Move region_scope_tree query to librustc_passes.

4 files changed, 683 insertions, 719 deletions

diff --git a/src/librustc/middle/region.rs b/src/librustc/middle/region.rs
new file mode 100644
index 00000000000..7f9c4aec3e3
--- /dev/null
+++ b/src/librustc/middle/region.rs
@@ -0,0 +1,670 @@
+//! This file builds up the `ScopeTree`, which describes
+//! the parent links in the region hierarchy.
+//!
+//! For more information about how MIR-based region-checking works,
+//! see the [rustc guide].
+//!
+//! [rustc guide]: https://rust-lang.github.io/rustc-guide/mir/borrowck.html
+
+use crate::hir;
+use crate::hir::def_id::DefId;
+use crate::hir::Node;
+use crate::ich::{NodeIdHashingMode, StableHashingContext};
+use crate::ty::{self, DefIdTree, TyCtxt};
+use crate::util::nodemap::FxHashMap;
+
+use rustc_data_structures::stable_hasher::{HashStable, StableHasher};
+use rustc_index::vec::Idx;
+use rustc_macros::HashStable;
+use syntax_pos::{Span, DUMMY_SP};
+
+use std::fmt;
+
+/// Represents a statically-describable scope that can be used to
+/// bound the lifetime/region for values.
+///
+/// `Node(node_id)`: Any AST node that has any scope at all has the
+/// `Node(node_id)` scope. Other variants represent special cases not
+/// immediately derivable from the abstract syntax tree structure.
+///
+/// `DestructionScope(node_id)` represents the scope of destructors
+/// implicitly-attached to `node_id` that run immediately after the
+/// expression for `node_id` itself. Not every AST node carries a
+/// `DestructionScope`, but those that are `terminating_scopes` do;
+/// see discussion with `ScopeTree`.
+///
+/// `Remainder { block, statement_index }` represents
+/// the scope of user code running immediately after the initializer
+/// expression for the indexed statement, until the end of the block.
+///
+/// So: the following code can be broken down into the scopes beneath:
+///
+/// ```text
+/// let a = f().g( 'b: { let x = d(); let y = d(); x.h(y)  }   ) ;
+///
+///                                                              +-+ (D12.)
+///                                                        +-+       (D11.)
+///                                              +---------+         (R10.)
+///                                              +-+                  (D9.)
+///                                   +----------+                    (M8.)
+///                                 +----------------------+          (R7.)
+///                                 +-+                               (D6.)
+///                      +----------+                                 (M5.)
+///                    +-----------------------------------+          (M4.)
+///         +--------------------------------------------------+      (M3.)
+///         +--+                                                      (M2.)
+/// +-----------------------------------------------------------+     (M1.)
+///
+///  (M1.): Node scope of the whole `let a = ...;` statement.
+///  (M2.): Node scope of the `f()` expression.
+///  (M3.): Node scope of the `f().g(..)` expression.
+///  (M4.): Node scope of the block labeled `'b:`.
+///  (M5.): Node scope of the `let x = d();` statement
+///  (D6.): DestructionScope for temporaries created during M5.
+///  (R7.): Remainder scope for block `'b:`, stmt 0 (let x = ...).
+///  (M8.): Node scope of the `let y = d();` statement.
+///  (D9.): DestructionScope for temporaries created during M8.
+/// (R10.): Remainder scope for block `'b:`, stmt 1 (let y = ...).
+/// (D11.): DestructionScope for temporaries and bindings from block `'b:`.
+/// (D12.): DestructionScope for temporaries created during M1 (e.g., f()).
+/// ```
+///
+/// Note that while the above picture shows the destruction scopes
+/// as following their corresponding node scopes, in the internal
+/// data structures of the compiler the destruction scopes are
+/// represented as enclosing parents. This is sound because we use the
+/// enclosing parent relationship just to ensure that referenced
+/// values live long enough; phrased another way, the starting point
+/// of each range is not really the important thing in the above
+/// picture, but rather the ending point.
+//
+// FIXME(pnkfelix): this currently derives `PartialOrd` and `Ord` to
+// placate the same deriving in `ty::FreeRegion`, but we may want to
+// actually attach a more meaningful ordering to scopes than the one
+// generated via deriving here.
+#[derive(
+    Clone,
+    PartialEq,
+    PartialOrd,
+    Eq,
+    Ord,
+    Hash,
+    Copy,
+    RustcEncodable,
+    RustcDecodable,
+    HashStable
+)]
+pub struct Scope {
+    pub id: hir::ItemLocalId,
+    pub data: ScopeData,
+}
+
+impl fmt::Debug for Scope {
+    fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
+        match self.data {
+            ScopeData::Node => write!(fmt, "Node({:?})", self.id),
+            ScopeData::CallSite => write!(fmt, "CallSite({:?})", self.id),
+            ScopeData::Arguments => write!(fmt, "Arguments({:?})", self.id),
+            ScopeData::Destruction => write!(fmt, "Destruction({:?})", self.id),
+            ScopeData::Remainder(fsi) => write!(
+                fmt,
+                "Remainder {{ block: {:?}, first_statement_index: {}}}",
+                self.id,
+                fsi.as_u32(),
+            ),
+        }
+    }
+}
+
+#[derive(
+    Clone,
+    PartialEq,
+    PartialOrd,
+    Eq,
+    Ord,
+    Hash,
+    Debug,
+    Copy,
+    RustcEncodable,
+    RustcDecodable,
+    HashStable
+)]
+pub enum ScopeData {
+    Node,
+
+    /// Scope of the call-site for a function or closure
+    /// (outlives the arguments as well as the body).
+    CallSite,
+
+    /// Scope of arguments passed to a function or closure
+    /// (they outlive its body).
+    Arguments,
+
+    /// Scope of destructors for temporaries of node-id.
+    Destruction,
+
+    /// Scope following a `let id = expr;` binding in a block.
+    Remainder(FirstStatementIndex),
+}
+
+rustc_index::newtype_index! {
+    /// Represents a subscope of `block` for a binding that is introduced
+    /// by `block.stmts[first_statement_index]`. Such subscopes represent
+    /// a suffix of the block. Note that each subscope does not include
+    /// the initializer expression, if any, for the statement indexed by
+    /// `first_statement_index`.
+    ///
+    /// For example, given `{ let (a, b) = EXPR_1; let c = EXPR_2; ... }`:
+    ///
+    /// * The subscope with `first_statement_index == 0` is scope of both
+    ///   `a` and `b`; it does not include EXPR_1, but does include
+    ///   everything after that first `let`. (If you want a scope that
+    ///   includes EXPR_1 as well, then do not use `Scope::Remainder`,
+    ///   but instead another `Scope` that encompasses the whole block,
+    ///   e.g., `Scope::Node`.
