rustc_query_system/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. The fingerprinting approach has
12//! a few advantages:
13//!
14//! * A `DepNode` can simply be serialized to disk and loaded in another session
15//! without the need to do any "rebasing" (like we have to do for Spans and
16//! NodeIds) or "retracing" (like we had to do for `DefId` in earlier
17//! implementations of the dependency graph).
18//! * A `Fingerprint` is just a bunch of bits, which allows `DepNode` to
19//! implement `Copy`, `Sync`, `Send`, `Freeze`, etc.
20//! * Since we just have a bit pattern, `DepNode` can be mapped from disk into
21//! memory without any post-processing (e.g., "abomination-style" pointer
22//! reconstruction).
23//! * Because a `DepNode` is self-contained, we can instantiate `DepNodes` that
24//! refer to things that do not exist anymore. In previous implementations
25//! `DepNode` contained a `DefId`. A `DepNode` referring to something that
26//! had been removed between the previous and the current compilation session
27//! could not be instantiated because the current compilation session
28//! contained no `DefId` for thing that had been removed.
29//!
30//! `DepNode` definition happens in `rustc_middle` with the
31//! `define_dep_nodes!()` macro. This macro defines the `DepKind` enum. Each
32//! `DepKind` has its own parameters that are needed at runtime in order to
33//! construct a valid `DepNode` fingerprint. However, only `CompileCodegenUnit`
34//! and `CompileMonoItem` are constructed explicitly (with
35//! `make_compile_codegen_unit` and `make_compile_mono_item`).
36//!
37//! Because the macro sees what parameters a given `DepKind` requires, it can
38//! "infer" some properties for each kind of `DepNode`:
39//!
40//! * Whether a `DepNode` of a given kind has any parameters at all. Some
41//! `DepNode`s could represent global concepts with only one value.
42//! * Whether it is possible, in principle, to reconstruct a query key from a
43//! given `DepNode`. Many `DepKind`s only require a single `DefId` parameter,
44//! in which case it is possible to map the node's fingerprint back to the
45//! `DefId` it was computed from. In other cases, too much information gets
46//! lost during fingerprint computation.
47//!
48//! `make_compile_codegen_unit` and `make_compile_mono_items`, together with
49//! `DepNode::new()`, ensure that only valid `DepNode` instances can be
50//! constructed. For example, the API does not allow for constructing
51//! parameterless `DepNode`s with anything other than a zeroed out fingerprint.
52//! More generally speaking, it relieves the user of the `DepNode` API of
53//! having to know how to compute the expected fingerprint for a given set of
54//! node parameters.
55//!
56//! [dependency graph]: https://rustc-dev-guide.rust-lang.org/query.html
57
58use std::fmt;
59use std::hash::Hash;
60
61use rustc_data_structures::AtomicRef;
62use rustc_data_structures::fingerprint::{Fingerprint, PackedFingerprint};
63use rustc_data_structures::stable_hasher::{HashStable, StableHasher, StableOrd, ToStableHashKey};
64use rustc_hir::definitions::DefPathHash;
65use rustc_macros::{Decodable, Encodable};
66
67use super::{DepContext, FingerprintStyle};
68use crate::ich::StableHashingContext;
69
70/// This serves as an index into arrays built by `make_dep_kind_array`.
71#[derive(Clone, Copy, PartialEq, Eq, Hash)]
72pub struct DepKind {
73 variant: u16,
74}
75
76impl DepKind {
77 #[inline]
78 pub const fn new(variant: u16) -> Self {
79 Self { variant }
80 }
81
82 #[inline]
83 pub const fn as_inner(&self) -> u16 {
84 self.variant
85 }
86
87 #[inline]
88 pub const fn as_usize(&self) -> usize {
89 self.variant as usize
90 }
91}
92
93pub fn default_dep_kind_debug(kind: DepKind, f: &mut fmt::Formatter<'_>) -> fmt::Result {
94 f.debug_struct("DepKind").field("variant", &kind.variant).finish()
95}
96
97pub static DEP_KIND_DEBUG: AtomicRef<fn(DepKind, &mut fmt::Formatter<'_>) -> fmt::Result> =
98 AtomicRef::new(&(default_dep_kind_debug as fn(_, &mut fmt::Formatter<'_>) -> _));
99
100impl fmt::Debug for DepKind {
101 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
102 (*DEP_KIND_DEBUG)(*self, f)
103 }
104}
105
106#[derive(Clone, Copy, PartialEq, Eq, Hash)]
107pub struct DepNode {
108 pub kind: DepKind,
109 pub hash: PackedFingerprint,
110}
111
112impl DepNode {
113 /// Creates a new, parameterless DepNode. This method will assert
114 /// that the DepNode corresponding to the given DepKind actually
115 /// does not require any parameters.
