compiler/rustc_middle/src/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::{
  12     self,
  13     interpret::{AllocId, Allocation},
  14 };
  15 use crate::ty::subst::SubstsRef;
  16 use crate::ty::{self, List, Ty, TyCtxt};
  17 use rustc_data_structures::fx::FxHashMap;
  18 use rustc_hir::def_id::{CrateNum, DefId};
  19 use rustc_serialize::{Decodable, Decoder, Encodable, Encoder};
  20 use rustc_span::Span;
  21 use std::convert::{TryFrom, TryInto};
  22 use std::hash::Hash;
  23 use std::intrinsics;
  24 use std::marker::DiscriminantKind;
  25
  26 /// The shorthand encoding uses an enum's variant index `usize`
  27 /// and is offset by this value so it never matches a real variant.
  28 /// This offset is also chosen so that the first byte is never < 0x80.
  29 pub const SHORTHAND_OFFSET: usize = 0x80;
  30
  31 pub trait EncodableWithShorthand<'tcx, E: TyEncoder<'tcx>>: Copy + Eq + Hash {
  32     type Variant: Encodable<E>;
  33     fn variant(&self) -> &Self::Variant;
  34 }
  35
  36 #[allow(rustc::usage_of_ty_tykind)]
  37 impl<'tcx, E: TyEncoder<'tcx>> EncodableWithShorthand<'tcx, E> for Ty<'tcx> {
  38     type Variant = ty::TyKind<'tcx>;
  39
  40     #[inline]
  41     fn variant(&self) -> &Self::Variant {
  42         self.kind()
  43     }
  44 }
  45
  46 impl<'tcx, E: TyEncoder<'tcx>> EncodableWithShorthand<'tcx, E> for ty::Predicate<'tcx> {
  47     type Variant = ty::PredicateKind<'tcx>;
  48     fn variant(&self) -> &Self::Variant {
  49         self.kind()
  50     }
  51 }
  52
  53 pub trait OpaqueEncoder: Encoder {
  54     fn opaque(&mut self) -> &mut rustc_serialize::opaque::Encoder;
  55     fn encoder_position(&self) -> usize;
  56 }
  57
  58 impl OpaqueEncoder for rustc_serialize::opaque::Encoder {
  59     #[inline]
  60     fn opaque(&mut self) -> &mut rustc_serialize::opaque::Encoder {
  61         self
  62     }
  63     #[inline]
  64     fn encoder_position(&self) -> usize {
  65         self.position()
  66     }
  67 }
  68
  69 pub trait TyEncoder<'tcx>: Encoder {
  70     const CLEAR_CROSS_CRATE: bool;
  71
  72     fn tcx(&self) -> TyCtxt<'tcx>;
  73     fn position(&self) -> usize;
  74     fn type_shorthands(&mut self) -> &mut FxHashMap<Ty<'tcx>, usize>;
  75     fn predicate_shorthands(&mut self) -> &mut FxHashMap<ty::Predicate<'tcx>, usize>;
  76     fn encode_alloc_id(&mut self, alloc_id: &AllocId) -> Result<(), Self::Error>;
  77 }
  78
  79 /// Trait for decoding to a reference.
  80 ///
  81 /// This is a separate trait from `Decodable` so that we can implement it for
  82 /// upstream types, such as `FxHashSet`.
  83 ///
  84 /// The `TyDecodable` derive macro will use this trait for fields that are
  85 /// references (and don't use a type alias to hide that).
  86 ///
  87 /// `Decodable` can still be implemented in cases where `Decodable` is required
  88 /// by a trait bound.
  89 pub trait RefDecodable<'tcx, D: TyDecoder<'tcx>> {
  90     fn decode(d: &mut D) -> Result<&'tcx Self, D::Error>;
  91 }
  92
  93 /// Encode the given value or a previously cached shorthand.
  94 pub fn encode_with_shorthand<E, T, M>(encoder: &mut E, value: &T, cache: M) -> Result<(), E::Error>
  95 where
  96     E: TyEncoder<'tcx>,
  97     M: for<'b> Fn(&'b mut E) -> &'b mut FxHashMap<T, usize>,
  98     T: EncodableWithShorthand<'tcx, E>,
  99     <T::Variant as DiscriminantKind>::Discriminant: Ord + TryFrom<usize>,
 100 {
 101     let existing_shorthand = cache(encoder).get(value).copied();
 102     if let Some(shorthand) = existing_shorthand {
 103         return encoder.emit_usize(shorthand);
 104     }
 105
 106     let variant = value.variant();
 107
 108     let start = encoder.position();
 109     variant.encode(encoder)?;
 110     let len = encoder.position() - start;
 111
 112     // The shorthand encoding uses the same usize as the
 113     // discriminant, with an offset so they can't conflict.
