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Lazy dominator tree construction in borrowck #106976

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Merged
merged 1 commit into from
Jan 21, 2023
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Lazy dominator tree construction in borrowck #106976

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4 changes: 2 additions & 2 deletions compiler/rustc_borrowck/src/diagnostics/conflict_errors.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -2193,7 +2193,7 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
let mut back_edge_stack = Vec::new();

predecessor_locations(self.body, location).for_each(|predecessor| {
if location.dominates(predecessor, &self.dominators) {
if location.dominates(predecessor, self.dominators()) {
back_edge_stack.push(predecessor)
} else {
stack.push(predecessor);
Expand Down Expand Up @@ -2305,7 +2305,7 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {

let mut has_predecessor = false;
predecessor_locations(self.body, location).for_each(|predecessor| {
if location.dominates(predecessor, &self.dominators) {
if location.dominates(predecessor, self.dominators()) {
back_edge_stack.push(predecessor)
} else {
stack.push(predecessor);
Expand Down
16 changes: 10 additions & 6 deletions compiler/rustc_borrowck/src/lib.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -5,6 +5,7 @@
#![feature(let_chains)]
#![feature(min_specialization)]
#![feature(never_type)]
#![feature(once_cell)]
#![feature(rustc_attrs)]
#![feature(stmt_expr_attributes)]
#![feature(trusted_step)]
Expand Down Expand Up @@ -39,6 +40,7 @@ use rustc_span::{Span, Symbol};

use either::Either;
use smallvec::SmallVec;
use std::cell::OnceCell;
use std::cell::RefCell;
use std::collections::BTreeMap;
use std::rc::Rc;
Expand Down Expand Up @@ -333,7 +335,7 @@ fn do_mir_borrowck<'tcx>(
used_mut: Default::default(),
used_mut_upvars: SmallVec::new(),
borrow_set: Rc::clone(&borrow_set),
dominators: Dominators::dummy(), // not used
dominators: Default::default(),
upvars: Vec::new(),
local_names: IndexVec::from_elem(None, &promoted_body.local_decls),
region_names: RefCell::default(),
Expand All @@ -346,8 +348,6 @@ fn do_mir_borrowck<'tcx>(
};
}

let dominators = body.basic_blocks.dominators();

let mut mbcx = MirBorrowckCtxt {
infcx,
param_env,
Expand All @@ -364,7 +364,7 @@ fn do_mir_borrowck<'tcx>(
used_mut: Default::default(),
used_mut_upvars: SmallVec::new(),
borrow_set: Rc::clone(&borrow_set),
dominators,
dominators: Default::default(),
upvars,
local_names,
region_names: RefCell::default(),
Expand Down Expand Up @@ -534,7 +534,7 @@ struct MirBorrowckCtxt<'cx, 'tcx> {
borrow_set: Rc<BorrowSet<'tcx>>,

/// Dominators for MIR
dominators: Dominators<BasicBlock>,
dominators: OnceCell<Dominators<BasicBlock>>,

/// Information about upvars not necessarily preserved in types or MIR
upvars: Vec<Upvar<'tcx>>,
Expand Down Expand Up @@ -1051,7 +1051,7 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {

(Read(kind), BorrowKind::Unique | BorrowKind::Mut { .. }) => {
// Reading from mere reservations of mutable-borrows is OK.
if !is_active(&this.dominators, borrow, location) {
if !is_active(this.dominators(), borrow, location) {
assert!(allow_two_phase_borrow(borrow.kind));
return Control::Continue;
}
Expand Down Expand Up @@ -2219,6 +2219,10 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
fn is_upvar_field_projection(&self, place_ref: PlaceRef<'tcx>) -> Option<Field> {
path_utils::is_upvar_field_projection(self.infcx.tcx, &self.upvars, place_ref, self.body())
}

fn dominators(&self) -> &Dominators<BasicBlock> {
self.dominators.get_or_init(|| self.body.basic_blocks.dominators())
}
}

mod error {
Expand Down
4 changes: 0 additions & 4 deletions compiler/rustc_data_structures/src/graph/dominators/mod.rs
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Expand Up @@ -268,10 +268,6 @@ pub struct Dominators<N: Idx> {
}

impl<Node: Idx> Dominators<Node> {
pub fn dummy() -> Self {
Self { post_order_rank: IndexVec::new(), immediate_dominators: IndexVec::new() }
}

pub fn is_reachable(&self, node: Node) -> bool {
self.immediate_dominators[node].is_some()
}
Expand Down