src/librustc_mir/hair/pattern/mod.rs

   1 //! Code to validate patterns/matches
   2
   3 mod _match;
   4 mod check_match;
   5
   6 pub use self::check_match::check_crate;
   7 pub(crate) use self::check_match::check_match;
   8
   9 use const_eval::{const_field, const_variant_index};
  10
  11 use hair::util::UserAnnotatedTyHelpers;
  12 use hair::constant::*;
  13
  14 use rustc::mir::{fmt_const_val, Field, BorrowKind, Mutability};
  15 use rustc::mir::{ProjectionElem, UserTypeAnnotation, UserTypeProjection, UserTypeProjections};
  16 use rustc::mir::interpret::{Scalar, GlobalId, ConstValue, sign_extend};
  17 use rustc::ty::{self, Region, TyCtxt, AdtDef, Ty, Lift};
  18 use rustc::ty::subst::{Substs, Kind};
  19 use rustc::ty::layout::VariantIdx;
  20 use rustc::hir::{self, PatKind, RangeEnd};
  21 use rustc::hir::def::{Def, CtorKind};
  22 use rustc::hir::pat_util::EnumerateAndAdjustIterator;
  23
  24 use rustc_data_structures::indexed_vec::Idx;
  25
  26 use std::cmp::Ordering;
  27 use std::fmt;
  28 use syntax::ast;
  29 use syntax::ptr::P;
  30 use syntax_pos::Span;
  31
  32 #[derive(Clone, Debug)]
  33 pub enum PatternError {
  34     AssociatedConstInPattern(Span),
  35     StaticInPattern(Span),
  36     FloatBug,
  37     NonConstPath(Span),
  38 }
  39
  40 #[derive(Copy, Clone, Debug)]
  41 pub enum BindingMode<'tcx> {
  42     ByValue,
  43     ByRef(Region<'tcx>, BorrowKind),
  44 }
  45
  46 #[derive(Clone, Debug)]
  47 pub struct FieldPattern<'tcx> {
  48     pub field: Field,
  49     pub pattern: Pattern<'tcx>,
  50 }
  51
  52 #[derive(Clone, Debug)]
  53 pub struct Pattern<'tcx> {
  54     pub ty: Ty<'tcx>,
  55     pub span: Span,
  56     pub kind: Box<PatternKind<'tcx>>,
  57 }
  58
  59
  60 #[derive(Clone, Debug)]
  61 pub(crate) struct PatternTypeProjections<'tcx> {
  62     contents: Vec<(PatternTypeProjection<'tcx>, Span)>,
  63 }
  64
  65 impl<'tcx> PatternTypeProjections<'tcx> {
  66     pub(crate) fn user_ty(self) -> UserTypeProjections<'tcx> {
  67         UserTypeProjections::from_projections(
  68             self.contents.into_iter().map(|(pat_ty_proj, span)| (pat_ty_proj.user_ty(), span)))
  69     }
  70
  71     pub(crate) fn none() -> Self {
  72         PatternTypeProjections { contents: vec![] }
  73     }
  74
  75     pub(crate) fn ref_binding(&self) -> Self {
  76         // FIXME(#55401): ignore for now
  77         PatternTypeProjections { contents: vec![] }
  78     }
  79
  80     fn map_projs(&self,
  81                  mut f: impl FnMut(&PatternTypeProjection<'tcx>) -> PatternTypeProjection<'tcx>)
  82                  -> Self
  83     {
  84         PatternTypeProjections {
  85             contents: self.contents
  86                 .iter()
  87                 .map(|(proj, span)| (f(proj), *span))
  88                 .collect(), }
  89     }
  90
  91     pub(crate) fn index(&self) -> Self { self.map_projs(|pat_ty_proj| pat_ty_proj.index()) }
  92
  93     pub(crate) fn subslice(&self, from: u32, to: u32) -> Self {
  94         self.map_projs(|pat_ty_proj| pat_ty_proj.subslice(from, to))
  95     }
  96
  97     pub(crate) fn deref(&self) -> Self { self.map_projs(|pat_ty_proj| pat_ty_proj.deref()) }
  98
  99     pub(crate) fn leaf(&self, field: Field) -> Self {
 100         self.map_projs(|pat_ty_proj| pat_ty_proj.leaf(field))
 101     }
 102
 103     pub(crate) fn variant(&self,
 104                           adt_def: &'tcx AdtDef,
 105                           variant_index: VariantIdx,
 106                           field: Field) -> Self {
 107         self.map_projs(|pat_ty_proj| pat_ty_proj.variant(adt_def, variant_index, field))
 108     }
 109
 110     pub(crate) fn add_user_type(&self, user_ty: &PatternTypeProjection<'tcx>, sp: Span) -> Self {
 111         let mut new = self.clone();
 112         new.contents.push((user_ty.clone(), sp));
 113         new
 114     }
 115 }
 116
 117 #[derive(Clone, Debug)]
 118 pub struct PatternTypeProjection<'tcx>(UserTypeProjection<'tcx>);
 119
 120 impl<'tcx> PatternTypeProjection<'tcx> {
 121     pub(crate) fn index(&self) -> Self {
 122         let mut new = self.clone();
 123         new.0.projs.push(ProjectionElem::Index(()));
 124         new
 125     }
 126
 127     pub(crate) fn subslice(&self, from: u32, to: u32) -> Self {
 128         let mut new = self.clone();
 129         new.0.projs.push(ProjectionElem::Subslice { from, to });
 130         new
 131     }
 132
 133     pub(crate) fn deref(&self) -> Self {
 134         let mut new = self.clone();
 135         new.0.projs.push(ProjectionElem::Deref);
 136         new
 137     }
 138
 139     pub(crate) fn leaf(&self, field: Field) -> Self {
 140         let mut new = self.clone();
 141         new.0.projs.push(ProjectionElem::Field(field, ()));
 142         new
 143     }
 144
 145     pub(crate) fn variant(&self,
 146                           adt_def: &'tcx AdtDef,
 147                           variant_index: VariantIdx,
 148                           field: Field) -> Self {
 149         let mut new = self.clone();
 150         new.0.projs.push(ProjectionElem::Downcast(adt_def, variant_index));
 151         new.0.projs.push(ProjectionElem::Field(field, ()));
 152         new
 153     }
 154
 155     pub(crate) fn from_canonical_ty(c_ty: ty::CanonicalTy<'tcx>) -> Self {
 156         Self::from_user_type(UserTypeAnnotation::Ty(c_ty))
 157     }
 158
 159     pub(crate) fn from_user_type(u_ty: UserTypeAnnotation<'tcx>) -> Self {
 160         Self::from_user_type_proj(UserTypeProjection { base: u_ty, projs: vec![], })
 161     }
 162
 163     pub(crate) fn from_user_type_proj(u_ty: UserTypeProjection<'tcx>) -> Self {
 164         PatternTypeProjection(u_ty)
 165     }
 166
 167     pub(crate) fn user_ty(self) -> UserTypeProjection<'tcx> { self.0 }
 168 }
 169
 170 #[derive(Clone, Debug)]
 171 pub enum PatternKind<'tcx> {
 172     Wild,
 173
 174     AscribeUserType {
