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 { 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<ConstantKind<'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 Some(match_pair) = candidate.match_pairs.iter().find(|mp| mp.place == *test_place) else {
133 match *match_pair.pattern.kind {
134 PatKind::Variant { adt_def: _, variant_index, .. } => {
135 // We have a pattern testing for variant `variant_index`
136 // set the corresponding index to true
137 variants.insert(variant_index);
141 // don't know how to add these patterns to a switch
147 pub(super) fn perform_test(
149 match_start_span: Span,
150 scrutinee_span: Span,
152 place_builder: PlaceBuilder<'tcx>,
154 make_target_blocks: impl FnOnce(&mut Self) -> Vec<BasicBlock>,
156 let place: Place<'tcx>;
157 if let Ok(test_place_builder) =
158 place_builder.try_upvars_resolved(self.tcx, self.typeck_results)
160 place = test_place_builder.into_place(self.tcx, self.typeck_results);
165 "perform_test({:?}, {:?}: {:?}, {:?})",
168 place.ty(&self.local_decls, self.tcx),
172 let source_info = self.source_info(test.span);
174 TestKind::Switch { adt_def, ref variants } => {
175 let target_blocks = make_target_blocks(self);
176 // Variants is a BitVec of indexes into adt_def.variants.
177 let num_enum_variants = adt_def.variants().len();
178 debug_assert_eq!(target_blocks.len(), num_enum_variants + 1);
179 let otherwise_block = *target_blocks.last().unwrap();
181 let switch_targets = SwitchTargets::new(
182 adt_def.discriminants(tcx).filter_map(|(idx, discr)| {
183 if variants.contains(idx) {
185 target_blocks[idx.index()],
187 "no canididates for tested discriminant: {:?}",
190 Some((discr.val, target_blocks[idx.index()]))
193 target_blocks[idx.index()],
195 "found canididates for untested discriminant: {:?}",
203 debug!("num_enum_variants: {}, variants: {:?}", num_enum_variants, variants);
204 let discr_ty = adt_def.repr().discr_type().to_ty(tcx);
205 let discr = self.temp(discr_ty, test.span);
206 self.cfg.push_assign(
208 self.source_info(scrutinee_span),
210 Rvalue::Discriminant(place),
214 self.source_info(match_start_span),
215 TerminatorKind::SwitchInt {
216 discr: Operand::Move(discr),
218 targets: switch_targets,
223 TestKind::SwitchInt { switch_ty, ref options } => {
224 let target_blocks = make_target_blocks(self);
225 let terminator = if *switch_ty.kind() == ty::Bool {
226 assert!(!options.is_empty() && options.len() <= 2);
227 let [first_bb, second_bb] = *target_blocks else {
228 bug!("`TestKind::SwitchInt` on `bool` should have two targets")
230 let (true_bb, false_bb) = match options[0] {
231 1 => (first_bb, second_bb),
232 0 => (second_bb, first_bb),
233 v => span_bug!(test.span, "expected boolean value but got {:?}", v),
235 TerminatorKind::if_(self.tcx, Operand::Copy(place), true_bb, false_bb)
237 // The switch may be inexhaustive so we have a catch all block
238 debug_assert_eq!(options.len() + 1, target_blocks.len());
239 let otherwise_block = *target_blocks.last().unwrap();
240 let switch_targets = SwitchTargets::new(
241 options.values().copied().zip(target_blocks),
244 TerminatorKind::SwitchInt {
245 discr: Operand::Copy(place),
247 targets: switch_targets,
250 self.cfg.terminate(block, self.source_info(match_start_span), terminator);
253 TestKind::Eq { value, ty } => {
255 // Use `PartialEq::eq` instead of `BinOp::Eq`
256 // (the binop can only handle primitives)
257 self.non_scalar_compare(
265 } else if let [success, fail] = *make_target_blocks(self) {
266 assert_eq!(value.ty(), ty);
267 let expect = self.literal_operand(test.span, value);
268 let val = Operand::Copy(place);
269 self.compare(block, success, fail, source_info, BinOp::Eq, expect, val);
271 bug!("`TestKind::Eq` should have two target blocks");
275 TestKind::Range(PatRange { lo, hi, ref end }) => {
276 let lower_bound_success = self.cfg.start_new_block();
277 let target_blocks = make_target_blocks(self);
279 // Test `val` by computing `lo <= val && val <= hi`, using primitive comparisons.
