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 crate::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 impl<'tcx> EncodableWithShorthand for Ty<'tcx> {
  31     type Variant = ty::TyKind<'tcx>;
  32     fn variant(&self) -> &Self::Variant {
  33         &self.sty
  34     }
  35 }
  36
  37 impl<'tcx> EncodableWithShorthand for ty::Predicate<'tcx> {
  38     type Variant = ty::Predicate<'tcx>;
  39     fn variant(&self) -> &Self::Variant {
  40         self
  41     }
  42 }
  43
  44 pub trait TyEncoder: Encoder {
  45     fn position(&self) -> usize;
  46 }
  47
  48 impl TyEncoder for opaque::Encoder {
  49     #[inline]
  50     fn position(&self) -> usize {
  51         self.position()
  52     }
  53 }
  54
  55 /// Encode the given value or a previously cached shorthand.
  56 pub fn encode_with_shorthand<E, T, M>(encoder: &mut E,
  57                                       value: &T,
  58                                       cache: M)
  59                                       -> Result<(), E::Error>
  60     where 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 = unsafe { 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_predicates<'tcx, E, C>(encoder: &mut E,
  95                                      predicates: &ty::GenericPredicates<'tcx>,
  96                                      cache: C)
  97                                      -> Result<(), E::Error>
  98     where E: TyEncoder,
  99           C: for<'b> Fn(&'b mut E) -> &'b mut FxHashMap<ty::Predicate<'tcx>, usize>,
 100 {
 101     predicates.parent.encode(encoder)?;
 102     predicates.predicates.len().encode(encoder)?;
 103     for (predicate, span) in &predicates.predicates {
 104         encode_with_shorthand(encoder, predicate, &cache)?;
 105         span.encode(encoder)?;
 106     }
 107     Ok(())
 108 }
 109
 110 pub trait TyDecoder<'a, 'tcx: 'a>: Decoder {
 111
 112     fn tcx(&self) -> TyCtxt<'a, 'tcx, '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<'a, 'tcx, D, T: ArenaAllocatable + Decodable>(
 136     decoder: &mut D
 137 ) -> Result<&'tcx T, D::Error>
 138     where D: TyDecoder<'a, 'tcx>,
 139           'tcx: 'a,
 140 {
 141     Ok(decoder.tcx().arena.alloc(Decodable::decode(decoder)?))
 142 }
 143
 144 #[inline]
 145 pub fn decode_arena_allocable_slice<'a, 'tcx, D, T: ArenaAllocatable + Decodable>(
 146     decoder: &mut D
 147 ) -> Result<&'tcx [T], D::Error>
 148     where D: TyDecoder<'a, 'tcx>,
 149           'tcx: 'a,
 150 {
 151     Ok(decoder.tcx().arena.alloc_from_iter(<Vec<T> as Decodable>::decode(decoder)?))
 152 }
 153
 154 #[inline]
 155 pub fn decode_cnum<'a, 'tcx, D>(decoder: &mut D) -> Result<CrateNum, D::Error>
 156     where D: TyDecoder<'a, 'tcx>,
 157           'tcx: 'a,
 158 {
 159     let cnum = CrateNum::from_u32(u32::decode(decoder)?);
 160     Ok(decoder.map_encoded_cnum_to_current(cnum))
 161 }
 162
 163 #[inline]
 164 pub fn decode_ty<'a, 'tcx, D>(decoder: &mut D) -> Result<Ty<'tcx>, D::Error>
 165     where D: TyDecoder<'a, 'tcx>,
 166           'tcx: 'a,
 167 {
 168     // Handle shorthands first, if we have an usize > 0x80.