+    ///
+    /// * The subscope with `first_statement_index == 1` is scope of `c`,
+    ///   and thus does not include EXPR_2, but covers the `...`.
+    pub struct FirstStatementIndex {
+        derive [HashStable]
+    }
+}
+
+// compilation error if size of `ScopeData` is not the same as a `u32`
+static_assert_size!(ScopeData, 4);
+
+impl Scope {
+    /// Returns a item-local ID associated with this scope.
+    ///
+    /// N.B., likely to be replaced as API is refined; e.g., pnkfelix
+    /// anticipates `fn entry_node_id` and `fn each_exit_node_id`.
+    pub fn item_local_id(&self) -> hir::ItemLocalId {
+        self.id
+    }
+
+    pub fn hir_id(&self, scope_tree: &ScopeTree) -> hir::HirId {
+        match scope_tree.root_body {
+            Some(hir_id) => hir::HirId { owner: hir_id.owner, local_id: self.item_local_id() },
+            None => hir::DUMMY_HIR_ID,
+        }
+    }
+
+    /// Returns the span of this `Scope`. Note that in general the
+    /// returned span may not correspond to the span of any `NodeId` in
+    /// the AST.
+    pub fn span(&self, tcx: TyCtxt<'_>, scope_tree: &ScopeTree) -> Span {
+        let hir_id = self.hir_id(scope_tree);
+        if hir_id == hir::DUMMY_HIR_ID {
+            return DUMMY_SP;
+        }
+        let span = tcx.hir().span(hir_id);
+        if let ScopeData::Remainder(first_statement_index) = self.data {
+            if let Node::Block(ref blk) = tcx.hir().get(hir_id) {
+                // Want span for scope starting after the
+                // indexed statement and ending at end of
+                // `blk`; reuse span of `blk` and shift `lo`
+                // forward to end of indexed statement.
+                //
+                // (This is the special case aluded to in the
+                // doc-comment for this method)
+
+                let stmt_span = blk.stmts[first_statement_index.index()].span;
+
+                // To avoid issues with macro-generated spans, the span
+                // of the statement must be nested in that of the block.
+                if span.lo() <= stmt_span.lo() && stmt_span.lo() <= span.hi() {
+                    return Span::new(stmt_span.lo(), span.hi(), span.ctxt());
+                }
+            }
+        }
+        span
+    }
+}
+
+pub type ScopeDepth = u32;
+
+/// The region scope tree encodes information about region relationships.
+#[derive(Default, Debug)]
+pub struct ScopeTree {
+    /// If not empty, this body is the root of this region hierarchy.
+    pub root_body: Option<hir::HirId>,
+
+    /// The parent of the root body owner, if the latter is an
+    /// an associated const or method, as impls/traits can also
+    /// have lifetime parameters free in this body.
+    pub root_parent: Option<hir::HirId>,
+
+    /// Maps from a scope ID to the enclosing scope id;
+    /// this is usually corresponding to the lexical nesting, though
+    /// in the case of closures the parent scope is the innermost
+    /// conditional expression or repeating block. (Note that the
+    /// enclosing scope ID for the block associated with a closure is
+    /// the closure itself.)
+    pub parent_map: FxHashMap<Scope, (Scope, ScopeDepth)>,
+
+    /// Maps from a variable or binding ID to the block in which that
+    /// variable is declared.
+    var_map: FxHashMap<hir::ItemLocalId, Scope>,
+
+    /// Maps from a `NodeId` to the associated destruction scope (if any).
+    destruction_scopes: FxHashMap<hir::ItemLocalId, Scope>,
+
+    /// `rvalue_scopes` includes entries for those expressions whose
+    /// cleanup scope is larger than the default. The map goes from the
+    /// expression ID to the cleanup scope id. For rvalues not present in
+    /// this table, the appropriate cleanup scope is the innermost
+    /// enclosing statement, conditional expression, or repeating
+    /// block (see `terminating_scopes`).
+    /// In constants, None is used to indicate that certain expressions
+    /// 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.
+    ///
+    /// HIR Visitor postorder indexes might seem like a peculiar
+    /// thing to care about. but it turns out that HIR bindings
+    /// and the temporary results of HIR expressions are never
+    /// storage-live at the end of HIR nodes with postorder indexes
+    /// lower than theirs, and therefore don't need to be suspended
+    /// at yield-points at these indexes.
+    ///
+    /// For an example, suppose we have some code such as:
+    /// ```rust,ignore (example)
+    ///     foo(f(), yield y, bar(g()))
+    /// ```
+    ///
+    /// With the HIR tree (calls numbered for expository purposes)
+    /// ```
+    ///     Call#0(foo, [Call#1(f), Yield(y), Call#2(bar, Call#3(g))])
+    /// ```
+    ///
+    /// Obviously, the result of `f()` was created before the yield
+    /// (and therefore needs to be kept valid over the yield) while
+    /// the result of `g()` occurs after the yield (and therefore
+    /// doesn't). If we want to infer that, we can look at the
+    /// postorder traversal:
+    /// ```plain,ignore
+    ///     `foo` `f` Call#1 `y` Yield `bar` `g` Call#3 Call#2 Call#0
+    /// ```
+    ///
+    /// In which we can easily see that `Call#1` occurs before the yield,
+    /// and `Call#3` after it.
+    ///
+    /// To see that this method works, consider:
+    ///
+    /// Let `D` be our binding/temporary and `U` be our other HIR node, with
+    /// `HIR-postorder(U) < HIR-postorder(D)` (in our example, U would be
+    /// the yield and D would be one of the calls). Let's show that
+    /// `D` is storage-dead at `U`.
+    ///
+    /// Remember that storage-live/storage-dead refers to the state of
+    /// the *storage*, and does not consider moves/drop flags.
+    ///
+    /// Then:
+    ///     1. From the ordering guarantee of HIR visitors (see
+    ///     `rustc::hir::intravisit`), `D` does not dominate `U`.
+    ///     2. Therefore, `D` is *potentially* storage-dead at `U` (because
+    ///     we might visit `U` without ever getting to `D`).
+    ///     3. However, we guarantee that at each HIR point, each
+    ///     binding/temporary is always either always storage-live
+    ///     or always storage-dead. This is what is being guaranteed
+    ///     by `terminating_scopes` including all blocks where the
+    ///     count of executions is not guaranteed.
+    ///     4. By `2.` and `3.`, `D` is *statically* storage-dead at `U`,
+    ///     QED.
