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_target::abi::VariantIdx;
  23
  24 use std::cmp::Ordering;
  25
  26 impl<'a, 'tcx> Builder<'a, 'tcx> {
  27     /// Identifies what test is needed to decide if `match_pair` is applicable.
  28     ///
  29     /// It is a bug to call this with a not-fully-simplified pattern.
  30     pub(super) fn test<'pat>(&mut self, match_pair: &MatchPair<'pat, 'tcx>) -> Test<'tcx> {
  31         match *match_pair.pattern.kind {
  32             PatKind::Variant { ref adt_def, substs: _, variant_index: _, subpatterns: _ } => Test {
  33                 span: match_pair.pattern.span,
  34                 kind: TestKind::Switch {
  35                     adt_def,
  36                     variants: BitSet::new_empty(adt_def.variants.len()),
  37                 },
  38             },
  39
  40             PatKind::Constant { .. } if is_switch_ty(match_pair.pattern.ty) => {
  41                 // For integers, we use a `SwitchInt` match, which allows
  42                 // us to handle more cases.
  43                 Test {
  44                     span: match_pair.pattern.span,
  45                     kind: TestKind::SwitchInt {
  46                         switch_ty: match_pair.pattern.ty,
  47
  48                         // these maps are empty to start; cases are
  49                         // added below in add_cases_to_switch
  50                         options: Default::default(),
  51                     },
  52                 }
  53             }
  54
  55             PatKind::Constant { value } => Test {
  56                 span: match_pair.pattern.span,
  57                 kind: TestKind::Eq { value, ty: match_pair.pattern.ty },
  58             },
  59
  60             PatKind::Range(range) => {
  61                 assert_eq!(range.lo.ty, match_pair.pattern.ty);
  62                 assert_eq!(range.hi.ty, match_pair.pattern.ty);
  63                 Test { span: match_pair.pattern.span, kind: TestKind::Range(range) }
  64             }
  65
  66             PatKind::Slice { ref prefix, ref slice, ref suffix } => {
  67                 let len = prefix.len() + suffix.len();
  68                 let op = if slice.is_some() { BinOp::Ge } else { BinOp::Eq };
  69                 Test { span: match_pair.pattern.span, kind: TestKind::Len { len: len as u64, op } }
  70             }
  71
  72             PatKind::Or { .. } => bug!("or-patterns should have already been handled"),
  73
  74             PatKind::AscribeUserType { .. }
  75             | PatKind::Array { .. }
  76             | PatKind::Wild
  77             | PatKind::Binding { .. }
  78             | PatKind::Leaf { .. }
  79             | PatKind::Deref { .. } => self.error_simplifyable(match_pair),
  80         }
  81     }
  82
  83     pub(super) fn add_cases_to_switch<'pat>(
  84         &mut self,
  85         test_place: &PlaceBuilder<'tcx>,
  86         candidate: &Candidate<'pat, 'tcx>,
  87         switch_ty: Ty<'tcx>,
  88         options: &mut FxIndexMap<&'tcx ty::Const<'tcx>, u128>,
  89     ) -> bool {
  90         let match_pair = match candidate.match_pairs.iter().find(|mp| mp.place == *test_place) {
  91             Some(match_pair) => match_pair,
  92             _ => {
  93                 return false;
  94             }
  95         };
  96
  97         match *match_pair.pattern.kind {
  98             PatKind::Constant { value } => {
  99                 options
 100                     .entry(value)
 101                     .or_insert_with(|| value.eval_bits(self.tcx, self.param_env, switch_ty));
 102                 true
 103             }
 104             PatKind::Variant { .. } => {
 105                 panic!("you should have called add_variants_to_switch instead!");
 106             }
 107             PatKind::Range(range) => {
 108                 // Check that none of the switch values are in the range.
