rust/compiler/rustc_middle/src/dep_graph/dep_node.rs
2022-10-01 15:58:42 +02:00

389 lines
14 KiB
Rust

//! Nodes in the dependency graph.
//!
//! A node in the [dependency graph] is represented by a [`DepNode`].
//! 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. The fingerprinting approach 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 the `define_dep_nodes!()` macro. This macro
//! defines the `DepKind` enum. Each `DepKind` has its own parameters that are
//! needed at runtime in order to construct a valid `DepNode` fingerprint.
//! However, only `CompileCodegenUnit` and `CompileMonoItem` are constructed
//! explicitly (with `make_compile_codegen_unit` cq `make_compile_mono_item`).
//!
//! 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.
//!
//! `make_compile_codegen_unit` and `make_compile_mono_items`, together with
//! `DepNode::new()`, ensures that only valid `DepNode` instances can be
//! constructed. For example, the API does not allow for constructing
//! parameterless `DepNode`s with anything other than a zeroed out fingerprint.
//! More generally speaking, it relieves the user of the `DepNode` API of
//! having to know how to compute the expected fingerprint for a given set of
//! node parameters.
//!
//! [dependency graph]: https://rustc-dev-guide.rust-lang.org/query.html
use crate::mir::mono::MonoItem;
use crate::ty::TyCtxt;
use rustc_data_structures::fingerprint::Fingerprint;
use rustc_hir::def_id::{CrateNum, DefId, LocalDefId};
use rustc_hir::definitions::DefPathHash;
use rustc_hir::{HirId, ItemLocalId, OwnerId};
use rustc_query_system::dep_graph::FingerprintStyle;
use rustc_span::symbol::Symbol;
use std::hash::Hash;
pub use rustc_query_system::dep_graph::{DepContext, DepNodeParams};
macro_rules! define_dep_nodes {
(
$($(#[$attr:meta])*
[$($modifiers:tt)*] fn $variant:ident($($K:tt)*) -> $V:ty,)*) => {
#[macro_export]
macro_rules! make_dep_kind_array {
($mod:ident) => {[ $($mod::$variant()),* ]};
}
/// This enum serves as an index into arrays built by `make_dep_kind_array`.
#[derive(Clone, Copy, Debug, PartialEq, Eq, Hash, Encodable, Decodable)]
#[allow(non_camel_case_types)]
pub enum DepKind {
$( $( #[$attr] )* $variant),*
}
pub(super) fn dep_kind_from_label_string(label: &str) -> Result<DepKind, ()> {
match label {
$(stringify!($variant) => Ok(DepKind::$variant),)*
_ => Err(()),
}
}
/// Contains variant => str representations for constructing
/// DepNode groups for tests.
#[allow(dead_code, non_upper_case_globals)]
pub mod label_strs {
$(
pub const $variant: &str = stringify!($variant);
)*
}
};
}
rustc_query_append!(define_dep_nodes![
/// We use this for most things when incr. comp. is turned off.
[] fn Null() -> (),
/// We use this to create a forever-red node.
[] fn Red() -> (),
[] fn TraitSelect() -> (),
[] fn CompileCodegenUnit() -> (),
[] fn CompileMonoItem() -> (),
]);
// WARNING: `construct` is generic and does not know that `CompileCodegenUnit` takes `Symbol`s as keys.
// Be very careful changing this type signature!
pub(crate) fn make_compile_codegen_unit(tcx: TyCtxt<'_>, name: Symbol) -> DepNode {
DepNode::construct(tcx, DepKind::CompileCodegenUnit, &name)
}
// WARNING: `construct` is generic and does not know that `CompileMonoItem` takes `MonoItem`s as keys.
// Be very careful changing this type signature!
pub(crate) fn make_compile_mono_item<'tcx>(
tcx: TyCtxt<'tcx>,
mono_item: &MonoItem<'tcx>,
) -> DepNode {
DepNode::construct(tcx, DepKind::CompileMonoItem, mono_item)
}
pub type DepNode = rustc_query_system::dep_graph::DepNode<DepKind>;
// 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);
pub trait DepNodeExt: Sized {
/// Extracts the DefId corresponding to this DepNode. This will work
/// if two conditions are met:
///
/// 1. The Fingerprint of the DepNode actually is a DefPathHash, and
/// 2. the item that the DefPath refers to exists in the current tcx.