+    ///
+    /// This property ought to not on (3) in an essential way -- it
+    /// is probably still correct even if we have "unrestricted" terminating
+    /// scopes. However, why use the complicated proof when a simple one
+    /// works?
+    ///
+    /// A subtle thing: `box` expressions, such as `box (&x, yield 2, &y)`. It
+    /// might seem that a `box` expression creates a `Box<T>` temporary
+    /// when it *starts* executing, at `HIR-preorder(BOX-EXPR)`. That might
+    /// be true in the MIR desugaring, but it is not important in the semantics.
+    ///
+    /// The reason is that semantically, until the `box` expression returns,
+    /// the values are still owned by their containing expressions. So
+    /// we'll see that `&x`.
+    pub yield_in_scope: FxHashMap<Scope, YieldData>,
+
+    /// The number of visit_expr and visit_pat calls done in the body.
+    /// Used to sanity check visit_expr/visit_pat call count when
+    /// calculating generator interiors.
+    pub body_expr_count: FxHashMap<hir::BodyId, usize>,
+}
+
+#[derive(Debug, Copy, Clone, RustcEncodable, RustcDecodable, HashStable)]
+pub struct YieldData {
+    /// The `Span` of the yield.
+    pub span: Span,
+    /// The number of expressions and patterns appearing before the `yield` in the body plus one.
+    pub expr_and_pat_count: usize,
+    pub source: hir::YieldSource,
+}
+
+impl<'tcx> ScopeTree {
+    pub fn record_scope_parent(&mut self, child: Scope, parent: Option<(Scope, ScopeDepth)>) {
+        debug!("{:?}.parent = {:?}", child, parent);
+
+        if let Some(p) = parent {
+            let prev = self.parent_map.insert(child, p);
+            assert!(prev.is_none());
+        }
+
+        // Record the destruction scopes for later so we can query them.
+        if let ScopeData::Destruction = child.data {
+            self.destruction_scopes.insert(child.item_local_id(), child);
+        }
+    }
+
+    pub fn each_encl_scope<E>(&self, mut e: E)
+    where
+        E: FnMut(Scope, Scope),
+    {
+        for (&child, &parent) in &self.parent_map {
+            e(child, parent.0)
+        }
+    }
+
+    pub fn each_var_scope<E>(&self, mut e: E)
+    where
+        E: FnMut(&hir::ItemLocalId, Scope),
+    {
+        for (child, &parent) in self.var_map.iter() {
+            e(child, parent)
+        }
+    }
+
+    pub fn opt_destruction_scope(&self, n: hir::ItemLocalId) -> Option<Scope> {
+        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());
+        self.var_map.insert(var, lifetime);
+    }
+
+    pub fn record_rvalue_scope(&mut self, var: hir::ItemLocalId, lifetime: Option<Scope>) {
+        debug!("record_rvalue_scope(sub={:?}, sup={:?})", var, lifetime);
+        if let Some(lifetime) = lifetime {
+            assert!(var != lifetime.item_local_id());
+        }
+        self.rvalue_scopes.insert(var, lifetime);
+    }
+
+    /// Returns the narrowest scope that encloses `id`, if any.
+    pub fn opt_encl_scope(&self, id: Scope) -> Option<Scope> {
+        self.parent_map.get(&id).cloned().map(|(p, _)| p)
+    }
+
+    /// Returns the narrowest scope that encloses `id`, if any.
+    #[allow(dead_code)] // used in cfg
+    pub fn encl_scope(&self, id: Scope) -> Scope {
+        self.opt_encl_scope(id).unwrap()
+    }
+
+    /// Returns the lifetime of the local variable `var_id`
+    pub fn var_scope(&self, var_id: hir::ItemLocalId) -> Scope {
+        self.var_map
+            .get(&var_id)
+            .cloned()
+            .unwrap_or_else(|| bug!("no enclosing scope for id {:?}", var_id))
+    }
+
+    /// Returns the scope when the temp created by `expr_id` will be cleaned up.
+    pub fn temporary_scope(&self, expr_id: hir::ItemLocalId) -> Option<Scope> {
+        // Check for a designated rvalue scope.
+        if let Some(&s) = self.rvalue_scopes.get(&expr_id) {
+            debug!("temporary_scope({:?}) = {:?} [custom]", expr_id, s);
+            return s;
+        }
+
+        // Otherwise, locate the innermost terminating scope
+        // if there's one. Static items, for instance, won't
+        // have an enclosing scope, hence no scope will be
+        // returned.
+        let mut id = Scope { id: expr_id, data: ScopeData::Node };
+
+        while let Some(&(p, _)) = self.parent_map.get(&id) {
+            match p.data {
+                ScopeData::Destruction => {
+                    debug!("temporary_scope({:?}) = {:?} [enclosing]", expr_id, id);
+                    return Some(id);
+                }
+                _ => id = p,
+            }
+        }
+
+        debug!("temporary_scope({:?}) = None", expr_id);
+        return None;
+    }
+
+    /// Returns the lifetime of the variable `id`.
+    pub fn var_region(&self, id: hir::ItemLocalId) -> ty::RegionKind {
+        let scope = ty::ReScope(self.var_scope(id));
+        debug!("var_region({:?}) = {:?}", id, scope);
+        scope
+    }
+
+    pub fn scopes_intersect(&self, scope1: Scope, scope2: Scope) -> bool {
+        self.is_subscope_of(scope1, scope2) || self.is_subscope_of(scope2, scope1)
+    }
+
+    /// Returns `true` if `subscope` is equal to or is lexically nested inside `superscope`, and
+    /// `false` otherwise.
+    pub fn is_subscope_of(&self, subscope: Scope, superscope: Scope) -> bool {
+        let mut s = subscope;
+        debug!("is_subscope_of({:?}, {:?})", subscope, superscope);
+        while superscope != s {
+            match self.opt_encl_scope(s) {
+                None => {
+                    debug!("is_subscope_of({:?}, {:?}, s={:?})=false", subscope, superscope, s);
+                    return false;
+                }
+                Some(scope) => s = scope,
+            }
+        }
+
+        debug!("is_subscope_of({:?}, {:?})=true", subscope, superscope);
+
+        return true;
+    }
+
+    /// Returns the ID of the innermost containing body.
+    pub fn containing_body(&self, mut scope: Scope) -> Option<hir::ItemLocalId> {
+        loop {
+            if let ScopeData::CallSite = scope.data {
+                return Some(scope.item_local_id());
+            }
+
+            scope = self.opt_encl_scope(scope)?;
+        }
+    }
+
+    /// Finds the nearest common ancestor of two scopes. That is, finds the
+    /// smallest scope which is greater than or equal to both `scope_a` and
+    /// `scope_b`.