 175         user_ty: PatternTypeProjection<'tcx>,
 176         subpattern: Pattern<'tcx>,
 177         user_ty_span: Span,
 178     },
 179
 180     /// x, ref x, x @ P, etc
 181     Binding {
 182         mutability: Mutability,
 183         name: ast::Name,
 184         mode: BindingMode<'tcx>,
 185         var: ast::NodeId,
 186         ty: Ty<'tcx>,
 187         subpattern: Option<Pattern<'tcx>>,
 188     },
 189
 190     /// Foo(...) or Foo{...} or Foo, where `Foo` is a variant name from an adt with >1 variants
 191     Variant {
 192         adt_def: &'tcx AdtDef,
 193         substs: &'tcx Substs<'tcx>,
 194         variant_index: VariantIdx,
 195         subpatterns: Vec<FieldPattern<'tcx>>,
 196     },
 197
 198     /// (...), Foo(...), Foo{...}, or Foo, where `Foo` is a variant name from an adt with 1 variant
 199     Leaf {
 200         subpatterns: Vec<FieldPattern<'tcx>>,
 201     },
 202
 203     /// box P, &P, &mut P, etc
 204     Deref {
 205         subpattern: Pattern<'tcx>,
 206     },
 207
 208     Constant {
 209         value: &'tcx ty::Const<'tcx>,
 210     },
 211
 212     Range(PatternRange<'tcx>),
 213
 214     /// matches against a slice, checking the length and extracting elements.
 215     /// irrefutable when there is a slice pattern and both `prefix` and `suffix` are empty.
 216     /// e.g., `&[ref xs..]`.
 217     Slice {
 218         prefix: Vec<Pattern<'tcx>>,
 219         slice: Option<Pattern<'tcx>>,
 220         suffix: Vec<Pattern<'tcx>>,
 221     },
 222
 223     /// fixed match against an array, irrefutable
 224     Array {
 225         prefix: Vec<Pattern<'tcx>>,
 226         slice: Option<Pattern<'tcx>>,
 227         suffix: Vec<Pattern<'tcx>>,
 228     },
 229 }
 230
 231 #[derive(Clone, Copy, Debug, PartialEq)]
 232 pub struct PatternRange<'tcx> {
 233     pub lo: &'tcx ty::Const<'tcx>,
 234     pub hi: &'tcx ty::Const<'tcx>,
 235     pub ty: Ty<'tcx>,
 236     pub end: RangeEnd,
 237 }
 238
 239 impl<'tcx> fmt::Display for Pattern<'tcx> {
 240     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
 241         match *self.kind {
 242             PatternKind::Wild => write!(f, "_"),
 243             PatternKind::AscribeUserType { ref subpattern, .. } =>
 244                 write!(f, "{}: _", subpattern),
 245             PatternKind::Binding { mutability, name, mode, ref subpattern, .. } => {
 246                 let is_mut = match mode {
 247                     BindingMode::ByValue => mutability == Mutability::Mut,
 248                     BindingMode::ByRef(_, bk) => {
 249                         write!(f, "ref ")?;
 250                         match bk { BorrowKind::Mut { .. } => true, _ => false }
 251                     }
 252                 };
 253                 if is_mut {
 254                     write!(f, "mut ")?;
 255                 }
 256                 write!(f, "{}", name)?;
 257                 if let Some(ref subpattern) = *subpattern {
 258                     write!(f, " @ {}", subpattern)?;
 259                 }
 260                 Ok(())
 261             }
 262             PatternKind::Variant { ref subpatterns, .. } |
 263             PatternKind::Leaf { ref subpatterns } => {
 264                 let variant = match *self.kind {
 265                     PatternKind::Variant { adt_def, variant_index, .. } => {
 266                         Some(&adt_def.variants[variant_index])
 267                     }
 268                     _ => if let ty::Adt(adt, _) = self.ty.sty {
 269                         if !adt.is_enum() {
 270                             Some(&adt.variants[VariantIdx::new(0)])
 271                         } else {
 272                             None
 273                         }
 274                     } else {
 275                         None
 276                     }
 277                 };
 278
 279                 let mut first = true;
 280                 let mut start_or_continue = || if first { first = false; "" } else { ", " };
 281
 282                 if let Some(variant) = variant {
 283                     write!(f, "{}", variant.ident)?;
 284
 285                     // Only for Adt we can have `S {...}`,
 286                     // which we handle separately here.
 287                     if variant.ctor_kind == CtorKind::Fictive {
 288                         write!(f, " {{ ")?;
 289
 290                         let mut printed = 0;
 291                         for p in subpatterns {
 292                             if let PatternKind::Wild = *p.pattern.kind {
 293                                 continue;
 294                             }
 295                             let name = variant.fields[p.field.index()].ident;
 296                             write!(f, "{}{}: {}", start_or_continue(), name, p.pattern)?;
 297                             printed += 1;
 298                         }
 299
 300                         if printed < variant.fields.len() {
 301                             write!(f, "{}..", start_or_continue())?;
 302                         }
 303
 304                         return write!(f, " }}");
 305                     }
 306                 }
 307
 308                 let num_fields = variant.map_or(subpatterns.len(), |v| v.fields.len());
 309                 if num_fields != 0 || variant.is_none() {
 310                     write!(f, "(")?;
 311                     for i in 0..num_fields {
 312                         write!(f, "{}", start_or_continue())?;
 313
 314                         // Common case: the field is where we expect it.
 315                         if let Some(p) = subpatterns.get(i) {
 316                             if p.field.index() == i {
 317                                 write!(f, "{}", p.pattern)?;
 318                                 continue;
 319                             }
 320                         }
 321
 322                         // Otherwise, we have to go looking for it.
