3 // After candidates have been simplified, the only match pairs that
4 // remain are those that require some sort of test. The functions here
5 // identify what tests are needed, perform the tests, and then filter
6 // the candidates based on the result.
8 use crate::build::expr::as_place::PlaceBuilder;
9 use crate::build::matches::{Candidate, MatchPair, Test, TestKind};
10 use crate::build::Builder;
11 use crate::thir::pattern::compare_const_vals;
12 use rustc_data_structures::fx::FxIndexMap;
13 use rustc_hir::{LangItem, RangeEnd};
14 use rustc_index::bit_set::BitSet;
15 use rustc_middle::mir::*;
16 use rustc_middle::thir::*;
17 use rustc_middle::ty::subst::{GenericArg, Subst};
18 use rustc_middle::ty::util::IntTypeExt;
19 use rustc_middle::ty::{self, adjustment::PointerCast, Ty, TyCtxt};
20 use rustc_span::def_id::DefId;
21 use rustc_span::symbol::{sym, Symbol};
23 use rustc_target::abi::VariantIdx;
25 use std::cmp::Ordering;
27 impl<'a, 'tcx> Builder<'a, 'tcx> {
28 /// Identifies what test is needed to decide if `match_pair` is applicable.
30 /// It is a bug to call this with a not-fully-simplified pattern.
31 pub(super) fn test<'pat>(&mut self, match_pair: &MatchPair<'pat, 'tcx>) -> Test<'tcx> {
32 match *match_pair.pattern.kind {
33 PatKind::Variant { ref adt_def, substs: _, variant_index: _, subpatterns: _ } => Test {
34 span: match_pair.pattern.span,
35 kind: TestKind::Switch {
37 variants: BitSet::new_empty(adt_def.variants.len()),
41 PatKind::Constant { .. } if is_switch_ty(match_pair.pattern.ty) => {
42 // For integers, we use a `SwitchInt` match, which allows
43 // us to handle more cases.
45 span: match_pair.pattern.span,
46 kind: TestKind::SwitchInt {
47 switch_ty: match_pair.pattern.ty,
49 // these maps are empty to start; cases are
50 // added below in add_cases_to_switch
51 options: Default::default(),
56 PatKind::Constant { value } => Test {
57 span: match_pair.pattern.span,
58 kind: TestKind::Eq { value, ty: match_pair.pattern.ty },
61 PatKind::Range(range) => {
62 assert_eq!(range.lo.ty, match_pair.pattern.ty);
63 assert_eq!(range.hi.ty, match_pair.pattern.ty);
64 Test { span: match_pair.pattern.span, kind: TestKind::Range(range) }
67 PatKind::Slice { ref prefix, ref slice, ref suffix } => {
68 let len = prefix.len() + suffix.len();
69 let op = if slice.is_some() { BinOp::Ge } else { BinOp::Eq };
70 Test { span: match_pair.pattern.span, kind: TestKind::Len { len: len as u64, op } }
73 PatKind::Or { .. } => bug!("or-patterns should have already been handled"),
75 PatKind::AscribeUserType { .. }
76 | PatKind::Array { .. }
78 | PatKind::Binding { .. }
79 | PatKind::Leaf { .. }
80 | PatKind::Deref { .. } => self.error_simplifyable(match_pair),
84 pub(super) fn add_cases_to_switch<'pat>(
86 test_place: &PlaceBuilder<'tcx>,
87 candidate: &Candidate<'pat, 'tcx>,
89 options: &mut FxIndexMap<&'tcx ty::Const<'tcx>, u128>,
91 let Some(match_pair) = candidate.match_pairs.iter().find(|mp| mp.place == *test_place) else {
95 match *match_pair.pattern.kind {
96 PatKind::Constant { value } => {
99 .or_insert_with(|| value.eval_bits(self.tcx, self.param_env, switch_ty));
102 PatKind::Variant { .. } => {
103 panic!("you should have called add_variants_to_switch instead!");
105 PatKind::Range(range) => {
106 // Check that none of the switch values are in the range.
