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Move lower_match_tree

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Nadrieril 2024-06-17 20:08:05 +02:00
parent 878ccd22fa
commit c0c6c32a45
1 changed files with 64 additions and 65 deletions
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129
compiler/rustc_mir_build/src/build/matches/mod.rs
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@ -380,71 +380,6 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
.collect()
}
/// Create the decision tree for the match expression, starting from `block`.
///
/// Modifies `candidates` to store the bindings and type ascriptions for
/// that candidate.
fn lower_match_tree<'pat>(
&mut self,
block: BasicBlock,
scrutinee_span: Span,
scrutinee_place_builder: &PlaceBuilder<'tcx>,
match_start_span: Span,
candidates: &mut [&mut Candidate<'pat, 'tcx>],
) {
// See the doc comment on `match_candidates` for why we have an
// otherwise block. Match checking will ensure this is actually
// unreachable.
let otherwise_block = self.cfg.start_new_block();
// This will generate code to test scrutinee_place and
// branch to the appropriate arm block
self.match_candidates(match_start_span, scrutinee_span, block, otherwise_block, candidates);
let source_info = self.source_info(scrutinee_span);
// Matching on a `scrutinee_place` with an uninhabited type doesn't
// generate any memory reads by itself, and so if the place "expression"
// contains unsafe operations like raw pointer dereferences or union
// field projections, we wouldn't know to require an `unsafe` block
// around a `match` equivalent to `std::intrinsics::unreachable()`.
// See issue #47412 for this hole being discovered in the wild.
//
// HACK(eddyb) Work around the above issue by adding a dummy inspection
// of `scrutinee_place`, specifically by applying `ReadForMatch`.
//
// NOTE: ReadForMatch also checks that the scrutinee is initialized.
// This is currently needed to not allow matching on an uninitialized,
// uninhabited value. If we get never patterns, those will check that
// the place is initialized, and so this read would only be used to
// check safety.
let cause_matched_place = FakeReadCause::ForMatchedPlace(None);
if let Some(scrutinee_place) = scrutinee_place_builder.try_to_place(self) {
self.cfg.push_fake_read(
otherwise_block,
source_info,
cause_matched_place,
scrutinee_place,
);
}
self.cfg.terminate(otherwise_block, source_info, TerminatorKind::Unreachable);
// Link each leaf candidate to the `pre_binding_block` of the next one.
let mut previous_candidate: Option<&mut Candidate<'_, '_>> = None;
for candidate in candidates {
candidate.visit_leaves(|leaf_candidate| {
if let Some(ref mut prev) = previous_candidate {
assert!(leaf_candidate.false_edge_start_block.is_some());
prev.next_candidate_start_block = leaf_candidate.false_edge_start_block;
}
previous_candidate = Some(leaf_candidate);
});
}
}
/// Lower the bindings, guards and arm bodies of a `match` expression.
///
/// The decision tree should have already been created
@ -1275,6 +1210,70 @@ pub(crate) struct ArmHasGuard(pub(crate) bool);
// Main matching algorithm
impl<'a, 'tcx> Builder<'a, 'tcx> {
/// The entrypoint of the matching algorithm. Create the decision tree for the match expression,
/// starting from `block`.
///
/// Modifies `candidates` to store the bindings and type ascriptions for
/// that candidate.
fn lower_match_tree<'pat>(
&mut self,
block: BasicBlock,
scrutinee_span: Span,
scrutinee_place_builder: &PlaceBuilder<'tcx>,
match_start_span: Span,
candidates: &mut [&mut Candidate<'pat, 'tcx>],
) {
// See the doc comment on `match_candidates` for why we have an
// otherwise block. Match checking will ensure this is actually
// unreachable.
let otherwise_block = self.cfg.start_new_block();
// This will generate code to test scrutinee_place and branch to the appropriate arm block
self.match_candidates(match_start_span, scrutinee_span, block, otherwise_block, candidates);
let source_info = self.source_info(scrutinee_span);
// Matching on a `scrutinee_place` with an uninhabited type doesn't
// generate any memory reads by itself, and so if the place "expression"
// contains unsafe operations like raw pointer dereferences or union
// field projections, we wouldn't know to require an `unsafe` block
// around a `match` equivalent to `std::intrinsics::unreachable()`.
// See issue #47412 for this hole being discovered in the wild.
//
// HACK(eddyb) Work around the above issue by adding a dummy inspection
// of `scrutinee_place`, specifically by applying `ReadForMatch`.
//
// NOTE: ReadForMatch also checks that the scrutinee is initialized.
// This is currently needed to not allow matching on an uninitialized,
// uninhabited value. If we get never patterns, those will check that
// the place is initialized, and so this read would only be used to
// check safety.
let cause_matched_place = FakeReadCause::ForMatchedPlace(None);
if let Some(scrutinee_place) = scrutinee_place_builder.try_to_place(self) {
self.cfg.push_fake_read(
otherwise_block,
source_info,
cause_matched_place,
scrutinee_place,
);
}
self.cfg.terminate(otherwise_block, source_info, TerminatorKind::Unreachable);
// Link each leaf candidate to the `false_edge_start_block` of the next one.
let mut previous_candidate: Option<&mut Candidate<'_, '_>> = None;
for candidate in candidates {
candidate.visit_leaves(|leaf_candidate| {
if let Some(ref mut prev) = previous_candidate {
assert!(leaf_candidate.false_edge_start_block.is_some());
prev.next_candidate_start_block = leaf_candidate.false_edge_start_block;
}
previous_candidate = Some(leaf_candidate);
});
}
}
/// The main match algorithm. It begins with a set of candidates
/// `candidates` and has the job of generating code to determine
/// which of these candidates, if any, is the correct one. The