1 //! Code related to match expressions. These are sufficiently complex to
2 //! warrant their own module and submodules. :) This main module includes the
3 //! high-level algorithm, the submodules contain the details.
5 //! This also includes code for pattern bindings in `let` statements and
6 //! function parameters.
8 use crate::build
::scope
::DropKind
;
9 use crate::build
::ForGuard
::{self, OutsideGuard, RefWithinGuard}
;
10 use crate::build
::{BlockAnd, BlockAndExtension, Builder}
;
11 use crate::build
::{GuardFrame, GuardFrameLocal, LocalsForNode}
;
12 use crate::hair
::{self, *}
;
13 use rustc
::hir
::HirId
;
15 use rustc
::middle
::region
;
16 use rustc
::ty
::{self, CanonicalUserTypeAnnotation, Ty}
;
17 use rustc
::ty
::layout
::VariantIdx
;
18 use rustc_data_structures
::bit_set
::BitSet
;
19 use rustc_data_structures
::fx
::{FxHashMap, FxHashSet}
;
20 use syntax
::ast
::Name
;
23 // helper functions, broken out by category:
28 use std
::convert
::TryFrom
;
30 impl<'a
, 'tcx
> Builder
<'a
, 'tcx
> {
31 /// Generates MIR for a `match` expression.
33 /// The MIR that we generate for a match looks like this.
38 /// [ 1. Evaluate Scrutinee (expression being matched on) ]
39 /// [ (fake read of scrutinee) ]
41 /// [ 2. Decision tree -- check discriminants ] <--------+
43 /// | (once a specific arm is chosen) |
45 /// [pre_binding_block] [otherwise_block]
47 /// [ 3. Create "guard bindings" for arm ] |
48 /// [ (create fake borrows) ] |
50 /// [ 4. Execute guard code ] |
51 /// [ (read fake borrows) ] --(guard is false)-----------+
53 /// | (guard results in true)
55 /// [ 5. Create real bindings and execute arm ]
60 /// All of the different arms have been stacked on top of each other to
61 /// simplify the diagram. For an arm with no guard the blocks marked 3 and
62 /// 4 and the fake borrows are omitted.
64 /// We generate MIR in the following steps:
66 /// 1. Evaluate the scrutinee and add the fake read of it.
67 /// 2. Create the prebinding and otherwise blocks.
68 /// 3. Create the decision tree and record the places that we bind or test.
69 /// 4. Determine the fake borrows that are needed from the above places.
70 /// Create the required temporaries for them.
71 /// 5. Create everything else: Create everything else: the guards and the
74 /// ## Fake Reads and borrows
76 /// Match exhaustiveness checking is not able to handle the case where the
77 /// place being matched on is mutated in the guards. There is an AST check
78 /// that tries to stop this but it is buggy and overly restrictive. Instead
79 /// we add "fake borrows" to the guards that prevent any mutation of the
80 /// place being matched. There are a some subtleties:
82 /// 1. Borrowing `*x` doesn't prevent assigning to `x`. If `x` is a shared
83 /// refence, the borrow isn't even tracked. As such we have to add fake
84 /// borrows of any prefixes of a place
85 /// 2. We don't want `match x { _ => (), }` to conflict with mutable
86 /// borrows of `x`, so we only add fake borrows for places which are
87 /// bound or tested by the match.
88 /// 3. We don't want the fake borrows to conflict with `ref mut` bindings,
89 /// so we use a special BorrowKind for them.
90 /// 4. The fake borrows may be of places in inactive variants, so it would
91 /// be UB to generate code for them. They therefore have to be removed
92 /// by a MIR pass run after borrow checking.
96 /// We don't want to have the exact structure of the decision tree be
97 /// visible through borrow checking. False edges ensure that the CFG as
98 /// seen by borrow checking doesn't encode this. False edges are added:
100 /// * From each prebinding block to the next prebinding block.
101 /// * From each otherwise block to the next prebinding block.
104 destination
: &Place
<'tcx
>,
106 mut block
: BasicBlock
,
107 scrutinee
: ExprRef
<'tcx
>,
108 arms
: Vec
<Arm
<'tcx
>>,
110 let tcx
= self.hir
.tcx();
112 // Step 1. Evaluate the scrutinee and add the fake read of it.
114 let scrutinee_span
= scrutinee
.span();
115 let scrutinee_place
= unpack
!(block
= self.as_place(block
, scrutinee
));
117 // Matching on a `scrutinee_place` with an uninhabited type doesn't
118 // generate any memory reads by itself, and so if the place "expression"
119 // contains unsafe operations like raw pointer dereferences or union
120 // field projections, we wouldn't know to require an `unsafe` block
121 // around a `match` equivalent to `std::intrinsics::unreachable()`.
122 // See issue #47412 for this hole being discovered in the wild.
124 // HACK(eddyb) Work around the above issue by adding a dummy inspection
125 // of `scrutinee_place`, specifically by applying `ReadForMatch`.
127 // NOTE: ReadForMatch also checks that the scrutinee is initialized.
128 // This is currently needed to not allow matching on an uninitialized,
129 // uninhabited value. If we get never patterns, those will check that
130 // the place is initialized, and so this read would only be used to
133 let source_info
= self.source_info(scrutinee_span
);
134 self.cfg
.push(block
, Statement
{
136 kind
: StatementKind
::FakeRead(
137 FakeReadCause
::ForMatchedPlace
,
138 scrutinee_place
.clone(),
142 // Step 2. Create the otherwise and prebinding blocks.
144 // create binding start block for link them by false edges
145 let candidate_count
= arms
.iter().map(|c
| c
.patterns
.len()).sum
::<usize>();
146 let pre_binding_blocks
: Vec
<_
> = (0..candidate_count
)
147 .map(|_
| self.cfg
.start_new_block())
150 let mut match_has_guard
= false;
152 let mut candidate_pre_binding_blocks
= pre_binding_blocks
.iter();
153 let mut next_candidate_pre_binding_blocks
= pre_binding_blocks
.iter().skip(1);
155 // Assemble a list of candidates: there is one candidate per pattern,
156 // which means there may be more than one candidate *per arm*.
157 let mut arm_candidates
: Vec
<_
> = arms
160 let arm_has_guard
= arm
.guard
.is_some();
161 match_has_guard
|= arm_has_guard
;
162 let arm_candidates
: Vec
<_
> = arm
.patterns
164 .zip(candidate_pre_binding_blocks
.by_ref())
166 |(pattern
, pre_binding_block
)| {
170 MatchPair
::new(scrutinee_place
.clone(), pattern
),
174 otherwise_block
: if arm_has_guard
{
175 Some(self.cfg
.start_new_block())
179 pre_binding_block
: *pre_binding_block
,
180 next_candidate_pre_binding_block
:
181 next_candidate_pre_binding_blocks
.next().copied(),
186 (arm
, arm_candidates
)
190 // Step 3. Create the decision tree and record the places that we bind or test.