+    pub fn nearest_common_ancestor(&self, scope_a: Scope, scope_b: Scope) -> Scope {
+        if scope_a == scope_b {
+            return scope_a;
+        }
+
+        let mut a = scope_a;
+        let mut b = scope_b;
+
+        // Get the depth of each scope's parent. If either scope has no parent,
+        // it must be the root, which means we can stop immediately because the
+        // root must be the nearest common ancestor. (In practice, this is
+        // moderately common.)
+        let (parent_a, parent_a_depth) = match self.parent_map.get(&a) {
+            Some(pd) => *pd,
+            None => return a,
+        };
+        let (parent_b, parent_b_depth) = match self.parent_map.get(&b) {
+            Some(pd) => *pd,
+            None => return b,
+        };
+
+        if parent_a_depth > parent_b_depth {
+            // `a` is lower than `b`. Move `a` up until it's at the same depth
+            // as `b`. The first move up is trivial because we already found
+            // `parent_a` above; the loop does the remaining N-1 moves.
+            a = parent_a;
+            for _ in 0..(parent_a_depth - parent_b_depth - 1) {
+                a = self.parent_map.get(&a).unwrap().0;
+            }
+        } else if parent_b_depth > parent_a_depth {
+            // `b` is lower than `a`.
+            b = parent_b;
+            for _ in 0..(parent_b_depth - parent_a_depth - 1) {
+                b = self.parent_map.get(&b).unwrap().0;
+            }
+        } else {
+            // Both scopes are at the same depth, and we know they're not equal
+            // because that case was tested for at the top of this function. So
+            // we can trivially move them both up one level now.
+            assert!(parent_a_depth != 0);
+            a = parent_a;
+            b = parent_b;
+        }
+
+        // Now both scopes are at the same level. We move upwards in lockstep
+        // until they match. In practice, this loop is almost always executed
+        // zero times because `a` is almost always a direct ancestor of `b` or
+        // vice versa.
+        while a != b {
+            a = self.parent_map.get(&a).unwrap().0;
+            b = self.parent_map.get(&b).unwrap().0;
+        }
+
+        a
+    }
+
+    /// Assuming that the provided region was defined within this `ScopeTree`,
+    /// returns the outermost `Scope` that the region outlives.
+    pub fn early_free_scope(&self, tcx: TyCtxt<'tcx>, br: &ty::EarlyBoundRegion) -> Scope {
+        let param_owner = tcx.parent(br.def_id).unwrap();
+
+        let param_owner_id = tcx.hir().as_local_hir_id(param_owner).unwrap();
+        let scope = tcx
+            .hir()
+            .maybe_body_owned_by(param_owner_id)
+            .map(|body_id| tcx.hir().body(body_id).value.hir_id.local_id)
+            .unwrap_or_else(|| {
+                // The lifetime was defined on node that doesn't own a body,
+                // which in practice can only mean a trait or an impl, that
+                // is the parent of a method, and that is enforced below.
+                if Some(param_owner_id) != self.root_parent {
+                    tcx.sess.delay_span_bug(
+                        DUMMY_SP,
+                        &format!(
+                            "free_scope: {:?} not recognized by the \
+                              region scope tree for {:?} / {:?}",
+                            param_owner,
+                            self.root_parent.map(|id| tcx.hir().local_def_id(id)),
+                            self.root_body.map(|hir_id| DefId::local(hir_id.owner))
+                        ),
+                    );
+                }
+
+                // The trait/impl lifetime is in scope for the method's body.
+                self.root_body.unwrap().local_id
+            });
+
+        Scope { id: scope, data: ScopeData::CallSite }
+    }
+
+    /// Assuming that the provided region was defined within this `ScopeTree`,
+    /// returns the outermost `Scope` that the region outlives.
+    pub fn free_scope(&self, tcx: TyCtxt<'tcx>, fr: &ty::FreeRegion) -> Scope {
+        let param_owner = match fr.bound_region {
+            ty::BoundRegion::BrNamed(def_id, _) => tcx.parent(def_id).unwrap(),
+            _ => fr.scope,
+        };
+
+        // Ensure that the named late-bound lifetimes were defined
+        // on the same function that they ended up being freed in.
+        assert_eq!(param_owner, fr.scope);
+
+        let param_owner_id = tcx.hir().as_local_hir_id(param_owner).unwrap();
+        let body_id = tcx.hir().body_owned_by(param_owner_id);
+        Scope { id: tcx.hir().body(body_id).value.hir_id.local_id, data: ScopeData::CallSite }
+    }
+
+    /// Checks whether the given scope contains a `yield`. If so,
+    /// returns `Some((span, expr_count))` with the span of a yield we found and
+    /// the number of expressions and patterns appearing before the `yield` in the body + 1.
+    /// If there a are multiple yields in a scope, the one with the highest number is returned.
+    pub fn yield_in_scope(&self, scope: Scope) -> Option<YieldData> {
+        self.yield_in_scope.get(&scope).cloned()
+    }
+
+    /// Gives the number of expressions visited in a body.
+    /// Used to sanity check visit_expr call count when
+    /// calculating generator interiors.
+    pub fn body_expr_count(&self, body_id: hir::BodyId) -> Option<usize> {
+        self.body_expr_count.get(&body_id).map(|r| *r)
+    }
+}
+
+impl<'a> HashStable<StableHashingContext<'a>> for ScopeTree {
+    fn hash_stable(&self, hcx: &mut StableHashingContext<'a>, hasher: &mut StableHasher) {
+        let ScopeTree {
+            root_body,
+            root_parent,
+            ref body_expr_count,
+            ref parent_map,
+            ref var_map,
+            ref destruction_scopes,
+            ref rvalue_scopes,
+            ref closure_tree,
+            ref yield_in_scope,
+        } = *self;
+
+        hcx.with_node_id_hashing_mode(NodeIdHashingMode::HashDefPath, |hcx| {
+            root_body.hash_stable(hcx, hasher);
+            root_parent.hash_stable(hcx, hasher);
+        });
+
+        body_expr_count.hash_stable(hcx, hasher);
+        parent_map.hash_stable(hcx, hasher);
+        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);
+    }
+}
diff --git a/src/librustc_interface/passes.rs b/src/librustc_interface/passes.rs
index b4522f4c665..1ab285c216c 100644
--- a/src/librustc_interface/passes.rs
+++ b/src/librustc_interface/passes.rs
@@ -686,7 +686,6 @@ pub fn default_provide(providers: &mut ty::query::Providers<'_>) {
     stability::provide(providers);
     rustc_passes::provide(providers);
     rustc_traits::provide(providers);
-    middle::region::provide(providers);
     rustc_metadata::provide(providers);
     lint::provide(providers);
     rustc_lint::provide(providers);
diff --git a/src/librustc_passes/lib.rs b/src/librustc_passes/lib.rs
index da781f2bae5..8a10c8fe89d 100644
--- a/src/librustc_passes/lib.rs
+++ b/src/librustc_passes/lib.rs
@@ -31,6 +31,7 @@ mod lib_features;
 mod liveness;
 pub mod loops;
 mod reachable;
+mod region;
 
 pub fn provide(providers: &mut Providers<'_>) {
     check_const::provide(providers);
@@ -41,4 +42,5 @@ pub fn provide(providers: &mut Providers<'_>) {
     liveness::provide(providers);
     intrinsicck::provide(providers);
     reachable::provide(providers);
+    region::provide(providers);
 }
diff --git a/src/librustc_passes/region.rs b/src/librustc_passes/region.rs
index 5126d3f7fde..b828e014cfc 100644
--- a/src/librustc_passes/region.rs
+++ b/src/librustc_passes/region.rs
@@ -6,362 +6,22 @@
 //!
