1 //! Nodes in the dependency graph.
3 //! A node in the [dependency graph] is represented by a [`DepNode`].
4 //! A `DepNode` consists of a [`DepKind`] (which
5 //! specifies the kind of thing it represents, like a piece of HIR, MIR, etc.)
6 //! and a [`Fingerprint`], a 128-bit hash value, the exact meaning of which
7 //! depends on the node's `DepKind`. Together, the kind and the fingerprint
8 //! fully identify a dependency node, even across multiple compilation sessions.
9 //! In other words, the value of the fingerprint does not depend on anything
10 //! that is specific to a given compilation session, like an unpredictable
11 //! interning key (e.g., `NodeId`, `DefId`, `Symbol`) or the numeric value of a
12 //! pointer. The concept behind this could be compared to how git commit hashes
13 //! uniquely identify a given commit. The fingerprinting approach has
16 //! * A `DepNode` can simply be serialized to disk and loaded in another session
17 //! without the need to do any "rebasing" (like we have to do for Spans and
18 //! NodeIds) or "retracing" (like we had to do for `DefId` in earlier
19 //! implementations of the dependency graph).
20 //! * A `Fingerprint` is just a bunch of bits, which allows `DepNode` to
21 //! implement `Copy`, `Sync`, `Send`, `Freeze`, etc.
22 //! * Since we just have a bit pattern, `DepNode` can be mapped from disk into
23 //! memory without any post-processing (e.g., "abomination-style" pointer
25 //! * Because a `DepNode` is self-contained, we can instantiate `DepNodes` that
26 //! refer to things that do not exist anymore. In previous implementations
27 //! `DepNode` contained a `DefId`. A `DepNode` referring to something that
28 //! had been removed between the previous and the current compilation session
29 //! could not be instantiated because the current compilation session
30 //! contained no `DefId` for thing that had been removed.
32 //! `DepNode` definition happens in the `define_dep_nodes!()` macro. This macro
33 //! defines the `DepKind` enum. Each `DepKind` has its own parameters that are
34 //! needed at runtime in order to construct a valid `DepNode` fingerprint.
35 //! However, only `CompileCodegenUnit` and `CompileMonoItem` are constructed
36 //! explicitly (with `make_compile_codegen_unit` cq `make_compile_mono_item`).
38 //! Because the macro sees what parameters a given `DepKind` requires, it can
39 //! "infer" some properties for each kind of `DepNode`:
41 //! * Whether a `DepNode` of a given kind has any parameters at all. Some
42 //! `DepNode`s could represent global concepts with only one value.
43 //! * Whether it is possible, in principle, to reconstruct a query key from a
44 //! given `DepNode`. Many `DepKind`s only require a single `DefId` parameter,
45 //! in which case it is possible to map the node's fingerprint back to the
46 //! `DefId` it was computed from. In other cases, too much information gets
47 //! lost during fingerprint computation.
49 //! `make_compile_codegen_unit` and `make_compile_mono_items`, together with
50 //! `DepNode::new()`, ensures that only valid `DepNode` instances can be
51 //! constructed. For example, the API does not allow for constructing
52 //! parameterless `DepNode`s with anything other than a zeroed out fingerprint.
53 //! More generally speaking, it relieves the user of the `DepNode` API of
54 //! having to know how to compute the expected fingerprint for a given set of
57 //! [dependency graph]: https://rustc-dev-guide.rust-lang.org/query.html
59 use crate::mir::mono::MonoItem;
60 use crate::ty::TyCtxt;
62 use rustc_data_structures::fingerprint::Fingerprint;
63 use rustc_hir::def_id::{CrateNum, DefId, LocalDefId};
64 use rustc_hir::definitions::DefPathHash;
66 use rustc_query_system::dep_graph::FingerprintStyle;
67 use rustc_span::symbol::Symbol;
70 pub use rustc_query_system::dep_graph::{DepContext, DepNodeParams};
72 /// This struct stores metadata about each DepKind.
74 /// Information is retrieved by indexing the `DEP_KINDS` array using the integer value
75 /// of the `DepKind`. Overall, this allows to implement `DepContext` using this manual
76 /// jump table instead of large matches.
77 pub struct DepKindStruct {
78 /// Anonymous queries cannot be replayed from one compiler invocation to the next.
79 /// When their result is needed, it is recomputed. They are useful for fine-grained
80 /// dependency tracking, and caching within one compiler invocation.
