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