 //! [rustc guide]: https://rust-lang.github.io/rustc-guide/mir/borrowck.html
 
-use crate::hir;
-use crate::hir::def_id::DefId;
-use crate::hir::intravisit::{self, NestedVisitorMap, Visitor};
-use crate::hir::Node;
-use crate::hir::{Arm, Block, Expr, Local, Pat, PatKind, Stmt};
-use crate::ich::{NodeIdHashingMode, StableHashingContext};
-use crate::ty::query::Providers;
-use crate::ty::{self, DefIdTree, TyCtxt};
-use crate::util::nodemap::{FxHashMap, FxHashSet};
-
-use rustc_data_structures::stable_hasher::{HashStable, StableHasher};
+use rustc::hir;
+use rustc::hir::def_id::DefId;
+use rustc::hir::intravisit::{self, NestedVisitorMap, Visitor};
+use rustc::hir::Node;
+use rustc::hir::{Arm, Block, Expr, Local, Pat, PatKind, Stmt};
+use rustc::middle::region::*;
+use rustc::ty::query::Providers;
+use rustc::ty::TyCtxt;
+use rustc::util::nodemap::FxHashSet;
+
 use rustc_index::vec::Idx;
-use rustc_macros::HashStable;
 use syntax::source_map;
-use syntax_pos::{Span, DUMMY_SP};
+use syntax_pos::Span;
 
-use std::fmt;
 use std::mem;
 
-/// Represents a statically-describable scope that can be used to
-/// bound the lifetime/region for values.
-///
-/// `Node(node_id)`: Any AST node that has any scope at all has the
-/// `Node(node_id)` scope. Other variants represent special cases not
-/// immediately derivable from the abstract syntax tree structure.
-///
-/// `DestructionScope(node_id)` represents the scope of destructors
-/// implicitly-attached to `node_id` that run immediately after the
-/// expression for `node_id` itself. Not every AST node carries a
-/// `DestructionScope`, but those that are `terminating_scopes` do;
-/// see discussion with `ScopeTree`.
-///
-/// `Remainder { block, statement_index }` represents
-/// the scope of user code running immediately after the initializer
-/// expression for the indexed statement, until the end of the block.
-///
-/// So: the following code can be broken down into the scopes beneath:
-///
-/// ```text
-/// let a = f().g( 'b: { let x = d(); let y = d(); x.h(y)  }   ) ;
-///
-///                                                              +-+ (D12.)
-///                                                        +-+       (D11.)
-///                                              +---------+         (R10.)
-///                                              +-+                  (D9.)
-///                                   +----------+                    (M8.)
-///                                 +----------------------+          (R7.)
-///                                 +-+                               (D6.)
-///                      +----------+                                 (M5.)
-///                    +-----------------------------------+          (M4.)
-///         +--------------------------------------------------+      (M3.)
-///         +--+                                                      (M2.)
-/// +-----------------------------------------------------------+     (M1.)
-///
-///  (M1.): Node scope of the whole `let a = ...;` statement.
-///  (M2.): Node scope of the `f()` expression.
-///  (M3.): Node scope of the `f().g(..)` expression.
-///  (M4.): Node scope of the block labeled `'b:`.
-///  (M5.): Node scope of the `let x = d();` statement
-///  (D6.): DestructionScope for temporaries created during M5.
-///  (R7.): Remainder scope for block `'b:`, stmt 0 (let x = ...).
-///  (M8.): Node scope of the `let y = d();` statement.
-///  (D9.): DestructionScope for temporaries created during M8.
-/// (R10.): Remainder scope for block `'b:`, stmt 1 (let y = ...).
-/// (D11.): DestructionScope for temporaries and bindings from block `'b:`.
-/// (D12.): DestructionScope for temporaries created during M1 (e.g., f()).
-/// ```
-///
-/// Note that while the above picture shows the destruction scopes
-/// as following their corresponding node scopes, in the internal
-/// data structures of the compiler the destruction scopes are
-/// represented as enclosing parents. This is sound because we use the
-/// enclosing parent relationship just to ensure that referenced
-/// values live long enough; phrased another way, the starting point
-/// of each range is not really the important thing in the above
-/// picture, but rather the ending point.
-//
-// FIXME(pnkfelix): this currently derives `PartialOrd` and `Ord` to
-// placate the same deriving in `ty::FreeRegion`, but we may want to
-// actually attach a more meaningful ordering to scopes than the one
-// generated via deriving here.
-#[derive(
-    Clone,
-    PartialEq,
-    PartialOrd,
-    Eq,
-    Ord,
-    Hash,
-    Copy,
-    RustcEncodable,
-    RustcDecodable,
-    HashStable
-)]
-pub struct Scope {
-    pub id: hir::ItemLocalId,
-    pub data: ScopeData,
-}
-
-impl fmt::Debug for Scope {
-    fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
-        match self.data {
-            ScopeData::Node => write!(fmt, "Node({:?})", self.id),
-            ScopeData::CallSite => write!(fmt, "CallSite({:?})", self.id),
-            ScopeData::Arguments => write!(fmt, "Arguments({:?})", self.id),
-            ScopeData::Destruction => write!(fmt, "Destruction({:?})", self.id),
-            ScopeData::Remainder(fsi) => write!(
-                fmt,
-                "Remainder {{ block: {:?}, first_statement_index: {}}}",
-                self.id,
-                fsi.as_u32(),
-            ),
-        }
-    }
-}
-
-#[derive(
-    Clone,
-    PartialEq,
-    PartialOrd,
-    Eq,
-    Ord,
-    Hash,
-    Debug,
-    Copy,
-    RustcEncodable,
-    RustcDecodable,
-    HashStable
-)]
-pub enum ScopeData {
-    Node,
-
-    /// Scope of the call-site for a function or closure
-    /// (outlives the arguments as well as the body).
