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, ToPredicate, 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 fn encode_spanned_predicates<'tcx, E, C>(
  99     encoder: &mut E,
 100     predicates: &'tcx [(ty::Predicate<'tcx>, Span)],
 101     cache: C,
 102 ) -> Result<(), E::Error>
 103 where
 104     E: TyEncoder,
 105     C: for<'b> Fn(&'b mut E) -> &'b mut FxHashMap<ty::Predicate<'tcx>, usize>,
 106 {
 107     predicates.len().encode(encoder)?;
 108     for (predicate, span) in predicates {
 109         encode_with_shorthand(encoder, predicate, &cache)?;
 110         span.encode(encoder)?;
 111     }
 112     Ok(())
 113 }
 114
 115 pub trait TyDecoder<'tcx>: Decoder {
 116     fn tcx(&self) -> TyCtxt<'tcx>;
 117
 118     fn peek_byte(&self) -> u8;
 119
 120     fn position(&self) -> usize;
 121
 122     fn cached_ty_for_shorthand<F>(
 123         &mut self,
 124         shorthand: usize,
 125         or_insert_with: F,
 126     ) -> Result<Ty<'tcx>, Self::Error>
 127     where
 128         F: FnOnce(&mut Self) -> Result<Ty<'tcx>, Self::Error>;
 129
 130     fn with_position<F, R>(&mut self, pos: usize, f: F) -> R
 131     where
 132         F: FnOnce(&mut Self) -> R;
 133
 134     fn map_encoded_cnum_to_current(&self, cnum: CrateNum) -> CrateNum;
 135
 136     fn positioned_at_shorthand(&self) -> bool {
 137         (self.peek_byte() & (SHORTHAND_OFFSET as u8)) != 0
 138     }
 139 }
 140
 141 #[inline]
 142 pub fn decode_arena_allocable<D, T: ArenaAllocatable + Decodable>(
 143     decoder: &mut D,
 144 ) -> Result<&'tcx T, D::Error>
 145 where
 146     D: TyDecoder<'tcx>,
 147 {
 148     Ok(decoder.tcx().arena.alloc(Decodable::decode(decoder)?))
 149 }
 150
 151 #[inline]
 152 pub fn decode_arena_allocable_slice<D, T: ArenaAllocatable + Decodable>(
 153     decoder: &mut D,
 154 ) -> Result<&'tcx [T], D::Error>
 155 where
 156     D: TyDecoder<'tcx>,
 157 {
 158     Ok(decoder.tcx().arena.alloc_from_iter(<Vec<T> as Decodable>::decode(decoder)?))
 159 }
 160
 161 #[inline]
 162 pub fn decode_cnum<D>(decoder: &mut D) -> Result<CrateNum, D::Error>
 163 where
 164     D: TyDecoder<'tcx>,
 165 {
 166     let cnum = CrateNum::from_u32(u32::decode(decoder)?);
 167     Ok(decoder.map_encoded_cnum_to_current(cnum))
 168 }
 169
 170 #[allow(rustc::usage_of_ty_tykind)]
 171 #[inline]
 172 pub fn decode_ty<D>(decoder: &mut D) -> Result<Ty<'tcx>, D::Error>
 173 where
 174     D: TyDecoder<'tcx>,
 175 {
 176     // Handle shorthands first, if we have an usize > 0x80.
 177     if decoder.positioned_at_shorthand() {
 178         let pos = decoder.read_usize()?;
 179         assert!(pos >= SHORTHAND_OFFSET);
 180         let shorthand = pos - SHORTHAND_OFFSET;
 181
 182         decoder.cached_ty_for_shorthand(shorthand, |decoder| {
 183             decoder.with_position(shorthand, Ty::decode)
 184         })
 185     } else {
 186         let tcx = decoder.tcx();
 187         Ok(tcx.mk_ty(ty::TyKind::decode(decoder)?))
 188     }
 189 }
 190
 191 #[inline]
 192 pub fn decode_spanned_predicates<D>(
 193     decoder: &mut D,
 194 ) -> Result<&'tcx [(ty::Predicate<'tcx>, Span)], D::Error>
 195 where
 196     D: TyDecoder<'tcx>,
 197 {
 198     let tcx = decoder.tcx();
 199     Ok(tcx.arena.alloc_from_iter(
 200         (0..decoder.read_usize()?)
