compiler/rustc_mir_build/src/build/matches/test.rs

   1 // Testing candidates
   2 //
   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.
   7
   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};
  22 use rustc_span::Span;
  23 use rustc_target::abi::VariantIdx;
  24
  25 use std::cmp::Ordering;
  26
  27 impl<'a, 'tcx> Builder<'a, 'tcx> {
  28     /// Identifies what test is needed to decide if `match_pair` is applicable.
  29     ///
  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 {
  36                     adt_def,
  37                     variants: BitSet::new_empty(adt_def.variants().len()),
  38                 },
  39             },
  40
  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.
  44                 Test {
  45                     span: match_pair.pattern.span,
  46                     kind: TestKind::SwitchInt {
  47                         switch_ty: match_pair.pattern.ty,
  48
  49                         // these maps are empty to start; cases are
  50                         // added below in add_cases_to_switch
  51                         options: Default::default(),
  52                     },
  53                 }
  54             }
  55
  56             PatKind::Constant { value } => Test {
  57                 span: match_pair.pattern.span,
  58                 kind: TestKind::Eq { value, ty: match_pair.pattern.ty },
  59             },
  60
  61             PatKind::Range(ref 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.clone()) }
  65             }
  66
  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 } }
  71             }
  72
  73             PatKind::Or { .. } => bug!("or-patterns should have already been handled"),
  74
  75             PatKind::AscribeUserType { .. }
  76             | PatKind::Array { .. }
  77             | PatKind::Wild
  78             | PatKind::Binding { .. }
  79             | PatKind::Leaf { .. }
  80             | PatKind::Deref { .. } => self.error_simplifyable(match_pair),
  81         }
  82     }
  83
  84     pub(super) fn add_cases_to_switch<'pat>(
  85         &mut self,
  86         test_place: &PlaceBuilder<'tcx>,
  87         candidate: &Candidate<'pat, 'tcx>,
  88         switch_ty: Ty<'tcx>,
  89         options: &mut FxIndexMap<ConstantKind<'tcx>, u128>,
  90     ) -> bool {
  91         let Some(match_pair) = candidate.match_pairs.iter().find(|mp| mp.place == *test_place) else {
  92             return false;
  93         };
  94
  95         match match_pair.pattern.kind {
  96             PatKind::Constant { value } => {
  97                 options
  98                     .entry(value)
  99                     .or_insert_with(|| value.eval_bits(self.tcx, self.param_env, switch_ty));
 100                 true
 101             }
 102             PatKind::Variant { .. } => {
 103                 panic!("you should have called add_variants_to_switch instead!");
 104             }
 105             PatKind::Range(ref 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)
 108             }
 109             PatKind::Slice { .. }
 110             | PatKind::Array { .. }
 111             | PatKind::Wild
 112             | PatKind::Or { .. }
 113             | PatKind::Binding { .. }
 114             | PatKind::AscribeUserType { .. }
 115             | PatKind::Leaf { .. }
 116             | PatKind::Deref { .. } => {
 117                 // don't know how to add these patterns to a switch
 118                 false
 119             }
 120         }
 121     }
 122
 123     pub(super) fn add_variants_to_switch<'pat>(
 124         &mut self,
 125         test_place: &PlaceBuilder<'tcx>,
 126         candidate: &Candidate<'pat, 'tcx>,
 127         variants: &mut BitSet<VariantIdx>,
 128     ) -> bool {
 129         let Some(match_pair) = candidate.match_pairs.iter().find(|mp| mp.place == *test_place) else {
 130             return false;
 131         };
 132
 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);
 138                 true
 139             }
 140             _ => {
 141                 // don't know how to add these patterns to a switch
 142                 false
 143             }
 144         }
 145     }
 146
 147     pub(super) fn perform_test(
 148         &mut self,
 149         match_start_span: Span,
 150         scrutinee_span: Span,
 151         block: BasicBlock,
 152         place_builder: PlaceBuilder<'tcx>,
 153         test: &Test<'tcx>,
 154         make_target_blocks: impl FnOnce(&mut Self) -> Vec<BasicBlock>,
 155     ) {
 156         let place: Place<'tcx>;
 157         if let Ok(test_place_builder) = place_builder.try_upvars_resolved(self.tcx, &self.upvars) {
 158             place = test_place_builder.into_place(self.tcx, &self.upvars);
 159         } else {
 160             return;
 161         }
 162         debug!(
 163             "perform_test({:?}, {:?}: {:?}, {:?})",
 164             block,
 165             place,
 166             place.ty(&self.local_decls, self.tcx),
 167             test
 168         );
 169
 170         let source_info = self.source_info(test.span);
 171         match test.kind {
 172             TestKind::Switch { adt_def, ref variants } => {
 173                 let target_blocks = make_target_blocks(self);
 174                 // Variants is a BitVec of indexes into adt_def.variants.
