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::matches::{Candidate, MatchPair, Test, TestKind};
9 use crate::build::Builder;
10 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::ty::util::IntTypeExt;
17 use rustc_middle::ty::{self, adjustment::PointerCast, Ty};
18 use rustc_span::symbol::sym;
19 use rustc_target::abi::VariantIdx;
21 use std::cmp::Ordering;
23 impl<'a, 'tcx> Builder<'a, 'tcx> {
24 /// Identifies what test is needed to decide if `match_pair` is applicable.
26 /// It is a bug to call this with a simplifiable pattern.
27 pub(super) fn test<'pat>(&mut self, match_pair: &MatchPair<'pat, 'tcx>) -> Test<'tcx> {
28 match *match_pair.pattern.kind {
29 PatKind::Variant { ref adt_def, substs: _, variant_index: _, subpatterns: _ } => Test {
30 span: match_pair.pattern.span,
31 kind: TestKind::Switch {
33 variants: BitSet::new_empty(adt_def.variants.len()),
37 PatKind::Constant { .. } if is_switch_ty(match_pair.pattern.ty) => {
38 // For integers, we use a `SwitchInt` match, which allows
39 // us to handle more cases.
41 span: match_pair.pattern.span,
42 kind: TestKind::SwitchInt {
43 switch_ty: match_pair.pattern.ty,
45 // these maps are empty to start; cases are
46 // added below in add_cases_to_switch
47 options: Default::default(),
52 PatKind::Constant { value } => Test {
53 span: match_pair.pattern.span,
54 kind: TestKind::Eq { value, ty: match_pair.pattern.ty.clone() },
57 PatKind::Range(range) => {
58 assert_eq!(range.lo.ty, match_pair.pattern.ty);
59 assert_eq!(range.hi.ty, match_pair.pattern.ty);
60 Test { span: match_pair.pattern.span, kind: TestKind::Range(range) }
63 PatKind::Slice { ref prefix, ref slice, ref suffix } => {
64 let len = prefix.len() + suffix.len();
65 let op = if slice.is_some() { BinOp::Ge } else { BinOp::Eq };
66 Test { span: match_pair.pattern.span, kind: TestKind::Len { len: len as u64, op } }
69 PatKind::Or { .. } => bug!("or-patterns should have already been handled"),
71 PatKind::AscribeUserType { .. }
72 | PatKind::Array { .. }
74 | PatKind::Binding { .. }
75 | PatKind::Leaf { .. }
76 | PatKind::Deref { .. } => self.error_simplifyable(match_pair),
80 pub(super) fn add_cases_to_switch<'pat>(
82 test_place: &Place<'tcx>,
83 candidate: &Candidate<'pat, 'tcx>,
85 options: &mut FxIndexMap<&'tcx ty::Const<'tcx>, u128>,
87 let match_pair = match candidate.match_pairs.iter().find(|mp| mp.place == *test_place) {
88 Some(match_pair) => match_pair,
94 match *match_pair.pattern.kind {
95 PatKind::Constant { value } => {
96 options.entry(value).or_insert_with(|| {
97 value.eval_bits(self.hir.tcx(), self.hir.param_env, switch_ty)
101 PatKind::Variant { .. } => {
102 panic!("you should have called add_variants_to_switch instead!");
104 PatKind::Range(range) => {
105 // Check that none of the switch values are in the range.
