Serialize dependency graph directly from DepGraph

Reduce memory usage by serializing dep graph directly from `DepGraph`,
rather than copying it into `SerializedDepGraph` and serializing that.

compiler/rustc_incremental/src/persist/save.rs

@@ -1,6 +1,6 @@
 use rustc_data_structures::fx::FxHashMap;
 use rustc_data_structures::sync::join;
-use rustc_middle::dep_graph::{DepGraph, DepKind, WorkProduct, WorkProductId};
+use rustc_middle::dep_graph::{DepGraph, WorkProduct, WorkProductId};
 use rustc_middle::ty::TyCtxt;
 use rustc_serialize::opaque::{FileEncodeResult, FileEncoder};
 use rustc_serialize::Encodable as RustcEncodable;
@@ -148,83 +148,15 @@ fn encode_dep_graph(tcx: TyCtxt<'_>, encoder: &mut FileEncoder) -> FileEncodeRes
     // First encode the commandline arguments hash
     tcx.sess.opts.dep_tracking_hash().encode(encoder)?;
 
-    // Encode the graph data.
-    let serialized_graph =
-        tcx.sess.time("incr_comp_serialize_dep_graph", || tcx.dep_graph.serialize());
-
     if tcx.sess.opts.debugging_opts.incremental_info {
-        #[derive(Clone)]
+        tcx.dep_graph.print_incremental_info();
-        struct Stat {
-            kind: DepKind,
-            node_counter: u64,
-            edge_counter: u64,
-        }
-
-        let total_node_count = serialized_graph.nodes.len();
-        let total_edge_count = serialized_graph.edge_list_data.len();
-
-        let mut counts: FxHashMap<_, Stat> =
-            FxHashMap::with_capacity_and_hasher(total_node_count, Default::default());
-
-        for (i, &node) in serialized_graph.nodes.iter_enumerated() {
-            let stat = counts.entry(node.kind).or_insert(Stat {
-                kind: node.kind,
-                node_counter: 0,
-                edge_counter: 0,
-            });
-
-            stat.node_counter += 1;
-            let (edge_start, edge_end) = serialized_graph.edge_list_indices[i];
-            stat.edge_counter += (edge_end - edge_start) as u64;
-        }
-
-        let mut counts: Vec<_> = counts.values().cloned().collect();
-        counts.sort_by_key(|s| -(s.node_counter as i64));
-
-        println!("[incremental]");
-        println!("[incremental] DepGraph Statistics");
-
-        const SEPARATOR: &str = "[incremental] --------------------------------\
-                                 ----------------------------------------------\
-                                 ------------";
-
-        println!("{}", SEPARATOR);
-        println!("[incremental]");
-        println!("[incremental] Total Node Count: {}", total_node_count);
-        println!("[incremental] Total Edge Count: {}", total_edge_count);
-        if let Some((total_edge_reads, total_duplicate_edge_reads)) =
-            tcx.dep_graph.edge_deduplication_data()
-        {
-            println!("[incremental] Total Edge Reads: {}", total_edge_reads);
-            println!("[incremental] Total Duplicate Edge Reads: {}", total_duplicate_edge_reads);
-        }
-        println!("[incremental]");
-        println!(
-            "[incremental]  {:<36}| {:<17}| {:<12}| {:<17}|",
-            "Node Kind", "Node Frequency", "Node Count", "Avg. Edge Count"
-        );
-        println!(
-            "[incremental] -------------------------------------\
-                  |------------------\
-                  |-------------\
-                  |------------------|"
-        );
-
-        for stat in counts.iter() {
-            println!(
-                "[incremental]  {:<36}|{:>16.1}% |{:>12} |{:>17.1} |",
-                format!("{:?}", stat.kind),
-                (100.0 * (stat.node_counter as f64)) / (total_node_count as f64), // percentage of all nodes
-                stat.node_counter,
-                (stat.edge_counter as f64) / (stat.node_counter as f64), // average edges per kind
-            );
-        }
-
-        println!("{}", SEPARATOR);
-        println!("[incremental]");
     }
 