 114     let discriminant = intrinsics::discriminant_value(variant);
 115     assert!(discriminant < SHORTHAND_OFFSET.try_into().ok().unwrap());
 116
 117     let shorthand = start + SHORTHAND_OFFSET;
 118
 119     // Get the number of bits that leb128 could fit
 120     // in the same space as the fully encoded type.
 121     let leb128_bits = len * 7;
 122
 123     // Check that the shorthand is a not longer than the
 124     // full encoding itself, i.e., it's an obvious win.
 125     if leb128_bits >= 64 || (shorthand as u64) < (1 << leb128_bits) {
 126         cache(encoder).insert(*value, shorthand);
 127     }
 128
 129     Ok(())
 130 }
 131
 132 impl<'tcx, E: TyEncoder<'tcx>> Encodable<E> for Ty<'tcx> {
 133     fn encode(&self, e: &mut E) -> Result<(), E::Error> {
 134         encode_with_shorthand(e, self, TyEncoder::type_shorthands)
 135     }
 136 }
 137
 138 impl<'tcx, E: TyEncoder<'tcx>> Encodable<E> for ty::Predicate<'tcx> {
 139     fn encode(&self, e: &mut E) -> Result<(), E::Error> {
 140         encode_with_shorthand(e, self, TyEncoder::predicate_shorthands)
 141     }
 142 }
 143
 144 impl<'tcx, E: TyEncoder<'tcx>> Encodable<E> for AllocId {
 145     fn encode(&self, e: &mut E) -> Result<(), E::Error> {
 146         e.encode_alloc_id(self)
 147     }
 148 }
 149
 150 macro_rules! encodable_via_deref {
 151     ($($t:ty),+) => {
 152         $(impl<'tcx, E: TyEncoder<'tcx>> Encodable<E> for $t {
 153             fn encode(&self, e: &mut E) -> Result<(), E::Error> {
 154                 (**self).encode(e)
 155             }
 156         })*
 157     }
 158 }
 159
 160 encodable_via_deref! {
 161     &'tcx ty::TypeckResults<'tcx>,
 162     ty::Region<'tcx>,
 163     &'tcx mir::Body<'tcx>,
 164     &'tcx mir::UnsafetyCheckResult,
 165     &'tcx mir::BorrowCheckResult<'tcx>
 166 }
 167
 168 pub trait TyDecoder<'tcx>: Decoder {
 169     const CLEAR_CROSS_CRATE: bool;
 170
 171     fn tcx(&self) -> TyCtxt<'tcx>;
 172
 173     fn peek_byte(&self) -> u8;
 174
 175     fn position(&self) -> usize;
 176
 177     fn cached_ty_for_shorthand<F>(
 178         &mut self,
 179         shorthand: usize,
 180         or_insert_with: F,
 181     ) -> Result<Ty<'tcx>, Self::Error>
 182     where
 183         F: FnOnce(&mut Self) -> Result<Ty<'tcx>, Self::Error>;
 184
 185     fn cached_predicate_for_shorthand<F>(
 186         &mut self,
 187         shorthand: usize,
 188         or_insert_with: F,
 189     ) -> Result<ty::Predicate<'tcx>, Self::Error>
 190     where
 191         F: FnOnce(&mut Self) -> Result<ty::Predicate<'tcx>, Self::Error>;
 192
 193     fn with_position<F, R>(&mut self, pos: usize, f: F) -> R
 194     where
 195         F: FnOnce(&mut Self) -> R;
 196
 197     fn map_encoded_cnum_to_current(&self, cnum: CrateNum) -> CrateNum;
 198
 199     fn positioned_at_shorthand(&self) -> bool {
 200         (self.peek_byte() & (SHORTHAND_OFFSET as u8)) != 0
 201     }
 202
 203     fn decode_alloc_id(&mut self) -> Result<AllocId, Self::Error>;
 204 }
 205
 206 #[inline]
 207 pub fn decode_arena_allocable<'tcx, D, T: ArenaAllocatable<'tcx> + Decodable<D>>(