 175                 let num_enum_variants = adt_def.variants().len();
 176                 debug_assert_eq!(target_blocks.len(), num_enum_variants + 1);
 177                 let otherwise_block = *target_blocks.last().unwrap();
 178                 let tcx = self.tcx;
 179                 let switch_targets = SwitchTargets::new(
 180                     adt_def.discriminants(tcx).filter_map(|(idx, discr)| {
 181                         if variants.contains(idx) {
 182                             debug_assert_ne!(
 183                                 target_blocks[idx.index()],
 184                                 otherwise_block,
 185                                 "no canididates for tested discriminant: {:?}",
 186                                 discr,
 187                             );
 188                             Some((discr.val, target_blocks[idx.index()]))
 189                         } else {
 190                             debug_assert_eq!(
 191                                 target_blocks[idx.index()],
 192                                 otherwise_block,
 193                                 "found canididates for untested discriminant: {:?}",
 194                                 discr,
 195                             );
 196                             None
 197                         }
 198                     }),
 199                     otherwise_block,
 200                 );
 201                 debug!("num_enum_variants: {}, variants: {:?}", num_enum_variants, variants);
 202                 let discr_ty = adt_def.repr().discr_type().to_ty(tcx);
 203                 let discr = self.temp(discr_ty, test.span);
 204                 self.cfg.push_assign(
 205                     block,
 206                     self.source_info(scrutinee_span),
 207                     discr,
 208                     Rvalue::Discriminant(place),
 209                 );
 210                 self.cfg.terminate(
 211                     block,
 212                     self.source_info(match_start_span),
 213                     TerminatorKind::SwitchInt {
 214                         discr: Operand::Move(discr),
 215                         switch_ty: discr_ty,
 216                         targets: switch_targets,
 217                     },
 218                 );
 219             }
 220
 221             TestKind::SwitchInt { switch_ty, ref options } => {
 222                 let target_blocks = make_target_blocks(self);
 223                 let terminator = if *switch_ty.kind() == ty::Bool {
 224                     assert!(!options.is_empty() && options.len() <= 2);
 225                     let [first_bb, second_bb] = *target_blocks else {
 226                         bug!("`TestKind::SwitchInt` on `bool` should have two targets")
 227                     };
 228                     let (true_bb, false_bb) = match options[0] {
 229                         1 => (first_bb, second_bb),
 230                         0 => (second_bb, first_bb),
 231                         v => span_bug!(test.span, "expected boolean value but got {:?}", v),
 232                     };
 233                     TerminatorKind::if_(self.tcx, Operand::Copy(place), true_bb, false_bb)
 234                 } else {
 235                     // The switch may be inexhaustive so we have a catch all block
 236                     debug_assert_eq!(options.len() + 1, target_blocks.len());
 237                     let otherwise_block = *target_blocks.last().unwrap();
 238                     let switch_targets = SwitchTargets::new(
 239                         options.values().copied().zip(target_blocks),
 240                         otherwise_block,
 241                     );
 242                     TerminatorKind::SwitchInt {
 243                         discr: Operand::Copy(place),
 244                         switch_ty,
 245                         targets: switch_targets,
 246                     }
 247                 };
 248                 self.cfg.terminate(block, self.source_info(match_start_span), terminator);
 249             }
 250
 251             TestKind::Eq { value, ty } => {
 252                 if !ty.is_scalar() {
 253                     // Use `PartialEq::eq` instead of `BinOp::Eq`
 254                     // (the binop can only handle primitives)
 255                     self.non_scalar_compare(
 256                         block,
 257                         make_target_blocks,
 258                         source_info,
 259                         value,
 260                         place,
 261                         ty,
 262                     );