-    tcx.sess.time("incr_comp_encode_serialized_dep_graph", || serialized_graph.encode(encoder))
+    // There is a tiny window between printing the incremental info above and encoding the dep
+    // graph below in which the dep graph could change, thus making the printed incremental info
+    // slightly out of date. If this matters to you, please feel free to submit a patch. :)
+
+    tcx.sess.time("incr_comp_encode_serialized_dep_graph", || tcx.dep_graph.encode(encoder))
 }
 
 fn encode_work_product_index(

compiler/rustc_query_system/src/dep_graph/graph.rs

@@ -7,6 +7,7 @@
 use rustc_data_structures::unlikely;
 use rustc_errors::Diagnostic;
 use rustc_index::vec::{Idx, IndexVec};
+use rustc_serialize::{Encodable, Encoder};
 
 use parking_lot::{Condvar, Mutex};
 use smallvec::{smallvec, SmallVec};
@@ -21,7 +22,7 @@
 use super::debug::EdgeFilter;
 use super::prev::PreviousDepGraph;
 use super::query::DepGraphQuery;
-use super::serialized::{SerializedDepGraph, SerializedDepNodeIndex};
+use super::serialized::SerializedDepNodeIndex;
 use super::{DepContext, DepKind, DepNode, WorkProductId};
 
 #[derive(Clone)]
@@ -148,7 +149,7 @@ pub fn query(&self) -> DepGraphQuery<K> {
         let mut edge_list_indices = Vec::with_capacity(node_count);
         let mut edge_list_data = Vec::with_capacity(edge_count);
 
-        // See `serialize` for notes on the approach used here.
+        // See `DepGraph`'s `Encodable` implementation for notes on the approach used here.
 
         edge_list_data.extend(data.unshared_edges.iter().map(|i| i.index()));
 
@@ -551,19 +552,6 @@ 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()
     }
 
-    pub fn edge_deduplication_data(&self) -> Option<(u64, u64)> {
-        if cfg!(debug_assertions) {
-            let current_dep_graph = &self.data.as_ref().unwrap().current;
-
-            Some((
-                current_dep_graph.total_read_count.load(Relaxed),
-                current_dep_graph.total_duplicate_read_count.load(Relaxed),
-            ))
-        } else {
-            None
-        }
-    }
-
     fn edge_count(&self, node_data: &LockGuard<'_, DepNodeData<K>>) -> usize {
         let data = self.data.as_ref().unwrap();
         let previous = &data.previous;
@@ -579,84 +567,6 @@ fn edge_count(&self, node_data: &LockGuard<'_, DepNodeData<K>>) -> usize {
         edge_count
     }
 
-    pub fn serialize(&self) -> SerializedDepGraph<K> {
-        type SDNI = SerializedDepNodeIndex;
-
-        let data = self.data.as_ref().unwrap();
-        let previous = &data.previous;
-
-        // Note locking order: `prev_index_to_index`, then `data`.
-        let prev_index_to_index = data.current.prev_index_to_index.lock();
-        let data = data.current.data.lock();
-        let node_count = data.hybrid_indices.len();
-        let edge_count = self.edge_count(&data);
-
-        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);
-
-        // `rustc_middle::ty::query::OnDiskCache` expects nodes to be in
-        // `DepNodeIndex` order. The edges in `edge_list_data`, on the other
-        // hand, don't need to be in a particular order, as long as each node
-        // can reference its edges as a contiguous range within it. This is why
-        // we're able to copy `unshared_edges` directly into `edge_list_data`.
-        // It meets the above requirements, and each non-dark-green node already
-        // knows the range of edges to reference within it, which they'll push
-        // onto `edge_list_indices`. Dark green nodes, however, don't have their
-        // edges in `unshared_edges`, so need to add them to `edge_list_data`.
-
-        edge_list_data.extend(data.unshared_edges.iter().map(|i| SDNI::new(i.index())));
-
-        for &hybrid_index in data.hybrid_indices.iter() {
-            match hybrid_index.into() {
-                HybridIndex::New(i) => {
-                    let new = &data.new;
-                    nodes.push(new.nodes[i]);
-                    fingerprints.push(new.fingerprints[i]);
-                    let edges = &new.edges[i];
-                    edge_list_indices.push((edges.start.as_u32(), edges.end.as_u32()));
-                }
-                HybridIndex::Red(i) => {
-                    let red = &data.red;
-                    nodes.push(previous.index_to_node(red.node_indices[i]));
-                    fingerprints.push(red.fingerprints[i]);
-                    let edges = &red.edges[i];
-                    edge_list_indices.push((edges.start.as_u32(), edges.end.as_u32()));
-                }
-                HybridIndex::LightGreen(i) => {
-                    let lg = &data.light_green;
-                    nodes.push(previous.index_to_node(lg.node_indices[i]));
-                    fingerprints.push(previous.fingerprint_by_index(lg.node_indices[i]));
-                    let edges = &lg.edges[i];
-                    edge_list_indices.push((edges.start.as_u32(), edges.end.as_u32()));
-                }
-                HybridIndex::DarkGreen(prev_index) => {
-                    nodes.push(previous.index_to_node(prev_index));
-                    fingerprints.push(previous.fingerprint_by_index(prev_index));
-
-                    let edges_iter = previous
-                        .edge_targets_from(prev_index)
-                        .iter()
-                        .map(|&dst| prev_index_to_index[dst].as_ref().unwrap());
-
-                    let start = edge_list_data.len() as u32;
-                    edge_list_data.extend(edges_iter.map(|i| SDNI::new(i.index())));
-                    let end = edge_list_data.len() as u32;
-                    edge_list_indices.push((start, end));
-                }
-            }
-        }
-
-        debug_assert_eq!(nodes.len(), node_count);
-        debug_assert_eq!(fingerprints.len(), node_count);
-        debug_assert_eq!(edge_list_indices.len(), node_count);
-        debug_assert_eq!(edge_list_data.len(), edge_count);
-        debug_assert!(edge_list_data.len() <= u32::MAX as usize);
-
-        SerializedDepGraph { nodes, fingerprints, edge_list_indices, edge_list_data }
-    }
-
     pub 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) {
@@ -997,12 +907,251 @@ pub fn register_reused_dep_nodes<Ctxt: DepContext<DepKind = K>>(&self, tcx: Ctxt
         }
     }
 
