src/librustc_mir/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::Builder;
   9 use crate::build::matches::{Candidate, MatchPair, Test, TestKind};
  10 use crate::hair::*;
  11 use crate::hair::pattern::compare_const_vals;
  12 use rustc_data_structures::bit_set::BitSet;
  13 use rustc_data_structures::fx::FxHashMap;
  14 use rustc::ty::{self, Ty};
  15 use rustc::ty::util::IntTypeExt;
  16 use rustc::ty::layout::VariantIdx;
  17 use rustc::mir::*;
  18 use rustc::hir::{RangeEnd, Mutability};
  19 use syntax_pos::Span;
  20 use std::cmp::Ordering;
  21
  22 impl<'a, 'gcx, 'tcx> Builder<'a, 'gcx, 'tcx> {
  23     /// Identifies what test is needed to decide if `match_pair` is applicable.
  24     ///
  25     /// It is a bug to call this with a simplifiable pattern.
  26     pub fn test<'pat>(&mut self, match_pair: &MatchPair<'pat, 'tcx>) -> Test<'tcx> {
  27         match *match_pair.pattern.kind {
  28             PatternKind::Variant { ref adt_def, substs: _, variant_index: _, subpatterns: _ } => {
  29                 Test {
  30                     span: match_pair.pattern.span,
  31                     kind: TestKind::Switch {
  32                         adt_def: adt_def.clone(),
  33                         variants: BitSet::new_empty(adt_def.variants.len()),
  34                     },
  35                 }
  36             }
  37
  38             PatternKind::Constant { .. }
  39             if is_switch_ty(match_pair.pattern.ty) => {
  40                 // for integers, we use a SwitchInt match, which allows
  41                 // us to handle more cases
  42                 Test {
  43                     span: match_pair.pattern.span,
  44                     kind: TestKind::SwitchInt {
  45                         switch_ty: match_pair.pattern.ty,
  46
  47                         // these maps are empty to start; cases are
  48                         // added below in add_cases_to_switch
  49                         options: vec![],
  50                         indices: Default::default(),
  51                     }
  52                 }
  53             }
  54
  55             PatternKind::Constant { value } => {
  56                 Test {
  57                     span: match_pair.pattern.span,
  58                     kind: TestKind::Eq {
  59                         value,
  60                         ty: match_pair.pattern.ty.clone()
  61                     }
  62                 }
  63             }
  64
  65             PatternKind::Range(range) => {
  66                 assert!(range.ty == match_pair.pattern.ty);
  67                 Test {
  68                     span: match_pair.pattern.span,
  69                     kind: TestKind::Range(range),
  70                 }
  71             }
  72
  73             PatternKind::Slice { ref prefix, ref slice, ref suffix }
  74                     if !match_pair.slice_len_checked => {
  75                 let len = prefix.len() + suffix.len();
  76                 let op = if slice.is_some() {
  77                     BinOp::Ge
  78                 } else {
  79                     BinOp::Eq
  80                 };
  81                 Test {
  82                     span: match_pair.pattern.span,
  83                     kind: TestKind::Len { len: len as u64, op: op },
  84                 }
  85             }
  86
  87             PatternKind::AscribeUserType { .. } |
  88             PatternKind::Array { .. } |
  89             PatternKind::Slice { .. } |
  90             PatternKind::Wild |
  91             PatternKind::Binding { .. } |
  92             PatternKind::Leaf { .. } |
  93             PatternKind::Deref { .. } => {
  94                 self.error_simplifyable(match_pair)
  95             }
  96         }
  97     }
  98
  99     pub fn add_cases_to_switch<'pat>(&mut self,
 100                                      test_place: &Place<'tcx>,
 101                                      candidate: &Candidate<'pat, 'tcx>,
 102                                      switch_ty: Ty<'tcx>,
 103                                      options: &mut Vec<u128>,
 104                                      indices: &mut FxHashMap<ty::Const<'tcx>, usize>)
 105                                      -> bool
 106     {
 107         let match_pair = match candidate.match_pairs.iter().find(|mp| mp.place == *test_place) {
 108             Some(match_pair) => match_pair,
 109             _ => { return false; }
 110         };
 111
 112         match *match_pair.pattern.kind {
 113             PatternKind::Constant { value } => {
 114                 let switch_ty = ty::ParamEnv::empty().and(switch_ty);
 115                 indices.entry(value)
 116                        .or_insert_with(|| {
 117                            options.push(value.unwrap_bits(self.hir.tcx(), switch_ty));
 118                            options.len() - 1
 119                        });
 120                 true
 121             }
 122             PatternKind::Variant { .. } => {
 123                 panic!("you should have called add_variants_to_switch instead!");
 124             }
 125             PatternKind::Range(range) => {
 126                 // Check that none of the switch values are in the range.
