Adding upstream version 1.64.0+dfsg1.upstream/1.64.0+dfsg1

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

7 files changed, 2035 insertions, 0 deletions

diff --git a/compiler/rustc_query_system/src/dep_graph/README.md b/compiler/rustc_query_system/src/dep_graph/README.md
new file mode 100644
index 000000000..b9d91cd35
--- /dev/null
+++ b/compiler/rustc_query_system/src/dep_graph/README.md
@@ -0,0 +1,4 @@
+To learn more about how dependency tracking works in rustc, see the [rustc
+guide].
+
+[rustc dev guide]: https://rustc-dev-guide.rust-lang.org/query.html
diff --git a/compiler/rustc_query_system/src/dep_graph/debug.rs b/compiler/rustc_query_system/src/dep_graph/debug.rs
new file mode 100644
index 000000000..f9f3169af
--- /dev/null
+++ b/compiler/rustc_query_system/src/dep_graph/debug.rs
@@ -0,0 +1,63 @@
+//! Code for debugging the dep-graph.
+
+use super::{DepKind, DepNode, DepNodeIndex};
+use rustc_data_structures::fx::FxHashMap;
+use rustc_data_structures::sync::Lock;
+use std::error::Error;
+
+/// A dep-node filter goes from a user-defined string to a query over
+/// nodes. Right now the format is like this:
+/// ```ignore (illustrative)
+/// x & y & z
+/// ```
+/// where the format-string of the dep-node must contain `x`, `y`, and
+/// `z`.
+#[derive(Debug)]
+pub struct DepNodeFilter {
+    text: String,
+}
+
+impl DepNodeFilter {
+    pub fn new(text: &str) -> Self {
+        DepNodeFilter { text: text.trim().to_string() }
+    }
+
+    /// Returns `true` if all nodes always pass the filter.
+    pub fn accepts_all(&self) -> bool {
+        self.text.is_empty()
+    }
+
+    /// Tests whether `node` meets the filter, returning true if so.
+    pub fn test<K: DepKind>(&self, node: &DepNode<K>) -> bool {
+        let debug_str = format!("{:?}", node);
+        self.text.split('&').map(|s| s.trim()).all(|f| debug_str.contains(f))
+    }
+}
+
+/// A filter like `F -> G` where `F` and `G` are valid dep-node
+/// filters. This can be used to test the source/target independently.
+pub struct EdgeFilter<K: DepKind> {
+    pub source: DepNodeFilter,
+    pub target: DepNodeFilter,
+    pub index_to_node: Lock<FxHashMap<DepNodeIndex, DepNode<K>>>,
+}
+
+impl<K: DepKind> EdgeFilter<K> {
+    pub fn new(test: &str) -> Result<EdgeFilter<K>, Box<dyn Error>> {
+        let parts: Vec<_> = test.split("->").collect();
+        if parts.len() != 2 {
+            Err(format!("expected a filter like `a&b -> c&d`, not `{}`", test).into())
+        } else {
+            Ok(EdgeFilter {
+                source: DepNodeFilter::new(parts[0]),
+                target: DepNodeFilter::new(parts[1]),
+                index_to_node: Lock::new(FxHashMap::default()),
+            })
+        }
+    }
+
+    #[cfg(debug_assertions)]
+    pub fn test(&self, source: &DepNode<K>, target: &DepNode<K>) -> bool {
+        self.source.test(source) && self.target.test(target)
+    }
+}
diff --git a/compiler/rustc_query_system/src/dep_graph/dep_node.rs b/compiler/rustc_query_system/src/dep_graph/dep_node.rs
new file mode 100644
index 000000000..162c274d8
--- /dev/null
+++ b/compiler/rustc_query_system/src/dep_graph/dep_node.rs
@@ -0,0 +1,176 @@
+//! 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, DepKind, FingerprintStyle};
+use crate::ich::StableHashingContext;
+
+use rustc_data_structures::fingerprint::{Fingerprint, PackedFingerprint};
+use rustc_data_structures::stable_hasher::{HashStable, StableHasher};
+use std::fmt;
+use std::hash::Hash;
+
+#[derive(Clone, Copy, PartialEq, Eq, PartialOrd, Ord, Hash, Encodable, Decodable)]
+pub struct DepNode<K> {
+    pub kind: K,
+    pub hash: PackedFingerprint,
+}
+
+impl<K: DepKind> DepNode<K> {
+    /// 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<Ctxt>(tcx: Ctxt, kind: K) -> DepNode<K>
+    where
+        Ctxt: super::DepContext<DepKind = K>,
+    {
+        debug_assert_eq!(tcx.fingerprint_style(kind), FingerprintStyle::Unit);
+        DepNode { kind, hash: Fingerprint::ZERO.into() }
+    }
+
+    pub fn construct<Ctxt, Key>(tcx: Ctxt, kind: K, arg: &Key) -> DepNode<K>
+    where
+        Ctxt: super::DepContext<DepKind = K>,
+        Key: DepNodeParams<Ctxt>,
+    {
+        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
+    }
+}
+
+impl<K: DepKind> fmt::Debug for DepNode<K> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        K::debug_node(self, f)
+    }
+}
+
+pub trait DepNodeParams<Ctxt: 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, _: Ctxt) -> Fingerprint {
+        panic!("Not implemented. Accidentally called on anonymous node?")
+    }
+
+    fn to_debug_str(&self, _: Ctxt) -> 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: Ctxt, dep_node: &DepNode<Ctxt::DepKind>) -> Option<Self>;
+}
+
+impl<Ctxt: DepContext, T> DepNodeParams<Ctxt> 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: Ctxt) -> 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, _: Ctxt) -> String {
+        format!("{:?}", *self)
+    }
+
+    #[inline(always)]
+    default fn recover(_: Ctxt, _: &DepNode<Ctxt::DepKind>) -> Option<Self> {
+        None
+    }
+}
+
+/// 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)
+    }
+}
diff --git a/compiler/rustc_query_system/src/dep_graph/graph.rs b/compiler/rustc_query_system/src/dep_graph/graph.rs
new file mode 100644
index 000000000..8ff561327
--- /dev/null
+++ b/compiler/rustc_query_system/src/dep_graph/graph.rs
@@ -0,0 +1,1288 @@
+use parking_lot::Mutex;
+use rustc_data_structures::fingerprint::Fingerprint;
+use rustc_data_structures::fx::{FxHashMap, FxHashSet};
+use rustc_data_structures::profiling::{EventId, QueryInvocationId, SelfProfilerRef};
+use rustc_data_structures::sharded::{self, Sharded};
+use rustc_data_structures::stable_hasher::{HashStable, StableHasher};
+use rustc_data_structures::steal::Steal;
+use rustc_data_structures::sync::{AtomicU32, AtomicU64, Lock, Lrc, Ordering};
+use rustc_index::vec::IndexVec;
+use rustc_serialize::opaque::{FileEncodeResult, FileEncoder};
+use smallvec::{smallvec, SmallVec};
+use std::assert_matches::assert_matches;
+use std::collections::hash_map::Entry;
+use std::fmt::Debug;
+use std::hash::Hash;
+use std::marker::PhantomData;
+use std::sync::atomic::Ordering::Relaxed;
+
+use super::query::DepGraphQuery;
+use super::serialized::{GraphEncoder, SerializedDepGraph, SerializedDepNodeIndex};
+use super::{DepContext, DepKind, DepNode, HasDepContext, WorkProductId};
+use crate::ich::StableHashingContext;
+use crate::query::{QueryContext, QuerySideEffects};
+
+#[cfg(debug_assertions)]
+use {super::debug::EdgeFilter, std::env};
+
+#[derive(Clone)]
+pub struct DepGraph<K: DepKind> {
+    data: Option<Lrc<DepGraphData<K>>>,
+
+    /// This field is used for assigning DepNodeIndices when running in
+    /// non-incremental mode. Even in non-incremental mode we make sure that
+    /// each task has a `DepNodeIndex` that uniquely identifies it. This unique
+    /// ID is used for self-profiling.
+    virtual_dep_node_index: Lrc<AtomicU32>,
+}
+
+rustc_index::newtype_index! {
+    pub struct DepNodeIndex { .. }
+}
+
+impl DepNodeIndex {
+    pub const INVALID: DepNodeIndex = DepNodeIndex::MAX;
+    pub const SINGLETON_DEPENDENCYLESS_ANON_NODE: DepNodeIndex = DepNodeIndex::from_u32(0);
+    pub const FOREVER_RED_NODE: DepNodeIndex = DepNodeIndex::from_u32(1);
+}
+
+impl std::convert::From<DepNodeIndex> for QueryInvocationId {
+    #[inline]
+    fn from(dep_node_index: DepNodeIndex) -> Self {
+        QueryInvocationId(dep_node_index.as_u32())
+    }
+}
+
+#[derive(PartialEq)]
+pub enum DepNodeColor {
+    Red,
+    Green(DepNodeIndex),
+}
+
+impl DepNodeColor {
+    #[inline]
+    pub fn is_green(self) -> bool {
+        match self {
+            DepNodeColor::Red => false,
+            DepNodeColor::Green(_) => true,
+        }
+    }
+}
+
+struct DepGraphData<K: DepKind> {
+    /// The new encoding of the dependency graph, optimized for red/green
+    /// tracking. The `current` field is the dependency graph of only the
+    /// current compilation session: We don't merge the previous dep-graph into
+    /// current one anymore, but we do reference shared data to save space.
+    current: CurrentDepGraph<K>,
+
+    /// The dep-graph from the previous compilation session. It contains all
+    /// nodes and edges as well as all fingerprints of nodes that have them.
+    previous: SerializedDepGraph<K>,
+
+    colors: DepNodeColorMap,
+
+    processed_side_effects: Mutex<FxHashSet<DepNodeIndex>>,
+
+    /// When we load, there may be `.o` files, cached MIR, or other such
+    /// things available to us. If we find that they are not dirty, we
+    /// load the path to the file storing those work-products here into
+    /// this map. We can later look for and extract that data.