106 self.values_not_contained_in_range(range, options).unwrap_or(false)
108 PatKind::Slice { .. }
109 | PatKind::Array { .. }
112 | PatKind::Binding { .. }
113 | PatKind::AscribeUserType { .. }
114 | PatKind::Leaf { .. }
115 | PatKind::Deref { .. } => {
116 // don't know how to add these patterns to a switch
122 pub(super) fn add_variants_to_switch<'pat>(
124 test_place: &Place<'tcx>,
125 candidate: &Candidate<'pat, 'tcx>,
126 variants: &mut BitSet<VariantIdx>,
128 let match_pair = match candidate.match_pairs.iter().find(|mp| mp.place == *test_place) {
129 Some(match_pair) => match_pair,
135 match *match_pair.pattern.kind {
136 PatKind::Variant { adt_def: _, variant_index, .. } => {
137 // We have a pattern testing for variant `variant_index`
138 // set the corresponding index to true
139 variants.insert(variant_index);
143 // don't know how to add these patterns to a switch
149 pub(super) fn perform_test(
154 make_target_blocks: impl FnOnce(&mut Self) -> Vec<BasicBlock>,
157 "perform_test({:?}, {:?}: {:?}, {:?})",
160 place.ty(&self.local_decls, self.hir.tcx()),
164 let source_info = self.source_info(test.span);
166 TestKind::Switch { adt_def, ref variants } => {
167 let target_blocks = make_target_blocks(self);
168 // Variants is a BitVec of indexes into adt_def.variants.
169 let num_enum_variants = adt_def.variants.len();
170 let used_variants = variants.count();
171 debug_assert_eq!(target_blocks.len(), num_enum_variants + 1);
172 let otherwise_block = *target_blocks.last().unwrap();
173 let mut targets = Vec::with_capacity(used_variants + 1);
174 let mut values = Vec::with_capacity(used_variants);
175 let tcx = self.hir.tcx();
176 for (idx, discr) in adt_def.discriminants(tcx) {
177 if variants.contains(idx) {
179 target_blocks[idx.index()],
181 "no canididates for tested discriminant: {:?}",
184 values.push(discr.val);
185 targets.push(target_blocks[idx.index()]);
188 target_blocks[idx.index()],
190 "found canididates for untested discriminant: {:?}",
195 targets.push(otherwise_block);
197 "num_enum_variants: {}, tested variants: {:?}, variants: {:?}",
198 num_enum_variants, values, variants
200 let discr_ty = adt_def.repr.discr_type().to_ty(tcx);
201 let discr = self.temp(discr_ty, test.span);
202 self.cfg.push_assign(block, source_info, discr, Rvalue::Discriminant(place));
203 assert_eq!(values.len() + 1, targets.len());
207 TerminatorKind::SwitchInt {
208 discr: Operand::Move(discr),
210 values: From::from(values),
216 TestKind::SwitchInt { switch_ty, ref options } => {
217 let target_blocks = make_target_blocks(self);
218 let terminator = if *switch_ty.kind() == ty::Bool {
219 assert!(!options.is_empty() && options.len() <= 2);
220 if let [first_bb, second_bb] = *target_blocks {
221 let (true_bb, false_bb) = match options[0] {
222 1 => (first_bb, second_bb),
223 0 => (second_bb, first_bb),
224 v => span_bug!(test.span, "expected boolean value but got {:?}", v),
226 TerminatorKind::if_(self.hir.tcx(), Operand::Copy(place), true_bb, false_bb)
228 bug!("`TestKind::SwitchInt` on `bool` should have two targets")
231 // The switch may be inexhaustive so we have a catch all block
232 debug_assert_eq!(options.len() + 1, target_blocks.len());
233 TerminatorKind::SwitchInt {
234 discr: Operand::Copy(place),
236 values: options.values().copied().collect(),
237 targets: target_blocks,
240 self.cfg.terminate(block, source_info, terminator);
243 TestKind::Eq { value, ty } => {
245 // Use `PartialEq::eq` instead of `BinOp::Eq`
246 // (the binop can only handle primitives)
247 self.non_scalar_compare(
256 if let [success, fail] = *make_target_blocks(self) {
257 assert_eq!(value.ty, ty);
258 let expect = self.literal_operand(test.span, value);
259 let val = Operand::Copy(place);
260 self.compare(block, success, fail, source_info, BinOp::Eq, expect, val);
262 bug!("`TestKind::Eq` should have two target blocks");
267 TestKind::Range(PatRange { ref lo, ref hi, ref end }) => {
268 let lower_bound_success = self.cfg.start_new_block();
269 let target_blocks = make_target_blocks(self);
271 // Test `val` by computing `lo <= val && val <= hi`, using primitive comparisons.
