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::util::IntTypeExt;
  18 use rustc_middle::ty::GenericArg;
  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     #[instrument(skip(self, make_target_blocks, place_builder), level = "debug")]
 148     pub(super) fn perform_test(
 149         &mut self,
 150         match_start_span: Span,
 151         scrutinee_span: Span,
 152         block: BasicBlock,
 153         place_builder: &PlaceBuilder<'tcx>,
 154         test: &Test<'tcx>,
 155         make_target_blocks: impl FnOnce(&mut Self) -> Vec<BasicBlock>,
 156     ) {
 157         let place = place_builder.to_place(self);
 158         let place_ty = place.ty(&self.local_decls, self.tcx);
 159         debug!(?place, ?place_ty,);
 160
 161         let source_info = self.source_info(test.span);
 162         match test.kind {
 163             TestKind::Switch { adt_def, ref variants } => {
 164                 let target_blocks = make_target_blocks(self);
 165                 // Variants is a BitVec of indexes into adt_def.variants.
 166                 let num_enum_variants = adt_def.variants().len();
 167                 debug_assert_eq!(target_blocks.len(), num_enum_variants + 1);
 168                 let otherwise_block = *target_blocks.last().unwrap();
 169                 let tcx = self.tcx;
 170                 let switch_targets = SwitchTargets::new(
 171                     adt_def.discriminants(tcx).filter_map(|(idx, discr)| {
 172                         if variants.contains(idx) {
 173                             debug_assert_ne!(
 174                                 target_blocks[idx.index()],
 175                                 otherwise_block,
 176                                 "no canididates for tested discriminant: {:?}",
 177                                 discr,
 178                             );
 179                             Some((discr.val, target_blocks[idx.index()]))
 180                         } else {
 181                             debug_assert_eq!(
 182                                 target_blocks[idx.index()],
 183                                 otherwise_block,
 184                                 "found canididates for untested discriminant: {:?}",
 185                                 discr,
 186                             );
 187                             None
 188                         }
 189                     }),
 190                     otherwise_block,
 191                 );
 192                 debug!("num_enum_variants: {}, variants: {:?}", num_enum_variants, variants);
 193                 let discr_ty = adt_def.repr().discr_type().to_ty(tcx);
 194                 let discr = self.temp(discr_ty, test.span);
 195                 self.cfg.push_assign(
 196                     block,
 197                     self.source_info(scrutinee_span),
 198                     discr,
 199                     Rvalue::Discriminant(place),
 200                 );
 201                 self.cfg.terminate(
 202                     block,
 203                     self.source_info(match_start_span),
 204                     TerminatorKind::SwitchInt {
 205                         discr: Operand::Move(discr),
 206                         targets: switch_targets,
 207                     },
 208                 );
 209             }
 210
 211             TestKind::SwitchInt { switch_ty, ref options } => {
 212                 let target_blocks = make_target_blocks(self);
 213                 let terminator = if *switch_ty.kind() == ty::Bool {
 214                     assert!(!options.is_empty() && options.len() <= 2);
 215                     let [first_bb, second_bb] = *target_blocks else {
 216                         bug!("`TestKind::SwitchInt` on `bool` should have two targets")
 217                     };
 218                     let (true_bb, false_bb) = match options[0] {
 219                         1 => (first_bb, second_bb),
 220                         0 => (second_bb, first_bb),
 221                         v => span_bug!(test.span, "expected boolean value but got {:?}", v),
 222                     };
 223                     TerminatorKind::if_(Operand::Copy(place), true_bb, false_bb)
 224                 } else {
 225                     // The switch may be inexhaustive so we have a catch all block
 226                     debug_assert_eq!(options.len() + 1, target_blocks.len());
 227                     let otherwise_block = *target_blocks.last().unwrap();
 228                     let switch_targets = SwitchTargets::new(
 229                         options.values().copied().zip(target_blocks),
 230                         otherwise_block,
 231                     );
 232                     TerminatorKind::SwitchInt {
 233                         discr: Operand::Copy(place),
 234                         targets: switch_targets,
 235                     }
 236                 };
 237                 self.cfg.terminate(block, self.source_info(match_start_span), terminator);
 238             }
 239
 240             TestKind::Eq { value, ty } => {
