metadata: record unused_generic_params

This commit records the results of `unused_generic_params` in crate
metadata, hopefully improving performance.

Signed-off-by: David Wood <david@davidtw.co>

src/librustc_metadata/rmeta/decoder.rs

@@ -1132,6 +1132,16 @@ impl<'a, 'tcx> CrateMetadataRef<'a> {
             .decode((self, tcx))
     }
 
+    fn get_unused_generic_params(&self, id: DefIndex) -> u64 {
+        self.root
+            .tables
+            .unused_generic_params
+            .get(self, id)
+            .filter(|_| !self.is_proc_macro(id))
+            .map(|params| params.decode(self))
+            .unwrap_or_default()
+    }
+
     fn get_promoted_mir(&self, tcx: TyCtxt<'tcx>, id: DefIndex) -> IndexVec<Promoted, Body<'tcx>> {
         self.root
             .tables

src/librustc_metadata/rmeta/decoder/cstore_impl.rs

@@ -113,6 +113,7 @@ provide! { <'tcx> tcx, def_id, other, cdata,
     }
     optimized_mir => { tcx.arena.alloc(cdata.get_optimized_mir(tcx, def_id.index)) }
     promoted_mir => { tcx.arena.alloc(cdata.get_promoted_mir(tcx, def_id.index)) }
+    unused_generic_params => { cdata.get_unused_generic_params(def_id.index) }
     mir_const_qualif => { cdata.mir_const_qualif(def_id.index) }
     fn_sig => { cdata.fn_sig(def_id.index, tcx) }
     inherent_impls => { cdata.get_inherent_implementations_for_type(tcx, def_id.index) }

src/librustc_metadata/rmeta/encoder.rs

@@ -1065,6 +1065,8 @@ impl EncodeContext<'tcx> {
         debug!("EntryBuilder::encode_mir({:?})", def_id);
         if self.tcx.mir_keys(LOCAL_CRATE).contains(&def_id) {
             record!(self.tables.mir[def_id.to_def_id()] <- self.tcx.optimized_mir(def_id));
+            record!(self.tables.unused_generic_params[def_id.to_def_id()] <-
+                    self.tcx.unused_generic_params(def_id));
         }
     }
 

src/librustc_metadata/rmeta/mod.rs

@@ -277,6 +277,7 @@ define_tables! {
     super_predicates: Table<DefIndex, Lazy!(ty::GenericPredicates<'tcx>)>,
     mir: Table<DefIndex, Lazy!(mir::Body<'tcx>)>,
     promoted_mir: Table<DefIndex, Lazy!(IndexVec<mir::Promoted, mir::Body<'tcx>>)>,
+    unused_generic_params: Table<DefIndex, Lazy<u64>>,
 }
 
 #[derive(Copy, Clone, RustcEncodable, RustcDecodable)]