83 /// Eval-always queries do not track their dependencies, and are always recomputed, even if
84 /// their inputs have not changed since the last compiler invocation. The result is still
85 /// cached within one compiler invocation.
86 pub is_eval_always: bool,
88 /// Whether the query key can be recovered from the hashed fingerprint.
89 /// See [DepNodeParams] trait for the behaviour of each key type.
90 pub fingerprint_style: FingerprintStyle,
92 /// The red/green evaluation system will try to mark a specific DepNode in the
93 /// dependency graph as green by recursively trying to mark the dependencies of
94 /// that `DepNode` as green. While doing so, it will sometimes encounter a `DepNode`
95 /// where we don't know if it is red or green and we therefore actually have
96 /// to recompute its value in order to find out. Since the only piece of
97 /// information that we have at that point is the `DepNode` we are trying to
98 /// re-evaluate, we need some way to re-run a query from just that. This is what
99 /// `force_from_dep_node()` implements.
101 /// In the general case, a `DepNode` consists of a `DepKind` and an opaque
102 /// GUID/fingerprint that will uniquely identify the node. This GUID/fingerprint
103 /// is usually constructed by computing a stable hash of the query-key that the
104 /// `DepNode` corresponds to. Consequently, it is not in general possible to go
105 /// back from hash to query-key (since hash functions are not reversible). For
106 /// this reason `force_from_dep_node()` is expected to fail from time to time
107 /// because we just cannot find out, from the `DepNode` alone, what the
108 /// corresponding query-key is and therefore cannot re-run the query.
110 /// The system deals with this case letting `try_mark_green` fail which forces
111 /// the root query to be re-evaluated.
113 /// Now, if `force_from_dep_node()` would always fail, it would be pretty useless.
114 /// Fortunately, we can use some contextual information that will allow us to
115 /// reconstruct query-keys for certain kinds of `DepNode`s. In particular, we
116 /// enforce by construction that the GUID/fingerprint of certain `DepNode`s is a
117 /// valid `DefPathHash`. Since we also always build a huge table that maps every
118 /// `DefPathHash` in the current codebase to the corresponding `DefId`, we have
119 /// everything we need to re-run the query.
121 /// Take the `mir_promoted` query as an example. Like many other queries, it
122 /// just has a single parameter: the `DefId` of the item it will compute the
123 /// validated MIR for. Now, when we call `force_from_dep_node()` on a `DepNode`
124 /// with kind `MirValidated`, we know that the GUID/fingerprint of the `DepNode`
125 /// is actually a `DefPathHash`, and can therefore just look up the corresponding
126 /// `DefId` in `tcx.def_path_hash_to_def_id`.
127 pub force_from_dep_node: Option<fn(tcx: TyCtxt<'_>, dep_node: DepNode) -> bool>,
129 /// Invoke a query to put the on-disk cached value in memory.
130 pub try_load_from_on_disk_cache: Option<fn(TyCtxt<'_>, DepNode)>,
135 pub fn fingerprint_style(self, tcx: TyCtxt<'_>) -> FingerprintStyle {
136 // Only fetch the DepKindStruct once.
137 let data = tcx.query_kind(self);
139 return FingerprintStyle::Opaque;
141 data.fingerprint_style
145 macro_rules! define_dep_nodes {
149 $variant:ident $(( $tuple_arg_ty:ty $(,)? ))*
153 macro_rules! make_dep_kind_array {
154 ($mod:ident) => {[ $($mod::$variant()),* ]};
157 /// This enum serves as an index into arrays built by `make_dep_kind_array`.
158 #[derive(Clone, Copy, Debug, PartialEq, Eq, Hash, Encodable, Decodable)]
159 #[allow(non_camel_case_types)]
164 fn dep_kind_from_label_string(label: &str) -> Result<DepKind, ()> {
166 $(stringify!($variant) => Ok(DepKind::$variant),)*
171 /// Contains variant => str representations for constructing
172 /// DepNode groups for tests.
173 #[allow(dead_code, non_upper_case_globals)]
176 pub const $variant: &str = stringify!($variant);
182 rustc_dep_node_append!([define_dep_nodes!][ <'tcx>
183 // We use this for most things when incr. comp. is turned off.
188 // WARNING: if `Symbol` is changed, make sure you update `make_compile_codegen_unit` below.
189 [] CompileCodegenUnit(Symbol),
191 // WARNING: if `MonoItem` is changed, make sure you update `make_compile_mono_item` below.
