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     #[cfg(bootstrap)]
  80     let discriminant = unsafe { intrinsics::discriminant_value(variant) };
  81     #[cfg(not(bootstrap))]
  82     let discriminant = intrinsics::discriminant_value(variant);
  83     assert!(discriminant < SHORTHAND_OFFSET as u64);
  84     let shorthand = start + SHORTHAND_OFFSET;
  85
  86     // Get the number of bits that leb128 could fit
  87     // in the same space as the fully encoded type.
  88     let leb128_bits = len * 7;
  89
  90     // Check that the shorthand is a not longer than the
  91     // full encoding itself, i.e., it's an obvious win.
  92     if leb128_bits >= 64 || (shorthand as u64) < (1 << leb128_bits) {
  93         cache(encoder).insert(value.clone(), shorthand);
  94     }
  95
  96     Ok(())
  97 }
  98
  99 pub fn encode_spanned_predicates<'tcx, E, C>(
 100     encoder: &mut E,
 101     predicates: &'tcx [(ty::Predicate<'tcx>, Span)],
 102     cache: C,
 103 ) -> Result<(), E::Error>
 104     where 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>(&mut self,
 123                                   shorthand: usize,
 124                                   or_insert_with: F)
 125                                   -> Result<Ty<'tcx>, Self::Error>
 126         where F: FnOnce(&mut Self) -> Result<Ty<'tcx>, Self::Error>;
 127
 128     fn with_position<F, R>(&mut self, pos: usize, f: F) -> R
 129         where F: FnOnce(&mut Self) -> R;
 130
 131     fn map_encoded_cnum_to_current(&self, cnum: CrateNum) -> CrateNum;
 132
 133     fn positioned_at_shorthand(&self) -> bool {
 134         (self.peek_byte() & (SHORTHAND_OFFSET as u8)) != 0
 135     }
 136 }
 137
 138 #[inline]
 139 pub fn decode_arena_allocable<D, T: ArenaAllocatable + Decodable>(
 140     decoder: &mut D,
 141 ) -> Result<&'tcx T, D::Error>
 142 where
 143     D: TyDecoder<'tcx>,
 144 {
 145     Ok(decoder.tcx().arena.alloc(Decodable::decode(decoder)?))
 146 }
 147
 148 #[inline]
 149 pub fn decode_arena_allocable_slice<D, T: ArenaAllocatable + Decodable>(
 150     decoder: &mut D,
 151 ) -> Result<&'tcx [T], D::Error>
 152 where
 153     D: TyDecoder<'tcx>,
 154 {
 155     Ok(decoder.tcx().arena.alloc_from_iter(<Vec<T> as Decodable>::decode(decoder)?))
 156 }
 157
 158 #[inline]
 159 pub fn decode_cnum<D>(decoder: &mut D) -> Result<CrateNum, D::Error>
 160 where
 161     D: TyDecoder<'tcx>,
 162 {
 163     let cnum = CrateNum::from_u32(u32::decode(decoder)?);
 164     Ok(decoder.map_encoded_cnum_to_current(cnum))
 165 }
 166
 167 #[allow(rustc::usage_of_ty_tykind)]
 168 #[inline]
 169 pub fn decode_ty<D>(decoder: &mut D) -> Result<Ty<'tcx>, D::Error>
 170 where
 171     D: TyDecoder<'tcx>,
 172 {
 173     // Handle shorthands first, if we have an usize > 0x80.
 174     if decoder.positioned_at_shorthand() {
 175         let pos = decoder.read_usize()?;
 176         assert!(pos >= SHORTHAND_OFFSET);
 177         let shorthand = pos - SHORTHAND_OFFSET;
 178
 179         decoder.cached_ty_for_shorthand(shorthand, |decoder| {
 180             decoder.with_position(shorthand, Ty::decode)
 181         })
 182     } else {
 183         let tcx = decoder.tcx();
 184         Ok(tcx.mk_ty(ty::TyKind::decode(decoder)?))
 185     }
 186 }
 187
 188 #[inline]
 189 pub fn decode_spanned_predicates<D>(
 190     decoder: &mut D,
 191 ) -> Result<&'tcx [(ty::Predicate<'tcx>, Span)], D::Error>
 192 where
 193     D: TyDecoder<'tcx>,
 194 {
 195     let tcx = decoder.tcx();
 196     Ok(tcx.arena.alloc_from_iter(
 197         (0..decoder.read_usize()?).map(|_| {
 198             // Handle shorthands first, if we have an usize > 0x80.