192 // The set of places that we are creating fake borrows of. If there are
193 // no match guards then we don't need any fake borrows, so don't track
195 let mut fake_borrows
= if match_has_guard
&& tcx
.generate_borrow_of_any_match_input() {
196 Some(FxHashSet
::default())
201 // These candidates are kept sorted such that the highest priority
202 // candidate comes first in the list. (i.e., same order as in source)
203 // As we gnerate the decision tree,
204 let candidates
= &mut arm_candidates
206 .flat_map(|(_
, candidates
)| candidates
)
207 .collect
::<Vec
<_
>>();
209 let outer_source_info
= self.source_info(span
);
211 // this will generate code to test scrutinee_place and
212 // branch to the appropriate arm block
213 self.match_candidates(
221 // Step 4. Determine the fake borrows that are needed from the above
222 // places. Create the required temporaries for them.
224 let fake_borrow_temps
= if let Some(ref borrows
) = fake_borrows
{
225 self.calculate_fake_borrows(borrows
, scrutinee_span
)
230 // Step 5. Create everything else: the guards and the arms.
231 let arm_end_blocks
: Vec
<_
> = arm_candidates
.into_iter().map(|(arm
, mut candidates
)| {
232 let arm_source_info
= self.source_info(arm
.span
);
233 let region_scope
= (arm
.scope
, arm_source_info
);
234 self.in_scope(region_scope
, arm
.lint_level
, |this
| {
235 let body
= this
.hir
.mirror(arm
.body
.clone());
236 let scope
= this
.declare_bindings(
240 ArmHasGuard(arm
.guard
.is_some()),
241 Some((Some(&scrutinee_place
), scrutinee_span
)),
245 if candidates
.len() == 1 {
246 arm_block
= this
.bind_and_guard_matched_candidate(
247 candidates
.pop().unwrap(),
254 arm_block
= this
.cfg
.start_new_block();
255 for candidate
in candidates
{
256 this
.clear_top_scope(arm
.scope
);
257 let binding_end
= this
.bind_and_guard_matched_candidate(
267 TerminatorKind
::Goto { target: arm_block }
,
272 if let Some(source_scope
) = scope
{
273 this
.source_scope
= source_scope
;
276 this
.into(destination
, arm_block
, body
)
280 // all the arm blocks will rejoin here
281 let end_block
= self.cfg
.start_new_block();
283 for arm_block
in arm_end_blocks
{
287 TerminatorKind
::Goto { target: end_block }
,
291 self.source_scope
= outer_source_info
.scope
;
296 pub(super) fn expr_into_pattern(
298 mut block
: BasicBlock
,
299 irrefutable_pat
: Pattern
<'tcx
>,
300 initializer
: ExprRef
<'tcx
>,
302 match *irrefutable_pat
.kind
{
303 // Optimize the case of `let x = ...` to write directly into `x`
304 PatternKind
::Binding
{
305 mode
: BindingMode
::ByValue
,
311 self.storage_live_binding(block
, var
, irrefutable_pat
.span
, OutsideGuard
);
312 unpack
!(block
= self.into(&place
, block
, initializer
));
315 // Inject a fake read, see comments on `FakeReadCause::ForLet`.
316 let source_info
= self.source_info(irrefutable_pat
.span
);
321 kind
: StatementKind
::FakeRead(FakeReadCause
::ForLet
, place
),
325 self.schedule_drop_for_binding(var
, irrefutable_pat
.span
, OutsideGuard
);
329 // Optimize the case of `let x: T = ...` to write directly
330 // into `x` and then require that `T == typeof(x)`.
332 // Weirdly, this is needed to prevent the
333 // `intrinsic-move-val.rs` test case from crashing. That
334 // test works with uninitialized values in a rather
335 // dubious way, so it may be that the test is kind of
337 PatternKind
::AscribeUserType
{
338 subpattern
: Pattern
{
339 kind
: box PatternKind
::Binding
{
340 mode
: BindingMode
::ByValue
,
347 ascription
: hair
::pattern
::Ascription
{
348 user_ty
: pat_ascription_ty
,
354 self.storage_live_binding(block
, var
, irrefutable_pat
.span
, OutsideGuard
);
355 unpack
!(block
= self.into(&place
, block
, initializer
));
357 // Inject a fake read, see comments on `FakeReadCause::ForLet`.
358 let pattern_source_info
= self.source_info(irrefutable_pat
.span
);
362 source_info
: pattern_source_info
,
363 kind
: StatementKind
::FakeRead(FakeReadCause
::ForLet
, place
.clone()),
367 let ty_source_info
= self.source_info(user_ty_span
);
368 let user_ty
= box pat_ascription_ty
.user_ty(
369 &mut self.canonical_user_type_annotations
,
370 place
.ty(&self.local_decls
, self.hir
.tcx()).ty
,
376 source_info
: ty_source_info
,
377 kind
: StatementKind
::AscribeUserType(
379 // We always use invariant as the variance here. This is because the
380 // variance field from the ascription refers to the variance to use
381 // when applying the type to the value being matched, but this
382 // ascription applies rather to the type of the binding. e.g., in this
389 // We are creating an ascription that defines the type of `x` to be
390 // exactly `T` (i.e., with invariance). The variance field, in
391 // contrast, is intended to be used to relate `T` to the type of
393 ty
::Variance
::Invariant
,
399 self.schedule_drop_for_binding(var
, irrefutable_pat
.span
, OutsideGuard
);
404 let place
= unpack
!(block
= self.as_place(block
, initializer
));
405 self.place_into_pattern(block
, irrefutable_pat
, &place
, true)
410 pub fn place_into_pattern(
413 irrefutable_pat
: Pattern
<'tcx
>,
414 initializer
: &Place
<'tcx
>,
415 set_match_place
: bool
,
417 // create a dummy candidate
418 let mut candidate
= Candidate
{
419 span
: irrefutable_pat
.span
,
420 match_pairs
: vec
![MatchPair
::new(initializer
.clone(), &irrefutable_pat
)],
424 // since we don't call `match_candidates`, next fields are unused
425 otherwise_block
: None
,
426 pre_binding_block
: block
,
427 next_candidate_pre_binding_block
: None
,
430 // Simplify the candidate. Since the pattern is irrefutable, this should
431 // always convert all match-pairs into bindings.
432 self.simplify_candidate(&mut candidate
);
434 if !candidate
.match_pairs
.is_empty() {
435 // ICE if no other errors have been emitted. This used to be a hard error that wouldn't
436 // be reached because `hair::pattern::check_match::check_match` wouldn't have let the
437 // compiler continue. In our tests this is only ever hit by
438 // `ui/consts/const-match-check.rs` with `--cfg eval1`, and that file already generates
439 // a different error before hand.