280 let lo = self.literal_operand(test.span, lo);
281 let hi = self.literal_operand(test.span, hi);
282 let val = Operand::Copy(place);
284 let [success, fail] = *target_blocks else {
285 bug!("`TestKind::Range` should have two target blocks");
296 let op = match *end {
297 RangeEnd::Included => BinOp::Le,
298 RangeEnd::Excluded => BinOp::Lt,
300 self.compare(lower_bound_success, success, fail, source_info, op, val, hi);
303 TestKind::Len { len, op } => {
304 let target_blocks = make_target_blocks(self);
306 let usize_ty = self.tcx.types.usize;
307 let actual = self.temp(usize_ty, test.span);
309 // actual = len(place)
310 self.cfg.push_assign(block, source_info, actual, Rvalue::Len(place));
313 let expected = self.push_usize(block, source_info, len);
315 let [true_bb, false_bb] = *target_blocks else {
316 bug!("`TestKind::Len` should have two target blocks");
318 // result = actual == expected OR result = actual < expected
319 // branch based on result
326 Operand::Move(actual),
327 Operand::Move(expected),
333 /// Compare using the provided built-in comparison operator
337 success_block: BasicBlock,
338 fail_block: BasicBlock,
339 source_info: SourceInfo,
342 right: Operand<'tcx>,
344 let bool_ty = self.tcx.types.bool;
345 let result = self.temp(bool_ty, source_info.span);
347 // result = op(left, right)
348 self.cfg.push_assign(
352 Rvalue::BinaryOp(op, Box::new((left, right))),
355 // branch based on result
359 TerminatorKind::if_(self.tcx, Operand::Move(result), success_block, fail_block),
363 /// Compare two `&T` values using `<T as std::compare::PartialEq>::eq`
364 fn non_scalar_compare(
367 make_target_blocks: impl FnOnce(&mut Self) -> Vec<BasicBlock>,
368 source_info: SourceInfo,
369 value: ConstantKind<'tcx>,
373 let mut expect = self.literal_operand(source_info.span, value);
374 let mut val = Operand::Copy(place);
376 // If we're using `b"..."` as a pattern, we need to insert an
377 // unsizing coercion, as the byte string has the type `&[u8; N]`.
379 // We want to do this even when the scrutinee is a reference to an
380 // array, so we can call `<[u8]>::eq` rather than having to find an
382 let unsize = |ty: Ty<'tcx>| match ty.kind() {
383 ty::Ref(region, rty, _) => match rty.kind() {
384 ty::Array(inner_ty, n) => Some((region, inner_ty, n)),
389 let opt_ref_ty = unsize(ty);
390 let opt_ref_test_ty = unsize(value.ty());
391 match (opt_ref_ty, opt_ref_test_ty) {
392 // nothing to do, neither is an array
394 (Some((region, elem_ty, _)), _) | (None, Some((region, elem_ty, _))) => {
397 ty = tcx.mk_imm_ref(*region, tcx.mk_slice(*elem_ty));
398 if opt_ref_ty.is_some() {
399 let temp = self.temp(ty, source_info.span);
400 self.cfg.push_assign(
404 Rvalue::Cast(CastKind::Pointer(PointerCast::Unsize), val, ty),
406 val = Operand::Move(temp);
408 if opt_ref_test_ty.is_some() {
409 let slice = self.temp(ty, source_info.span);
410 self.cfg.push_assign(
414 Rvalue::Cast(CastKind::Pointer(PointerCast::Unsize), expect, ty),
416 expect = Operand::Move(slice);
421 let ty::Ref(_, deref_ty, _) = *ty.kind() else {
422 bug!("non_scalar_compare called on non-reference type: {}", ty);
425 let eq_def_id = self.tcx.require_lang_item(LangItem::PartialEq, None);
426 let method = trait_method(self.tcx, eq_def_id, sym::eq, deref_ty, &[deref_ty.into()]);
428 let bool_ty = self.tcx.types.bool;
429 let eq_result = self.temp(bool_ty, source_info.span);
430 let eq_block = self.cfg.start_new_block();
434 TerminatorKind::Call {
435 func: Operand::Constant(Box::new(Constant {
436 span: source_info.span,
438 // FIXME(#54571): This constant comes from user input (a
439 // constant in a pattern). Are there forms where users can add
440 // type annotations here? For example, an associated constant?
