src/librustc_middle/ty/codec.rs

   1 // This module contains some shared code for encoding and decoding various
   2 // things from the `ty` module, and in particular implements support for
   3 // "shorthands" which allow to have pointers back into the already encoded
   4 // stream instead of re-encoding the same thing twice.
   5 //
   6 // The functionality in here is shared between persisting to crate metadata and
   7 // persisting to incr. comp. caches.
   8
   9 use crate::arena::ArenaAllocatable;
  10 use crate::infer::canonical::{CanonicalVarInfo, CanonicalVarInfos};
  11 use crate::mir::{self, interpret::Allocation};
  12 use crate::ty::subst::SubstsRef;
  13 use crate::ty::{self, List, Ty, TyCtxt};
  14 use rustc_data_structures::fx::FxHashMap;
  15 use rustc_hir::def_id::{CrateNum, DefId};
  16 use rustc_serialize::{opaque, Decodable, Decoder, Encodable, Encoder};
  17 use rustc_span::Span;
  18 use std::convert::{TryFrom, TryInto};
  19 use std::hash::Hash;
  20 use std::intrinsics;
  21 use std::marker::DiscriminantKind;
  22
  23 /// The shorthand encoding uses an enum's variant index `usize`
  24 /// and is offset by this value so it never matches a real variant.
  25 /// This offset is also chosen so that the first byte is never < 0x80.
  26 pub const SHORTHAND_OFFSET: usize = 0x80;
  27
  28 pub trait EncodableWithShorthand: Clone + Eq + Hash {
  29     type Variant: Encodable;
  30     fn variant(&self) -> &Self::Variant;
  31 }
  32
  33 #[allow(rustc::usage_of_ty_tykind)]
  34 impl<'tcx> EncodableWithShorthand for Ty<'tcx> {
  35     type Variant = ty::TyKind<'tcx>;
  36     fn variant(&self) -> &Self::Variant {
  37         &self.kind
  38     }
  39 }
  40
  41 impl<'tcx> EncodableWithShorthand for ty::Predicate<'tcx> {
  42     type Variant = ty::PredicateKind<'tcx>;
  43     fn variant(&self) -> &Self::Variant {
  44         self.kind()
  45     }
  46 }
  47
  48 pub trait TyEncoder: Encoder {
  49     fn position(&self) -> usize;
  50 }
  51
  52 impl TyEncoder for opaque::Encoder {
  53     #[inline]
  54     fn position(&self) -> usize {
  55         self.position()
  56     }
  57 }
  58
  59 /// Encode the given value or a previously cached shorthand.
  60 pub fn encode_with_shorthand<E, T, M>(encoder: &mut E, value: &T, cache: M) -> Result<(), E::Error>
  61 where
  62     E: TyEncoder,
  63     M: for<'b> Fn(&'b mut E) -> &'b mut FxHashMap<T, usize>,
  64     T: EncodableWithShorthand,
  65     <T::Variant as DiscriminantKind>::Discriminant: Ord + TryFrom<usize>,
  66 {
  67     let existing_shorthand = cache(encoder).get(value).cloned();
  68     if let Some(shorthand) = existing_shorthand {
  69         return encoder.emit_usize(shorthand);
  70     }
  71
  72     let variant = value.variant();
  73
  74     let start = encoder.position();
  75     variant.encode(encoder)?;
  76     let len = encoder.position() - start;
  77
  78     // The shorthand encoding uses the same usize as the
  79     // discriminant, with an offset so they can't conflict.
  80     let discriminant = intrinsics::discriminant_value(variant);
  81     assert!(discriminant < SHORTHAND_OFFSET.try_into().ok().unwrap());
  82
  83     let shorthand = start + SHORTHAND_OFFSET;
  84
  85     // Get the number of bits that leb128 could fit
  86     // in the same space as the fully encoded type.
  87     let leb128_bits = len * 7;
  88
  89     // Check that the shorthand is a not longer than the
  90     // full encoding itself, i.e., it's an obvious win.
