From 7fe68571fa22d6504b3c14303cc4389cd5a92a24 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Tomasz=20Mi=C4=85sko?= <tomasz.miasko@gmail.com>
Date: Tue, 17 Jan 2023 00:00:00 +0000
Subject: [PATCH] Lazy dominator tree construction in borrowck
Motivated by the observation that sometimes constructed dominator tree
was never queried.
---
.../src/diagnostics/conflict_errors.rs | 4 ++--
compiler/rustc_borrowck/src/lib.rs | 16 ++++++++++------
.../src/graph/dominators/mod.rs | 4 ----
3 files changed, 12 insertions(+), 12 deletions(-)
diff --git a/compiler/rustc_borrowck/src/diagnostics/conflict_errors.rs b/compiler/rustc_borrowck/src/diagnostics/conflict_errors.rs
index e512099b93b..e5a36259fa4 100644
--- a/compiler/rustc_borrowck/src/diagnostics/conflict_errors.rs
+++ b/compiler/rustc_borrowck/src/diagnostics/conflict_errors.rs
@@ -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);
@@ -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);
diff --git a/compiler/rustc_borrowck/src/lib.rs b/compiler/rustc_borrowck/src/lib.rs
index 278ffed0747..f2685241724 100644
--- a/compiler/rustc_borrowck/src/lib.rs
+++ b/compiler/rustc_borrowck/src/lib.rs
@@ -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)]
@@ -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;
@@ -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(),
@@ -346,8 +348,6 @@ fn do_mir_borrowck<'tcx>(
};
}
- let dominators = body.basic_blocks.dominators();
-
let mut mbcx = MirBorrowckCtxt {
infcx,
param_env,
@@ -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(),
@@ -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>>,
@@ -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;
}
@@ -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 {
diff --git a/compiler/rustc_data_structures/src/graph/dominators/mod.rs b/compiler/rustc_data_structures/src/graph/dominators/mod.rs
index ea2a4388b92..434291e8374 100644
--- a/compiler/rustc_data_structures/src/graph/dominators/mod.rs
+++ b/compiler/rustc_data_structures/src/graph/dominators/mod.rs
@@ -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()
}