440 self.hir
.tcx().sess
.delay_span_bug(
441 candidate
.match_pairs
[0].pattern
.span
,
443 "match pairs {:?} remaining after simplifying irrefutable pattern",
444 candidate
.match_pairs
,
449 // for matches and function arguments, the place that is being matched
450 // can be set when creating the variables. But the place for
451 // let PATTERN = ... might not even exist until we do the assignment.
452 // so we set it here instead
454 for binding
in &candidate
.bindings
{
455 let local
= self.var_local_id(binding
.var_id
, OutsideGuard
);
457 if let Some(ClearCrossCrate
::Set(BindingForm
::Var(VarBindingForm
{
458 opt_match_place
: Some((ref mut match_place
, _
)),
460 }))) = self.local_decls
[local
].is_user_variable
462 *match_place
= Some(initializer
.clone());
464 bug
!("Let binding to non-user variable.")
469 self.ascribe_types(block
, &candidate
.ascriptions
);
471 // now apply the bindings, which will also declare the variables
472 self.bind_matched_candidate_for_arm_body(block
, &candidate
.bindings
);
477 /// Declares the bindings of the given patterns and returns the visibility
478 /// scope for the bindings in these patterns, if such a scope had to be
479 /// created. NOTE: Declaring the bindings should always be done in their
481 pub fn declare_bindings(
483 mut visibility_scope
: Option
<SourceScope
>,
485 pattern
: &Pattern
<'tcx
>,
486 has_guard
: ArmHasGuard
,
487 opt_match_place
: Option
<(Option
<&Place
<'tcx
>>, Span
)>,
488 ) -> Option
<SourceScope
> {
489 debug
!("declare_bindings: pattern={:?}", pattern
);
492 UserTypeProjections
::none(),
493 &mut |this
, mutability
, name
, mode
, var
, span
, ty
, user_ty
| {
494 if visibility_scope
.is_none() {
496 Some(this
.new_source_scope(scope_span
, LintLevel
::Inherited
, None
));
498 let source_info
= SourceInfo { span, scope: this.source_scope }
;
499 let visibility_scope
= visibility_scope
.unwrap();
500 this
.declare_binding(
510 opt_match_place
.map(|(x
, y
)| (x
.cloned(), y
)),
518 pub fn storage_live_binding(
525 let local_id
= self.var_local_id(var
, for_guard
);
526 let source_info
= self.source_info(span
);
531 kind
: StatementKind
::StorageLive(local_id
),
534 let var_ty
= self.local_decls
[local_id
].ty
;
535 let region_scope
= self.hir
.region_scope_tree
.var_scope(var
.local_id
);
536 self.schedule_drop(span
, region_scope
, local_id
, var_ty
, DropKind
::Storage
);
537 Place
::Base(PlaceBase
::Local(local_id
))
540 pub fn schedule_drop_for_binding(&mut self, var
: HirId
, span
: Span
, for_guard
: ForGuard
) {
541 let local_id
= self.var_local_id(var
, for_guard
);
542 let var_ty
= self.local_decls
[local_id
].ty
;
543 let region_scope
= self.hir
.region_scope_tree
.var_scope(var
.local_id
);
553 pub(super) fn visit_bindings(
555 pattern
: &Pattern
<'tcx
>,
556 pattern_user_ty
: UserTypeProjections
,
568 debug
!("visit_bindings: pattern={:?} pattern_user_ty={:?}", pattern
, pattern_user_ty
);
569 match *pattern
.kind
{
570 PatternKind
::Binding
{
579 f(self, mutability
, name
, mode
, var
, pattern
.span
, ty
, pattern_user_ty
.clone());
580 if let Some(subpattern
) = subpattern
.as_ref() {
581 self.visit_bindings(subpattern
, pattern_user_ty
, f
);
590 | PatternKind
::Slice
{
595 let from
= u32::try_from(prefix
.len()).unwrap();
596 let to
= u32::try_from(suffix
.len()).unwrap();
597 for subpattern
in prefix
{
598 self.visit_bindings(subpattern
, pattern_user_ty
.clone().index(), f
);
600 for subpattern
in slice
{
601 self.visit_bindings(subpattern
, pattern_user_ty
.clone().subslice(from
, to
), f
);
603 for subpattern
in suffix
{
604 self.visit_bindings(subpattern
, pattern_user_ty
.clone().index(), f
);
608 PatternKind
::Constant { .. }
| PatternKind
::Range { .. }
| PatternKind
::Wild
=> {}
610 PatternKind
::Deref { ref subpattern }
=> {
611 self.visit_bindings(subpattern
, pattern_user_ty
.deref(), f
);
614 PatternKind
::AscribeUserType
{
616 ascription
: hair
::pattern
::Ascription
{
622 // This corresponds to something like
625 // let A::<'a>(_): A<'static> = ...;
628 // Note that the variance doesn't apply here, as we are tracking the effect
629 // of `user_ty` on any bindings contained with subpattern.
630 let annotation
= CanonicalUserTypeAnnotation
{
632 user_ty
: user_ty
.user_ty
,
633 inferred_ty
: subpattern
.ty
,
635 let projection
= UserTypeProjection
{
636 base
: self.canonical_user_type_annotations
.push(annotation
),
639 let subpattern_user_ty
= pattern_user_ty
.push_projection(&projection
, user_ty_span
);
640 self.visit_bindings(subpattern
, subpattern_user_ty
, f
)
643 PatternKind
::Leaf { ref subpatterns }
=> {
644 for subpattern
in subpatterns
{
645 let subpattern_user_ty
= pattern_user_ty
.clone().leaf(subpattern
.field
);
646 debug
!("visit_bindings: subpattern_user_ty={:?}", subpattern_user_ty
);
647 self.visit_bindings(&subpattern
.pattern
, subpattern_user_ty
, f
);
651 PatternKind
::Variant { adt_def, substs: _, variant_index, ref subpatterns }
=> {
652 for subpattern
in subpatterns
{
653 let subpattern_user_ty
= pattern_user_ty
.clone().variant(
654 adt_def
, variant_index
, subpattern
.field
);
655 self.visit_bindings(&subpattern
.pattern
, subpattern_user_ty
, f
);
663 pub struct Candidate
<'pat
, 'tcx
> {
664 // span of the original pattern that gave rise to this candidate
667 // all of these must be satisfied...
668 match_pairs
: Vec
<MatchPair
<'pat
, 'tcx
>>,
670 // ...these bindings established...
671 bindings
: Vec
<Binding
<'tcx
>>,
673 // ...and these types asserted...
674 ascriptions
: Vec
<Ascription
<'tcx
>>,
676 // ...and the guard must be evaluated, if false branch to Block...
677 otherwise_block
: Option
<BasicBlock
>,
679 // ...and the blocks for add false edges between candidates
680 pre_binding_block
: BasicBlock
,
681 next_candidate_pre_binding_block
: Option
<BasicBlock
>,
684 #[derive(Clone, Debug)]
685 struct Binding
<'tcx
> {
691 mutability
: Mutability
,
692 binding_mode
: BindingMode
,
695 /// Indicates that the type of `source` must be a subtype of the
696 /// user-given type `user_ty`; this is basically a no-op but can
697 /// influence region inference.