-    CallSite,
-
-    /// Scope of arguments passed to a function or closure
-    /// (they outlive its body).
-    Arguments,
-
-    /// Scope of destructors for temporaries of node-id.
-    Destruction,
-
-    /// Scope following a `let id = expr;` binding in a block.
-    Remainder(FirstStatementIndex),
-}
-
-rustc_index::newtype_index! {
-    /// Represents a subscope of `block` for a binding that is introduced
-    /// by `block.stmts[first_statement_index]`. Such subscopes represent
-    /// a suffix of the block. Note that each subscope does not include
-    /// the initializer expression, if any, for the statement indexed by
-    /// `first_statement_index`.
-    ///
-    /// For example, given `{ let (a, b) = EXPR_1; let c = EXPR_2; ... }`:
-    ///
-    /// * The subscope with `first_statement_index == 0` is scope of both
-    ///   `a` and `b`; it does not include EXPR_1, but does include
-    ///   everything after that first `let`. (If you want a scope that
-    ///   includes EXPR_1 as well, then do not use `Scope::Remainder`,
-    ///   but instead another `Scope` that encompasses the whole block,
-    ///   e.g., `Scope::Node`.
-    ///
-    /// * The subscope with `first_statement_index == 1` is scope of `c`,
-    ///   and thus does not include EXPR_2, but covers the `...`.
-    pub struct FirstStatementIndex {
-        derive [HashStable]
-    }
-}
-
-// compilation error if size of `ScopeData` is not the same as a `u32`
-static_assert_size!(ScopeData, 4);
-
-impl Scope {
-    /// Returns a item-local ID associated with this scope.
-    ///
-    /// N.B., likely to be replaced as API is refined; e.g., pnkfelix
-    /// anticipates `fn entry_node_id` and `fn each_exit_node_id`.
-    pub fn item_local_id(&self) -> hir::ItemLocalId {
-        self.id
-    }
-
-    pub fn hir_id(&self, scope_tree: &ScopeTree) -> hir::HirId {
-        match scope_tree.root_body {
-            Some(hir_id) => hir::HirId { owner: hir_id.owner, local_id: self.item_local_id() },
-            None => hir::DUMMY_HIR_ID,
-        }
-    }
-
-    /// Returns the span of this `Scope`. Note that in general the
-    /// returned span may not correspond to the span of any `NodeId` in
-    /// the AST.
-    pub fn span(&self, tcx: TyCtxt<'_>, scope_tree: &ScopeTree) -> Span {
-        let hir_id = self.hir_id(scope_tree);
-        if hir_id == hir::DUMMY_HIR_ID {
-            return DUMMY_SP;
-        }
-        let span = tcx.hir().span(hir_id);
-        if let ScopeData::Remainder(first_statement_index) = self.data {
-            if let Node::Block(ref blk) = tcx.hir().get(hir_id) {
-                // Want span for scope starting after the
-                // indexed statement and ending at end of
-                // `blk`; reuse span of `blk` and shift `lo`
-                // forward to end of indexed statement.
-                //
-                // (This is the special case aluded to in the
-                // doc-comment for this method)
-
-                let stmt_span = blk.stmts[first_statement_index.index()].span;
-
-                // To avoid issues with macro-generated spans, the span
-                // of the statement must be nested in that of the block.
-                if span.lo() <= stmt_span.lo() && stmt_span.lo() <= span.hi() {
-                    return Span::new(stmt_span.lo(), span.hi(), span.ctxt());
-                }
-            }
-        }
-        span
-    }
-}
-
-pub type ScopeDepth = u32;
-
-/// The region scope tree encodes information about region relationships.
-#[derive(Default, Debug)]
-pub struct ScopeTree {
-    /// If not empty, this body is the root of this region hierarchy.
-    root_body: Option<hir::HirId>,
-
-    /// The parent of the root body owner, if the latter is an
-    /// an associated const or method, as impls/traits can also
-    /// have lifetime parameters free in this body.
-    root_parent: Option<hir::HirId>,
-
-    /// Maps from a scope ID to the enclosing scope id;
-    /// this is usually corresponding to the lexical nesting, though
-    /// in the case of closures the parent scope is the innermost
-    /// conditional expression or repeating block. (Note that the
-    /// enclosing scope ID for the block associated with a closure is
-    /// the closure itself.)
-    parent_map: FxHashMap<Scope, (Scope, ScopeDepth)>,
-
-    /// Maps from a variable or binding ID to the block in which that
-    /// variable is declared.
-    var_map: FxHashMap<hir::ItemLocalId, Scope>,
-
-    /// Maps from a `NodeId` to the associated destruction scope (if any).
-    destruction_scopes: FxHashMap<hir::ItemLocalId, Scope>,
-
-    /// `rvalue_scopes` includes entries for those expressions whose
-    /// cleanup scope is larger than the default. The map goes from the
-    /// expression ID to the cleanup scope id. For rvalues not present in
-    /// this table, the appropriate cleanup scope is the innermost
-    /// enclosing statement, conditional expression, or repeating
-    /// block (see `terminating_scopes`).
-    /// In constants, None is used to indicate that certain expressions
-    /// 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.
-    ///
-    /// HIR Visitor postorder indexes might seem like a peculiar
-    /// thing to care about. but it turns out that HIR bindings
-    /// and the temporary results of HIR expressions are never
-    /// storage-live at the end of HIR nodes with postorder indexes
-    /// lower than theirs, and therefore don't need to be suspended
-    /// at yield-points at these indexes.
-    ///
-    /// For an example, suppose we have some code such as:
-    /// ```rust,ignore (example)
-    ///     foo(f(), yield y, bar(g()))
-    /// ```
-    ///
-    /// With the HIR tree (calls numbered for expository purposes)
-    /// ```
-    ///     Call#0(foo, [Call#1(f), Yield(y), Call#2(bar, Call#3(g))])
-    /// ```
-    ///
-    /// Obviously, the result of `f()` was created before the yield
-    /// (and therefore needs to be kept valid over the yield) while
-    /// the result of `g()` occurs after the yield (and therefore
-    /// doesn't). If we want to infer that, we can look at the
-    /// postorder traversal:
-    /// ```plain,ignore
-    ///     `foo` `f` Call#1 `y` Yield `bar` `g` Call#3 Call#2 Call#0
-    /// ```
-    ///
-    /// In which we can easily see that `Call#1` occurs before the yield,
-    /// and `Call#3` after it.