441 // Need to experiment.
446 args: vec![val, expect],
447 destination: eq_result,
448 target: Some(eq_block),
450 from_hir_call: false,
451 fn_span: source_info.span,
454 self.diverge_from(block);
456 let [success_block, fail_block] = *make_target_blocks(self) else {
457 bug!("`TestKind::Eq` should have two target blocks")
463 TerminatorKind::if_(self.tcx, Operand::Move(eq_result), success_block, fail_block),
467 /// Given that we are performing `test` against `test_place`, this job
468 /// sorts out what the status of `candidate` will be after the test. See
469 /// `test_candidates` for the usage of this function. The returned index is
470 /// the index that this candidate should be placed in the
471 /// `target_candidates` vec. The candidate may be modified to update its
474 /// So, for example, if this candidate is `x @ Some(P0)` and the `Test` is
475 /// a variant test, then we would modify the candidate to be `(x as
476 /// Option).0 @ P0` and return the index corresponding to the variant
479 /// However, in some cases, the test may just not be relevant to candidate.
480 /// For example, suppose we are testing whether `foo.x == 22`, but in one
481 /// match arm we have `Foo { x: _, ... }`... in that case, the test for
482 /// what value `x` has has no particular relevance to this candidate. In
483 /// such cases, this function just returns None without doing anything.
484 /// This is used by the overall `match_candidates` algorithm to structure
485 /// the match as a whole. See `match_candidates` for more details.
487 /// FIXME(#29623). In some cases, we have some tricky choices to make. for
488 /// example, if we are testing that `x == 22`, but the candidate is `x @
489 /// 13..55`, what should we do? In the event that the test is true, we know
490 /// that the candidate applies, but in the event of false, we don't know
491 /// that it *doesn't* apply. For now, we return false, indicate that the
492 /// test does not apply to this candidate, but it might be we can get
493 /// tighter match code if we do something a bit different.
494 pub(super) fn sort_candidate<'pat>(
496 test_place: &PlaceBuilder<'tcx>,
498 candidate: &mut Candidate<'pat, 'tcx>,
500 // Find the match_pair for this place (if any). At present,
501 // afaik, there can be at most one. (In the future, if we
502 // adopted a more general `@` operator, there might be more
503 // than one, but it'd be very unusual to have two sides that
504 // both require tests; you'd expect one side to be simplified
506 let (match_pair_index, match_pair) =
507 candidate.match_pairs.iter().enumerate().find(|&(_, mp)| mp.place == *test_place)?;
509 match (&test.kind, &*match_pair.pattern.kind) {
510 // If we are performing a variant switch, then this
511 // informs variant patterns, but nothing else.
513 &TestKind::Switch { adt_def: tested_adt_def, .. },
514 &PatKind::Variant { adt_def, variant_index, ref subpatterns, .. },
516 assert_eq!(adt_def, tested_adt_def);
517 self.candidate_after_variant_switch(
524 Some(variant_index.as_usize())
527 (&TestKind::Switch { .. }, _) => None,
529 // If we are performing a switch over integers, then this informs integer
530 // equality, but nothing else.
532 // FIXME(#29623) we could use PatKind::Range to rule
533 // things out here, in some cases.
535 &TestKind::SwitchInt { switch_ty: _, ref options },
536 &PatKind::Constant { ref value },
537 ) if is_switch_ty(match_pair.pattern.ty) => {
538 let index = options.get_index_of(value).unwrap();
539 self.candidate_without_match_pair(match_pair_index, candidate);
543 (&TestKind::SwitchInt { switch_ty: _, ref options }, &PatKind::Range(range)) => {
545 self.values_not_contained_in_range(range, options).unwrap_or(false);
548 // No switch values are contained in the pattern range,
549 // so the pattern can be matched only if this test fails.
