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//! This module defines the `DepNode` type which the compiler uses to represent
//! nodes in the dependency graph. A `DepNode` consists of a `DepKind` (which
//! specifies the kind of thing it represents, like a piece of HIR, MIR, etc)
//! and a `Fingerprint`, a 128 bit hash value the exact meaning of which
//! depends on the node's `DepKind`. Together, the kind and the fingerprint
//! fully identify a dependency node, even across multiple compilation sessions.
//! In other words, the value of the fingerprint does not depend on anything
//! that is specific to a given compilation session, like an unpredictable
//! interning key (e.g., NodeId, DefId, Symbol) or the numeric value of a
//! pointer. The concept behind this could be compared to how git commit hashes
//! uniquely identify a given commit and has a few advantages:
//!
//! * A `DepNode` can simply be serialized to disk and loaded in another session
//! without the need to do any "rebasing (like we have to do for Spans and
//! NodeIds) or "retracing" like we had to do for `DefId` in earlier
//! implementations of the dependency graph.
//! * A `Fingerprint` is just a bunch of bits, which allows `DepNode` to
//! implement `Copy`, `Sync`, `Send`, `Freeze`, etc.
//! * Since we just have a bit pattern, `DepNode` can be mapped from disk into
//! memory without any post-processing (e.g., "abomination-style" pointer
//! reconstruction).
//! * Because a `DepNode` is self-contained, we can instantiate `DepNodes` that
//! refer to things that do not exist anymore. In previous implementations
//! `DepNode` contained a `DefId`. A `DepNode` referring to something that
//! had been removed between the previous and the current compilation session
//! could not be instantiated because the current compilation session
//! contained no `DefId` for thing that had been removed.
//!
//! `DepNode` definition happens in `rustc_middle` with the `define_dep_nodes!()` macro.
//! This macro defines the `DepKind` enum and a corresponding `DepConstructor` enum. The
//! `DepConstructor` enum links a `DepKind` to the parameters that are needed at runtime in order
//! to construct a valid `DepNode` fingerprint.
//!
//! Because the macro sees what parameters a given `DepKind` requires, it can
//! "infer" some properties for each kind of `DepNode`:
//!
//! * Whether a `DepNode` of a given kind has any parameters at all. Some
//! `DepNode`s could represent global concepts with only one value.
//! * Whether it is possible, in principle, to reconstruct a query key from a
//! given `DepNode`. Many `DepKind`s only require a single `DefId` parameter,
//! in which case it is possible to map the node's fingerprint back to the
//! `DefId` it was computed from. In other cases, too much information gets
//! lost during fingerprint computation.
use super::{DepContext, FingerprintStyle};
use crate::ich::StableHashingContext;
use rustc_data_structures::fingerprint::{Fingerprint, PackedFingerprint};
use rustc_data_structures::stable_hasher::{HashStable, StableHasher, StableOrd, ToStableHashKey};
use rustc_data_structures::AtomicRef;
use rustc_hir::definitions::DefPathHash;
use std::fmt;
use std::hash::Hash;
/// This serves as an index into arrays built by `make_dep_kind_array`.
#[derive(Clone, Copy, PartialEq, Eq, Hash)]
pub struct DepKind {
variant: u16,
}
impl DepKind {
#[inline]
pub const fn new(variant: u16) -> Self {
Self { variant }
}
#[inline]
pub const fn as_inner(&self) -> u16 {
self.variant
}
#[inline]
pub const fn as_usize(&self) -> usize {
self.variant as usize
}
}
static_assert_size!(DepKind, 2);
pub fn default_dep_kind_debug(kind: DepKind, f: &mut fmt::Formatter<'_>) -> fmt::Result {
f.debug_struct("DepKind").field("variant", &kind.variant).finish()
}
pub static DEP_KIND_DEBUG: AtomicRef<fn(DepKind, &mut fmt::Formatter<'_>) -> fmt::Result> =
AtomicRef::new(&(default_dep_kind_debug as fn(_, &mut fmt::Formatter<'_>) -> _));
impl fmt::Debug for DepKind {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
(*DEP_KIND_DEBUG)(*self, f)
}
}
#[derive(Clone, Copy, PartialEq, Eq, Hash)]
pub struct DepNode {
pub kind: DepKind,
pub hash: PackedFingerprint,
}
// We keep a lot of `DepNode`s in memory during compilation. It's not
// required that their size stay the same, but we don't want to change
// it inadvertently. This assert just ensures we're aware of any change.