-    ///
-    /// To see that this method works, consider:
-    ///
-    /// Let `D` be our binding/temporary and `U` be our other HIR node, with
-    /// `HIR-postorder(U) < HIR-postorder(D)` (in our example, U would be
-    /// the yield and D would be one of the calls). Let's show that
-    /// `D` is storage-dead at `U`.
-    ///
-    /// Remember that storage-live/storage-dead refers to the state of
-    /// the *storage*, and does not consider moves/drop flags.
-    ///
-    /// Then:
-    ///     1. From the ordering guarantee of HIR visitors (see
-    ///     `rustc::hir::intravisit`), `D` does not dominate `U`.
-    ///     2. Therefore, `D` is *potentially* storage-dead at `U` (because
-    ///     we might visit `U` without ever getting to `D`).
-    ///     3. However, we guarantee that at each HIR point, each
-    ///     binding/temporary is always either always storage-live
-    ///     or always storage-dead. This is what is being guaranteed
-    ///     by `terminating_scopes` including all blocks where the
-    ///     count of executions is not guaranteed.
-    ///     4. By `2.` and `3.`, `D` is *statically* storage-dead at `U`,
-    ///     QED.
-    ///
-    /// This property ought to not on (3) in an essential way -- it
-    /// is probably still correct even if we have "unrestricted" terminating
-    /// scopes. However, why use the complicated proof when a simple one
-    /// works?
-    ///
-    /// A subtle thing: `box` expressions, such as `box (&x, yield 2, &y)`. It
-    /// might seem that a `box` expression creates a `Box<T>` temporary
-    /// when it *starts* executing, at `HIR-preorder(BOX-EXPR)`. That might
-    /// be true in the MIR desugaring, but it is not important in the semantics.
-    ///
-    /// The reason is that semantically, until the `box` expression returns,
-    /// the values are still owned by their containing expressions. So
-    /// we'll see that `&x`.
-    yield_in_scope: FxHashMap<Scope, YieldData>,
-
-    /// The number of visit_expr and visit_pat calls done in the body.
-    /// Used to sanity check visit_expr/visit_pat call count when
-    /// calculating generator interiors.
-    body_expr_count: FxHashMap<hir::BodyId, usize>,
-}
-
-#[derive(Debug, Copy, Clone, RustcEncodable, RustcDecodable, HashStable)]
-pub struct YieldData {
-    /// The `Span` of the yield.
-    pub span: Span,
-    /// The number of expressions and patterns appearing before the `yield` in the body plus one.
-    pub expr_and_pat_count: usize,
-    pub source: hir::YieldSource,
-}
-
 #[derive(Debug, Copy, Clone)]
 pub struct Context {
     /// The root of the current region tree. This is typically the id
@@ -419,344 +79,6 @@ struct RegionResolutionVisitor<'tcx> {
     terminating_scopes: FxHashSet<hir::ItemLocalId>,
 }
 
-struct ExprLocatorVisitor {
-    hir_id: hir::HirId,
-    result: Option<usize>,
-    expr_and_pat_count: usize,
-}
-
-// This visitor has to have the same `visit_expr` calls as `RegionResolutionVisitor`
-// since `expr_count` is compared against the results there.
-impl<'tcx> Visitor<'tcx> for ExprLocatorVisitor {
-    fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
-        NestedVisitorMap::None
-    }
-
-    fn visit_pat(&mut self, pat: &'tcx Pat<'tcx>) {
-        intravisit::walk_pat(self, pat);
-
-        self.expr_and_pat_count += 1;
-
-        if pat.hir_id == self.hir_id {
-            self.result = Some(self.expr_and_pat_count);
-        }
-    }
-
-    fn visit_expr(&mut self, expr: &'tcx Expr<'tcx>) {
-        debug!("ExprLocatorVisitor - pre-increment {} expr = {:?}", self.expr_and_pat_count, expr);
-
-        intravisit::walk_expr(self, expr);
-
-        self.expr_and_pat_count += 1;
-
-        debug!("ExprLocatorVisitor - post-increment {} expr = {:?}", self.expr_and_pat_count, expr);
-
-        if expr.hir_id == self.hir_id {
-            self.result = Some(self.expr_and_pat_count);
-        }
-    }
-}
-
-impl<'tcx> ScopeTree {
-    pub fn record_scope_parent(&mut self, child: Scope, parent: Option<(Scope, ScopeDepth)>) {
-        debug!("{:?}.parent = {:?}", child, parent);
-
-        if let Some(p) = parent {
-            let prev = self.parent_map.insert(child, p);
-            assert!(prev.is_none());
-        }
-
-        // Record the destruction scopes for later so we can query them.
-        if let ScopeData::Destruction = child.data {
-            self.destruction_scopes.insert(child.item_local_id(), child);
-        }
-    }
-
-    pub fn each_encl_scope<E>(&self, mut e: E)
-    where
-        E: FnMut(Scope, Scope),
-    {
-        for (&child, &parent) in &self.parent_map {
-            e(child, parent.0)
-        }
-    }
-
-    pub fn each_var_scope<E>(&self, mut e: E)
-    where
-        E: FnMut(&hir::ItemLocalId, Scope),
-    {
-        for (child, &parent) in self.var_map.iter() {
-            e(child, parent)
-        }
-    }
-
-    pub fn opt_destruction_scope(&self, n: hir::ItemLocalId) -> Option<Scope> {
-        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.
-    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());
-    }
-
-    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());
-        self.var_map.insert(var, lifetime);
-    }
-
-    fn record_rvalue_scope(&mut self, var: hir::ItemLocalId, lifetime: Option<Scope>) {
-        debug!("record_rvalue_scope(sub={:?}, sup={:?})", var, lifetime);
-        if let Some(lifetime) = lifetime {
-            assert!(var != lifetime.item_local_id());
-        }
-        self.rvalue_scopes.insert(var, lifetime);
-    }
-
-    /// Returns the narrowest scope that encloses `id`, if any.
-    pub fn opt_encl_scope(&self, id: Scope) -> Option<Scope> {
-        self.parent_map.get(&id).cloned().map(|(p, _)| p)
-    }
-
-    /// Returns the narrowest scope that encloses `id`, if any.
