src/librustc/ty/codec.rs

   1 // Copyright 2017 The Rust Project Developers. See the COPYRIGHT
   2 // file at the top-level directory of this distribution and at
   3 // http://rust-lang.org/COPYRIGHT.
   4 //
   5 // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
   6 // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
   7 // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
   8 // option. This file may not be copied, modified, or distributed
   9 // except according to those terms.
  10
  11 // This module contains some shared code for encoding and decoding various
  12 // things from the `ty` module, and in particular implements support for
  13 // "shorthands" which allow to have pointers back into the already encoded
  14 // stream instead of re-encoding the same thing twice.
  15 //
  16 // The functionality in here is shared between persisting to crate metadata and
  17 // persisting to incr. comp. caches.
  18
  19 use hir::def_id::{DefId, CrateNum};
  20 use infer::canonical::{CanonicalVarInfo, CanonicalVarInfos};
  21 use rustc_data_structures::fx::FxHashMap;
  22 use rustc_serialize::{Decodable, Decoder, Encoder, Encodable, opaque};
  23 use std::hash::Hash;
  24 use std::intrinsics;
  25 use ty::{self, Ty, TyCtxt};
  26 use ty::subst::Substs;
  27 use mir::interpret::Allocation;
  28
  29 /// The shorthand encoding uses an enum's variant index `usize`
  30 /// and is offset by this value so it never matches a real variant.
  31 /// This offset is also chosen so that the first byte is never < 0x80.
  32 pub const SHORTHAND_OFFSET: usize = 0x80;
  33
  34 pub trait EncodableWithShorthand: Clone + Eq + Hash {
  35     type Variant: Encodable;
  36     fn variant(&self) -> &Self::Variant;
  37 }
  38
  39 impl<'tcx> EncodableWithShorthand for Ty<'tcx> {
  40     type Variant = ty::TyKind<'tcx>;
  41     fn variant(&self) -> &Self::Variant {
  42         &self.sty
  43     }
  44 }
  45
  46 impl<'tcx> EncodableWithShorthand for ty::Predicate<'tcx> {
  47     type Variant = ty::Predicate<'tcx>;
  48     fn variant(&self) -> &Self::Variant {
  49         self
  50     }
  51 }
  52
  53 pub trait TyEncoder: Encoder {
  54     fn position(&self) -> usize;
  55 }
  56
  57 impl TyEncoder for opaque::Encoder {
  58     #[inline]
  59     fn position(&self) -> usize {
  60         self.position()
  61     }
  62 }
  63
  64 /// Encode the given value or a previously cached shorthand.
  65 pub fn encode_with_shorthand<E, T, M>(encoder: &mut E,
  66                                       value: &T,
  67                                       cache: M)
  68                                       -> Result<(), E::Error>
  69     where E: TyEncoder,
  70           M: for<'b> Fn(&'b mut E) -> &'b mut FxHashMap<T, usize>,
  71           T: EncodableWithShorthand,
  72 {
  73     let existing_shorthand = cache(encoder).get(value).cloned();
  74     if let Some(shorthand) = existing_shorthand {
  75         return encoder.emit_usize(shorthand);
  76     }
  77
  78     let variant = value.variant();
  79
  80     let start = encoder.position();
  81     variant.encode(encoder)?;
  82     let len = encoder.position() - start;
  83
  84     // The shorthand encoding uses the same usize as the
  85     // discriminant, with an offset so they can't conflict.
  86     let discriminant = unsafe { intrinsics::discriminant_value(variant) };
  87     assert!(discriminant < SHORTHAND_OFFSET as u64);
  88     let shorthand = start + SHORTHAND_OFFSET;
  89
  90     // Get the number of bits that leb128 could fit
  91     // in the same space as the fully encoded type.
  92     let leb128_bits = len * 7;
  93
  94     // Check that the shorthand is a not longer than the
  95     // full encoding itself, i.e. it's an obvious win.