 109                 self.values_not_contained_in_range(range, options).unwrap_or(false)
 110             }
 111             PatKind::Slice { .. }
 112             | PatKind::Array { .. }
 113             | PatKind::Wild
 114             | PatKind::Or { .. }
 115             | PatKind::Binding { .. }
 116             | PatKind::AscribeUserType { .. }
 117             | PatKind::Leaf { .. }
 118             | PatKind::Deref { .. } => {
 119                 // don't know how to add these patterns to a switch
 120                 false
 121             }
 122         }
 123     }
 124
 125     pub(super) fn add_variants_to_switch<'pat>(
 126         &mut self,
 127         test_place: &PlaceBuilder<'tcx>,
 128         candidate: &Candidate<'pat, 'tcx>,
 129         variants: &mut BitSet<VariantIdx>,
 130     ) -> bool {
 131         let match_pair = match candidate.match_pairs.iter().find(|mp| mp.place == *test_place) {
 132             Some(match_pair) => match_pair,
 133             _ => {
 134                 return false;
 135             }
 136         };
 137
 138         match *match_pair.pattern.kind {
 139             PatKind::Variant { adt_def: _, variant_index, .. } => {
 140                 // We have a pattern testing for variant `variant_index`
 141                 // set the corresponding index to true
 142                 variants.insert(variant_index);
 143                 true
 144             }
 145             _ => {
 146                 // don't know how to add these patterns to a switch
 147                 false
 148             }
 149         }
 150     }
 151
 152     pub(super) fn perform_test(
 153         &mut self,
 154         block: BasicBlock,
 155         place_builder: PlaceBuilder<'tcx>,
 156         test: &Test<'tcx>,
 157         make_target_blocks: impl FnOnce(&mut Self) -> Vec<BasicBlock>,
 158     ) {
 159         let place: Place<'tcx>;
 160         if let Ok(test_place_builder) =
 161             place_builder.try_upvars_resolved(self.tcx, self.typeck_results)
 162         {
 163             place = test_place_builder.into_place(self.tcx, self.typeck_results);
 164         } else {
 165             return;
 166         }
 167         debug!(
 168             "perform_test({:?}, {:?}: {:?}, {:?})",
 169             block,
 170             place,
 171             place.ty(&self.local_decls, self.tcx),
 172             test
 173         );
 174
 175         let source_info = self.source_info(test.span);
 176         match test.kind {
 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();
 183                 let tcx = self.tcx;
 184                 let switch_targets = SwitchTargets::new(
 185                     adt_def.discriminants(tcx).filter_map(|(idx, discr)| {
 186                         if variants.contains(idx) {
 187                             debug_assert_ne!(
 188                                 target_blocks[idx.index()],
 189                                 otherwise_block,
 190                                 "no canididates for tested discriminant: {:?}",
 191                                 discr,
 192                             );
 193                             Some((discr.val, target_blocks[idx.index()]))
 194                         } else {
 195                             debug_assert_eq!(
 196                                 target_blocks[idx.index()],
 197                                 otherwise_block,
 198                                 "found canididates for untested discriminant: {:?}",
 199                                 discr,
 200                             );
 201                             None
 202                         }
 203                     }),
 204                     otherwise_block,
 205                 );
 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(block, source_info, discr, Rvalue::Discriminant(place));
 210                 self.cfg.terminate(
 211                     block,
 212                     source_info,
 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                     if let [first_bb, second_bb] = *target_blocks {
 226                         let (true_bb, false_bb) = match options[0] {
 227                             1 => (first_bb, second_bb),
 228                             0 => (second_bb, first_bb),
 229                             v => span_bug!(test.span, "expected boolean value but got {:?}", v),
 230                         };
 231                         TerminatorKind::if_(self.tcx, Operand::Copy(place), true_bb, false_bb)
 232                     } else {
 233                         bug!("`TestKind::SwitchInt` on `bool` should have two targets")
 234                     }
 235                 } else {
 236                     // The switch may be inexhaustive so we have a catch all block
 237                     debug_assert_eq!(options.len() + 1, target_blocks.len());
 238                     let otherwise_block = *target_blocks.last().unwrap();
 239                     let switch_targets = SwitchTargets::new(
 240                         options.values().copied().zip(target_blocks),
 241                         otherwise_block,
 242                     );
