diff --git a/compiler/rustc_mir_build/src/build/matches/mod.rs b/compiler/rustc_mir_build/src/build/matches/mod.rs
index 7474b4b37d7..3b90856db2c 100644
--- a/compiler/rustc_mir_build/src/build/matches/mod.rs
+++ b/compiler/rustc_mir_build/src/build/matches/mod.rs
@@ -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)
}
diff --git a/compiler/rustc_mir_build/src/build/matches/util.rs b/compiler/rustc_mir_build/src/build/matches/util.rs
index 637cef29e18..2351f69a914 100644
--- a/compiler/rustc_mir_build/src/build/matches/util.rs
+++ b/compiler/rustc_mir_build/src/build/matches/util.rs
@@ -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),
+ });
+ }
+ }
+}