698 #[derive(Clone, Debug)]
699 struct Ascription
<'tcx
> {
702 user_ty
: PatternTypeProjection
<'tcx
>,
703 variance
: ty
::Variance
,
706 #[derive(Clone, Debug)]
707 pub struct MatchPair
<'pat
, 'tcx
> {
711 // ... must match this pattern.
712 pattern
: &'pat Pattern
<'tcx
>,
715 #[derive(Clone, Debug, PartialEq)]
716 enum TestKind
<'tcx
> {
717 /// Test the branches of enum.
719 /// The enum being tested
720 adt_def
: &'tcx ty
::AdtDef
,
721 /// The set of variants that we should create a branch for. We also
722 /// create an additional "otherwise" case.
723 variants
: BitSet
<VariantIdx
>,
726 /// Test what value an `integer`, `bool` or `char` has.
728 /// The type of the value that we're testing.
730 /// The (ordered) set of values that we test for.
732 /// For integers and `char`s we create a branch to each of the values in
733 /// `options`, as well as an "otherwise" branch for all other values, even
734 /// in the (rare) case that options is exhaustive.
736 /// For `bool` we always generate two edges, one for `true` and one for
739 /// Reverse map used to ensure that the values in `options` are unique.
740 indices
: FxHashMap
<&'tcx ty
::Const
<'tcx
>, usize>,
743 /// Test for equality with value, possibly after an unsizing coercion to
746 value
: &'tcx ty
::Const
<'tcx
>,
747 // Integer types are handled by `SwitchInt`, and constants with ADT
748 // types are converted back into patterns, so this can only be `&str`,
749 // `&[T]`, `f32` or `f64`.
753 /// Test whether the value falls within an inclusive or exclusive range
754 Range(PatternRange
<'tcx
>),
756 /// Test length of the slice is equal to len
764 pub struct Test
<'tcx
> {
766 kind
: TestKind
<'tcx
>,
769 /// ArmHasGuard is isomorphic to a boolean flag. It indicates whether
770 /// a match arm has a guard expression attached to it.
771 #[derive(Copy, Clone, Debug)]
772 pub(crate) struct ArmHasGuard(pub bool
);
774 ///////////////////////////////////////////////////////////////////////////
775 // Main matching algorithm
777 impl<'a
, 'tcx
> Builder
<'a
, 'tcx
> {
778 /// The main match algorithm. It begins with a set of candidates
779 /// `candidates` and has the job of generating code to determine
780 /// which of these candidates, if any, is the correct one. The
781 /// candidates are sorted such that the first item in the list
782 /// has the highest priority. When a candidate is found to match
783 /// the value, we will generate a branch to the appropriate
784 /// prebinding block.
786 /// If we find that *NONE* of the candidates apply, we branch to the
787 /// `otherwise_block`. In principle, this means that the input list was not
788 /// exhaustive, though at present we sometimes are not smart enough to
789 /// recognize all exhaustive inputs.
791 /// It might be surprising that the input can be inexhaustive.
792 /// Indeed, initially, it is not, because all matches are
793 /// exhaustive in Rust. But during processing we sometimes divide
794 /// up the list of candidates and recurse with a non-exhaustive
795 /// list. This is important to keep the size of the generated code
796 /// under control. See `test_candidates` for more details.
798 /// If `fake_borrows` is Some, then places which need fake borrows
799 /// will be added to it.
800 fn match_candidates
<'pat
>(
803 start_block
: &mut Option
<BasicBlock
>,
804 otherwise_block
: Option
<BasicBlock
>,
805 candidates
: &mut [&mut Candidate
<'pat
, 'tcx
>],
806 fake_borrows
: &mut Option
<FxHashSet
<Place
<'tcx
>>>,
809 "matched_candidate(span={:?}, candidates={:?}, start_block={:?}, otherwise_block={:?})",
816 // Start by simplifying candidates. Once this process is complete, all
817 // the match pairs which remain require some form of test, whether it
818 // be a switch or pattern comparison.
819 for candidate
in &mut *candidates
{
820 self.simplify_candidate(candidate
);
823 // The candidates are sorted by priority. Check to see whether the
824 // higher priority candidates (and hence at the front of the slice)
825 // have satisfied all their match pairs.
826 let fully_matched
= candidates
828 .take_while(|c
| c
.match_pairs
.is_empty())
831 "match_candidates: {:?} candidates fully matched",
834 let (matched_candidates
, unmatched_candidates
) = candidates
.split_at_mut(fully_matched
);
836 let block
: BasicBlock
;
838 if !matched_candidates
.is_empty() {
839 let otherwise_block
= self.select_matched_candidates(
845 if let Some(last_otherwise_block
) = otherwise_block
{
846 block
= last_otherwise_block
848 // Any remaining candidates are unreachable.
849 if unmatched_candidates
.is_empty() {
852 block
= self.cfg
.start_new_block();
855 block
= *start_block
.get_or_insert_with(|| self.cfg
.start_new_block());
858 // If there are no candidates that still need testing, we're
859 // done. Since all matches are exhaustive, execution should
860 // never reach this point.
861 if unmatched_candidates
.is_empty() {
862 let source_info
= self.source_info(span
);
863 if let Some(otherwise
) = otherwise_block
{
867 TerminatorKind
::Goto { target: otherwise }
,
873 TerminatorKind
::Unreachable
,
879 // Test for the remaining candidates.
880 self.test_candidates(
882 unmatched_candidates
,
889 /// Link up matched candidates. For example, if we have something like
893 /// Some(x) if cond => ...
895 /// Some(x) if cond => ...
898 /// We generate real edges from:
899 /// * `block` to the prebinding_block of the first pattern,
900 /// * the otherwise block of the first pattern to the second pattern,
901 /// * the otherwise block of the third pattern to the a block with an
902 /// Unreachable terminator.
904 /// As well as that we add fake edges from the otherwise blocks to the
905 /// prebinding block of the next candidate in the original set of
907 fn select_matched_candidates(
909 matched_candidates
: &mut [&mut Candidate
<'_
, 'tcx
>],
910 start_block
: &mut Option
<BasicBlock
>,
911 fake_borrows
: &mut Option
<FxHashSet
<Place
<'tcx
>>>,
912 ) -> Option
<BasicBlock
> {
914 !matched_candidates
.is_empty(),
915 "select_matched_candidates called with no candidates",
918 // Insert a borrows of prefixes of places that are bound and are
919 // behind a dereference projection.
921 // These borrows are taken to avoid situations like the following:
924 // _ if { x = &[0]; false } => (),
925 // y => (), // Out of bounds array access!