 127                 self.values_not_contained_in_range(range, indices)
 128                     .unwrap_or(false)
 129             }
 130             PatternKind::Slice { .. } |
 131             PatternKind::Array { .. } |
 132             PatternKind::Wild |
 133             PatternKind::Binding { .. } |
 134             PatternKind::AscribeUserType { .. } |
 135             PatternKind::Leaf { .. } |
 136             PatternKind::Deref { .. } => {
 137                 // don't know how to add these patterns to a switch
 138                 false
 139             }
 140         }
 141     }
 142
 143     pub fn add_variants_to_switch<'pat>(&mut self,
 144                                         test_place: &Place<'tcx>,
 145                                         candidate: &Candidate<'pat, 'tcx>,
 146                                         variants: &mut BitSet<VariantIdx>)
 147                                         -> bool
 148     {
 149         let match_pair = match candidate.match_pairs.iter().find(|mp| mp.place == *test_place) {
 150             Some(match_pair) => match_pair,
 151             _ => { return false; }
 152         };
 153
 154         match *match_pair.pattern.kind {
 155             PatternKind::Variant { adt_def: _ , variant_index,  .. } => {
 156                 // We have a pattern testing for variant `variant_index`
 157                 // set the corresponding index to true
 158                 variants.insert(variant_index);
 159                 true
 160             }
 161             _ => {
 162                 // don't know how to add these patterns to a switch
 163                 false
 164             }
 165         }
 166     }
 167
 168     /// Generates the code to perform a test.
 169     pub fn perform_test(&mut self,
 170                         block: BasicBlock,
 171                         place: &Place<'tcx>,
 172                         test: &Test<'tcx>)
 173                         -> Vec<BasicBlock> {
 174         debug!("perform_test({:?}, {:?}: {:?}, {:?})",
 175                block,
 176                place,
 177                place.ty(&self.local_decls, self.hir.tcx()),
 178                test);
 179         let source_info = self.source_info(test.span);
 180         match test.kind {
 181             TestKind::Switch { adt_def, ref variants } => {
 182                 // Variants is a BitVec of indexes into adt_def.variants.
 183                 let num_enum_variants = adt_def.variants.len();
 184                 let used_variants = variants.count();
 185                 let mut otherwise_block = None;
 186                 let mut target_blocks = Vec::with_capacity(num_enum_variants);
 187                 let mut targets = Vec::with_capacity(used_variants + 1);
 188                 let mut values = Vec::with_capacity(used_variants);
 189                 let tcx = self.hir.tcx();
 190                 for (idx, discr) in adt_def.discriminants(tcx) {
 191                     target_blocks.push(if variants.contains(idx) {
 192                         values.push(discr.val);
 193                         let block = self.cfg.start_new_block();
 194                         targets.push(block);
 195                         block
 196                     } else {
 197                         *otherwise_block
 198                             .get_or_insert_with(|| self.cfg.start_new_block())
 199                     });
 200                 }
 201                 targets.push(
 202                     otherwise_block
 203                         .unwrap_or_else(|| self.unreachable_block()),
 204                 );
 205                 debug!("num_enum_variants: {}, tested variants: {:?}, variants: {:?}",
 206                        num_enum_variants, values, 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,
 210                                      Rvalue::Discriminant(place.clone()));
 211                 assert_eq!(values.len() + 1, targets.len());
 212                 self.cfg.terminate(block, source_info, TerminatorKind::SwitchInt {
 213                     discr: Operand::Move(discr),
 214                     switch_ty: discr_ty,
 215                     values: From::from(values),
 216                     targets,
 217                 });
 218                 target_blocks
 219             }
 220
 221             TestKind::SwitchInt { switch_ty, ref options, indices: _ } => {
 222                 let (ret, terminator) = if switch_ty.sty == ty::Bool {
 223                     assert!(options.len() > 0 && options.len() <= 2);
 224                     let (true_bb, false_bb) = (self.cfg.start_new_block(),
 225                                                self.cfg.start_new_block());
 226                     let ret = match options[0] {
 227                         1 => vec![true_bb, false_bb],
 228                         0 => vec![false_bb, true_bb],