///
/// Condition (1) is determined by the DepKind variant of the
/// DepNode. Condition (2) might not be fulfilled if a DepNode
/// refers to something from the previous compilation session that
/// has been removed.
fn extract_def_id(&self, tcx: TyCtxt<'_>) -> Option<DefId>;
/// Used in testing
fn from_label_string(
tcx: TyCtxt<'_>,
label: &str,
def_path_hash: DefPathHash,
) -> Result<Self, ()>;
/// Used in testing
fn has_label_string(label: &str) -> bool;
}
impl DepNodeExt for DepNode {
/// Extracts the DefId corresponding to this DepNode. This will work
/// if two conditions are met:
///
/// 1. The Fingerprint of the DepNode actually is a DefPathHash, and
/// 2. the item that the DefPath refers to exists in the current tcx.
///
/// Condition (1) is determined by the DepKind variant of the
/// DepNode. Condition (2) might not be fulfilled if a DepNode
/// refers to something from the previous compilation session that
/// has been removed.
fn extract_def_id<'tcx>(&self, tcx: TyCtxt<'tcx>) -> Option<DefId> {
if tcx.fingerprint_style(self.kind) == FingerprintStyle::DefPathHash {
Some(tcx.def_path_hash_to_def_id(DefPathHash(self.hash.into()), &mut || {
panic!("Failed to extract DefId: {:?} {}", self.kind, self.hash)
}))
} else {
None
}
}
/// Used in testing
fn from_label_string(
tcx: TyCtxt<'_>,
label: &str,
def_path_hash: DefPathHash,
) -> Result<DepNode, ()> {
let kind = dep_kind_from_label_string(label)?;
match tcx.fingerprint_style(kind) {
FingerprintStyle::Opaque | FingerprintStyle::HirId => Err(()),
FingerprintStyle::Unit => Ok(DepNode::new_no_params(tcx, kind)),
FingerprintStyle::DefPathHash => {
Ok(DepNode::from_def_path_hash(tcx, def_path_hash, kind))
}
}
}
/// Used in testing
fn has_label_string(label: &str) -> bool {
dep_kind_from_label_string(label).is_ok()
}
}
impl<'tcx> DepNodeParams<TyCtxt<'tcx>> for () {
#[inline(always)]
fn fingerprint_style() -> FingerprintStyle {
FingerprintStyle::Unit
}
#[inline(always)]
fn to_fingerprint(&self, _: TyCtxt<'tcx>) -> Fingerprint {
Fingerprint::ZERO
}
#[inline(always)]
fn recover(_: TyCtxt<'tcx>, _: &DepNode) -> Option<Self> {
Some(())
}
}
impl<'tcx> DepNodeParams<TyCtxt<'tcx>> for DefId {
#[inline(always)]
fn fingerprint_style() -> FingerprintStyle {
FingerprintStyle::DefPathHash
}
#[inline(always)]
fn to_fingerprint(&self, tcx: TyCtxt<'tcx>) -> Fingerprint {
tcx.def_path_hash(*self).0
}
#[inline(always)]
fn to_debug_str(&self, tcx: TyCtxt<'tcx>) -> String {
tcx.def_path_str(*self)
}
#[inline(always)]
fn recover(tcx: TyCtxt<'tcx>, dep_node: &DepNode) -> Option<Self> {
dep_node.extract_def_id(tcx)
}
}
impl<'tcx> DepNodeParams<TyCtxt<'tcx>> for LocalDefId {
#[inline(always)]
fn fingerprint_style() -> FingerprintStyle {
FingerprintStyle::DefPathHash
}
#[inline(always)]
fn to_fingerprint(&self, tcx: TyCtxt<'tcx>) -> Fingerprint {
self.to_def_id().to_fingerprint(tcx)
}
#[inline(always)]
fn to_debug_str(&self, tcx: TyCtxt<'tcx>) -> String {
self.to_def_id().to_debug_str(tcx)
}
#[inline(always)]
fn recover(tcx: TyCtxt<'tcx>, dep_node: &DepNode) -> Option<Self> {
dep_node.extract_def_id(tcx).map(|id| id.expect_local())
}
}
impl<'tcx> DepNodeParams<TyCtxt<'tcx>> for OwnerId {
#[inline(always)]
fn fingerprint_style() -> FingerprintStyle {
FingerprintStyle::DefPathHash