929 // // y is bound by reference in the guard and then by copy in the
930 // // arm, so y is 2 in the arm!
931 // y if { y == 1 && (x = &2) == () } => y,
934 if let Some(fake_borrows
) = fake_borrows
{
935 for Binding { source, .. }
936 in matched_candidates
.iter().flat_map(|candidate
| &candidate
.bindings
)
938 let mut cursor
= source
;
939 while let Place
::Projection(box Projection { base, elem }
) = cursor
{
941 if let ProjectionElem
::Deref
= elem
{
942 fake_borrows
.insert(cursor
.clone());
949 let fully_matched_with_guard
= matched_candidates
951 .position(|c
| c
.otherwise_block
.is_none())
952 .unwrap_or(matched_candidates
.len() - 1);
954 let (reachable_candidates
, unreachable_candidates
)
955 = matched_candidates
.split_at_mut(fully_matched_with_guard
+ 1);
957 let first_candidate
= &reachable_candidates
[0];
958 let first_prebinding_block
= first_candidate
.pre_binding_block
;
960 if let Some(start_block
) = *start_block
{
961 let source_info
= self.source_info(first_candidate
.span
);
965 TerminatorKind
::Goto { target: first_prebinding_block }
,
968 *start_block
= Some(first_prebinding_block
);
971 for window
in reachable_candidates
.windows(2) {
972 if let [first_candidate
, second_candidate
] = window
{
973 let source_info
= self.source_info(first_candidate
.span
);
974 if let Some(otherwise_block
) = first_candidate
.otherwise_block
{
977 second_candidate
.pre_binding_block
,
978 first_candidate
.next_candidate_pre_binding_block
,
982 bug
!("candidate other than the last has no guard");
985 bug
!("<[_]>::windows returned incorrectly sized window");
989 debug
!("match_candidates: add false edges for unreachable {:?}", unreachable_candidates
);
990 for candidate
in unreachable_candidates
{
991 if let Some(otherwise
) = candidate
.otherwise_block
{
992 let source_info
= self.source_info(candidate
.span
);
993 let unreachable
= self.cfg
.start_new_block();
997 candidate
.next_candidate_pre_binding_block
,
1000 self.cfg
.terminate(unreachable
, source_info
, TerminatorKind
::Unreachable
);
1004 let last_candidate
= reachable_candidates
.last().unwrap();
1006 if let Some(otherwise
) = last_candidate
.otherwise_block
{
1007 let source_info
= self.source_info(last_candidate
.span
);
1008 let block
= self.cfg
.start_new_block();
1012 last_candidate
.next_candidate_pre_binding_block
,
1021 /// This is the most subtle part of the matching algorithm. At
1022 /// this point, the input candidates have been fully simplified,
1023 /// and so we know that all remaining match-pairs require some
1024 /// sort of test. To decide what test to do, we take the highest
1025 /// priority candidate (last one in the list) and extract the
1026 /// first match-pair from the list. From this we decide what kind
1027 /// of test is needed using `test`, defined in the `test` module.
1029 /// *Note:* taking the first match pair is somewhat arbitrary, and
1030 /// we might do better here by choosing more carefully what to
1033 /// For example, consider the following possible match-pairs:
1035 /// 1. `x @ Some(P)` -- we will do a `Switch` to decide what variant `x` has
1036 /// 2. `x @ 22` -- we will do a `SwitchInt`
1037 /// 3. `x @ 3..5` -- we will do a range test
1040 /// Once we know what sort of test we are going to perform, this
1041 /// Tests may also help us with other candidates. So we walk over
1042 /// the candidates (from high to low priority) and check. This
1043 /// gives us, for each outcome of the test, a transformed list of
1044 /// candidates. For example, if we are testing the current
1045 /// variant of `x.0`, and we have a candidate `{x.0 @ Some(v), x.1
1046 /// @ 22}`, then we would have a resulting candidate of `{(x.0 as
1047 /// Some).0 @ v, x.1 @ 22}`. Note that the first match-pair is now
1048 /// simpler (and, in fact, irrefutable).
1050 /// But there may also be candidates that the test just doesn't
1051 /// apply to. The classical example involves wildcards:
1054 /// # let (x, y, z) = (true, true, true);
1055 /// match (x, y, z) {
1056 /// (true, _, true) => true, // (0)
1057 /// (_, true, _) => true, // (1)
1058 /// (false, false, _) => false, // (2)
1059 /// (true, _, false) => false, // (3)
1063 /// In that case, after we test on `x`, there are 2 overlapping candidate
1066 /// - If the outcome is that `x` is true, candidates 0, 1, and 3
1067 /// - If the outcome is that `x` is false, candidates 1 and 2
1069 /// Here, the traditional "decision tree" method would generate 2
1070 /// separate code-paths for the 2 separate cases.
1072 /// In some cases, this duplication can create an exponential amount of
1073 /// code. This is most easily seen by noticing that this method terminates
1074 /// with precisely the reachable arms being reachable - but that problem
1075 /// is trivially NP-complete:
1078 /// match (var0, var1, var2, var3, ..) {
1079 /// (true, _, _, false, true, ...) => false,
1080 /// (_, true, true, false, _, ...) => false,
1081 /// (false, _, false, false, _, ...) => false,
1087 /// Here the last arm is reachable only if there is an assignment to
1088 /// the variables that does not match any of the literals. Therefore,
1089 /// compilation would take an exponential amount of time in some cases.
1091 /// That kind of exponential worst-case might not occur in practice, but
1092 /// our simplistic treatment of constants and guards would make it occur
1093 /// in very common situations - for example #29740:
1097 /// "foo" if foo_guard => ...,
1098 /// "bar" if bar_guard => ...,
1099 /// "baz" if baz_guard => ...,
1104 /// Here we first test the match-pair `x @ "foo"`, which is an `Eq` test.
1106 /// It might seem that we would end up with 2 disjoint candidate
1107 /// sets, consisting of the first candidate or the other 3, but our
1108 /// algorithm doesn't reason about "foo" being distinct from the other
1109 /// constants; it considers the latter arms to potentially match after
1110 /// both outcomes, which obviously leads to an exponential amount
1113 /// To avoid these kinds of problems, our algorithm tries to ensure
1114 /// the amount of generated tests is linear. When we do a k-way test,
1115 /// we return an additional "unmatched" set alongside the obvious `k`
1116 /// sets. When we encounter a candidate that would be present in more
1117 /// than one of the sets, we put it and all candidates below it into the
1118 /// "unmatched" set. This ensures these `k+1` sets are disjoint.
1120 /// After we perform our test, we branch into the appropriate candidate
1121 /// set and recurse with `match_candidates`. These sub-matches are
1122 /// obviously inexhaustive - as we discarded our otherwise set - so
1123 /// we set their continuation to do `match_candidates` on the
1124 /// "unmatched" set (which is again inexhaustive).
