rfcs/issues/811) Nested method calls
//
// The lifetimes for a call or method call look as follows:
//
// call.id
// - arg0.id
// - ...
// - argN.id
// - call.callee_id
//
// The idea is that call.callee_id represents *the time when
// the invoked function is actually running* and call.id
// represents *the time to prepare the arguments and make the
// call*. See the section "Borrows in Calls" borrowck/README.md
// for an extended explanation of why this distinction is
// important.
//
// record_superlifetime(new_cx, expr.callee_id);
}
_ => {}
}
}
visitor.enter_node_scope_with_dtor(expr.hir_id.local_id, terminating);
let prev_pessimistic = visitor.pessimistic_yield;
@ -417,6 +291,53 @@ fn resolve_expr<'tcx>(visitor: &mut ScopeResolutionVisitor<'tcx>, expr: &'tcx hi
// properly, we can't miss any types.
match expr.kind {
// Conditional or repeating scopes are always terminating
// scopes, meaning that temporaries cannot outlive them.
// This ensures fixed size stacks.
hir::ExprKind::Binary(
source_map::Spanned { node: hir::BinOpKind::And | hir::BinOpKind::Or, .. },
left,
right,
) => {
// expr is a short circuiting operator (|| or &&). As its
// functionality can't be overridden by traits, it always
// processes bool sub-expressions. bools are Copy and thus we
// can drop any temporaries in evaluation (read) order
// (with the exception of potentially failing let expressions).
// We achieve this by enclosing the operands in a terminating
// scope, both the LHS and the RHS.
// We optimize this a little in the presence of chains.
// Chains like a && b && c get lowered to AND(AND(a, b), c).
// In here, b and c are RHS, while a is the only LHS operand in
// that chain. This holds true for longer chains as well: the
// leading operand is always the only LHS operand that is not a
// binop itself. Putting a binop like AND(a, b) into a
// terminating scope is not useful, thus we only put the LHS
// into a terminating scope if it is not a binop.
let terminate_lhs = match left.kind {
// let expressions can create temporaries that live on
hir::ExprKind::Let(_) => false,
// binops already drop their temporaries, so there is no
// need to put them into a terminating scope.
// This is purely an optimization to reduce the number of
// terminating scopes.
hir::ExprKind::Binary(
source_map::Spanned { node: hir::BinOpKind::And | hir::BinOpKind::Or, .. },
..,
) => false,
// otherwise: mark it as terminating
_ => true,
};
// `Let` expressions (in a let-chain) shouldn't be terminating, as their temporaries
// should live beyond the immediate expression
let terminate_rhs = !matches!(right.kind, hir::ExprKind::Let(_));
resolve_expr(visitor, left, terminate_lhs);
resolve_expr(visitor, right, terminate_rhs);
}
// Manually recurse over closures, because they are nested bodies
// that share the parent environment. We handle const blocks in
// `visit_inline_const`.
@ -485,9 +406,9 @@ fn resolve_expr<'tcx>(visitor: &mut ScopeResolutionVisitor<'tcx>, expr: &'tcx hi
visitor.enter_scope(Scope { local_id: then.hir_id.local_id, data });
visitor.cx.var_parent = visitor.cx.parent;
visitor.visit_expr(cond);
visitor.visit_expr(then);
resolve_expr(visitor, then, true);
visitor.cx = expr_cx;
visitor.visit_expr(otherwise);
resolve_expr(visitor, otherwise, true);
}
hir::ExprKind::If(cond, then, None) => {
@ -500,10 +421,20 @@ fn resolve_expr<'tcx>(visitor: &mut ScopeResolutionVisitor<'tcx>, expr: &'tcx hi
visitor.enter_scope(Scope { local_id: then.hir_id.local_id, data });
visitor.cx.var_parent = visitor.cx.parent;
visitor.visit_expr(cond);
visitor.visit_expr(then);
resolve_expr(visitor, then, true);
visitor.cx = expr_cx;
}
hir::ExprKind::Loop(body, _, _, _) => {
resolve_block(visitor, body, true);
}
hir::ExprKind::DropTemps(expr) => {
// `DropTemps(expr)` does not denote a conditional scope.
