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Rollup merge of #121715 - Nadrieril:testcase-or, r=matthewjasper

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match lowering: pre-simplify or-patterns too

This is the final part of my work to simplify match pairs early: now we do it for or-patterns too. This makes it possible to collect fake borrows separately from the main match lowering algorithm. That'll enable more simplifications of or-pattern handling.

Note: I was tempted to have `Candidate` contain a `FlatPat`, but there are so many places that use `candidate.match_pairs` etc directly that I chose not to.

r? `@matthewjasper`
This commit is contained in:
Matthias Krüger 2024-03-02 10:09:35 +01:00 committed by GitHub
commit b2c933a1b9
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3 changed files with 155 additions and 122 deletions
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172
compiler/rustc_mir_build/src/build/matches/mod.rs
View File

@ -321,20 +321,14 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
// The set of places that we are creating fake borrows of. If there are // 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 // no match guards then we don't need any fake borrows, so don't track
// them. // them.
let mut fake_borrows = match_has_guard.then(FxIndexSet::default); let fake_borrows = match_has_guard
.then(|| util::FakeBorrowCollector::collect_fake_borrows(self, candidates));
let otherwise_block = self.cfg.start_new_block(); let otherwise_block = self.cfg.start_new_block();
// This will generate code to test scrutinee_place and // This will generate code to test scrutinee_place and
// branch to the appropriate arm block // branch to the appropriate arm block
self.match_candidates( self.match_candidates(match_start_span, scrutinee_span, block, otherwise_block, candidates);
match_start_span,
scrutinee_span,
block,
otherwise_block,
candidates,
&mut fake_borrows,
);
// See the doc comment on `match_candidates` for why we may have an // See the doc comment on `match_candidates` for why we may have an
// otherwise block. Match checking will ensure this is actually // otherwise block. Match checking will ensure this is actually
@ -944,6 +938,40 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
} }
} }
/// A pattern in a form suitable for generating code.
#[derive(Debug, Clone)]
struct FlatPat<'pat, 'tcx> {
/// [`Span`] of the original pattern.
span: Span,
/// To match the pattern, all of these must be satisfied...
// Invariant: all the `MatchPair`s are recursively simplified.
// Invariant: or-patterns must be sorted to the end.
match_pairs: Vec<MatchPair<'pat, 'tcx>>,
/// ...these bindings established...
bindings: Vec<Binding<'tcx>>,
/// ...and these types asserted.
ascriptions: Vec<Ascription<'tcx>>,
}
impl<'tcx, 'pat> FlatPat<'pat, 'tcx> {
fn new(
place: PlaceBuilder<'tcx>,
pattern: &'pat Pat<'tcx>,
cx: &mut Builder<'_, 'tcx>,
) -> Self {
let mut match_pairs = vec![MatchPair::new(place, pattern, cx)];
let mut bindings = Vec::new();
let mut ascriptions = Vec::new();
cx.simplify_match_pairs(&mut match_pairs, &mut bindings, &mut ascriptions);
FlatPat { span: pattern.span, match_pairs, bindings, ascriptions }
}
}
#[derive(Debug)] #[derive(Debug)]
struct Candidate<'pat, 'tcx> { struct Candidate<'pat, 'tcx> {
/// [`Span`] of the original pattern that gave rise to this candidate. /// [`Span`] of the original pattern that gave rise to this candidate.
@ -958,11 +986,11 @@ struct Candidate<'pat, 'tcx> {
match_pairs: Vec<MatchPair<'pat, 'tcx>>, match_pairs: Vec<MatchPair<'pat, 'tcx>>,
/// ...these bindings established... /// ...these bindings established...
// Invariant: not mutated outside `Candidate::new()`. // Invariant: not mutated after candidate creation.
bindings: Vec<Binding<'tcx>>, bindings: Vec<Binding<'tcx>>,
/// ...and these types asserted... /// ...and these types asserted...
// Invariant: not mutated outside `Candidate::new()`. // Invariant: not mutated after candidate creation.
ascriptions: Vec<Ascription<'tcx>>, ascriptions: Vec<Ascription<'tcx>>,
/// ...and if this is non-empty, one of these subcandidates also has to match... /// ...and if this is non-empty, one of these subcandidates also has to match...