1126 /// If you apply this to the above test, you basically wind up
1127 /// with an if-else-if chain, testing each candidate in turn,
1128 /// which is precisely what we want.
1130 /// In addition to avoiding exponential-time blowups, this algorithm
1131 /// also has nice property that each guard and arm is only generated
1133 fn test_candidates
<'pat
, 'b
, 'c
>(
1136 mut candidates
: &'b
mut [&'c
mut Candidate
<'pat
, 'tcx
>],
1138 mut otherwise_block
: Option
<BasicBlock
>,
1139 fake_borrows
: &mut Option
<FxHashSet
<Place
<'tcx
>>>,
1141 // extract the match-pair from the highest priority candidate
1142 let match_pair
= &candidates
.first().unwrap().match_pairs
[0];
1143 let mut test
= self.test(match_pair
);
1144 let match_place
= match_pair
.place
.clone();
1146 // most of the time, the test to perform is simply a function
1147 // of the main candidate; but for a test like SwitchInt, we
1148 // may want to add cases based on the candidates that are
1151 TestKind
::SwitchInt
{
1156 for candidate
in candidates
.iter() {
1157 if !self.add_cases_to_switch(
1172 for candidate
in candidates
.iter() {
1173 if !self.add_variants_to_switch(&match_place
, candidate
, variants
) {
1181 // Insert a Shallow borrow of any places that is switched on.
1182 fake_borrows
.as_mut().map(|fb
| {
1183 fb
.insert(match_place
.clone())
1186 // perform the test, branching to one of N blocks. For each of
1187 // those N possible outcomes, create a (initially empty)
1188 // vector of candidates. Those are the candidates that still
1189 // apply if the test has that particular outcome.
1191 "match_candidates: test={:?} match_pair={:?}",
1194 let mut target_candidates
: Vec
<Vec
<&mut Candidate
<'pat
, 'tcx
>>> = vec
![];
1195 target_candidates
.resize_with(test
.targets(), Default
::default);
1197 let total_candidate_count
= candidates
.len();
1199 // Sort the candidates into the appropriate vector in
1200 // `target_candidates`. Note that at some point we may
1201 // encounter a candidate where the test is not relevant; at
1202 // that point, we stop sorting.
1203 while let Some(candidate
) = candidates
.first_mut() {
1204 if let Some(idx
) = self.sort_candidate(&match_place
, &test
, candidate
) {
1205 let (candidate
, rest
) = candidates
.split_first_mut().unwrap();
1206 target_candidates
[idx
].push(candidate
);
1212 // at least the first candidate ought to be tested
1213 assert
!(total_candidate_count
> candidates
.len());
1214 debug
!("tested_candidates: {}", total_candidate_count
- candidates
.len());
1215 debug
!("untested_candidates: {}", candidates
.len());
1217 // HACK(matthewjasper) This is a closure so that we can let the test
1218 // create its blocks before the rest of the match. This currently
1219 // improves the speed of llvm when optimizing long string literal
1221 let make_target_blocks
= move |this
: &mut Self| -> Vec
<BasicBlock
> {
1222 // For each outcome of test, process the candidates that still
1223 // apply. Collect a list of blocks where control flow will
1224 // branch if one of the `target_candidate` sets is not
1226 if !candidates
.is_empty() {
1227 let remainder_start
= &mut None
;
1228 this
.match_candidates(
1235 otherwise_block
= Some(remainder_start
.unwrap());
1238 target_candidates
.into_iter().map(|mut candidates
| {
1239 if candidates
.len() != 0 {
1240 let candidate_start
= &mut None
;
1241 this
.match_candidates(
1248 candidate_start
.unwrap()
1250 *otherwise_block
.get_or_insert_with(|| {
1251 let unreachable
= this
.cfg
.start_new_block();
1252 let source_info
= this
.source_info(span
);
1256 TerminatorKind
::Unreachable
,
1272 // Determine the fake borrows that are needed to ensure that the place
1273 // will evaluate to the same thing until an arm has been chosen.
1274 fn calculate_fake_borrows
<'b
>(
1276 fake_borrows
: &'b FxHashSet
<Place
<'tcx
>>,
1278 ) -> Vec
<(&'b Place
<'tcx
>, Local
)> {
1279 let tcx
= self.hir
.tcx();
1281 debug
!("add_fake_borrows fake_borrows = {:?}", fake_borrows
);
1283 let mut all_fake_borrows
= Vec
::with_capacity(fake_borrows
.len());
1285 // Insert a Shallow borrow of the prefixes of any fake borrows.
1286 for place
in fake_borrows
1288 let mut prefix_cursor
= place
;
1289 while let Place
::Projection(box Projection { base, elem }
) = prefix_cursor
{
1290 if let ProjectionElem
::Deref
= elem
{
1291 // Insert a shallow borrow after a deref. For other
1292 // projections the borrow of prefix_cursor will
1293 // conflict with any mutation of base.
1294 all_fake_borrows
.push(base
);
1296 prefix_cursor
= base
;
1299 all_fake_borrows
.push(place
);
1302 // Deduplicate and ensure a deterministic order.
1303 all_fake_borrows
.sort();
1304 all_fake_borrows
.dedup();
1306 debug
!("add_fake_borrows all_fake_borrows = {:?}", all_fake_borrows
);
1308 all_fake_borrows
.into_iter().map(|matched_place
| {
1309 let fake_borrow_deref_ty
= matched_place
.ty(&self.local_decls
, tcx
).ty
;
1310 let fake_borrow_ty
= tcx
.mk_imm_ref(tcx
.lifetimes
.re_erased
, fake_borrow_deref_ty
);
1311 let fake_borrow_temp
= self.local_decls
.push(
1312 LocalDecl
::new_temp(fake_borrow_ty
, temp_span
)
1315 (matched_place
, fake_borrow_temp
)
1320 ///////////////////////////////////////////////////////////////////////////
1321 // Pattern binding - used for `let` and function parameters as well.
1323 impl<'a
, 'tcx
> Builder
<'a
, 'tcx
> {
1324 /// Initializes each of the bindings from the candidate by
1325 /// moving/copying/ref'ing the source as appropriate. Tests the guard, if
1326 /// any, and then branches to the arm. Returns the block for the case where
1327 /// the guard fails.
1329 /// Note: we check earlier that if there is a guard, there cannot be move
1330 /// bindings (unless feature(bind_by_move_pattern_guards) is used). This
1331 /// isn't really important for the self-consistency of this fn, but the
1332 /// reason for it should be clear: after we've done the assignments, if
1333 /// there were move bindings, further tests would be a use-after-move.
1334 /// bind_by_move_pattern_guards avoids this by only moving the binding once
1335 /// the guard has evaluated to true (see below).