 208     decoder: &mut D,
 209 ) -> Result<&'tcx T, D::Error>
 210 where
 211     D: TyDecoder<'tcx>,
 212 {
 213     Ok(decoder.tcx().arena.alloc(Decodable::decode(decoder)?))
 214 }
 215
 216 #[inline]
 217 pub fn decode_arena_allocable_slice<'tcx, D, T: ArenaAllocatable<'tcx> + Decodable<D>>(
 218     decoder: &mut D,
 219 ) -> Result<&'tcx [T], D::Error>
 220 where
 221     D: TyDecoder<'tcx>,
 222 {
 223     Ok(decoder.tcx().arena.alloc_from_iter(<Vec<T> as Decodable<D>>::decode(decoder)?))
 224 }
 225
 226 impl<'tcx, D: TyDecoder<'tcx>> Decodable<D> for Ty<'tcx> {
 227     #[allow(rustc::usage_of_ty_tykind)]
 228     fn decode(decoder: &mut D) -> Result<Ty<'tcx>, D::Error> {
 229         // Handle shorthands first, if we have an usize > 0x80.
 230         if decoder.positioned_at_shorthand() {
 231             let pos = decoder.read_usize()?;
 232             assert!(pos >= SHORTHAND_OFFSET);
 233             let shorthand = pos - SHORTHAND_OFFSET;
 234
 235             decoder.cached_ty_for_shorthand(shorthand, |decoder| {
 236                 decoder.with_position(shorthand, Ty::decode)
 237             })
 238         } else {
 239             let tcx = decoder.tcx();
 240             Ok(tcx.mk_ty(ty::TyKind::decode(decoder)?))
 241         }
 242     }
 243 }
 244
 245 impl<'tcx, D: TyDecoder<'tcx>> Decodable<D> for ty::Predicate<'tcx> {
 246     fn decode(decoder: &mut D) -> Result<ty::Predicate<'tcx>, D::Error> {
 247         // Handle shorthands first, if we have an usize > 0x80.
 248         let predicate_kind = if decoder.positioned_at_shorthand() {
 249             let pos = decoder.read_usize()?;
 250             assert!(pos >= SHORTHAND_OFFSET);
 251             let shorthand = pos - SHORTHAND_OFFSET;
 252
 253             decoder.with_position(shorthand, ty::PredicateKind::decode)
 254         } else {
 255             ty::PredicateKind::decode(decoder)
 256         }?;
 257         let predicate = decoder.tcx().mk_predicate(predicate_kind);
 258         Ok(predicate)
 259     }
 260 }
 261
 262 impl<'tcx, D: TyDecoder<'tcx>> Decodable<D> for SubstsRef<'tcx> {
 263     fn decode(decoder: &mut D) -> Result<Self, D::Error> {
 264         let len = decoder.read_usize()?;
 265         let tcx = decoder.tcx();
 266         Ok(tcx.mk_substs((0..len).map(|_| Decodable::decode(decoder)))?)
 267     }
 268 }
 269
 270 impl<'tcx, D: TyDecoder<'tcx>> Decodable<D> for mir::Place<'tcx> {
 271     fn decode(decoder: &mut D) -> Result<Self, D::Error> {
 272         let local: mir::Local = Decodable::decode(decoder)?;
 273         let len = decoder.read_usize()?;
 274         let projection: &'tcx List<mir::PlaceElem<'tcx>> =
 275             decoder.tcx().mk_place_elems((0..len).map(|_| Decodable::decode(decoder)))?;