 263                 } else if let [success, fail] = *make_target_blocks(self) {
 264                     assert_eq!(value.ty(), ty);
 265                     let expect = self.literal_operand(test.span, value);
 266                     let val = Operand::Copy(place);
 267                     self.compare(block, success, fail, source_info, BinOp::Eq, expect, val);
 268                 } else {
 269                     bug!("`TestKind::Eq` should have two target blocks");
 270                 }
 271             }
 272
 273             TestKind::Range(box PatRange { lo, hi, ref end }) => {
 274                 let lower_bound_success = self.cfg.start_new_block();
 275                 let target_blocks = make_target_blocks(self);
 276
 277                 // Test `val` by computing `lo <= val && val <= hi`, using primitive comparisons.
 278                 let lo = self.literal_operand(test.span, lo);
 279                 let hi = self.literal_operand(test.span, hi);
 280                 let val = Operand::Copy(place);
 281
 282                 let [success, fail] = *target_blocks else {
 283                     bug!("`TestKind::Range` should have two target blocks");
 284                 };
 285                 self.compare(
 286                     block,
 287                     lower_bound_success,
 288                     fail,
 289                     source_info,
 290                     BinOp::Le,
 291                     lo,
 292                     val.clone(),
 293                 );
 294                 let op = match *end {
 295                     RangeEnd::Included => BinOp::Le,
 296                     RangeEnd::Excluded => BinOp::Lt,
 297                 };
 298                 self.compare(lower_bound_success, success, fail, source_info, op, val, hi);
 299             }
 300
 301             TestKind::Len { len, op } => {
 302                 let target_blocks = make_target_blocks(self);
 303
 304                 let usize_ty = self.tcx.types.usize;
 305                 let actual = self.temp(usize_ty, test.span);
 306
 307                 // actual = len(place)
 308                 self.cfg.push_assign(block, source_info, actual, Rvalue::Len(place));
 309
 310                 // expected = <N>
 311                 let expected = self.push_usize(block, source_info, len);
 312
 313                 let [true_bb, false_bb] = *target_blocks else {
 314                     bug!("`TestKind::Len` should have two target blocks");
 315                 };
 316                 // result = actual == expected OR result = actual < expected
 317                 // branch based on result
 318                 self.compare(
 319                     block,
 320                     true_bb,
 321                     false_bb,
 322                     source_info,
 323                     op,
 324                     Operand::Move(actual),
 325                     Operand::Move(expected),
 326                 );
 327             }
 328         }
 329     }
 330
 331     /// Compare using the provided built-in comparison operator
 332     fn compare(
 333         &mut self,
 334         block: BasicBlock,
 335         success_block: BasicBlock,
 336         fail_block: BasicBlock,
 337         source_info: SourceInfo,
 338         op: BinOp,
 339         left: Operand<'tcx>,
 340         right: Operand<'tcx>,
 341     ) {
 342         let bool_ty = self.tcx.types.bool;
 343         let result = self.temp(bool_ty, source_info.span);
 344
 345         // result = op(left, right)
 346         self.cfg.push_assign(
 347             block,
 348             source_info,
 349             result,
 350             Rvalue::BinaryOp(op, Box::new((left, right))),
 351         );
 352
 353         // branch based on result
 354         self.cfg.terminate(
 355             block,
 356             source_info,
 357             TerminatorKind::if_(self.tcx, Operand::Move(result), success_block, fail_block),
 358         );
 359     }
 360
 361     /// Compare two `&T` values using `<T as std::compare::PartialEq>::eq`
 362     fn non_scalar_compare(
 363         &mut self,
 364         block: BasicBlock,
 365         make_target_blocks: impl FnOnce(&mut Self) -> Vec<BasicBlock>,
 366         source_info: SourceInfo,
 367         value: ConstantKind<'tcx>,
 368         place: Place<'tcx>,
 369         mut ty: Ty<'tcx>,
 370     ) {
 371         let mut expect = self.literal_operand(source_info.span, value);
 372         let mut val = Operand::Copy(place);
 373
 374         // If we're using `b"..."` as a pattern, we need to insert an
 375         // unsizing coercion, as the byte string has the type `&[u8; N]`.