116 pub fn new_no_params<Tcx>(tcx: Tcx, kind: DepKind) -> DepNode
117 where
118 Tcx: super::DepContext,
119 {
120 debug_assert_eq!(tcx.fingerprint_style(kind), FingerprintStyle::Unit);
121 DepNode { kind, hash: Fingerprint::ZERO.into() }
122 }
123
124 pub fn construct<Tcx, Key>(tcx: Tcx, kind: DepKind, arg: &Key) -> DepNode
125 where
126 Tcx: super::DepContext,
127 Key: DepNodeParams<Tcx>,
128 {
129 let hash = arg.to_fingerprint(tcx);
130 let dep_node = DepNode { kind, hash: hash.into() };
131
132 #[cfg(debug_assertions)]
133 {
134 if !tcx.fingerprint_style(kind).reconstructible()
135 && (tcx.sess().opts.unstable_opts.incremental_info
136 || tcx.sess().opts.unstable_opts.query_dep_graph)
137 {
138 tcx.dep_graph().register_dep_node_debug_str(dep_node, || arg.to_debug_str(tcx));
139 }
140 }
141
142 dep_node
143 }
144
145 /// Construct a DepNode from the given DepKind and DefPathHash. This
146 /// method will assert that the given DepKind actually requires a
147 /// single DefId/DefPathHash parameter.
148 pub fn from_def_path_hash<Tcx>(tcx: Tcx, def_path_hash: DefPathHash, kind: DepKind) -> Self
149 where
150 Tcx: super::DepContext,
151 {
152 debug_assert!(tcx.fingerprint_style(kind) == FingerprintStyle::DefPathHash);
153 DepNode { kind, hash: def_path_hash.0.into() }
154 }
155}
156
157pub fn default_dep_node_debug(node: DepNode, f: &mut fmt::Formatter<'_>) -> fmt::Result {
158 f.debug_struct("DepNode").field("kind", &node.kind).field("hash", &node.hash).finish()
159}
160
161pub static DEP_NODE_DEBUG: AtomicRef<fn(DepNode, &mut fmt::Formatter<'_>) -> fmt::Result> =
162 AtomicRef::new(&(default_dep_node_debug as fn(_, &mut fmt::Formatter<'_>) -> _));
163
164impl fmt::Debug for DepNode {
165 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
166 (*DEP_NODE_DEBUG)(*self, f)
167 }
168}
169
170pub trait DepNodeParams<Tcx: DepContext>: fmt::Debug + Sized {
171 fn fingerprint_style() -> FingerprintStyle;
172
173 /// This method turns the parameters of a DepNodeConstructor into an opaque
174 /// Fingerprint to be used in DepNode.
175 /// Not all DepNodeParams support being turned into a Fingerprint (they
176 /// don't need to if the corresponding DepNode is anonymous).
177 fn to_fingerprint(&self, _: Tcx) -> Fingerprint {
178 panic!("Not implemented. Accidentally called on anonymous node?")
179 }
180
181 fn to_debug_str(&self, _: Tcx) -> String {
182 format!("{self:?}")
183 }
184
185 /// This method tries to recover the query key from the given `DepNode`,
186 /// something which is needed when forcing `DepNode`s during red-green
187 /// evaluation. The query system will only call this method if
188 /// `fingerprint_style()` is not `FingerprintStyle::Opaque`.
189 /// It is always valid to return `None` here, in which case incremental
190 /// compilation will treat the query as having changed instead of forcing it.
191 fn recover(tcx: Tcx, dep_node: &DepNode) -> Option<Self>;
192}
193
194impl<Tcx: DepContext, T> DepNodeParams<Tcx> for T
195where
196 T: for<'a> HashStable<StableHashingContext<'a>> + fmt::Debug,
197{
198 #[inline(always)]
199 default fn fingerprint_style() -> FingerprintStyle {
200 FingerprintStyle::Opaque
201 }
202
203 #[inline(always)]
204 default fn to_fingerprint(&self, tcx: Tcx) -> Fingerprint {
205 tcx.with_stable_hashing_context(|mut hcx| {
206 let mut hasher = StableHasher::new();
207 self.hash_stable(&mut hcx, &mut hasher);
208 hasher.finish()
209 })
210 }
211
212 #[inline(always)]
213 default fn to_debug_str(&self, _: Tcx) -> String {
214 format!("{:?}", *self)
215 }
216
217 #[inline(always)]
218 default fn recover(_: Tcx, _: &DepNode) -> Option<Self> {
219 None
220 }
221}
222
223/// This struct stores metadata about each DepKind.
224///
225/// Information is retrieved by indexing the `DEP_KINDS` array using the integer value
226/// of the `DepKind`. Overall, this allows to implement `DepContext` using this manual
227/// jump table instead of large matches.
228pub struct DepKindStruct<Tcx: DepContext> {
229 /// Anonymous queries cannot be replayed from one compiler invocation to the next.
230 /// When their result is needed, it is recomputed. They are useful for fine-grained
231 /// dependency tracking, and caching within one compiler invocation.
232 pub is_anon: bool,
233
234 /// Eval-always queries do not track their dependencies, and are always recomputed, even if
235 /// their inputs have not changed since the last compiler invocation. The result is still
236 /// cached within one compiler invocation.
237 pub is_eval_always: bool,
238
239 /// Whether the query key can be recovered from the hashed fingerprint.
