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