 323                         if let Some(p) = subpatterns.iter().find(|p| p.field.index() == i) {
 324                             write!(f, "{}", p.pattern)?;
 325                         } else {
 326                             write!(f, "_")?;
 327                         }
 328                     }
 329                     write!(f, ")")?;
 330                 }
 331
 332                 Ok(())
 333             }
 334             PatternKind::Deref { ref subpattern } => {
 335                 match self.ty.sty {
 336                     ty::Adt(def, _) if def.is_box() => write!(f, "box ")?,
 337                     ty::Ref(_, _, mutbl) => {
 338                         write!(f, "&")?;
 339                         if mutbl == hir::MutMutable {
 340                             write!(f, "mut ")?;
 341                         }
 342                     }
 343                     _ => bug!("{} is a bad Deref pattern type", self.ty)
 344                 }
 345                 write!(f, "{}", subpattern)
 346             }
 347             PatternKind::Constant { value } => {
 348                 fmt_const_val(f, value)
 349             }
 350             PatternKind::Range(PatternRange { lo, hi, ty: _, end }) => {
 351                 fmt_const_val(f, lo)?;
 352                 match end {
 353                     RangeEnd::Included => write!(f, "..=")?,
 354                     RangeEnd::Excluded => write!(f, "..")?,
 355                 }
 356                 fmt_const_val(f, hi)
 357             }
 358             PatternKind::Slice { ref prefix, ref slice, ref suffix } |
 359             PatternKind::Array { ref prefix, ref slice, ref suffix } => {
 360                 let mut first = true;
 361                 let mut start_or_continue = || if first { first = false; "" } else { ", " };
 362                 write!(f, "[")?;
 363                 for p in prefix {
 364                     write!(f, "{}{}", start_or_continue(), p)?;
 365                 }
 366                 if let Some(ref slice) = *slice {
 367                     write!(f, "{}", start_or_continue())?;
 368                     match *slice.kind {
 369                         PatternKind::Wild => {}
 370                         _ => write!(f, "{}", slice)?
 371                     }
 372                     write!(f, "..")?;
 373                 }
 374                 for p in suffix {
 375                     write!(f, "{}{}", start_or_continue(), p)?;
 376                 }
 377                 write!(f, "]")
 378             }
 379         }
 380     }
 381 }
 382
 383 pub struct PatternContext<'a, 'tcx: 'a> {
 384     pub tcx: TyCtxt<'a, 'tcx, 'tcx>,
 385     pub param_env: ty::ParamEnv<'tcx>,
 386     pub tables: &'a ty::TypeckTables<'tcx>,
 387     pub substs: &'tcx Substs<'tcx>,
 388     pub errors: Vec<PatternError>,
 389 }
 390
 391 impl<'a, 'tcx> Pattern<'tcx> {
 392     pub fn from_hir(tcx: TyCtxt<'a, 'tcx, 'tcx>,
 393                     param_env_and_substs: ty::ParamEnvAnd<'tcx, &'tcx Substs<'tcx>>,
 394                     tables: &'a ty::TypeckTables<'tcx>,
 395                     pat: &'tcx hir::Pat) -> Self {
 396         let mut pcx = PatternContext::new(tcx, param_env_and_substs, tables);
 397         let result = pcx.lower_pattern(pat);
 398         if !pcx.errors.is_empty() {
 399             let msg = format!("encountered errors lowering pattern: {:?}", pcx.errors);
 400             tcx.sess.delay_span_bug(pat.span, &msg);
 401         }
 402         debug!("Pattern::from_hir({:?}) = {:?}", pat, result);
 403         result
 404     }
 405 }
 406
 407 impl<'a, 'tcx> PatternContext<'a, 'tcx> {
 408     pub fn new(tcx: TyCtxt<'a, 'tcx, 'tcx>,
 409                param_env_and_substs: ty::ParamEnvAnd<'tcx, &'tcx Substs<'tcx>>,
 410                tables: &'a ty::TypeckTables<'tcx>) -> Self {
 411         PatternContext {
 412             tcx,
 413             param_env: param_env_and_substs.param_env,
 414             tables,
 415             substs: param_env_and_substs.value,
 416             errors: vec![]
 417         }
 418     }
 419
 420     pub fn lower_pattern(&mut self, pat: &'tcx hir::Pat) -> Pattern<'tcx> {
 421         // When implicit dereferences have been inserted in this pattern, the unadjusted lowered
 422         // pattern has the type that results *after* dereferencing. For example, in this code:
 423         //
 424         // ```
 425         // match &&Some(0i32) {
 426         //     Some(n) => { ... },
 427         //     _ => { ... },
 428         // }
 429         // ```
 430         //
 431         // the type assigned to `Some(n)` in `unadjusted_pat` would be `Option<i32>` (this is
 432         // determined in rustc_typeck::check::match). The adjustments would be
 433         //
 434         // `vec![&&Option<i32>, &Option<i32>]`.
 435         //
 436         // Applying the adjustments, we want to instead output `&&Some(n)` (as a HAIR pattern). So
 437         // we wrap the unadjusted pattern in `PatternKind::Deref` repeatedly, consuming the
 438         // adjustments in *reverse order* (last-in-first-out, so that the last `Deref` inserted
 439         // gets the least-dereferenced type).