 243                     TerminatorKind::SwitchInt {
 244                         discr: Operand::Copy(place),
 245                         switch_ty,
 246                         targets: switch_targets,
 247                     }
 248                 };
 249                 self.cfg.terminate(block, source_info, terminator);
 250             }
 251
 252             TestKind::Eq { value, ty } => {
 253                 if !ty.is_scalar() {
 254                     // Use `PartialEq::eq` instead of `BinOp::Eq`
 255                     // (the binop can only handle primitives)
 256                     self.non_scalar_compare(
 257                         block,
 258                         make_target_blocks,
 259                         source_info,
 260                         value,
 261                         place,
 262                         ty,
 263                     );
 264                 } else if let [success, fail] = *make_target_blocks(self) {
 265                     assert_eq!(value.ty, ty);
 266                     let expect = self.literal_operand(test.span, value);
 267                     let val = Operand::Copy(place);
 268                     self.compare(block, success, fail, source_info, BinOp::Eq, expect, val);
 269                 } else {
 270                     bug!("`TestKind::Eq` should have two target blocks");
 271                 }
 272             }
 273
 274             TestKind::Range(PatRange { ref lo, ref hi, ref end }) => {
 275                 let lower_bound_success = self.cfg.start_new_block();
 276                 let target_blocks = make_target_blocks(self);
 277
 278                 // Test `val` by computing `lo <= val && val <= hi`, using primitive comparisons.
 279                 let lo = self.literal_operand(test.span, lo);
 280                 let hi = self.literal_operand(test.span, hi);
 281                 let val = Operand::Copy(place);
 282
 283                 if let [success, fail] = *target_blocks {
 284                     self.compare(
 285                         block,
 286                         lower_bound_success,
 287                         fail,
 288                         source_info,
 289                         BinOp::Le,
 290                         lo,
 291                         val.clone(),
 292                     );
 293                     let op = match *end {
 294                         RangeEnd::Included => BinOp::Le,
 295                         RangeEnd::Excluded => BinOp::Lt,
 296                     };
 297                     self.compare(lower_bound_success, success, fail, source_info, op, val, hi);
 298                 } else {
 299                     bug!("`TestKind::Range` should have two target blocks");
 300                 }
 301             }
 302
 303             TestKind::Len { len, op } => {
 304                 let target_blocks = make_target_blocks(self);
 305
 306                 let usize_ty = self.tcx.types.usize;
 307                 let actual = self.temp(usize_ty, test.span);
 308
 309                 // actual = len(place)
 310                 self.cfg.push_assign(block, source_info, actual, Rvalue::Len(place));
 311
 312                 // expected = <N>
 313                 let expected = self.push_usize(block, source_info, len);
 314
 315                 if let [true_bb, false_bb] = *target_blocks {
 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                 } else {
 328                     bug!("`TestKind::Len` should have two target blocks");
 329                 }
 330             }
 331         }
 332     }
 333
 334     /// Compare using the provided built-in comparison operator
 335     fn compare(
 336         &mut self,
 337         block: BasicBlock,
 338         success_block: BasicBlock,
 339         fail_block: BasicBlock,
 340         source_info: SourceInfo,
 341         op: BinOp,
 342         left: Operand<'tcx>,
 343         right: Operand<'tcx>,
 344     ) {
 345         let bool_ty = self.tcx.types.bool;
 346         let result = self.temp(bool_ty, source_info.span);
 347
 348         // result = op(left, right)
 349         self.cfg.push_assign(block, source_info, result, Rvalue::BinaryOp(op, box (left, right)));
 350
 351         // branch based on result
 352         self.cfg.terminate(
 353             block,
 354             source_info,
 355             TerminatorKind::if_(self.tcx, Operand::Move(result), success_block, fail_block),
 356         );
 357     }
 358
 359     /// Compare two `&T` values using `<T as std::compare::PartialEq>::eq`
 360     fn non_scalar_compare(
 361         &mut self,
 362         block: BasicBlock,
 363         make_target_blocks: impl FnOnce(&mut Self) -> Vec<BasicBlock>,
 364         source_info: SourceInfo,
 365         value: &'tcx ty::Const<'tcx>,
 366         place: Place<'tcx>,
 367         mut ty: Ty<'tcx>,
 368     ) {
 369         let mut expect = self.literal_operand(source_info.span, value);
 370         let mut val = Operand::Copy(place);
 371
 372         // If we're using `b"..."` as a pattern, we need to insert an
 373         // unsizing coercion, as the byte string has the type `&[u8; N]`.