+    previous_work_products: FxHashMap<WorkProductId, WorkProduct>,
+
+    dep_node_debug: Lock<FxHashMap<DepNode<K>, String>>,
+
+    /// Used by incremental compilation tests to assert that
+    /// a particular query result was decoded from disk
+    /// (not just marked green)
+    debug_loaded_from_disk: Lock<FxHashSet<DepNode<K>>>,
+}
+
+pub fn hash_result<R>(hcx: &mut StableHashingContext<'_>, result: &R) -> Fingerprint
+where
+    R: for<'a> HashStable<StableHashingContext<'a>>,
+{
+    let mut stable_hasher = StableHasher::new();
+    result.hash_stable(hcx, &mut stable_hasher);
+    stable_hasher.finish()
+}
+
+impl<K: DepKind> DepGraph<K> {
+    pub fn new(
+        profiler: &SelfProfilerRef,
+        prev_graph: SerializedDepGraph<K>,
+        prev_work_products: FxHashMap<WorkProductId, WorkProduct>,
+        encoder: FileEncoder,
+        record_graph: bool,
+        record_stats: bool,
+    ) -> DepGraph<K> {
+        let prev_graph_node_count = prev_graph.node_count();
+
+        let current = CurrentDepGraph::new(
+            profiler,
+            prev_graph_node_count,
+            encoder,
+            record_graph,
+            record_stats,
+        );
+
+        let colors = DepNodeColorMap::new(prev_graph_node_count);
+
+        // Instantiate a dependy-less node only once for anonymous queries.
+        let _green_node_index = current.intern_new_node(
+            profiler,
+            DepNode { kind: DepKind::NULL, hash: current.anon_id_seed.into() },
+            smallvec![],
+            Fingerprint::ZERO,
+        );
+        assert_eq!(_green_node_index, DepNodeIndex::SINGLETON_DEPENDENCYLESS_ANON_NODE);
+
+        // Instantiate a dependy-less red node only once for anonymous queries.
+        let (_red_node_index, _prev_and_index) = current.intern_node(
+            profiler,
+            &prev_graph,
+            DepNode { kind: DepKind::RED, hash: Fingerprint::ZERO.into() },
+            smallvec![],
+            None,
+            false,
+        );
+        assert_eq!(_red_node_index, DepNodeIndex::FOREVER_RED_NODE);
+        assert!(matches!(_prev_and_index, None | Some((_, DepNodeColor::Red))));
+
+        DepGraph {
+            data: Some(Lrc::new(DepGraphData {
+                previous_work_products: prev_work_products,
+                dep_node_debug: Default::default(),
+                current,
+                processed_side_effects: Default::default(),
+                previous: prev_graph,
+                colors,
+                debug_loaded_from_disk: Default::default(),
+            })),
+            virtual_dep_node_index: Lrc::new(AtomicU32::new(0)),
+        }
+    }
+
+    pub fn new_disabled() -> DepGraph<K> {
+        DepGraph { data: None, virtual_dep_node_index: Lrc::new(AtomicU32::new(0)) }
+    }
+
+    /// Returns `true` if we are actually building the full dep-graph, and `false` otherwise.
+    #[inline]
+    pub fn is_fully_enabled(&self) -> bool {
+        self.data.is_some()
+    }
+
+    pub fn with_query(&self, f: impl Fn(&DepGraphQuery<K>)) {
+        if let Some(data) = &self.data {
+            data.current.encoder.borrow().with_query(f)
+        }
+    }
+
+    pub fn assert_ignored(&self) {
+        if let Some(..) = self.data {
+            K::read_deps(|task_deps| {
+                assert_matches!(
+                    task_deps,
+                    TaskDepsRef::Ignore,
+                    "expected no task dependency tracking"
+                );
+            })
+        }
+    }
+
+    pub fn with_ignore<OP, R>(&self, op: OP) -> R
+    where
+        OP: FnOnce() -> R,
+    {
+        K::with_deps(TaskDepsRef::Ignore, op)
+    }
+
+    /// Used to wrap the deserialization of a query result from disk,
+    /// This method enforces that no new `DepNodes` are created during
+    /// query result deserialization.
+    ///
+    /// Enforcing this makes the query dep graph simpler - all nodes
+    /// must be created during the query execution, and should be
+    /// created from inside the 'body' of a query (the implementation
+    /// provided by a particular compiler crate).
+    ///
+    /// Consider the case of three queries `A`, `B`, and `C`, where
+    /// `A` invokes `B` and `B` invokes `C`:
+    ///
+    /// `A -> B -> C`
+    ///
+    /// Suppose that decoding the result of query `B` required re-computing
+    /// the query `C`. If we did not create a fresh `TaskDeps` when
+    /// decoding `B`, we would still be using the `TaskDeps` for query `A`
+    /// (if we needed to re-execute `A`). This would cause us to create
+    /// a new edge `A -> C`. If this edge did not previously
+    /// exist in the `DepGraph`, then we could end up with a different
+    /// `DepGraph` at the end of compilation, even if there were no
+    /// meaningful changes to the overall program (e.g. a newline was added).
+    /// In addition, this edge might cause a subsequent compilation run
+    /// to try to force `C` before marking other necessary nodes green. If
+    /// `C` did not exist in the new compilation session, then we could
+    /// get an ICE. Normally, we would have tried (and failed) to mark
+    /// some other query green (e.g. `item_children`) which was used
+    /// to obtain `C`, which would prevent us from ever trying to force
+    /// a non-existent `D`.
+    ///
+    /// It might be possible to enforce that all `DepNode`s read during
+    /// deserialization already exist in the previous `DepGraph`. In
+    /// the above example, we would invoke `D` during the deserialization
+    /// of `B`. Since we correctly create a new `TaskDeps` from the decoding
+    /// of `B`, this would result in an edge `B -> D`. If that edge already
+    /// existed (with the same `DepPathHash`es), then it should be correct
+    /// to allow the invocation of the query to proceed during deserialization
+    /// of a query result. We would merely assert that the dep-graph fragment
+    /// that would have been added by invoking `C` while decoding `B`
+    /// is equivalent to the dep-graph fragment that we already instantiated for B
+    /// (at the point where we successfully marked B as green).
+    ///
+    /// However, this would require additional complexity
+    /// in the query infrastructure, and is not currently needed by the
+    /// decoding of any query results. Should the need arise in the future,
+    /// we should consider extending the query system with this functionality.
+    pub fn with_query_deserialization<OP, R>(&self, op: OP) -> R
+    where
+        OP: FnOnce() -> R,
+    {
+        K::with_deps(TaskDepsRef::Forbid, op)
+    }
+
+    /// Starts a new dep-graph task. Dep-graph tasks are specified
+    /// using a free function (`task`) and **not** a closure -- this
+    /// is intentional because we want to exercise tight control over
+    /// what state they have access to. In particular, we want to
+    /// prevent implicit 'leaks' of tracked state into the task (which
+    /// could then be read without generating correct edges in the
+    /// dep-graph -- see the [rustc dev guide] for more details on
+    /// the dep-graph). To this end, the task function gets exactly two
+    /// pieces of state: the context `cx` and an argument `arg`. Both
+    /// of these bits of state must be of some type that implements
+    /// `DepGraphSafe` and hence does not leak.
+    ///
+    /// The choice of two arguments is not fundamental. One argument
+    /// would work just as well, since multiple values can be
+    /// collected using tuples. However, using two arguments works out
+    /// to be quite convenient, since it is common to need a context
+    /// (`cx`) and some argument (e.g., a `DefId` identifying what
+    /// item to process).
+    ///
+    /// For cases where you need some other number of arguments:
+    ///
+    /// - If you only need one argument, just use `()` for the `arg`
+    ///   parameter.
+    /// - If you need 3+ arguments, use a tuple for the
+    ///   `arg` parameter.
+    ///
+    /// [rustc dev guide]: https://rustc-dev-guide.rust-lang.org/incremental-compilation.html
+    pub fn with_task<Ctxt: HasDepContext<DepKind = K>, A: Debug, R>(
+        &self,
+        key: DepNode<K>,
+        cx: Ctxt,
+        arg: A,
+        task: fn(Ctxt, A) -> R,
+        hash_result: Option<fn(&mut StableHashingContext<'_>, &R) -> Fingerprint>,
+    ) -> (R, DepNodeIndex) {
+        if self.is_fully_enabled() {
+            self.with_task_impl(key, cx, arg, task, hash_result)
+        } else {
+            // Incremental compilation is turned off. We just execute the task
+            // without tracking. We still provide a dep-node index that uniquely
+            // identifies the task so that we have a cheap way of referring to
+            // the query for self-profiling.
+            (task(cx, arg), self.next_virtual_depnode_index())
+        }
+    }
+
+    fn with_task_impl<Ctxt: HasDepContext<DepKind = K>, A: Debug, R>(
+        &self,
+        key: DepNode<K>,
+        cx: Ctxt,
+        arg: A,
+        task: fn(Ctxt, A) -> R,
+        hash_result: Option<fn(&mut StableHashingContext<'_>, &R) -> Fingerprint>,
+    ) -> (R, DepNodeIndex) {
+        // This function is only called when the graph is enabled.
+        let data = self.data.as_ref().unwrap();
+
+        // If the following assertion triggers, it can have two reasons:
+        // 1. Something is wrong with DepNode creation, either here or
+        //    in `DepGraph::try_mark_green()`.
+        // 2. Two distinct query keys get mapped to the same `DepNode`
+        //    (see for example #48923).