 376         //
 377         // We want to do this even when the scrutinee is a reference to an
 378         // array, so we can call `<[u8]>::eq` rather than having to find an
 379         // `<[u8; N]>::eq`.
 380         let unsize = |ty: Ty<'tcx>| match ty.kind() {
 381             ty::Ref(region, rty, _) => match rty.kind() {
 382                 ty::Array(inner_ty, n) => Some((region, inner_ty, n)),
 383                 _ => None,
 384             },
 385             _ => None,
 386         };
 387         let opt_ref_ty = unsize(ty);
 388         let opt_ref_test_ty = unsize(value.ty());
 389         match (opt_ref_ty, opt_ref_test_ty) {
 390             // nothing to do, neither is an array
 391             (None, None) => {}
 392             (Some((region, elem_ty, _)), _) | (None, Some((region, elem_ty, _))) => {
 393                 let tcx = self.tcx;
 394                 // make both a slice
 395                 ty = tcx.mk_imm_ref(*region, tcx.mk_slice(*elem_ty));
 396                 if opt_ref_ty.is_some() {
 397                     let temp = self.temp(ty, source_info.span);
 398                     self.cfg.push_assign(
 399                         block,
 400                         source_info,
 401                         temp,
 402                         Rvalue::Cast(CastKind::Pointer(PointerCast::Unsize), val, ty),
 403                     );
 404                     val = Operand::Move(temp);
 405                 }
 406                 if opt_ref_test_ty.is_some() {
 407                     let slice = self.temp(ty, source_info.span);
 408                     self.cfg.push_assign(
 409                         block,
 410                         source_info,
 411                         slice,
 412                         Rvalue::Cast(CastKind::Pointer(PointerCast::Unsize), expect, ty),
 413                     );
 414                     expect = Operand::Move(slice);
 415                 }
 416             }
 417         }
 418
 419         let ty::Ref(_, deref_ty, _) = *ty.kind() else {
 420             bug!("non_scalar_compare called on non-reference type: {}", ty);
 421         };
 422
 423         let eq_def_id = self.tcx.require_lang_item(LangItem::PartialEq, None);
 424         let method = trait_method(self.tcx, eq_def_id, sym::eq, deref_ty, &[deref_ty.into()]);
 425
 426         let bool_ty = self.tcx.types.bool;
 427         let eq_result = self.temp(bool_ty, source_info.span);
 428         let eq_block = self.cfg.start_new_block();
 429         self.cfg.terminate(
 430             block,
 431             source_info,
 432             TerminatorKind::Call {
 433                 func: Operand::Constant(Box::new(Constant {
 434                     span: source_info.span,
 435
 436                     // FIXME(#54571): This constant comes from user input (a
 437                     // constant in a pattern).  Are there forms where users can add
 438                     // type annotations here?  For example, an associated constant?
 439                     // Need to experiment.
