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::hash::Hash;
  19 use std::intrinsics;
  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, value: &T, cache: M) -> Result<(), E::Error>
  59 where
  60     E: TyEncoder,
  61     M: for<'b> Fn(&'b mut E) -> &'b mut FxHashMap<T, usize>,
  62     T: EncodableWithShorthand,
  63 {
  64     let existing_shorthand = cache(encoder).get(value).cloned();
  65     if let Some(shorthand) = existing_shorthand {
  66         return encoder.emit_usize(shorthand);
  67     }
  68
  69     let variant = value.variant();
  70
  71     let start = encoder.position();
  72     variant.encode(encoder)?;
  73     let len = encoder.position() - start;
  74
  75     // The shorthand encoding uses the same usize as the
  76     // discriminant, with an offset so they can't conflict.
  77     let discriminant = intrinsics::discriminant_value(variant);
  78     assert!(discriminant < SHORTHAND_OFFSET as u64);
  79     let shorthand = start + SHORTHAND_OFFSET;
  80
  81     // Get the number of bits that leb128 could fit
  82     // in the same space as the fully encoded type.
  83     let leb128_bits = len * 7;
  84
  85     // Check that the shorthand is a not longer than the
  86     // full encoding itself, i.e., it's an obvious win.
  87     if leb128_bits >= 64 || (shorthand as u64) < (1 << leb128_bits) {
  88         cache(encoder).insert(value.clone(), shorthand);
  89     }
  90
  91     Ok(())
  92 }
  93
  94 pub fn encode_spanned_predicates<'tcx, E, C>(
  95     encoder: &mut E,
  96     predicates: &'tcx [(ty::Predicate<'tcx>, Span)],
  97     cache: C,
  98 ) -> Result<(), E::Error>
  99 where
 100     E: TyEncoder,
 101     C: for<'b> Fn(&'b mut E) -> &'b mut FxHashMap<ty::Predicate<'tcx>, usize>,
 102 {
 103     predicates.len().encode(encoder)?;
 104     for (predicate, span) in predicates {
 105         encode_with_shorthand(encoder, predicate, &cache)?;
 106         span.encode(encoder)?;
 107     }
 108     Ok(())
 109 }
 110
 111 pub trait TyDecoder<'tcx>: Decoder {
 112     fn tcx(&self) -> TyCtxt<'tcx>;
 113
 114     fn peek_byte(&self) -> u8;
 115
 116     fn position(&self) -> usize;
 117
 118     fn cached_ty_for_shorthand<F>(
 119         &mut self,
 120         shorthand: usize,
 121         or_insert_with: F,
 122     ) -> Result<Ty<'tcx>, Self::Error>
 123     where
 124         F: FnOnce(&mut Self) -> Result<Ty<'tcx>, Self::Error>;
 125
 126     fn with_position<F, R>(&mut self, pos: usize, f: F) -> R
 127     where
 128         F: FnOnce(&mut Self) -> R;
 129
 130     fn map_encoded_cnum_to_current(&self, cnum: CrateNum) -> CrateNum;
 131
 132     fn positioned_at_shorthand(&self) -> bool {
 133         (self.peek_byte() & (SHORTHAND_OFFSET as u8)) != 0
 134     }
 135 }
 136
 137 #[inline]
 138 pub fn decode_arena_allocable<D, T: ArenaAllocatable + Decodable>(
 139     decoder: &mut D,
 140 ) -> Result<&'tcx T, D::Error>
 141 where
 142     D: TyDecoder<'tcx>,
 143 {
 144     Ok(decoder.tcx().arena.alloc(Decodable::decode(decoder)?))
 145 }
 146
 147 #[inline]
 148 pub fn decode_arena_allocable_slice<D, T: ArenaAllocatable + Decodable>(
 149     decoder: &mut D,
 150 ) -> Result<&'tcx [T], D::Error>
 151 where
 152     D: TyDecoder<'tcx>,
 153 {
 154     Ok(decoder.tcx().arena.alloc_from_iter(<Vec<T> as Decodable>::decode(decoder)?))
 155 }
 156
 157 #[inline]
 158 pub fn decode_cnum<D>(decoder: &mut D) -> Result<CrateNum, D::Error>
 159 where
 160     D: TyDecoder<'tcx>,
 161 {
 162     let cnum = CrateNum::from_u32(u32::decode(decoder)?);
 163     Ok(decoder.map_encoded_cnum_to_current(cnum))
 164 }
 165
 166 #[allow(rustc::usage_of_ty_tykind)]
 167 #[inline]
 168 pub fn decode_ty<D>(decoder: &mut D) -> Result<Ty<'tcx>, D::Error>
 169 where
 170     D: TyDecoder<'tcx>,
 171 {
 172     // Handle shorthands first, if we have an usize > 0x80.
 173     if decoder.positioned_at_shorthand() {
 174         let pos = decoder.read_usize()?;
 175         assert!(pos >= SHORTHAND_OFFSET);
 176         let shorthand = pos - SHORTHAND_OFFSET;
 177
 178         decoder.cached_ty_for_shorthand(shorthand, |decoder| {
 179             decoder.with_position(shorthand, Ty::decode)
 180         })
 181     } else {
 182         let tcx = decoder.tcx();
 183         Ok(tcx.mk_ty(ty::TyKind::decode(decoder)?))
 184     }
 185 }
 186
 187 #[inline]
 188 pub fn decode_spanned_predicates<D>(
 189     decoder: &mut D,
 190 ) -> Result<&'tcx [(ty::Predicate<'tcx>, Span)], D::Error>
 191 where
 192     D: TyDecoder<'tcx>,
 193 {
 194     let tcx = decoder.tcx();
 195     Ok(tcx.arena.alloc_from_iter(
 196         (0..decoder.read_usize()?)