+        assert!(
+            !self.dep_node_exists(&key),
+            "forcing query with already existing `DepNode`\n\
+                 - query-key: {:?}\n\
+                 - dep-node: {:?}",
+            arg,
+            key
+        );
+
+        let task_deps = if cx.dep_context().is_eval_always(key.kind) {
+            None
+        } else {
+            Some(Lock::new(TaskDeps {
+                #[cfg(debug_assertions)]
+                node: Some(key),
+                reads: SmallVec::new(),
+                read_set: Default::default(),
+                phantom_data: PhantomData,
+            }))
+        };
+
+        let task_deps_ref = match &task_deps {
+            Some(deps) => TaskDepsRef::Allow(deps),
+            None => TaskDepsRef::Ignore,
+        };
+
+        let result = K::with_deps(task_deps_ref, || task(cx, arg));
+        let edges = task_deps.map_or_else(|| smallvec![], |lock| lock.into_inner().reads);
+
+        let dcx = cx.dep_context();
+        let hashing_timer = dcx.profiler().incr_result_hashing();
+        let current_fingerprint =
+            hash_result.map(|f| dcx.with_stable_hashing_context(|mut hcx| f(&mut hcx, &result)));
+
+        let print_status = cfg!(debug_assertions) && dcx.sess().opts.unstable_opts.dep_tasks;
+
+        // Intern the new `DepNode`.
+        let (dep_node_index, prev_and_color) = data.current.intern_node(
+            dcx.profiler(),
+            &data.previous,
+            key,
+            edges,
+            current_fingerprint,
+            print_status,
+        );
+
+        hashing_timer.finish_with_query_invocation_id(dep_node_index.into());
+
+        if let Some((prev_index, color)) = prev_and_color {
+            debug_assert!(
+                data.colors.get(prev_index).is_none(),
+                "DepGraph::with_task() - Duplicate DepNodeColor \
+                            insertion for {:?}",
+                key
+            );
+
+            data.colors.insert(prev_index, color);
+        }
+
+        (result, dep_node_index)
+    }
+
+    /// Executes something within an "anonymous" task, that is, a task the
+    /// `DepNode` of which is determined by the list of inputs it read from.
+    pub fn with_anon_task<Ctxt: DepContext<DepKind = K>, OP, R>(
+        &self,
+        cx: Ctxt,
+        dep_kind: K,
+        op: OP,
+    ) -> (R, DepNodeIndex)
+    where
+        OP: FnOnce() -> R,
+    {
+        debug_assert!(!cx.is_eval_always(dep_kind));
+
+        if let Some(ref data) = self.data {
+            let task_deps = Lock::new(TaskDeps::default());
+            let result = K::with_deps(TaskDepsRef::Allow(&task_deps), op);
+            let task_deps = task_deps.into_inner();
+            let task_deps = task_deps.reads;
+
+            let dep_node_index = match task_deps.len() {
+                0 => {
+                    // Because the dep-node id of anon nodes is computed from the sets of its
+                    // dependencies we already know what the ID of this dependency-less node is
+                    // going to be (i.e. equal to the precomputed
+                    // `SINGLETON_DEPENDENCYLESS_ANON_NODE`). As a consequence we can skip creating
+                    // a `StableHasher` and sending the node through interning.
+                    DepNodeIndex::SINGLETON_DEPENDENCYLESS_ANON_NODE
+                }
+                1 => {
+                    // When there is only one dependency, don't bother creating a node.
+                    task_deps[0]
+                }
+                _ => {
+                    // The dep node indices are hashed here instead of hashing the dep nodes of the
+                    // dependencies. These indices may refer to different nodes per session, but this isn't
+                    // a problem here because we that ensure the final dep node hash is per session only by
+                    // combining it with the per session random number `anon_id_seed`. This hash only need
+                    // to map the dependencies to a single value on a per session basis.
+                    let mut hasher = StableHasher::new();
+                    task_deps.hash(&mut hasher);
+
+                    let target_dep_node = DepNode {
+                        kind: dep_kind,
+                        // Fingerprint::combine() is faster than sending Fingerprint
+                        // through the StableHasher (at least as long as StableHasher
+                        // is so slow).
+                        hash: data.current.anon_id_seed.combine(hasher.finish()).into(),
+                    };
+
+                    data.current.intern_new_node(
+                        cx.profiler(),
+                        target_dep_node,
+                        task_deps,
+                        Fingerprint::ZERO,
+                    )
+                }
+            };
+
+            (result, dep_node_index)
+        } else {
+            (op(), self.next_virtual_depnode_index())
+        }
+    }
+
+    #[inline]
+    pub fn read_index(&self, dep_node_index: DepNodeIndex) {
+        if let Some(ref data) = self.data {
+            K::read_deps(|task_deps| {
+                let mut task_deps = match task_deps {
+                    TaskDepsRef::Allow(deps) => deps.lock(),
+                    TaskDepsRef::Ignore => return,
+                    TaskDepsRef::Forbid => {
+                        panic!("Illegal read of: {:?}", dep_node_index)
+                    }
+                };
+                let task_deps = &mut *task_deps;
+
+                if cfg!(debug_assertions) {
+                    data.current.total_read_count.fetch_add(1, Relaxed);
+                }
+
+                // As long as we only have a low number of reads we can avoid doing a hash
+                // insert and potentially allocating/reallocating the hashmap
+                let new_read = if task_deps.reads.len() < TASK_DEPS_READS_CAP {
+                    task_deps.reads.iter().all(|other| *other != dep_node_index)
+                } else {
+                    task_deps.read_set.insert(dep_node_index)
+                };
+                if new_read {
+                    task_deps.reads.push(dep_node_index);
+                    if task_deps.reads.len() == TASK_DEPS_READS_CAP {
+                        // Fill `read_set` with what we have so far so we can use the hashset
+                        // next time
+                        task_deps.read_set.extend(task_deps.reads.iter().copied());
+                    }
+
+                    #[cfg(debug_assertions)]
+                    {
+                        if let Some(target) = task_deps.node {
+                            if let Some(ref forbidden_edge) = data.current.forbidden_edge {
+                                let src = forbidden_edge.index_to_node.lock()[&dep_node_index];
+                                if forbidden_edge.test(&src, &target) {
+                                    panic!("forbidden edge {:?} -> {:?} created", src, target)
+                                }
+                            }
+                        }
+                    }
+                } else if cfg!(debug_assertions) {
+                    data.current.total_duplicate_read_count.fetch_add(1, Relaxed);
+                }
+            })
+        }
+    }
+
+    #[inline]
+    pub fn dep_node_index_of(&self, dep_node: &DepNode<K>) -> DepNodeIndex {
+        self.dep_node_index_of_opt(dep_node).unwrap()
+    }
+
+    #[inline]
+    pub fn dep_node_index_of_opt(&self, dep_node: &DepNode<K>) -> Option<DepNodeIndex> {
+        let data = self.data.as_ref().unwrap();
+        let current = &data.current;
+
+        if let Some(prev_index) = data.previous.node_to_index_opt(dep_node) {
+            current.prev_index_to_index.lock()[prev_index]
+        } else {
+            current.new_node_to_index.get_shard_by_value(dep_node).lock().get(dep_node).copied()
+        }
+    }
+
+    #[inline]
+    pub fn dep_node_exists(&self, dep_node: &DepNode<K>) -> bool {
+        self.data.is_some() && self.dep_node_index_of_opt(dep_node).is_some()
+    }
+
+    pub fn prev_fingerprint_of(&self, dep_node: &DepNode<K>) -> Option<Fingerprint> {
+        self.data.as_ref().unwrap().previous.fingerprint_of(dep_node)
+    }
+
+    /// Checks whether a previous work product exists for `v` and, if
+    /// so, return the path that leads to it. Used to skip doing work.
+    pub fn previous_work_product(&self, v: &WorkProductId) -> Option<WorkProduct> {
+        self.data.as_ref().and_then(|data| data.previous_work_products.get(v).cloned())
+    }
+
+    /// Access the map of work-products created during the cached run. Only
+    /// used during saving of the dep-graph.
+    pub fn previous_work_products(&self) -> &FxHashMap<WorkProductId, WorkProduct> {
+        &self.data.as_ref().unwrap().previous_work_products
+    }
+
+    pub fn mark_debug_loaded_from_disk(&self, dep_node: DepNode<K>) {
+        self.data.as_ref().unwrap().debug_loaded_from_disk.lock().insert(dep_node);
+    }
+
+    pub fn debug_was_loaded_from_disk(&self, dep_node: DepNode<K>) -> bool {
+        self.data.as_ref().unwrap().debug_loaded_from_disk.lock().contains(&dep_node)
+    }
+
+    #[inline(always)]
+    pub fn register_dep_node_debug_str<F>(&self, dep_node: DepNode<K>, debug_str_gen: F)
+    where
+        F: FnOnce() -> String,
+    {
+        let dep_node_debug = &self.data.as_ref().unwrap().dep_node_debug;
+
+        if dep_node_debug.borrow().contains_key(&dep_node) {
+            return;
+        }
+        let debug_str = debug_str_gen();
+        dep_node_debug.borrow_mut().insert(dep_node, debug_str);
+    }
+
+    pub fn dep_node_debug_str(&self, dep_node: DepNode<K>) -> Option<String> {
+        self.data.as_ref()?.dep_node_debug.borrow().get(&dep_node).cloned()
+    }
+
+    fn node_color(&self, dep_node: &DepNode<K>) -> Option<DepNodeColor> {
+        if let Some(ref data) = self.data {
+            if let Some(prev_index) = data.previous.node_to_index_opt(dep_node) {
+                return data.colors.get(prev_index);
+            } else {
+                // This is a node that did not exist in the previous compilation session.
+                return None;
+            }
+        }
+
+        None
+    }
+
+    /// Try to mark a node index for the node dep_node.
+    ///
+    /// A node will have an index, when it's already been marked green, or when we can mark it
+    /// green. This function will mark the current task as a reader of the specified node, when
+    /// a node index can be found for that node.