 440                     user_ty: None,
 441
 442                     literal: method,
 443                 })),
 444                 args: vec![val, expect],
 445                 destination: eq_result,
 446                 target: Some(eq_block),
 447                 cleanup: None,
 448                 from_hir_call: false,
 449                 fn_span: source_info.span,
 450             },
 451         );
 452         self.diverge_from(block);
 453
 454         let [success_block, fail_block] = *make_target_blocks(self) else {
 455             bug!("`TestKind::Eq` should have two target blocks")
 456         };
 457         // check the result
 458         self.cfg.terminate(
 459             eq_block,
 460             source_info,
 461             TerminatorKind::if_(self.tcx, Operand::Move(eq_result), success_block, fail_block),
 462         );
 463     }
 464
 465     /// Given that we are performing `test` against `test_place`, this job
 466     /// sorts out what the status of `candidate` will be after the test. See
 467     /// `test_candidates` for the usage of this function. The returned index is
 468     /// the index that this candidate should be placed in the
 469     /// `target_candidates` vec. The candidate may be modified to update its
 470     /// `match_pairs`.
 471     ///
 472     /// So, for example, if this candidate is `x @ Some(P0)` and the `Test` is
 473     /// a variant test, then we would modify the candidate to be `(x as
 474     /// Option).0 @ P0` and return the index corresponding to the variant
 475     /// `Some`.
 476     ///
 477     /// However, in some cases, the test may just not be relevant to candidate.
 478     /// For example, suppose we are testing whether `foo.x == 22`, but in one
 479     /// match arm we have `Foo { x: _, ... }`... in that case, the test for
 480     /// what value `x` has has no particular relevance to this candidate. In
 481     /// such cases, this function just returns None without doing anything.
 482     /// This is used by the overall `match_candidates` algorithm to structure
 483     /// the match as a whole. See `match_candidates` for more details.
 484     ///
 485     /// FIXME(#29623). In some cases, we have some tricky choices to make.  for
 486     /// example, if we are testing that `x == 22`, but the candidate is `x @
 487     /// 13..55`, what should we do? In the event that the test is true, we know
 488     /// that the candidate applies, but in the event of false, we don't know
 489     /// that it *doesn't* apply. For now, we return false, indicate that the
 490     /// test does not apply to this candidate, but it might be we can get
 491     /// tighter match code if we do something a bit different.
 492     pub(super) fn sort_candidate<'pat>(
 493         &mut self,
 494         test_place: &PlaceBuilder<'tcx>,
 495         test: &Test<'tcx>,
 496         candidate: &mut Candidate<'pat, 'tcx>,
 497     ) -> Option<usize> {
 498         // Find the match_pair for this place (if any). At present,
 499         // afaik, there can be at most one. (In the future, if we
 500         // adopted a more general `@` operator, there might be more
 501         // than one, but it'd be very unusual to have two sides that
 502         // both require tests; you'd expect one side to be simplified
 503         // away.)
 504         let (match_pair_index, match_pair) =
 505             candidate.match_pairs.iter().enumerate().find(|&(_, mp)| mp.place == *test_place)?;
 506
 507         match (&test.kind, &match_pair.pattern.kind) {
 508             // If we are performing a variant switch, then this
 509             // informs variant patterns, but nothing else.
 510             (
 511                 &TestKind::Switch { adt_def: tested_adt_def, .. },
 512                 &PatKind::Variant { adt_def, variant_index, ref subpatterns, .. },
 513             ) => {
 514                 assert_eq!(adt_def, tested_adt_def);
 515                 self.candidate_after_variant_switch(
 516                     match_pair_index,
 517                     adt_def,
 518                     variant_index,
 519                     subpatterns,
 520                     candidate,
 521                 );
 522                 Some(variant_index.as_usize())
 523             }
 524
 525             (&TestKind::Switch { .. }, _) => None,
 526
 527             // If we are performing a switch over integers, then this informs integer
 528             // equality, but nothing else.
 529             //
 530             // FIXME(#29623) we could use PatKind::Range to rule
 531             // things out here, in some cases.
