Remove closure_tree

compiler/rustc_middle/src/middle/region.rs

@@ -235,18 +235,6 @@ pub struct ScopeTree {
     /// escape into 'static and should have no local cleanup scope.
     rvalue_scopes: FxHashMap<hir::ItemLocalId, Option<Scope>>,
 
-    /// Encodes the hierarchy of fn bodies. Every fn body (including
-    /// closures) forms its own distinct region hierarchy, rooted in
-    /// the block that is the fn body. This map points from the ID of
-    /// that root block to the ID of the root block for the enclosing
-    /// fn, if any. Thus the map structures the fn bodies into a
-    /// hierarchy based on their lexical mapping. This is used to
-    /// handle the relationships between regions in a fn and in a
-    /// closure defined by that fn. See the "Modeling closures"
-    /// section of the README in infer::region_constraints for
-    /// more details.
-    closure_tree: FxHashMap<hir::ItemLocalId, hir::ItemLocalId>,
-
     /// If there are any `yield` nested within a scope, this map
     /// stores the `Span` of the last one and its index in the
     /// postorder of the Visitor traversal on the HIR.
@@ -356,23 +344,6 @@ impl ScopeTree {
         self.destruction_scopes.get(&n).cloned()
     }
 
-    /// Records that `sub_closure` is defined within `sup_closure`. These IDs
-    /// should be the ID of the block that is the fn body, which is
-    /// also the root of the region hierarchy for that fn.
-    pub fn record_closure_parent(
-        &mut self,
-        sub_closure: hir::ItemLocalId,
-        sup_closure: hir::ItemLocalId,
-    ) {
-        debug!(
-            "record_closure_parent(sub_closure={:?}, sup_closure={:?})",
-            sub_closure, sup_closure
-        );
-        assert!(sub_closure != sup_closure);
-        let previous = self.closure_tree.insert(sub_closure, sup_closure);
-        assert!(previous.is_none());
-    }
-
     pub fn record_var_scope(&mut self, var: hir::ItemLocalId, lifetime: Scope) {
         debug!("record_var_scope(sub={:?}, sup={:?})", var, lifetime);
         assert!(var != lifetime.item_local_id());
@@ -474,7 +445,6 @@ impl<'a> HashStable<StableHashingContext<'a>> for ScopeTree {
             ref var_map,
             ref destruction_scopes,
             ref rvalue_scopes,
-            ref closure_tree,
             ref yield_in_scope,
         } = *self;
 
@@ -488,7 +458,6 @@ impl<'a> HashStable<StableHashingContext<'a>> for ScopeTree {
         var_map.hash_stable(hcx, hasher);
         destruction_scopes.hash_stable(hcx, hasher);
         rvalue_scopes.hash_stable(hcx, hasher);
-        closure_tree.hash_stable(hcx, hasher);
         yield_in_scope.hash_stable(hcx, hasher);
     }
 }

compiler/rustc_passes/src/region.rs

@@ -23,14 +23,6 @@ use std::mem;
 
 #[derive(Debug, Copy, Clone)]
 pub struct Context {
-    /// The root of the current region tree. This is typically the id
-    /// of the innermost fn body. Each fn forms its own disjoint tree
-    /// in the region hierarchy. These fn bodies are themselves
-    /// arranged into a tree. See the "Modeling closures" section of
-    /// the README in `rustc_trait_selection::infer::region_constraints`
-    /// for more details.
-    root_id: Option<hir::ItemLocalId>,
-
     /// The scope that contains any new variables declared, plus its depth in
     /// the scope tree.
     var_parent: Option<(Scope, ScopeDepth)>,
@@ -743,11 +735,6 @@ impl<'tcx> Visitor<'tcx> for RegionResolutionVisitor<'tcx> {
         let outer_pessimistic_yield = mem::replace(&mut self.pessimistic_yield, false);
         self.terminating_scopes.insert(body.value.hir_id.local_id);
 
-        if let Some(root_id) = self.cx.root_id {
-            self.scope_tree.record_closure_parent(body.value.hir_id.local_id, root_id);
-        }
-        self.cx.root_id = Some(body.value.hir_id.local_id);
-
         self.enter_scope(Scope { id: body.value.hir_id.local_id, data: ScopeData::CallSite });
         self.enter_scope(Scope { id: body.value.hir_id.local_id, data: ScopeData::Arguments });
 
@@ -824,7 +811,7 @@ fn region_scope_tree(tcx: TyCtxt<'_>, def_id: DefId) -> &ScopeTree {
             tcx,
             scope_tree: ScopeTree::default(),
             expr_and_pat_count: 0,
-            cx: Context { root_id: None, parent: None, var_parent: None },
+            cx: Context { parent: None, var_parent: None },
             terminating_scopes: Default::default(),
             pessimistic_yield: false,
             fixup_scopes: vec![],