 199             let predicate = if decoder.positioned_at_shorthand() {
 200                 let pos = decoder.read_usize()?;
 201                 assert!(pos >= SHORTHAND_OFFSET);
 202                 let shorthand = pos - SHORTHAND_OFFSET;
 203
 204                 decoder.with_position(shorthand, ty::Predicate::decode)
 205             } else {
 206                 ty::Predicate::decode(decoder)
 207             }?;
 208             Ok((predicate, Decodable::decode(decoder)?))
 209         })
 210         .collect::<Result<Vec<_>, _>>()?,
 211     ))
 212 }
 213
 214 #[inline]
 215 pub fn decode_substs<D>(decoder: &mut D) -> Result<SubstsRef<'tcx>, D::Error>
 216 where
 217     D: TyDecoder<'tcx>,
 218 {
 219     let len = decoder.read_usize()?;
 220     let tcx = decoder.tcx();
 221     Ok(tcx.mk_substs((0..len).map(|_| Decodable::decode(decoder)))?)
 222 }
 223
 224 #[inline]
 225 pub fn decode_place<D>(decoder: &mut D) -> Result<mir::Place<'tcx>, D::Error>
 226 where
 227     D: TyDecoder<'tcx>,
 228 {
 229     let base: mir::PlaceBase<'tcx> = Decodable::decode(decoder)?;
 230     let len = decoder.read_usize()?;
 231     let projection: &'tcx List<mir::PlaceElem<'tcx>> =
 232         decoder.tcx().mk_place_elems((0..len).map(|_| Decodable::decode(decoder)))?;
 233     Ok(mir::Place { base, projection })
 234 }
 235
 236 #[inline]
 237 pub fn decode_region<D>(decoder: &mut D) -> Result<ty::Region<'tcx>, D::Error>
 238 where
 239     D: TyDecoder<'tcx>,
 240 {
 241     Ok(decoder.tcx().mk_region(Decodable::decode(decoder)?))
 242 }
 243
 244 #[inline]
 245 pub fn decode_ty_slice<D>(decoder: &mut D) -> Result<&'tcx ty::List<Ty<'tcx>>, D::Error>
 246 where
 247     D: TyDecoder<'tcx>,
 248 {
 249     let len = decoder.read_usize()?;
 250     Ok(decoder.tcx().mk_type_list((0..len).map(|_| Decodable::decode(decoder)))?)
 251 }
 252
 253 #[inline]
 254 pub fn decode_adt_def<D>(decoder: &mut D) -> Result<&'tcx ty::AdtDef, D::Error>
 255 where
 256     D: TyDecoder<'tcx>,
 257 {
 258     let def_id = DefId::decode(decoder)?;
 259     Ok(decoder.tcx().adt_def(def_id))
 260 }
 261
 262 #[inline]
 263 pub fn decode_existential_predicate_slice<D>(
 264     decoder: &mut D,
 265 ) -> Result<&'tcx ty::List<ty::ExistentialPredicate<'tcx>>, D::Error>
 266 where
 267     D: TyDecoder<'tcx>,
 268 {
 269     let len = decoder.read_usize()?;
 270     Ok(decoder.tcx()
 271               .mk_existential_predicates((0..len).map(|_| Decodable::decode(decoder)))?)
 272 }
 273
 274 #[inline]
 275 pub fn decode_canonical_var_infos<D>(decoder: &mut D) -> Result<CanonicalVarInfos<'tcx>, D::Error>
 276 where
 277     D: TyDecoder<'tcx>,
 278 {
 279     let len = decoder.read_usize()?;
 280     let interned: Result<Vec<CanonicalVarInfo>, _> = (0..len).map(|_| Decodable::decode(decoder))
 281                                                              .collect();
 282     Ok(decoder.tcx()
 283               .intern_canonical_var_infos(interned?.as_slice()))
 284 }
 285
 286 #[inline]
 287 pub fn decode_const<D>(decoder: &mut D) -> Result<&'tcx ty::Const<'tcx>, D::Error>