 532             (
 533                 &TestKind::SwitchInt { switch_ty: _, ref options },
 534                 &PatKind::Constant { ref value },
 535             ) if is_switch_ty(match_pair.pattern.ty) => {
 536                 let index = options.get_index_of(value).unwrap();
 537                 self.candidate_without_match_pair(match_pair_index, candidate);
 538                 Some(index)
 539             }
 540
 541             (&TestKind::SwitchInt { switch_ty: _, ref options }, &PatKind::Range(ref range)) => {
 542                 let not_contained =
 543                     self.values_not_contained_in_range(&*range, options).unwrap_or(false);
 544
 545                 if not_contained {
 546                     // No switch values are contained in the pattern range,
 547                     // so the pattern can be matched only if this test fails.
 548                     let otherwise = options.len();
 549                     Some(otherwise)
 550                 } else {
 551                     None
 552                 }
 553             }
 554
 555             (&TestKind::SwitchInt { .. }, _) => None,
 556
 557             (
 558                 &TestKind::Len { len: test_len, op: BinOp::Eq },
 559                 &PatKind::Slice { ref prefix, ref slice, ref suffix },
 560             ) => {
 561                 let pat_len = (prefix.len() + suffix.len()) as u64;
 562                 match (test_len.cmp(&pat_len), slice) {
 563                     (Ordering::Equal, &None) => {
 564                         // on true, min_len = len = $actual_length,
 565                         // on false, len != $actual_length
 566                         self.candidate_after_slice_test(
 567                             match_pair_index,
 568                             candidate,
 569                             prefix,
 570                             slice,
 571                             suffix,
 572                         );
 573                         Some(0)
 574                     }
 575                     (Ordering::Less, _) => {
 576                         // test_len < pat_len. If $actual_len = test_len,
 577                         // then $actual_len < pat_len and we don't have
 578                         // enough elements.
 579                         Some(1)
 580                     }
 581                     (Ordering::Equal | Ordering::Greater, &Some(_)) => {
 582                         // This can match both if $actual_len = test_len >= pat_len,
 583                         // and if $actual_len > test_len. We can't advance.
 584                         None
 585                     }
 586                     (Ordering::Greater, &None) => {
 587                         // test_len != pat_len, so if $actual_len = test_len, then
 588                         // $actual_len != pat_len.
 589                         Some(1)
 590                     }
 591                 }
 592             }
 593
 594             (
 595                 &TestKind::Len { len: test_len, op: BinOp::Ge },
 596                 &PatKind::Slice { ref prefix, ref slice, ref suffix },
 597             ) => {
 598                 // the test is `$actual_len >= test_len`
 599                 let pat_len = (prefix.len() + suffix.len()) as u64;
 600                 match (test_len.cmp(&pat_len), slice) {
 601                     (Ordering::Equal, &Some(_)) => {
 602                         // $actual_len >= test_len = pat_len,
 603                         // so we can match.
 604                         self.candidate_after_slice_test(
 605                             match_pair_index,
 606                             candidate,
 607                             prefix,
 608                             slice,
 609                             suffix,
 610                         );
 611                         Some(0)
 612                     }
 613                     (Ordering::Less, _) | (Ordering::Equal, &None) => {
 614                         // test_len <= pat_len. If $actual_len < test_len,
 615                         // then it is also < pat_len, so the test passing is
 616                         // necessary (but insufficient).
 617                         Some(0)
 618                     }
 619                     (Ordering::Greater, &None) => {
 620                         // test_len > pat_len. If $actual_len >= test_len > pat_len,
 621                         // then we know we won't have a match.
 622                         Some(1)
 623                     }
 624                     (Ordering::Greater, &Some(_)) => {
 625                         // test_len < pat_len, and is therefore less
 626                         // strict. This can still go both ways.
 627                         None
 628                     }
 629                 }
 630             }
 631
 632             (&TestKind::Range(ref test), &PatKind::Range(ref pat)) => {
 633                 use std::cmp::Ordering::*;
 634
 635                 if test == pat {
 636                     self.candidate_without_match_pair(match_pair_index, candidate);
 637                     return Some(0);
 638                 }
 639
 640                 // For performance, it's important to only do the second
 641                 // `compare_const_vals` if necessary.