 374         //
 375         // We want to do this even when the scrutinee is a reference to an
 376         // array, so we can call `<[u8]>::eq` rather than having to find an
 377         // `<[u8; N]>::eq`.
 378         let unsize = |ty: Ty<'tcx>| match ty.kind() {
 379             ty::Ref(region, rty, _) => match rty.kind() {
 380                 ty::Array(inner_ty, n) => Some((region, inner_ty, n)),
 381                 _ => None,
 382             },
 383             _ => None,
 384         };
 385         let opt_ref_ty = unsize(ty);
 386         let opt_ref_test_ty = unsize(value.ty);
 387         match (opt_ref_ty, opt_ref_test_ty) {
 388             // nothing to do, neither is an array
 389             (None, None) => {}
 390             (Some((region, elem_ty, _)), _) | (None, Some((region, elem_ty, _))) => {
 391                 let tcx = self.tcx;
 392                 // make both a slice
 393                 ty = tcx.mk_imm_ref(region, tcx.mk_slice(elem_ty));
 394                 if opt_ref_ty.is_some() {
 395                     let temp = self.temp(ty, source_info.span);
 396                     self.cfg.push_assign(
 397                         block,
 398                         source_info,
 399                         temp,
 400                         Rvalue::Cast(CastKind::Pointer(PointerCast::Unsize), val, ty),
 401                     );
 402                     val = Operand::Move(temp);
 403                 }
 404                 if opt_ref_test_ty.is_some() {
 405                     let slice = self.temp(ty, source_info.span);
 406                     self.cfg.push_assign(
 407                         block,
 408                         source_info,
 409                         slice,
 410                         Rvalue::Cast(CastKind::Pointer(PointerCast::Unsize), expect, ty),
 411                     );
 412                     expect = Operand::Move(slice);
 413                 }
 414             }
 415         }
 416
 417         let deref_ty = match *ty.kind() {
 418             ty::Ref(_, deref_ty, _) => deref_ty,
 419             _ => bug!("non_scalar_compare called on non-reference type: {}", ty),
 420         };
 421
 422         let eq_def_id = self.tcx.require_lang_item(LangItem::PartialEq, None);
 423         let method = trait_method(self.tcx, eq_def_id, sym::eq, deref_ty, &[deref_ty.into()]);
 424
 425         let bool_ty = self.tcx.types.bool;
 426         let eq_result = self.temp(bool_ty, source_info.span);
 427         let eq_block = self.cfg.start_new_block();
 428         self.cfg.terminate(
 429             block,
 430             source_info,
 431             TerminatorKind::Call {
 432                 func: Operand::Constant(box Constant {
 433                     span: source_info.span,
 434
 435                     // FIXME(#54571): This constant comes from user input (a
 436                     // constant in a pattern).  Are there forms where users can add
 437                     // type annotations here?  For example, an associated constant?
 438                     // Need to experiment.