+    pub fn print_incremental_info(&self) {
+        #[derive(Clone)]
+        struct Stat<Kind: DepKind> {
+            kind: Kind,
+            node_counter: u64,
+            edge_counter: u64,
+        }
+
+        let data = self.data.as_ref().unwrap();
+        let prev = &data.previous;
+        let current = &data.current;
+        let data = current.data.lock();
+
+        let mut stats: FxHashMap<_, Stat<K>> = FxHashMap::with_hasher(Default::default());
+
+        for &hybrid_index in data.hybrid_indices.iter() {
+            let (kind, edge_count) = match hybrid_index.into() {
+                HybridIndex::New(new_index) => {
+                    let kind = data.new.nodes[new_index].kind;
+                    let edge_range = &data.new.edges[new_index];
+                    (kind, edge_range.end.as_usize() - edge_range.start.as_usize())
+                }
+                HybridIndex::Red(red_index) => {
+                    let kind = prev.index_to_node(data.red.node_indices[red_index]).kind;
+                    let edge_range = &data.red.edges[red_index];
+                    (kind, edge_range.end.as_usize() - edge_range.start.as_usize())
+                }
+                HybridIndex::LightGreen(lg_index) => {
+                    let kind = prev.index_to_node(data.light_green.node_indices[lg_index]).kind;
+                    let edge_range = &data.light_green.edges[lg_index];
+                    (kind, edge_range.end.as_usize() - edge_range.start.as_usize())
+                }
+                HybridIndex::DarkGreen(prev_index) => {
+                    let kind = prev.index_to_node(prev_index).kind;
+                    let edge_count = prev.edge_targets_from(prev_index).len();
+                    (kind, edge_count)
+                }
+            };
+
+            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 total_node_count = data.hybrid_indices.len();
+        let total_edge_count = self.edge_count(&data);
+
+        // Drop the lock guard.
+        std::mem::drop(data);
+
+        let mut stats: Vec<_> = stats.values().cloned().collect();
+        stats.sort_by_key(|s| -(s.node_counter as i64));
+
+        const SEPARATOR: &str = "[incremental] --------------------------------\
+                                 ----------------------------------------------\
+                                 ------------";
+
+        println!("[incremental]");
+        println!("[incremental] DepGraph Statistics");
+        println!("{}", SEPARATOR);
+        println!("[incremental]");
+        println!("[incremental] Total Node Count: {}", total_node_count);
+        println!("[incremental] Total Edge Count: {}", total_edge_count);
+
+        if cfg!(debug_assertions) {
+            let total_edge_reads = current.total_read_count.load(Relaxed);
+            let total_duplicate_edge_reads = current.total_duplicate_read_count.load(Relaxed);
+
+            println!("[incremental] Total Edge Reads: {}", total_edge_reads);
+            println!("[incremental] Total Duplicate Edge Reads: {}", total_duplicate_edge_reads);
+        }
+
+        println!("[incremental]");
+
+        println!(
+            "[incremental]  {:<36}| {:<17}| {:<12}| {:<17}|",
+            "Node Kind", "Node Frequency", "Node Count", "Avg. Edge Count"
+        );
+
+        println!(
+            "[incremental] -------------------------------------\
+                  |------------------\
+                  |-------------\
+                  |------------------|"
+        );
+
+        for stat in stats {
+            let node_kind_ratio = (100.0 * (stat.node_counter as f64)) / (total_node_count as f64);
+            let node_kind_avg_edges = (stat.edge_counter as f64) / (stat.node_counter as f64);
+
+            println!(
+                "[incremental]  {:<36}|{:>16.1}% |{:>12} |{:>17.1} |",
+                format!("{:?}", stat.kind),
+                node_kind_ratio,
+                stat.node_counter,
+                node_kind_avg_edges,
+            );
+        }
+
+        println!("{}", SEPARATOR);
+        println!("[incremental]");
+    }
+
     fn next_virtual_depnode_index(&self) -> DepNodeIndex {
         let index = self.virtual_dep_node_index.fetch_add(1, Relaxed);
         DepNodeIndex::from_u32(index)
     }
 }
 