 642                 let no_overlap = if matches!(
 643                     (compare_const_vals(self.tcx, test.hi, pat.lo, self.param_env)?, test.end),
 644                     (Less, _) | (Equal, RangeEnd::Excluded) // test < pat
 645                 ) || matches!(
 646                     (compare_const_vals(self.tcx, test.lo, pat.hi, self.param_env)?, pat.end),
 647                     (Greater, _) | (Equal, RangeEnd::Excluded) // test > pat
 648                 ) {
 649                     Some(1)
 650                 } else {
 651                     None
 652                 };
 653
 654                 // If the testing range does not overlap with pattern range,
 655                 // the pattern can be matched only if this test fails.
 656                 no_overlap
 657             }
 658
 659             (&TestKind::Range(ref range), &PatKind::Constant { value }) => {
 660                 if let Some(false) = self.const_range_contains(&*range, value) {
 661                     // `value` is not contained in the testing range,
 662                     // so `value` can be matched only if this test fails.
 663                     Some(1)
 664                 } else {
 665                     None
 666                 }
 667             }
 668
 669             (&TestKind::Range { .. }, _) => None,
 670
 671             (&TestKind::Eq { .. } | &TestKind::Len { .. }, _) => {
 672                 // The call to `self.test(&match_pair)` below is not actually used to generate any
 673                 // MIR. Instead, we just want to compare with `test` (the parameter of the method)
 674                 // to see if it is the same.
 675                 //
 676                 // However, at this point we can still encounter or-patterns that were extracted
 677                 // from previous calls to `sort_candidate`, so we need to manually address that
 678                 // case to avoid panicking in `self.test()`.
 679                 if let PatKind::Or { .. } = &match_pair.pattern.kind {
 680                     return None;
 681                 }
 682
 683                 // These are all binary tests.
 684                 //
 685                 // FIXME(#29623) we can be more clever here
 686                 let pattern_test = self.test(&match_pair);
 687                 if pattern_test.kind == test.kind {
 688                     self.candidate_without_match_pair(match_pair_index, candidate);
 689                     Some(0)
 690                 } else {
 691                     None
 692                 }
 693             }
 694         }
 695     }
 696
 697     fn candidate_without_match_pair(
 698         &mut self,
 699         match_pair_index: usize,
 700         candidate: &mut Candidate<'_, 'tcx>,
 701     ) {
 702         candidate.match_pairs.remove(match_pair_index);
 703     }
 704
 705     fn candidate_after_slice_test<'pat>(
 706         &mut self,
 707         match_pair_index: usize,
 708         candidate: &mut Candidate<'pat, 'tcx>,
 709         prefix: &'pat [Box<Pat<'tcx>>],
 710         opt_slice: &'pat Option<Box<Pat<'tcx>>>,
 711         suffix: &'pat [Box<Pat<'tcx>>],
 712     ) {
 713         let removed_place = candidate.match_pairs.remove(match_pair_index).place;
 714         self.prefix_slice_suffix(
 715             &mut candidate.match_pairs,
 716             &removed_place,
 717             prefix,
 718             opt_slice,
 719             suffix,
 720         );
 721     }
 722
 723     fn candidate_after_variant_switch<'pat>(
 724         &mut self,
 725         match_pair_index: usize,
 726         adt_def: ty::AdtDef<'tcx>,
 727         variant_index: VariantIdx,
 728         subpatterns: &'pat [FieldPat<'tcx>],
 729         candidate: &mut Candidate<'pat, 'tcx>,
 730     ) {
 731         let match_pair = candidate.match_pairs.remove(match_pair_index);
 732
 733         // So, if we have a match-pattern like `x @ Enum::Variant(P1, P2)`,
 734         // we want to create a set of derived match-patterns like
 735         // `(x as Variant).0 @ P1` and `(x as Variant).1 @ P1`.