 439                     user_ty: None,
 440
 441                     literal: method.into(),
 442                 }),
 443                 args: vec![val, expect],
 444                 destination: Some((eq_result, eq_block)),
 445                 cleanup: None,
 446                 from_hir_call: false,
 447                 fn_span: source_info.span,
 448             },
 449         );
 450         self.diverge_from(block);
 451
 452         if let [success_block, fail_block] = *make_target_blocks(self) {
 453             // check the result
 454             self.cfg.terminate(
 455                 eq_block,
 456                 source_info,
 457                 TerminatorKind::if_(self.tcx, Operand::Move(eq_result), success_block, fail_block),
 458             );
 459         } else {
 460             bug!("`TestKind::Eq` should have two target blocks")
 461         }
 462     }
 463
 464     /// Given that we are performing `test` against `test_place`, this job
 465     /// sorts out what the status of `candidate` will be after the test. See
 466     /// `test_candidates` for the usage of this function. The returned index is
 467     /// the index that this candidate should be placed in the
 468     /// `target_candidates` vec. The candidate may be modified to update its
 469     /// `match_pairs`.
 470     ///
 471     /// So, for example, if this candidate is `x @ Some(P0)` and the `Test` is
 472     /// a variant test, then we would modify the candidate to be `(x as
 473     /// Option).0 @ P0` and return the index corresponding to the variant
 474     /// `Some`.
 475     ///
 476     /// However, in some cases, the test may just not be relevant to candidate.
 477     /// For example, suppose we are testing whether `foo.x == 22`, but in one
 478     /// match arm we have `Foo { x: _, ... }`... in that case, the test for
 479     /// what value `x` has has no particular relevance to this candidate. In
 480     /// such cases, this function just returns None without doing anything.
 481     /// This is used by the overall `match_candidates` algorithm to structure
 482     /// the match as a whole. See `match_candidates` for more details.
 483     ///
 484     /// FIXME(#29623). In some cases, we have some tricky choices to make.  for
 485     /// example, if we are testing that `x == 22`, but the candidate is `x @
 486     /// 13..55`, what should we do? In the event that the test is true, we know
 487     /// that the candidate applies, but in the event of false, we don't know
 488     /// that it *doesn't* apply. For now, we return false, indicate that the
 489     /// test does not apply to this candidate, but it might be we can get
 490     /// tighter match code if we do something a bit different.
 491     pub(super) fn sort_candidate<'pat>(
 492         &mut self,
 493         test_place: &PlaceBuilder<'tcx>,
 494         test: &Test<'tcx>,
 495         candidate: &mut Candidate<'pat, 'tcx>,
 496     ) -> Option<usize> {
 497         // Find the match_pair for this place (if any). At present,
 498         // afaik, there can be at most one. (In the future, if we
 499         // adopted a more general `@` operator, there might be more
 500         // than one, but it'd be very unusual to have two sides that
 501         // both require tests; you'd expect one side to be simplified
 502         // away.)
 503         let (match_pair_index, match_pair) =
 504             candidate.match_pairs.iter().enumerate().find(|&(_, mp)| mp.place == *test_place)?;
 505
 506         match (&test.kind, &*match_pair.pattern.kind) {
 507             // If we are performing a variant switch, then this
 508             // informs variant patterns, but nothing else.
 509             (
 510                 &TestKind::Switch { adt_def: tested_adt_def, .. },
 511                 &PatKind::Variant { adt_def, variant_index, ref subpatterns, .. },
 512             ) => {
 513                 assert_eq!(adt_def, tested_adt_def);
 514                 self.candidate_after_variant_switch(
 515                     match_pair_index,
 516                     adt_def,
 517                     variant_index,
 518                     subpatterns,
 519                     candidate,
 520                 );
 521                 Some(variant_index.as_usize())
 522             }
 523
 524             (&TestKind::Switch { .. }, _) => None,
 525
 526             // If we are performing a switch over integers, then this informs integer
 527             // equality, but nothing else.
 528             //
 529             // FIXME(#29623) we could use PatKind::Range to rule
 530             // things out here, in some cases.
 531             (
 532                 &TestKind::SwitchInt { switch_ty: _, ref options },
 533                 &PatKind::Constant { ref value },
 534             ) if is_switch_ty(match_pair.pattern.ty) => {
 535                 let index = options.get_index_of(value).unwrap();
 536                 self.candidate_without_match_pair(match_pair_index, candidate);
 537                 Some(index)
 538             }
 539
 540             (&TestKind::SwitchInt { switch_ty: _, ref options }, &PatKind::Range(range)) => {
 541                 let not_contained =
 542                     self.values_not_contained_in_range(range, options).unwrap_or(false);
 543
 544                 if not_contained {
 545                     // No switch values are contained in the pattern range,
 546                     // so the pattern can be matched only if this test fails.