240 /// See [DepNodeParams] trait for the behaviour of each key type.
241 pub fingerprint_style: FingerprintStyle,
242
243 /// The red/green evaluation system will try to mark a specific DepNode in the
244 /// dependency graph as green by recursively trying to mark the dependencies of
245 /// that `DepNode` as green. While doing so, it will sometimes encounter a `DepNode`
246 /// where we don't know if it is red or green and we therefore actually have
247 /// to recompute its value in order to find out. Since the only piece of
248 /// information that we have at that point is the `DepNode` we are trying to
249 /// re-evaluate, we need some way to re-run a query from just that. This is what
250 /// `force_from_dep_node()` implements.
251 ///
252 /// In the general case, a `DepNode` consists of a `DepKind` and an opaque
253 /// GUID/fingerprint that will uniquely identify the node. This GUID/fingerprint
254 /// is usually constructed by computing a stable hash of the query-key that the
255 /// `DepNode` corresponds to. Consequently, it is not in general possible to go
256 /// back from hash to query-key (since hash functions are not reversible). For
257 /// this reason `force_from_dep_node()` is expected to fail from time to time
258 /// because we just cannot find out, from the `DepNode` alone, what the
259 /// corresponding query-key is and therefore cannot re-run the query.
260 ///
261 /// The system deals with this case letting `try_mark_green` fail which forces
262 /// the root query to be re-evaluated.
263 ///
264 /// Now, if `force_from_dep_node()` would always fail, it would be pretty useless.
265 /// Fortunately, we can use some contextual information that will allow us to
266 /// reconstruct query-keys for certain kinds of `DepNode`s. In particular, we
267 /// enforce by construction that the GUID/fingerprint of certain `DepNode`s is a
268 /// valid `DefPathHash`. Since we also always build a huge table that maps every
269 /// `DefPathHash` in the current codebase to the corresponding `DefId`, we have
270 /// everything we need to re-run the query.
271 ///
272 /// Take the `mir_promoted` query as an example. Like many other queries, it
273 /// just has a single parameter: the `DefId` of the item it will compute the
274 /// validated MIR for. Now, when we call `force_from_dep_node()` on a `DepNode`
275 /// with kind `MirValidated`, we know that the GUID/fingerprint of the `DepNode`
276 /// is actually a `DefPathHash`, and can therefore just look up the corresponding
277 /// `DefId` in `tcx.def_path_hash_to_def_id`.
278 pub force_from_dep_node: Option<fn(tcx: Tcx, dep_node: DepNode) -> bool>,
279
280 /// Invoke a query to put the on-disk cached value in memory.
281 pub try_load_from_on_disk_cache: Option<fn(Tcx, DepNode)>,
282
283 /// The name of this dep kind.
284 pub name: &'static &'static str,
285}
286
287/// A "work product" corresponds to a `.o` (or other) file that we
288/// save in between runs. These IDs do not have a `DefId` but rather
289/// some independent path or string that persists between runs without
290/// the need to be mapped or unmapped. (This ensures we can serialize
291/// them even in the absence of a tcx.)
292#[derive(Clone, Copy, Debug, PartialEq, Eq, PartialOrd, Ord, Hash, Encodable, Decodable)]
293pub struct WorkProductId {
294 hash: Fingerprint,
295}
296
297impl WorkProductId {
298 pub fn from_cgu_name(cgu_name: &str) -> WorkProductId {
299 let mut hasher = StableHasher::new();
300 cgu_name.hash(&mut hasher);
301 WorkProductId { hash: hasher.finish() }
302 }
303}
304
305impl<HCX> HashStable<HCX> for WorkProductId {
306 #[inline]
307 fn hash_stable(&self, hcx: &mut HCX, hasher: &mut StableHasher) {
308 self.hash.hash_stable(hcx, hasher)
309 }
310}
311impl<HCX> ToStableHashKey<HCX> for WorkProductId {
312 type KeyType = Fingerprint;
313 #[inline]
314 fn to_stable_hash_key(&self, _: &HCX) -> Self::KeyType {
315 self.hash
316 }
317}
318impl StableOrd for WorkProductId {
319 // Fingerprint can use unstable (just a tuple of `u64`s), so WorkProductId can as well
320 const CAN_USE_UNSTABLE_SORT: bool = true;
321
322 // `WorkProductId` sort order is not affected by (de)serialization.
323 const THIS_IMPLEMENTATION_HAS_BEEN_TRIPLE_CHECKED: () = ();
324}
325
326// Some types are used a lot. Make sure they don't unintentionally get bigger.
327#[cfg(target_pointer_width = "64")]
328mod size_asserts {
329 use rustc_data_structures::static_assert_size;
330
331 use super::*;
332 // tidy-alphabetical-start
333 static_assert_size!(DepKind, 2);
334 #[cfg(any(target_arch = "x86", target_arch = "x86_64"))]
335 static_assert_size!(DepNode, 18);
336 #[cfg(not(any(target_arch = "x86", target_arch = "x86_64")))]
337 static_assert_size!(DepNode, 24);
338 // tidy-alphabetical-end
339}