 440         let unadjusted_pat = self.lower_pattern_unadjusted(pat);
 441         self.tables
 442             .pat_adjustments()
 443             .get(pat.hir_id)
 444             .unwrap_or(&vec![])
 445             .iter()
 446             .rev()
 447             .fold(unadjusted_pat, |pat, ref_ty| {
 448                     debug!("{:?}: wrapping pattern with type {:?}", pat, ref_ty);
 449                     Pattern {
 450                         span: pat.span,
 451                         ty: ref_ty,
 452                         kind: Box::new(PatternKind::Deref { subpattern: pat }),
 453                     }
 454                 },
 455             )
 456     }
 457
 458     fn lower_pattern_unadjusted(&mut self, pat: &'tcx hir::Pat) -> Pattern<'tcx> {
 459         let mut ty = self.tables.node_id_to_type(pat.hir_id);
 460
 461         let kind = match pat.node {
 462             PatKind::Wild => PatternKind::Wild,
 463
 464             PatKind::Lit(ref value) => self.lower_lit(value),
 465
 466             PatKind::Range(ref lo_expr, ref hi_expr, end) => {
 467                 match (self.lower_lit(lo_expr), self.lower_lit(hi_expr)) {
 468                     (PatternKind::Constant { value: lo },
 469                      PatternKind::Constant { value: hi }) => {
 470                         use std::cmp::Ordering;
 471                         let cmp = compare_const_vals(
 472                             self.tcx,
 473                             lo,
 474                             hi,
 475                             self.param_env.and(ty),
 476                         );
 477                         match (end, cmp) {
 478                             (RangeEnd::Excluded, Some(Ordering::Less)) =>
 479                                 PatternKind::Range(PatternRange { lo, hi, ty, end }),
 480                             (RangeEnd::Excluded, _) => {
 481                                 span_err!(
 482                                     self.tcx.sess,
 483                                     lo_expr.span,
 484                                     E0579,
 485                                     "lower range bound must be less than upper",
 486                                 );
 487                                 PatternKind::Wild
 488                             }
 489                             (RangeEnd::Included, Some(Ordering::Equal)) => {
 490                                 PatternKind::Constant { value: lo }
 491                             }
 492                             (RangeEnd::Included, Some(Ordering::Less)) => {
 493                                 PatternKind::Range(PatternRange { lo, hi, ty, end })
 494                             }
 495                             (RangeEnd::Included, _) => {
 496                                 let mut err = struct_span_err!(
 497                                     self.tcx.sess,
 498                                     lo_expr.span,
 499                                     E0030,
 500                                     "lower range bound must be less than or equal to upper"
 501                                 );
 502                                 err.span_label(
 503                                     lo_expr.span,
 504                                     "lower bound larger than upper bound",
 505                                 );
 506                                 if self.tcx.sess.teach(&err.get_code().unwrap()) {
 507                                     err.note("When matching against a range, the compiler \
 508                                               verifies that the range is non-empty. Range \
 509                                               patterns include both end-points, so this is \
 510                                               equivalent to requiring the start of the range \
 511                                               to be less than or equal to the end of the range.");
 512                                 }
 513                                 err.emit();
 514                                 PatternKind::Wild
 515                             }
 516                         }
 517                     }
 518                     _ => PatternKind::Wild
 519                 }
 520             }
 521
 522             PatKind::Path(ref qpath) => {
 523                 return self.lower_path(qpath, pat.hir_id, pat.span);
 524             }
 525
 526             PatKind::Ref(ref subpattern, _) |
 527             PatKind::Box(ref subpattern) => {
 528                 PatternKind::Deref { subpattern: self.lower_pattern(subpattern) }
 529             }
 530
 531             PatKind::Slice(ref prefix, ref slice, ref suffix) => {
 532                 match ty.sty {
 533                     ty::Ref(_, ty, _) =>
 534                         PatternKind::Deref {
 535                             subpattern: Pattern {
 536                                 ty,
 537                                 span: pat.span,
 538                                 kind: Box::new(self.slice_or_array_pattern(
 539                                     pat.span, ty, prefix, slice, suffix))
 540                             },
 541                         },
 542                     ty::Slice(..) |
 543                     ty::Array(..) =>
 544                         self.slice_or_array_pattern(pat.span, ty, prefix, slice, suffix),
 545                     ty::Error => { // Avoid ICE
 546                         return Pattern { span: pat.span, ty, kind: Box::new(PatternKind::Wild) };
 547                     }
 548                     ref sty =>
 549                         span_bug!(
 550                             pat.span,
 551                             "unexpanded type for vector pattern: {:?}",
 552                             sty),
 553                 }
 554             }
 555
 556             PatKind::Tuple(ref subpatterns, ddpos) => {
 557                 match ty.sty {
 558                     ty::Tuple(ref tys) => {
 559                         let subpatterns =
 560                             subpatterns.iter()
 561                                        .enumerate_and_adjust(tys.len(), ddpos)
 562                                        .map(|(i, subpattern)| FieldPattern {
 563                                             field: Field::new(i),
 564                                             pattern: self.lower_pattern(subpattern)
 565                                        })
 566                                        .collect();
 567
 568                         PatternKind::Leaf { subpatterns }
 569                     }
 570                     ty::Error => { // Avoid ICE (#50577)
 571                         return Pattern { span: pat.span, ty, kind: Box::new(PatternKind::Wild) };
 572                     }
 573                     ref sty => span_bug!(pat.span, "unexpected type for tuple pattern: {:?}", sty),
 574                 }
 575             }
 576
 577             PatKind::Binding(_, id, ident, ref sub) => {
 578                 let var_ty = self.tables.node_id_to_type(pat.hir_id);
 579                 let region = match var_ty.sty {
 580                     ty::Ref(r, _, _) => Some(r),
 581                     ty::Error => { // Avoid ICE
 582                         return Pattern { span: pat.span, ty, kind: Box::new(PatternKind::Wild) };
 583                     }
 584                     _ => None,
 585                 };
 586                 let bm = *self.tables.pat_binding_modes().get(pat.hir_id)
 587                                                          .expect("missing binding mode");
 588                 let (mutability, mode) = match bm {
 589                     ty::BindByValue(hir::MutMutable) =>
 590                         (Mutability::Mut, BindingMode::ByValue),
 591                     ty::BindByValue(hir::MutImmutable) =>
 592                         (Mutability::Not, BindingMode::ByValue),
 593                     ty::BindByReference(hir::MutMutable) =>
 594                         (Mutability::Not, BindingMode::ByRef(
 595                             region.unwrap(), BorrowKind::Mut { allow_two_phase_borrow: false })),
 596                     ty::BindByReference(hir::MutImmutable) =>
 597                         (Mutability::Not, BindingMode::ByRef(
 598                             region.unwrap(), BorrowKind::Shared)),
 599                 };
 600
 601                 // A ref x pattern is the same node used for x, and as such it has
 602                 // x's type, which is &T, where we want T (the type being matched).