 288 where
 289     D: TyDecoder<'tcx>,
 290 {
 291     Ok(decoder.tcx().mk_const(Decodable::decode(decoder)?))
 292 }
 293
 294 #[inline]
 295 pub fn decode_allocation<D>(decoder: &mut D) -> Result<&'tcx Allocation, D::Error>
 296 where
 297     D: TyDecoder<'tcx>,
 298 {
 299     Ok(decoder.tcx().intern_const_alloc(Decodable::decode(decoder)?))
 300 }
 301
 302 #[macro_export]
 303 macro_rules! __impl_decoder_methods {
 304     ($($name:ident -> $ty:ty;)*) => {
 305         $(
 306             fn $name(&mut self) -> Result<$ty, Self::Error> {
 307                 self.opaque.$name()
 308             }
 309         )*
 310     }
 311 }
 312
 313 #[macro_export]
 314 macro_rules! impl_arena_allocatable_decoder {
 315     ([]$args:tt) => {};
 316     ([decode $(, $attrs:ident)*]
 317      [[$DecoderName:ident [$($typaram:tt),*]], [$name:ident: $ty:ty], $tcx:lifetime]) => {
 318         impl<$($typaram),*> SpecializedDecoder<&$tcx $ty> for $DecoderName<$($typaram),*> {
 319             #[inline]
 320             fn specialized_decode(&mut self) -> Result<&$tcx $ty, Self::Error> {
 321                 decode_arena_allocable(self)
 322             }
 323         }
 324
 325         impl<$($typaram),*> SpecializedDecoder<&$tcx [$ty]> for $DecoderName<$($typaram),*> {
 326             #[inline]
 327             fn specialized_decode(&mut self) -> Result<&$tcx [$ty], Self::Error> {
 328                 decode_arena_allocable_slice(self)
 329             }
 330         }
 331     };
 332     ([$ignore:ident $(, $attrs:ident)*]$args:tt) => {
 333         impl_arena_allocatable_decoder!([$($attrs),*]$args);
 334     };
 335 }
 336
 337 #[macro_export]
 338 macro_rules! impl_arena_allocatable_decoders {
 339     ($args:tt, [$($a:tt $name:ident: $ty:ty,)*], $tcx:lifetime) => {
 340         $(
 341             impl_arena_allocatable_decoder!($a [$args, [$name: $ty], $tcx]);
 342         )*
 343     }
 344 }
 345
 346 #[macro_export]
 347 macro_rules! implement_ty_decoder {
 348     ($DecoderName:ident <$($typaram:tt),*>) => {
 349         mod __ty_decoder_impl {
 350             use std::borrow::Cow;
 351
 352             use rustc_serialize::{Decoder, SpecializedDecoder};
 353
 354             use $crate::infer::canonical::CanonicalVarInfos;
 355             use $crate::ty;
 356             use $crate::ty::codec::*;
 357             use $crate::ty::subst::SubstsRef;
 358             use $crate::hir::def_id::{CrateNum};
 359
 360             use syntax_pos::Span;
 361
 362             use super::$DecoderName;
 363
 364             impl<$($typaram ),*> Decoder for $DecoderName<$($typaram),*> {
 365                 type Error = String;
 366
 367                 __impl_decoder_methods! {
 368                     read_nil -> ();
 369
 370                     read_u128 -> u128;
 371                     read_u64 -> u64;
 372                     read_u32 -> u32;
 373                     read_u16 -> u16;
 374                     read_u8 -> u8;
 375                     read_usize -> usize;
 376
 377                     read_i128 -> i128;
 378                     read_i64 -> i64;
 379                     read_i32 -> i32;
 380                     read_i16 -> i16;
 381                     read_i8 -> i8;
 382                     read_isize -> isize;
 383
 384                     read_bool -> bool;
 385                     read_f64 -> f64;
 386                     read_f32 -> f32;
 387                     read_char -> char;
 388                     read_str -> Cow<'_, str>;
 389                 }
 390
 391                 fn error(&mut self, err: &str) -> Self::Error {
 392                     self.opaque.error(err)
 393                 }
 394             }
 395
 396             // FIXME(#36588): These impls are horribly unsound as they allow
 397             // the caller to pick any lifetime for `'tcx`, including `'static`,
 398             // by using the unspecialized proxies to them.