107 self.values_not_contained_in_range(range, options).unwrap_or(false)
109 PatKind::Slice { .. }
110 | PatKind::Array { .. }
113 | PatKind::Binding { .. }
114 | PatKind::AscribeUserType { .. }
115 | PatKind::Leaf { .. }
116 | PatKind::Deref { .. } => {
117 // don't know how to add these patterns to a switch
123 pub(super) fn add_variants_to_switch<'pat>(
125 test_place: &PlaceBuilder<'tcx>,
126 candidate: &Candidate<'pat, 'tcx>,
127 variants: &mut BitSet<VariantIdx>,
129 let match_pair = match candidate.match_pairs.iter().find(|mp| mp.place == *test_place) {
130 Some(match_pair) => match_pair,
136 match *match_pair.pattern.kind {
137 PatKind::Variant { adt_def: _, variant_index, .. } => {
138 // We have a pattern testing for variant `variant_index`
139 // set the corresponding index to true
140 variants.insert(variant_index);
144 // don't know how to add these patterns to a switch
150 pub(super) fn perform_test(
152 match_start_span: Span,
153 scrutinee_span: Span,
155 place_builder: PlaceBuilder<'tcx>,
157 make_target_blocks: impl FnOnce(&mut Self) -> Vec<BasicBlock>,
159 let place: Place<'tcx>;
160 if let Ok(test_place_builder) =
161 place_builder.try_upvars_resolved(self.tcx, self.typeck_results)
163 place = test_place_builder.into_place(self.tcx, self.typeck_results);
168 "perform_test({:?}, {:?}: {:?}, {:?})",
171 place.ty(&self.local_decls, self.tcx),
175 let source_info = self.source_info(test.span);
177 TestKind::Switch { adt_def, ref variants } => {
178 let target_blocks = make_target_blocks(self);
179 // Variants is a BitVec of indexes into adt_def.variants.
180 let num_enum_variants = adt_def.variants.len();
181 debug_assert_eq!(target_blocks.len(), num_enum_variants + 1);
182 let otherwise_block = *target_blocks.last().unwrap();
184 let switch_targets = SwitchTargets::new(
185 adt_def.discriminants(tcx).filter_map(|(idx, discr)| {
186 if variants.contains(idx) {
188 target_blocks[idx.index()],
190 "no canididates for tested discriminant: {:?}",
193 Some((discr.val, target_blocks[idx.index()]))
196 target_blocks[idx.index()],
198 "found canididates for untested discriminant: {:?}",
206 debug!("num_enum_variants: {}, variants: {:?}", num_enum_variants, variants);
207 let discr_ty = adt_def.repr.discr_type().to_ty(tcx);
208 let discr = self.temp(discr_ty, test.span);
209 self.cfg.push_assign(
211 self.source_info(scrutinee_span),
213 Rvalue::Discriminant(place),
217 self.source_info(match_start_span),
218 TerminatorKind::SwitchInt {
219 discr: Operand::Move(discr),
221 targets: switch_targets,
226 TestKind::SwitchInt { switch_ty, ref options } => {
227 let target_blocks = make_target_blocks(self);
228 let terminator = if *switch_ty.kind() == ty::Bool {
229 assert!(!options.is_empty() && options.len() <= 2);
230 let [first_bb, second_bb] = *target_blocks else {
231 bug!("`TestKind::SwitchInt` on `bool` should have two targets")
233 let (true_bb, false_bb) = match options[0] {
234 1 => (first_bb, second_bb),
235 0 => (second_bb, first_bb),
236 v => span_bug!(test.span, "expected boolean value but got {:?}", v),
238 TerminatorKind::if_(self.tcx, Operand::Copy(place), true_bb, false_bb)
240 // The switch may be inexhaustive so we have a catch all block
241 debug_assert_eq!(options.len() + 1, target_blocks.len());
242 let otherwise_block = *target_blocks.last().unwrap();
243 let switch_targets = SwitchTargets::new(
244 options.values().copied().zip(target_blocks),
247 TerminatorKind::SwitchInt {
248 discr: Operand::Copy(place),
250 targets: switch_targets,
253 self.cfg.terminate(block, self.source_info(match_start_span), terminator);
256 TestKind::Eq { value, ty } => {
258 // Use `PartialEq::eq` instead of `BinOp::Eq`
259 // (the binop can only handle primitives)
260 self.non_scalar_compare(
268 } else if let [success, fail] = *make_target_blocks(self) {
269 assert_eq!(value.ty, ty);
270 let expect = self.literal_operand(test.span, value);
271 let val = Operand::Copy(place);
272 self.compare(block, success, fail, source_info, BinOp::Eq, expect, val);
274 bug!("`TestKind::Eq` should have two target blocks");
278 TestKind::Range(PatRange { ref lo, ref hi, ref end }) => {
279 let lower_bound_success = self.cfg.start_new_block();
280 let target_blocks = make_target_blocks(self);
282 // Test `val` by computing `lo <= val && val <= hi`, using primitive comparisons.
