src/librustc_middle/dep_graph/dep_node.rs

   1 //! This module defines the `DepNode` type which the compiler uses to represent
   2 //! nodes in the dependency graph. A `DepNode` consists of a `DepKind` (which
   3 //! specifies the kind of thing it represents, like a piece of HIR, MIR, etc)
   4 //! and a `Fingerprint`, a 128 bit hash value the exact meaning of which
   5 //! depends on the node's `DepKind`. Together, the kind and the fingerprint
   6 //! fully identify a dependency node, even across multiple compilation sessions.
   7 //! In other words, the value of the fingerprint does not depend on anything
   8 //! that is specific to a given compilation session, like an unpredictable
   9 //! interning key (e.g., NodeId, DefId, Symbol) or the numeric value of a
  10 //! pointer. The concept behind this could be compared to how git commit hashes
  11 //! uniquely identify a given commit and has a few advantages:
  12 //!
  13 //! * A `DepNode` can simply be serialized to disk and loaded in another session
  14 //!   without the need to do any "rebasing (like we have to do for Spans and
  15 //!   NodeIds) or "retracing" like we had to do for `DefId` in earlier
  16 //!   implementations of the dependency graph.
  17 //! * A `Fingerprint` is just a bunch of bits, which allows `DepNode` to
  18 //!   implement `Copy`, `Sync`, `Send`, `Freeze`, etc.
  19 //! * Since we just have a bit pattern, `DepNode` can be mapped from disk into
  20 //!   memory without any post-processing (e.g., "abomination-style" pointer
  21 //!   reconstruction).
  22 //! * Because a `DepNode` is self-contained, we can instantiate `DepNodes` that
  23 //!   refer to things that do not exist anymore. In previous implementations
  24 //!   `DepNode` contained a `DefId`. A `DepNode` referring to something that
  25 //!   had been removed between the previous and the current compilation session
  26 //!   could not be instantiated because the current compilation session
  27 //!   contained no `DefId` for thing that had been removed.
  28 //!
  29 //! `DepNode` definition happens in the `define_dep_nodes!()` macro. This macro
  30 //! defines the `DepKind` enum and a corresponding `DepConstructor` enum. The
  31 //! `DepConstructor` enum links a `DepKind` to the parameters that are needed at
  32 //! runtime in order to construct a valid `DepNode` fingerprint.
  33 //!
  34 //! Because the macro sees what parameters a given `DepKind` requires, it can
  35 //! "infer" some properties for each kind of `DepNode`:
  36 //!
  37 //! * Whether a `DepNode` of a given kind has any parameters at all. Some
  38 //!   `DepNode`s could represent global concepts with only one value.
  39 //! * Whether it is possible, in principle, to reconstruct a query key from a
  40 //!   given `DepNode`. Many `DepKind`s only require a single `DefId` parameter,
  41 //!   in which case it is possible to map the node's fingerprint back to the
  42 //!   `DefId` it was computed from. In other cases, too much information gets
  43 //!   lost during fingerprint computation.
  44 //!
  45 //! The `DepConstructor` enum, together with `DepNode::new()` ensures that only
  46 //! valid `DepNode` instances can be constructed. For example, the API does not
  47 //! allow for constructing parameterless `DepNode`s with anything other
  48 //! than a zeroed out fingerprint. More generally speaking, it relieves the
  49 //! user of the `DepNode` API of having to know how to compute the expected
  50 //! fingerprint for a given set of node parameters.
  51
  52 use crate::mir::interpret::{GlobalId, LitToConstInput};
  53 use crate::traits;
  54 use crate::traits::query::{
  55     CanonicalPredicateGoal, CanonicalProjectionGoal, CanonicalTyGoal,
  56     CanonicalTypeOpAscribeUserTypeGoal, CanonicalTypeOpEqGoal, CanonicalTypeOpNormalizeGoal,
  57     CanonicalTypeOpProvePredicateGoal, CanonicalTypeOpSubtypeGoal,
  58 };
  59 use crate::ty::subst::{GenericArg, SubstsRef};
  60 use crate::ty::{self, ParamEnvAnd, Ty, TyCtxt};
  61
  62 use rustc_data_structures::fingerprint::Fingerprint;
  63 use rustc_hir::def_id::{CrateNum, DefId, LocalDefId, CRATE_DEF_INDEX};
  64 use rustc_hir::definitions::DefPathHash;
  65 use rustc_hir::HirId;
  66 use rustc_span::symbol::Symbol;
  67 use std::hash::Hash;
  68
  69 pub use rustc_query_system::dep_graph::{DepContext, DepNodeParams};
  70
  71 // erase!() just makes tokens go away. It's used to specify which macro argument
  72 // is repeated (i.e., which sub-expression of the macro we are in) but don't need
  73 // to actually use any of the arguments.