 547                     let otherwise = options.len();
 548                     Some(otherwise)
 549                 } else {
 550                     None
 551                 }
 552             }
 553
 554             (&TestKind::SwitchInt { .. }, _) => None,
 555
 556             (
 557                 &TestKind::Len { len: test_len, op: BinOp::Eq },
 558                 &PatKind::Slice { ref prefix, ref slice, ref suffix },
 559             ) => {
 560                 let pat_len = (prefix.len() + suffix.len()) as u64;
 561                 match (test_len.cmp(&pat_len), slice) {
 562                     (Ordering::Equal, &None) => {
 563                         // on true, min_len = len = $actual_length,
 564                         // on false, len != $actual_length
 565                         self.candidate_after_slice_test(
 566                             match_pair_index,
 567                             candidate,
 568                             prefix,
 569                             slice.as_ref(),
 570                             suffix,
 571                         );
 572                         Some(0)
 573                     }
 574                     (Ordering::Less, _) => {
 575                         // test_len < pat_len. If $actual_len = test_len,
 576                         // then $actual_len < pat_len and we don't have
 577                         // enough elements.
 578                         Some(1)
 579                     }
 580                     (Ordering::Equal | Ordering::Greater, &Some(_)) => {
 581                         // This can match both if $actual_len = test_len >= pat_len,
 582                         // and if $actual_len > test_len. We can't advance.
 583                         None
 584                     }
 585                     (Ordering::Greater, &None) => {
 586                         // test_len != pat_len, so if $actual_len = test_len, then
 587                         // $actual_len != pat_len.
 588                         Some(1)
 589                     }
 590                 }
 591             }
 592
 593             (
 594                 &TestKind::Len { len: test_len, op: BinOp::Ge },
 595                 &PatKind::Slice { ref prefix, ref slice, ref suffix },
 596             ) => {
 597                 // the test is `$actual_len >= test_len`
 598                 let pat_len = (prefix.len() + suffix.len()) as u64;
 599                 match (test_len.cmp(&pat_len), slice) {
 600                     (Ordering::Equal, &Some(_)) => {
 601                         // $actual_len >= test_len = pat_len,
 602                         // so we can match.
 603                         self.candidate_after_slice_test(
 604                             match_pair_index,
 605                             candidate,
 606                             prefix,
 607                             slice.as_ref(),
 608                             suffix,
 609                         );
 610                         Some(0)
 611                     }
 612                     (Ordering::Less, _) | (Ordering::Equal, &None) => {
 613                         // test_len <= pat_len. If $actual_len < test_len,
 614                         // then it is also < pat_len, so the test passing is
 615                         // necessary (but insufficient).
 616                         Some(0)
 617                     }
 618                     (Ordering::Greater, &None) => {
 619                         // test_len > pat_len. If $actual_len >= test_len > pat_len,
 620                         // then we know we won't have a match.
 621                         Some(1)
 622                     }
 623                     (Ordering::Greater, &Some(_)) => {
 624                         // test_len < pat_len, and is therefore less
 625                         // strict. This can still go both ways.
