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Use deep fake borrows for deref patterns

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This commit is contained in:
Nadrieril 2024-04-06 00:29:45 +02:00
parent 50531806ee
commit 436c61266c
4 changed files with 56 additions and 28 deletions
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17
compiler/rustc_mir_build/src/build/matches/mod.rs
View File

@ -375,10 +375,10 @@ fn lower_match_tree<'pat>(
match_start_span: Span,
match_has_guard: bool,
candidates: &mut [&mut Candidate<'pat, 'tcx>],
) -> Vec<(Place<'tcx>, Local)> {
) -> Vec<(Place<'tcx>, Local, FakeBorrowKind)> {
// 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 fake_borrows: Vec<(Place<'tcx>, Local)> = if match_has_guard {
let fake_borrows: Vec<(Place<'tcx>, Local, FakeBorrowKind)> = if match_has_guard {
util::collect_fake_borrows(
self,
candidates,
@ -457,7 +457,7 @@ fn lower_match_arms(
scrutinee_span: Span,
arm_candidates: Vec<(&'_ Arm<'tcx>, Candidate<'_, 'tcx>)>,
outer_source_info: SourceInfo,
fake_borrow_temps: Vec<(Place<'tcx>, Local)>,
fake_borrow_temps: Vec<(Place<'tcx>, Local, FakeBorrowKind)>,
) -> BlockAnd<()> {
let arm_end_blocks: Vec<_> = arm_candidates
.into_iter()
@ -541,7 +541,7 @@ fn bind_pattern(
&mut self,
outer_source_info: SourceInfo,
candidate: Candidate<'_, 'tcx>,
fake_borrow_temps: &[(Place<'tcx>, Local)],
fake_borrow_temps: &[(Place<'tcx>, Local, FakeBorrowKind)],
scrutinee_span: Span,
arm_match_scope: Option<(&Arm<'tcx>, region::Scope)>,
storages_alive: bool,
@ -1975,7 +1975,7 @@ fn bind_and_guard_matched_candidate<'pat>(
&mut self,
candidate: Candidate<'pat, 'tcx>,
parent_data: &[PatternExtraData<'tcx>],
fake_borrows: &[(Place<'tcx>, Local)],
fake_borrows: &[(Place<'tcx>, Local, FakeBorrowKind)],
scrutinee_span: Span,
arm_match_scope: Option<(&Arm<'tcx>, region::Scope)>,
schedule_drops: bool,
@ -2105,9 +2105,8 @@ fn bind_and_guard_matched_candidate<'pat>(
let re_erased = tcx.lifetimes.re_erased;
let scrutinee_source_info = self.source_info(scrutinee_span);
for &(place, temp) in fake_borrows {
let borrow =
Rvalue::Ref(re_erased, BorrowKind::Fake(FakeBorrowKind::Shallow), place);
for &(place, temp, kind) in fake_borrows {
let borrow = Rvalue::Ref(re_erased, BorrowKind::Fake(kind), place);
self.cfg.push_assign(block, scrutinee_source_info, Place::from(temp), borrow);
}
@ -2130,7 +2129,7 @@ fn bind_and_guard_matched_candidate<'pat>(
let guard_frame = self.guard_context.pop().unwrap();
debug!("Exiting guard building context with locals: {:?}", guard_frame);
for &(_, temp) in fake_borrows {
for &(_, temp, _) in fake_borrows {
let cause = FakeReadCause::ForMatchGuard;
self.cfg.push_fake_read(post_guard_block, guard_end, cause, Place::from(temp));
}