 201             .map(|_| {
 202                 // Handle shorthands first, if we have an usize > 0x80.
 203                 let predicate_kind = if decoder.positioned_at_shorthand() {
 204                     let pos = decoder.read_usize()?;
 205                     assert!(pos >= SHORTHAND_OFFSET);
 206                     let shorthand = pos - SHORTHAND_OFFSET;
 207
 208                     decoder.with_position(shorthand, ty::PredicateKind::decode)
 209                 } else {
 210                     ty::PredicateKind::decode(decoder)
 211                 }?;
 212                 let predicate = predicate_kind.to_predicate(tcx);
 213                 Ok((predicate, Decodable::decode(decoder)?))
 214             })
 215             .collect::<Result<Vec<_>, _>>()?,
 216     ))
 217 }
 218
 219 #[inline]
 220 pub fn decode_substs<D>(decoder: &mut D) -> Result<SubstsRef<'tcx>, D::Error>
 221 where
 222     D: TyDecoder<'tcx>,
 223 {
 224     let len = decoder.read_usize()?;
 225     let tcx = decoder.tcx();
 226     Ok(tcx.mk_substs((0..len).map(|_| Decodable::decode(decoder)))?)
 227 }
 228
 229 #[inline]
 230 pub fn decode_place<D>(decoder: &mut D) -> Result<mir::Place<'tcx>, D::Error>
 231 where
 232     D: TyDecoder<'tcx>,
 233 {
 234     let local: mir::Local = Decodable::decode(decoder)?;
 235     let len = decoder.read_usize()?;
 236     let projection: &'tcx List<mir::PlaceElem<'tcx>> =
 237         decoder.tcx().mk_place_elems((0..len).map(|_| Decodable::decode(decoder)))?;
 238     Ok(mir::Place { local, projection })
 239 }
 240
 241 #[inline]
 242 pub fn decode_region<D>(decoder: &mut D) -> Result<ty::Region<'tcx>, D::Error>
 243 where
 244     D: TyDecoder<'tcx>,
 245 {
 246     Ok(decoder.tcx().mk_region(Decodable::decode(decoder)?))
 247 }
 248
 249 #[inline]
 250 pub fn decode_ty_slice<D>(decoder: &mut D) -> Result<&'tcx ty::List<Ty<'tcx>>, D::Error>
 251 where
 252     D: TyDecoder<'tcx>,
 253 {
 254     let len = decoder.read_usize()?;
 255     Ok(decoder.tcx().mk_type_list((0..len).map(|_| Decodable::decode(decoder)))?)
 256 }
 257
 258 #[inline]
 259 pub fn decode_adt_def<D>(decoder: &mut D) -> Result<&'tcx ty::AdtDef, D::Error>
 260 where
 261     D: TyDecoder<'tcx>,
 262 {
 263     let def_id = DefId::decode(decoder)?;
 264     Ok(decoder.tcx().adt_def(def_id))
 265 }
 266
 267 #[inline]
 268 pub fn decode_existential_predicate_slice<D>(
 269     decoder: &mut D,
 270 ) -> Result<&'tcx ty::List<ty::ExistentialPredicate<'tcx>>, D::Error>
 271 where
 272     D: TyDecoder<'tcx>,
 273 {
 274     let len = decoder.read_usize()?;
 275     Ok(decoder.tcx().mk_existential_predicates((0..len).map(|_| Decodable::decode(decoder)))?)
 276 }
 277
 278 #[inline]
 279 pub fn decode_canonical_var_infos<D>(decoder: &mut D) -> Result<CanonicalVarInfos<'tcx>, D::Error>
 280 where
 281     D: TyDecoder<'tcx>,
 282 {
 283     let len = decoder.read_usize()?;
 284     let interned: Result<Vec<CanonicalVarInfo>, _> =
 285         (0..len).map(|_| Decodable::decode(decoder)).collect();
 286     Ok(decoder.tcx().intern_canonical_var_infos(interned?.as_slice()))
 287 }
 288
 289 #[inline]
 290 pub fn decode_const<D>(decoder: &mut D) -> Result<&'tcx ty::Const<'tcx>, D::Error>