 241                 let tcx = self.tcx;
 242                 if let ty::Adt(def, _) = ty.kind() && Some(def.did()) == tcx.lang_items().string() {
 243                     if !tcx.features().string_deref_patterns {
 244                         bug!("matching on `String` went through without enabling string_deref_patterns");
 245                     }
 246                     let re_erased = tcx.lifetimes.re_erased;
 247                     let ref_string = self.temp(tcx.mk_imm_ref(re_erased, ty), test.span);
 248                     let ref_str_ty = tcx.mk_imm_ref(re_erased, tcx.types.str_);
 249                     let ref_str = self.temp(ref_str_ty, test.span);
 250                     let deref = tcx.require_lang_item(LangItem::Deref, None);
 251                     let method = trait_method(tcx, deref, sym::deref, [ty]);
 252                     let eq_block = self.cfg.start_new_block();
 253                     self.cfg.push_assign(block, source_info, ref_string, Rvalue::Ref(re_erased, BorrowKind::Shared, place));
 254                     self.cfg.terminate(
 255                         block,
 256                         source_info,
 257                         TerminatorKind::Call {
 258                             func: Operand::Constant(Box::new(Constant {
 259                                 span: test.span,
 260                                 user_ty: None,
 261                                 literal: method,
 262                             })),
 263                             args: vec![Operand::Move(ref_string)],
 264                             destination: ref_str,
 265                             target: Some(eq_block),
 266                             cleanup: None,
 267                             from_hir_call: false,
 268                             fn_span: source_info.span
 269                         }
 270                     );
 271                     self.non_scalar_compare(eq_block, make_target_blocks, source_info, value, ref_str, ref_str_ty);
 272                     return;
 273                 }
 274                 if !ty.is_scalar() {
 275                     // Use `PartialEq::eq` instead of `BinOp::Eq`
 276                     // (the binop can only handle primitives)
 277                     self.non_scalar_compare(
 278                         block,
 279                         make_target_blocks,
 280                         source_info,
 281                         value,
 282                         place,
 283                         ty,
 284                     );
 285                 } else if let [success, fail] = *make_target_blocks(self) {
 286                     assert_eq!(value.ty(), ty);
 287                     let expect = self.literal_operand(test.span, value);
 288                     let val = Operand::Copy(place);
 289                     self.compare(block, success, fail, source_info, BinOp::Eq, expect, val);
 290                 } else {
 291                     bug!("`TestKind::Eq` should have two target blocks");
 292                 }
 293             }
 294
 295             TestKind::Range(box PatRange { lo, hi, ref end }) => {
 296                 let lower_bound_success = self.cfg.start_new_block();
 297                 let target_blocks = make_target_blocks(self);
 298
 299                 // Test `val` by computing `lo <= val && val <= hi`, using primitive comparisons.
 300                 let lo = self.literal_operand(test.span, lo);
 301                 let hi = self.literal_operand(test.span, hi);
 302                 let val = Operand::Copy(place);
 303
 304                 let [success, fail] = *target_blocks else {
 305                     bug!("`TestKind::Range` should have two target blocks");
 306                 };
 307                 self.compare(
 308                     block,
 309                     lower_bound_success,
 310                     fail,
 311                     source_info,
 312                     BinOp::Le,
 313                     lo,
 314                     val.clone(),
 315                 );
 316                 let op = match *end {
 317                     RangeEnd::Included => BinOp::Le,
 318                     RangeEnd::Excluded => BinOp::Lt,
 319                 };
 320                 self.compare(lower_bound_success, success, fail, source_info, op, val, hi);
 321             }
 322
 323             TestKind::Len { len, op } => {
 324                 let target_blocks = make_target_blocks(self);
 325
 326                 let usize_ty = self.tcx.types.usize;
 327                 let actual = self.temp(usize_ty, test.span);
 328
 329                 // actual = len(place)
 330                 self.cfg.push_assign(block, source_info, actual, Rvalue::Len(place));
 331
 332                 // expected = <N>
 333                 let expected = self.push_usize(block, source_info, len);
 334
 335                 let [true_bb, false_bb] = *target_blocks else {
 336                     bug!("`TestKind::Len` should have two target blocks");
 337                 };
 338                 // result = actual == expected OR result = actual < expected