1336 fn bind_and_guard_matched_candidate
<'pat
>(
1338 candidate
: Candidate
<'pat
, 'tcx
>,
1339 guard
: Option
<Guard
<'tcx
>>,
1340 fake_borrows
: &Vec
<(&Place
<'tcx
>, Local
)>,
1341 scrutinee_span
: Span
,
1342 region_scope
: (region
::Scope
, SourceInfo
),
1344 debug
!("bind_and_guard_matched_candidate(candidate={:?})", candidate
);
1346 debug_assert
!(candidate
.match_pairs
.is_empty());
1348 let candidate_source_info
= self.source_info(candidate
.span
);
1350 let mut block
= candidate
.pre_binding_block
;
1352 // If we are adding our own statements, then we need a fresh block.
1353 let create_fresh_block
= candidate
.next_candidate_pre_binding_block
.is_some()
1354 || !candidate
.bindings
.is_empty()
1355 || !candidate
.ascriptions
.is_empty()
1358 if create_fresh_block
{
1359 let fresh_block
= self.cfg
.start_new_block();
1363 candidate
.next_candidate_pre_binding_block
,
1364 candidate_source_info
,
1366 block
= fresh_block
;
1367 self.ascribe_types(block
, &candidate
.ascriptions
);
1372 // rust-lang/rust#27282: The `autoref` business deserves some
1373 // explanation here.
1375 // The intent of the `autoref` flag is that when it is true,
1376 // then any pattern bindings of type T will map to a `&T`
1377 // within the context of the guard expression, but will
1378 // continue to map to a `T` in the context of the arm body. To
1379 // avoid surfacing this distinction in the user source code
1380 // (which would be a severe change to the language and require
1381 // far more revision to the compiler), when `autoref` is true,
1382 // then any occurrence of the identifier in the guard
1383 // expression will automatically get a deref op applied to it.
1385 // So an input like:
1388 // let place = Foo::new();
1389 // match place { foo if inspect(foo)
1390 // => feed(foo), ... }
1393 // will be treated as if it were really something like:
1396 // let place = Foo::new();
1397 // match place { Foo { .. } if { let tmp1 = &place; inspect(*tmp1) }
1398 // => { let tmp2 = place; feed(tmp2) }, ... }
1400 // And an input like:
1403 // let place = Foo::new();
1404 // match place { ref mut foo if inspect(foo)
1405 // => feed(foo), ... }
1408 // will be treated as if it were really something like:
1411 // let place = Foo::new();
1412 // match place { Foo { .. } if { let tmp1 = & &mut place; inspect(*tmp1) }
1413 // => { let tmp2 = &mut place; feed(tmp2) }, ... }
1416 // In short, any pattern binding will always look like *some*
1417 // kind of `&T` within the guard at least in terms of how the
1418 // MIR-borrowck views it, and this will ensure that guard
1419 // expressions cannot mutate their the match inputs via such
1420 // bindings. (It also ensures that guard expressions can at
1421 // most *copy* values from such bindings; non-Copy things
1422 // cannot be moved via pattern bindings in guard expressions.)
1426 // Implementation notes (under assumption `autoref` is true).
1428 // To encode the distinction above, we must inject the
1429 // temporaries `tmp1` and `tmp2`.
1431 // There are two cases of interest: binding by-value, and binding by-ref.
1433 // 1. Binding by-value: Things are simple.
1435 // * Establishing `tmp1` creates a reference into the
1436 // matched place. This code is emitted by
1437 // bind_matched_candidate_for_guard.
1439 // * `tmp2` is only initialized "lazily", after we have
1440 // checked the guard. Thus, the code that can trigger
1441 // moves out of the candidate can only fire after the
1442 // guard evaluated to true. This initialization code is
1443 // emitted by bind_matched_candidate_for_arm.
1445 // 2. Binding by-reference: Things are tricky.
1447 // * Here, the guard expression wants a `&&` or `&&mut`
1448 // into the original input. This means we need to borrow
1449 // the reference that we create for the arm.
1450 // * So we eagerly create the reference for the arm and then take a
1451 // reference to that.
1452 if let Some(guard
) = guard
{
1453 let tcx
= self.hir
.tcx();
1455 self.bind_matched_candidate_for_guard(
1457 &candidate
.bindings
,
1459 let guard_frame
= GuardFrame
{
1463 .map(|b
| GuardFrameLocal
::new(b
.var_id
, b
.binding_mode
))
1466 debug
!("Entering guard building context: {:?}", guard_frame
);
1467 self.guard_context
.push(guard_frame
);
1469 let re_erased
= tcx
.lifetimes
.re_erased
;
1470 let scrutinee_source_info
= self.source_info(scrutinee_span
);
1471 for &(place
, temp
) in fake_borrows
{
1472 let borrow
= Rvalue
::Ref(
1474 BorrowKind
::Shallow
,
1477 self.cfg
.push_assign(
1479 scrutinee_source_info
,
1485 // the block to branch to if the guard fails; if there is no
1486 // guard, this block is simply unreachable
1487 let guard
= match guard
{
1488 Guard
::If(e
) => self.hir
.mirror(e
),
1490 let source_info
= self.source_info(guard
.span
);
1491 let guard_end
= self.source_info(tcx
.sess
.source_map().end_point(guard
.span
));
1492 let (post_guard_block
, otherwise_post_guard_block
)
1493 = self.test_bool(block
, guard
, source_info
);
1494 let guard_frame
= self.guard_context
.pop().unwrap();
1496 "Exiting guard building context with locals: {:?}",
1500 for &(_
, temp
) in fake_borrows
{
1501 self.cfg
.push(post_guard_block
, Statement
{
1502 source_info
: guard_end
,
1503 kind
: StatementKind
::FakeRead(
1504 FakeReadCause
::ForMatchGuard
,
1513 otherwise_post_guard_block
,
1514 candidate
.otherwise_block
.unwrap(),
1517 // We want to ensure that the matched candidates are bound
1518 // after we have confirmed this candidate *and* any
1519 // associated guard; Binding them on `block` is too soon,
1520 // because that would be before we've checked the result
1523 // But binding them on the arm is *too late*, because
1524 // then all of the candidates for a single arm would be
1525 // bound in the same place, that would cause a case like:
1529 // (mut x, 1) | (2, mut x) if { true } => { ... }
1530 // ... // ^^^^^^^ (this is `arm_block`)
1534 // would yield a `arm_block` something like:
1537 // StorageLive(_4); // _4 is `x`
1538 // _4 = &mut (_1.0: i32); // this is handling `(mut x, 1)` case
1539 // _4 = &mut (_1.1: i32); // this is handling `(2, mut x)` case
1542 // and that is clearly not correct.
1543 let by_value_bindings
= candidate
.bindings
.iter().filter(|binding
| {
1544 if let BindingMode
::ByValue
= binding
.binding_mode { true }
else { false }
1546 // Read all of the by reference bindings to ensure that the
1547 // place they refer to can't be modified by the guard.