@ -984,25 +1012,21 @@ impl<'tcx, 'pat> Candidate<'pat, 'tcx> {
has_guard: bool, has_guard: bool,
cx: &mut Builder<'_, 'tcx>, cx: &mut Builder<'_, 'tcx>,
) -> Self { ) -> Self {
let mut candidate = Candidate { Self::from_flat_pat(FlatPat::new(place, pattern, cx), has_guard)
span: pattern.span, }
fn from_flat_pat(flat_pat: FlatPat<'pat, 'tcx>, has_guard: bool) -> Self {
Candidate {
span: flat_pat.span,
match_pairs: flat_pat.match_pairs,
bindings: flat_pat.bindings,
ascriptions: flat_pat.ascriptions,
has_guard, has_guard,
match_pairs: vec![MatchPair::new(place, pattern, cx)],
bindings: Vec::new(),
ascriptions: Vec::new(),
subcandidates: Vec::new(), subcandidates: Vec::new(),
otherwise_block: None, otherwise_block: None,
pre_binding_block: None, pre_binding_block: None,
next_candidate_pre_binding_block: None, next_candidate_pre_binding_block: None,
}; }
cx.simplify_match_pairs(
&mut candidate.match_pairs,
&mut candidate.bindings,
&mut candidate.ascriptions,
);
candidate
} }
/// Visit the leaf candidates (those with no subcandidates) contained in /// Visit the leaf candidates (those with no subcandidates) contained in
@ -1065,7 +1089,7 @@ enum TestCase<'pat, 'tcx> {
Constant { value: mir::Const<'tcx> }, Constant { value: mir::Const<'tcx> },
Range(&'pat PatRange<'tcx>), Range(&'pat PatRange<'tcx>),
Slice { len: usize, variable_length: bool }, Slice { len: usize, variable_length: bool },
Or, Or { pats: Box<[FlatPat<'pat, 'tcx>]> },
} }
#[derive(Debug, Clone)] #[derive(Debug, Clone)]
@ -1208,7 +1232,7 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
/// ///
/// Note how we test `x` twice. This is the tradeoff of backtracking automata: we prefer smaller /// Note how we test `x` twice. This is the tradeoff of backtracking automata: we prefer smaller
/// code size at the expense of non-optimal code paths. /// code size at the expense of non-optimal code paths.
#[instrument(skip(self, fake_borrows), level = "debug")] #[instrument(skip(self), level = "debug")]
fn match_candidates<'pat>( fn match_candidates<'pat>(
&mut self, &mut self,
span: Span, span: Span,
@ -1216,11 +1240,10 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
start_block: BasicBlock, start_block: BasicBlock,
otherwise_block: BasicBlock, otherwise_block: BasicBlock,
candidates: &mut [&mut Candidate<'pat, 'tcx>], candidates: &mut [&mut Candidate<'pat, 'tcx>],
fake_borrows: &mut Option<FxIndexSet<Place<'tcx>>>,
) { ) {
let mut split_or_candidate = false; let mut split_or_candidate = false;
for candidate in &mut *candidates { for candidate in &mut *candidates {
if let [MatchPair { pattern: Pat { kind: PatKind::Or { pats }, .. }, place, .. }] = if let [MatchPair { test_case: TestCase::Or { pats, .. }, .. }] =
&*candidate.match_pairs &*candidate.match_pairs
{ {
// Split a candidate in which the only match-pair is an or-pattern into multiple // Split a candidate in which the only match-pair is an or-pattern into multiple
@ -1232,8 +1255,7 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
// } // }
// //
// only generates a single switch. // only generates a single switch.
candidate.subcandidates = candidate.subcandidates = self.create_or_subcandidates(pats, candidate.has_guard);
self.create_or_subcandidates(place, pats, candidate.has_guard);
candidate.match_pairs.pop(); candidate.match_pairs.pop();
split_or_candidate = true; split_or_candidate = true;
} }
@ -1254,7 +1276,6 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
start_block, start_block,
otherwise_block, otherwise_block,
&mut *new_candidates, &mut *new_candidates,
fake_borrows,
); );
} else { } else {
self.match_simplified_candidates( self.match_simplified_candidates(
@ -1263,7 +1284,6 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
start_block, start_block,
otherwise_block, otherwise_block,
candidates, candidates,
fake_borrows,
); );
} }
}); });
@ -1276,7 +1296,6 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
mut start_block: BasicBlock, mut start_block: BasicBlock,
otherwise_block: BasicBlock, otherwise_block: BasicBlock,
candidates: &mut [&mut Candidate<'_, 'tcx>], candidates: &mut [&mut Candidate<'_, 'tcx>],
fake_borrows: &mut Option<FxIndexSet<Place<'tcx>>>,
) { ) {
match candidates { match candidates {
[] => { [] => {
@ -1288,14 +1307,13 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
[first, remaining @ ..] if first.match_pairs.is_empty() => { [first, remaining @ ..] if first.match_pairs.is_empty() => {
// The first candidate has satisfied all its match pairs; we link it up and continue // The first candidate has satisfied all its match pairs; we link it up and continue
// with the remaining candidates. // with the remaining candidates.