+    pub fn try_mark_green<Ctxt: QueryContext<DepKind = K>>(
+        &self,
+        tcx: Ctxt,
+        dep_node: &DepNode<K>,
+    ) -> Option<(SerializedDepNodeIndex, DepNodeIndex)> {
+        debug_assert!(!tcx.dep_context().is_eval_always(dep_node.kind));
+
+        // Return None if the dep graph is disabled
+        let data = self.data.as_ref()?;
+
+        // Return None if the dep node didn't exist in the previous session
+        let prev_index = data.previous.node_to_index_opt(dep_node)?;
+
+        match data.colors.get(prev_index) {
+            Some(DepNodeColor::Green(dep_node_index)) => Some((prev_index, dep_node_index)),
+            Some(DepNodeColor::Red) => None,
+            None => {
+                // This DepNode and the corresponding query invocation existed
+                // in the previous compilation session too, so we can try to
+                // mark it as green by recursively marking all of its
+                // dependencies green.
+                self.try_mark_previous_green(tcx, data, prev_index, &dep_node)
+                    .map(|dep_node_index| (prev_index, dep_node_index))
+            }
+        }
+    }
+
+    fn try_mark_parent_green<Ctxt: QueryContext<DepKind = K>>(
+        &self,
+        tcx: Ctxt,
+        data: &DepGraphData<K>,
+        parent_dep_node_index: SerializedDepNodeIndex,
+        dep_node: &DepNode<K>,
+    ) -> Option<()> {
+        let dep_dep_node_color = data.colors.get(parent_dep_node_index);
+        let dep_dep_node = &data.previous.index_to_node(parent_dep_node_index);
+
+        match dep_dep_node_color {
+            Some(DepNodeColor::Green(_)) => {
+                // This dependency has been marked as green before, we are
+                // still fine and can continue with checking the other
+                // dependencies.
+                debug!(
+                    "try_mark_previous_green({:?}) --- found dependency {:?} to \
+                            be immediately green",
+                    dep_node, dep_dep_node,
+                );
+                return Some(());
+            }
+            Some(DepNodeColor::Red) => {
+                // We found a dependency the value of which has changed
+                // compared to the previous compilation session. We cannot
+                // mark the DepNode as green and also don't need to bother
+                // with checking any of the other dependencies.
+                debug!(
+                    "try_mark_previous_green({:?}) - END - dependency {:?} was immediately red",
+                    dep_node, dep_dep_node,
+                );
+                return None;
+            }
+            None => {}
+        }
+
+        // We don't know the state of this dependency. If it isn't
+        // an eval_always node, let's try to mark it green recursively.
+        if !tcx.dep_context().is_eval_always(dep_dep_node.kind) {
+            debug!(
+                "try_mark_previous_green({:?}) --- state of dependency {:?} ({}) \
+                                 is unknown, trying to mark it green",
+                dep_node, dep_dep_node, dep_dep_node.hash,
+            );
+
+            let node_index =
+                self.try_mark_previous_green(tcx, data, parent_dep_node_index, dep_dep_node);
+            if node_index.is_some() {
+                debug!(
+                    "try_mark_previous_green({:?}) --- managed to MARK dependency {:?} as green",
+                    dep_node, dep_dep_node
+                );
+                return Some(());
+            }
+        }
+
+        // We failed to mark it green, so we try to force the query.
+        debug!(
+            "try_mark_previous_green({:?}) --- trying to force dependency {:?}",
+            dep_node, dep_dep_node
+        );
+        if !tcx.dep_context().try_force_from_dep_node(*dep_dep_node) {
+            // The DepNode could not be forced.
+            debug!(
+                "try_mark_previous_green({:?}) - END - dependency {:?} could not be forced",
+                dep_node, dep_dep_node
+            );
+            return None;
+        }
+
+        let dep_dep_node_color = data.colors.get(parent_dep_node_index);
+
+        match dep_dep_node_color {
+            Some(DepNodeColor::Green(_)) => {
+                debug!(
+                    "try_mark_previous_green({:?}) --- managed to FORCE dependency {:?} to green",
+                    dep_node, dep_dep_node
+                );
+                return Some(());
+            }
+            Some(DepNodeColor::Red) => {
+                debug!(
+                    "try_mark_previous_green({:?}) - END - dependency {:?} was red after forcing",
+                    dep_node, dep_dep_node
+                );
+                return None;
+            }
+            None => {}
+        }
+
+        if !tcx.dep_context().sess().has_errors_or_delayed_span_bugs() {
+            panic!("try_mark_previous_green() - Forcing the DepNode should have set its color")
+        }
+
+        // If the query we just forced has resulted in
+        // some kind of compilation error, we cannot rely on
+        // the dep-node color having been properly updated.
+        // This means that the query system has reached an
+        // invalid state. We let the compiler continue (by
+        // returning `None`) so it can emit error messages
+        // and wind down, but rely on the fact that this
+        // invalid state will not be persisted to the
+        // incremental compilation cache because of
+        // compilation errors being present.
+        debug!(
+            "try_mark_previous_green({:?}) - END - dependency {:?} resulted in compilation error",
+            dep_node, dep_dep_node
+        );
+        return None;
+    }
+
+    /// Try to mark a dep-node which existed in the previous compilation session as green.
+    fn try_mark_previous_green<Ctxt: QueryContext<DepKind = K>>(
+        &self,
+        tcx: Ctxt,
+        data: &DepGraphData<K>,
+        prev_dep_node_index: SerializedDepNodeIndex,
+        dep_node: &DepNode<K>,
+    ) -> Option<DepNodeIndex> {
+        debug!("try_mark_previous_green({:?}) - BEGIN", dep_node);
+
+        #[cfg(not(parallel_compiler))]
+        {
+            debug_assert!(!self.dep_node_exists(dep_node));
+            debug_assert!(data.colors.get(prev_dep_node_index).is_none());
+        }
+
+        // We never try to mark eval_always nodes as green
+        debug_assert!(!tcx.dep_context().is_eval_always(dep_node.kind));
+
+        debug_assert_eq!(data.previous.index_to_node(prev_dep_node_index), *dep_node);
+
+        let prev_deps = data.previous.edge_targets_from(prev_dep_node_index);
+
+        for &dep_dep_node_index in prev_deps {
+            self.try_mark_parent_green(tcx, data, dep_dep_node_index, dep_node)?
+        }
+
+        // If we got here without hitting a `return` that means that all
+        // dependencies of this DepNode could be marked as green. Therefore we
+        // can also mark this DepNode as green.
+
+        // There may be multiple threads trying to mark the same dep node green concurrently
+
+        // We allocating an entry for the node in the current dependency graph and
+        // adding all the appropriate edges imported from the previous graph
+        let dep_node_index = data.current.promote_node_and_deps_to_current(
+            tcx.dep_context().profiler(),
+            &data.previous,
+            prev_dep_node_index,
+        );
+
+        // ... emitting any stored diagnostic ...
+
+        // FIXME: Store the fact that a node has diagnostics in a bit in the dep graph somewhere
+        // Maybe store a list on disk and encode this fact in the DepNodeState
+        let side_effects = tcx.load_side_effects(prev_dep_node_index);
+
+        #[cfg(not(parallel_compiler))]
+        debug_assert!(
+            data.colors.get(prev_dep_node_index).is_none(),
+            "DepGraph::try_mark_previous_green() - Duplicate DepNodeColor \
+                      insertion for {:?}",
+            dep_node
+        );
+
+        if !side_effects.is_empty() {
+            self.emit_side_effects(tcx, data, dep_node_index, side_effects);
+        }
+
+        // ... and finally storing a "Green" entry in the color map.
+        // Multiple threads can all write the same color here
+        data.colors.insert(prev_dep_node_index, DepNodeColor::Green(dep_node_index));
+
+        debug!("try_mark_previous_green({:?}) - END - successfully marked as green", dep_node);
+        Some(dep_node_index)
+    }
+
+    /// Atomically emits some loaded diagnostics.
+    /// This may be called concurrently on multiple threads for the same dep node.
+    #[cold]
+    #[inline(never)]
+    fn emit_side_effects<Ctxt: QueryContext<DepKind = K>>(
+        &self,
+        tcx: Ctxt,
+        data: &DepGraphData<K>,
+        dep_node_index: DepNodeIndex,
+        side_effects: QuerySideEffects,
+    ) {
+        let mut processed = data.processed_side_effects.lock();
+
+        if processed.insert(dep_node_index) {
+            // We were the first to insert the node in the set so this thread
+            // must process side effects
+
+            // Promote the previous diagnostics to the current session.
+            tcx.store_side_effects(dep_node_index, side_effects.clone());
+
+            let handle = tcx.dep_context().sess().diagnostic();
+
+            for mut diagnostic in side_effects.diagnostics {
+                handle.emit_diagnostic(&mut diagnostic);
+            }
+        }
+    }
+
+    // Returns true if the given node has been marked as red during the
+    // current compilation session. Used in various assertions
+    pub fn is_red(&self, dep_node: &DepNode<K>) -> bool {
+        self.node_color(dep_node) == Some(DepNodeColor::Red)
+    }
+
+    // Returns true if the given node has been marked as green during the
+    // current compilation session. Used in various assertions
+    pub fn is_green(&self, dep_node: &DepNode<K>) -> bool {
+        self.node_color(dep_node).map_or(false, |c| c.is_green())
+    }
+
+    // This method loads all on-disk cacheable query results into memory, so
+    // they can be written out to the new cache file again. Most query results
+    // will already be in memory but in the case where we marked something as
+    // green but then did not need the value, that value will never have been
+    // loaded from disk.
+    //
+    // This method will only load queries that will end up in the disk cache.
+    // Other queries will not be executed.
+    pub fn exec_cache_promotions<Ctxt: DepContext<DepKind = K>>(&self, tcx: Ctxt) {
+        let _prof_timer = tcx.profiler().generic_activity("incr_comp_query_cache_promotion");
+
+        let data = self.data.as_ref().unwrap();
+        for prev_index in data.colors.values.indices() {
+            match data.colors.get(prev_index) {
+                Some(DepNodeColor::Green(_)) => {
+                    let dep_node = data.previous.index_to_node(prev_index);
+                    tcx.try_load_from_on_disk_cache(dep_node);
+                }
+                None | Some(DepNodeColor::Red) => {
+                    // We can skip red nodes because a node can only be marked
+                    // as red if the query result was recomputed and thus is
+                    // already in memory.