 603                 if let ty::BindByReference(_) = bm {
 604                     if let ty::Ref(_, rty, _) = ty.sty {
 605                         ty = rty;
 606                     } else {
 607                         bug!("`ref {}` has wrong type {}", ident, ty);
 608                     }
 609                 }
 610
 611                 PatternKind::Binding {
 612                     mutability,
 613                     mode,
 614                     name: ident.name,
 615                     var: id,
 616                     ty: var_ty,
 617                     subpattern: self.lower_opt_pattern(sub),
 618                 }
 619             }
 620
 621             PatKind::TupleStruct(ref qpath, ref subpatterns, ddpos) => {
 622                 let def = self.tables.qpath_def(qpath, pat.hir_id);
 623                 let adt_def = match ty.sty {
 624                     ty::Adt(adt_def, _) => adt_def,
 625                     ty::Error => { // Avoid ICE (#50585)
 626                         return Pattern { span: pat.span, ty, kind: Box::new(PatternKind::Wild) };
 627                     }
 628                     _ => span_bug!(pat.span,
 629                                    "tuple struct pattern not applied to an ADT {:?}",
 630                                    ty.sty),
 631                 };
 632                 let variant_def = adt_def.variant_of_def(def);
 633
 634                 let subpatterns =
 635                         subpatterns.iter()
 636                                    .enumerate_and_adjust(variant_def.fields.len(), ddpos)
 637                                    .map(|(i, field)| FieldPattern {
 638                                        field: Field::new(i),
 639                                        pattern: self.lower_pattern(field),
 640                                    })
 641                     .collect();
 642
 643                 self.lower_variant_or_leaf(def, pat.hir_id, pat.span, ty, subpatterns)
 644             }
 645
 646             PatKind::Struct(ref qpath, ref fields, _) => {
 647                 let def = self.tables.qpath_def(qpath, pat.hir_id);
 648                 let subpatterns =
 649                     fields.iter()
 650                           .map(|field| {
 651                               FieldPattern {
 652                                   field: Field::new(self.tcx.field_index(field.node.id,
 653                                                                          self.tables)),
 654                                   pattern: self.lower_pattern(&field.node.pat),
 655                               }
 656                           })
 657                           .collect();
 658
 659                 self.lower_variant_or_leaf(def, pat.hir_id, pat.span, ty, subpatterns)
 660             }
 661         };
 662
 663         Pattern {
 664             span: pat.span,
 665             ty,
 666             kind: Box::new(kind),
 667         }
 668     }
 669
 670     fn lower_patterns(&mut self, pats: &'tcx [P<hir::Pat>]) -> Vec<Pattern<'tcx>> {
 671         pats.iter().map(|p| self.lower_pattern(p)).collect()
 672     }
 673
 674     fn lower_opt_pattern(&mut self, pat: &'tcx Option<P<hir::Pat>>) -> Option<Pattern<'tcx>>
 675     {
 676         pat.as_ref().map(|p| self.lower_pattern(p))
 677     }
 678
 679     fn flatten_nested_slice_patterns(
 680         &mut self,
 681         prefix: Vec<Pattern<'tcx>>,
 682         slice: Option<Pattern<'tcx>>,
 683         suffix: Vec<Pattern<'tcx>>)
 684         -> (Vec<Pattern<'tcx>>, Option<Pattern<'tcx>>, Vec<Pattern<'tcx>>)
 685     {
 686         let orig_slice = match slice {
 687             Some(orig_slice) => orig_slice,
 688             None => return (prefix, slice, suffix)
 689         };
 690         let orig_prefix = prefix;
 691         let orig_suffix = suffix;
 692
 693         // dance because of intentional borrow-checker stupidity.
 694         let kind = *orig_slice.kind;
 695         match kind {
 696             PatternKind::Slice { prefix, slice, mut suffix } |
 697             PatternKind::Array { prefix, slice, mut suffix } => {
 698                 let mut orig_prefix = orig_prefix;
 699
 700                 orig_prefix.extend(prefix);
 701                 suffix.extend(orig_suffix);
 702
 703                 (orig_prefix, slice, suffix)
 704             }
 705             _ => {
 706                 (orig_prefix, Some(Pattern {
 707                     kind: box kind, ..orig_slice
 708                 }), orig_suffix)
 709             }
 710         }
 711     }
 712
 713     fn slice_or_array_pattern(
 714         &mut self,
 715         span: Span,
 716         ty: Ty<'tcx>,
 717         prefix: &'tcx [P<hir::Pat>],
 718         slice: &'tcx Option<P<hir::Pat>>,
 719         suffix: &'tcx [P<hir::Pat>])
 720         -> PatternKind<'tcx>
 721     {
 722         let prefix = self.lower_patterns(prefix);
 723         let slice = self.lower_opt_pattern(slice);
 724         let suffix = self.lower_patterns(suffix);
 725         let (prefix, slice, suffix) =
 726             self.flatten_nested_slice_patterns(prefix, slice, suffix);
 727
 728         match ty.sty {
 729             ty::Slice(..) => {
 730                 // matching a slice or fixed-length array
 731                 PatternKind::Slice { prefix: prefix, slice: slice, suffix: suffix }
 732             }
 733
 734             ty::Array(_, len) => {
 735                 // fixed-length array
 736                 let len = len.unwrap_usize(self.tcx);
 737                 assert!(len >= prefix.len() as u64 + suffix.len() as u64);
 738                 PatternKind::Array { prefix: prefix, slice: slice, suffix: suffix }
 739             }
 740
 741             _ => {
 742                 span_bug!(span, "bad slice pattern type {:?}", ty);
 743             }
 744         }
 745     }
 746
 747     fn lower_variant_or_leaf(
 748         &mut self,
 749         def: Def,
 750         hir_id: hir::HirId,
 751         span: Span,
 752         ty: Ty<'tcx>,
 753         subpatterns: Vec<FieldPattern<'tcx>>,
 754     ) -> PatternKind<'tcx> {
 755         let mut kind = match def {
 756             Def::Variant(variant_id) | Def::VariantCtor(variant_id, ..) => {
 757                 let enum_id = self.tcx.parent_def_id(variant_id).unwrap();
 758                 let adt_def = self.tcx.adt_def(enum_id);
 759                 if adt_def.is_enum() {
 760                     let substs = match ty.sty {
 761                         ty::Adt(_, substs) |
 762                         ty::FnDef(_, substs) => substs,
 763                         ty::Error => {  // Avoid ICE (#50585)
 764                             return PatternKind::Wild;
 765                         }
 766                         _ => bug!("inappropriate type for def: {:?}", ty.sty),
 767                     };
 768                     PatternKind::Variant {
 769                         adt_def,