start_block = self.select_matched_candidate(first, start_block, fake_borrows); start_block = self.select_matched_candidate(first, start_block);
self.match_simplified_candidates( self.match_simplified_candidates(
span, span,
scrutinee_span, scrutinee_span,
start_block, start_block,
otherwise_block, otherwise_block,
remaining, remaining,
fake_borrows,
) )
} }
candidates => { candidates => {
@ -1306,7 +1324,6 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
candidates, candidates,
start_block, start_block,
otherwise_block, otherwise_block,
fake_borrows,
); );
} }
} }
@ -1341,43 +1358,11 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
&mut self, &mut self,
candidate: &mut Candidate<'_, 'tcx>, candidate: &mut Candidate<'_, 'tcx>,
start_block: BasicBlock, start_block: BasicBlock,
fake_borrows: &mut Option<FxIndexSet<Place<'tcx>>>,
) -> BasicBlock { ) -> BasicBlock {
assert!(candidate.otherwise_block.is_none()); assert!(candidate.otherwise_block.is_none());
assert!(candidate.pre_binding_block.is_none()); assert!(candidate.pre_binding_block.is_none());
assert!(candidate.subcandidates.is_empty()); 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); candidate.pre_binding_block = Some(start_block);
let otherwise_block = self.cfg.start_new_block(); let otherwise_block = self.cfg.start_new_block();
if candidate.has_guard { if candidate.has_guard {
@ -1448,38 +1433,22 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
candidates: &mut [&mut Candidate<'_, 'tcx>], candidates: &mut [&mut Candidate<'_, 'tcx>],
start_block: BasicBlock, start_block: BasicBlock,
otherwise_block: BasicBlock, otherwise_block: BasicBlock,
fake_borrows: &mut Option<FxIndexSet<Place<'tcx>>>,
) { ) {
let (first_candidate, remaining_candidates) = candidates.split_first_mut().unwrap(); let (first_candidate, remaining_candidates) = candidates.split_first_mut().unwrap();
assert!(first_candidate.subcandidates.is_empty()); assert!(first_candidate.subcandidates.is_empty());
if !matches!(first_candidate.match_pairs[0].pattern.kind, PatKind::Or { .. }) { if !matches!(first_candidate.match_pairs[0].test_case, TestCase::Or { .. }) {
self.test_candidates( self.test_candidates(span, scrutinee_span, candidates, start_block, otherwise_block);
span,
scrutinee_span,
candidates,
start_block,
otherwise_block,
fake_borrows,
);
return; return;
} }
let match_pairs = mem::take(&mut first_candidate.match_pairs); let match_pairs = mem::take(&mut first_candidate.match_pairs);
let (first_match_pair, remaining_match_pairs) = match_pairs.split_first().unwrap(); let (first_match_pair, remaining_match_pairs) = match_pairs.split_first().unwrap();
let PatKind::Or { ref pats } = &first_match_pair.pattern.kind else { unreachable!() }; let TestCase::Or { ref pats } = &first_match_pair.test_case else { unreachable!() };
let remainder_start = self.cfg.start_new_block(); let remainder_start = self.cfg.start_new_block();
let or_span = first_match_pair.pattern.span; let or_span = first_match_pair.pattern.span;
// Test the alternatives of this or-pattern. // Test the alternatives of this or-pattern.
self.test_or_pattern( self.test_or_pattern(first_candidate, start_block, remainder_start, pats, or_span);
first_candidate,
start_block,
remainder_start,
pats,
or_span,
&first_match_pair.place,
fake_borrows,
);
if !remaining_match_pairs.is_empty() { if !remaining_match_pairs.is_empty() {
// If more match pairs remain, test them after each subcandidate. // If more match pairs remain, test them after each subcandidate.