 339                 // branch based on result
 340                 self.compare(
 341                     block,
 342                     true_bb,
 343                     false_bb,
 344                     source_info,
 345                     op,
 346                     Operand::Move(actual),
 347                     Operand::Move(expected),
 348                 );
 349             }
 350         }
 351     }
 352
 353     /// Compare using the provided built-in comparison operator
 354     fn compare(
 355         &mut self,
 356         block: BasicBlock,
 357         success_block: BasicBlock,
 358         fail_block: BasicBlock,
 359         source_info: SourceInfo,
 360         op: BinOp,
 361         left: Operand<'tcx>,
 362         right: Operand<'tcx>,
 363     ) {
 364         let bool_ty = self.tcx.types.bool;
 365         let result = self.temp(bool_ty, source_info.span);
 366
 367         // result = op(left, right)
 368         self.cfg.push_assign(
 369             block,
 370             source_info,
 371             result,
 372             Rvalue::BinaryOp(op, Box::new((left, right))),
 373         );
 374
 375         // branch based on result
 376         self.cfg.terminate(
 377             block,
 378             source_info,
 379             TerminatorKind::if_(Operand::Move(result), success_block, fail_block),
 380         );
 381     }
 382
 383     /// Compare two `&T` values using `<T as std::compare::PartialEq>::eq`
 384     fn non_scalar_compare(
 385         &mut self,
 386         block: BasicBlock,
 387         make_target_blocks: impl FnOnce(&mut Self) -> Vec<BasicBlock>,
 388         source_info: SourceInfo,
 389         value: ConstantKind<'tcx>,
 390         place: Place<'tcx>,
 391         mut ty: Ty<'tcx>,
 392     ) {
 393         let mut expect = self.literal_operand(source_info.span, value);
 394         let mut val = Operand::Copy(place);
 395
 396         // If we're using `b"..."` as a pattern, we need to insert an
 397         // unsizing coercion, as the byte string has the type `&[u8; N]`.
 398         //
 399         // We want to do this even when the scrutinee is a reference to an
 400         // array, so we can call `<[u8]>::eq` rather than having to find an
 401         // `<[u8; N]>::eq`.
 402         let unsize = |ty: Ty<'tcx>| match ty.kind() {
 403             ty::Ref(region, rty, _) => match rty.kind() {
 404                 ty::Array(inner_ty, n) => Some((region, inner_ty, n)),
 405                 _ => None,
 406             },
 407             _ => None,
 408         };
 409         let opt_ref_ty = unsize(ty);
 410         let opt_ref_test_ty = unsize(value.ty());
 411         match (opt_ref_ty, opt_ref_test_ty) {
 412             // nothing to do, neither is an array
 413             (None, None) => {}
 414             (Some((region, elem_ty, _)), _) | (None, Some((region, elem_ty, _))) => {
 415                 let tcx = self.tcx;
 416                 // make both a slice
 417                 ty = tcx.mk_imm_ref(*region, tcx.mk_slice(*elem_ty));
 418                 if opt_ref_ty.is_some() {
 419                     let temp = self.temp(ty, source_info.span);
 420                     self.cfg.push_assign(
 421                         block,
 422                         source_info,
 423                         temp,
 424                         Rvalue::Cast(CastKind::Pointer(PointerCast::Unsize), val, ty),
 425                     );
 426                     val = Operand::Move(temp);
 427                 }
 428                 if opt_ref_test_ty.is_some() {
 429                     let slice = self.temp(ty, source_info.span);
 430                     self.cfg.push_assign(
 431                         block,
 432                         source_info,
 433                         slice,
 434                         Rvalue::Cast(CastKind::Pointer(PointerCast::Unsize), expect, ty),
 435                     );
 436                     expect = Operand::Move(slice);
 437                 }
 438             }
 439         }
 440
 441         let ty::Ref(_, deref_ty, _) = *ty.kind() else {
 442             bug!("non_scalar_compare called on non-reference type: {}", ty);
 443         };
 444
 445         let eq_def_id = self.tcx.require_lang_item(LangItem::PartialEq, Some(source_info.span));
 446         let method = trait_method(self.tcx, eq_def_id, sym::eq, [deref_ty, deref_ty]);
 447
 448         let bool_ty = self.tcx.types.bool;
 449         let eq_result = self.temp(bool_ty, source_info.span);
 450         let eq_block = self.cfg.start_new_block();
 451         self.cfg.terminate(
 452             block,
 453             source_info,
 454             TerminatorKind::Call {
 455                 func: Operand::Constant(Box::new(Constant {
 456                     span: source_info.span,
 457
 458                     // FIXME(#54571): This constant comes from user input (a
 459                     // constant in a pattern). Are there forms where users can add
 460                     // type annotations here?  For example, an associated constant?
