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