550 let otherwise = options.len();
557 (&TestKind::SwitchInt { .. }, _) => None,
560 &TestKind::Len { len: test_len, op: BinOp::Eq },
561 &PatKind::Slice { ref prefix, ref slice, ref suffix },
563 let pat_len = (prefix.len() + suffix.len()) as u64;
564 match (test_len.cmp(&pat_len), slice) {
565 (Ordering::Equal, &None) => {
566 // on true, min_len = len = $actual_length,
567 // on false, len != $actual_length
568 self.candidate_after_slice_test(
577 (Ordering::Less, _) => {
578 // test_len < pat_len. If $actual_len = test_len,
579 // then $actual_len < pat_len and we don't have
583 (Ordering::Equal | Ordering::Greater, &Some(_)) => {
584 // This can match both if $actual_len = test_len >= pat_len,
585 // and if $actual_len > test_len. We can't advance.
588 (Ordering::Greater, &None) => {
589 // test_len != pat_len, so if $actual_len = test_len, then
590 // $actual_len != pat_len.
597 &TestKind::Len { len: test_len, op: BinOp::Ge },
598 &PatKind::Slice { ref prefix, ref slice, ref suffix },
600 // the test is `$actual_len >= test_len`
601 let pat_len = (prefix.len() + suffix.len()) as u64;
602 match (test_len.cmp(&pat_len), slice) {
603 (Ordering::Equal, &Some(_)) => {
604 // $actual_len >= test_len = pat_len,
606 self.candidate_after_slice_test(
615 (Ordering::Less, _) | (Ordering::Equal, &None) => {
616 // test_len <= pat_len. If $actual_len < test_len,
617 // then it is also < pat_len, so the test passing is
618 // necessary (but insufficient).
621 (Ordering::Greater, &None) => {
622 // test_len > pat_len. If $actual_len >= test_len > pat_len,
623 // then we know we won't have a match.
626 (Ordering::Greater, &Some(_)) => {
627 // test_len < pat_len, and is therefore less
628 // strict. This can still go both ways.
634 (&TestKind::Range(test), &PatKind::Range(pat)) => {
635 use std::cmp::Ordering::*;
638 self.candidate_without_match_pair(match_pair_index, candidate);
642 // For performance, it's important to only do the second
643 // `compare_const_vals` if necessary.
644 let no_overlap = if matches!(
645 (compare_const_vals(self.tcx, test.hi, pat.lo, self.param_env)?, test.end),
646 (Less, _) | (Equal, RangeEnd::Excluded) // test < pat
648 (compare_const_vals(self.tcx, test.lo, pat.hi, self.param_env)?, pat.end),
649 (Greater, _) | (Equal, RangeEnd::Excluded) // test > pat
656 // If the testing range does not overlap with pattern range,
657 // the pattern can be matched only if this test fails.
661 (&TestKind::Range(range), &PatKind::Constant { value }) => {
662 if let Some(false) = self.const_range_contains(range, value) {
663 // `value` is not contained in the testing range,
664 // so `value` can be matched only if this test fails.
671 (&TestKind::Range { .. }, _) => None,
673 (&TestKind::Eq { .. } | &TestKind::Len { .. }, _) => {
674 // The call to `self.test(&match_pair)` below is not actually used to generate any
675 // MIR. Instead, we just want to compare with `test` (the parameter of the method)
676 // to see if it is the same.
678 // However, at this point we can still encounter or-patterns that were extracted
679 // from previous calls to `sort_candidate`, so we need to manually address that
680 // case to avoid panicking in `self.test()`.
681 if let PatKind::Or { .. } = &*match_pair.pattern.kind {
685 // These are all binary tests.
