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:
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
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.
29 //! `DepNode` definition happens in `librustc_middle` with the `define_dep_nodes!()` macro.
30 //! This macro defines the `DepKind` enum and a corresponding `DepConstructor` enum. The
31 //! `DepConstructor` enum links a `DepKind` to the parameters that are needed at runtime in order
32 //! to construct a valid `DepNode` fingerprint.
34 //! Because the macro sees what parameters a given `DepKind` requires, it can
35 //! "infer" some properties for each kind of `DepNode`:
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.
45 use super::{DepContext, DepKind};
47 use rustc_data_structures::fingerprint::{Fingerprint, PackedFingerprint};
48 use rustc_data_structures::stable_hasher::{HashStable, StableHasher};
53 #[derive(Clone, Copy, PartialEq, Eq, PartialOrd, Ord, Hash, Encodable, Decodable)]
54 pub struct DepNode<K> {
56 pub hash: PackedFingerprint,
59 impl<K: DepKind> DepNode<K> {
60 /// Creates a new, parameterless DepNode. This method will assert
61 /// that the DepNode corresponding to the given DepKind actually
62 /// does not require any parameters.
63 pub fn new_no_params(kind: K) -> DepNode<K> {
64 debug_assert!(!kind.has_params());
65 DepNode { kind, hash: PackedFingerprint(Fingerprint::ZERO) }
68 pub fn construct<Ctxt, Key>(tcx: Ctxt, kind: K, arg: &Key) -> DepNode<K>
70 Ctxt: crate::query::QueryContext<DepKind = K>,
71 Key: DepNodeParams<Ctxt>,
73 let hash = arg.to_fingerprint(tcx);
74 let dep_node = DepNode { kind, hash: PackedFingerprint(hash) };
76 #[cfg(debug_assertions)]
78 if !kind.can_reconstruct_query_key() && tcx.debug_dep_node() {
79 tcx.dep_graph().register_dep_node_debug_str(dep_node, || arg.to_debug_str(tcx));
87 impl<K: DepKind> fmt::Debug for DepNode<K> {
88 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
89 K::debug_node(self, f)
93 pub trait DepNodeParams<Ctxt: DepContext>: fmt::Debug + Sized {
94 fn can_reconstruct_query_key() -> bool;
96 /// This method turns the parameters of a DepNodeConstructor into an opaque
97 /// Fingerprint to be used in DepNode.
98 /// Not all DepNodeParams support being turned into a Fingerprint (they
99 /// don't need to if the corresponding DepNode is anonymous).
100 fn to_fingerprint(&self, _: Ctxt) -> Fingerprint {
101 panic!("Not implemented. Accidentally called on anonymous node?")
104 fn to_debug_str(&self, _: Ctxt) -> String {
105 format!("{:?}", self)
108 /// This method tries to recover the query key from the given `DepNode`,
109 /// something which is needed when forcing `DepNode`s during red-green
110 /// evaluation. The query system will only call this method if
111 /// `can_reconstruct_query_key()` is `true`.
112 /// It is always valid to return `None` here, in which case incremental
113 /// compilation will treat the query as having changed instead of forcing it.
114 fn recover(tcx: Ctxt, dep_node: &DepNode<Ctxt::DepKind>) -> Option<Self>;
117 impl<Ctxt: DepContext, T> DepNodeParams<Ctxt> for T
119 T: HashStable<Ctxt::StableHashingContext> + fmt::Debug,
122 default fn can_reconstruct_query_key() -> bool {
126 default fn to_fingerprint(&self, tcx: Ctxt) -> Fingerprint {
127 let mut hcx = tcx.create_stable_hashing_context();
128 let mut hasher = StableHasher::new();
130 self.hash_stable(&mut hcx, &mut hasher);
135 default fn to_debug_str(&self, _: Ctxt) -> String {
136 format!("{:?}", *self)
139 default fn recover(_: Ctxt, _: &DepNode<Ctxt::DepKind>) -> Option<Self> {
144 impl<Ctxt: DepContext> DepNodeParams<Ctxt> for () {
145 fn to_fingerprint(&self, _: Ctxt) -> Fingerprint {
150 /// A "work product" corresponds to a `.o` (or other) file that we
151 /// save in between runs. These IDs do not have a `DefId` but rather
152 /// some independent path or string that persists between runs without
153 /// the need to be mapped or unmapped. (This ensures we can serialize
154 /// them even in the absence of a tcx.)
155 #[derive(Clone, Copy, Debug, PartialEq, Eq, PartialOrd, Ord, Hash)]
156 #[derive(Encodable, Decodable)]
157 pub struct WorkProductId {
162 pub fn from_cgu_name(cgu_name: &str) -> WorkProductId {
163 let mut hasher = StableHasher::new();
164 cgu_name.len().hash(&mut hasher);
165 cgu_name.hash(&mut hasher);
166 WorkProductId { hash: hasher.finish() }
170 impl<HCX> HashStable<HCX> for WorkProductId {
172 fn hash_stable(&self, hcx: &mut HCX, hasher: &mut StableHasher) {
173 self.hash.hash_stable(hcx, hasher)