@ -1500,7 +1469,6 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
&mut [leaf_candidate], &mut [leaf_candidate],
or_start, or_start,
or_otherwise, or_otherwise,
fake_borrows,
); );
}); });
} }
@ -1512,12 +1480,11 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
remainder_start, remainder_start,
otherwise_block, otherwise_block,
remaining_candidates, remaining_candidates,
fake_borrows,
); );
} }
#[instrument( #[instrument(
skip(self, start_block, otherwise_block, or_span, place, fake_borrows, candidate, pats), skip(self, start_block, otherwise_block, or_span, candidate, pats),
level = "debug" level = "debug"
)] )]
fn test_or_pattern<'pat>( fn test_or_pattern<'pat>(
@ -1525,15 +1492,14 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
candidate: &mut Candidate<'pat, 'tcx>, candidate: &mut Candidate<'pat, 'tcx>,
start_block: BasicBlock, start_block: BasicBlock,
otherwise_block: BasicBlock, otherwise_block: BasicBlock,
pats: &'pat [Box<Pat<'tcx>>], pats: &[FlatPat<'pat, 'tcx>],
or_span: Span, or_span: Span,
place: &PlaceBuilder<'tcx>,
fake_borrows: &mut Option<FxIndexSet<Place<'tcx>>>,
) { ) {
debug!("candidate={:#?}\npats={:#?}", candidate, pats); debug!("candidate={:#?}\npats={:#?}", candidate, pats);
let mut or_candidates: Vec<_> = pats let mut or_candidates: Vec<_> = pats
.iter() .iter()
.map(|pat| Candidate::new(place.clone(), pat, candidate.has_guard, self)) .cloned()
.map(|flat_pat| Candidate::from_flat_pat(flat_pat, candidate.has_guard))
.collect(); .collect();
let mut or_candidate_refs: Vec<_> = or_candidates.iter_mut().collect(); let mut or_candidate_refs: Vec<_> = or_candidates.iter_mut().collect();
self.match_candidates( self.match_candidates(
@ -1542,7 +1508,6 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
start_block, start_block,
otherwise_block, otherwise_block,
&mut or_candidate_refs, &mut or_candidate_refs,
fake_borrows,
); );
candidate.subcandidates = or_candidates; candidate.subcandidates = or_candidates;
self.merge_trivial_subcandidates(candidate, self.source_info(or_span)); self.merge_trivial_subcandidates(candidate, self.source_info(or_span));
@ -1602,7 +1567,6 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
fn pick_test( fn pick_test(
&mut self, &mut self,
candidates: &mut [&mut Candidate<'_, 'tcx>], candidates: &mut [&mut Candidate<'_, 'tcx>],
fake_borrows: &mut Option<FxIndexSet<Place<'tcx>>>,
) -> (PlaceBuilder<'tcx>, Test<'tcx>) { ) -> (PlaceBuilder<'tcx>, Test<'tcx>) {
// Extract the match-pair from the highest priority candidate // Extract the match-pair from the highest priority candidate
let match_pair = &candidates.first().unwrap().match_pairs[0]; let match_pair = &candidates.first().unwrap().match_pairs[0];
@ -1631,13 +1595,6 @@ 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) (match_place, test)
} }
@ -1811,10 +1768,9 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
candidates: &'b mut [&'c mut Candidate<'pat, 'tcx>], candidates: &'b mut [&'c mut Candidate<'pat, 'tcx>],
start_block: BasicBlock, start_block: BasicBlock,
otherwise_block: BasicBlock, otherwise_block: BasicBlock,
fake_borrows: &mut Option<FxIndexSet<Place<'tcx>>>,
) { ) {
// Extract the match-pair from the highest priority candidate and build a test from it. // Extract the match-pair from the highest priority candidate and build a test from it.
let (match_place, test) = self.pick_test(candidates, fake_borrows); let (match_place, test) = self.pick_test(candidates);
// For each of the N possible test outcomes, build the vector of candidates that applies if // For each of the N possible test outcomes, build the vector of candidates that applies if
// the test has that particular outcome. // the test has that particular outcome.