687 // FIXME(#29623) we can be more clever here
688 let pattern_test = self.test(&match_pair);
689 if pattern_test.kind == test.kind {
690 self.candidate_without_match_pair(match_pair_index, candidate);
699 fn candidate_without_match_pair(
701 match_pair_index: usize,
702 candidate: &mut Candidate<'_, 'tcx>,
704 candidate.match_pairs.remove(match_pair_index);
707 fn candidate_after_slice_test<'pat>(
709 match_pair_index: usize,
710 candidate: &mut Candidate<'pat, 'tcx>,
711 prefix: &'pat [Pat<'tcx>],
712 opt_slice: Option<&'pat Pat<'tcx>>,
713 suffix: &'pat [Pat<'tcx>],
715 let removed_place = candidate.match_pairs.remove(match_pair_index).place;
716 self.prefix_slice_suffix(
717 &mut candidate.match_pairs,
725 fn candidate_after_variant_switch<'pat>(
727 match_pair_index: usize,
728 adt_def: ty::AdtDef<'tcx>,
729 variant_index: VariantIdx,
730 subpatterns: &'pat [FieldPat<'tcx>],
731 candidate: &mut Candidate<'pat, 'tcx>,
733 let match_pair = candidate.match_pairs.remove(match_pair_index);
735 // So, if we have a match-pattern like `x @ Enum::Variant(P1, P2)`,
736 // we want to create a set of derived match-patterns like
737 // `(x as Variant).0 @ P1` and `(x as Variant).1 @ P1`.
739 ProjectionElem::Downcast(Some(adt_def.variant(variant_index).name), variant_index);
740 let downcast_place = match_pair.place.project(elem); // `(x as Variant)`
741 let consequent_match_pairs = subpatterns.iter().map(|subpattern| {
742 // e.g., `(x as Variant).0`
743 let place = downcast_place.clone().field(subpattern.field, subpattern.pattern.ty);
744 // e.g., `(x as Variant).0 @ P1`
745 MatchPair::new(place, &subpattern.pattern)
748 candidate.match_pairs.extend(consequent_match_pairs);
751 fn error_simplifyable<'pat>(&mut self, match_pair: &MatchPair<'pat, 'tcx>) -> ! {
752 span_bug!(match_pair.pattern.span, "simplifyable pattern found: {:?}", match_pair.pattern)
755 fn const_range_contains(
757 range: PatRange<'tcx>,
758 value: ConstantKind<'tcx>,
760 use std::cmp::Ordering::*;
762 // For performance, it's important to only do the second
763 // `compare_const_vals` if necessary.
765 matches!(compare_const_vals(self.tcx, range.lo, value, self.param_env)?, Less | Equal)
767 (compare_const_vals(self.tcx, value, range.hi, self.param_env)?, range.end),
768 (Less, _) | (Equal, RangeEnd::Included)
773 fn values_not_contained_in_range(
775 range: PatRange<'tcx>,
776 options: &FxIndexMap<ConstantKind<'tcx>, u128>,
778 for &val in options.keys() {
779 if self.const_range_contains(range, val)? {
789 pub(super) fn targets(&self) -> usize {
791 TestKind::Eq { .. } | TestKind::Range(_) | TestKind::Len { .. } => 2,
792 TestKind::Switch { adt_def, .. } => {
793 // While the switch that we generate doesn't test for all
794 // variants, we have a target for each variant and the
795 // otherwise case, and we make sure that all of the cases not
796 // specified have the same block.
797 adt_def.variants().len() + 1
799 TestKind::SwitchInt { switch_ty, ref options, .. } => {
800 if switch_ty.is_bool() {
801 // `bool` is special cased in `perform_test` to always
802 // branch to two blocks.
812 fn is_switch_ty(ty: Ty<'_>) -> bool {
813 ty.is_integral() || ty.is_char() || ty.is_bool()
816 fn trait_method<'tcx>(
821 params: &[GenericArg<'tcx>],
822 ) -> ConstantKind<'tcx> {
823 let substs = tcx.mk_substs_trait(self_ty, params);
825 // The unhygienic comparison here is acceptable because this is only
826 // used on known traits.
828 .associated_items(trait_def_id)
829 .filter_by_name_unhygienic(method_name)
830 .find(|item| item.kind == ty::AssocKind::Fn)
831 .expect("trait method not found");
833 let method_ty = tcx.bound_type_of(item.def_id);
834 let method_ty = method_ty.subst(tcx, substs);
836 ConstantKind::zero_sized(method_ty)