283 let lo = self.literal_operand(test.span, lo);
284 let hi = self.literal_operand(test.span, hi);
285 let val = Operand::Copy(place);
287 let [success, fail] = *target_blocks else {
288 bug!("`TestKind::Range` should have two target blocks");
299 let op = match *end {
300 RangeEnd::Included => BinOp::Le,
301 RangeEnd::Excluded => BinOp::Lt,
303 self.compare(lower_bound_success, success, fail, source_info, op, val, hi);
306 TestKind::Len { len, op } => {
307 let target_blocks = make_target_blocks(self);
309 let usize_ty = self.tcx.types.usize;
310 let actual = self.temp(usize_ty, test.span);
312 // actual = len(place)
313 self.cfg.push_assign(block, source_info, actual, Rvalue::Len(place));
316 let expected = self.push_usize(block, source_info, len);
318 let [true_bb, false_bb] = *target_blocks else {
319 bug!("`TestKind::Len` should have two target blocks");
321 // result = actual == expected OR result = actual < expected
322 // branch based on result
329 Operand::Move(actual),
330 Operand::Move(expected),
336 /// Compare using the provided built-in comparison operator
340 success_block: BasicBlock,
341 fail_block: BasicBlock,
342 source_info: SourceInfo,
345 right: Operand<'tcx>,
347 let bool_ty = self.tcx.types.bool;
348 let result = self.temp(bool_ty, source_info.span);
350 // result = op(left, right)
351 self.cfg.push_assign(
355 Rvalue::BinaryOp(op, Box::new((left, right))),
358 // branch based on result
362 TerminatorKind::if_(self.tcx, Operand::Move(result), success_block, fail_block),
366 /// Compare two `&T` values using `<T as std::compare::PartialEq>::eq`
367 fn non_scalar_compare(
370 make_target_blocks: impl FnOnce(&mut Self) -> Vec<BasicBlock>,
371 source_info: SourceInfo,
372 value: &'tcx ty::Const<'tcx>,
376 let mut expect = self.literal_operand(source_info.span, value);
377 let mut val = Operand::Copy(place);
379 // If we're using `b"..."` as a pattern, we need to insert an
380 // unsizing coercion, as the byte string has the type `&[u8; N]`.
382 // We want to do this even when the scrutinee is a reference to an
383 // array, so we can call `<[u8]>::eq` rather than having to find an
385 let unsize = |ty: Ty<'tcx>| match ty.kind() {
386 ty::Ref(region, rty, _) => match rty.kind() {
387 ty::Array(inner_ty, n) => Some((region, inner_ty, n)),
392 let opt_ref_ty = unsize(ty);
393 let opt_ref_test_ty = unsize(value.ty);
394 match (opt_ref_ty, opt_ref_test_ty) {
395 // nothing to do, neither is an array
397 (Some((region, elem_ty, _)), _) | (None, Some((region, elem_ty, _))) => {
400 ty = tcx.mk_imm_ref(region, tcx.mk_slice(elem_ty));
401 if opt_ref_ty.is_some() {
402 let temp = self.temp(ty, source_info.span);
403 self.cfg.push_assign(
407 Rvalue::Cast(CastKind::Pointer(PointerCast::Unsize), val, ty),
409 val = Operand::Move(temp);
411 if opt_ref_test_ty.is_some() {
412 let slice = self.temp(ty, source_info.span);
413 self.cfg.push_assign(
417 Rvalue::Cast(CastKind::Pointer(PointerCast::Unsize), expect, ty),
419 expect = Operand::Move(slice);
424 let deref_ty = match *ty.kind() {
425 ty::Ref(_, deref_ty, _) => deref_ty,
426 _ => bug!("non_scalar_compare called on non-reference type: {}", ty),
429 let eq_def_id = self.tcx.require_lang_item(LangItem::PartialEq, None);
430 let method = trait_method(self.tcx, eq_def_id, sym::eq, deref_ty, &[deref_ty.into()]);
432 let bool_ty = self.tcx.types.bool;
433 let eq_result = self.temp(bool_ty, source_info.span);
434 let eq_block = self.cfg.start_new_block();
438 TerminatorKind::Call {
439 func: Operand::Constant(Box::new(Constant {
440 span: source_info.span,
442 // FIXME(#54571): This constant comes from user input (a
443 // constant in a pattern). Are there forms where users can add
444 // type annotations here? For example, an associated constant?