 229                         v => span_bug!(test.span, "expected boolean value but got {:?}", v)
 230                     };
 231                     (ret, TerminatorKind::if_(self.hir.tcx(), Operand::Copy(place.clone()),
 232                                               true_bb, false_bb))
 233                 } else {
 234                     // The switch may be inexhaustive so we
 235                     // add a catch all block
 236                     let otherwise = self.cfg.start_new_block();
 237                     let targets: Vec<_> =
 238                         options.iter()
 239                                .map(|_| self.cfg.start_new_block())
 240                                .chain(Some(otherwise))
 241                                .collect();
 242                     (targets.clone(), TerminatorKind::SwitchInt {
 243                         discr: Operand::Copy(place.clone()),
 244                         switch_ty,
 245                         values: options.clone().into(),
 246                         targets,
 247                     })
 248                 };
 249                 self.cfg.terminate(block, source_info, terminator);
 250                 ret
 251             }
 252
 253             TestKind::Eq { value, mut ty } => {
 254                 let val = Operand::Copy(place.clone());
 255                 let mut expect = self.literal_operand(test.span, ty, value);
 256                 // Use PartialEq::eq instead of BinOp::Eq
 257                 // (the binop can only handle primitives)
 258                 let fail = self.cfg.start_new_block();
 259                 if !ty.is_scalar() {
 260                     // If we're using b"..." as a pattern, we need to insert an
 261                     // unsizing coercion, as the byte string has the type &[u8; N].
 262                     //
 263                     // We want to do this even when the scrutinee is a reference to an
 264                     // array, so we can call `<[u8]>::eq` rather than having to find an
 265                     // `<[u8; N]>::eq`.
 266                     let unsize = |ty: Ty<'tcx>| match ty.sty {
 267                         ty::Ref(region, rty, _) => match rty.sty {
 268                             ty::Array(inner_ty, n) => Some((region, inner_ty, n)),
 269                             _ => None,
 270                         },
 271                         _ => None,
 272                     };
 273                     let opt_ref_ty = unsize(ty);
 274                     let opt_ref_test_ty = unsize(value.ty);
 275                     let mut place = place.clone();
 276                     match (opt_ref_ty, opt_ref_test_ty) {
 277                         // nothing to do, neither is an array
 278                         (None, None) => {},
 279                         (Some((region, elem_ty, _)), _) |
 280                         (None, Some((region, elem_ty, _))) => {
 281                             let tcx = self.hir.tcx();
 282                             // make both a slice
 283                             ty = tcx.mk_imm_ref(region, tcx.mk_slice(elem_ty));
 284                             if opt_ref_ty.is_some() {
 285                                 place = self.temp(ty, test.span);
 286                                 self.cfg.push_assign(block, source_info, &place,
 287                                                     Rvalue::Cast(CastKind::Unsize, val, ty));
 288                             }
 289                             if opt_ref_test_ty.is_some() {
 290                                 let array = self.literal_operand(
 291                                     test.span,
 292                                     value.ty,
 293                                     value,
 294                                 );
 295
 296                                 let slice = self.temp(ty, test.span);
 297                                 self.cfg.push_assign(block, source_info, &slice,
 298                                                     Rvalue::Cast(CastKind::Unsize, array, ty));
 299                                 expect = Operand::Move(slice);
 300                             }
 301                         },
 302                     }
 303                     let eq_def_id = self.hir.tcx().lang_items().eq_trait().unwrap();
 304                     let (mty, method) = self.hir.trait_method(eq_def_id, "eq", ty, &[ty.into()]);
 305                     let method = self.hir.tcx().mk_lazy_const(ty::LazyConst::Evaluated(method));
 306
 307                     let re_erased = self.hir.tcx().types.re_erased;
 308                     // take the argument by reference
 309                     let tam = ty::TypeAndMut {
 310                         ty,
 311                         mutbl: Mutability::MutImmutable,
 312                     };
 313                     let ref_ty = self.hir.tcx().mk_ref(re_erased, tam);
 314
 315                     // let lhs_ref_place = &lhs;