+                }
+            }
+        }
+    }
+
+    pub fn print_incremental_info(&self) {
+        if let Some(data) = &self.data {
+            data.current.encoder.borrow().print_incremental_info(
+                data.current.total_read_count.load(Relaxed),
+                data.current.total_duplicate_read_count.load(Relaxed),
+            )
+        }
+    }
+
+    pub fn encode(&self, profiler: &SelfProfilerRef) -> FileEncodeResult {
+        if let Some(data) = &self.data {
+            data.current.encoder.steal().finish(profiler)
+        } else {
+            Ok(0)
+        }
+    }
+
+    pub(crate) fn next_virtual_depnode_index(&self) -> DepNodeIndex {
+        let index = self.virtual_dep_node_index.fetch_add(1, Relaxed);
+        DepNodeIndex::from_u32(index)
+    }
+}
+
+/// A "work product" is an intermediate result that we save into the
+/// incremental directory for later re-use. The primary example are
+/// the object files that we save for each partition at code
+/// generation time.
+///
+/// Each work product is associated with a dep-node, representing the
+/// process that produced the work-product. If that dep-node is found
+/// to be dirty when we load up, then we will delete the work-product
+/// at load time. If the work-product is found to be clean, then we
+/// will keep a record in the `previous_work_products` list.
+///
+/// In addition, work products have an associated hash. This hash is
+/// an extra hash that can be used to decide if the work-product from
+/// a previous compilation can be re-used (in addition to the dirty
+/// edges check).
+///
+/// As the primary example, consider the object files we generate for
+/// each partition. In the first run, we create partitions based on
+/// the symbols that need to be compiled. For each partition P, we
+/// hash the symbols in P and create a `WorkProduct` record associated
+/// with `DepNode::CodegenUnit(P)`; the hash is the set of symbols
+/// in P.
+///
+/// The next time we compile, if the `DepNode::CodegenUnit(P)` is
+/// judged to be clean (which means none of the things we read to
+/// generate the partition were found to be dirty), it will be loaded
+/// into previous work products. We will then regenerate the set of
+/// symbols in the partition P and hash them (note that new symbols
+/// may be added -- for example, new monomorphizations -- even if
+/// nothing in P changed!). We will compare that hash against the
+/// previous hash. If it matches up, we can reuse the object file.
+#[derive(Clone, Debug, Encodable, Decodable)]
+pub struct WorkProduct {
+    pub cgu_name: String,
+    /// Saved files associated with this CGU. In each key/value pair, the value is the path to the
+    /// saved file and the key is some identifier for the type of file being saved.
+    ///
+    /// By convention, file extensions are currently used as identifiers, i.e. the key "o" maps to
+    /// the object file's path, and "dwo" to the dwarf object file's path.
+    pub saved_files: FxHashMap<String, String>,
+}
+
+// Index type for `DepNodeData`'s edges.
+rustc_index::newtype_index! {
+    struct EdgeIndex { .. }
+}
+
+/// `CurrentDepGraph` stores the dependency graph for the current session. It
+/// will be populated as we run queries or tasks. We never remove nodes from the
+/// graph: they are only added.
+///
+/// The nodes in it are identified by a `DepNodeIndex`. We avoid keeping the nodes
+/// in memory.  This is important, because these graph structures are some of the
+/// largest in the compiler.
+///
+/// For this reason, we avoid storing `DepNode`s more than once as map
+/// keys. The `new_node_to_index` map only contains nodes not in the previous
+/// graph, and we map nodes in the previous graph to indices via a two-step
+/// mapping. `SerializedDepGraph` maps from `DepNode` to `SerializedDepNodeIndex`,
+/// and the `prev_index_to_index` vector (which is more compact and faster than
+/// using a map) maps from `SerializedDepNodeIndex` to `DepNodeIndex`.
+///
+/// This struct uses three locks internally. The `data`, `new_node_to_index`,
+/// and `prev_index_to_index` fields are locked separately. Operations that take
+/// a `DepNodeIndex` typically just access the `data` field.
+///
+/// We only need to manipulate at most two locks simultaneously:
+/// `new_node_to_index` and `data`, or `prev_index_to_index` and `data`. When
+/// manipulating both, we acquire `new_node_to_index` or `prev_index_to_index`
+/// first, and `data` second.
+pub(super) struct CurrentDepGraph<K: DepKind> {
+    encoder: Steal<GraphEncoder<K>>,
+    new_node_to_index: Sharded<FxHashMap<DepNode<K>, DepNodeIndex>>,
+    prev_index_to_index: Lock<IndexVec<SerializedDepNodeIndex, Option<DepNodeIndex>>>,
+
+    /// Used to trap when a specific edge is added to the graph.
+    /// This is used for debug purposes and is only active with `debug_assertions`.
+    #[cfg(debug_assertions)]
+    forbidden_edge: Option<EdgeFilter<K>>,
+
+    /// Anonymous `DepNode`s are nodes whose IDs we compute from the list of
+    /// their edges. This has the beneficial side-effect that multiple anonymous
+    /// nodes can be coalesced into one without changing the semantics of the
+    /// dependency graph. However, the merging of nodes can lead to a subtle
+    /// problem during red-green marking: The color of an anonymous node from
+    /// the current session might "shadow" the color of the node with the same
+    /// ID from the previous session. In order to side-step this problem, we make
+    /// sure that anonymous `NodeId`s allocated in different sessions don't overlap.
+    /// This is implemented by mixing a session-key into the ID fingerprint of
+    /// each anon node. The session-key is just a random number generated when
+    /// the `DepGraph` is created.
+    anon_id_seed: Fingerprint,
+
+    /// These are simple counters that are for profiling and
+    /// debugging and only active with `debug_assertions`.
+    total_read_count: AtomicU64,
+    total_duplicate_read_count: AtomicU64,
+
+    /// The cached event id for profiling node interning. This saves us
+    /// from having to look up the event id every time we intern a node
+    /// which may incur too much overhead.
+    /// This will be None if self-profiling is disabled.
+    node_intern_event_id: Option<EventId>,
+}
+
+impl<K: DepKind> CurrentDepGraph<K> {
+    fn new(
+        profiler: &SelfProfilerRef,
+        prev_graph_node_count: usize,
+        encoder: FileEncoder,
+        record_graph: bool,
+        record_stats: bool,
+    ) -> CurrentDepGraph<K> {
+        use std::time::{SystemTime, UNIX_EPOCH};
+
+        let duration = SystemTime::now().duration_since(UNIX_EPOCH).unwrap();
+        let nanos = duration.as_secs() * 1_000_000_000 + duration.subsec_nanos() as u64;
+        let mut stable_hasher = StableHasher::new();
+        nanos.hash(&mut stable_hasher);
+        let anon_id_seed = stable_hasher.finish();
+
+        #[cfg(debug_assertions)]
+        let forbidden_edge = match env::var("RUST_FORBID_DEP_GRAPH_EDGE") {
+            Ok(s) => match EdgeFilter::new(&s) {
+                Ok(f) => Some(f),
+                Err(err) => panic!("RUST_FORBID_DEP_GRAPH_EDGE invalid: {}", err),
+            },
+            Err(_) => None,
+        };
+
+        // We store a large collection of these in `prev_index_to_index` during
+        // non-full incremental builds, and want to ensure that the element size
+        // doesn't inadvertently increase.
+        static_assert_size!(Option<DepNodeIndex>, 4);
+
+        let new_node_count_estimate = 102 * prev_graph_node_count / 100 + 200;
+
+        let node_intern_event_id = profiler
+            .get_or_alloc_cached_string("incr_comp_intern_dep_graph_node")
+            .map(EventId::from_label);
+
+        CurrentDepGraph {
+            encoder: Steal::new(GraphEncoder::new(
+                encoder,
+                prev_graph_node_count,
+                record_graph,
+                record_stats,
+            )),
+            new_node_to_index: Sharded::new(|| {
+                FxHashMap::with_capacity_and_hasher(
+                    new_node_count_estimate / sharded::SHARDS,
+                    Default::default(),
+                )
+            }),
+            prev_index_to_index: Lock::new(IndexVec::from_elem_n(None, prev_graph_node_count)),
+            anon_id_seed,
+            #[cfg(debug_assertions)]
+            forbidden_edge,
+            total_read_count: AtomicU64::new(0),
+            total_duplicate_read_count: AtomicU64::new(0),
+            node_intern_event_id,
+        }
+    }
+
+    #[cfg(debug_assertions)]
+    fn record_edge(&self, dep_node_index: DepNodeIndex, key: DepNode<K>) {
+        if let Some(forbidden_edge) = &self.forbidden_edge {
+            forbidden_edge.index_to_node.lock().insert(dep_node_index, key);
+        }
+    }
+
+    /// Writes the node to the current dep-graph and allocates a `DepNodeIndex` for it.
+    /// Assumes that this is a node that has no equivalent in the previous dep-graph.
+    fn intern_new_node(
+        &self,
+        profiler: &SelfProfilerRef,
+        key: DepNode<K>,
+        edges: EdgesVec,
+        current_fingerprint: Fingerprint,
+    ) -> DepNodeIndex {
+        match self.new_node_to_index.get_shard_by_value(&key).lock().entry(key) {
+            Entry::Occupied(entry) => *entry.get(),
+            Entry::Vacant(entry) => {
+                let dep_node_index =
+                    self.encoder.borrow().send(profiler, key, current_fingerprint, edges);
+                entry.insert(dep_node_index);
+                #[cfg(debug_assertions)]
+                self.record_edge(dep_node_index, key);
+                dep_node_index
+            }
+        }
+    }
+
+    fn intern_node(
+        &self,
+        profiler: &SelfProfilerRef,
+        prev_graph: &SerializedDepGraph<K>,
+        key: DepNode<K>,
+        edges: EdgesVec,
+        fingerprint: Option<Fingerprint>,
+        print_status: bool,
+    ) -> (DepNodeIndex, Option<(SerializedDepNodeIndex, DepNodeColor)>) {
+        let print_status = cfg!(debug_assertions) && print_status;
+
+        // Get timer for profiling `DepNode` interning
+        let _node_intern_timer =
+            self.node_intern_event_id.map(|eid| profiler.generic_activity_with_event_id(eid));
+
+        if let Some(prev_index) = prev_graph.node_to_index_opt(&key) {
+            // Determine the color and index of the new `DepNode`.