 736         let elem =
 737             ProjectionElem::Downcast(Some(adt_def.variant(variant_index).name), variant_index);
 738         let downcast_place = match_pair.place.project(elem); // `(x as Variant)`
 739         let consequent_match_pairs = subpatterns.iter().map(|subpattern| {
 740             // e.g., `(x as Variant).0`
 741             let place = downcast_place.clone().field(subpattern.field, subpattern.pattern.ty);
 742             // e.g., `(x as Variant).0 @ P1`
 743             MatchPair::new(place, &subpattern.pattern)
 744         });
 745
 746         candidate.match_pairs.extend(consequent_match_pairs);
 747     }
 748
 749     fn error_simplifyable<'pat>(&mut self, match_pair: &MatchPair<'pat, 'tcx>) -> ! {
 750         span_bug!(match_pair.pattern.span, "simplifyable pattern found: {:?}", match_pair.pattern)
 751     }
 752
 753     fn const_range_contains(
 754         &self,
 755         range: &PatRange<'tcx>,
 756         value: ConstantKind<'tcx>,
 757     ) -> Option<bool> {
 758         use std::cmp::Ordering::*;
 759
 760         // For performance, it's important to only do the second
 761         // `compare_const_vals` if necessary.
 762         Some(
 763             matches!(compare_const_vals(self.tcx, range.lo, value, self.param_env)?, Less | Equal)
 764                 && matches!(
 765                     (compare_const_vals(self.tcx, value, range.hi, self.param_env)?, range.end),
 766                     (Less, _) | (Equal, RangeEnd::Included)
 767                 ),
 768         )
 769     }
 770
 771     fn values_not_contained_in_range(
 772         &self,
 773         range: &PatRange<'tcx>,
 774         options: &FxIndexMap<ConstantKind<'tcx>, u128>,
 775     ) -> Option<bool> {
 776         for &val in options.keys() {
 777             if self.const_range_contains(range, val)? {
 778                 return Some(false);
 779             }
 780         }
 781
 782         Some(true)
 783     }
 784 }
 785
 786 impl Test<'_> {
 787     pub(super) fn targets(&self) -> usize {
 788         match self.kind {
 789             TestKind::Eq { .. } | TestKind::Range(_) | TestKind::Len { .. } => 2,
 790             TestKind::Switch { adt_def, .. } => {
 791                 // While the switch that we generate doesn't test for all
 792                 // variants, we have a target for each variant and the
 793                 // otherwise case, and we make sure that all of the cases not
 794                 // specified have the same block.
 795                 adt_def.variants().len() + 1
 796             }
 797             TestKind::SwitchInt { switch_ty, ref options, .. } => {
 798                 if switch_ty.is_bool() {
 799                     // `bool` is special cased in `perform_test` to always
 800                     // branch to two blocks.
 801                     2
 802                 } else {
 803                     options.len() + 1
 804                 }
 805             }
 806         }
 807     }
 808 }
 809
 810 fn is_switch_ty(ty: Ty<'_>) -> bool {
 811     ty.is_integral() || ty.is_char() || ty.is_bool()
 812 }
 813
 814 fn trait_method<'tcx>(
 815     tcx: TyCtxt<'tcx>,
 816     trait_def_id: DefId,
 817     method_name: Symbol,
 818     self_ty: Ty<'tcx>,
 819     params: &[GenericArg<'tcx>],
 820 ) -> ConstantKind<'tcx> {
 821     let substs = tcx.mk_substs_trait(self_ty, params);
 822
 823     // The unhygienic comparison here is acceptable because this is only
 824     // used on known traits.
 825     let item = tcx
 826         .associated_items(trait_def_id)
 827         .filter_by_name_unhygienic(method_name)
 828         .find(|item| item.kind == ty::AssocKind::Fn)
 829         .expect("trait method not found");
 830
 831     let method_ty = tcx.bound_type_of(item.def_id);
 832     let method_ty = method_ty.subst(tcx, substs);
 833
 834     ConstantKind::zero_sized(method_ty)
 835 }