  96     if leb128_bits >= 64 || (shorthand as u64) < (1 << leb128_bits) {
  97         cache(encoder).insert(value.clone(), shorthand);
  98     }
  99
 100     Ok(())
 101 }
 102
 103 pub fn encode_predicates<'tcx, E, C>(encoder: &mut E,
 104                                      predicates: &ty::GenericPredicates<'tcx>,
 105                                      cache: C)
 106                                      -> Result<(), E::Error>
 107     where E: TyEncoder,
 108           C: for<'b> Fn(&'b mut E) -> &'b mut FxHashMap<ty::Predicate<'tcx>, usize>,
 109 {
 110     predicates.parent.encode(encoder)?;
 111     predicates.predicates.len().encode(encoder)?;
 112     for (predicate, span) in &predicates.predicates {
 113         encode_with_shorthand(encoder, predicate, &cache)?;
 114         span.encode(encoder)?;
 115     }
 116     Ok(())
 117 }
 118
 119 pub trait TyDecoder<'a, 'tcx: 'a>: Decoder {
 120
 121     fn tcx(&self) -> TyCtxt<'a, 'tcx, 'tcx>;
 122
 123     fn peek_byte(&self) -> u8;
 124
 125     fn position(&self) -> usize;
 126
 127     fn cached_ty_for_shorthand<F>(&mut self,
 128                                   shorthand: usize,
 129                                   or_insert_with: F)
 130                                   -> Result<Ty<'tcx>, Self::Error>
 131         where F: FnOnce(&mut Self) -> Result<Ty<'tcx>, Self::Error>;
 132
 133     fn with_position<F, R>(&mut self, pos: usize, f: F) -> R
 134         where F: FnOnce(&mut Self) -> R;
 135
 136     fn map_encoded_cnum_to_current(&self, cnum: CrateNum) -> CrateNum;
 137
 138     fn positioned_at_shorthand(&self) -> bool {
 139         (self.peek_byte() & (SHORTHAND_OFFSET as u8)) != 0
 140     }
 141 }
 142
 143 #[inline]
 144 pub fn decode_cnum<'a, 'tcx, D>(decoder: &mut D) -> Result<CrateNum, D::Error>
 145     where D: TyDecoder<'a, 'tcx>,
 146           'tcx: 'a,
 147 {
 148     let cnum = CrateNum::from_u32(u32::decode(decoder)?);
 149     Ok(decoder.map_encoded_cnum_to_current(cnum))
 150 }
 151
 152 #[inline]
 153 pub fn decode_ty<'a, 'tcx, D>(decoder: &mut D) -> Result<Ty<'tcx>, D::Error>
 154     where D: TyDecoder<'a, 'tcx>,
 155           'tcx: 'a,
 156 {
 157     // Handle shorthands first, if we have an usize > 0x80.
 158     if decoder.positioned_at_shorthand() {
 159         let pos = decoder.read_usize()?;
 160         assert!(pos >= SHORTHAND_OFFSET);
 161         let shorthand = pos - SHORTHAND_OFFSET;
 162
 163         decoder.cached_ty_for_shorthand(shorthand, |decoder| {
 164             decoder.with_position(shorthand, Ty::decode)
 165         })
 166     } else {
 167         let tcx = decoder.tcx();
 168         Ok(tcx.mk_ty(ty::TyKind::decode(decoder)?))
 169     }
 170 }
 171
 172 #[inline]
 173 pub fn decode_predicates<'a, 'tcx, D>(decoder: &mut D)
 174                                       -> Result<ty::GenericPredicates<'tcx>, D::Error>
 175     where D: TyDecoder<'a, 'tcx>,
 176           'tcx: 'a,
 177 {
 178     Ok(ty::GenericPredicates {
 179         parent: Decodable::decode(decoder)?,
 180         predicates: (0..decoder.read_usize()?).map(|_| {
 181             // Handle shorthands first, if we have an usize > 0x80.
 182             let predicate = if decoder.positioned_at_shorthand() {
 183                 let pos = decoder.read_usize()?;
 184                 assert!(pos >= SHORTHAND_OFFSET);
 185                 let shorthand = pos - SHORTHAND_OFFSET;
 186
 187                 decoder.with_position(shorthand, ty::Predicate::decode)
 188             } else {
 189                 ty::Predicate::decode(decoder)
 190             }?;
 191             Ok((predicate, Decodable::decode(decoder)?))
 192         })
 193         .collect::<Result<Vec<_>, _>>()?,
 194     })
 195 }
 196
 197 #[inline]
 198 pub fn decode_substs<'a, 'tcx, D>(decoder: &mut D) -> Result<&'tcx Substs<'tcx>, D::Error>
 199     where D: TyDecoder<'a, 'tcx>,
 200           'tcx: 'a,
 201 {
 202     let len = decoder.read_usize()?;
 203     let tcx = decoder.tcx();
 204     Ok(tcx.mk_substs((0..len).map(|_| Decodable::decode(decoder)))?)
 205 }
 206
 207 #[inline]
 208 pub fn decode_region<'a, 'tcx, D>(decoder: &mut D) -> Result<ty::Region<'tcx>, D::Error>