  74 macro_rules! erase {
  75     ($x:tt) => {{}};
  76 }
  77
  78 macro_rules! is_anon_attr {
  79     (anon) => {
  80         true
  81     };
  82     ($attr:ident) => {
  83         false
  84     };
  85 }
  86
  87 macro_rules! is_eval_always_attr {
  88     (eval_always) => {
  89         true
  90     };
  91     ($attr:ident) => {
  92         false
  93     };
  94 }
  95
  96 macro_rules! contains_anon_attr {
  97     ($($attr:ident $(($($attr_args:tt)*))* ),*) => ({$(is_anon_attr!($attr) | )* false});
  98 }
  99
 100 macro_rules! contains_eval_always_attr {
 101     ($($attr:ident $(($($attr_args:tt)*))* ),*) => ({$(is_eval_always_attr!($attr) | )* false});
 102 }
 103
 104 macro_rules! define_dep_nodes {
 105     (<$tcx:tt>
 106     $(
 107         [$($attrs:tt)*]
 108         $variant:ident $(( $tuple_arg_ty:ty $(,)? ))*
 109       ,)*
 110     ) => (
 111         #[derive(Clone, Copy, Debug, PartialEq, Eq, PartialOrd, Ord, Hash,
 112                  RustcEncodable, RustcDecodable)]
 113         #[allow(non_camel_case_types)]
 114         pub enum DepKind {
 115             $($variant),*
 116         }
 117
 118         impl DepKind {
 119             #[allow(unreachable_code)]
 120             pub fn can_reconstruct_query_key<$tcx>(&self) -> bool {
 121                 match *self {
 122                     $(
 123                         DepKind :: $variant => {
 124                             if contains_anon_attr!($($attrs)*) {
 125                                 return false;
 126                             }
 127
 128                             // tuple args
 129                             $({
 130                                 return <$tuple_arg_ty as DepNodeParams<TyCtxt<'_>>>
 131                                     ::CAN_RECONSTRUCT_QUERY_KEY;
 132                             })*
 133
 134                             true
 135                         }
 136                     )*
 137                 }
 138             }
 139
 140             pub fn is_anon(&self) -> bool {
 141                 match *self {
 142                     $(
 143                         DepKind :: $variant => { contains_anon_attr!($($attrs)*) }
 144                     )*
 145                 }
 146             }
 147
 148             pub fn is_eval_always(&self) -> bool {
 149                 match *self {
 150                     $(
 151                         DepKind :: $variant => { contains_eval_always_attr!($($attrs)*) }
 152                     )*
 153                 }
 154             }
 155
 156             #[allow(unreachable_code)]
 157             pub fn has_params(&self) -> bool {
 158                 match *self {
 159                     $(
 160                         DepKind :: $variant => {
 161                             // tuple args
 162                             $({
 163                                 erase!($tuple_arg_ty);
 164                                 return true;
 165                             })*
 166
 167                             false
 168                         }
 169                     )*
 170                 }
 171             }
 172         }
 173
 174         pub struct DepConstructor;
 175
 176         #[allow(non_camel_case_types)]
 177         impl DepConstructor {
 178             $(
 179                 #[inline(always)]
 180                 #[allow(unreachable_code, non_snake_case)]
 181                 pub fn $variant(_tcx: TyCtxt<'_>, $(arg: $tuple_arg_ty)*) -> DepNode {
 182                     // tuple args
 183                     $({
 184                         erase!($tuple_arg_ty);
 185                         return DepNode::construct(_tcx, DepKind::$variant, &arg)
 186                     })*
 187
 188                     return DepNode::construct(_tcx, DepKind::$variant, &())
 189                 }
 190             )*
 191         }
 192
 193         pub type DepNode = rustc_query_system::dep_graph::DepNode<DepKind>;
 194
 195         pub trait DepNodeExt: Sized {
 196             /// Construct a DepNode from the given DepKind and DefPathHash. This
 197             /// method will assert that the given DepKind actually requires a
 198             /// single DefId/DefPathHash parameter.