+impl<E: Encoder, K: DepKind + Encodable<E>> Encodable<E> for DepGraph<K> {
+    fn encode(&self, e: &mut E) -> Result<(), E::Error> {
+        // We used to serialize the dep graph by creating and serializing a `SerializedDepGraph`
+        // using data copied from the `DepGraph`. But copying created a large memory spike, so we
+        // now serialize directly from the `DepGraph` as if it's a `SerializedDepGraph`. Because we
+        // deserialize that data into a `SerializedDepGraph` in the next compilation session, we
+        // need `DepGraph`'s `Encodable` and `SerializedDepGraph`'s `Decodable` implementations to
+        // be in sync. If you update this encoding, be sure to update the decoding, and vice-versa.
+
+        let data = self.data.as_ref().unwrap();
+        let prev = &data.previous;
+
+        // Note locking order: `prev_index_to_index`, then `data`.
+        let prev_index_to_index = data.current.prev_index_to_index.lock();
+        let data = data.current.data.lock();
+        let new = &data.new;
+        let red = &data.red;
+        let lg = &data.light_green;
+
+        let node_count = data.hybrid_indices.len();
+        let edge_count = self.edge_count(&data);
+
+        // `rustc_middle::ty::query::OnDiskCache` expects nodes to be encoded in `DepNodeIndex`
+        // order. The edges in `edge_list_data` don't need to be in a particular order, as long as
+        // each node references its edges as a contiguous range within it. Therefore, we can encode
+        // `edge_list_data` directly from `unshared_edges`. It meets the above requirements, as
+        // each non-dark-green node already knows the range of edges to reference within it, which
+        // they'll encode in `edge_list_indices`. Dark green nodes, however, don't have their edges
+        // in `unshared_edges`, so need to add them to `edge_list_data`.
+
+        use HybridIndex::*;
+
+        // Encoded values (nodes, etc.) are explicitly typed below to avoid inadvertently
+        // serializing data in the wrong format (i.e. one incompatible with `SerializedDepGraph`).
+        e.emit_struct("SerializedDepGraph", 4, |e| {
+            e.emit_struct_field("nodes", 0, |e| {
+                // `SerializedDepGraph` expects this to be encoded as a sequence of `DepNode`s.
+                e.emit_seq(node_count, |e| {
+                    for (seq_index, &hybrid_index) in data.hybrid_indices.iter().enumerate() {
+                        let node: DepNode<K> = match hybrid_index.into() {
+                            New(i) => new.nodes[i],
+                            Red(i) => prev.index_to_node(red.node_indices[i]),
+                            LightGreen(i) => prev.index_to_node(lg.node_indices[i]),
+                            DarkGreen(prev_index) => prev.index_to_node(prev_index),
+                        };
+
+                        e.emit_seq_elt(seq_index, |e| node.encode(e))?;
+                    }
+
+                    Ok(())
+                })
+            })?;
+
+            e.emit_struct_field("fingerprints", 1, |e| {
+                // `SerializedDepGraph` expects this to be encoded as a sequence of `Fingerprints`s.
+                e.emit_seq(node_count, |e| {
+                    for (seq_index, &hybrid_index) in data.hybrid_indices.iter().enumerate() {
+                        let fingerprint: Fingerprint = match hybrid_index.into() {
+                            New(i) => new.fingerprints[i],
+                            Red(i) => red.fingerprints[i],
+                            LightGreen(i) => prev.fingerprint_by_index(lg.node_indices[i]),