 461                     // Need to experiment.
 462                     user_ty: None,
 463
 464                     literal: method,
 465                 })),
 466                 args: vec![val, expect],
 467                 destination: eq_result,
 468                 target: Some(eq_block),
 469                 cleanup: None,
 470                 from_hir_call: false,
 471                 fn_span: source_info.span,
 472             },
 473         );
 474         self.diverge_from(block);
 475
 476         let [success_block, fail_block] = *make_target_blocks(self) else {
 477             bug!("`TestKind::Eq` should have two target blocks")
 478         };
 479         // check the result
 480         self.cfg.terminate(
 481             eq_block,
 482             source_info,
 483             TerminatorKind::if_(Operand::Move(eq_result), success_block, fail_block),
 484         );
 485     }
 486
 487     /// Given that we are performing `test` against `test_place`, this job
 488     /// sorts out what the status of `candidate` will be after the test. See
 489     /// `test_candidates` for the usage of this function. The returned index is
 490     /// the index that this candidate should be placed in the
 491     /// `target_candidates` vec. The candidate may be modified to update its
 492     /// `match_pairs`.
 493     ///
 494     /// So, for example, if this candidate is `x @ Some(P0)` and the `Test` is
 495     /// a variant test, then we would modify the candidate to be `(x as
 496     /// Option).0 @ P0` and return the index corresponding to the variant
 497     /// `Some`.
 498     ///
 499     /// However, in some cases, the test may just not be relevant to candidate.
 500     /// For example, suppose we are testing whether `foo.x == 22`, but in one
 501     /// match arm we have `Foo { x: _, ... }`... in that case, the test for
 502     /// what value `x` has has no particular relevance to this candidate. In
 503     /// such cases, this function just returns None without doing anything.
 504     /// This is used by the overall `match_candidates` algorithm to structure
 505     /// the match as a whole. See `match_candidates` for more details.
 506     ///
 507     /// FIXME(#29623). In some cases, we have some tricky choices to make. for
 508     /// example, if we are testing that `x == 22`, but the candidate is `x @
 509     /// 13..55`, what should we do? In the event that the test is true, we know
 510     /// that the candidate applies, but in the event of false, we don't know
 511     /// that it *doesn't* apply. For now, we return false, indicate that the
 512     /// test does not apply to this candidate, but it might be we can get
 513     /// tighter match code if we do something a bit different.
 514     pub(super) fn sort_candidate<'pat>(
 515         &mut self,
 516         test_place: &PlaceBuilder<'tcx>,
 517         test: &Test<'tcx>,
 518         candidate: &mut Candidate<'pat, 'tcx>,
 519     ) -> Option<usize> {
 520         // Find the match_pair for this place (if any). At present,
 521         // afaik, there can be at most one. (In the future, if we
 522         // adopted a more general `@` operator, there might be more
 523         // than one, but it'd be very unusual to have two sides that
 524         // both require tests; you'd expect one side to be simplified
 525         // away.)
 526         let (match_pair_index, match_pair) =
 527             candidate.match_pairs.iter().enumerate().find(|&(_, mp)| mp.place == *test_place)?;
 528
 529         match (&test.kind, &match_pair.pattern.kind) {
 530             // If we are performing a variant switch, then this
 531             // informs variant patterns, but nothing else.