  91     if leb128_bits >= 64 || (shorthand as u64) < (1 << leb128_bits) {
  92         cache(encoder).insert(value.clone(), shorthand);
  93     }
  94
  95     Ok(())
  96 }
  97
  98 pub trait TyDecoder<'tcx>: Decoder {
  99     fn tcx(&self) -> TyCtxt<'tcx>;
 100
 101     fn peek_byte(&self) -> u8;
 102
 103     fn position(&self) -> usize;
 104
 105     fn cached_ty_for_shorthand<F>(
 106         &mut self,
 107         shorthand: usize,
 108         or_insert_with: F,
 109     ) -> Result<Ty<'tcx>, Self::Error>
 110     where
 111         F: FnOnce(&mut Self) -> Result<Ty<'tcx>, Self::Error>;
 112
 113     fn cached_predicate_for_shorthand<F>(
 114         &mut self,
 115         shorthand: usize,
 116         or_insert_with: F,
 117     ) -> Result<ty::Predicate<'tcx>, Self::Error>
 118     where
 119         F: FnOnce(&mut Self) -> Result<ty::Predicate<'tcx>, Self::Error>;
 120
 121     fn with_position<F, R>(&mut self, pos: usize, f: F) -> R
 122     where
 123         F: FnOnce(&mut Self) -> R;
 124
 125     fn map_encoded_cnum_to_current(&self, cnum: CrateNum) -> CrateNum;
 126
 127     fn positioned_at_shorthand(&self) -> bool {
 128         (self.peek_byte() & (SHORTHAND_OFFSET as u8)) != 0
 129     }
 130 }
 131
 132 #[inline]
 133 pub fn decode_arena_allocable<'tcx, D, T: ArenaAllocatable<'tcx> + Decodable>(
 134     decoder: &mut D,
 135 ) -> Result<&'tcx T, D::Error>
 136 where
 137     D: TyDecoder<'tcx>,
 138 {
 139     Ok(decoder.tcx().arena.alloc(Decodable::decode(decoder)?))
 140 }
 141
 142 #[inline]
 143 pub fn decode_arena_allocable_slice<'tcx, D, T: ArenaAllocatable<'tcx> + Decodable>(
 144     decoder: &mut D,
 145 ) -> Result<&'tcx [T], D::Error>
 146 where
 147     D: TyDecoder<'tcx>,
 148 {
 149     Ok(decoder.tcx().arena.alloc_from_iter(<Vec<T> as Decodable>::decode(decoder)?))
 150 }
 151
 152 #[inline]
 153 pub fn decode_cnum<D>(decoder: &mut D) -> Result<CrateNum, D::Error>
 154 where
 155     D: TyDecoder<'tcx>,
 156 {
 157     let cnum = CrateNum::from_u32(u32::decode(decoder)?);
 158     Ok(decoder.map_encoded_cnum_to_current(cnum))
 159 }
 160
 161 #[allow(rustc::usage_of_ty_tykind)]
 162 #[inline]
 163 pub fn decode_ty<D>(decoder: &mut D) -> Result<Ty<'tcx>, D::Error>
 164 where
 165     D: TyDecoder<'tcx>,
 166 {
 167     // Handle shorthands first, if we have an usize > 0x80.
 168     if decoder.positioned_at_shorthand() {
 169         let pos = decoder.read_usize()?;
 170         assert!(pos >= SHORTHAND_OFFSET);
 171         let shorthand = pos - SHORTHAND_OFFSET;
 172
 173         decoder.cached_ty_for_shorthand(shorthand, |decoder| {
 174             decoder.with_position(shorthand, Ty::decode)
 175         })
 176     } else {
 177         let tcx = decoder.tcx();
 178         Ok(tcx.mk_ty(ty::TyKind::decode(decoder)?))
 179     }
 180 }
 181
 182 #[inline]
 183 pub fn decode_predicate<D>(decoder: &mut D) -> Result<ty::Predicate<'tcx>, D::Error>
 184 where
 185     D: TyDecoder<'tcx>,
 186 {
 187     // Handle shorthands first, if we have an usize > 0x80.