 276         Ok(mir::Place { local, projection })
 277     }
 278 }
 279
 280 impl<'tcx, D: TyDecoder<'tcx>> Decodable<D> for ty::Region<'tcx> {
 281     fn decode(decoder: &mut D) -> Result<Self, D::Error> {
 282         Ok(decoder.tcx().mk_region(Decodable::decode(decoder)?))
 283     }
 284 }
 285
 286 impl<'tcx, D: TyDecoder<'tcx>> Decodable<D> for CanonicalVarInfos<'tcx> {
 287     fn decode(decoder: &mut D) -> Result<Self, D::Error> {
 288         let len = decoder.read_usize()?;
 289         let interned: Result<Vec<CanonicalVarInfo>, _> =
 290             (0..len).map(|_| Decodable::decode(decoder)).collect();
 291         Ok(decoder.tcx().intern_canonical_var_infos(interned?.as_slice()))
 292     }
 293 }
 294
 295 impl<'tcx, D: TyDecoder<'tcx>> Decodable<D> for AllocId {
 296     fn decode(decoder: &mut D) -> Result<Self, D::Error> {
 297         decoder.decode_alloc_id()
 298     }
 299 }
 300
 301 impl<'tcx, D: TyDecoder<'tcx>> Decodable<D> for ty::SymbolName<'tcx> {
 302     fn decode(decoder: &mut D) -> Result<Self, D::Error> {
 303         Ok(ty::SymbolName::new(decoder.tcx(), &decoder.read_str()?))
 304     }
 305 }
 306
 307 macro_rules! impl_decodable_via_ref {
 308     ($($t:ty),+) => {
 309         $(impl<'tcx, D: TyDecoder<'tcx>> Decodable<D> for $t {
 310             fn decode(decoder: &mut D) -> Result<Self, D::Error> {
 311                 RefDecodable::decode(decoder)
 312             }
 313         })*
 314     }
 315 }
 316
 317 impl<'tcx, D: TyDecoder<'tcx>> RefDecodable<'tcx, D> for ty::AdtDef {
 318     fn decode(decoder: &mut D) -> Result<&'tcx Self, D::Error> {
 319         let def_id = <DefId as Decodable<D>>::decode(decoder)?;
 320         Ok(decoder.tcx().adt_def(def_id))
 321     }
 322 }
 323
 324 impl<'tcx, D: TyDecoder<'tcx>> RefDecodable<'tcx, D> for ty::List<Ty<'tcx>> {
 325     fn decode(decoder: &mut D) -> Result<&'tcx Self, D::Error> {
 326         let len = decoder.read_usize()?;
 327         Ok(decoder.tcx().mk_type_list((0..len).map(|_| Decodable::decode(decoder)))?)
 328     }
 329 }
 330
 331 impl<'tcx, D: TyDecoder<'tcx>> RefDecodable<'tcx, D> for ty::List<ty::ExistentialPredicate<'tcx>> {
 332     fn decode(decoder: &mut D) -> Result<&'tcx Self, D::Error> {
 333         let len = decoder.read_usize()?;
 334         Ok(decoder.tcx().mk_existential_predicates((0..len).map(|_| Decodable::decode(decoder)))?)
 335     }
 336 }
 337
 338 impl<'tcx, D: TyDecoder<'tcx>> RefDecodable<'tcx, D> for ty::Const<'tcx> {
 339     fn decode(decoder: &mut D) -> Result<&'tcx Self, D::Error> {
 340         Ok(decoder.tcx().mk_const(Decodable::decode(decoder)?))
 341     }
 342 }
 343
 344 impl<'tcx, D: TyDecoder<'tcx>> RefDecodable<'tcx, D> for Allocation {
 345     fn decode(decoder: &mut D) -> Result<&'tcx Self, D::Error> {
 346         Ok(decoder.tcx().intern_const_alloc(Decodable::decode(decoder)?))
 347     }
 348 }
 349
 350 impl<'tcx, D: TyDecoder<'tcx>> RefDecodable<'tcx, D> for [(ty::Predicate<'tcx>, Span)] {
 351     fn decode(decoder: &mut D) -> Result<&'tcx Self, D::Error> {
 352         Ok(decoder.tcx().arena.alloc_from_iter(
 353             (0..decoder.read_usize()?)
 354                 .map(|_| Decodable::decode(decoder))
 355                 .collect::<Result<Vec<_>, _>>()?,
 356         ))
 357     }
 358 }
 359
 360 impl<'tcx, D: TyDecoder<'tcx>> RefDecodable<'tcx, D> for [mir::abstract_const::Node<'tcx>] {
 361     fn decode(decoder: &mut D) -> Result<&'tcx Self, D::Error> {
 362         Ok(decoder.tcx().arena.alloc_from_iter(
 363             (0..decoder.read_usize()?)
