Cache the specialization_graph query

Fixes rust-lang#48987

src/librustc/traits/specialize/specialization_graph.rs

@@ -36,6 +36,7 @@ use util::nodemap::{DefIdMap, FxHashMap};
 ///   parents of a given specializing impl, which is needed for extracting
 ///   default items amongst other things. In the simple "chain" rule, every impl
 ///   has at most one parent.
+#[derive(RustcEncodable, RustcDecodable)]
 pub struct Graph {
     // all impls have a parent; the "root" impls have as their parent the def_id
     // of the trait
@@ -47,6 +48,7 @@ pub struct Graph {
 
 /// Children of a given impl, grouped into blanket/non-blanket varieties as is
 /// done in `TraitDef`.
+#[derive(RustcEncodable, RustcDecodable)]
 struct Children {
     // Impls of a trait (or specializations of a given impl). To allow for
     // quicker lookup, the impls are indexed by a simplified version of their

src/librustc/ty/fast_reject.rs

@@ -28,7 +28,7 @@ pub type SimplifiedType = SimplifiedTypeGen<DefId>;
 /// because we sometimes need to use SimplifiedTypeGen values as stable sorting
 /// keys (in which case we use a DefPathHash as id-type) but in the general case
 /// the non-stable but fast to construct DefId-version is the better choice.
-#[derive(Clone, Copy, Debug, PartialEq, Eq, Hash, PartialOrd, Ord)]
+#[derive(Clone, Copy, Debug, PartialEq, Eq, Hash, PartialOrd, Ord, RustcEncodable, RustcDecodable)]
 pub enum SimplifiedTypeGen<D>
     where D: Copy + Debug + Ord + Eq + Hash
 {

src/librustc/ty/maps/config.rs

@@ -709,3 +709,4 @@ impl_disk_cacheable_query!(type_of, |def_id| def_id.is_local());
 impl_disk_cacheable_query!(predicates_of, |def_id| def_id.is_local());
 impl_disk_cacheable_query!(used_trait_imports, |def_id| def_id.is_local());
 impl_disk_cacheable_query!(trans_fn_attrs, |_| true);
+impl_disk_cacheable_query!(specialization_graph_of, |_| true);

src/librustc/ty/maps/on_disk_cache.rs

@@ -221,6 +221,7 @@ impl<'sess> OnDiskCache<'sess> {
                 encode_query_results::<symbol_name, _>(tcx, enc, qri)?;
                 encode_query_results::<check_match, _>(tcx, enc, qri)?;
                 encode_query_results::<trans_fn_attrs, _>(tcx, enc, qri)?;
+                encode_query_results::<specialization_graph_of, _>(tcx, enc, qri)?;
             }
 
             // Encode diagnostics

src/librustc/ty/maps/plumbing.rs

@@ -1001,4 +1001,5 @@ impl_load_from_cache!(
     PredicatesOfItem => predicates_of,
     UsedTraitImports => used_trait_imports,
     TransFnAttrs => trans_fn_attrs,
+    SpecializationGraph => specialization_graph_of,
 );