1548 for binding
in by_value_bindings
.clone() {
1549 let local_id
= self.var_local_id(binding
.var_id
, RefWithinGuard
);
1550 let place
= Place
::from(local_id
);
1554 source_info
: guard_end
,
1555 kind
: StatementKind
::FakeRead(FakeReadCause
::ForGuardBinding
, place
),
1559 self.bind_matched_candidate_for_arm_body(
1566 assert
!(candidate
.otherwise_block
.is_none());
1567 // (Here, it is not too early to bind the matched
1568 // candidate on `block`, because there is no guard result
1569 // that we have to inspect before we bind them.)
1570 self.bind_matched_candidate_for_arm_body(block
, &candidate
.bindings
);
1575 /// Append `AscribeUserType` statements onto the end of `block`
1576 /// for each ascription
1577 fn ascribe_types(&mut self, block
: BasicBlock
, ascriptions
: &[Ascription
<'tcx
>]) {
1578 for ascription
in ascriptions
{
1579 let source_info
= self.source_info(ascription
.span
);
1582 "adding user ascription at span {:?} of place {:?} and {:?}",
1588 let user_ty
= box ascription
.user_ty
.clone().user_ty(
1589 &mut self.canonical_user_type_annotations
,
1590 ascription
.source
.ty(&self.local_decls
, self.hir
.tcx()).ty
,
1597 kind
: StatementKind
::AscribeUserType(
1598 ascription
.source
.clone(),
1599 ascription
.variance
,
1607 fn bind_matched_candidate_for_guard(
1610 bindings
: &[Binding
<'tcx
>],
1612 debug
!("bind_matched_candidate_for_guard(block={:?}, bindings={:?})", block
, bindings
);
1614 // Assign each of the bindings. Since we are binding for a
1615 // guard expression, this will never trigger moves out of the
1617 let re_erased
= self.hir
.tcx().lifetimes
.re_erased
;
1618 for binding
in bindings
{
1619 let source_info
= self.source_info(binding
.span
);
1621 // For each pattern ident P of type T, `ref_for_guard` is
1622 // a reference R: &T pointing to the location matched by
1623 // the pattern, and every occurrence of P within a guard
1626 self.storage_live_binding(block
, binding
.var_id
, binding
.span
, RefWithinGuard
);
1627 match binding
.binding_mode
{
1628 BindingMode
::ByValue
=> {
1629 let rvalue
= Rvalue
::Ref(re_erased
, BorrowKind
::Shared
, binding
.source
.clone());
1631 .push_assign(block
, source_info
, &ref_for_guard
, rvalue
);
1633 BindingMode
::ByRef(borrow_kind
) => {
1634 let value_for_arm
= self.storage_live_binding(
1641 let rvalue
= Rvalue
::Ref(re_erased
, borrow_kind
, binding
.source
.clone());
1643 .push_assign(block
, source_info
, &value_for_arm
, rvalue
);
1644 let rvalue
= Rvalue
::Ref(re_erased
, BorrowKind
::Shared
, value_for_arm
);
1646 .push_assign(block
, source_info
, &ref_for_guard
, rvalue
);
1652 fn bind_matched_candidate_for_arm_body
<'b
>(
1655 bindings
: impl IntoIterator
<Item
= &'b Binding
<'tcx
>>,
1657 debug
!("bind_matched_candidate_for_arm_body(block={:?})", block
);
1659 let re_erased
= self.hir
.tcx().lifetimes
.re_erased
;
1660 // Assign each of the bindings. This may trigger moves out of the candidate.
1661 for binding
in bindings
{
1662 let source_info
= self.source_info(binding
.span
);
1664 self.storage_live_binding(block
, binding
.var_id
, binding
.span
, OutsideGuard
);
1665 self.schedule_drop_for_binding(binding
.var_id
, binding
.span
, OutsideGuard
);
1666 let rvalue
= match binding
.binding_mode
{
1667 BindingMode
::ByValue
=> {
1668 Rvalue
::Use(self.consume_by_copy_or_move(binding
.source
.clone()))
1670 BindingMode
::ByRef(borrow_kind
) => {
1671 Rvalue
::Ref(re_erased
, borrow_kind
, binding
.source
.clone())
1674 self.cfg
.push_assign(block
, source_info
, &local
, rvalue
);
1678 /// Each binding (`ref mut var`/`ref var`/`mut var`/`var`, where the bound
1679 /// `var` has type `T` in the arm body) in a pattern maps to 2 locals. The
1680 /// first local is a binding for occurrences of `var` in the guard, which
1681 /// will have type `&T`. The second local is a binding for occurrences of
1682 /// `var` in the arm body, which will have type `T`.
1685 source_info
: SourceInfo
,
1686 visibility_scope
: SourceScope
,
1687 mutability
: Mutability
,
1692 user_ty
: UserTypeProjections
,
1693 has_guard
: ArmHasGuard
,
1694 opt_match_place
: Option
<(Option
<Place
<'tcx
>>, Span
)>,
1698 "declare_binding(var_id={:?}, name={:?}, mode={:?}, var_ty={:?}, \
1699 visibility_scope={:?}, source_info={:?})",
1700 var_id
, name
, mode
, var_ty
, visibility_scope
, source_info
1703 let tcx
= self.hir
.tcx();
1704 let binding_mode
= match mode
{
1705 BindingMode
::ByValue
=> ty
::BindingMode
::BindByValue(mutability
.into()),
1706 BindingMode
::ByRef(_
) => ty
::BindingMode
::BindByReference(mutability
.into()),
1708 debug
!("declare_binding: user_ty={:?}", user_ty
);
1709 let local
= LocalDecl
::<'tcx
> {
1717 is_block_tail
: None
,
1718 is_user_variable
: Some(ClearCrossCrate
::Set(BindingForm
::Var(VarBindingForm
{
1720 // hypothetically, `visit_bindings` could try to unzip
1721 // an outermost hir::Ty as we descend, matching up
1722 // idents in pat; but complex w/ unclear UI payoff.
1723 // Instead, just abandon providing diagnostic info.
1729 let for_arm_body
= self.local_decls
.push(local
);
1730 let locals
= if has_guard
.0 {
1731 let ref_for_guard
= self.local_decls
.push(LocalDecl
::<'tcx
> {
1732 // This variable isn't mutated but has a name, so has to be
1733 // immutable to avoid the unused mut lint.
1734 mutability
: Mutability
::Not
,
1735 ty
: tcx
.mk_imm_ref(tcx
.lifetimes
.re_erased
, var_ty
),
1736 user_ty
: UserTypeProjections
::none(),
1741 is_block_tail
: None
,
1742 is_user_variable
: Some(ClearCrossCrate
::Set(BindingForm
::RefForGuard
)),
1744 LocalsForNode
::ForGuard
{
1749 LocalsForNode
::One(for_arm_body
)
1751 debug
!("declare_binding: vars={:?}", locals
);
1752 self.var_indices
.insert(var_id
, locals
);