+                            DarkGreen(prev_index) => prev.fingerprint_by_index(prev_index),
+                        };
+
+                        e.emit_seq_elt(seq_index, |e| fingerprint.encode(e))?;
+                    }
+
+                    Ok(())
+                })
+            })?;
+
+            e.emit_struct_field("edge_list_indices", 2, |e| {
+                // `SerializedDepGraph` expects this to be encoded as a sequence of `(u32, u32)`s.
+                e.emit_seq(node_count, |e| {
+                    // Dark green node edges start after the unshared (all other nodes') edges.
+                    let mut dark_green_edge_index = data.unshared_edges.len();
+
+                    for (seq_index, &hybrid_index) in data.hybrid_indices.iter().enumerate() {
+                        let edge_indices: (u32, u32) = match hybrid_index.into() {
+                            New(i) => (new.edges[i].start.as_u32(), new.edges[i].end.as_u32()),
+                            Red(i) => (red.edges[i].start.as_u32(), red.edges[i].end.as_u32()),
+                            LightGreen(i) => (lg.edges[i].start.as_u32(), lg.edges[i].end.as_u32()),
+                            DarkGreen(prev_index) => {
+                                let edge_count = prev.edge_targets_from(prev_index).len();
+                                let start = dark_green_edge_index as u32;
+                                dark_green_edge_index += edge_count;
+                                let end = dark_green_edge_index as u32;
+                                (start, end)
+                            }
+                        };
+
+                        e.emit_seq_elt(seq_index, |e| edge_indices.encode(e))?;
+                    }
+
+                    assert_eq!(dark_green_edge_index, edge_count);
+
+                    Ok(())
+                })
+            })?;
+
+            e.emit_struct_field("edge_list_data", 3, |e| {
+                // `SerializedDepGraph` expects this to be encoded as a sequence of
+                // `SerializedDepNodeIndex`.
+                e.emit_seq(edge_count, |e| {
+                    for (seq_index, &edge) in data.unshared_edges.iter().enumerate() {
+                        let serialized_edge = SerializedDepNodeIndex::new(edge.index());
+                        e.emit_seq_elt(seq_index, |e| serialized_edge.encode(e))?;
+                    }
+
+                    let mut seq_index = data.unshared_edges.len();
+
+                    for &hybrid_index in data.hybrid_indices.iter() {
+                        if let DarkGreen(prev_index) = hybrid_index.into() {
+                            for &edge in prev.edge_targets_from(prev_index) {
+                                // Dark green node edges are stored in the previous graph
+                                // and must be converted to edges in the current graph,
+                                // and then serialized as `SerializedDepNodeIndex`.
+                                let serialized_edge = SerializedDepNodeIndex::new(
+                                    prev_index_to_index[edge].as_ref().unwrap().index(),
+                                );
+
+                                e.emit_seq_elt(seq_index, |e| serialized_edge.encode(e))?;
+                                seq_index += 1;
+                            }
+                        }
+                    }
+
+                    assert_eq!(seq_index, edge_count);
+
+                    Ok(())
+                })
+            })
+        })
+    }
+}
+
 /// 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

