rustc: don't keep a second reference to the HIR map in middle::region.

src/librustc/middle/region.rs

@@ -264,12 +264,10 @@ struct RegionResolutionVisitor<'a, 'tcx: 'a> {
     tcx: TyCtxt<'a, 'tcx, 'tcx>,
 
     // Generated maps:
-    region_maps: &'a mut RegionMaps,
+    region_maps: RegionMaps,
 
     cx: Context,
 
-    map: &'a hir_map::Map<'tcx>,
-
     /// `terminating_scopes` is a set containing the ids of each
     /// statement, or conditional/repeating expression. These scopes
     /// are calling "terminating scopes" because, when attempting to
@@ -1105,7 +1103,7 @@ impl<'a, 'tcx> Visitor<'tcx> for RegionResolutionVisitor<'a, 'tcx> {
 
     fn visit_body(&mut self, body: &'tcx hir::Body) {
         let body_id = body.id();
-        let owner_id = self.map.body_owner(body_id);
+        let owner_id = self.tcx.hir.body_owner(body_id);
 
         debug!("visit_body(id={:?}, span={:?}, body.id={:?}, cx.parent={:?})",
                owner_id,
@@ -1170,37 +1168,38 @@ fn region_maps<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>, def_id: DefId)
         return tcx.region_maps(closure_base_def_id);
     }
 
-    let mut maps = RegionMaps::new();
-
     let id = tcx.hir.as_local_node_id(def_id).unwrap();
-    if let Some(body) = tcx.hir.maybe_body_owned_by(id) {
-        maps.root_body = Some(body);
+    let maps = if let Some(body) = tcx.hir.maybe_body_owned_by(id) {
+        let mut visitor = RegionResolutionVisitor {
+            tcx,
+            region_maps: RegionMaps::new(),
+            cx: Context {
+                root_id: None,
+                parent: None,
+                var_parent: None,
+            },
+            terminating_scopes: NodeSet(),
+        };
+
+        visitor.region_maps.root_body = Some(body);
 
         // If the item is an associated const or a method,
         // record its impl/trait parent, as it can also have
         // lifetime parameters free in this body.
         match tcx.hir.get(id) {
             hir::map::NodeImplItem(_) |
             hir::map::NodeTraitItem(_) => {
-                maps.root_parent = Some(tcx.hir.get_parent(id));
+                visitor.region_maps.root_parent = Some(tcx.hir.get_parent(id));
             }
             _ => {}
         }
 
-        let mut visitor = RegionResolutionVisitor {
-            tcx: tcx,
-            region_maps: &mut maps,
-            map: &tcx.hir,
-            cx: Context {
-                root_id: None,
-                parent: None,
-                var_parent: None,
-            },
-            terminating_scopes: NodeSet(),
-        };
-
         visitor.visit_body(tcx.hir.body(body));
-    }
+
+        visitor.region_maps
+    } else {
+        RegionMaps::new()
+    };
 
     Rc::new(maps)
 }