 188     if decoder.positioned_at_shorthand() {
 189         let pos = decoder.read_usize()?;
 190         assert!(pos >= SHORTHAND_OFFSET);
 191         let shorthand = pos - SHORTHAND_OFFSET;
 192
 193         decoder.cached_predicate_for_shorthand(shorthand, |decoder| {
 194             decoder.with_position(shorthand, ty::Predicate::decode)
 195         })
 196     } else {
 197         let tcx = decoder.tcx();
 198         Ok(tcx.mk_predicate(ty::PredicateKind::decode(decoder)?))
 199     }
 200 }
 201
 202 #[inline]
 203 pub fn decode_spanned_predicates<D>(
 204     decoder: &mut D,
 205 ) -> Result<&'tcx [(ty::Predicate<'tcx>, Span)], D::Error>
 206 where
 207     D: TyDecoder<'tcx>,
 208 {
 209     let tcx = decoder.tcx();
 210     Ok(tcx.arena.alloc_from_iter(
 211         (0..decoder.read_usize()?)
 212             .map(|_| Decodable::decode(decoder))
 213             .collect::<Result<Vec<_>, _>>()?,
 214     ))
 215 }
 216
 217 #[inline]
 218 pub fn decode_substs<D>(decoder: &mut D) -> Result<SubstsRef<'tcx>, D::Error>
 219 where
 220     D: TyDecoder<'tcx>,
 221 {
 222     let len = decoder.read_usize()?;
 223     let tcx = decoder.tcx();
 224     Ok(tcx.mk_substs((0..len).map(|_| Decodable::decode(decoder)))?)
 225 }
 226
 227 #[inline]
 228 pub fn decode_place<D>(decoder: &mut D) -> Result<mir::Place<'tcx>, D::Error>
 229 where
 230     D: TyDecoder<'tcx>,
 231 {
 232     let local: mir::Local = Decodable::decode(decoder)?;
 233     let len = decoder.read_usize()?;
 234     let projection: &'tcx List<mir::PlaceElem<'tcx>> =
 235         decoder.tcx().mk_place_elems((0..len).map(|_| Decodable::decode(decoder)))?;
 236     Ok(mir::Place { local, projection })
 237 }
 238
 239 #[inline]
 240 pub fn decode_region<D>(decoder: &mut D) -> Result<ty::Region<'tcx>, D::Error>
 241 where
 242     D: TyDecoder<'tcx>,
 243 {
 244     Ok(decoder.tcx().mk_region(Decodable::decode(decoder)?))
 245 }
 246
 247 #[inline]
 248 pub fn decode_ty_slice<D>(decoder: &mut D) -> Result<&'tcx ty::List<Ty<'tcx>>, D::Error>
 249 where
 250     D: TyDecoder<'tcx>,
 251 {
 252     let len = decoder.read_usize()?;
 253     Ok(decoder.tcx().mk_type_list((0..len).map(|_| Decodable::decode(decoder)))?)
 254 }
 255
 256 #[inline]
 257 pub fn decode_adt_def<D>(decoder: &mut D) -> Result<&'tcx ty::AdtDef, D::Error>
 258 where
 259     D: TyDecoder<'tcx>,
 260 {
 261     let def_id = DefId::decode(decoder)?;
 262     Ok(decoder.tcx().adt_def(def_id))
 263 }
 264
 265 #[inline]
 266 pub fn decode_symbol_name<D>(decoder: &mut D) -> Result<ty::SymbolName<'tcx>, D::Error>
 267 where
 268     D: TyDecoder<'tcx>,
 269 {
 270     Ok(ty::SymbolName::new(decoder.tcx(), &decoder.read_str()?))
 271 }
 272
 273 #[inline]
 274 pub fn decode_existential_predicate_slice<D>(
 275     decoder: &mut D,
 276 ) -> Result<&'tcx ty::List<ty::ExistentialPredicate<'tcx>>, D::Error>
 277 where
 278     D: TyDecoder<'tcx>,
 279 {
 280     let len = decoder.read_usize()?;