445 // Need to experiment.
448 literal: method.into(),
450 args: vec![val, expect],
451 destination: Some((eq_result, eq_block)),
453 from_hir_call: false,
454 fn_span: source_info.span,
457 self.diverge_from(block);
459 let [success_block, fail_block] = *make_target_blocks(self) else {
460 bug!("`TestKind::Eq` should have two target blocks")
466 TerminatorKind::if_(self.tcx, Operand::Move(eq_result), success_block, fail_block),
470 /// Given that we are performing `test` against `test_place`, this job
471 /// sorts out what the status of `candidate` will be after the test. See
472 /// `test_candidates` for the usage of this function. The returned index is
473 /// the index that this candidate should be placed in the
474 /// `target_candidates` vec. The candidate may be modified to update its
477 /// So, for example, if this candidate is `x @ Some(P0)` and the `Test` is
478 /// a variant test, then we would modify the candidate to be `(x as
479 /// Option).0 @ P0` and return the index corresponding to the variant
482 /// However, in some cases, the test may just not be relevant to candidate.
483 /// For example, suppose we are testing whether `foo.x == 22`, but in one
484 /// match arm we have `Foo { x: _, ... }`... in that case, the test for
485 /// what value `x` has has no particular relevance to this candidate. In
486 /// such cases, this function just returns None without doing anything.
487 /// This is used by the overall `match_candidates` algorithm to structure
488 /// the match as a whole. See `match_candidates` for more details.
490 /// FIXME(#29623). In some cases, we have some tricky choices to make. for
491 /// example, if we are testing that `x == 22`, but the candidate is `x @
492 /// 13..55`, what should we do? In the event that the test is true, we know
493 /// that the candidate applies, but in the event of false, we don't know
494 /// that it *doesn't* apply. For now, we return false, indicate that the
495 /// test does not apply to this candidate, but it might be we can get
496 /// tighter match code if we do something a bit different.
497 pub(super) fn sort_candidate<'pat>(
499 test_place: &PlaceBuilder<'tcx>,
501 candidate: &mut Candidate<'pat, 'tcx>,
503 // Find the match_pair for this place (if any). At present,
504 // afaik, there can be at most one. (In the future, if we
505 // adopted a more general `@` operator, there might be more
506 // than one, but it'd be very unusual to have two sides that
507 // both require tests; you'd expect one side to be simplified
509 let (match_pair_index, match_pair) =
510 candidate.match_pairs.iter().enumerate().find(|&(_, mp)| mp.place == *test_place)?;
512 match (&test.kind, &*match_pair.pattern.kind) {
513 // If we are performing a variant switch, then this
514 // informs variant patterns, but nothing else.
516 &TestKind::Switch { adt_def: tested_adt_def, .. },
517 &PatKind::Variant { adt_def, variant_index, ref subpatterns, .. },
519 assert_eq!(adt_def, tested_adt_def);
520 self.candidate_after_variant_switch(
527 Some(variant_index.as_usize())
530 (&TestKind::Switch { .. }, _) => None,
532 // If we are performing a switch over integers, then this informs integer
533 // equality, but nothing else.
535 // FIXME(#29623) we could use PatKind::Range to rule
536 // things out here, in some cases.
538 &TestKind::SwitchInt { switch_ty: _, ref options },
539 &PatKind::Constant { ref value },
540 ) if is_switch_ty(match_pair.pattern.ty) => {
541 let index = options.get_index_of(value).unwrap();
542 self.candidate_without_match_pair(match_pair_index, candidate);
546 (&TestKind::SwitchInt { switch_ty: _, ref options }, &PatKind::Range(range)) => {
548 self.values_not_contained_in_range(range, options).unwrap_or(false);
551 // No switch values are contained in the pattern range,
552 // so the pattern can be matched only if this test fails.
