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