compiler/rustc_query_system/src/dep_graph/prev.rs

@@ -3,7 +3,7 @@
 use rustc_data_structures::fingerprint::Fingerprint;
 use rustc_data_structures::fx::FxHashMap;
 
-#[derive(Debug, Encodable, Decodable)]
+#[derive(Debug)]
 pub struct PreviousDepGraph<K: DepKind> {
     data: SerializedDepGraph<K>,
     index: FxHashMap<DepNode<K>, SerializedDepNodeIndex>,

compiler/rustc_query_system/src/dep_graph/serialized.rs

@@ -3,6 +3,7 @@
 use super::{DepKind, DepNode};
 use rustc_data_structures::fingerprint::Fingerprint;
 use rustc_index::vec::IndexVec;
+use rustc_serialize::{Decodable, Decoder};
 
 // The maximum value of `SerializedDepNodeIndex` leaves the upper two bits
 // unused so that we can store multiple index types in `CompressedHybridIndex`,
@@ -14,7 +15,7 @@ pub struct SerializedDepNodeIndex {
 }
 
 /// Data for use when recompiling the **current crate**.
-#[derive(Debug, Encodable, Decodable)]
+#[derive(Debug)]
 pub struct SerializedDepGraph<K: DepKind> {
     /// The set of all DepNodes in the graph
     pub nodes: IndexVec<SerializedDepNodeIndex, DepNode<K>>,
@@ -48,3 +49,79 @@ pub fn edge_targets_from(&self, source: SerializedDepNodeIndex) -> &[SerializedD
         &self.edge_list_data[targets.0 as usize..targets.1 as usize]
     }
 }
+
+impl<D: Decoder, K: DepKind + Decodable<D>> Decodable<D> for SerializedDepGraph<K> {
+    fn decode(d: &mut D) -> Result<SerializedDepGraph<K>, D::Error> {
+        // We used to serialize the dep graph by creating and serializing a `SerializedDepGraph`
+        // using data copied from the `DepGraph`. But copying created a large memory spike, so we
+        // now serialize directly from the `DepGraph` as if it's a `SerializedDepGraph`. Because we
+        // deserialize that data into a `SerializedDepGraph` in the next compilation session, we
+        // need `DepGraph`'s `Encodable` and `SerializedDepGraph`'s `Decodable` implementations to
+        // be in sync. If you update this decoding, be sure to update the encoding, and vice-versa.
+        //
+        // We mimic the sequence of `Encode` and `Encodable` method calls used by the `DepGraph`'s
+        // `Encodable` implementation with the corresponding sequence of `Decode` and `Decodable`
+        // method calls. E.g. `Decode::read_struct` pairs with `Encode::emit_struct`, `DepNode`'s
+        // `decode` pairs with `DepNode`'s `encode`, and so on. Any decoding methods not associated
+        // with corresponding encoding methods called in `DepGraph`'s `Encodable` implementation
+        // are off limits, because we'd be relying on their implementation details.
+        //
+        // For example, because we know it happens to do the right thing, its tempting to just use
+        // `IndexVec`'s `Decodable` implementation to decode into some of the collections below,
+        // even though `DepGraph` doesn't use its `Encodable` implementation. But the `IndexVec`
+        // implementation could change, and we'd have a bug.
+        //
+        // Variables below are explicitly typed so that anyone who changes the `SerializedDepGraph`
+        // representation without updating this function will encounter a compilation error, and
+        // know to update this and possibly the `DepGraph` `Encodable` implementation accordingly
+        // (the latter should serialize data in a format compatible with our representation).
+
+        d.read_struct("SerializedDepGraph", 4, |d| {
+            let nodes: IndexVec<SerializedDepNodeIndex, DepNode<K>> =
+                d.read_struct_field("nodes", 0, |d| {
+                    d.read_seq(|d, len| {
+                        let mut v = IndexVec::with_capacity(len);
+                        for i in 0..len {
+                            v.push(d.read_seq_elt(i, |d| Decodable::decode(d))?);
+                        }
+                        Ok(v)
+                    })
+                })?;
+
+            let fingerprints: IndexVec<SerializedDepNodeIndex, Fingerprint> =
+                d.read_struct_field("fingerprints", 1, |d| {
+                    d.read_seq(|d, len| {
+                        let mut v = IndexVec::with_capacity(len);
+                        for i in 0..len {
+                            v.push(d.read_seq_elt(i, |d| Decodable::decode(d))?);
+                        }
+                        Ok(v)
+                    })
+                })?;
+
+            let edge_list_indices: IndexVec<SerializedDepNodeIndex, (u32, u32)> = d
+                .read_struct_field("edge_list_indices", 2, |d| {
+                    d.read_seq(|d, len| {
+                        let mut v = IndexVec::with_capacity(len);
+                        for i in 0..len {
+                            v.push(d.read_seq_elt(i, |d| Decodable::decode(d))?);
+                        }
+                        Ok(v)
+                    })
+                })?;
+
+            let edge_list_data: Vec<SerializedDepNodeIndex> =
+                d.read_struct_field("edge_list_data", 3, |d| {
+                    d.read_seq(|d, len| {
+                        let mut v = Vec::with_capacity(len);
+                        for i in 0..len {
+                            v.push(d.read_seq_elt(i, |d| Decodable::decode(d))?);
+                        }
+                        Ok(v)
+                    })
+                })?;
+
+            Ok(SerializedDepGraph { nodes, fingerprints, edge_list_indices, edge_list_data })
+        })
+    }
+}