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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
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+++ 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)
+    }
+}