192 // Only used by rustc_codegen_cranelift
193 [] CompileMonoItem(MonoItem),
196 // WARNING: `construct` is generic and does not know that `CompileCodegenUnit` takes `Symbol`s as keys.
197 // Be very careful changing this type signature!
198 crate fn make_compile_codegen_unit(tcx: TyCtxt<'_>, name: Symbol) -> DepNode {
199 DepNode::construct(tcx, DepKind::CompileCodegenUnit, &name)
202 // WARNING: `construct` is generic and does not know that `CompileMonoItem` takes `MonoItem`s as keys.
203 // Be very careful changing this type signature!
204 crate fn make_compile_mono_item<'tcx>(tcx: TyCtxt<'tcx>, mono_item: &MonoItem<'tcx>) -> DepNode {
205 DepNode::construct(tcx, DepKind::CompileMonoItem, mono_item)
208 pub type DepNode = rustc_query_system::dep_graph::DepNode<DepKind>;
210 // We keep a lot of `DepNode`s in memory during compilation. It's not
211 // required that their size stay the same, but we don't want to change
212 // it inadvertently. This assert just ensures we're aware of any change.
213 #[cfg(any(target_arch = "x86", target_arch = "x86_64"))]
214 static_assert_size!(DepNode, 18);
216 #[cfg(not(any(target_arch = "x86", target_arch = "x86_64")))]
217 static_assert_size!(DepNode, 24);
219 pub trait DepNodeExt: Sized {
220 /// Construct a DepNode from the given DepKind and DefPathHash. This
221 /// method will assert that the given DepKind actually requires a
222 /// single DefId/DefPathHash parameter.
223 fn from_def_path_hash(tcx: TyCtxt<'_>, def_path_hash: DefPathHash, kind: DepKind) -> Self;
225 /// Extracts the DefId corresponding to this DepNode. This will work
226 /// if two conditions are met:
228 /// 1. The Fingerprint of the DepNode actually is a DefPathHash, and
229 /// 2. the item that the DefPath refers to exists in the current tcx.
231 /// Condition (1) is determined by the DepKind variant of the
232 /// DepNode. Condition (2) might not be fulfilled if a DepNode
233 /// refers to something from the previous compilation session that
234 /// has been removed.
235 fn extract_def_id(&self, tcx: TyCtxt<'_>) -> Option<DefId>;
238 fn from_label_string(
241 def_path_hash: DefPathHash,
242 ) -> Result<Self, ()>;
245 fn has_label_string(label: &str) -> bool;
248 impl DepNodeExt for DepNode {
249 /// Construct a DepNode from the given DepKind and DefPathHash. This
250 /// method will assert that the given DepKind actually requires a
251 /// single DefId/DefPathHash parameter.
252 fn from_def_path_hash(tcx: TyCtxt<'_>, def_path_hash: DefPathHash, kind: DepKind) -> DepNode {
253 debug_assert!(kind.fingerprint_style(tcx) == FingerprintStyle::DefPathHash);
254 DepNode { kind, hash: def_path_hash.0.into() }
257 /// Extracts the DefId corresponding to this DepNode. This will work
258 /// if two conditions are met:
260 /// 1. The Fingerprint of the DepNode actually is a DefPathHash, and
261 /// 2. the item that the DefPath refers to exists in the current tcx.
263 /// Condition (1) is determined by the DepKind variant of the
264 /// DepNode. Condition (2) might not be fulfilled if a DepNode
265 /// refers to something from the previous compilation session that
266 /// has been removed.