 281     Ok(decoder.tcx().mk_existential_predicates((0..len).map(|_| Decodable::decode(decoder)))?)
 282 }
 283
 284 #[inline]
 285 pub fn decode_canonical_var_infos<D>(decoder: &mut D) -> Result<CanonicalVarInfos<'tcx>, D::Error>
 286 where
 287     D: TyDecoder<'tcx>,
 288 {
 289     let len = decoder.read_usize()?;
 290     let interned: Result<Vec<CanonicalVarInfo>, _> =
 291         (0..len).map(|_| Decodable::decode(decoder)).collect();
 292     Ok(decoder.tcx().intern_canonical_var_infos(interned?.as_slice()))
 293 }
 294
 295 #[inline]
 296 pub fn decode_const<D>(decoder: &mut D) -> Result<&'tcx ty::Const<'tcx>, D::Error>
 297 where
 298     D: TyDecoder<'tcx>,
 299 {
 300     Ok(decoder.tcx().mk_const(Decodable::decode(decoder)?))
 301 }
 302
 303 #[inline]
 304 pub fn decode_allocation<D>(decoder: &mut D) -> Result<&'tcx Allocation, D::Error>
 305 where
 306     D: TyDecoder<'tcx>,
 307 {
 308     Ok(decoder.tcx().intern_const_alloc(Decodable::decode(decoder)?))
 309 }
 310
 311 #[macro_export]
 312 macro_rules! __impl_decoder_methods {
 313     ($($name:ident -> $ty:ty;)*) => {
 314         $(
 315             #[inline]
 316             fn $name(&mut self) -> Result<$ty, Self::Error> {
 317                 self.opaque.$name()
 318             }
 319         )*
 320     }
 321 }
 322
 323 #[macro_export]
 324 macro_rules! impl_arena_allocatable_decoder {
 325     ([]$args:tt) => {};
 326     ([decode $(, $attrs:ident)*]
 327      [[$DecoderName:ident [$($typaram:tt),*]], [$name:ident: $ty:ty, $gen_ty:ty], $tcx:lifetime]) => {
 328          // FIXME(#36588): These impls are horribly unsound as they allow
 329          // the caller to pick any lifetime for `'tcx`, including `'static`.
 330         #[allow(unused_lifetimes)]
 331         impl<'_x, '_y, '_z, '_w, '_a, $($typaram),*> SpecializedDecoder<&'_a $gen_ty>
 332         for $DecoderName<$($typaram),*>
 333         where &'_a $gen_ty: UseSpecializedDecodable
 334         {
 335             #[inline]
 336             fn specialized_decode(&mut self) -> Result<&'_a $gen_ty, Self::Error> {
 337                 unsafe {
 338                     std::mem::transmute::<
 339                         Result<&$tcx $ty, Self::Error>,
 340                         Result<&'_a $gen_ty, Self::Error>,
 341                     >(decode_arena_allocable(self))
 342                 }
 343             }
 344         }
 345
 346         #[allow(unused_lifetimes)]
 347         impl<'_x, '_y, '_z, '_w, '_a, $($typaram),*> SpecializedDecoder<&'_a [$gen_ty]>
 348         for $DecoderName<$($typaram),*>
 349         where &'_a [$gen_ty]: UseSpecializedDecodable
 350         {
 351             #[inline]
 352             fn specialized_decode(&mut self) -> Result<&'_a [$gen_ty], Self::Error> {
 353                 unsafe {
 354                     std::mem::transmute::<
 355                         Result<&$tcx [$ty], Self::Error>,
 356                         Result<&'_a [$gen_ty], Self::Error>,
 357                     >(decode_arena_allocable_slice(self))
 358                 }
 359             }
 360         }
 361     };
 362     ([$ignore:ident $(, $attrs:ident)*]$args:tt) => {
 363         impl_arena_allocatable_decoder!([$($attrs),*]$args);
 364     };
 365 }
 366
 367 #[macro_export]
 368 macro_rules! impl_arena_allocatable_decoders {
 369     ($args:tt, [$($a:tt $name:ident: $ty:ty, $gen_ty:ty;)*], $tcx:lifetime) => {
 370         $(
 371             impl_arena_allocatable_decoder!($a [$args, [$name: $ty, $gen_ty], $tcx]);
 372         )*
 373     }
 374 }
 375
 376 #[macro_export]
 377 macro_rules! implement_ty_decoder {
 378     ($DecoderName:ident <$($typaram:tt),*>) => {
 379         mod __ty_decoder_impl {
 380             use std::borrow::Cow;
 381             use std::mem::transmute;
 382
 383             use rustc_serialize::{Decoder, SpecializedDecoder, UseSpecializedDecodable};
 384
 385             use $crate::infer::canonical::CanonicalVarInfos;
 386             use $crate::ty;