 199             fn from_def_path_hash(def_path_hash: DefPathHash, kind: DepKind) -> Self;
 200
 201             /// Extracts the DefId corresponding to this DepNode. This will work
 202             /// if two conditions are met:
 203             ///
 204             /// 1. The Fingerprint of the DepNode actually is a DefPathHash, and
 205             /// 2. the item that the DefPath refers to exists in the current tcx.
 206             ///
 207             /// Condition (1) is determined by the DepKind variant of the
 208             /// DepNode. Condition (2) might not be fulfilled if a DepNode
 209             /// refers to something from the previous compilation session that
 210             /// has been removed.
 211             fn extract_def_id(&self, tcx: TyCtxt<'_>) -> Option<DefId>;
 212
 213             /// Used in testing
 214             fn from_label_string(label: &str, def_path_hash: DefPathHash)
 215                 -> Result<Self, ()>;
 216
 217             /// Used in testing
 218             fn has_label_string(label: &str) -> bool;
 219         }
 220
 221         impl DepNodeExt for DepNode {
 222             /// Construct a DepNode from the given DepKind and DefPathHash. This
 223             /// method will assert that the given DepKind actually requires a
 224             /// single DefId/DefPathHash parameter.
 225             fn from_def_path_hash(def_path_hash: DefPathHash, kind: DepKind) -> DepNode {
 226                 debug_assert!(kind.can_reconstruct_query_key() && kind.has_params());
 227                 DepNode {
 228                     kind,
 229                     hash: def_path_hash.0,
 230                 }
 231             }
 232
 233             /// Extracts the DefId corresponding to this DepNode. This will work
 234             /// if two conditions are met:
 235             ///
 236             /// 1. The Fingerprint of the DepNode actually is a DefPathHash, and
 237             /// 2. the item that the DefPath refers to exists in the current tcx.
 238             ///
 239             /// Condition (1) is determined by the DepKind variant of the
 240             /// DepNode. Condition (2) might not be fulfilled if a DepNode
 241             /// refers to something from the previous compilation session that
 242             /// has been removed.
 243             fn extract_def_id(&self, tcx: TyCtxt<'tcx>) -> Option<DefId> {
 244                 if self.kind.can_reconstruct_query_key() {
 245                     let def_path_hash = DefPathHash(self.hash);
 246                     tcx.def_path_hash_to_def_id.as_ref()?.get(&def_path_hash).cloned()
 247                 } else {
 248                     None
 249                 }
 250             }
 251
 252             /// Used in testing
 253             fn from_label_string(label: &str, def_path_hash: DefPathHash) -> Result<DepNode, ()> {
 254                 let kind = match label {
 255                     $(
 256                         stringify!($variant) => DepKind::$variant,
 257                     )*
 258                     _ => return Err(()),
 259                 };
 260
 261                 if !kind.can_reconstruct_query_key() {
 262                     return Err(());
 263                 }
 264
 265                 if kind.has_params() {
 266                     Ok(DepNode::from_def_path_hash(def_path_hash, kind))
 267                 } else {
 268                     Ok(DepNode::new_no_params(kind))
 269                 }
 270             }
 271
 272             /// Used in testing
 273             fn has_label_string(label: &str) -> bool {
 274                 match label {
 275                     $(
 276                         stringify!($variant) => true,
 277                     )*
 278                     _ => false,
 279                 }
 280             }
 281         }
 282
 283         /// Contains variant => str representations for constructing
 284         /// DepNode groups for tests.
 285         #[allow(dead_code, non_upper_case_globals)]
 286         pub mod label_strs {
 287            $(
 288                 pub const $variant: &str = stringify!($variant);
 289             )*
 290         }
 291     );
 292 }
 293
 294 rustc_dep_node_append!([define_dep_nodes!][ <'tcx>
 295     // We use this for most things when incr. comp. is turned off.
 296     [] Null,
 297
 298     // Represents metadata from an extern crate.