553 let otherwise = options.len();
560 (&TestKind::SwitchInt { .. }, _) => None,
563 &TestKind::Len { len: test_len, op: BinOp::Eq },
564 &PatKind::Slice { ref prefix, ref slice, ref suffix },
566 let pat_len = (prefix.len() + suffix.len()) as u64;
567 match (test_len.cmp(&pat_len), slice) {
568 (Ordering::Equal, &None) => {
569 // on true, min_len = len = $actual_length,
570 // on false, len != $actual_length
571 self.candidate_after_slice_test(
580 (Ordering::Less, _) => {
581 // test_len < pat_len. If $actual_len = test_len,
582 // then $actual_len < pat_len and we don't have
586 (Ordering::Equal | Ordering::Greater, &Some(_)) => {
587 // This can match both if $actual_len = test_len >= pat_len,
588 // and if $actual_len > test_len. We can't advance.
591 (Ordering::Greater, &None) => {
592 // test_len != pat_len, so if $actual_len = test_len, then
593 // $actual_len != pat_len.
600 &TestKind::Len { len: test_len, op: BinOp::Ge },
601 &PatKind::Slice { ref prefix, ref slice, ref suffix },
603 // the test is `$actual_len >= test_len`
604 let pat_len = (prefix.len() + suffix.len()) as u64;
605 match (test_len.cmp(&pat_len), slice) {
606 (Ordering::Equal, &Some(_)) => {
607 // $actual_len >= test_len = pat_len,
609 self.candidate_after_slice_test(
618 (Ordering::Less, _) | (Ordering::Equal, &None) => {
619 // test_len <= pat_len. If $actual_len < test_len,
620 // then it is also < pat_len, so the test passing is
621 // necessary (but insufficient).
624 (Ordering::Greater, &None) => {
625 // test_len > pat_len. If $actual_len >= test_len > pat_len,
626 // then we know we won't have a match.
629 (Ordering::Greater, &Some(_)) => {
630 // test_len < pat_len, and is therefore less
631 // strict. This can still go both ways.
637 (&TestKind::Range(test), &PatKind::Range(pat)) => {
639 self.candidate_without_match_pair(match_pair_index, candidate);
643 let no_overlap = (|| {
644 use rustc_hir::RangeEnd::*;
645 use std::cmp::Ordering::*;
649 let test_ty = test.lo.ty;
650 let lo = compare_const_vals(tcx, test.lo, pat.hi, self.param_env, test_ty)?;
651 let hi = compare_const_vals(tcx, test.hi, pat.lo, self.param_env, test_ty)?;
653 match (test.end, pat.end, lo, hi) {
656 (_, Excluded, Equal, _) |
659 (Excluded, _, _, Equal) => Some(true),
664 if let Some(true) = no_overlap {
665 // Testing range does not overlap with pattern range,
666 // so the pattern can be matched only if this test fails.
673 (&TestKind::Range(range), &PatKind::Constant { value }) => {
674 if let Some(false) = self.const_range_contains(range, value) {
675 // `value` is not contained in the testing range,
676 // so `value` can be matched only if this test fails.
683 (&TestKind::Range { .. }, _) => None,
685 (&TestKind::Eq { .. } | &TestKind::Len { .. }, _) => {
686 // The call to `self.test(&match_pair)` below is not actually used to generate any
687 // MIR. Instead, we just want to compare with `test` (the parameter of the method)
688 // to see if it is the same.
690 // However, at this point we can still encounter or-patterns that were extracted
691 // from previous calls to `sort_candidate`, so we need to manually address that
692 // case to avoid panicking in `self.test()`.
693 if let PatKind::Or { .. } = &*match_pair.pattern.kind {
697 // These are all binary tests.