 626                         None
 627                     }
 628                 }
 629             }
 630
 631             (&TestKind::Range(test), &PatKind::Range(pat)) => {
 632                 if test == pat {
 633                     self.candidate_without_match_pair(match_pair_index, candidate);
 634                     return Some(0);
 635                 }
 636
 637                 let no_overlap = (|| {
 638                     use rustc_hir::RangeEnd::*;
 639                     use std::cmp::Ordering::*;
 640
 641                     let tcx = self.tcx;
 642
 643                     let test_ty = test.lo.ty;
 644                     let lo = compare_const_vals(tcx, test.lo, pat.hi, self.param_env, test_ty)?;
 645                     let hi = compare_const_vals(tcx, test.hi, pat.lo, self.param_env, test_ty)?;
 646
 647                     match (test.end, pat.end, lo, hi) {
 648                         // pat < test
 649                         (_, _, Greater, _) |
 650                         (_, Excluded, Equal, _) |
 651                         // pat > test
 652                         (_, _, _, Less) |
 653                         (Excluded, _, _, Equal) => Some(true),
 654                         _ => Some(false),
 655                     }
 656                 })();
 657
 658                 if let Some(true) = no_overlap {
 659                     // Testing range does not overlap with pattern range,
 660                     // so the pattern can be matched only if this test fails.
 661                     Some(1)
 662                 } else {
 663                     None
 664                 }
 665             }
 666
 667             (&TestKind::Range(range), &PatKind::Constant { value }) => {
 668                 if let Some(false) = self.const_range_contains(range, value) {
 669                     // `value` is not contained in the testing range,
 670                     // so `value` can be matched only if this test fails.
 671                     Some(1)
 672                 } else {
 673                     None
 674                 }
 675             }
 676
 677             (&TestKind::Range { .. }, _) => None,
 678
 679             (&TestKind::Eq { .. } | &TestKind::Len { .. }, _) => {
 680                 // The call to `self.test(&match_pair)` below is not actually used to generate any
 681                 // MIR. Instead, we just want to compare with `test` (the parameter of the method)
 682                 // to see if it is the same.
 683                 //
 684                 // However, at this point we can still encounter or-patterns that were extracted
 685                 // from previous calls to `sort_candidate`, so we need to manually address that
 686                 // case to avoid panicking in `self.test()`.
 687                 if let PatKind::Or { .. } = &*match_pair.pattern.kind {
 688                     return None;
 689                 }
 690
 691                 // These are all binary tests.
 692                 //
 693                 // FIXME(#29623) we can be more clever here
 694                 let pattern_test = self.test(&match_pair);
 695                 if pattern_test.kind == test.kind {
 696                     self.candidate_without_match_pair(match_pair_index, candidate);
 697                     Some(0)
 698                 } else {
 699                     None
 700                 }
 701             }
 702         }
 703     }
 704
 705     fn candidate_without_match_pair(
 706         &mut self,
 707         match_pair_index: usize,
 708         candidate: &mut Candidate<'_, 'tcx>,
 709     ) {
 710         candidate.match_pairs.remove(match_pair_index);
 711     }
 712
 713     fn candidate_after_slice_test<'pat>(
 714         &mut self,
 715         match_pair_index: usize,
 716         candidate: &mut Candidate<'pat, 'tcx>,
 717         prefix: &'pat [Pat<'tcx>],
 718         opt_slice: Option<&'pat Pat<'tcx>>,
 719         suffix: &'pat [Pat<'tcx>],
 720     ) {
 721         let removed_place = candidate.match_pairs.remove(match_pair_index).place;
 722         self.prefix_slice_suffix(
 723             &mut candidate.match_pairs,
 724             &removed_place,
 725             prefix,
 726             opt_slice,
 727             suffix,
 728         );
 729     }
 730
 731     fn candidate_after_variant_switch<'pat>(
 732         &mut self,
 733         match_pair_index: usize,
 734         adt_def: &'tcx ty::AdtDef,
 735         variant_index: VariantIdx,
 736         subpatterns: &'pat [FieldPat<'tcx>],
 737         candidate: &mut Candidate<'pat, 'tcx>,
 738     ) {
 739         let match_pair = candidate.match_pairs.remove(match_pair_index);
 740
 741         // So, if we have a match-pattern like `x @ Enum::Variant(P1, P2)`,
 742         // we want to create a set of derived match-patterns like
 743         // `(x as Variant).0 @ P1` and `(x as Variant).1 @ P1`.