272 let lo = self.literal_operand(test.span, lo);
273 let hi = self.literal_operand(test.span, hi);
274 let val = Operand::Copy(place);
276 if let [success, fail] = *target_blocks {
286 let op = match *end {
287 RangeEnd::Included => BinOp::Le,
288 RangeEnd::Excluded => BinOp::Lt,
290 self.compare(lower_bound_success, success, fail, source_info, op, val, hi);
292 bug!("`TestKind::Range` should have two target blocks");
296 TestKind::Len { len, op } => {
297 let target_blocks = make_target_blocks(self);
299 let usize_ty = self.hir.usize_ty();
300 let actual = self.temp(usize_ty, test.span);
302 // actual = len(place)
303 self.cfg.push_assign(block, source_info, actual, Rvalue::Len(place));
306 let expected = self.push_usize(block, source_info, len);
308 if let [true_bb, false_bb] = *target_blocks {
309 // result = actual == expected OR result = actual < expected
310 // branch based on result
317 Operand::Move(actual),
318 Operand::Move(expected),
321 bug!("`TestKind::Len` should have two target blocks");
327 /// Compare using the provided built-in comparison operator
331 success_block: BasicBlock,
332 fail_block: BasicBlock,
333 source_info: SourceInfo,
336 right: Operand<'tcx>,
338 let bool_ty = self.hir.bool_ty();
339 let result = self.temp(bool_ty, source_info.span);
341 // result = op(left, right)
342 self.cfg.push_assign(block, source_info, result, Rvalue::BinaryOp(op, left, right));
344 // branch based on result
348 TerminatorKind::if_(self.hir.tcx(), Operand::Move(result), success_block, fail_block),
352 /// Compare two `&T` values using `<T as std::compare::PartialEq>::eq`
353 fn non_scalar_compare(
356 make_target_blocks: impl FnOnce(&mut Self) -> Vec<BasicBlock>,
357 source_info: SourceInfo,
358 value: &'tcx ty::Const<'tcx>,
362 let mut expect = self.literal_operand(source_info.span, value);
363 let mut val = Operand::Copy(place);
365 // If we're using `b"..."` as a pattern, we need to insert an
366 // unsizing coercion, as the byte string has the type `&[u8; N]`.
368 // We want to do this even when the scrutinee is a reference to an
369 // array, so we can call `<[u8]>::eq` rather than having to find an
371 let unsize = |ty: Ty<'tcx>| match ty.kind() {
372 ty::Ref(region, rty, _) => match rty.kind() {
373 ty::Array(inner_ty, n) => Some((region, inner_ty, n)),
378 let opt_ref_ty = unsize(ty);
379 let opt_ref_test_ty = unsize(value.ty);
380 match (opt_ref_ty, opt_ref_test_ty) {
381 // nothing to do, neither is an array
383 (Some((region, elem_ty, _)), _) | (None, Some((region, elem_ty, _))) => {
384 let tcx = self.hir.tcx();
386 ty = tcx.mk_imm_ref(region, tcx.mk_slice(elem_ty));
387 if opt_ref_ty.is_some() {
388 let temp = self.temp(ty, source_info.span);
389 self.cfg.push_assign(
393 Rvalue::Cast(CastKind::Pointer(PointerCast::Unsize), val, ty),
395 val = Operand::Move(temp);
397 if opt_ref_test_ty.is_some() {
398 let slice = self.temp(ty, source_info.span);
399 self.cfg.push_assign(
403 Rvalue::Cast(CastKind::Pointer(PointerCast::Unsize), expect, ty),
405 expect = Operand::Move(slice);
410 let deref_ty = match *ty.kind() {
411 ty::Ref(_, deref_ty, _) => deref_ty,
412 _ => bug!("non_scalar_compare called on non-reference type: {}", ty),
415 let eq_def_id = self.hir.tcx().require_lang_item(LangItem::PartialEq, None);
416 let method = self.hir.trait_method(eq_def_id, sym::eq, deref_ty, &[deref_ty.into()]);
418 let bool_ty = self.hir.bool_ty();
419 let eq_result = self.temp(bool_ty, source_info.span);
420 let eq_block = self.cfg.start_new_block();
421 let cleanup = self.diverge_cleanup();
425 TerminatorKind::Call {
426 func: Operand::Constant(box Constant {
427 span: source_info.span,
429 // FIXME(#54571): This constant comes from user input (a
430 // constant in a pattern). Are there forms where users can add
431 // type annotations here? For example, an associated constant?