 316                     let ref_rvalue = Rvalue::Ref(re_erased, BorrowKind::Shared, place);
 317                     let lhs_ref_place = self.temp(ref_ty, test.span);
 318                     self.cfg.push_assign(block, source_info, &lhs_ref_place, ref_rvalue);
 319                     let val = Operand::Move(lhs_ref_place);
 320
 321                     // let rhs_place = rhs;
 322                     let rhs_place = self.temp(ty, test.span);
 323                     self.cfg.push_assign(block, source_info, &rhs_place, Rvalue::Use(expect));
 324
 325                     // let rhs_ref_place = &rhs_place;
 326                     let ref_rvalue = Rvalue::Ref(re_erased, BorrowKind::Shared, rhs_place);
 327                     let rhs_ref_place = self.temp(ref_ty, test.span);
 328                     self.cfg.push_assign(block, source_info, &rhs_ref_place, ref_rvalue);
 329                     let expect = Operand::Move(rhs_ref_place);
 330
 331                     let bool_ty = self.hir.bool_ty();
 332                     let eq_result = self.temp(bool_ty, test.span);
 333                     let eq_block = self.cfg.start_new_block();
 334                     let cleanup = self.diverge_cleanup();
 335                     self.cfg.terminate(block, source_info, TerminatorKind::Call {
 336                         func: Operand::Constant(box Constant {
 337                             span: test.span,
 338                             ty: mty,
 339
 340                             // FIXME(#54571): This constant comes from user
 341                             // input (a constant in a pattern).  Are
 342                             // there forms where users can add type
 343                             // annotations here?  For example, an
 344                             // associated constant? Need to
 345                             // experiment.
 346                             user_ty: None,
 347
 348                             literal: method,
 349                         }),
 350                         args: vec![val, expect],
 351                         destination: Some((eq_result.clone(), eq_block)),
 352                         cleanup: Some(cleanup),
 353                         from_hir_call: false,
 354                     });
 355
 356                     // check the result
 357                     let block = self.cfg.start_new_block();
 358                     self.cfg.terminate(eq_block, source_info,
 359                                        TerminatorKind::if_(self.hir.tcx(),
 360                                                            Operand::Move(eq_result),
 361                                                            block, fail));
 362                     vec![block, fail]
 363                 } else {
 364                     let block = self.compare(block, fail, test.span, BinOp::Eq, expect, val);
 365                     vec![block, fail]
 366                 }
 367             }
 368
 369             TestKind::Range(PatternRange { ref lo, ref hi, ty, ref end }) => {
 370                 // Test `val` by computing `lo <= val && val <= hi`, using primitive comparisons.
 371                 let lo = self.literal_operand(test.span, ty.clone(), lo.clone());
 372                 let hi = self.literal_operand(test.span, ty.clone(), hi.clone());
 373                 let val = Operand::Copy(place.clone());
 374
 375                 let fail = self.cfg.start_new_block();
 376                 let block = self.compare(block, fail, test.span, BinOp::Le, lo, val.clone());
 377                 let block = match *end {
 378                     RangeEnd::Included => self.compare(block, fail, test.span, BinOp::Le, val, hi),
 379                     RangeEnd::Excluded => self.compare(block, fail, test.span, BinOp::Lt, val, hi),
 380                 };
 381
 382                 vec![block, fail]
 383             }
 384
 385             TestKind::Len { len, op } => {
 386                 let (usize_ty, bool_ty) = (self.hir.usize_ty(), self.hir.bool_ty());
 387                 let (actual, result) = (self.temp(usize_ty, test.span),
 388                                         self.temp(bool_ty, test.span));
 389
 390                 // actual = len(place)
 391                 self.cfg.push_assign(block, source_info,
 392                                      &actual, Rvalue::Len(place.clone()));
 393
 394                 // expected = <N>
 395                 let expected = self.push_usize(block, source_info, len);
 396
 397                 // result = actual == expected OR result = actual < expected
 398                 self.cfg.push_assign(block, source_info, &result,
 399                                      Rvalue::BinaryOp(op,
 400                                                       Operand::Move(actual),
 401                                                       Operand::Move(expected)));
 402
 403                 // branch based on result