 532             (
 533                 &TestKind::Switch { adt_def: tested_adt_def, .. },
 534                 &PatKind::Variant { adt_def, variant_index, ref subpatterns, .. },
 535             ) => {
 536                 assert_eq!(adt_def, tested_adt_def);
 537                 self.candidate_after_variant_switch(
 538                     match_pair_index,
 539                     adt_def,
 540                     variant_index,
 541                     subpatterns,
 542                     candidate,
 543                 );
 544                 Some(variant_index.as_usize())
 545             }
 546
 547             (&TestKind::Switch { .. }, _) => None,
 548
 549             // If we are performing a switch over integers, then this informs integer
 550             // equality, but nothing else.
 551             //
 552             // FIXME(#29623) we could use PatKind::Range to rule
 553             // things out here, in some cases.
 554             (TestKind::SwitchInt { switch_ty: _, options }, PatKind::Constant { value })
 555                 if is_switch_ty(match_pair.pattern.ty) =>
 556             {
 557                 let index = options.get_index_of(value).unwrap();
 558                 self.candidate_without_match_pair(match_pair_index, candidate);
 559                 Some(index)
 560             }
 561
 562             (TestKind::SwitchInt { switch_ty: _, options }, PatKind::Range(range)) => {
 563                 let not_contained =
 564                     self.values_not_contained_in_range(&*range, options).unwrap_or(false);
 565
 566                 if not_contained {
 567                     // No switch values are contained in the pattern range,
 568                     // so the pattern can be matched only if this test fails.
 569                     let otherwise = options.len();
 570                     Some(otherwise)
 571                 } else {
 572                     None
 573                 }
 574             }
 575
 576             (&TestKind::SwitchInt { .. }, _) => None,
 577
 578             (
 579                 &TestKind::Len { len: test_len, op: BinOp::Eq },
 580                 PatKind::Slice { prefix, slice, suffix },
 581             ) => {
 582                 let pat_len = (prefix.len() + suffix.len()) as u64;
 583                 match (test_len.cmp(&pat_len), slice) {
 584                     (Ordering::Equal, &None) => {
 585                         // on true, min_len = len = $actual_length,
 586                         // on false, len != $actual_length
 587                         self.candidate_after_slice_test(
 588                             match_pair_index,
 589                             candidate,
 590                             prefix,
 591                             slice,
 592                             suffix,
 593                         );
 594                         Some(0)
 595                     }
 596                     (Ordering::Less, _) => {
 597                         // test_len < pat_len. If $actual_len = test_len,
 598                         // then $actual_len < pat_len and we don't have
 599                         // enough elements.
 600                         Some(1)
 601                     }
 602                     (Ordering::Equal | Ordering::Greater, &Some(_)) => {
 603                         // This can match both if $actual_len = test_len >= pat_len,
 604                         // and if $actual_len > test_len. We can't advance.
 605                         None
 606                     }
 607                     (Ordering::Greater, &None) => {
 608                         // test_len != pat_len, so if $actual_len = test_len, then
 609                         // $actual_len != pat_len.
 610                         Some(1)
 611                     }
 612                 }
 613             }
 614
 615             (
 616                 &TestKind::Len { len: test_len, op: BinOp::Ge },
 617                 PatKind::Slice { prefix, slice, suffix },
 618             ) => {
 619                 // the test is `$actual_len >= test_len`
 620                 let pat_len = (prefix.len() + suffix.len()) as u64;
 621                 match (test_len.cmp(&pat_len), slice) {
 622                     (Ordering::Equal, &Some(_)) => {
 623                         // $actual_len >= test_len = pat_len,
 624                         // so we can match.
 625                         self.candidate_after_slice_test(
 626                             match_pair_index,
 627                             candidate,
 628                             prefix,
 629                             slice,
 630                             suffix,
 631                         );
 632                         Some(0)
 633                     }
 634                     (Ordering::Less, _) | (Ordering::Equal, &None) => {
 635                         // test_len <= pat_len. If $actual_len < test_len,
 636                         // then it is also < pat_len, so the test passing is
 637                         // necessary (but insufficient).
 638                         Some(0)
 639                     }
 640                     (Ordering::Greater, &None) => {
 641                         // test_len > pat_len. If $actual_len >= test_len > pat_len,
 642                         // then we know we won't have a match.