699 // FIXME(#29623) we can be more clever here
700 let pattern_test = self.test(&match_pair);
701 if pattern_test.kind == test.kind {
702 self.candidate_without_match_pair(match_pair_index, candidate);
711 fn candidate_without_match_pair(
713 match_pair_index: usize,
714 candidate: &mut Candidate<'_, 'tcx>,
716 candidate.match_pairs.remove(match_pair_index);
719 fn candidate_after_slice_test<'pat>(
721 match_pair_index: usize,
722 candidate: &mut Candidate<'pat, 'tcx>,
723 prefix: &'pat [Pat<'tcx>],
724 opt_slice: Option<&'pat Pat<'tcx>>,
725 suffix: &'pat [Pat<'tcx>],
727 let removed_place = candidate.match_pairs.remove(match_pair_index).place;
728 self.prefix_slice_suffix(
729 &mut candidate.match_pairs,
737 fn candidate_after_variant_switch<'pat>(
739 match_pair_index: usize,
740 adt_def: &'tcx ty::AdtDef,
741 variant_index: VariantIdx,
742 subpatterns: &'pat [FieldPat<'tcx>],
743 candidate: &mut Candidate<'pat, 'tcx>,
745 let match_pair = candidate.match_pairs.remove(match_pair_index);
747 // So, if we have a match-pattern like `x @ Enum::Variant(P1, P2)`,
748 // we want to create a set of derived match-patterns like
749 // `(x as Variant).0 @ P1` and `(x as Variant).1 @ P1`.
751 ProjectionElem::Downcast(Some(adt_def.variants[variant_index].name), variant_index);
752 let downcast_place = match_pair.place.project(elem); // `(x as Variant)`
753 let consequent_match_pairs = subpatterns.iter().map(|subpattern| {
754 // e.g., `(x as Variant).0`
755 let place = downcast_place.clone().field(subpattern.field, subpattern.pattern.ty);
756 // e.g., `(x as Variant).0 @ P1`
757 MatchPair::new(place, &subpattern.pattern)
760 candidate.match_pairs.extend(consequent_match_pairs);
763 fn error_simplifyable<'pat>(&mut self, match_pair: &MatchPair<'pat, 'tcx>) -> ! {
764 span_bug!(match_pair.pattern.span, "simplifyable pattern found: {:?}", match_pair.pattern)
767 fn const_range_contains(
769 range: PatRange<'tcx>,
770 value: &'tcx ty::Const<'tcx>,
772 use std::cmp::Ordering::*;
776 let a = compare_const_vals(tcx, range.lo, value, self.param_env, range.lo.ty)?;
777 let b = compare_const_vals(tcx, value, range.hi, self.param_env, range.lo.ty)?;
779 match (b, range.end) {
780 (Less, _) | (Equal, RangeEnd::Included) if a != Greater => Some(true),
785 fn values_not_contained_in_range(
787 range: PatRange<'tcx>,
788 options: &FxIndexMap<&'tcx ty::Const<'tcx>, u128>,
790 for &val in options.keys() {
791 if self.const_range_contains(range, val)? {
801 pub(super) fn targets(&self) -> usize {
803 TestKind::Eq { .. } | TestKind::Range(_) | TestKind::Len { .. } => 2,
804 TestKind::Switch { adt_def, .. } => {
805 // While the switch that we generate doesn't test for all
806 // variants, we have a target for each variant and the
807 // otherwise case, and we make sure that all of the cases not
808 // specified have the same block.
809 adt_def.variants.len() + 1
811 TestKind::SwitchInt { switch_ty, ref options, .. } => {
812 if switch_ty.is_bool() {
813 // `bool` is special cased in `perform_test` to always
814 // branch to two blocks.
824 fn is_switch_ty(ty: Ty<'_>) -> bool {
825 ty.is_integral() || ty.is_char() || ty.is_bool()
828 fn trait_method<'tcx>(
833 params: &[GenericArg<'tcx>],
834 ) -> &'tcx ty::Const<'tcx> {
835 let substs = tcx.mk_substs_trait(self_ty, params);
837 // The unhygienic comparison here is acceptable because this is only
838 // used on known traits.
840 .associated_items(trait_def_id)
841 .filter_by_name_unhygienic(method_name)
842 .find(|item| item.kind == ty::AssocKind::Fn)
843 .expect("trait method not found");
845 let method_ty = tcx.type_of(item.def_id);
846 let method_ty = method_ty.subst(tcx, substs);
847 ty::Const::zero_sized(tcx, method_ty)