 404                 let (false_bb, true_bb) = (self.cfg.start_new_block(),
 405                                            self.cfg.start_new_block());
 406                 self.cfg.terminate(block, source_info,
 407                                    TerminatorKind::if_(self.hir.tcx(), Operand::Move(result),
 408                                                        true_bb, false_bb));
 409                 vec![true_bb, false_bb]
 410             }
 411         }
 412     }
 413
 414     fn compare(&mut self,
 415                block: BasicBlock,
 416                fail_block: BasicBlock,
 417                span: Span,
 418                op: BinOp,
 419                left: Operand<'tcx>,
 420                right: Operand<'tcx>) -> BasicBlock {
 421         let bool_ty = self.hir.bool_ty();
 422         let result = self.temp(bool_ty, span);
 423
 424         // result = op(left, right)
 425         let source_info = self.source_info(span);
 426         self.cfg.push_assign(block, source_info, &result,
 427                              Rvalue::BinaryOp(op, left, right));
 428
 429         // branch based on result
 430         let target_block = self.cfg.start_new_block();
 431         self.cfg.terminate(block, source_info,
 432                            TerminatorKind::if_(self.hir.tcx(), Operand::Move(result),
 433                                                target_block, fail_block));
 434         target_block
 435     }
 436
 437     /// Given that we are performing `test` against `test_place`,
 438     /// this job sorts out what the status of `candidate` will be
 439     /// after the test. The `resulting_candidates` vector stores, for
 440     /// each possible outcome of `test`, a vector of the candidates
 441     /// that will result. This fn should add a (possibly modified)
 442     /// clone of candidate into `resulting_candidates` wherever
 443     /// appropriate.
 444     ///
 445     /// So, for example, if this candidate is `x @ Some(P0)` and the
 446     /// test is a variant test, then we would add `(x as Option).0 @
 447     /// P0` to the `resulting_candidates` entry corresponding to the
 448     /// variant `Some`.
 449     ///
 450     /// However, in some cases, the test may just not be relevant to
 451     /// candidate. For example, suppose we are testing whether `foo.x == 22`,
 452     /// but in one match arm we have `Foo { x: _, ... }`... in that case,
 453     /// the test for what value `x` has has no particular relevance
 454     /// to this candidate. In such cases, this function just returns false
 455     /// without doing anything. This is used by the overall `match_candidates`
 456     /// algorithm to structure the match as a whole. See `match_candidates` for
 457     /// more details.
 458     ///
 459     /// FIXME(#29623). In some cases, we have some tricky choices to
 460     /// make.  for example, if we are testing that `x == 22`, but the
 461     /// candidate is `x @ 13..55`, what should we do? In the event
 462     /// that the test is true, we know that the candidate applies, but
 463     /// in the event of false, we don't know that it *doesn't*
 464     /// apply. For now, we return false, indicate that the test does
 465     /// not apply to this candidate, but it might be we can get
 466     /// tighter match code if we do something a bit different.
 467     pub fn sort_candidate<'pat>(&mut self,
 468                                 test_place: &Place<'tcx>,
 469                                 test: &Test<'tcx>,
 470                                 candidate: &Candidate<'pat, 'tcx>,
 471                                 resulting_candidates: &mut [Vec<Candidate<'pat, 'tcx>>])
 472                                 -> bool {
 473         // Find the match_pair for this place (if any). At present,
 474         // afaik, there can be at most one. (In the future, if we
 475         // adopted a more general `@` operator, there might be more
 476         // than one, but it'd be very unusual to have two sides that
 477         // both require tests; you'd expect one side to be simplified
 478         // away.)
 479         let tested_match_pair = candidate.match_pairs.iter()
 480                                                      .enumerate()
 481                                                      .find(|&(_, mp)| mp.place == *test_place);
 482         let (match_pair_index, match_pair) = match tested_match_pair {
 483             Some(pair) => pair,
 484             None => {
 485                 // We are not testing this place. Therefore, this
 486                 // candidate applies to ALL outcomes.
 487                 return false;
 488             }
 489         };
 490
 491         match (&test.kind, &*match_pair.pattern.kind) {
 492             // If we are performing a variant switch, then this
 493             // informs variant patterns, but nothing else.