}
#[inline(always)]
fn to_fingerprint(&self, tcx: TyCtxt<'tcx>) -> Fingerprint {
self.to_def_id().to_fingerprint(tcx)
}
#[inline(always)]
fn to_debug_str(&self, tcx: TyCtxt<'tcx>) -> String {
self.to_def_id().to_debug_str(tcx)
}
#[inline(always)]
fn recover(tcx: TyCtxt<'tcx>, dep_node: &DepNode) -> Option<Self> {
dep_node.extract_def_id(tcx).map(|id| OwnerId { def_id: id.expect_local() })
}
}
impl<'tcx> DepNodeParams<TyCtxt<'tcx>> for CrateNum {
#[inline(always)]
fn fingerprint_style() -> FingerprintStyle {
FingerprintStyle::DefPathHash
}
#[inline(always)]
fn to_fingerprint(&self, tcx: TyCtxt<'tcx>) -> Fingerprint {
let def_id = self.as_def_id();
def_id.to_fingerprint(tcx)
}
#[inline(always)]
fn to_debug_str(&self, tcx: TyCtxt<'tcx>) -> String {
tcx.crate_name(*self).to_string()
}
#[inline(always)]
fn recover(tcx: TyCtxt<'tcx>, dep_node: &DepNode) -> Option<Self> {
dep_node.extract_def_id(tcx).map(|id| id.krate)
}
}
impl<'tcx> DepNodeParams<TyCtxt<'tcx>> for (DefId, DefId) {
#[inline(always)]
fn fingerprint_style() -> FingerprintStyle {
FingerprintStyle::Opaque
}
// We actually would not need to specialize the implementation of this
// method but it's faster to combine the hashes than to instantiate a full
// hashing context and stable-hashing state.
#[inline(always)]
fn to_fingerprint(&self, tcx: TyCtxt<'tcx>) -> Fingerprint {
let (def_id_0, def_id_1) = *self;
let def_path_hash_0 = tcx.def_path_hash(def_id_0);
let def_path_hash_1 = tcx.def_path_hash(def_id_1);
def_path_hash_0.0.combine(def_path_hash_1.0)
}
#[inline(always)]
fn to_debug_str(&self, tcx: TyCtxt<'tcx>) -> String {
let (def_id_0, def_id_1) = *self;
format!("({}, {})", tcx.def_path_debug_str(def_id_0), tcx.def_path_debug_str(def_id_1))
}
}
impl<'tcx> DepNodeParams<TyCtxt<'tcx>> for HirId {
#[inline(always)]
fn fingerprint_style() -> FingerprintStyle {
FingerprintStyle::HirId
}
// We actually would not need to specialize the implementation of this
// method but it's faster to combine the hashes than to instantiate a full
// hashing context and stable-hashing state.
#[inline(always)]
fn to_fingerprint(&self, tcx: TyCtxt<'tcx>) -> Fingerprint {
let HirId { owner, local_id } = *self;
let def_path_hash = tcx.def_path_hash(owner.to_def_id());
Fingerprint::new(
// `owner` is local, so is completely defined by the local hash
def_path_hash.local_hash(),
local_id.as_u32().into(),
)
}
#[inline(always)]
fn to_debug_str(&self, tcx: TyCtxt<'tcx>) -> String {
let HirId { owner, local_id } = *self;
format!("{}.{}", tcx.def_path_str(owner.to_def_id()), local_id.as_u32())
}
#[inline(always)]
fn recover(tcx: TyCtxt<'tcx>, dep_node: &DepNode) -> Option<Self> {
if tcx.fingerprint_style(dep_node.kind) == FingerprintStyle::HirId {
let (local_hash, local_id) = Fingerprint::from(dep_node.hash).as_value();
let def_path_hash = DefPathHash::new(tcx.sess.local_stable_crate_id(), local_hash);
let def_id = tcx
.def_path_hash_to_def_id(def_path_hash, &mut || {
panic!("Failed to extract HirId: {:?} {}", dep_node.kind, dep_node.hash)
})
.expect_local();
let local_id = local_id
.try_into()
.unwrap_or_else(|_| panic!("local id should be u32, found {:?}", local_id));
Some(HirId { owner: OwnerId { def_id }, local_id: ItemLocalId::from_u32(local_id) })
} else {
None
}
}
}