432 // Need to experiment.
437 args: vec![val, expect],
438 destination: Some((eq_result, eq_block)),
439 cleanup: Some(cleanup),
440 from_hir_call: false,
441 fn_span: source_info.span,
445 if let [success_block, fail_block] = *make_target_blocks(self) {
452 Operand::Move(eq_result),
458 bug!("`TestKind::Eq` should have two target blocks")
462 /// Given that we are performing `test` against `test_place`, this job
463 /// sorts out what the status of `candidate` will be after the test. See
464 /// `test_candidates` for the usage of this function. The returned index is
465 /// the index that this candidate should be placed in the
466 /// `target_candidates` vec. The candidate may be modified to update its
469 /// So, for example, if this candidate is `x @ Some(P0)` and the `Test` is
470 /// a variant test, then we would modify the candidate to be `(x as
471 /// Option).0 @ P0` and return the index corresponding to the variant
474 /// However, in some cases, the test may just not be relevant to candidate.
475 /// For example, suppose we are testing whether `foo.x == 22`, but in one
476 /// match arm we have `Foo { x: _, ... }`... in that case, the test for
477 /// what value `x` has has no particular relevance to this candidate. In
478 /// such cases, this function just returns None without doing anything.
479 /// This is used by the overall `match_candidates` algorithm to structure
480 /// the match as a whole. See `match_candidates` for more details.
482 /// FIXME(#29623). In some cases, we have some tricky choices to make. for
483 /// example, if we are testing that `x == 22`, but the candidate is `x @
484 /// 13..55`, what should we do? In the event that the test is true, we know
485 /// that the candidate applies, but in the event of false, we don't know
486 /// that it *doesn't* apply. For now, we return false, indicate that the
487 /// test does not apply to this candidate, but it might be we can get
488 /// tighter match code if we do something a bit different.
489 pub(super) fn sort_candidate<'pat>(
491 test_place: &Place<'tcx>,
493 candidate: &mut Candidate<'pat, 'tcx>,
495 // Find the match_pair for this place (if any). At present,
496 // afaik, there can be at most one. (In the future, if we
497 // adopted a more general `@` operator, there might be more
498 // than one, but it'd be very unusual to have two sides that
499 // both require tests; you'd expect one side to be simplified
501 let (match_pair_index, match_pair) =
502 candidate.match_pairs.iter().enumerate().find(|&(_, mp)| mp.place == *test_place)?;
504 match (&test.kind, &*match_pair.pattern.kind) {
505 // If we are performing a variant switch, then this
506 // informs variant patterns, but nothing else.
508 &TestKind::Switch { adt_def: tested_adt_def, .. },
509 &PatKind::Variant { adt_def, variant_index, ref subpatterns, .. },
511 assert_eq!(adt_def, tested_adt_def);
512 self.candidate_after_variant_switch(
519 Some(variant_index.as_usize())
522 (&TestKind::Switch { .. }, _) => None,
524 // If we are performing a switch over integers, then this informs integer
525 // equality, but nothing else.
527 // FIXME(#29623) we could use PatKind::Range to rule
528 // things out here, in some cases.