 494             (&TestKind::Switch { adt_def: tested_adt_def, .. },
 495              &PatternKind::Variant { adt_def, variant_index, ref subpatterns, .. }) => {
 496                 assert_eq!(adt_def, tested_adt_def);
 497                 let new_candidate =
 498                     self.candidate_after_variant_switch(match_pair_index,
 499                                                         adt_def,
 500                                                         variant_index,
 501                                                         subpatterns,
 502                                                         candidate);
 503                 resulting_candidates[variant_index.as_usize()].push(new_candidate);
 504                 true
 505             }
 506             (&TestKind::Switch { .. }, _) => false,
 507
 508             // If we are performing a switch over integers, then this informs integer
 509             // equality, but nothing else.
 510             //
 511             // FIXME(#29623) we could use PatternKind::Range to rule
 512             // things out here, in some cases.
 513             (&TestKind::SwitchInt { switch_ty: _, options: _, ref indices },
 514              &PatternKind::Constant { ref value })
 515             if is_switch_ty(match_pair.pattern.ty) => {
 516                 let index = indices[value];
 517                 let new_candidate = self.candidate_without_match_pair(match_pair_index,
 518                                                                       candidate);
 519                 resulting_candidates[index].push(new_candidate);
 520                 true
 521             }
 522
 523             (&TestKind::SwitchInt { switch_ty: _, ref options, ref indices },
 524              &PatternKind::Range(range)) => {
 525                 let not_contained = self
 526                     .values_not_contained_in_range(range, indices)
 527                     .unwrap_or(false);
 528
 529                 if not_contained {
 530                     // No switch values are contained in the pattern range,
 531                     // so the pattern can be matched only if this test fails.
 532                     let otherwise = options.len();
 533                     resulting_candidates[otherwise].push(candidate.clone());
 534                     true
 535                 } else {
 536                     false
 537                 }
 538             }
 539
 540             (&TestKind::SwitchInt { .. }, _) => false,
 541
 542
 543             (&TestKind::Len { len: test_len, op: BinOp::Eq },
 544              &PatternKind::Slice { ref prefix, ref slice, ref suffix }) => {
 545                 let pat_len = (prefix.len() + suffix.len()) as u64;
 546                 match (test_len.cmp(&pat_len), slice) {
 547                     (Ordering::Equal, &None) => {
 548                         // on true, min_len = len = $actual_length,
 549                         // on false, len != $actual_length
 550                         resulting_candidates[0].push(
 551                             self.candidate_after_slice_test(match_pair_index,
 552                                                             candidate,
 553                                                             prefix,
 554                                                             slice.as_ref(),
 555                                                             suffix)
 556                         );
 557                         true
 558                     }
 559                     (Ordering::Less, _) => {
 560                         // test_len < pat_len. If $actual_len = test_len,
 561                         // then $actual_len < pat_len and we don't have
 562                         // enough elements.
 563                         resulting_candidates[1].push(candidate.clone());
 564                         true
 565                     }
 566                     (Ordering::Equal, &Some(_)) | (Ordering::Greater, &Some(_)) => {
 567                         // This can match both if $actual_len = test_len >= pat_len,
 568                         // and if $actual_len > test_len. We can't advance.
 569                         false
 570                     }
 571                     (Ordering::Greater, &None) => {
 572                         // test_len != pat_len, so if $actual_len = test_len, then
 573                         // $actual_len != pat_len.
 574                         resulting_candidates[1].push(candidate.clone());
 575                         true
 576                     }
 577                 }
 578             }
 579
 580             (&TestKind::Len { len: test_len, op: BinOp::Ge },
 581              &PatternKind::Slice { ref prefix, ref slice, ref suffix }) => {
 582                 // the test is `$actual_len >= test_len`
 583                 let pat_len = (prefix.len() + suffix.len()) as u64;
 584                 match (test_len.cmp(&pat_len), slice) {
 585                     (Ordering::Equal, &Some(_))  => {
 586                         // $actual_len >= test_len = pat_len,
 587                         // so we can match.
 588                         resulting_candidates[0].push(
 589                             self.candidate_after_slice_test(match_pair_index,
 590                                                             candidate,
 591                                                             prefix,
 592                                                             slice.as_ref(),
 593                                                             suffix)
 594                         );
 595                         true
 596                     }
 597                     (Ordering::Less, _) | (Ordering::Equal, &None) => {
 598                         // test_len <= pat_len. If $actual_len < test_len,
 599                         // then it is also < pat_len, so the test passing is
 600                         // necessary (but insufficient).