 364                 .map(|_| Decodable::decode(decoder))
 365                 .collect::<Result<Vec<_>, _>>()?,
 366         ))
 367     }
 368 }
 369
 370 impl<'tcx, D: TyDecoder<'tcx>> RefDecodable<'tcx, D> for [mir::abstract_const::NodeId] {
 371     fn decode(decoder: &mut D) -> Result<&'tcx Self, D::Error> {
 372         Ok(decoder.tcx().arena.alloc_from_iter(
 373             (0..decoder.read_usize()?)
 374                 .map(|_| Decodable::decode(decoder))
 375                 .collect::<Result<Vec<_>, _>>()?,
 376         ))
 377     }
 378 }
 379
 380 impl_decodable_via_ref! {
 381     &'tcx ty::TypeckResults<'tcx>,
 382     &'tcx ty::List<Ty<'tcx>>,
 383     &'tcx ty::List<ty::ExistentialPredicate<'tcx>>,
 384     &'tcx Allocation,
 385     &'tcx mir::Body<'tcx>,
 386     &'tcx mir::UnsafetyCheckResult,
 387     &'tcx mir::BorrowCheckResult<'tcx>
 388 }
 389
 390 #[macro_export]
 391 macro_rules! __impl_decoder_methods {
 392     ($($name:ident -> $ty:ty;)*) => {
 393         $(
 394             #[inline]
 395             fn $name(&mut self) -> Result<$ty, Self::Error> {
 396                 self.opaque.$name()
 397             }
 398         )*
 399     }
 400 }
 401
 402 macro_rules! impl_arena_allocatable_decoder {
 403     ([]$args:tt) => {};
 404     ([decode $(, $attrs:ident)*]
 405      [[$name:ident: $ty:ty], $tcx:lifetime]) => {
 406         impl<$tcx, D: TyDecoder<$tcx>> RefDecodable<$tcx, D> for $ty {
 407             #[inline]
 408             fn decode(decoder: &mut D) -> Result<&$tcx Self, D::Error> {
 409                 decode_arena_allocable(decoder)
 410             }
 411         }
 412
 413         impl<$tcx, D: TyDecoder<$tcx>> RefDecodable<$tcx, D> for [$ty] {
 414             #[inline]
 415             fn decode(decoder: &mut D) -> Result<&$tcx Self, D::Error> {
 416                 decode_arena_allocable_slice(decoder)
 417             }
 418         }
 419     };
 420     ([$ignore:ident $(, $attrs:ident)*]$args:tt) => {
 421         impl_arena_allocatable_decoder!([$($attrs),*]$args);
 422     };
 423 }
 424
 425 macro_rules! impl_arena_allocatable_decoders {
 426     ([], [$($a:tt $name:ident: $ty:ty,)*], $tcx:lifetime) => {
 427         $(
 428             impl_arena_allocatable_decoder!($a [[$name: $ty], $tcx]);
 429         )*
 430     }
 431 }
 432
 433 rustc_hir::arena_types!(impl_arena_allocatable_decoders, [], 'tcx);
 434 arena_types!(impl_arena_allocatable_decoders, [], 'tcx);
 435
 436 #[macro_export]
 437 macro_rules! implement_ty_decoder {
 438     ($DecoderName:ident <$($typaram:tt),*>) => {
 439         mod __ty_decoder_impl {
 440             use std::borrow::Cow;
 441             use rustc_serialize::Decoder;
 442
 443             use super::$DecoderName;
 444
 445             impl<$($typaram ),*> Decoder for $DecoderName<$($typaram),*> {
 446                 type Error = String;
 447
 448                 $crate::__impl_decoder_methods! {
 449                     read_nil -> ();
 450
 451                     read_u128 -> u128;
 452                     read_u64 -> u64;
 453                     read_u32 -> u32;
 454                     read_u16 -> u16;
 455                     read_u8 -> u8;
 456                     read_usize -> usize;
 457
 458                     read_i128 -> i128;
 459                     read_i64 -> i64;
 460                     read_i32 -> i32;
 461                     read_i16 -> i16;
 462                     read_i8 -> i8;
 463                     read_isize -> isize;
 464
 465                     read_bool -> bool;
 466                     read_f64 -> f64;
 467                     read_f32 -> f32;
 468                     read_char -> char;
 469                     read_str -> Cow<'_, str>;
 470                 }
 471
 472                 fn error(&mut self, err: &str) -> Self::Error {
 473                     self.opaque.error(err)
 474                 }
 475             }
 476         }
 477     }
 478 }