 291 where
 292     D: TyDecoder<'tcx>,
 293 {
 294     Ok(decoder.tcx().mk_const(Decodable::decode(decoder)?))
 295 }
 296
 297 #[inline]
 298 pub fn decode_allocation<D>(decoder: &mut D) -> Result<&'tcx Allocation, D::Error>
 299 where
 300     D: TyDecoder<'tcx>,
 301 {
 302     Ok(decoder.tcx().intern_const_alloc(Decodable::decode(decoder)?))
 303 }
 304
 305 #[macro_export]
 306 macro_rules! __impl_decoder_methods {
 307     ($($name:ident -> $ty:ty;)*) => {
 308         $(
 309             #[inline]
 310             fn $name(&mut self) -> Result<$ty, Self::Error> {
 311                 self.opaque.$name()
 312             }
 313         )*
 314     }
 315 }
 316
 317 #[macro_export]
 318 macro_rules! impl_arena_allocatable_decoder {
 319     ([]$args:tt) => {};
 320     ([decode $(, $attrs:ident)*]
 321      [[$DecoderName:ident [$($typaram:tt),*]], [$name:ident: $ty:ty], $tcx:lifetime]) => {
 322         impl<$($typaram),*> SpecializedDecoder<&$tcx $ty> for $DecoderName<$($typaram),*> {
 323             #[inline]
 324             fn specialized_decode(&mut self) -> Result<&$tcx $ty, Self::Error> {
 325                 decode_arena_allocable(self)
 326             }
 327         }
 328
 329         impl<$($typaram),*> SpecializedDecoder<&$tcx [$ty]> for $DecoderName<$($typaram),*> {
 330             #[inline]
 331             fn specialized_decode(&mut self) -> Result<&$tcx [$ty], Self::Error> {
 332                 decode_arena_allocable_slice(self)
 333             }
 334         }
 335     };
 336     ([$ignore:ident $(, $attrs:ident)*]$args:tt) => {
 337         impl_arena_allocatable_decoder!([$($attrs),*]$args);
 338     };
 339 }
 340
 341 #[macro_export]
 342 macro_rules! impl_arena_allocatable_decoders {
 343     ($args:tt, [$($a:tt $name:ident: $ty:ty,)*], $tcx:lifetime) => {
 344         $(
 345             impl_arena_allocatable_decoder!($a [$args, [$name: $ty], $tcx]);
 346         )*
 347     }
 348 }
 349
 350 #[macro_export]
 351 macro_rules! implement_ty_decoder {
 352     ($DecoderName:ident <$($typaram:tt),*>) => {
 353         mod __ty_decoder_impl {
 354             use std::borrow::Cow;
 355
 356             use rustc_serialize::{Decoder, SpecializedDecoder};
 357
 358             use $crate::infer::canonical::CanonicalVarInfos;
 359             use $crate::ty;
 360             use $crate::ty::codec::*;
 361             use $crate::ty::subst::SubstsRef;
 362             use rustc_hir::def_id::{CrateNum};
 363
 364             use rustc_span::Span;
 365
 366             use super::$DecoderName;
 367
 368             impl<$($typaram ),*> Decoder for $DecoderName<$($typaram),*> {
 369                 type Error = String;
 370
 371                 __impl_decoder_methods! {
 372                     read_nil -> ();
 373
 374                     read_u128 -> u128;
 375                     read_u64 -> u64;
 376                     read_u32 -> u32;
 377                     read_u16 -> u16;
 378                     read_u8 -> u8;
 379                     read_usize -> usize;
 380
 381                     read_i128 -> i128;
 382                     read_i64 -> i64;
 383                     read_i32 -> i32;
 384                     read_i16 -> i16;
 385                     read_i8 -> i8;
 386                     read_isize -> isize;
 387
 388                     read_bool -> bool;
 389                     read_f64 -> f64;
 390                     read_f32 -> f32;
 391                     read_char -> char;
 392                     read_str -> Cow<'_, str>;
 393                 }
 394
 395                 fn error(&mut self, err: &str) -> Self::Error {
 396                     self.opaque.error(err)
 397                 }
 398             }
 399
 400             // FIXME(#36588): These impls are horribly unsound as they allow
 401             // the caller to pick any lifetime for `'tcx`, including `'static`,
 402             // by using the unspecialized proxies to them.