@ -1831,7 +1787,6 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
remainder_start, remainder_start,
otherwise_block, otherwise_block,
remaining_candidates, remaining_candidates,
fake_borrows,
); );
remainder_start remainder_start
} else { } else {
@ -1853,7 +1808,6 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
candidate_start, candidate_start,
remainder_start, remainder_start,
&mut *candidates, &mut *candidates,
fake_borrows,
); );
candidate_start candidate_start
} else { } else {

19
compiler/rustc_mir_build/src/build/matches/simplify.rs
View File

@ -12,10 +12,8 @@
//! sort of test: for example, testing which variant an enum is, or //! sort of test: for example, testing which variant an enum is, or
//! testing a value against a constant. //! testing a value against a constant.
use crate::build::expr::as_place::PlaceBuilder; use crate::build::matches::{Ascription, Binding, Candidate, FlatPat, MatchPair, TestCase};
use crate::build::matches::{Ascription, Binding, Candidate, MatchPair, TestCase};
use crate::build::Builder; use crate::build::Builder;
use rustc_middle::thir::{Pat, PatKind};
use std::mem; use std::mem;
@ -100,7 +98,7 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
// Move or-patterns to the end, because they can result in us // Move or-patterns to the end, because they can result in us
// creating additional candidates, so we want to test them as // creating additional candidates, so we want to test them as
// late as possible. // late as possible.
match_pairs.sort_by_key(|pair| matches!(pair.pattern.kind, PatKind::Or { .. })); match_pairs.sort_by_key(|pair| matches!(pair.test_case, TestCase::Or { .. }));
debug!(simplified = ?match_pairs, "simplify_match_pairs"); debug!(simplified = ?match_pairs, "simplify_match_pairs");
} }
@ -108,18 +106,17 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
/// single-or-pattern case. /// single-or-pattern case.
pub(super) fn create_or_subcandidates<'pat>( pub(super) fn create_or_subcandidates<'pat>(
&mut self, &mut self,
place: &PlaceBuilder<'tcx>, pats: &[FlatPat<'pat, 'tcx>],
pats: &'pat [Box<Pat<'tcx>>],
has_guard: bool, has_guard: bool,
) -> Vec<Candidate<'pat, 'tcx>> { ) -> Vec<Candidate<'pat, 'tcx>> {
pats.iter() pats.iter()
.map(|box pat| { .cloned()
let mut candidate = Candidate::new(place.clone(), pat, has_guard, self); .map(|flat_pat| {
if let [MatchPair { pattern: Pat { kind: PatKind::Or { pats }, .. }, place, .. }] = let mut candidate = Candidate::from_flat_pat(flat_pat, has_guard);
if let [MatchPair { test_case: TestCase::Or { pats, .. }, .. }] =
&*candidate.match_pairs &*candidate.match_pairs
{ {
candidate.subcandidates = candidate.subcandidates = self.create_or_subcandidates(pats, has_guard);
self.create_or_subcandidates(place, pats, candidate.has_guard);
candidate.match_pairs.pop(); candidate.match_pairs.pop();
} }
candidate candidate

86
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::expr::as_place::{PlaceBase, PlaceBuilder};
use crate::build::matches::{MatchPair, TestCase}; use crate::build::matches::{Binding, Candidate, FlatPat, MatchPair, TestCase};
use crate::build::Builder; use crate::build::Builder;
use rustc_data_structures::fx::FxIndexSet;
use rustc_infer::infer::type_variable::{TypeVariableOrigin, TypeVariableOriginKind}; use rustc_infer::infer::type_variable::{TypeVariableOrigin, TypeVariableOriginKind};
use rustc_middle::mir::*; use rustc_middle::mir::*;
use rustc_middle::thir::{self, *}; use rustc_middle::thir::{self, *};
@ -121,7 +122,9 @@ impl<'pat, 'tcx> MatchPair<'pat, 'tcx> {
let mut subpairs = Vec::new(); let mut subpairs = Vec::new();
let test_case = match pattern.kind { let test_case = match pattern.kind {
PatKind::Never | PatKind::Wild | PatKind::Error(_) => default_irrefutable(), PatKind::Never | PatKind::Wild | PatKind::Error(_) => default_irrefutable(),
PatKind::Or { .. } => TestCase::Or, PatKind::Or { ref pats } => TestCase::Or {
pats: pats.iter().map(|pat| FlatPat::new(place.clone(), pat, cx)).collect(),
},
PatKind::Range(ref range) => { PatKind::Range(ref range) => {
if range.is_full_range(cx.tcx) == Some(true) { if range.is_full_range(cx.tcx) == Some(true) {
@ -258,3 +261,82 @@ impl<'pat, 'tcx> MatchPair<'pat, 'tcx> {
MatchPair { place, test_case, subpairs, pattern } 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),
});
}
}
}