 770                         substs,
 771                         variant_index: adt_def.variant_index_with_id(variant_id),
 772                         subpatterns,
 773                     }
 774                 } else {
 775                     PatternKind::Leaf { subpatterns }
 776                 }
 777             }
 778
 779             Def::Struct(..) | Def::StructCtor(..) | Def::Union(..) |
 780             Def::TyAlias(..) | Def::AssociatedTy(..) | Def::SelfTy(..) | Def::SelfCtor(..) => {
 781                 PatternKind::Leaf { subpatterns }
 782             }
 783
 784             _ => {
 785                 self.errors.push(PatternError::NonConstPath(span));
 786                 PatternKind::Wild
 787             }
 788         };
 789
 790         if let Some(user_ty) = self.user_substs_applied_to_ty_of_hir_id(hir_id) {
 791             let subpattern = Pattern {
 792                 span,
 793                 ty,
 794                 kind: Box::new(kind),
 795             };
 796
 797             debug!("pattern user_ty = {:?} for pattern at {:?}", user_ty, span);
 798
 799             let pat_ty = PatternTypeProjection::from_user_type(user_ty);
 800             kind = PatternKind::AscribeUserType {
 801                 subpattern,
 802                 user_ty: pat_ty,
 803                 user_ty_span: span,
 804             };
 805         }
 806
 807         kind
 808     }
 809
 810     /// Takes a HIR Path. If the path is a constant, evaluates it and feeds
 811     /// it to `const_to_pat`. Any other path (like enum variants without fields)
 812     /// is converted to the corresponding pattern via `lower_variant_or_leaf`
 813     fn lower_path(&mut self,
 814                   qpath: &hir::QPath,
 815                   id: hir::HirId,
 816                   span: Span)
 817                   -> Pattern<'tcx> {
 818         let ty = self.tables.node_id_to_type(id);
 819         let def = self.tables.qpath_def(qpath, id);
 820         let is_associated_const = match def {
 821             Def::AssociatedConst(_) => true,
 822             _ => false,
 823         };
 824         let kind = match def {
 825             Def::Const(def_id) | Def::AssociatedConst(def_id) => {
 826                 let substs = self.tables.node_substs(id);
 827                 match ty::Instance::resolve(
 828                     self.tcx,
 829                     self.param_env,
 830                     def_id,
 831                     substs,
 832                 ) {
 833                     Some(instance) => {
 834                         let cid = GlobalId {
 835                             instance,
 836                             promoted: None,
 837                         };
 838                         match self.tcx.at(span).const_eval(self.param_env.and(cid)) {
 839                             Ok(value) => {
 840                                 return self.const_to_pat(instance, value, id, span)
 841                             },
 842                             Err(_) => {
 843                                 self.tcx.sess.span_err(
 844                                     span,
 845                                     "could not evaluate constant pattern",
 846                                 );
 847                                 PatternKind::Wild
 848                             }
 849                         }
 850                     },
 851                     None => {
 852                         self.errors.push(if is_associated_const {
 853                             PatternError::AssociatedConstInPattern(span)
 854                         } else {
 855                             PatternError::StaticInPattern(span)
 856                         });
 857                         PatternKind::Wild
 858                     },
 859                 }
 860             }
 861             _ => self.lower_variant_or_leaf(def, id, span, ty, vec![]),
 862         };
 863
 864         Pattern {
 865             span,
 866             ty,
 867             kind: Box::new(kind),
 868         }
 869     }
 870
 871     /// Converts literals, paths and negation of literals to patterns.
 872     /// The special case for negation exists to allow things like -128i8
 873     /// which would overflow if we tried to evaluate 128i8 and then negate
 874     /// afterwards.
 875     fn lower_lit(&mut self, expr: &'tcx hir::Expr) -> PatternKind<'tcx> {
 876         match expr.node {
 877             hir::ExprKind::Lit(ref lit) => {
 878                 let ty = self.tables.expr_ty(expr);
 879                 match lit_to_const(&lit.node, self.tcx, ty, false) {
 880                     Ok(val) => {
 881                         let instance = ty::Instance::new(
 882                             self.tables.local_id_root.expect("literal outside any scope"),
 883                             self.substs,
 884                         );
 885                         *self.const_to_pat(instance, val, expr.hir_id, lit.span).kind
 886                     },
 887                     Err(LitToConstError::UnparseableFloat) => {
 888                         self.errors.push(PatternError::FloatBug);
 889                         PatternKind::Wild
 890                     },
 891                     Err(LitToConstError::Reported) => PatternKind::Wild,
 892                 }
 893             },
 894             hir::ExprKind::Path(ref qpath) => *self.lower_path(qpath, expr.hir_id, expr.span).kind,
 895             hir::ExprKind::Unary(hir::UnNeg, ref expr) => {
 896                 let ty = self.tables.expr_ty(expr);
 897                 let lit = match expr.node {
 898                     hir::ExprKind::Lit(ref lit) => lit,
 899                     _ => span_bug!(expr.span, "not a literal: {:?}", expr),
 900                 };
 901                 match lit_to_const(&lit.node, self.tcx, ty, true) {
 902                     Ok(val) => {
 903                         let instance = ty::Instance::new(
 904                             self.tables.local_id_root.expect("literal outside any scope"),
 905                             self.substs,
 906                         );
 907                         *self.const_to_pat(instance, val, expr.hir_id, lit.span).kind
 908                     },
 909                     Err(LitToConstError::UnparseableFloat) => {
 910                         self.errors.push(PatternError::FloatBug);
 911                         PatternKind::Wild
 912                     },
 913                     Err(LitToConstError::Reported) => PatternKind::Wild,
 914                 }
 915             }
 916             _ => span_bug!(expr.span, "not a literal: {:?}", expr),
 917         }
 918     }
 919
 920     /// Converts an evaluated constant to a pattern (if possible).
 921     /// This means aggregate values (like structs and enums) are converted
 922     /// to a pattern that matches the value (as if you'd compare via eq).