 299     [eval_always] CrateMetadata(CrateNum),
 300
 301     [anon] TraitSelect,
 302
 303     [] CompileCodegenUnit(Symbol),
 304 ]);
 305
 306 impl<'tcx> DepNodeParams<TyCtxt<'tcx>> for DefId {
 307     const CAN_RECONSTRUCT_QUERY_KEY: bool = true;
 308
 309     fn to_fingerprint(&self, tcx: TyCtxt<'tcx>) -> Fingerprint {
 310         tcx.def_path_hash(*self).0
 311     }
 312
 313     fn to_debug_str(&self, tcx: TyCtxt<'tcx>) -> String {
 314         tcx.def_path_str(*self)
 315     }
 316
 317     fn recover(tcx: TyCtxt<'tcx>, dep_node: &DepNode) -> Option<Self> {
 318         dep_node.extract_def_id(tcx)
 319     }
 320 }
 321
 322 impl<'tcx> DepNodeParams<TyCtxt<'tcx>> for LocalDefId {
 323     const CAN_RECONSTRUCT_QUERY_KEY: bool = true;
 324
 325     fn to_fingerprint(&self, tcx: TyCtxt<'tcx>) -> Fingerprint {
 326         self.to_def_id().to_fingerprint(tcx)
 327     }
 328
 329     fn to_debug_str(&self, tcx: TyCtxt<'tcx>) -> String {
 330         self.to_def_id().to_debug_str(tcx)
 331     }
 332
 333     fn recover(tcx: TyCtxt<'tcx>, dep_node: &DepNode) -> Option<Self> {
 334         dep_node.extract_def_id(tcx).map(|id| id.expect_local())
 335     }
 336 }
 337
 338 impl<'tcx> DepNodeParams<TyCtxt<'tcx>> for CrateNum {
 339     const CAN_RECONSTRUCT_QUERY_KEY: bool = true;
 340
 341     fn to_fingerprint(&self, tcx: TyCtxt<'tcx>) -> Fingerprint {
 342         let def_id = DefId { krate: *self, index: CRATE_DEF_INDEX };
 343         tcx.def_path_hash(def_id).0
 344     }
 345
 346     fn to_debug_str(&self, tcx: TyCtxt<'tcx>) -> String {
 347         tcx.crate_name(*self).to_string()
 348     }
 349
 350     fn recover(tcx: TyCtxt<'tcx>, dep_node: &DepNode) -> Option<Self> {
 351         dep_node.extract_def_id(tcx).map(|id| id.krate)
 352     }
 353 }
 354
 355 impl<'tcx> DepNodeParams<TyCtxt<'tcx>> for (DefId, DefId) {
 356     const CAN_RECONSTRUCT_QUERY_KEY: bool = false;
 357
 358     // We actually would not need to specialize the implementation of this
 359     // method but it's faster to combine the hashes than to instantiate a full
 360     // hashing context and stable-hashing state.
 361     fn to_fingerprint(&self, tcx: TyCtxt<'tcx>) -> Fingerprint {
 362         let (def_id_0, def_id_1) = *self;
 363
 364         let def_path_hash_0 = tcx.def_path_hash(def_id_0);
 365         let def_path_hash_1 = tcx.def_path_hash(def_id_1);
 366
 367         def_path_hash_0.0.combine(def_path_hash_1.0)
 368     }
 369
 370     fn to_debug_str(&self, tcx: TyCtxt<'tcx>) -> String {
 371         let (def_id_0, def_id_1) = *self;
 372
 373         format!("({}, {})", tcx.def_path_debug_str(def_id_0), tcx.def_path_debug_str(def_id_1))
 374     }
 375 }
 376
 377 impl<'tcx> DepNodeParams<TyCtxt<'tcx>> for HirId {
 378     const CAN_RECONSTRUCT_QUERY_KEY: bool = false;
 379
 380     // We actually would not need to specialize the implementation of this
 381     // method but it's faster to combine the hashes than to instantiate a full
 382     // hashing context and stable-hashing state.
 383     fn to_fingerprint(&self, tcx: TyCtxt<'tcx>) -> Fingerprint {
 384         let HirId { owner, local_id } = *self;
 385
 386         let def_path_hash = tcx.def_path_hash(owner.to_def_id());
 387         let local_id = Fingerprint::from_smaller_hash(local_id.as_u32().into());
 388
 389         def_path_hash.0.combine(local_id)
 390     }
 391 }