 399
 400             arena_types!(impl_arena_allocatable_decoders, [$DecoderName [$($typaram),*]], 'tcx);
 401
 402             impl<$($typaram),*> SpecializedDecoder<CrateNum>
 403             for $DecoderName<$($typaram),*> {
 404                 fn specialized_decode(&mut self) -> Result<CrateNum, Self::Error> {
 405                     decode_cnum(self)
 406                 }
 407             }
 408
 409             impl<$($typaram),*> SpecializedDecoder<ty::Ty<'tcx>>
 410             for $DecoderName<$($typaram),*> {
 411                 fn specialized_decode(&mut self) -> Result<ty::Ty<'tcx>, Self::Error> {
 412                     decode_ty(self)
 413                 }
 414             }
 415
 416             impl<$($typaram),*> SpecializedDecoder<&'tcx [(ty::Predicate<'tcx>, Span)]>
 417             for $DecoderName<$($typaram),*> {
 418                 fn specialized_decode(&mut self)
 419                                       -> Result<&'tcx [(ty::Predicate<'tcx>, Span)], Self::Error> {
 420                     decode_spanned_predicates(self)
 421                 }
 422             }
 423
 424             impl<$($typaram),*> SpecializedDecoder<SubstsRef<'tcx>>
 425             for $DecoderName<$($typaram),*> {
 426                 fn specialized_decode(&mut self) -> Result<SubstsRef<'tcx>, Self::Error> {
 427                     decode_substs(self)
 428                 }
 429             }
 430
 431             impl<$($typaram),*> SpecializedDecoder<$crate::mir::Place<'tcx>>
 432             for $DecoderName<$($typaram),*> {
 433                 fn specialized_decode(
 434                     &mut self
 435                 ) -> Result<$crate::mir::Place<'tcx>, Self::Error> {
 436                     decode_place(self)
 437                 }
 438             }
 439
 440             impl<$($typaram),*> SpecializedDecoder<ty::Region<'tcx>>
 441             for $DecoderName<$($typaram),*> {
 442                 fn specialized_decode(&mut self) -> Result<ty::Region<'tcx>, Self::Error> {
 443                     decode_region(self)
 444                 }
 445             }
 446
 447             impl<$($typaram),*> SpecializedDecoder<&'tcx ty::List<ty::Ty<'tcx>>>
 448             for $DecoderName<$($typaram),*> {
 449                 fn specialized_decode(&mut self)
 450                                       -> Result<&'tcx ty::List<ty::Ty<'tcx>>, Self::Error> {
 451                     decode_ty_slice(self)
 452                 }
 453             }
 454
 455             impl<$($typaram),*> SpecializedDecoder<&'tcx ty::AdtDef>
 456             for $DecoderName<$($typaram),*> {
 457                 fn specialized_decode(&mut self) -> Result<&'tcx ty::AdtDef, Self::Error> {
 458                     decode_adt_def(self)
 459                 }
 460             }
 461
 462             impl<$($typaram),*> SpecializedDecoder<&'tcx ty::List<ty::ExistentialPredicate<'tcx>>>
 463                 for $DecoderName<$($typaram),*> {
 464                 fn specialized_decode(&mut self)
 465                     -> Result<&'tcx ty::List<ty::ExistentialPredicate<'tcx>>, Self::Error> {
 466                     decode_existential_predicate_slice(self)
 467                 }
 468             }
 469
 470             impl<$($typaram),*> SpecializedDecoder<CanonicalVarInfos<'tcx>>
 471                 for $DecoderName<$($typaram),*> {
 472                 fn specialized_decode(&mut self)
 473                     -> Result<CanonicalVarInfos<'tcx>, Self::Error> {
 474                     decode_canonical_var_infos(self)
 475                 }
 476             }
 477
 478             impl<$($typaram),*> SpecializedDecoder<&'tcx $crate::ty::Const<'tcx>>
 479             for $DecoderName<$($typaram),*> {
 480                 fn specialized_decode(&mut self) -> Result<&'tcx ty::Const<'tcx>, Self::Error> {
 481                     decode_const(self)
 482                 }
 483             }
 484
 485             impl<$($typaram),*> SpecializedDecoder<&'tcx $crate::mir::interpret::Allocation>
 486             for $DecoderName<$($typaram),*> {
 487                 fn specialized_decode(
 488                     &mut self
 489                 ) -> Result<&'tcx $crate::mir::interpret::Allocation, Self::Error> {
 490                     decode_allocation(self)
 491                 }
 492             }
 493         }
 494     }
 495 }