 403
 404             rustc_hir::arena_types!(impl_arena_allocatable_decoders, [$DecoderName [$($typaram),*]], 'tcx);
 405             arena_types!(impl_arena_allocatable_decoders, [$DecoderName [$($typaram),*]], 'tcx);
 406
 407             impl<$($typaram),*> SpecializedDecoder<CrateNum>
 408             for $DecoderName<$($typaram),*> {
 409                 fn specialized_decode(&mut self) -> Result<CrateNum, Self::Error> {
 410                     decode_cnum(self)
 411                 }
 412             }
 413
 414             impl<$($typaram),*> SpecializedDecoder<ty::Ty<'tcx>>
 415             for $DecoderName<$($typaram),*> {
 416                 fn specialized_decode(&mut self) -> Result<ty::Ty<'tcx>, Self::Error> {
 417                     decode_ty(self)
 418                 }
 419             }
 420
 421             impl<$($typaram),*> SpecializedDecoder<&'tcx [(ty::Predicate<'tcx>, Span)]>
 422             for $DecoderName<$($typaram),*> {
 423                 fn specialized_decode(&mut self)
 424                                       -> Result<&'tcx [(ty::Predicate<'tcx>, Span)], Self::Error> {
 425                     decode_spanned_predicates(self)
 426                 }
 427             }
 428
 429             impl<$($typaram),*> SpecializedDecoder<SubstsRef<'tcx>>
 430             for $DecoderName<$($typaram),*> {
 431                 fn specialized_decode(&mut self) -> Result<SubstsRef<'tcx>, Self::Error> {
 432                     decode_substs(self)
 433                 }
 434             }
 435
 436             impl<$($typaram),*> SpecializedDecoder<$crate::mir::Place<'tcx>>
 437             for $DecoderName<$($typaram),*> {
 438                 fn specialized_decode(
 439                     &mut self
 440                 ) -> Result<$crate::mir::Place<'tcx>, Self::Error> {
 441                     decode_place(self)
 442                 }
 443             }
 444
 445             impl<$($typaram),*> SpecializedDecoder<ty::Region<'tcx>>
 446             for $DecoderName<$($typaram),*> {
 447                 fn specialized_decode(&mut self) -> Result<ty::Region<'tcx>, Self::Error> {
 448                     decode_region(self)
 449                 }
 450             }
 451
 452             impl<$($typaram),*> SpecializedDecoder<&'tcx ty::List<ty::Ty<'tcx>>>
 453             for $DecoderName<$($typaram),*> {
 454                 fn specialized_decode(&mut self)
 455                                       -> Result<&'tcx ty::List<ty::Ty<'tcx>>, Self::Error> {
 456                     decode_ty_slice(self)
 457                 }
 458             }
 459
 460             impl<$($typaram),*> SpecializedDecoder<&'tcx ty::AdtDef>
 461             for $DecoderName<$($typaram),*> {
 462                 fn specialized_decode(&mut self) -> Result<&'tcx ty::AdtDef, Self::Error> {
 463                     decode_adt_def(self)
 464                 }
 465             }
 466
 467             impl<$($typaram),*> SpecializedDecoder<&'tcx ty::List<ty::ExistentialPredicate<'tcx>>>
 468                 for $DecoderName<$($typaram),*> {
 469                 fn specialized_decode(&mut self)
 470                     -> Result<&'tcx ty::List<ty::ExistentialPredicate<'tcx>>, Self::Error> {
 471                     decode_existential_predicate_slice(self)
 472                 }
 473             }
 474
 475             impl<$($typaram),*> SpecializedDecoder<CanonicalVarInfos<'tcx>>
 476                 for $DecoderName<$($typaram),*> {
 477                 fn specialized_decode(&mut self)
 478                     -> Result<CanonicalVarInfos<'tcx>, Self::Error> {
 479                     decode_canonical_var_infos(self)
 480                 }
 481             }
 482
 483             impl<$($typaram),*> SpecializedDecoder<&'tcx $crate::ty::Const<'tcx>>
 484             for $DecoderName<$($typaram),*> {
 485                 fn specialized_decode(&mut self) -> Result<&'tcx ty::Const<'tcx>, Self::Error> {
 486                     decode_const(self)
 487                 }
 488             }
 489
 490             impl<$($typaram),*> SpecializedDecoder<&'tcx $crate::mir::interpret::Allocation>
 491             for $DecoderName<$($typaram),*> {
 492                 fn specialized_decode(
 493                     &mut self
 494                 ) -> Result<&'tcx $crate::mir::interpret::Allocation, Self::Error> {
 495                     decode_allocation(self)
 496                 }
 497             }
 498         }
 499     }
 500 }