 169     if decoder.positioned_at_shorthand() {
 170         let pos = decoder.read_usize()?;
 171         assert!(pos >= SHORTHAND_OFFSET);
 172         let shorthand = pos - SHORTHAND_OFFSET;
 173
 174         decoder.cached_ty_for_shorthand(shorthand, |decoder| {
 175             decoder.with_position(shorthand, Ty::decode)
 176         })
 177     } else {
 178         let tcx = decoder.tcx();
 179         Ok(tcx.mk_ty(ty::TyKind::decode(decoder)?))
 180     }
 181 }
 182
 183 #[inline]
 184 pub fn decode_predicates<'a, 'tcx, D>(decoder: &mut D)
 185                                       -> Result<ty::GenericPredicates<'tcx>, D::Error>
 186     where D: TyDecoder<'a, 'tcx>,
 187           'tcx: 'a,
 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<'a, 'tcx, D>(decoder: &mut D) -> Result<SubstsRef<'tcx>, D::Error>
 210     where D: TyDecoder<'a, 'tcx>,
 211           'tcx: 'a,
 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<'a, 'tcx, D>(decoder: &mut D) -> Result<ty::Region<'tcx>, D::Error>
 220     where D: TyDecoder<'a, 'tcx>,
 221           'tcx: 'a,
 222 {
 223     Ok(decoder.tcx().mk_region(Decodable::decode(decoder)?))
 224 }
 225
 226 #[inline]
 227 pub fn decode_ty_slice<'a, 'tcx, D>(decoder: &mut D)
 228                                     -> Result<&'tcx ty::List<Ty<'tcx>>, D::Error>
 229     where D: TyDecoder<'a, 'tcx>,
 230           'tcx: 'a,
 231 {
 232     let len = decoder.read_usize()?;
 233     Ok(decoder.tcx().mk_type_list((0..len).map(|_| Decodable::decode(decoder)))?)
 234 }
 235
 236 #[inline]
 237 pub fn decode_adt_def<'a, 'tcx, D>(decoder: &mut D)
 238                                    -> Result<&'tcx ty::AdtDef, D::Error>
 239     where D: TyDecoder<'a, 'tcx>,
 240           'tcx: 'a,
 241 {
 242     let def_id = DefId::decode(decoder)?;
 243     Ok(decoder.tcx().adt_def(def_id))
 244 }
 245
 246 #[inline]
 247 pub fn decode_existential_predicate_slice<'a, 'tcx, D>(decoder: &mut D)
 248     -> Result<&'tcx ty::List<ty::ExistentialPredicate<'tcx>>, D::Error>
 249     where D: TyDecoder<'a, 'tcx>,
 250           'tcx: 'a,
 251 {
 252     let len = decoder.read_usize()?;
 253     Ok(decoder.tcx()
 254               .mk_existential_predicates((0..len).map(|_| Decodable::decode(decoder)))?)
 255 }
 256
 257 #[inline]
 258 pub fn decode_canonical_var_infos<'a, 'tcx, D>(decoder: &mut D)
 259     -> Result<CanonicalVarInfos<'tcx>, D::Error>
 260     where D: TyDecoder<'a, 'tcx>,
 261           'tcx: 'a,
 262 {
 263     let len = decoder.read_usize()?;
 264     let interned: Result<Vec<CanonicalVarInfo>, _> = (0..len).map(|_| Decodable::decode(decoder))
 265                                                              .collect();
 266     Ok(decoder.tcx()
 267               .intern_canonical_var_infos(interned?.as_slice()))
 268 }
 269
 270 #[inline]
 271 pub fn decode_const<'a, 'tcx, D>(decoder: &mut D)
 272                                  -> Result<&'tcx ty::Const<'tcx>, D::Error>
 273     where D: TyDecoder<'a, 'tcx>,
 274           'tcx: 'a,
 275 {
 276     Ok(decoder.tcx().mk_const(Decodable::decode(decoder)?))
 277 }
 278
 279 #[inline]
 280 pub fn decode_allocation<'a, 'tcx, D>(decoder: &mut D)