 387             use $crate::ty::codec::*;
 388             use $crate::ty::subst::InternalSubsts;
 389             use rustc_hir::def_id::CrateNum;
 390
 391             use rustc_span::Span;
 392
 393             use super::$DecoderName;
 394
 395             impl<$($typaram ),*> Decoder for $DecoderName<$($typaram),*> {
 396                 type Error = String;
 397
 398                 __impl_decoder_methods! {
 399                     read_nil -> ();
 400
 401                     read_u128 -> u128;
 402                     read_u64 -> u64;
 403                     read_u32 -> u32;
 404                     read_u16 -> u16;
 405                     read_u8 -> u8;
 406                     read_usize -> usize;
 407
 408                     read_i128 -> i128;
 409                     read_i64 -> i64;
 410                     read_i32 -> i32;
 411                     read_i16 -> i16;
 412                     read_i8 -> i8;
 413                     read_isize -> isize;
 414
 415                     read_bool -> bool;
 416                     read_f64 -> f64;
 417                     read_f32 -> f32;
 418                     read_char -> char;
 419                     read_str -> Cow<'_, str>;
 420                 }
 421
 422                 fn error(&mut self, err: &str) -> Self::Error {
 423                     self.opaque.error(err)
 424                 }
 425             }
 426
 427             // FIXME(#36588): These impls are horribly unsound as they allow
 428             // the caller to pick any lifetime for `'tcx`, including `'static`.
 429
 430             arena_types!(impl_arena_allocatable_decoders, [$DecoderName [$($typaram),*]], 'tcx);
 431
 432             impl<$($typaram),*> SpecializedDecoder<CrateNum>
 433             for $DecoderName<$($typaram),*> {
 434                 fn specialized_decode(&mut self) -> Result<CrateNum, Self::Error> {
 435                     decode_cnum(self)
 436                 }
 437             }
 438
 439             impl<'_x, '_y, $($typaram),*> SpecializedDecoder<&'_x ty::TyS<'_y>>
 440             for $DecoderName<$($typaram),*>
 441             where &'_x ty::TyS<'_y>: UseSpecializedDecodable
 442             {
 443                 fn specialized_decode(&mut self) -> Result<&'_x ty::TyS<'_y>, Self::Error> {
 444                     unsafe {
 445                         transmute::<
 446                             Result<ty::Ty<'tcx>, Self::Error>,
 447                             Result<&'_x ty::TyS<'_y>, Self::Error>,
 448                         >(decode_ty(self))
 449                     }
 450                 }
 451             }
 452
 453             impl<'_x, $($typaram),*> SpecializedDecoder<ty::Predicate<'_x>>
 454             for $DecoderName<$($typaram),*> {
 455                 fn specialized_decode(&mut self) -> Result<ty::Predicate<'_x>, Self::Error> {
 456                     unsafe {
 457                         transmute::<
 458                             Result<ty::Predicate<'tcx>, Self::Error>,
 459                             Result<ty::Predicate<'_x>, Self::Error>,
 460                         >(decode_predicate(self))
 461                     }
 462                 }
 463             }
 464
 465             impl<'_x, '_y, $($typaram),*> SpecializedDecoder<&'_x [(ty::Predicate<'_y>, Span)]>
 466             for $DecoderName<$($typaram),*>
 467             where &'_x [(ty::Predicate<'_y>, Span)]: UseSpecializedDecodable {
 468                 fn specialized_decode(&mut self)
 469                                       -> Result<&'_x [(ty::Predicate<'_y>, Span)], Self::Error>
 470                 {
 471                     unsafe { transmute(decode_spanned_predicates(self)) }
 472                 }
 473             }
 474
 475             impl<'_x, '_y, $($typaram),*> SpecializedDecoder<&'_x InternalSubsts<'_y>>
 476             for $DecoderName<$($typaram),*>
 477             where &'_x InternalSubsts<'_y>: UseSpecializedDecodable {