+            if let Some(fingerprint) = fingerprint {
+                if fingerprint == prev_graph.fingerprint_by_index(prev_index) {
+                    if print_status {
+                        eprintln!("[task::green] {:?}", key);
+                    }
+
+                    // This is a green node: it existed in the previous compilation,
+                    // its query was re-executed, and it has the same result as before.
+                    let mut prev_index_to_index = self.prev_index_to_index.lock();
+
+                    let dep_node_index = match prev_index_to_index[prev_index] {
+                        Some(dep_node_index) => dep_node_index,
+                        None => {
+                            let dep_node_index =
+                                self.encoder.borrow().send(profiler, key, fingerprint, edges);
+                            prev_index_to_index[prev_index] = Some(dep_node_index);
+                            dep_node_index
+                        }
+                    };
+
+                    #[cfg(debug_assertions)]
+                    self.record_edge(dep_node_index, key);
+                    (dep_node_index, Some((prev_index, DepNodeColor::Green(dep_node_index))))
+                } else {
+                    if print_status {
+                        eprintln!("[task::red] {:?}", key);
+                    }
+
+                    // This is a red node: it existed in the previous compilation, its query
+                    // was re-executed, but it has a different result from before.
+                    let mut prev_index_to_index = self.prev_index_to_index.lock();
+
+                    let dep_node_index = match prev_index_to_index[prev_index] {
+                        Some(dep_node_index) => dep_node_index,
+                        None => {
+                            let dep_node_index =
+                                self.encoder.borrow().send(profiler, key, fingerprint, edges);
+                            prev_index_to_index[prev_index] = Some(dep_node_index);
+                            dep_node_index
+                        }
+                    };
+
+                    #[cfg(debug_assertions)]
+                    self.record_edge(dep_node_index, key);
+                    (dep_node_index, Some((prev_index, DepNodeColor::Red)))
+                }
+            } else {
+                if print_status {
+                    eprintln!("[task::unknown] {:?}", key);
+                }
+
+                // This is a red node, effectively: it existed in the previous compilation
+                // session, its query was re-executed, but it doesn't compute a result hash
+                // (i.e. it represents a `no_hash` query), so we have no way of determining
+                // whether or not the result was the same as before.
+                let mut prev_index_to_index = self.prev_index_to_index.lock();
+
+                let dep_node_index = match prev_index_to_index[prev_index] {
+                    Some(dep_node_index) => dep_node_index,
+                    None => {
+                        let dep_node_index =
+                            self.encoder.borrow().send(profiler, key, Fingerprint::ZERO, edges);
+                        prev_index_to_index[prev_index] = Some(dep_node_index);
+                        dep_node_index
+                    }
+                };
+
+                #[cfg(debug_assertions)]
+                self.record_edge(dep_node_index, key);
+                (dep_node_index, Some((prev_index, DepNodeColor::Red)))
+            }
+        } else {
+            if print_status {
+                eprintln!("[task::new] {:?}", key);
+            }
+
+            let fingerprint = fingerprint.unwrap_or(Fingerprint::ZERO);
+
+            // This is a new node: it didn't exist in the previous compilation session.
+            let dep_node_index = self.intern_new_node(profiler, key, edges, fingerprint);
+
+            (dep_node_index, None)
+        }
+    }
+
+    fn promote_node_and_deps_to_current(
+        &self,
+        profiler: &SelfProfilerRef,
+        prev_graph: &SerializedDepGraph<K>,
+        prev_index: SerializedDepNodeIndex,
+    ) -> DepNodeIndex {
+        self.debug_assert_not_in_new_nodes(prev_graph, prev_index);
+
+        let mut prev_index_to_index = self.prev_index_to_index.lock();
+
+        match prev_index_to_index[prev_index] {
+            Some(dep_node_index) => dep_node_index,
+            None => {
+                let key = prev_graph.index_to_node(prev_index);
+                let dep_node_index = self.encoder.borrow().send(
+                    profiler,
+                    key,
+                    prev_graph.fingerprint_by_index(prev_index),
+                    prev_graph
+                        .edge_targets_from(prev_index)
+                        .iter()
+                        .map(|i| prev_index_to_index[*i].unwrap())
+                        .collect(),
+                );
+                prev_index_to_index[prev_index] = Some(dep_node_index);
+                #[cfg(debug_assertions)]
+                self.record_edge(dep_node_index, key);
+                dep_node_index
+            }
+        }
+    }
+
+    #[inline]
+    fn debug_assert_not_in_new_nodes(
+        &self,
+        prev_graph: &SerializedDepGraph<K>,
+        prev_index: SerializedDepNodeIndex,
+    ) {
+        let node = &prev_graph.index_to_node(prev_index);
+        debug_assert!(
+            !self.new_node_to_index.get_shard_by_value(node).lock().contains_key(node),
+            "node from previous graph present in new node collection"
+        );
+    }
+}
+
+/// The capacity of the `reads` field `SmallVec`
+const TASK_DEPS_READS_CAP: usize = 8;
+type EdgesVec = SmallVec<[DepNodeIndex; TASK_DEPS_READS_CAP]>;
+
+#[derive(Debug, Clone, Copy)]
+pub enum TaskDepsRef<'a, K: DepKind> {
+    /// New dependencies can be added to the
+    /// `TaskDeps`. This is used when executing a 'normal' query
+    /// (no `eval_always` modifier)
+    Allow(&'a Lock<TaskDeps<K>>),
+    /// New dependencies are ignored. This is used when
+    /// executing an `eval_always` query, since there's no
+    /// need to track dependencies for a query that's always
+    /// re-executed. This is also used for `dep_graph.with_ignore`
+    Ignore,
+    /// Any attempt to add new dependencies will cause a panic.
+    /// This is used when decoding a query result from disk,
+    /// to ensure that the decoding process doesn't itself
+    /// require the execution of any queries.
+    Forbid,
+}
+
+#[derive(Debug)]
+pub struct TaskDeps<K: DepKind> {
+    #[cfg(debug_assertions)]
+    node: Option<DepNode<K>>,
+    reads: EdgesVec,
+    read_set: FxHashSet<DepNodeIndex>,
+    phantom_data: PhantomData<DepNode<K>>,
+}
+
+impl<K: DepKind> Default for TaskDeps<K> {
+    fn default() -> Self {
+        Self {
+            #[cfg(debug_assertions)]
+            node: None,
+            reads: EdgesVec::new(),
+            read_set: FxHashSet::default(),
+            phantom_data: PhantomData,
+        }
+    }
+}
+
+// A data structure that stores Option<DepNodeColor> values as a contiguous
+// array, using one u32 per entry.
+struct DepNodeColorMap {
+    values: IndexVec<SerializedDepNodeIndex, AtomicU32>,
+}
+
+const COMPRESSED_NONE: u32 = 0;
+const COMPRESSED_RED: u32 = 1;
+const COMPRESSED_FIRST_GREEN: u32 = 2;
+
+impl DepNodeColorMap {
+    fn new(size: usize) -> DepNodeColorMap {
+        DepNodeColorMap { values: (0..size).map(|_| AtomicU32::new(COMPRESSED_NONE)).collect() }
+    }
+
+    #[inline]
+    fn get(&self, index: SerializedDepNodeIndex) -> Option<DepNodeColor> {
+        match self.values[index].load(Ordering::Acquire) {
+            COMPRESSED_NONE => None,
+            COMPRESSED_RED => Some(DepNodeColor::Red),
+            value => {
+                Some(DepNodeColor::Green(DepNodeIndex::from_u32(value - COMPRESSED_FIRST_GREEN)))
+            }
+        }
+    }
+
+    fn insert(&self, index: SerializedDepNodeIndex, color: DepNodeColor) {
+        self.values[index].store(
+            match color {
+                DepNodeColor::Red => COMPRESSED_RED,
+                DepNodeColor::Green(index) => index.as_u32() + COMPRESSED_FIRST_GREEN,
+            },
+            Ordering::Release,
+        )
+    }
+}
diff --git a/compiler/rustc_query_system/src/dep_graph/mod.rs b/compiler/rustc_query_system/src/dep_graph/mod.rs
new file mode 100644
index 000000000..342d95ca4
--- /dev/null
+++ b/compiler/rustc_query_system/src/dep_graph/mod.rs
@@ -0,0 +1,106 @@
+pub mod debug;
+mod dep_node;
+mod graph;
+mod query;
+mod serialized;
+
+pub use dep_node::{DepNode, DepNodeParams, WorkProductId};
+pub use graph::{
+    hash_result, DepGraph, DepNodeColor, DepNodeIndex, TaskDeps, TaskDepsRef, WorkProduct,
+};
+pub use query::DepGraphQuery;
+pub use serialized::{SerializedDepGraph, SerializedDepNodeIndex};
+
+use crate::ich::StableHashingContext;
+use rustc_data_structures::profiling::SelfProfilerRef;
+use rustc_serialize::{opaque::FileEncoder, Encodable};
+use rustc_session::Session;
+
+use std::fmt;
+use std::hash::Hash;
+
+pub trait DepContext: Copy {
+    type DepKind: self::DepKind;
+
+    /// Create a hashing context for hashing new results.
+    fn with_stable_hashing_context<R>(&self, f: impl FnOnce(StableHashingContext<'_>) -> R) -> R;
+
+    /// Access the DepGraph.