#[cfg(any(target_arch = "x86", target_arch = "x86_64"))]
static_assert_size!(DepNode, 18);
#[cfg(not(any(target_arch = "x86", target_arch = "x86_64")))]
static_assert_size!(DepNode, 24);
impl DepNode {
/// Creates a new, parameterless DepNode. This method will assert
/// that the DepNode corresponding to the given DepKind actually
/// does not require any parameters.
pub fn new_no_params<Tcx>(tcx: Tcx, kind: DepKind) -> DepNode
where
Tcx: super::DepContext,
{
debug_assert_eq!(tcx.fingerprint_style(kind), FingerprintStyle::Unit);
DepNode { kind, hash: Fingerprint::ZERO.into() }
}
pub fn construct<Tcx, Key>(tcx: Tcx, kind: DepKind, arg: &Key) -> DepNode
where
Tcx: super::DepContext,
Key: DepNodeParams<Tcx>,
{
let hash = arg.to_fingerprint(tcx);
let dep_node = DepNode { kind, hash: hash.into() };
#[cfg(debug_assertions)]
{
if !tcx.fingerprint_style(kind).reconstructible()
&& (tcx.sess().opts.unstable_opts.incremental_info
|| tcx.sess().opts.unstable_opts.query_dep_graph)
{
tcx.dep_graph().register_dep_node_debug_str(dep_node, || arg.to_debug_str(tcx));
}
}
dep_node
}
/// Construct a DepNode from the given DepKind and DefPathHash. This
/// method will assert that the given DepKind actually requires a
/// single DefId/DefPathHash parameter.
pub fn from_def_path_hash<Tcx>(tcx: Tcx, def_path_hash: DefPathHash, kind: DepKind) -> Self
where
Tcx: super::DepContext,
{
debug_assert!(tcx.fingerprint_style(kind) == FingerprintStyle::DefPathHash);
DepNode { kind, hash: def_path_hash.0.into() }
}
}
pub fn default_dep_node_debug(node: DepNode, f: &mut fmt::Formatter<'_>) -> fmt::Result {
f.debug_struct("DepNode").field("kind", &node.kind).field("hash", &node.hash).finish()
}
pub static DEP_NODE_DEBUG: AtomicRef<fn(DepNode, &mut fmt::Formatter<'_>) -> fmt::Result> =
AtomicRef::new(&(default_dep_node_debug as fn(_, &mut fmt::Formatter<'_>) -> _));
impl fmt::Debug for DepNode {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
(*DEP_NODE_DEBUG)(*self, f)
}
}
pub trait DepNodeParams<Tcx: DepContext>: fmt::Debug + Sized {
fn fingerprint_style() -> FingerprintStyle;
/// This method turns the parameters of a DepNodeConstructor into an opaque
/// Fingerprint to be used in DepNode.
/// Not all DepNodeParams support being turned into a Fingerprint (they
/// don't need to if the corresponding DepNode is anonymous).
fn to_fingerprint(&self, _: Tcx) -> Fingerprint {
panic!("Not implemented. Accidentally called on anonymous node?")
}
fn to_debug_str(&self, _: Tcx) -> String {
format!("{self:?}")
}
/// This method tries to recover the query key from the given `DepNode`,
/// something which is needed when forcing `DepNode`s during red-green
/// evaluation. The query system will only call this method if
/// `fingerprint_style()` is not `FingerprintStyle::Opaque`.
/// It is always valid to return `None` here, in which case incremental
/// compilation will treat the query as having changed instead of forcing it.
fn recover(tcx: Tcx, dep_node: &DepNode) -> Option<Self>;
}
impl<Tcx: DepContext, T> DepNodeParams<Tcx> for T
where
T: for<'a> HashStable<StableHashingContext<'a>> + fmt::Debug,
{
#[inline(always)]
default fn fingerprint_style() -> FingerprintStyle {
FingerprintStyle::Opaque
}
#[inline(always)]
default fn to_fingerprint(&self, tcx: Tcx) -> Fingerprint {
tcx.with_stable_hashing_context(|mut hcx| {
let mut hasher = StableHasher::new();
self.hash_stable(&mut hcx, &mut hasher);
hasher.finish()
})
}
#[inline(always)]
default fn to_debug_str(&self, _: Tcx) -> String {
format!("{:?}", *self)
}
#[inline(always)]
default fn recover(_: Tcx, _: &DepNode) -> Option<Self> {
None
}
}
/// This struct stores metadata about each DepKind.