530 &TestKind::SwitchInt { switch_ty: _, ref options },
531 &PatKind::Constant { ref value },
532 ) if is_switch_ty(match_pair.pattern.ty) => {
533 let index = options.get_index_of(value).unwrap();
534 self.candidate_without_match_pair(match_pair_index, candidate);
538 (&TestKind::SwitchInt { switch_ty: _, ref options }, &PatKind::Range(range)) => {
540 self.values_not_contained_in_range(range, options).unwrap_or(false);
543 // No switch values are contained in the pattern range,
544 // so the pattern can be matched only if this test fails.
545 let otherwise = options.len();
552 (&TestKind::SwitchInt { .. }, _) => None,
555 &TestKind::Len { len: test_len, op: BinOp::Eq },
556 &PatKind::Slice { ref prefix, ref slice, ref suffix },
558 let pat_len = (prefix.len() + suffix.len()) as u64;
559 match (test_len.cmp(&pat_len), slice) {
560 (Ordering::Equal, &None) => {
561 // on true, min_len = len = $actual_length,
562 // on false, len != $actual_length
563 self.candidate_after_slice_test(
572 (Ordering::Less, _) => {
573 // test_len < pat_len. If $actual_len = test_len,
574 // then $actual_len < pat_len and we don't have
578 (Ordering::Equal | Ordering::Greater, &Some(_)) => {
579 // This can match both if $actual_len = test_len >= pat_len,
580 // and if $actual_len > test_len. We can't advance.
583 (Ordering::Greater, &None) => {
584 // test_len != pat_len, so if $actual_len = test_len, then
585 // $actual_len != pat_len.
592 &TestKind::Len { len: test_len, op: BinOp::Ge },
593 &PatKind::Slice { ref prefix, ref slice, ref suffix },
595 // the test is `$actual_len >= test_len`
596 let pat_len = (prefix.len() + suffix.len()) as u64;
597 match (test_len.cmp(&pat_len), slice) {
598 (Ordering::Equal, &Some(_)) => {
599 // $actual_len >= test_len = pat_len,
601 self.candidate_after_slice_test(
610 (Ordering::Less, _) | (Ordering::Equal, &None) => {
611 // test_len <= pat_len. If $actual_len < test_len,
612 // then it is also < pat_len, so the test passing is
613 // necessary (but insufficient).
616 (Ordering::Greater, &None) => {
617 // test_len > pat_len. If $actual_len >= test_len > pat_len,
618 // then we know we won't have a match.
621 (Ordering::Greater, &Some(_)) => {
622 // test_len < pat_len, and is therefore less
623 // strict. This can still go both ways.
629 (&TestKind::Range(test), &PatKind::Range(pat)) => {
631 self.candidate_without_match_pair(match_pair_index, candidate);
635 let no_overlap = (|| {
636 use rustc_hir::RangeEnd::*;
637 use std::cmp::Ordering::*;
639 let tcx = self.hir.tcx();
641 let test_ty = test.lo.ty;
642 let lo = compare_const_vals(tcx, test.lo, pat.hi, self.hir.param_env, test_ty)?;
643 let hi = compare_const_vals(tcx, test.hi, pat.lo, self.hir.param_env, test_ty)?;
645 match (test.end, pat.end, lo, hi) {
648 (_, Excluded, Equal, _) |
651 (Excluded, _, _, Equal) => Some(true),
656 if let Some(true) = no_overlap {
657 // Testing range does not overlap with pattern range,
658 // so the pattern can be matched only if this test fails.
665 (&TestKind::Range(range), &PatKind::Constant { value }) => {
666 if let Some(false) = self.const_range_contains(range, value) {
667 // `value` is not contained in the testing range,
668 // so `value` can be matched only if this test fails.
675 (&TestKind::Range { .. }, _) => None,
677 (&TestKind::Eq { .. } | &TestKind::Len { .. }, _) => {
678 // These are all binary tests.