 197             .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::PredicateKind::decode)
 205                 } else {
 206                     ty::PredicateKind::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 local: mir::Local = 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 { local, 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().mk_existential_predicates((0..len).map(|_| Decodable::decode(decoder)))?)
 271 }
 272
 273 #[inline]
 274 pub fn decode_canonical_var_infos<D>(decoder: &mut D) -> Result<CanonicalVarInfos<'tcx>, D::Error>
 275 where
 276     D: TyDecoder<'tcx>,
 277 {
 278     let len = decoder.read_usize()?;
 279     let interned: Result<Vec<CanonicalVarInfo>, _> =
 280         (0..len).map(|_| Decodable::decode(decoder)).collect();
 281     Ok(decoder.tcx().intern_canonical_var_infos(interned?.as_slice()))
 282 }
 283
 284 #[inline]
 285 pub fn decode_const<D>(decoder: &mut D) -> Result<&'tcx ty::Const<'tcx>, D::Error>
 286 where
 287     D: TyDecoder<'tcx>,
 288 {
 289     Ok(decoder.tcx().mk_const(Decodable::decode(decoder)?))
 290 }
 291
 292 #[inline]
 293 pub fn decode_allocation<D>(decoder: &mut D) -> Result<&'tcx Allocation, D::Error>
 294 where
 295     D: TyDecoder<'tcx>,
 296 {
 297     Ok(decoder.tcx().intern_const_alloc(Decodable::decode(decoder)?))
 298 }
 299
 300 #[macro_export]
 301 macro_rules! __impl_decoder_methods {
 302     ($($name:ident -> $ty:ty;)*) => {
 303         $(
 304             #[inline]
 305             fn $name(&mut self) -> Result<$ty, Self::Error> {
 306                 self.opaque.$name()
 307             }
 308         )*
 309     }
 310 }
 311
 312 #[macro_export]
 313 macro_rules! impl_arena_allocatable_decoder {
 314     ([]$args:tt) => {};
 315     ([decode $(, $attrs:ident)*]
 316      [[$DecoderName:ident [$($typaram:tt),*]], [$name:ident: $ty:ty], $tcx:lifetime]) => {
 317         impl<$($typaram),*> SpecializedDecoder<&$tcx $ty> for $DecoderName<$($typaram),*> {
 318             #[inline]
 319             fn specialized_decode(&mut self) -> Result<&$tcx $ty, Self::Error> {
 320                 decode_arena_allocable(self)
 321             }
 322         }
 323
 324         impl<$($typaram),*> SpecializedDecoder<&$tcx [$ty]> for $DecoderName<$($typaram),*> {
 325             #[inline]
 326             fn specialized_decode(&mut self) -> Result<&$tcx [$ty], Self::Error> {
 327                 decode_arena_allocable_slice(self)
 328             }
 329         }
 330     };
 331     ([$ignore:ident $(, $attrs:ident)*]$args:tt) => {
 332         impl_arena_allocatable_decoder!([$($attrs),*]$args);
 333     };
 334 }
 335
 336 #[macro_export]
 337 macro_rules! impl_arena_allocatable_decoders {
 338     ($args:tt, [$($a:tt $name:ident: $ty:ty,)*], $tcx:lifetime) => {
 339         $(
 340             impl_arena_allocatable_decoder!($a [$args, [$name: $ty], $tcx]);
 341         )*
 342     }
 343 }
 344
 345 #[macro_export]
 346 macro_rules! implement_ty_decoder {
 347     ($DecoderName:ident <$($typaram:tt),*>) => {
 348         mod __ty_decoder_impl {
 349             use std::borrow::Cow;
 350
 351             use rustc_serialize::{Decoder, SpecializedDecoder};
 352
 353             use $crate::infer::canonical::CanonicalVarInfos;
 354             use $crate::ty;
 355             use $crate::ty::codec::*;
 356             use $crate::ty::subst::SubstsRef;
 357             use rustc_hir::def_id::{CrateNum};
 358
 359             use rustc_span::Span;
 360
 361             use super::$DecoderName;
 362
 363             impl<$($typaram ),*> Decoder for $DecoderName<$($typaram),*> {
 364                 type Error = String;
 365
 366                 __impl_decoder_methods! {
 367                     read_nil -> ();
 368
 369                     read_u128 -> u128;
 370                     read_u64 -> u64;
 371                     read_u32 -> u32;
 372                     read_u16 -> u16;
 373                     read_u8 -> u8;
 374                     read_usize -> usize;
 375
 376                     read_i128 -> i128;
 377                     read_i64 -> i64;
 378                     read_i32 -> i32;
 379                     read_i16 -> i16;
 380                     read_i8 -> i8;
 381                     read_isize -> isize;
 382
 383                     read_bool -> bool;
 384                     read_f64 -> f64;
 385                     read_f32 -> f32;
 386                     read_char -> char;
 387                     read_str -> Cow<'_, str>;
 388                 }
 389
 390                 fn error(&mut self, err: &str) -> Self::Error {
 391                     self.opaque.error(err)
 392                 }
 393             }
 394
 395             // FIXME(#36588): These impls are horribly unsound as they allow
 396             // the caller to pick any lifetime for `'tcx`, including `'static`,
 397             // by using the unspecialized proxies to them.
 398
 399             rustc_hir::arena_types!(impl_arena_allocatable_decoders, [$DecoderName [$($typaram),*]], 'tcx);
 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 }