 478                 fn specialized_decode(&mut self) -> Result<&'_x InternalSubsts<'_y>, Self::Error> {
 479                     unsafe { transmute(decode_substs(self)) }
 480                 }
 481             }
 482
 483             impl<'_x, $($typaram),*> SpecializedDecoder<$crate::mir::Place<'_x>>
 484             for $DecoderName<$($typaram),*> {
 485                 fn specialized_decode(
 486                     &mut self
 487                 ) -> Result<$crate::mir::Place<'_x>, Self::Error> {
 488                     unsafe { transmute(decode_place(self)) }
 489                 }
 490             }
 491
 492             impl<'_x, $($typaram),*> SpecializedDecoder<ty::Region<'_x>>
 493             for $DecoderName<$($typaram),*> {
 494                 fn specialized_decode(&mut self) -> Result<ty::Region<'_x>, Self::Error> {
 495                     unsafe { transmute(decode_region(self)) }
 496                 }
 497             }
 498
 499             impl<'_x, '_y, '_z, $($typaram),*> SpecializedDecoder<&'_x ty::List<&'_y ty::TyS<'_z>>>
 500             for $DecoderName<$($typaram),*>
 501             where &'_x ty::List<&'_y ty::TyS<'_z>>: UseSpecializedDecodable {
 502                 fn specialized_decode(&mut self)
 503                                       -> Result<&'_x ty::List<&'_y ty::TyS<'_z>>, Self::Error> {
 504                     unsafe { transmute(decode_ty_slice(self)) }
 505                 }
 506             }
 507
 508             impl<'_x, $($typaram),*> SpecializedDecoder<&'_x ty::AdtDef>
 509             for $DecoderName<$($typaram),*> {
 510                 fn specialized_decode(&mut self) -> Result<&'_x ty::AdtDef, Self::Error> {
 511                     unsafe { transmute(decode_adt_def(self)) }
 512                 }
 513             }
 514
 515             impl<'_x, $($typaram),*> SpecializedDecoder<ty::SymbolName<'_x>>
 516             for $DecoderName<$($typaram),*> {
 517                 fn specialized_decode(&mut self) -> Result<ty::SymbolName<'_x>, Self::Error> {
 518                     unsafe { transmute(decode_symbol_name(self)) }
 519                 }
 520             }
 521
 522             impl<'_x, '_y, $($typaram),*> SpecializedDecoder<&'_x ty::List<ty::ExistentialPredicate<'_y>>>
 523             for $DecoderName<$($typaram),*>
 524             where &'_x ty::List<ty::ExistentialPredicate<'_y>>: UseSpecializedDecodable {
 525                 fn specialized_decode(&mut self)
 526                     -> Result<&'_x ty::List<ty::ExistentialPredicate<'_y>>, Self::Error> {
 527                         unsafe { transmute(decode_existential_predicate_slice(self)) }
 528                 }
 529             }
 530
 531             impl<'_x, $($typaram),*> SpecializedDecoder<CanonicalVarInfos<'_x>>
 532                 for $DecoderName<$($typaram),*> {
 533                 fn specialized_decode(&mut self)
 534                     -> Result<CanonicalVarInfos<'_x>, Self::Error> {
 535                         unsafe { transmute(decode_canonical_var_infos(self)) }
 536                 }
 537             }
 538
 539             impl<'_x, '_y, $($typaram),*> SpecializedDecoder<&'_x $crate::ty::Const<'_y>>
 540             for $DecoderName<$($typaram),*>
 541             where &'_x $crate::ty::Const<'_y>: UseSpecializedDecodable {
 542                 fn specialized_decode(&mut self) -> Result<&'_x ty::Const<'_y>, Self::Error> {
 543                     unsafe { transmute(decode_const(self)) }
 544                 }
 545             }
 546
 547             impl<'_x, $($typaram),*> SpecializedDecoder<&'_x $crate::mir::interpret::Allocation>
 548             for $DecoderName<$($typaram),*> {
 549                 fn specialized_decode(
 550                     &mut self
 551                 ) -> Result<&'_x $crate::mir::interpret::Allocation, Self::Error> {
 552                     unsafe { transmute(decode_allocation(self)) }
 553                 }
 554             }
 555         }
 556     };
 557 }