 643                         Some(1)
 644                     }
 645                     (Ordering::Greater, &Some(_)) => {
 646                         // test_len < pat_len, and is therefore less
 647                         // strict. This can still go both ways.
 648                         None
 649                     }
 650                 }
 651             }
 652
 653             (TestKind::Range(test), PatKind::Range(pat)) => {
 654                 use std::cmp::Ordering::*;
 655
 656                 if test == pat {
 657                     self.candidate_without_match_pair(match_pair_index, candidate);
 658                     return Some(0);
 659                 }
 660
 661                 // For performance, it's important to only do the second
 662                 // `compare_const_vals` if necessary.
 663                 let no_overlap = if matches!(
 664                     (compare_const_vals(self.tcx, test.hi, pat.lo, self.param_env)?, test.end),
 665                     (Less, _) | (Equal, RangeEnd::Excluded) // test < pat
 666                 ) || matches!(
 667                     (compare_const_vals(self.tcx, test.lo, pat.hi, self.param_env)?, pat.end),
 668                     (Greater, _) | (Equal, RangeEnd::Excluded) // test > pat
 669                 ) {
 670                     Some(1)
 671                 } else {
 672                     None
 673                 };
 674
 675                 // If the testing range does not overlap with pattern range,
 676                 // the pattern can be matched only if this test fails.
 677                 no_overlap
 678             }
 679
 680             (TestKind::Range(range), &PatKind::Constant { value }) => {
 681                 if let Some(false) = self.const_range_contains(&*range, value) {
 682                     // `value` is not contained in the testing range,
 683                     // so `value` can be matched only if this test fails.
 684                     Some(1)
 685                 } else {
 686                     None
 687                 }
 688             }
 689
 690             (&TestKind::Range { .. }, _) => None,
 691
 692             (&TestKind::Eq { .. } | &TestKind::Len { .. }, _) => {
 693                 // The call to `self.test(&match_pair)` below is not actually used to generate any
 694                 // MIR. Instead, we just want to compare with `test` (the parameter of the method)
 695                 // to see if it is the same.
 696                 //
 697                 // However, at this point we can still encounter or-patterns that were extracted
 698                 // from previous calls to `sort_candidate`, so we need to manually address that
 699                 // case to avoid panicking in `self.test()`.
 700                 if let PatKind::Or { .. } = &match_pair.pattern.kind {
 701                     return None;
 702                 }
 703
 704                 // These are all binary tests.
 705                 //
 706                 // FIXME(#29623) we can be more clever here
 707                 let pattern_test = self.test(&match_pair);
 708                 if pattern_test.kind == test.kind {
 709                     self.candidate_without_match_pair(match_pair_index, candidate);
 710                     Some(0)
 711                 } else {
 712                     None
 713                 }
 714             }
 715         }
 716     }
 717
 718     fn candidate_without_match_pair(
 719         &mut self,
 720         match_pair_index: usize,
 721         candidate: &mut Candidate<'_, 'tcx>,
 722     ) {
 723         candidate.match_pairs.remove(match_pair_index);
 724     }
 725
 726     fn candidate_after_slice_test<'pat>(
 727         &mut self,
 728         match_pair_index: usize,
 729         candidate: &mut Candidate<'pat, 'tcx>,
 730         prefix: &'pat [Box<Pat<'tcx>>],
 731         opt_slice: &'pat Option<Box<Pat<'tcx>>>,
 732         suffix: &'pat [Box<Pat<'tcx>>],
 733     ) {
 734         let removed_place = candidate.match_pairs.remove(match_pair_index).place;
 735         self.prefix_slice_suffix(
 736             &mut candidate.match_pairs,
 737             &removed_place,
 738             prefix,
 739             opt_slice,
 740             suffix,
 741         );
 742     }
 743
 744     fn candidate_after_variant_switch<'pat>(
 745         &mut self,
 746         match_pair_index: usize,
 747         adt_def: ty::AdtDef<'tcx>,
 748         variant_index: VariantIdx,
 749         subpatterns: &'pat [FieldPat<'tcx>],
 750         candidate: &mut Candidate<'pat, 'tcx>,
 751     ) {
 752         let match_pair = candidate.match_pairs.remove(match_pair_index);
 753
 754         // So, if we have a match-pattern like `x @ Enum::Variant(P1, P2)`,
 755         // we want to create a set of derived match-patterns like
 756         // `(x as Variant).0 @ P1` and `(x as Variant).1 @ P1`.