 209     where D: TyDecoder<'a, 'tcx>,
 210           'tcx: 'a,
 211 {
 212     Ok(decoder.tcx().mk_region(Decodable::decode(decoder)?))
 213 }
 214
 215 #[inline]
 216 pub fn decode_ty_slice<'a, 'tcx, D>(decoder: &mut D)
 217                                     -> Result<&'tcx ty::List<Ty<'tcx>>, D::Error>
 218     where D: TyDecoder<'a, 'tcx>,
 219           'tcx: 'a,
 220 {
 221     let len = decoder.read_usize()?;
 222     Ok(decoder.tcx().mk_type_list((0..len).map(|_| Decodable::decode(decoder)))?)
 223 }
 224
 225 #[inline]
 226 pub fn decode_adt_def<'a, 'tcx, D>(decoder: &mut D)
 227                                    -> Result<&'tcx ty::AdtDef, D::Error>
 228     where D: TyDecoder<'a, 'tcx>,
 229           'tcx: 'a,
 230 {
 231     let def_id = DefId::decode(decoder)?;
 232     Ok(decoder.tcx().adt_def(def_id))
 233 }
 234
 235 #[inline]
 236 pub fn decode_existential_predicate_slice<'a, 'tcx, D>(decoder: &mut D)
 237     -> Result<&'tcx ty::List<ty::ExistentialPredicate<'tcx>>, D::Error>
 238     where D: TyDecoder<'a, 'tcx>,
 239           'tcx: 'a,
 240 {
 241     let len = decoder.read_usize()?;
 242     Ok(decoder.tcx()
 243               .mk_existential_predicates((0..len).map(|_| Decodable::decode(decoder)))?)
 244 }
 245
 246 #[inline]
 247 pub fn decode_canonical_var_infos<'a, 'tcx, D>(decoder: &mut D)
 248     -> Result<CanonicalVarInfos<'tcx>, D::Error>
 249     where D: TyDecoder<'a, 'tcx>,
 250           'tcx: 'a,
 251 {
 252     let len = decoder.read_usize()?;
 253     let interned: Result<Vec<CanonicalVarInfo>, _> = (0..len).map(|_| Decodable::decode(decoder))
 254                                                              .collect();
 255     Ok(decoder.tcx()
 256               .intern_canonical_var_infos(interned?.as_slice()))
 257 }
 258
 259 #[inline]
 260 pub fn decode_const<'a, 'tcx, D>(decoder: &mut D)
 261                                  -> Result<&'tcx ty::Const<'tcx>, D::Error>
 262     where D: TyDecoder<'a, 'tcx>,
 263           'tcx: 'a,
 264 {
 265     Ok(decoder.tcx().mk_const(Decodable::decode(decoder)?))
 266 }
 267
 268 #[inline]
 269 pub fn decode_allocation<'a, 'tcx, D>(decoder: &mut D)
 270     -> Result<&'tcx Allocation, D::Error>
 271     where D: TyDecoder<'a, 'tcx>,
 272           'tcx: 'a,
 273 {
 274     Ok(decoder.tcx().intern_const_alloc(Decodable::decode(decoder)?))
 275 }
 276
 277 #[macro_export]
 278 macro_rules! __impl_decoder_methods {
 279     ($($name:ident -> $ty:ty;)*) => {
 280         $(fn $name(&mut self) -> Result<$ty, Self::Error> {
 281             self.opaque.$name()
 282         })*
 283     }
 284 }
 285
 286 #[macro_export]
 287 macro_rules! implement_ty_decoder {
 288     ($DecoderName:ident <$($typaram:tt),*>) => {
 289         mod __ty_decoder_impl {
 290             use super::$DecoderName;
 291             use $crate::infer::canonical::CanonicalVarInfos;
 292             use $crate::ty;
 293             use $crate::ty::codec::*;
 294             use $crate::ty::subst::Substs;
 295             use $crate::hir::def_id::{CrateNum};
 296             use rustc_serialize::{Decoder, SpecializedDecoder};
 297             use std::borrow::Cow;
 298
 299             impl<$($typaram ),*> Decoder for $DecoderName<$($typaram),*> {
 300                 type Error = String;
 301
 302                 __impl_decoder_methods! {
 303                     read_nil -> ();
 304
 305                     read_u128 -> u128;
 306                     read_u64 -> u64;
 307                     read_u32 -> u32;
 308                     read_u16 -> u16;
 309                     read_u8 -> u8;
 310                     read_usize -> usize;
 311
 312                     read_i128 -> i128;
 313                     read_i64 -> i64;
 314                     read_i32 -> i32;
 315                     read_i16 -> i16;
 316                     read_i8 -> i8;
 317                     read_isize -> isize;
 318
 319                     read_bool -> bool;
 320                     read_f64 -> f64;
 321                     read_f32 -> f32;
 322                     read_char -> char;
 323                     read_str -> Cow<'_, str>;
 324                 }
 325
 326                 fn error(&mut self, err: &str) -> Self::Error {
 327                     self.opaque.error(err)
 328                 }
 329             }
 330
 331             // FIXME(#36588) These impls are horribly unsound as they allow
 332             // the caller to pick any lifetime for 'tcx, including 'static,
 333             // by using the unspecialized proxies to them.