 601                         resulting_candidates[0].push(candidate.clone());
 602                         true
 603                     }
 604                     (Ordering::Greater, &None) => {
 605                         // test_len > pat_len. If $actual_len >= test_len > pat_len,
 606                         // then we know we won't have a match.
 607                         resulting_candidates[1].push(candidate.clone());
 608                         true
 609                     }
 610                     (Ordering::Greater, &Some(_)) => {
 611                         // test_len < pat_len, and is therefore less
 612                         // strict. This can still go both ways.
 613                         false
 614                     }
 615                 }
 616             }
 617
 618             (&TestKind::Range(test),
 619              &PatternKind::Range(pat)) => {
 620                 if test == pat {
 621                     resulting_candidates[0]
 622                         .push(self.candidate_without_match_pair(
 623                             match_pair_index,
 624                             candidate,
 625                         ));
 626                     return true;
 627                 }
 628
 629                 let no_overlap = (|| {
 630                     use std::cmp::Ordering::*;
 631                     use rustc::hir::RangeEnd::*;
 632
 633                     let param_env = ty::ParamEnv::empty().and(test.ty);
 634                     let tcx = self.hir.tcx();
 635
 636                     let lo = compare_const_vals(tcx, test.lo, pat.hi, param_env)?;
 637                     let hi = compare_const_vals(tcx, test.hi, pat.lo, param_env)?;
 638
 639                     match (test.end, pat.end, lo, hi) {
 640                         // pat < test
 641                         (_, _, Greater, _) |
 642                         (_, Excluded, Equal, _) |
 643                         // pat > test
 644                         (_, _, _, Less) |
 645                         (Excluded, _, _, Equal) => Some(true),
 646                         _ => Some(false),
 647                     }
 648                 })();
 649
 650                 if no_overlap == Some(true) {
 651                     // Testing range does not overlap with pattern range,
 652                     // so the pattern can be matched only if this test fails.
 653                     resulting_candidates[1].push(candidate.clone());
 654                     true
 655                 } else {
 656                     false
 657                 }
 658             }
 659
 660             (&TestKind::Range(range), &PatternKind::Constant { value }) => {
 661                 if self.const_range_contains(range, value) == Some(false) {
 662                     // `value` is not contained in the testing range,
 663                     // so `value` can be matched only if this test fails.
 664                     resulting_candidates[1].push(candidate.clone());
 665                     true
 666                 } else {
 667                     false
 668                 }
 669             }
 670
 671             (&TestKind::Range { .. }, _) => false,
 672
 673
 674             (&TestKind::Eq { .. }, _) |
 675             (&TestKind::Len { .. }, _) => {
 676                 // These are all binary tests.
 677                 //
 678                 // FIXME(#29623) we can be more clever here
 679                 let pattern_test = self.test(&match_pair);
 680                 if pattern_test.kind == test.kind {
 681                     let new_candidate = self.candidate_without_match_pair(match_pair_index,
 682                                                                           candidate);
 683                     resulting_candidates[0].push(new_candidate);
 684                     true
 685                 } else {
 686                     false
 687                 }
 688             }
 689         }
 690     }
 691
 692     fn candidate_without_match_pair<'pat>(&mut self,
 693                                           match_pair_index: usize,
 694                                           candidate: &Candidate<'pat, 'tcx>)
 695                                           -> Candidate<'pat, 'tcx> {
 696         let other_match_pairs =
 697             candidate.match_pairs.iter()
 698                                  .enumerate()
 699                                  .filter(|&(index, _)| index != match_pair_index)
 700                                  .map(|(_, mp)| mp.clone())
 701                                  .collect();
 702         Candidate {
 703             span: candidate.span,
 704             match_pairs: other_match_pairs,
 705             bindings: candidate.bindings.clone(),
 706             ascriptions: candidate.ascriptions.clone(),
 707             guard: candidate.guard.clone(),
 708             arm_index: candidate.arm_index,
 709             pat_index: candidate.pat_index,
