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Collect fake borrows ahead of time

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This commit is contained in:
Nadrieril 2024-02-28 00:06:02 +01:00
parent 29666118b6
commit ca5edfa724
2 changed files with 83 additions and 40 deletions
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41
compiler/rustc_mir_build/src/build/matches/mod.rs
View File

@ -315,7 +315,8 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
// The set of places that we are creating fake borrows of. If there are
// no match guards then we don't need any fake borrows, so don't track
// them.
let mut fake_borrows = match_has_guard.then(FxIndexSet::default);
let mut fake_borrows = match_has_guard
.then(|| util::FakeBorrowCollector::collect_fake_borrows(self, candidates));
let otherwise_block = self.cfg.start_new_block();
@ -1373,37 +1374,6 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
assert!(candidate.pre_binding_block.is_none());
assert!(candidate.subcandidates.is_empty());
if let Some(fake_borrows) = fake_borrows {
// Insert a borrows of prefixes of places that are bound and are
// behind a dereference projection.
//
// These borrows are taken to avoid situations like the following:
//
// match x[10] {
// _ if { x = &[0]; false } => (),
// y => (), // Out of bounds array access!
// }
//
// match *x {
// // y is bound by reference in the guard and then by copy in the
// // arm, so y is 2 in the arm!
// y if { y == 1 && (x = &2) == () } => y,
// _ => 3,
// }
for Binding { source, .. } in &candidate.bindings {
if let Some(i) =
source.projection.iter().rposition(|elem| elem == ProjectionElem::Deref)
{
let proj_base = &source.projection[..i];
fake_borrows.insert(Place {
local: source.local,
projection: self.tcx.mk_place_elems(proj_base),
});
}
}
}
candidate.pre_binding_block = Some(start_block);
let otherwise_block = self.cfg.start_new_block();
if candidate.has_guard {
@ -1656,13 +1626,6 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
_ => {}
}
// Insert a Shallow borrow of any places that is switched on.
if let Some(fb) = fake_borrows
&& let Some(resolved_place) = match_place.try_to_place(self)
{
fb.insert(resolved_place);
}
(match_place, test)
}

82
compiler/rustc_mir_build/src/build/matches/util.rs
View File

@ -1,6 +1,7 @@
use crate::build::expr::as_place::{PlaceBase, PlaceBuilder};
use crate::build::matches::{FlatPat, MatchPair, TestCase};
use crate::build::matches::{Binding, Candidate, FlatPat, MatchPair, TestCase};
use crate::build::Builder;
use rustc_data_structures::fx::FxIndexSet;
use rustc_infer::infer::type_variable::{TypeVariableOrigin, TypeVariableOriginKind};
use rustc_middle::mir::*;
use rustc_middle::thir::{self, *};
@ -260,3 +261,82 @@ impl<'pat, 'tcx> MatchPair<'pat, 'tcx> {
MatchPair { place, test_case, subpairs, pattern }
}
}
pub(super) struct FakeBorrowCollector<'a, 'b, 'tcx> {
cx: &'a mut Builder<'b, 'tcx>,
fake_borrows: FxIndexSet<Place<'tcx>>,
}
impl<'a, 'b, 'tcx> FakeBorrowCollector<'a, 'b, 'tcx> {
pub(super) fn collect_fake_borrows(
cx: &'a mut Builder<'b, 'tcx>,
candidates: &[&mut Candidate<'_, 'tcx>],
) -> FxIndexSet<Place<'tcx>> {
let mut collector = Self { cx, fake_borrows: FxIndexSet::default() };
for candidate in candidates.iter() {
collector.visit_candidate(candidate);
}
collector.fake_borrows
}
fn visit_candidate(&mut self, candidate: &Candidate<'_, 'tcx>) {
for binding in &candidate.bindings {
self.visit_binding(binding);
}
for match_pair in &candidate.match_pairs {
self.visit_match_pair(match_pair);
}
}
fn visit_flat_pat(&mut self, flat_pat: &FlatPat<'_, 'tcx>) {
for binding in &flat_pat.bindings {
self.visit_binding(binding);
}
for match_pair in &flat_pat.match_pairs {
self.visit_match_pair(match_pair);
}
}
fn visit_match_pair(&mut self, match_pair: &MatchPair<'_, 'tcx>) {
if let TestCase::Or { pats, .. } = &match_pair.test_case {
for flat_pat in pats.iter() {
self.visit_flat_pat(flat_pat)
}
} else {
// Insert a Shallow borrow of any place that is switched on.
if let Some(resolved_place) = match_pair.place.try_to_place(self.cx) {
self.fake_borrows.insert(resolved_place);
}
for subpair in &match_pair.subpairs {
self.visit_match_pair(subpair);
}
}
}
fn visit_binding(&mut self, Binding { source, .. }: &Binding<'tcx>) {
// Insert a borrows of prefixes of places that are bound and are
// behind a dereference projection.
//
// These borrows are taken to avoid situations like the following:
//
// match x[10] {
// _ if { x = &[0]; false } => (),
// y => (), // Out of bounds array access!
// }
//
// match *x {
// // y is bound by reference in the guard and then by copy in the
// // arm, so y is 2 in the arm!
// y if { y == 1 && (x = &2) == () } => y,
// _ => 3,
// }
if let Some(i) = source.projection.iter().rposition(|elem| elem == ProjectionElem::Deref) {
let proj_base = &source.projection[..i];
self.fake_borrows.insert(Place {
local: source.local,
projection: self.cx.tcx.mk_place_elems(proj_base),
});
}
}
}