680 // FIXME(#29623) we can be more clever here
681 let pattern_test = self.test(&match_pair);
682 if pattern_test.kind == test.kind {
683 self.candidate_without_match_pair(match_pair_index, candidate);
692 fn candidate_without_match_pair(
694 match_pair_index: usize,
695 candidate: &mut Candidate<'_, 'tcx>,
697 candidate.match_pairs.remove(match_pair_index);
700 fn candidate_after_slice_test<'pat>(
702 match_pair_index: usize,
703 candidate: &mut Candidate<'pat, 'tcx>,
704 prefix: &'pat [Pat<'tcx>],
705 opt_slice: Option<&'pat Pat<'tcx>>,
706 suffix: &'pat [Pat<'tcx>],
708 let removed_place = candidate.match_pairs.remove(match_pair_index).place;
709 self.prefix_slice_suffix(
710 &mut candidate.match_pairs,
718 fn candidate_after_variant_switch<'pat>(
720 match_pair_index: usize,
721 adt_def: &'tcx ty::AdtDef,
722 variant_index: VariantIdx,
723 subpatterns: &'pat [FieldPat<'tcx>],
724 candidate: &mut Candidate<'pat, 'tcx>,
726 let match_pair = candidate.match_pairs.remove(match_pair_index);
727 let tcx = self.hir.tcx();
729 // So, if we have a match-pattern like `x @ Enum::Variant(P1, P2)`,
730 // we want to create a set of derived match-patterns like
731 // `(x as Variant).0 @ P1` and `(x as Variant).1 @ P1`.
732 let elem = ProjectionElem::Downcast(
733 Some(adt_def.variants[variant_index].ident.name),
736 let downcast_place = tcx.mk_place_elem(match_pair.place, elem); // `(x as Variant)`
737 let consequent_match_pairs = subpatterns.iter().map(|subpattern| {
738 // e.g., `(x as Variant).0`
739 let place = tcx.mk_place_field(downcast_place, subpattern.field, subpattern.pattern.ty);
740 // e.g., `(x as Variant).0 @ P1`
741 MatchPair::new(place, &subpattern.pattern)
744 candidate.match_pairs.extend(consequent_match_pairs);
747 fn error_simplifyable<'pat>(&mut self, match_pair: &MatchPair<'pat, 'tcx>) -> ! {
748 span_bug!(match_pair.pattern.span, "simplifyable pattern found: {:?}", match_pair.pattern)
751 fn const_range_contains(
753 range: PatRange<'tcx>,
754 value: &'tcx ty::Const<'tcx>,
756 use std::cmp::Ordering::*;
758 let tcx = self.hir.tcx();
760 let a = compare_const_vals(tcx, range.lo, value, self.hir.param_env, range.lo.ty)?;
761 let b = compare_const_vals(tcx, value, range.hi, self.hir.param_env, range.lo.ty)?;
763 match (b, range.end) {
764 (Less, _) | (Equal, RangeEnd::Included) if a != Greater => Some(true),
769 fn values_not_contained_in_range(
771 range: PatRange<'tcx>,
772 options: &FxIndexMap<&'tcx ty::Const<'tcx>, u128>,
774 for &val in options.keys() {
775 if self.const_range_contains(range, val)? {
785 pub(super) fn targets(&self) -> usize {
787 TestKind::Eq { .. } | TestKind::Range(_) | TestKind::Len { .. } => 2,
788 TestKind::Switch { adt_def, .. } => {
789 // While the switch that we generate doesn't test for all
790 // variants, we have a target for each variant and the
791 // otherwise case, and we make sure that all of the cases not
792 // specified have the same block.
793 adt_def.variants.len() + 1
795 TestKind::SwitchInt { switch_ty, ref options, .. } => {
796 if switch_ty.is_bool() {
797 // `bool` is special cased in `perform_test` to always
798 // branch to two blocks.
808 fn is_switch_ty(ty: Ty<'_>) -> bool {
809 ty.is_integral() || ty.is_char() || ty.is_bool()