// Rather, we want to achieve the same behavior as `{ let _t = expr; _t }`.
resolve_expr(visitor, expr, true);
}
_ => intravisit::walk_expr(visitor, expr),
}
@ -786,12 +717,12 @@ impl<'tcx> ScopeResolutionVisitor<'tcx> {
self.cx.parent = Some(child_scope);
}
fn enter_node_scope_with_dtor(&mut self, id: hir::ItemLocalId) {
fn enter_node_scope_with_dtor(&mut self, id: hir::ItemLocalId, terminating: bool) {
// If node was previously marked as a terminating scope during the
// recursive visit of its parent node in the HIR, then we need to
// account for the destruction scope representing the scope of
// the destructors that run immediately after it completes.
if self.terminating_scopes.contains(&id) {
if terminating {
self.enter_scope(Scope { local_id: id, data: ScopeData::Destruction });
}
self.enter_scope(Scope { local_id: id, data: ScopeData::Node });
@ -803,13 +734,11 @@ impl<'tcx> ScopeResolutionVisitor<'tcx> {
// visited the body.
let outer_ec = mem::replace(&mut self.expr_and_pat_count, 0);
let outer_cx = self.cx;
let outer_ts = mem::take(&mut self.terminating_scopes);
// The 'pessimistic yield' flag is set to true when we are
// processing a `+=` statement and have to make pessimistic
// control flow assumptions. This doesn't apply to nested
// bodies within the `+=` statements. See #69307.
let outer_pessimistic_yield = mem::replace(&mut self.pessimistic_yield, false);
self.terminating_scopes.insert(hir_id.local_id);
self.enter_scope(Scope { local_id: hir_id.local_id, data: ScopeData::CallSite });
self.enter_scope(Scope { local_id: hir_id.local_id, data: ScopeData::Arguments });
@ -819,14 +748,13 @@ impl<'tcx> ScopeResolutionVisitor<'tcx> {
// Restore context we had at the start.
self.expr_and_pat_count = outer_ec;
self.cx = outer_cx;
self.terminating_scopes = outer_ts;
self.pessimistic_yield = outer_pessimistic_yield;
}
}
impl<'tcx> Visitor<'tcx> for ScopeResolutionVisitor<'tcx> {
fn visit_block(&mut self, b: &'tcx Block<'tcx>) {
resolve_block(self, b);
resolve_block(self, b, false);
}
fn visit_body(&mut self, body: &hir::Body<'tcx>) {
@ -850,7 +778,7 @@ impl<'tcx> Visitor<'tcx> for ScopeResolutionVisitor<'tcx> {
}
// The body of the every fn is a root scope.
this.visit_expr(body.value)
resolve_expr(this, body.value, true);
} else {
// Only functions have an outer terminating (drop) scope, while
// temporaries in constant initializers may be 'static, but only
@ -871,6 +799,10 @@ impl<'tcx> Visitor<'tcx> for ScopeResolutionVisitor<'tcx> {
// (i.e., `'static`), which means that after `g` returns, it drops,
// and all the associated destruction scope rules apply.
this.cx.var_parent = None;
this.enter_scope(Scope {
local_id: body.value.hir_id.local_id,
data: ScopeData::Destruction,
});
resolve_local(this, None, Some(body.value));
}
})
@ -886,7 +818,7 @@ impl<'tcx> Visitor<'tcx> for ScopeResolutionVisitor<'tcx> {
resolve_stmt(self, s);
}
fn visit_expr(&mut self, ex: &'tcx Expr<'tcx>) {
resolve_expr(self, ex);
resolve_expr(self, ex, false);
}
fn visit_local(&mut self, l: &'tcx LetStmt<'tcx>) {
resolve_local(self, Some(l.pat), l.init)
@ -916,7 +848,6 @@ pub(crate) fn region_scope_tree(tcx: TyCtxt<'_>, def_id: DefId) -> &ScopeTree {
scope_tree: ScopeTree::default(),
expr_and_pat_count: 0,
cx: Context { parent: None, var_parent: None },
terminating_scopes: Default::default(),
pessimistic_yield: false,
fixup_scopes: vec![],
};