 281     -> Result<&'tcx Allocation, D::Error>
 282     where D: TyDecoder<'a, 'tcx>,
 283           'tcx: 'a,
 284 {
 285     Ok(decoder.tcx().intern_const_alloc(Decodable::decode(decoder)?))
 286 }
 287
 288 #[macro_export]
 289 macro_rules! __impl_decoder_methods {
 290     ($($name:ident -> $ty:ty;)*) => {
 291         $(fn $name(&mut self) -> Result<$ty, Self::Error> {
 292             self.opaque.$name()
 293         })*
 294     }
 295 }
 296
 297 #[macro_export]
 298 macro_rules! impl_arena_allocatable_decoder {
 299     ([]$args:tt) => {};
 300     ([decode $(, $attrs:ident)*]
 301      [[$DecoderName:ident [$($typaram:tt),*]], [$name:ident: $ty:ty], $tcx:lifetime]) => {
 302         impl<$($typaram),*> SpecializedDecoder<&$tcx $ty> for $DecoderName<$($typaram),*> {
 303             #[inline]
 304             fn specialized_decode(&mut self) -> Result<&$tcx $ty, Self::Error> {
 305                 decode_arena_allocable(self)
 306             }
 307         }
 308
 309         impl<$($typaram),*> SpecializedDecoder<&$tcx [$ty]> for $DecoderName<$($typaram),*> {
 310             #[inline]
 311             fn specialized_decode(&mut self) -> Result<&$tcx [$ty], Self::Error> {
 312                 decode_arena_allocable_slice(self)
 313             }
 314         }
 315     };
 316     ([$ignore:ident $(, $attrs:ident)*]$args:tt) => {
 317         impl_arena_allocatable_decoder!([$($attrs),*]$args);
 318     };
 319 }
 320
 321 #[macro_export]
 322 macro_rules! impl_arena_allocatable_decoders {
 323     ($args:tt, [$($a:tt $name:ident: $ty:ty,)*], $tcx:lifetime) => {
 324         $(
 325             impl_arena_allocatable_decoder!($a [$args, [$name: $ty], $tcx]);
 326         )*
 327     }
 328 }
 329
 330 #[macro_export]
 331 macro_rules! implement_ty_decoder {
 332     ($DecoderName:ident <$($typaram:tt),*>) => {
 333         mod __ty_decoder_impl {
 334             use super::$DecoderName;
 335             use $crate::infer::canonical::CanonicalVarInfos;
 336             use $crate::ty;
 337             use $crate::ty::codec::*;
 338             use $crate::ty::subst::SubstsRef;
 339             use $crate::hir::def_id::{CrateNum};
 340             use crate::rustc_serialize::{Decoder, SpecializedDecoder};
 341             use std::borrow::Cow;
 342
 343             impl<$($typaram ),*> Decoder for $DecoderName<$($typaram),*> {
 344                 type Error = String;
 345
 346                 __impl_decoder_methods! {
 347                     read_nil -> ();
 348
 349                     read_u128 -> u128;
 350                     read_u64 -> u64;
 351                     read_u32 -> u32;
 352                     read_u16 -> u16;
 353                     read_u8 -> u8;
 354                     read_usize -> usize;
 355
 356                     read_i128 -> i128;
 357                     read_i64 -> i64;
 358                     read_i32 -> i32;
 359                     read_i16 -> i16;
 360                     read_i8 -> i8;
 361                     read_isize -> isize;
 362
 363                     read_bool -> bool;
 364                     read_f64 -> f64;
 365                     read_f32 -> f32;
 366                     read_char -> char;
 367                     read_str -> Cow<'_, str>;
 368                 }
 369
 370                 fn error(&mut self, err: &str) -> Self::Error {
 371                     self.opaque.error(err)
 372                 }
 373             }
 374
 375             // FIXME(#36588) These impls are horribly unsound as they allow
 376             // the caller to pick any lifetime for 'tcx, including 'static,
 377             // by using the unspecialized proxies to them.