 923     fn const_to_pat(
 924         &self,
 925         instance: ty::Instance<'tcx>,
 926         cv: &'tcx ty::Const<'tcx>,
 927         id: hir::HirId,
 928         span: Span,
 929     ) -> Pattern<'tcx> {
 930         debug!("const_to_pat: cv={:#?}", cv);
 931         let adt_subpattern = |i, variant_opt| {
 932             let field = Field::new(i);
 933             let val = const_field(
 934                 self.tcx, self.param_env, instance,
 935                 variant_opt, field, cv,
 936             ).expect("field access failed");
 937             self.const_to_pat(instance, val, id, span)
 938         };
 939         let adt_subpatterns = |n, variant_opt| {
 940             (0..n).map(|i| {
 941                 let field = Field::new(i);
 942                 FieldPattern {
 943                     field,
 944                     pattern: adt_subpattern(i, variant_opt),
 945                 }
 946             }).collect::<Vec<_>>()
 947         };
 948         let kind = match cv.ty.sty {
 949             ty::Float(_) => {
 950                 let id = self.tcx.hir().hir_to_node_id(id);
 951                 self.tcx.lint_node(
 952                     ::rustc::lint::builtin::ILLEGAL_FLOATING_POINT_LITERAL_PATTERN,
 953                     id,
 954                     span,
 955                     "floating-point types cannot be used in patterns",
 956                 );
 957                 PatternKind::Constant {
 958                     value: cv,
 959                 }
 960             },
 961             ty::Adt(adt_def, _) if adt_def.is_union() => {
 962                 // Matching on union fields is unsafe, we can't hide it in constants
 963                 self.tcx.sess.span_err(span, "cannot use unions in constant patterns");
 964                 PatternKind::Wild
 965             }
 966             ty::Adt(adt_def, _) if !self.tcx.has_attr(adt_def.did, "structural_match") => {
 967                 let msg = format!("to use a constant of type `{}` in a pattern, \
 968                                     `{}` must be annotated with `#[derive(PartialEq, Eq)]`",
 969                                     self.tcx.item_path_str(adt_def.did),
 970                                     self.tcx.item_path_str(adt_def.did));
 971                 self.tcx.sess.span_err(span, &msg);
 972                 PatternKind::Wild
 973             },
 974             ty::Adt(adt_def, substs) if adt_def.is_enum() => {
 975                 let variant_index = const_variant_index(
 976                     self.tcx, self.param_env, instance, cv
 977                 ).expect("const_variant_index failed");
 978                 let subpatterns = adt_subpatterns(
 979                     adt_def.variants[variant_index].fields.len(),
 980                     Some(variant_index),
 981                 );
 982                 PatternKind::Variant {
 983                     adt_def,
 984                     substs,
 985                     variant_index,
 986                     subpatterns,
 987                 }
 988             },
 989             ty::Adt(adt_def, _) => {
 990                 let struct_var = adt_def.non_enum_variant();
 991                 PatternKind::Leaf {
 992                     subpatterns: adt_subpatterns(struct_var.fields.len(), None),
 993                 }
 994             }
 995             ty::Tuple(fields) => {
 996                 PatternKind::Leaf {
 997                     subpatterns: adt_subpatterns(fields.len(), None),
 998                 }
 999             }
1000             ty::Array(_, n) => {
1001                 PatternKind::Array {
1002                     prefix: (0..n.unwrap_usize(self.tcx))
1003                         .map(|i| adt_subpattern(i as usize, None))
1004                         .collect(),
1005                     slice: None,
1006                     suffix: Vec::new(),
1007                 }
1008             }
1009             _ => {
1010                 PatternKind::Constant {
1011                     value: cv,
1012                 }
1013             },
1014         };
1015
1016         Pattern {
1017             span,
1018             ty: cv.ty,
1019             kind: Box::new(kind),
1020         }
1021     }
1022 }
1023
1024 impl UserAnnotatedTyHelpers<'tcx, 'tcx> for PatternContext<'_, 'tcx> {
1025     fn tcx(&self) -> TyCtxt<'_, 'tcx, 'tcx> {
1026         self.tcx
1027     }
1028
1029     fn tables(&self) -> &ty::TypeckTables<'tcx> {
1030         self.tables
1031     }
1032 }
1033
1034
1035 pub trait PatternFoldable<'tcx> : Sized {
1036     fn fold_with<F: PatternFolder<'tcx>>(&self, folder: &mut F) -> Self {
1037         self.super_fold_with(folder)
1038     }
1039
1040     fn super_fold_with<F: PatternFolder<'tcx>>(&self, folder: &mut F) -> Self;
1041 }
1042
1043 pub trait PatternFolder<'tcx> : Sized {
1044     fn fold_pattern(&mut self, pattern: &Pattern<'tcx>) -> Pattern<'tcx> {
1045         pattern.super_fold_with(self)
1046     }
1047
1048     fn fold_pattern_kind(&mut self, kind: &PatternKind<'tcx>) -> PatternKind<'tcx> {
1049         kind.super_fold_with(self)
1050     }
1051 }
1052
1053
1054 impl<'tcx, T: PatternFoldable<'tcx>> PatternFoldable<'tcx> for Box<T> {
1055     fn super_fold_with<F: PatternFolder<'tcx>>(&self, folder: &mut F) -> Self {
1056         let content: T = (**self).fold_with(folder);
1057         box content
1058     }
1059 }
1060
1061 impl<'tcx, T: PatternFoldable<'tcx>> PatternFoldable<'tcx> for Vec<T> {
1062     fn super_fold_with<F: PatternFolder<'tcx>>(&self, folder: &mut F) -> Self {
1063         self.iter().map(|t| t.fold_with(folder)).collect()
1064     }
1065 }
1066
1067 impl<'tcx, T: PatternFoldable<'tcx>> PatternFoldable<'tcx> for Option<T> {
1068     fn super_fold_with<F: PatternFolder<'tcx>>(&self, folder: &mut F) -> Self{
1069         self.as_ref().map(|t| t.fold_with(folder))
1070     }
1071 }
1072
1073 macro_rules! CloneImpls {
1074     (<$lt_tcx:tt> $($ty:ty),+) => {
1075         $(
1076             impl<$lt_tcx> PatternFoldable<$lt_tcx> for $ty {
1077                 fn super_fold_with<F: PatternFolder<$lt_tcx>>(&self, _: &mut F) -> Self {
1078                     Clone::clone(self)
1079                 }
1080             }
1081         )+
1082     }
1083 }
1084
1085 CloneImpls!{ <'tcx>
1086     Span, Field, Mutability, ast::Name, ast::NodeId, usize, &'tcx ty::Const<'tcx>,
1087     Region<'tcx>, Ty<'tcx>, BindingMode<'tcx>, &'tcx AdtDef,
1088     &'tcx Substs<'tcx>, &'tcx Kind<'tcx>, UserTypeAnnotation<'tcx>,
1089     UserTypeProjection<'tcx>, PatternTypeProjection<'tcx>
1090 }
1091
1092 impl<'tcx> PatternFoldable<'tcx> for FieldPattern<'tcx> {
1093     fn super_fold_with<F: PatternFolder<'tcx>>(&self, folder: &mut F) -> Self {
1094         FieldPattern {
1095             field: self.field.fold_with(folder),
1096             pattern: self.pattern.fold_with(folder)
1097         }
1098     }
1099 }
1100
1101 impl<'tcx> PatternFoldable<'tcx> for Pattern<'tcx> {
1102     fn fold_with<F: PatternFolder<'tcx>>(&self, folder: &mut F) -> Self {
1103         folder.fold_pattern(self)
1104     }
1105