 744         let elem = ProjectionElem::Downcast(
 745             Some(adt_def.variants[variant_index].ident.name),
 746             variant_index,
 747         );
 748         let downcast_place = match_pair.place.project(elem); // `(x as Variant)`
 749         let consequent_match_pairs = subpatterns.iter().map(|subpattern| {
 750             // e.g., `(x as Variant).0`
 751             let place = downcast_place.clone().field(subpattern.field, subpattern.pattern.ty);
 752             // e.g., `(x as Variant).0 @ P1`
 753             MatchPair::new(place, &subpattern.pattern)
 754         });
 755
 756         candidate.match_pairs.extend(consequent_match_pairs);
 757     }
 758
 759     fn error_simplifyable<'pat>(&mut self, match_pair: &MatchPair<'pat, 'tcx>) -> ! {
 760         span_bug!(match_pair.pattern.span, "simplifyable pattern found: {:?}", match_pair.pattern)
 761     }
 762
 763     fn const_range_contains(
 764         &self,
 765         range: PatRange<'tcx>,
 766         value: &'tcx ty::Const<'tcx>,
 767     ) -> Option<bool> {
 768         use std::cmp::Ordering::*;
 769
 770         let tcx = self.tcx;
 771
 772         let a = compare_const_vals(tcx, range.lo, value, self.param_env, range.lo.ty)?;
 773         let b = compare_const_vals(tcx, value, range.hi, self.param_env, range.lo.ty)?;
 774
 775         match (b, range.end) {
 776             (Less, _) | (Equal, RangeEnd::Included) if a != Greater => Some(true),
 777             _ => Some(false),
 778         }
 779     }
 780
 781     fn values_not_contained_in_range(
 782         &self,
 783         range: PatRange<'tcx>,
 784         options: &FxIndexMap<&'tcx ty::Const<'tcx>, u128>,
 785     ) -> Option<bool> {
 786         for &val in options.keys() {
 787             if self.const_range_contains(range, val)? {
 788                 return Some(false);
 789             }
 790         }
 791
 792         Some(true)
 793     }
 794 }
 795
 796 impl Test<'_> {
 797     pub(super) fn targets(&self) -> usize {
 798         match self.kind {
 799             TestKind::Eq { .. } | TestKind::Range(_) | TestKind::Len { .. } => 2,
 800             TestKind::Switch { adt_def, .. } => {
 801                 // While the switch that we generate doesn't test for all
 802                 // variants, we have a target for each variant and the
 803                 // otherwise case, and we make sure that all of the cases not
 804                 // specified have the same block.
 805                 adt_def.variants.len() + 1
 806             }
 807             TestKind::SwitchInt { switch_ty, ref options, .. } => {
 808                 if switch_ty.is_bool() {
 809                     // `bool` is special cased in `perform_test` to always
 810                     // branch to two blocks.
 811                     2
 812                 } else {
 813                     options.len() + 1
 814                 }
 815             }
 816         }
 817     }
 818 }
 819
 820 fn is_switch_ty(ty: Ty<'_>) -> bool {
 821     ty.is_integral() || ty.is_char() || ty.is_bool()
 822 }
 823
 824 fn trait_method<'tcx>(
 825     tcx: TyCtxt<'tcx>,
 826     trait_def_id: DefId,
 827     method_name: Symbol,
 828     self_ty: Ty<'tcx>,
 829     params: &[GenericArg<'tcx>],
 830 ) -> &'tcx ty::Const<'tcx> {
 831     let substs = tcx.mk_substs_trait(self_ty, params);
 832
 833     // The unhygienic comparison here is acceptable because this is only
 834     // used on known traits.
 835     let item = tcx
 836         .associated_items(trait_def_id)
 837         .filter_by_name_unhygienic(method_name)
 838         .find(|item| item.kind == ty::AssocKind::Fn)
 839         .expect("trait method not found");
 840
 841     let method_ty = tcx.type_of(item.def_id);
 842     let method_ty = method_ty.subst(tcx, substs);
 843     ty::Const::zero_sized(tcx, method_ty)
 844 }