 710             pre_binding_block: candidate.pre_binding_block,
 711             next_candidate_pre_binding_block: candidate.next_candidate_pre_binding_block,
 712         }
 713     }
 714
 715     fn candidate_after_slice_test<'pat>(&mut self,
 716                                         match_pair_index: usize,
 717                                         candidate: &Candidate<'pat, 'tcx>,
 718                                         prefix: &'pat [Pattern<'tcx>],
 719                                         opt_slice: Option<&'pat Pattern<'tcx>>,
 720                                         suffix: &'pat [Pattern<'tcx>])
 721                                         -> Candidate<'pat, 'tcx> {
 722         let mut new_candidate =
 723             self.candidate_without_match_pair(match_pair_index, candidate);
 724         self.prefix_slice_suffix(
 725             &mut new_candidate.match_pairs,
 726             &candidate.match_pairs[match_pair_index].place,
 727             prefix,
 728             opt_slice,
 729             suffix);
 730
 731         new_candidate
 732     }
 733
 734     fn candidate_after_variant_switch<'pat>(&mut self,
 735                                             match_pair_index: usize,
 736                                             adt_def: &'tcx ty::AdtDef,
 737                                             variant_index: VariantIdx,
 738                                             subpatterns: &'pat [FieldPattern<'tcx>],
 739                                             candidate: &Candidate<'pat, 'tcx>)
 740                                             -> Candidate<'pat, 'tcx> {
 741         let match_pair = &candidate.match_pairs[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 = ProjectionElem::Downcast(adt_def, variant_index);
 747         let downcast_place = match_pair.place.clone().elem(elem); // `(x as Variant)`
 748         let consequent_match_pairs =
 749             subpatterns.iter()
 750                        .map(|subpattern| {
 751                            // e.g., `(x as Variant).0`
 752                            let place = downcast_place.clone().field(subpattern.field,
 753                                                                       subpattern.pattern.ty);
 754                            // e.g., `(x as Variant).0 @ P1`
 755                            MatchPair::new(place, &subpattern.pattern)
 756                        });
 757
 758         // In addition, we need all the other match pairs from the old candidate.
 759         let other_match_pairs =
 760             candidate.match_pairs.iter()
 761                                  .enumerate()
 762                                  .filter(|&(index, _)| index != match_pair_index)
 763                                  .map(|(_, mp)| mp.clone());
 764
 765         let all_match_pairs = consequent_match_pairs.chain(other_match_pairs).collect();
 766
 767         Candidate {
 768             span: candidate.span,
 769             match_pairs: all_match_pairs,
 770             bindings: candidate.bindings.clone(),
 771             ascriptions: candidate.ascriptions.clone(),
 772             guard: candidate.guard.clone(),
 773             arm_index: candidate.arm_index,
 774             pat_index: candidate.pat_index,
 775             pre_binding_block: candidate.pre_binding_block,
 776             next_candidate_pre_binding_block: candidate.next_candidate_pre_binding_block,
 777         }
 778     }
 779
 780     fn error_simplifyable<'pat>(&mut self, match_pair: &MatchPair<'pat, 'tcx>) -> ! {
 781         span_bug!(match_pair.pattern.span,
 782                   "simplifyable pattern found: {:?}",
 783                   match_pair.pattern)
 784     }
 785
 786     fn const_range_contains(
 787         &self,
 788         range: PatternRange<'tcx>,
 789         value: ty::Const<'tcx>,
 790     ) -> Option<bool> {
 791         use std::cmp::Ordering::*;
 792
 793         let param_env = ty::ParamEnv::empty().and(range.ty);
 794         let tcx = self.hir.tcx();
 795
 796         let a = compare_const_vals(tcx, range.lo, value, param_env)?;
 797         let b = compare_const_vals(tcx, value, range.hi, param_env)?;
 798
 799         match (b, range.end) {
 800             (Less, _) |
 801             (Equal, RangeEnd::Included) if a != Greater => Some(true),
 802             _ => Some(false),
 803         }
 804     }
 805
 806     fn values_not_contained_in_range(
 807         &self,
 808         range: PatternRange<'tcx>,
 809         indices: &FxHashMap<ty::Const<'tcx>, usize>,
 810     ) -> Option<bool> {
 811         for &val in indices.keys() {
 812             if self.const_range_contains(range, val)? {
 813                 return Some(false);
 814             }
 815         }
 816
 817         Some(true)
 818     }
 819 }
 820
 821 fn is_switch_ty<'tcx>(ty: Ty<'tcx>) -> bool {
 822     ty.is_integral() || ty.is_char() || ty.is_bool()
 823 }