///
/// Information is retrieved by indexing the `DEP_KINDS` array using the integer value
/// of the `DepKind`. Overall, this allows to implement `DepContext` using this manual
/// jump table instead of large matches.
pub struct DepKindStruct<Tcx: DepContext> {
/// Anonymous queries cannot be replayed from one compiler invocation to the next.
/// When their result is needed, it is recomputed. They are useful for fine-grained
/// dependency tracking, and caching within one compiler invocation.
pub is_anon: bool,
/// Eval-always queries do not track their dependencies, and are always recomputed, even if
/// their inputs have not changed since the last compiler invocation. The result is still
/// cached within one compiler invocation.
pub is_eval_always: bool,
/// Whether the query key can be recovered from the hashed fingerprint.
/// See [DepNodeParams] trait for the behaviour of each key type.
pub fingerprint_style: FingerprintStyle,
/// The red/green evaluation system will try to mark a specific DepNode in the
/// dependency graph as green by recursively trying to mark the dependencies of
/// that `DepNode` as green. While doing so, it will sometimes encounter a `DepNode`
/// where we don't know if it is red or green and we therefore actually have
/// to recompute its value in order to find out. Since the only piece of
/// information that we have at that point is the `DepNode` we are trying to
/// re-evaluate, we need some way to re-run a query from just that. This is what
/// `force_from_dep_node()` implements.
///
/// In the general case, a `DepNode` consists of a `DepKind` and an opaque
/// GUID/fingerprint that will uniquely identify the node. This GUID/fingerprint
/// is usually constructed by computing a stable hash of the query-key that the
/// `DepNode` corresponds to. Consequently, it is not in general possible to go
/// back from hash to query-key (since hash functions are not reversible). For
/// this reason `force_from_dep_node()` is expected to fail from time to time
/// because we just cannot find out, from the `DepNode` alone, what the
/// corresponding query-key is and therefore cannot re-run the query.
///
/// The system deals with this case letting `try_mark_green` fail which forces
/// the root query to be re-evaluated.
///
/// Now, if `force_from_dep_node()` would always fail, it would be pretty useless.
/// Fortunately, we can use some contextual information that will allow us to
/// reconstruct query-keys for certain kinds of `DepNode`s. In particular, we
/// enforce by construction that the GUID/fingerprint of certain `DepNode`s is a
/// valid `DefPathHash`. Since we also always build a huge table that maps every
/// `DefPathHash` in the current codebase to the corresponding `DefId`, we have
/// everything we need to re-run the query.
///
/// Take the `mir_promoted` query as an example. Like many other queries, it
/// just has a single parameter: the `DefId` of the item it will compute the
/// validated MIR for. Now, when we call `force_from_dep_node()` on a `DepNode`
/// with kind `MirValidated`, we know that the GUID/fingerprint of the `DepNode`
/// is actually a `DefPathHash`, and can therefore just look up the corresponding
/// `DefId` in `tcx.def_path_hash_to_def_id`.
pub force_from_dep_node: Option<fn(tcx: Tcx, dep_node: DepNode) -> bool>,
/// Invoke a query to put the on-disk cached value in memory.
pub try_load_from_on_disk_cache: Option<fn(Tcx, DepNode)>,
/// The name of this dep kind.
pub name: &'static &'static str,
}
/// A "work product" corresponds to a `.o` (or other) file that we
/// save in between runs. These IDs do not have a `DefId` but rather
/// some independent path or string that persists between runs without
/// the need to be mapped or unmapped. (This ensures we can serialize
/// them even in the absence of a tcx.)
#[derive(Clone, Copy, Debug, PartialEq, Eq, PartialOrd, Ord, Hash)]
#[derive(Encodable, Decodable)]
pub struct WorkProductId {
hash: Fingerprint,
}
impl WorkProductId {
pub fn from_cgu_name(cgu_name: &str) -> WorkProductId {
let mut hasher = StableHasher::new();
cgu_name.hash(&mut hasher);
WorkProductId { hash: hasher.finish() }
}
}
impl<HCX> HashStable<HCX> for WorkProductId {
#[inline]
fn hash_stable(&self, hcx: &mut HCX, hasher: &mut StableHasher) {
self.hash.hash_stable(hcx, hasher)
}
}
impl<HCX> ToStableHashKey<HCX> for WorkProductId {
type KeyType = Fingerprint;
#[inline]
fn to_stable_hash_key(&self, _: &HCX) -> Self::KeyType {
self.hash
}
}
unsafe impl StableOrd for WorkProductId {
// Fingerprint can use unstable (just a tuple of `u64`s), so WorkProductId can as well
const CAN_USE_UNSTABLE_SORT: bool = true;
}