1106     fn super_fold_with<F: PatternFolder<'tcx>>(&self, folder: &mut F) -> Self {
1107         Pattern {
1108             ty: self.ty.fold_with(folder),
1109             span: self.span.fold_with(folder),
1110             kind: self.kind.fold_with(folder)
1111         }
1112     }
1113 }
1114
1115 impl<'tcx> PatternFoldable<'tcx> for PatternKind<'tcx> {
1116     fn fold_with<F: PatternFolder<'tcx>>(&self, folder: &mut F) -> Self {
1117         folder.fold_pattern_kind(self)
1118     }
1119
1120     fn super_fold_with<F: PatternFolder<'tcx>>(&self, folder: &mut F) -> Self {
1121         match *self {
1122             PatternKind::Wild => PatternKind::Wild,
1123             PatternKind::AscribeUserType {
1124                 ref subpattern,
1125                 ref user_ty,
1126                 user_ty_span,
1127             } => PatternKind::AscribeUserType {
1128                 subpattern: subpattern.fold_with(folder),
1129                 user_ty: user_ty.fold_with(folder),
1130                 user_ty_span,
1131             },
1132             PatternKind::Binding {
1133                 mutability,
1134                 name,
1135                 mode,
1136                 var,
1137                 ty,
1138                 ref subpattern,
1139             } => PatternKind::Binding {
1140                 mutability: mutability.fold_with(folder),
1141                 name: name.fold_with(folder),
1142                 mode: mode.fold_with(folder),
1143                 var: var.fold_with(folder),
1144                 ty: ty.fold_with(folder),
1145                 subpattern: subpattern.fold_with(folder),
1146             },
1147             PatternKind::Variant {
1148                 adt_def,
1149                 substs,
1150                 variant_index,
1151                 ref subpatterns,
1152             } => PatternKind::Variant {
1153                 adt_def: adt_def.fold_with(folder),
1154                 substs: substs.fold_with(folder),
1155                 variant_index,
1156                 subpatterns: subpatterns.fold_with(folder)
1157             },
1158             PatternKind::Leaf {
1159                 ref subpatterns,
1160             } => PatternKind::Leaf {
1161                 subpatterns: subpatterns.fold_with(folder),
1162             },
1163             PatternKind::Deref {
1164                 ref subpattern,
1165             } => PatternKind::Deref {
1166                 subpattern: subpattern.fold_with(folder),
1167             },
1168             PatternKind::Constant {
1169                 value
1170             } => PatternKind::Constant {
1171                 value: value.fold_with(folder)
1172             },
1173             PatternKind::Range(PatternRange {
1174                 lo,
1175                 hi,
1176                 ty,
1177                 end,
1178             }) => PatternKind::Range(PatternRange {
1179                 lo: lo.fold_with(folder),
1180                 hi: hi.fold_with(folder),
1181                 ty: ty.fold_with(folder),
1182                 end,
1183             }),
1184             PatternKind::Slice {
1185                 ref prefix,
1186                 ref slice,
1187                 ref suffix,
1188             } => PatternKind::Slice {
1189                 prefix: prefix.fold_with(folder),
1190                 slice: slice.fold_with(folder),
1191                 suffix: suffix.fold_with(folder)
1192             },
1193             PatternKind::Array {
1194                 ref prefix,
1195                 ref slice,
1196                 ref suffix
1197             } => PatternKind::Array {
1198                 prefix: prefix.fold_with(folder),
1199                 slice: slice.fold_with(folder),
1200                 suffix: suffix.fold_with(folder)
1201             },
1202         }
1203     }
1204 }
1205
1206 pub fn compare_const_vals<'a, 'gcx, 'tcx>(
1207     tcx: TyCtxt<'a, 'gcx, 'tcx>,
1208     a: &'tcx ty::Const<'tcx>,
1209     b: &'tcx ty::Const<'tcx>,
1210     ty: ty::ParamEnvAnd<'tcx, Ty<'tcx>>,
1211 ) -> Option<Ordering> {
1212     trace!("compare_const_vals: {:?}, {:?}", a, b);
1213
1214     let from_bool = |v: bool| {
1215         if v {
1216             Some(Ordering::Equal)
1217         } else {
1218             None
1219         }
1220     };
1221
1222     let fallback = || from_bool(a == b);
1223
1224     // Use the fallback if any type differs
1225     if a.ty != b.ty || a.ty != ty.value {
1226         return fallback();
1227     }
1228
1229     let tcx = tcx.global_tcx();
1230     let (a, b, ty) = (a, b, ty).lift_to_tcx(tcx).unwrap();
1231
1232     // FIXME: This should use assert_bits(ty) instead of use_bits
1233     // but triggers possibly bugs due to mismatching of arrays and slices
1234     if let (Some(a), Some(b)) = (a.to_bits(tcx, ty), b.to_bits(tcx, ty)) {
1235         use ::rustc_apfloat::Float;
1236         return match ty.value.sty {
1237             ty::Float(ast::FloatTy::F32) => {
1238                 let l = ::rustc_apfloat::ieee::Single::from_bits(a);
1239                 let r = ::rustc_apfloat::ieee::Single::from_bits(b);
1240                 l.partial_cmp(&r)
1241             },
1242             ty::Float(ast::FloatTy::F64) => {
1243                 let l = ::rustc_apfloat::ieee::Double::from_bits(a);
1244                 let r = ::rustc_apfloat::ieee::Double::from_bits(b);
1245                 l.partial_cmp(&r)
1246             },
1247             ty::Int(_) => {
1248                 let layout = tcx.layout_of(ty).ok()?;
1249                 assert!(layout.abi.is_signed());
1250                 let a = sign_extend(a, layout.size);
1251                 let b = sign_extend(b, layout.size);
1252                 Some((a as i128).cmp(&(b as i128)))
1253             },
1254             _ => Some(a.cmp(&b)),
1255         }
1256     }
1257
1258     if let ty::Str = ty.value.sty {
1259         match (a.val, b.val) {
1260             (
1261                 ConstValue::ScalarPair(
1262                     Scalar::Ptr(ptr_a),
1263                     len_a,
1264                 ),
1265                 ConstValue::ScalarPair(
1266                     Scalar::Ptr(ptr_b),
1267                     len_b,
1268                 ),
1269             ) if ptr_a.offset.bytes() == 0 && ptr_b.offset.bytes() == 0 => {
1270                 if let Ok(len_a) = len_a.to_bits(tcx.data_layout.pointer_size) {
1271                     if let Ok(len_b) = len_b.to_bits(tcx.data_layout.pointer_size) {
1272                         if len_a == len_b {
1273                             let map = tcx.alloc_map.lock();
1274                             let alloc_a = map.unwrap_memory(ptr_a.alloc_id);
1275                             let alloc_b = map.unwrap_memory(ptr_b.alloc_id);
1276                             if alloc_a.bytes.len() as u128 == len_a {
1277                                 return from_bool(alloc_a == alloc_b);
1278                             }
1279                         }
1280                     }
1281                 }
1282             }
1283             _ => (),
1284         }
1285     }
1286
1287     fallback()
1288 }