 378
 379             arena_types!(impl_arena_allocatable_decoders, [$DecoderName [$($typaram),*]], 'tcx);
 380
 381             impl<$($typaram),*> SpecializedDecoder<CrateNum>
 382             for $DecoderName<$($typaram),*> {
 383                 fn specialized_decode(&mut self) -> Result<CrateNum, Self::Error> {
 384                     decode_cnum(self)
 385                 }
 386             }
 387
 388             impl<$($typaram),*> SpecializedDecoder<ty::Ty<'tcx>>
 389             for $DecoderName<$($typaram),*> {
 390                 fn specialized_decode(&mut self) -> Result<ty::Ty<'tcx>, Self::Error> {
 391                     decode_ty(self)
 392                 }
 393             }
 394
 395             impl<$($typaram),*> SpecializedDecoder<ty::GenericPredicates<'tcx>>
 396             for $DecoderName<$($typaram),*> {
 397                 fn specialized_decode(&mut self)
 398                                       -> Result<ty::GenericPredicates<'tcx>, Self::Error> {
 399                     decode_predicates(self)
 400                 }
 401             }
 402
 403             impl<$($typaram),*> SpecializedDecoder<SubstsRef<'tcx>>
 404             for $DecoderName<$($typaram),*> {
 405                 fn specialized_decode(&mut self) -> Result<SubstsRef<'tcx>, Self::Error> {
 406                     decode_substs(self)
 407                 }
 408             }
 409
 410             impl<$($typaram),*> SpecializedDecoder<ty::Region<'tcx>>
 411             for $DecoderName<$($typaram),*> {
 412                 fn specialized_decode(&mut self) -> Result<ty::Region<'tcx>, Self::Error> {
 413                     decode_region(self)
 414                 }
 415             }
 416
 417             impl<$($typaram),*> SpecializedDecoder<&'tcx ty::List<ty::Ty<'tcx>>>
 418             for $DecoderName<$($typaram),*> {
 419                 fn specialized_decode(&mut self)
 420                                       -> Result<&'tcx ty::List<ty::Ty<'tcx>>, Self::Error> {
 421                     decode_ty_slice(self)
 422                 }
 423             }
 424
 425             impl<$($typaram),*> SpecializedDecoder<&'tcx ty::AdtDef>
 426             for $DecoderName<$($typaram),*> {
 427                 fn specialized_decode(&mut self) -> Result<&'tcx ty::AdtDef, Self::Error> {
 428                     decode_adt_def(self)
 429                 }
 430             }
 431
 432             impl<$($typaram),*> SpecializedDecoder<&'tcx ty::List<ty::ExistentialPredicate<'tcx>>>
 433                 for $DecoderName<$($typaram),*> {
 434                 fn specialized_decode(&mut self)
 435                     -> Result<&'tcx ty::List<ty::ExistentialPredicate<'tcx>>, Self::Error> {
 436                     decode_existential_predicate_slice(self)
 437                 }
 438             }
 439
 440             impl<$($typaram),*> SpecializedDecoder<CanonicalVarInfos<'tcx>>
 441                 for $DecoderName<$($typaram),*> {
 442                 fn specialized_decode(&mut self)
 443                     -> Result<CanonicalVarInfos<'tcx>, Self::Error> {
 444                     decode_canonical_var_infos(self)
 445                 }
 446             }
 447
 448             impl<$($typaram),*> SpecializedDecoder<&'tcx $crate::ty::Const<'tcx>>
 449             for $DecoderName<$($typaram),*> {
 450                 fn specialized_decode(&mut self) -> Result<&'tcx ty::Const<'tcx>, Self::Error> {
 451                     decode_const(self)
 452                 }
 453             }
 454
 455             impl<$($typaram),*> SpecializedDecoder<&'tcx $crate::mir::interpret::Allocation>
 456             for $DecoderName<$($typaram),*> {
 457                 fn specialized_decode(
 458                     &mut self
 459                 ) -> Result<&'tcx $crate::mir::interpret::Allocation, Self::Error> {
 460                     decode_allocation(self)
 461                 }
 462             }
 463         }
 464     }
 465 }