 757         let downcast_place = match_pair.place.downcast(adt_def, variant_index); // `(x as Variant)`
 758         let consequent_match_pairs = subpatterns.iter().map(|subpattern| {
 759             // e.g., `(x as Variant).0`
 760             let place = downcast_place
 761                 .clone_project(PlaceElem::Field(subpattern.field, subpattern.pattern.ty));
 762             // e.g., `(x as Variant).0 @ P1`
 763             MatchPair::new(place, &subpattern.pattern, self)
 764         });
 765
 766         candidate.match_pairs.extend(consequent_match_pairs);
 767     }
 768
 769     fn error_simplifyable<'pat>(&mut self, match_pair: &MatchPair<'pat, 'tcx>) -> ! {
 770         span_bug!(match_pair.pattern.span, "simplifyable pattern found: {:?}", match_pair.pattern)
 771     }
 772
 773     fn const_range_contains(
 774         &self,
 775         range: &PatRange<'tcx>,
 776         value: ConstantKind<'tcx>,
 777     ) -> Option<bool> {
 778         use std::cmp::Ordering::*;
 779
 780         // For performance, it's important to only do the second
 781         // `compare_const_vals` if necessary.
 782         Some(
 783             matches!(compare_const_vals(self.tcx, range.lo, value, self.param_env)?, Less | Equal)
 784                 && matches!(
 785                     (compare_const_vals(self.tcx, value, range.hi, self.param_env)?, range.end),
 786                     (Less, _) | (Equal, RangeEnd::Included)
 787                 ),
 788         )
 789     }
 790
 791     fn values_not_contained_in_range(
 792         &self,
 793         range: &PatRange<'tcx>,
 794         options: &FxIndexMap<ConstantKind<'tcx>, u128>,
 795     ) -> Option<bool> {
 796         for &val in options.keys() {
 797             if self.const_range_contains(range, val)? {
 798                 return Some(false);
 799             }
 800         }
 801
 802         Some(true)
 803     }
 804 }
 805
 806 impl Test<'_> {
 807     pub(super) fn targets(&self) -> usize {
 808         match self.kind {
 809             TestKind::Eq { .. } | TestKind::Range(_) | TestKind::Len { .. } => 2,
 810             TestKind::Switch { adt_def, .. } => {
 811                 // While the switch that we generate doesn't test for all
 812                 // variants, we have a target for each variant and the
 813                 // otherwise case, and we make sure that all of the cases not
 814                 // specified have the same block.
 815                 adt_def.variants().len() + 1
 816             }
 817             TestKind::SwitchInt { switch_ty, ref options, .. } => {
 818                 if switch_ty.is_bool() {
 819                     // `bool` is special cased in `perform_test` to always
 820                     // branch to two blocks.
 821                     2
 822                 } else {
 823                     options.len() + 1
 824                 }
 825             }
 826         }
 827     }
 828 }
 829
 830 fn is_switch_ty(ty: Ty<'_>) -> bool {
 831     ty.is_integral() || ty.is_char() || ty.is_bool()
 832 }
 833
 834 fn trait_method<'tcx>(
 835     tcx: TyCtxt<'tcx>,
 836     trait_def_id: DefId,
 837     method_name: Symbol,
 838     substs: impl IntoIterator<Item = impl Into<GenericArg<'tcx>>>,
 839 ) -> ConstantKind<'tcx> {
 840     // The unhygienic comparison here is acceptable because this is only
 841     // used on known traits.
 842     let item = tcx
 843         .associated_items(trait_def_id)
 844         .filter_by_name_unhygienic(method_name)
 845         .find(|item| item.kind == ty::AssocKind::Fn)
 846         .expect("trait method not found");
 847
 848     let method_ty = tcx.mk_fn_def(item.def_id, substs);
 849
 850     ConstantKind::zero_sized(method_ty)
 851 }