+    fn dep_graph(&self) -> &DepGraph<Self::DepKind>;
+
+    /// Access the profiler.
+    fn profiler(&self) -> &SelfProfilerRef;
+
+    /// Access the compiler session.
+    fn sess(&self) -> &Session;
+
+    /// Return whether this kind always require evaluation.
+    fn is_eval_always(&self, kind: Self::DepKind) -> bool;
+
+    fn fingerprint_style(&self, kind: Self::DepKind) -> FingerprintStyle;
+
+    /// Try to force a dep node to execute and see if it's green.
+    fn try_force_from_dep_node(&self, dep_node: DepNode<Self::DepKind>) -> bool;
+
+    /// Load data from the on-disk cache.
+    fn try_load_from_on_disk_cache(&self, dep_node: DepNode<Self::DepKind>);
+}
+
+pub trait HasDepContext: Copy {
+    type DepKind: self::DepKind;
+    type DepContext: self::DepContext<DepKind = Self::DepKind>;
+
+    fn dep_context(&self) -> &Self::DepContext;
+}
+
+impl<T: DepContext> HasDepContext for T {
+    type DepKind = T::DepKind;
+    type DepContext = Self;
+
+    fn dep_context(&self) -> &Self::DepContext {
+        self
+    }
+}
+
+/// Describes the contents of the fingerprint generated by a given query.
+#[derive(Debug, PartialEq, Eq, Copy, Clone)]
+pub enum FingerprintStyle {
+    /// The fingerprint is actually a DefPathHash.
+    DefPathHash,
+    /// Query key was `()` or equivalent, so fingerprint is just zero.
+    Unit,
+    /// Some opaque hash.
+    Opaque,
+}
+
+impl FingerprintStyle {
+    #[inline]
+    pub fn reconstructible(self) -> bool {
+        match self {
+            FingerprintStyle::DefPathHash | FingerprintStyle::Unit => true,
+            FingerprintStyle::Opaque => false,
+        }
+    }
+}
+
+/// Describe the different families of dependency nodes.
+pub trait DepKind: Copy + fmt::Debug + Eq + Hash + Send + Encodable<FileEncoder> + 'static {
+    /// DepKind to use when incr. comp. is turned off.
+    const NULL: Self;
+
+    /// DepKind to use to create the initial forever-red node.
+    const RED: Self;
+
+    /// Implementation of `std::fmt::Debug` for `DepNode`.
+    fn debug_node(node: &DepNode<Self>, f: &mut fmt::Formatter<'_>) -> fmt::Result;
+
+    /// Execute the operation with provided dependencies.
+    fn with_deps<OP, R>(deps: TaskDepsRef<'_, Self>, op: OP) -> R
+    where
+        OP: FnOnce() -> R;
+
+    /// Access dependencies from current implicit context.
+    fn read_deps<OP>(op: OP)
+    where
+        OP: for<'a> FnOnce(TaskDepsRef<'a, Self>);
+}
diff --git a/compiler/rustc_query_system/src/dep_graph/query.rs b/compiler/rustc_query_system/src/dep_graph/query.rs
new file mode 100644
index 000000000..27b3b5e13
--- /dev/null
+++ b/compiler/rustc_query_system/src/dep_graph/query.rs
@@ -0,0 +1,68 @@
+use rustc_data_structures::fx::FxHashMap;
+use rustc_data_structures::graph::implementation::{Direction, Graph, NodeIndex, INCOMING};
+use rustc_index::vec::IndexVec;
+
+use super::{DepKind, DepNode, DepNodeIndex};
+
+pub struct DepGraphQuery<K> {
+    pub graph: Graph<DepNode<K>, ()>,
+    pub indices: FxHashMap<DepNode<K>, NodeIndex>,
+    pub dep_index_to_index: IndexVec<DepNodeIndex, Option<NodeIndex>>,
+}
+
+impl<K: DepKind> DepGraphQuery<K> {
+    pub fn new(prev_node_count: usize) -> DepGraphQuery<K> {
+        let node_count = prev_node_count + prev_node_count / 4;
+        let edge_count = 6 * node_count;
+
+        let graph = Graph::with_capacity(node_count, edge_count);
+        let indices = FxHashMap::default();
+        let dep_index_to_index = IndexVec::new();
+
+        DepGraphQuery { graph, indices, dep_index_to_index }
+    }
+
+    pub fn push(&mut self, index: DepNodeIndex, node: DepNode<K>, edges: &[DepNodeIndex]) {
+        let source = self.graph.add_node(node);
+        if index.index() >= self.dep_index_to_index.len() {
+            self.dep_index_to_index.resize(index.index() + 1, None);
+        }
+        self.dep_index_to_index[index] = Some(source);
+        self.indices.insert(node, source);
+
+        for &target in edges.iter() {
+            let target = self.dep_index_to_index[target];
+            // We may miss the edges that are pushed while the `DepGraphQuery` is being accessed.
+            // Skip them to issues.
+            if let Some(target) = target {
+                self.graph.add_edge(source, target, ());
+            }
+        }
+    }
+
+    pub fn nodes(&self) -> Vec<&DepNode<K>> {
+        self.graph.all_nodes().iter().map(|n| &n.data).collect()
+    }
+
+    pub fn edges(&self) -> Vec<(&DepNode<K>, &DepNode<K>)> {
+        self.graph
+            .all_edges()
+            .iter()
+            .map(|edge| (edge.source(), edge.target()))
+            .map(|(s, t)| (self.graph.node_data(s), self.graph.node_data(t)))
+            .collect()
+    }
+
+    fn reachable_nodes(&self, node: &DepNode<K>, direction: Direction) -> Vec<&DepNode<K>> {
+        if let Some(&index) = self.indices.get(node) {
+            self.graph.depth_traverse(index, direction).map(|s| self.graph.node_data(s)).collect()
+        } else {
+            vec![]
+        }
+    }
+
+    /// All nodes that can reach `node`.
+    pub fn transitive_predecessors(&self, node: &DepNode<K>) -> Vec<&DepNode<K>> {
+        self.reachable_nodes(node, INCOMING)
+    }
+}
diff --git a/compiler/rustc_query_system/src/dep_graph/serialized.rs b/compiler/rustc_query_system/src/dep_graph/serialized.rs
new file mode 100644
index 000000000..3b20ec70d
--- /dev/null
+++ b/compiler/rustc_query_system/src/dep_graph/serialized.rs
@@ -0,0 +1,330 @@
+//! The data that we will serialize and deserialize.
+//!
+//! The dep-graph is serialized as a sequence of NodeInfo, with the dependencies
+//! specified inline.  The total number of nodes and edges are stored as the last
+//! 16 bytes of the file, so we can find them easily at decoding time.
+//!
+//! The serialisation is performed on-demand when each node is emitted. Using this
+//! scheme, we do not need to keep the current graph in memory.
+//!
+//! The deserialization is performed manually, in order to convert from the stored
+//! sequence of NodeInfos to the different arrays in SerializedDepGraph.  Since the
+//! node and edge count are stored at the end of the file, all the arrays can be
+//! pre-allocated with the right length.
+
+use super::query::DepGraphQuery;
+use super::{DepKind, DepNode, DepNodeIndex};
+use rustc_data_structures::fingerprint::Fingerprint;
+use rustc_data_structures::fx::FxHashMap;
+use rustc_data_structures::profiling::SelfProfilerRef;
+use rustc_data_structures::sync::Lock;
+use rustc_index::vec::{Idx, IndexVec};
+use rustc_serialize::opaque::{FileEncodeResult, FileEncoder, IntEncodedWithFixedSize, MemDecoder};
+use rustc_serialize::{Decodable, Decoder, Encodable};
+use smallvec::SmallVec;
+use std::convert::TryInto;
+
+// The maximum value of `SerializedDepNodeIndex` leaves the upper two bits
+// unused so that we can store multiple index types in `CompressedHybridIndex`,
+// and use those bits to encode which index type it contains.
+rustc_index::newtype_index! {
+    pub struct SerializedDepNodeIndex {
+        MAX = 0x7FFF_FFFF
+    }
+}
+
+/// Data for use when recompiling the **current crate**.
+#[derive(Debug)]
+pub struct SerializedDepGraph<K: DepKind> {
+    /// The set of all DepNodes in the graph
+    nodes: IndexVec<SerializedDepNodeIndex, DepNode<K>>,
+    /// The set of all Fingerprints in the graph. Each Fingerprint corresponds to
+    /// the DepNode at the same index in the nodes vector.
+    fingerprints: IndexVec<SerializedDepNodeIndex, Fingerprint>,
+    /// For each DepNode, stores the list of edges originating from that
+    /// DepNode. Encoded as a [start, end) pair indexing into edge_list_data,
+    /// which holds the actual DepNodeIndices of the target nodes.
+    edge_list_indices: IndexVec<SerializedDepNodeIndex, (u32, u32)>,
+    /// A flattened list of all edge targets in the graph. Edge sources are
+    /// implicit in edge_list_indices.
+    edge_list_data: Vec<SerializedDepNodeIndex>,
+    /// Reciprocal map to `nodes`.