267 fn extract_def_id<'tcx>(&self, tcx: TyCtxt<'tcx>) -> Option<DefId> {
268 if self.kind.fingerprint_style(tcx) == FingerprintStyle::DefPathHash {
269 Some(tcx.def_path_hash_to_def_id(DefPathHash(self.hash.into()), &mut || {
270 panic!("Failed to extract DefId: {:?} {}", self.kind, self.hash)
278 fn from_label_string(
281 def_path_hash: DefPathHash,
282 ) -> Result<DepNode, ()> {
283 let kind = dep_kind_from_label_string(label)?;
285 match kind.fingerprint_style(tcx) {
286 FingerprintStyle::Opaque => Err(()),
287 FingerprintStyle::Unit => Ok(DepNode::new_no_params(tcx, kind)),
288 FingerprintStyle::DefPathHash => {
289 Ok(DepNode::from_def_path_hash(tcx, def_path_hash, kind))
295 fn has_label_string(label: &str) -> bool {
296 dep_kind_from_label_string(label).is_ok()
300 impl<'tcx> DepNodeParams<TyCtxt<'tcx>> for () {
302 fn fingerprint_style() -> FingerprintStyle {
303 FingerprintStyle::Unit
307 fn to_fingerprint(&self, _: TyCtxt<'tcx>) -> Fingerprint {
312 fn recover(_: TyCtxt<'tcx>, _: &DepNode) -> Option<Self> {
317 impl<'tcx> DepNodeParams<TyCtxt<'tcx>> for DefId {
319 fn fingerprint_style() -> FingerprintStyle {
320 FingerprintStyle::DefPathHash
324 fn to_fingerprint(&self, tcx: TyCtxt<'tcx>) -> Fingerprint {
325 tcx.def_path_hash(*self).0
329 fn to_debug_str(&self, tcx: TyCtxt<'tcx>) -> String {
330 tcx.def_path_str(*self)
334 fn recover(tcx: TyCtxt<'tcx>, dep_node: &DepNode) -> Option<Self> {
335 dep_node.extract_def_id(tcx)
339 impl<'tcx> DepNodeParams<TyCtxt<'tcx>> for LocalDefId {
341 fn fingerprint_style() -> FingerprintStyle {
342 FingerprintStyle::DefPathHash
346 fn to_fingerprint(&self, tcx: TyCtxt<'tcx>) -> Fingerprint {
347 self.to_def_id().to_fingerprint(tcx)
351 fn to_debug_str(&self, tcx: TyCtxt<'tcx>) -> String {
352 self.to_def_id().to_debug_str(tcx)
356 fn recover(tcx: TyCtxt<'tcx>, dep_node: &DepNode) -> Option<Self> {
357 dep_node.extract_def_id(tcx).map(|id| id.expect_local())
361 impl<'tcx> DepNodeParams<TyCtxt<'tcx>> for CrateNum {
363 fn fingerprint_style() -> FingerprintStyle {
364 FingerprintStyle::DefPathHash
368 fn to_fingerprint(&self, tcx: TyCtxt<'tcx>) -> Fingerprint {
369 let def_id = self.as_def_id();
370 def_id.to_fingerprint(tcx)
374 fn to_debug_str(&self, tcx: TyCtxt<'tcx>) -> String {
375 tcx.crate_name(*self).to_string()
379 fn recover(tcx: TyCtxt<'tcx>, dep_node: &DepNode) -> Option<Self> {
380 dep_node.extract_def_id(tcx).map(|id| id.krate)
384 impl<'tcx> DepNodeParams<TyCtxt<'tcx>> for (DefId, DefId) {
386 fn fingerprint_style() -> FingerprintStyle {
387 FingerprintStyle::Opaque
390 // We actually would not need to specialize the implementation of this
391 // method but it's faster to combine the hashes than to instantiate a full
392 // hashing context and stable-hashing state.
394 fn to_fingerprint(&self, tcx: TyCtxt<'tcx>) -> Fingerprint {
395 let (def_id_0, def_id_1) = *self;
397 let def_path_hash_0 = tcx.def_path_hash(def_id_0);
398 let def_path_hash_1 = tcx.def_path_hash(def_id_1);
400 def_path_hash_0.0.combine(def_path_hash_1.0)
404 fn to_debug_str(&self, tcx: TyCtxt<'tcx>) -> String {
405 let (def_id_0, def_id_1) = *self;
407 format!("({}, {})", tcx.def_path_debug_str(def_id_0), tcx.def_path_debug_str(def_id_1))
411 impl<'tcx> DepNodeParams<TyCtxt<'tcx>> for HirId {
413 fn fingerprint_style() -> FingerprintStyle {
414 FingerprintStyle::Opaque
417 // We actually would not need to specialize the implementation of this
418 // method but it's faster to combine the hashes than to instantiate a full
419 // hashing context and stable-hashing state.
421 fn to_fingerprint(&self, tcx: TyCtxt<'tcx>) -> Fingerprint {
422 let HirId { owner, local_id } = *self;
424 let def_path_hash = tcx.def_path_hash(owner.to_def_id());
425 let local_id = Fingerprint::from_smaller_hash(local_id.as_u32().into());
427 def_path_hash.0.combine(local_id)