41
compiler/rustc_mir_build/src/build/matches/util.rs
View File

@ -1,7 +1,7 @@
use crate::build::expr::as_place::{PlaceBase, PlaceBuilder};
use crate::build::matches::{Binding, Candidate, FlatPat, MatchPair, TestCase};
use crate::build::Builder;
use rustc_data_structures::fx::FxIndexSet;
use rustc_data_structures::fx::FxIndexMap;
use rustc_infer::infer::type_variable::TypeVariableOrigin;
use rustc_middle::mir::*;
use rustc_middle::thir::{self, *};
@ -271,7 +271,11 @@ pub(super) struct FakeBorrowCollector<'a, 'b, 'tcx> {
/// Base of the scrutinee place. Used to distinguish bindings inside the scrutinee place from
/// bindings inside deref patterns.
scrutinee_base: PlaceBase,
fake_borrows: FxIndexSet<Place<'tcx>>,
/// Store for each place the kind of borrow to take. In case of conflicts, we take the strongest
/// borrow (i.e. Deep > Shallow).
/// Invariant: for any place in `fake_borrows`, all the prefixes of this place that are
/// dereferences are also borrowed with the same of stronger borrow kind.
fake_borrows: FxIndexMap<Place<'tcx>, FakeBorrowKind>,
}
/// Determine the set of places that have to be stable across match guards.
@ -314,9 +318,9 @@ pub(super) fn collect_fake_borrows<'tcx>(
candidates: &[&mut Candidate<'_, 'tcx>],
temp_span: Span,
scrutinee_base: PlaceBase,
) -> Vec<(Place<'tcx>, Local)> {
) -> Vec<(Place<'tcx>, Local, FakeBorrowKind)> {
let mut collector =
FakeBorrowCollector { cx, scrutinee_base, fake_borrows: FxIndexSet::default() };
FakeBorrowCollector { cx, scrutinee_base, fake_borrows: FxIndexMap::default() };
for candidate in candidates.iter() {
collector.visit_candidate(candidate);
}
@ -325,40 +329,40 @@ pub(super) fn collect_fake_borrows<'tcx>(
let tcx = cx.tcx;
fake_borrows
.iter()
.copied()
.map(|matched_place| {
.map(|(matched_place, borrow_kind)| {
let fake_borrow_deref_ty = matched_place.ty(&cx.local_decls, tcx).ty;
let fake_borrow_ty =
Ty::new_imm_ref(tcx, tcx.lifetimes.re_erased, fake_borrow_deref_ty);
let mut fake_borrow_temp = LocalDecl::new(fake_borrow_ty, temp_span);
fake_borrow_temp.local_info = ClearCrossCrate::Set(Box::new(LocalInfo::FakeBorrow));
let fake_borrow_temp = cx.local_decls.push(fake_borrow_temp);
(matched_place, fake_borrow_temp)
(*matched_place, fake_borrow_temp, *borrow_kind)
})
.collect()
}
impl<'a, 'b, 'tcx> FakeBorrowCollector<'a, 'b, 'tcx> {
// Fake borrow this place and its dereference prefixes.
fn fake_borrow(&mut self, place: Place<'tcx>) {
let new = self.fake_borrows.insert(place);
if !new {
fn fake_borrow(&mut self, place: Place<'tcx>, kind: FakeBorrowKind) {
if self.fake_borrows.get(&place).is_some_and(|k| *k >= kind) {
return;
}
self.fake_borrows.insert(place, kind);
// Also fake borrow the prefixes of any fake borrow.
self.fake_borrow_deref_prefixes(place);
self.fake_borrow_deref_prefixes(place, kind);
}
// Fake borrow the prefixes of this place that are dereferences.
fn fake_borrow_deref_prefixes(&mut self, place: Place<'tcx>) {
fn fake_borrow_deref_prefixes(&mut self, place: Place<'tcx>, kind: FakeBorrowKind) {
for (place_ref, elem) in place.as_ref().iter_projections().rev() {
if let ProjectionElem::Deref = elem {
// Insert a shallow borrow after a deref. For other projections the borrow of
// `place_ref` will conflict with any mutation of `place.base`.
let new = self.fake_borrows.insert(place_ref.to_place(self.cx.tcx));
if !new {
let place = place_ref.to_place(self.cx.tcx);
if self.fake_borrows.get(&place).is_some_and(|k| *k >= kind) {
return;
}
self.fake_borrows.insert(place, kind);
}
}
}
@ -399,15 +403,14 @@ fn visit_match_pair(&mut self, match_pair: &MatchPair<'_, 'tcx>) {
// // UB because we reached the unreachable.
// }
// ```
// FIXME(deref_patterns): Hence we fake borrow using a non-shallow borrow.
// Hence we fake borrow using a deep borrow.
if let Some(place) = match_pair.place {
// FIXME(deref_patterns): use a non-shallow borrow.
self.fake_borrow(place);
self.fake_borrow(place, FakeBorrowKind::Deep);
}
} else {
// Insert a Shallow borrow of any place that is switched on.
if let Some(place) = match_pair.place {
self.fake_borrow(place);
self.fake_borrow(place, FakeBorrowKind::Shallow);
}
for subpair in &match_pair.subpairs {
@ -447,7 +450,7 @@ fn visit_binding(&mut self, Binding { source, .. }: &Binding<'tcx>) {
// _ if { u = true; false } => (),
// x => (),
// }
self.fake_borrow_deref_prefixes(*source);
self.fake_borrow_deref_prefixes(*source, FakeBorrowKind::Shallow);
}
}

14
tests/ui/pattern/deref-patterns/fake_borrows.rs Normal file
View File

@ -0,0 +1,14 @@
#![feature(deref_patterns)]
#![allow(incomplete_features)]
#[rustfmt::skip]
fn main() {
let mut b = Box::new(false);
match b {
deref!(true) => {}
_ if { *b = true; false } => {}
//~^ ERROR cannot assign `*b` in match guard
deref!(false) => {}
_ => {},
}
}

12
tests/ui/pattern/deref-patterns/fake_borrows.stderr Normal file
View File

@ -0,0 +1,12 @@
error[E0510]: cannot assign `*b` in match guard
--> $DIR/fake_borrows.rs:9:16
|
LL | match b {
| - value is immutable in match guard
LL | deref!(true) => {}
LL | _ if { *b = true; false } => {}
| ^^^^^^^^^ cannot assign
error: aborting due to 1 previous error
For more information about this error, try `rustc --explain E0510`.