+    index: FxHashMap<DepNode<K>, SerializedDepNodeIndex>,
+}
+
+impl<K: DepKind> Default for SerializedDepGraph<K> {
+    fn default() -> Self {
+        SerializedDepGraph {
+            nodes: Default::default(),
+            fingerprints: Default::default(),
+            edge_list_indices: Default::default(),
+            edge_list_data: Default::default(),
+            index: Default::default(),
+        }
+    }
+}
+
+impl<K: DepKind> SerializedDepGraph<K> {
+    #[inline]
+    pub fn edge_targets_from(&self, source: SerializedDepNodeIndex) -> &[SerializedDepNodeIndex] {
+        let targets = self.edge_list_indices[source];
+        &self.edge_list_data[targets.0 as usize..targets.1 as usize]
+    }
+
+    #[inline]
+    pub fn index_to_node(&self, dep_node_index: SerializedDepNodeIndex) -> DepNode<K> {
+        self.nodes[dep_node_index]
+    }
+
+    #[inline]
+    pub fn node_to_index_opt(&self, dep_node: &DepNode<K>) -> Option<SerializedDepNodeIndex> {
+        self.index.get(dep_node).cloned()
+    }
+
+    #[inline]
+    pub fn fingerprint_of(&self, dep_node: &DepNode<K>) -> Option<Fingerprint> {
+        self.index.get(dep_node).map(|&node_index| self.fingerprints[node_index])
+    }
+
+    #[inline]
+    pub fn fingerprint_by_index(&self, dep_node_index: SerializedDepNodeIndex) -> Fingerprint {
+        self.fingerprints[dep_node_index]
+    }
+
+    pub fn node_count(&self) -> usize {
+        self.index.len()
+    }
+}
+
+impl<'a, K: DepKind + Decodable<MemDecoder<'a>>> Decodable<MemDecoder<'a>>
+    for SerializedDepGraph<K>
+{
+    #[instrument(level = "debug", skip(d))]
+    fn decode(d: &mut MemDecoder<'a>) -> SerializedDepGraph<K> {
+        let start_position = d.position();
+
+        // The last 16 bytes are the node count and edge count.
+        debug!("position: {:?}", d.position());
+        d.set_position(d.data.len() - 2 * IntEncodedWithFixedSize::ENCODED_SIZE);
+        debug!("position: {:?}", d.position());
+
+        let node_count = IntEncodedWithFixedSize::decode(d).0 as usize;
+        let edge_count = IntEncodedWithFixedSize::decode(d).0 as usize;
+        debug!(?node_count, ?edge_count);
+
+        debug!("position: {:?}", d.position());
+        d.set_position(start_position);
+        debug!("position: {:?}", d.position());
+
+        let mut nodes = IndexVec::with_capacity(node_count);
+        let mut fingerprints = IndexVec::with_capacity(node_count);
+        let mut edge_list_indices = IndexVec::with_capacity(node_count);
+        let mut edge_list_data = Vec::with_capacity(edge_count);
+
+        for _index in 0..node_count {
+            let dep_node: DepNode<K> = Decodable::decode(d);
+            let _i: SerializedDepNodeIndex = nodes.push(dep_node);
+            debug_assert_eq!(_i.index(), _index);
+
+            let fingerprint: Fingerprint = Decodable::decode(d);
+            let _i: SerializedDepNodeIndex = fingerprints.push(fingerprint);
+            debug_assert_eq!(_i.index(), _index);
+
+            // Deserialize edges -- sequence of DepNodeIndex
+            let len = d.read_usize();
+            let start = edge_list_data.len().try_into().unwrap();
+            for _ in 0..len {
+                let edge = Decodable::decode(d);
+                edge_list_data.push(edge);
+            }
+            let end = edge_list_data.len().try_into().unwrap();
+            let _i: SerializedDepNodeIndex = edge_list_indices.push((start, end));
+            debug_assert_eq!(_i.index(), _index);
+        }
+
+        let index: FxHashMap<_, _> =
+            nodes.iter_enumerated().map(|(idx, &dep_node)| (dep_node, idx)).collect();
+
+        SerializedDepGraph { nodes, fingerprints, edge_list_indices, edge_list_data, index }
+    }
+}
+
+#[derive(Debug, Encodable, Decodable)]
+pub struct NodeInfo<K: DepKind> {
+    node: DepNode<K>,
+    fingerprint: Fingerprint,
+    edges: SmallVec<[DepNodeIndex; 8]>,
+}
+
+struct Stat<K: DepKind> {
+    kind: K,
+    node_counter: u64,
+    edge_counter: u64,
+}
+
+struct EncoderState<K: DepKind> {
+    encoder: FileEncoder,
+    total_node_count: usize,
+    total_edge_count: usize,
+    stats: Option<FxHashMap<K, Stat<K>>>,
+}
+
+impl<K: DepKind> EncoderState<K> {
+    fn new(encoder: FileEncoder, record_stats: bool) -> Self {
+        Self {
+            encoder,
+            total_edge_count: 0,
+            total_node_count: 0,
+            stats: record_stats.then(FxHashMap::default),
+        }
+    }
+
+    fn encode_node(
+        &mut self,
+        node: &NodeInfo<K>,
+        record_graph: &Option<Lock<DepGraphQuery<K>>>,
+    ) -> DepNodeIndex {
+        let index = DepNodeIndex::new(self.total_node_count);
+        self.total_node_count += 1;
+
+        let edge_count = node.edges.len();
+        self.total_edge_count += edge_count;
+
+        if let Some(record_graph) = &record_graph {
+            // Do not ICE when a query is called from within `with_query`.
+            if let Some(record_graph) = &mut record_graph.try_lock() {
+                record_graph.push(index, node.node, &node.edges);
+            }
+        }
+
+        if let Some(stats) = &mut self.stats {
+            let kind = node.node.kind;
+
+            let stat = stats.entry(kind).or_insert(Stat { kind, node_counter: 0, edge_counter: 0 });
+            stat.node_counter += 1;
+            stat.edge_counter += edge_count as u64;
+        }
+
+        let encoder = &mut self.encoder;
+        node.encode(encoder);
+        index
+    }
+
+    fn finish(self, profiler: &SelfProfilerRef) -> FileEncodeResult {
+        let Self { mut encoder, total_node_count, total_edge_count, stats: _ } = self;
+
+        let node_count = total_node_count.try_into().unwrap();
+        let edge_count = total_edge_count.try_into().unwrap();
+
+        debug!(?node_count, ?edge_count);
+        debug!("position: {:?}", encoder.position());
+        IntEncodedWithFixedSize(node_count).encode(&mut encoder);
+        IntEncodedWithFixedSize(edge_count).encode(&mut encoder);
+        debug!("position: {:?}", encoder.position());
+        // Drop the encoder so that nothing is written after the counts.
+        let result = encoder.finish();
+        if let Ok(position) = result {
+            // FIXME(rylev): we hardcode the dep graph file name so we
+            // don't need a dependency on rustc_incremental just for that.
+            profiler.artifact_size("dep_graph", "dep-graph.bin", position as u64);
+        }
+        result
+    }
+}
+
+pub struct GraphEncoder<K: DepKind> {
+    status: Lock<EncoderState<K>>,
+    record_graph: Option<Lock<DepGraphQuery<K>>>,
+}
+
+impl<K: DepKind + Encodable<FileEncoder>> GraphEncoder<K> {
+    pub fn new(
+        encoder: FileEncoder,
+        prev_node_count: usize,
+        record_graph: bool,
+        record_stats: bool,
+    ) -> Self {
+        let record_graph =
+            if record_graph { Some(Lock::new(DepGraphQuery::new(prev_node_count))) } else { None };
+        let status = Lock::new(EncoderState::new(encoder, record_stats));
+        GraphEncoder { status, record_graph }
+    }
+
+    pub(crate) fn with_query(&self, f: impl Fn(&DepGraphQuery<K>)) {
+        if let Some(record_graph) = &self.record_graph {
+            f(&record_graph.lock())
+        }
+    }
+
+    pub(crate) fn print_incremental_info(
+        &self,
+        total_read_count: u64,
+        total_duplicate_read_count: u64,
+    ) {
+        let status = self.status.lock();
+        if let Some(record_stats) = &status.stats {
+            let mut stats: Vec<_> = record_stats.values().collect();
+            stats.sort_by_key(|s| -(s.node_counter as i64));
+
+            const SEPARATOR: &str = "[incremental] --------------------------------\
+                                     ----------------------------------------------\
+                                     ------------";
+
+            eprintln!("[incremental]");
+            eprintln!("[incremental] DepGraph Statistics");
+            eprintln!("{}", SEPARATOR);
+            eprintln!("[incremental]");
+            eprintln!("[incremental] Total Node Count: {}", status.total_node_count);
+            eprintln!("[incremental] Total Edge Count: {}", status.total_edge_count);
+
+            if cfg!(debug_assertions) {
+                eprintln!("[incremental] Total Edge Reads: {}", total_read_count);
+                eprintln!(
+                    "[incremental] Total Duplicate Edge Reads: {}",
+                    total_duplicate_read_count
+                );
+            }
+
+            eprintln!("[incremental]");
+            eprintln!(
+                "[incremental]  {:<36}| {:<17}| {:<12}| {:<17}|",
+                "Node Kind", "Node Frequency", "Node Count", "Avg. Edge Count"
+            );
+            eprintln!("{}", SEPARATOR);
+
+            for stat in stats {
+                let node_kind_ratio =
+                    (100.0 * (stat.node_counter as f64)) / (status.total_node_count as f64);
+                let node_kind_avg_edges = (stat.edge_counter as f64) / (stat.node_counter as f64);
+
+                eprintln!(
+                    "[incremental]  {:<36}|{:>16.1}% |{:>12} |{:>17.1} |",
+                    format!("{:?}", stat.kind),
+                    node_kind_ratio,
+                    stat.node_counter,
+                    node_kind_avg_edges,
+                );
+            }
+
+            eprintln!("{}", SEPARATOR);
+            eprintln!("[incremental]");
+        }
+    }
+
+    pub(crate) fn send(
+        &self,
+        profiler: &SelfProfilerRef,
+        node: DepNode<K>,
+        fingerprint: Fingerprint,
+        edges: SmallVec<[DepNodeIndex; 8]>,
+    ) -> DepNodeIndex {
+        let _prof_timer = profiler.generic_activity("incr_comp_encode_dep_graph");
+        let node = NodeInfo { node, fingerprint, edges };
+        self.status.lock().encode_node(&node, &self.record_graph)
+    }
+
+    pub fn finish(self, profiler: &SelfProfilerRef) -> FileEncodeResult {
+        let _prof_timer = profiler.generic_activity("incr_comp_encode_dep_graph");
+        self.status.into_inner().finish(profiler)
+    }
+}