 334
 335             impl<$($typaram),*> SpecializedDecoder<CrateNum>
 336             for $DecoderName<$($typaram),*> {
 337                 fn specialized_decode(&mut self) -> Result<CrateNum, Self::Error> {
 338                     decode_cnum(self)
 339                 }
 340             }
 341
 342             impl<$($typaram),*> SpecializedDecoder<ty::Ty<'tcx>>
 343             for $DecoderName<$($typaram),*> {
 344                 fn specialized_decode(&mut self) -> Result<ty::Ty<'tcx>, Self::Error> {
 345                     decode_ty(self)
 346                 }
 347             }
 348
 349             impl<$($typaram),*> SpecializedDecoder<ty::GenericPredicates<'tcx>>
 350             for $DecoderName<$($typaram),*> {
 351                 fn specialized_decode(&mut self)
 352                                       -> Result<ty::GenericPredicates<'tcx>, Self::Error> {
 353                     decode_predicates(self)
 354                 }
 355             }
 356
 357             impl<$($typaram),*> SpecializedDecoder<&'tcx Substs<'tcx>>
 358             for $DecoderName<$($typaram),*> {
 359                 fn specialized_decode(&mut self) -> Result<&'tcx Substs<'tcx>, Self::Error> {
 360                     decode_substs(self)
 361                 }
 362             }
 363
 364             impl<$($typaram),*> SpecializedDecoder<ty::Region<'tcx>>
 365             for $DecoderName<$($typaram),*> {
 366                 fn specialized_decode(&mut self) -> Result<ty::Region<'tcx>, Self::Error> {
 367                     decode_region(self)
 368                 }
 369             }
 370
 371             impl<$($typaram),*> SpecializedDecoder<&'tcx ty::List<ty::Ty<'tcx>>>
 372             for $DecoderName<$($typaram),*> {
 373                 fn specialized_decode(&mut self)
 374                                       -> Result<&'tcx ty::List<ty::Ty<'tcx>>, Self::Error> {
 375                     decode_ty_slice(self)
 376                 }
 377             }
 378
 379             impl<$($typaram),*> SpecializedDecoder<&'tcx ty::AdtDef>
 380             for $DecoderName<$($typaram),*> {
 381                 fn specialized_decode(&mut self) -> Result<&'tcx ty::AdtDef, Self::Error> {
 382                     decode_adt_def(self)
 383                 }
 384             }
 385
 386             impl<$($typaram),*> SpecializedDecoder<&'tcx ty::List<ty::ExistentialPredicate<'tcx>>>
 387                 for $DecoderName<$($typaram),*> {
 388                 fn specialized_decode(&mut self)
 389                     -> Result<&'tcx ty::List<ty::ExistentialPredicate<'tcx>>, Self::Error> {
 390                     decode_existential_predicate_slice(self)
 391                 }
 392             }
 393
 394             impl<$($typaram),*> SpecializedDecoder<CanonicalVarInfos<'tcx>>
 395                 for $DecoderName<$($typaram),*> {
 396                 fn specialized_decode(&mut self)
 397                     -> Result<CanonicalVarInfos<'tcx>, Self::Error> {
 398                     decode_canonical_var_infos(self)
 399                 }
 400             }
 401
 402             impl<$($typaram),*> SpecializedDecoder<&'tcx $crate::ty::Const<'tcx>>
 403             for $DecoderName<$($typaram),*> {
 404                 fn specialized_decode(&mut self) -> Result<&'tcx ty::Const<'tcx>, Self::Error> {
 405                     decode_const(self)
 406                 }
 407             }
 408
 409             impl<$($typaram),*> SpecializedDecoder<&'tcx $crate::mir::interpret::Allocation>
 410             for $DecoderName<$($typaram),*> {
 411                 fn specialized_decode(
 412                     &mut self
 413                 ) -> Result<&'tcx $crate::mir::interpret::Allocation, Self::Error> {
 414                     decode_allocation(self)
 415                 }
 416             }
 417         }
 418     }
 419 }