-    #[allow(dead_code)] // used in cfg
-    pub fn encl_scope(&self, id: Scope) -> Scope {
-        self.opt_encl_scope(id).unwrap()
-    }
-
-    /// Returns the lifetime of the local variable `var_id`
-    pub fn var_scope(&self, var_id: hir::ItemLocalId) -> Scope {
-        self.var_map
-            .get(&var_id)
-            .cloned()
-            .unwrap_or_else(|| bug!("no enclosing scope for id {:?}", var_id))
-    }
-
-    /// Returns the scope when the temp created by `expr_id` will be cleaned up.
-    pub fn temporary_scope(&self, expr_id: hir::ItemLocalId) -> Option<Scope> {
-        // Check for a designated rvalue scope.
-        if let Some(&s) = self.rvalue_scopes.get(&expr_id) {
-            debug!("temporary_scope({:?}) = {:?} [custom]", expr_id, s);
-            return s;
-        }
-
-        // Otherwise, locate the innermost terminating scope
-        // if there's one. Static items, for instance, won't
-        // have an enclosing scope, hence no scope will be
-        // returned.
-        let mut id = Scope { id: expr_id, data: ScopeData::Node };
-
-        while let Some(&(p, _)) = self.parent_map.get(&id) {
-            match p.data {
-                ScopeData::Destruction => {
-                    debug!("temporary_scope({:?}) = {:?} [enclosing]", expr_id, id);
-                    return Some(id);
-                }
-                _ => id = p,
-            }
-        }
-
-        debug!("temporary_scope({:?}) = None", expr_id);
-        return None;
-    }
-
-    /// Returns the lifetime of the variable `id`.
-    pub fn var_region(&self, id: hir::ItemLocalId) -> ty::RegionKind {
-        let scope = ty::ReScope(self.var_scope(id));
-        debug!("var_region({:?}) = {:?}", id, scope);
-        scope
-    }
-
-    pub fn scopes_intersect(&self, scope1: Scope, scope2: Scope) -> bool {
-        self.is_subscope_of(scope1, scope2) || self.is_subscope_of(scope2, scope1)
-    }
-
-    /// Returns `true` if `subscope` is equal to or is lexically nested inside `superscope`, and
-    /// `false` otherwise.
-    pub fn is_subscope_of(&self, subscope: Scope, superscope: Scope) -> bool {
-        let mut s = subscope;
-        debug!("is_subscope_of({:?}, {:?})", subscope, superscope);
-        while superscope != s {
-            match self.opt_encl_scope(s) {
-                None => {
-                    debug!("is_subscope_of({:?}, {:?}, s={:?})=false", subscope, superscope, s);
-                    return false;
-                }
-                Some(scope) => s = scope,
-            }
-        }
-
-        debug!("is_subscope_of({:?}, {:?})=true", subscope, superscope);
-
-        return true;
-    }
-
-    /// Returns the ID of the innermost containing body.
-    pub fn containing_body(&self, mut scope: Scope) -> Option<hir::ItemLocalId> {
-        loop {
-            if let ScopeData::CallSite = scope.data {
-                return Some(scope.item_local_id());
-            }
-
-            scope = self.opt_encl_scope(scope)?;
-        }
-    }
-
-    /// Finds the nearest common ancestor of two scopes. That is, finds the
-    /// smallest scope which is greater than or equal to both `scope_a` and
-    /// `scope_b`.
-    pub fn nearest_common_ancestor(&self, scope_a: Scope, scope_b: Scope) -> Scope {
-        if scope_a == scope_b {
-            return scope_a;
-        }
-
-        let mut a = scope_a;
-        let mut b = scope_b;
-
-        // Get the depth of each scope's parent. If either scope has no parent,
-        // it must be the root, which means we can stop immediately because the
-        // root must be the nearest common ancestor. (In practice, this is
-        // moderately common.)
-        let (parent_a, parent_a_depth) = match self.parent_map.get(&a) {
-            Some(pd) => *pd,
-            None => return a,
-        };
-        let (parent_b, parent_b_depth) = match self.parent_map.get(&b) {
-            Some(pd) => *pd,
-            None => return b,
-        };
-
-        if parent_a_depth > parent_b_depth {
-            // `a` is lower than `b`. Move `a` up until it's at the same depth
-            // as `b`. The first move up is trivial because we already found
-            // `parent_a` above; the loop does the remaining N-1 moves.
-            a = parent_a;
-            for _ in 0..(parent_a_depth - parent_b_depth - 1) {
-                a = self.parent_map.get(&a).unwrap().0;
-            }
-        } else if parent_b_depth > parent_a_depth {
-            // `b` is lower than `a`.
-            b = parent_b;
-            for _ in 0..(parent_b_depth - parent_a_depth - 1) {
-                b = self.parent_map.get(&b).unwrap().0;
-            }
-        } else {
-            // Both scopes are at the same depth, and we know they're not equal
-            // because that case was tested for at the top of this function. So
-            // we can trivially move them both up one level now.
-            assert!(parent_a_depth != 0);
-            a = parent_a;
-            b = parent_b;
-        }
-
-        // Now both scopes are at the same level. We move upwards in lockstep
-        // until they match. In practice, this loop is almost always executed
-        // zero times because `a` is almost always a direct ancestor of `b` or
-        // vice versa.
-        while a != b {
-            a = self.parent_map.get(&a).unwrap().0;
-            b = self.parent_map.get(&b).unwrap().0;
-        }
-
-        a
-    }
-
-    /// Assuming that the provided region was defined within this `ScopeTree`,
-    /// returns the outermost `Scope` that the region outlives.
-    pub fn early_free_scope(&self, tcx: TyCtxt<'tcx>, br: &ty::EarlyBoundRegion) -> Scope {
-        let param_owner = tcx.parent(br.def_id).unwrap();
-
-        let param_owner_id = tcx.hir().as_local_hir_id(param_owner).unwrap();
-        let scope = tcx
-            .hir()
-            .maybe_body_owned_by(param_owner_id)
-            .map(|body_id| tcx.hir().body(body_id).value.hir_id.local_id)
-            .unwrap_or_else(|| {
-                // The lifetime was defined on node that doesn't own a body,
-                // which in practice can only mean a trait or an impl, that
-                // is the parent of a method, and that is enforced below.
-                if Some(param_owner_id) != self.root_parent {
-                    tcx.sess.delay_span_bug(
-                        DUMMY_SP,
-                        &format!(
-                            "free_scope: {:?} not recognized by the \
-                              region scope tree for {:?} / {:?}",
-                            param_owner,
-                            self.root_parent.map(|id| tcx.hir().local_def_id(id)),
-                            self.root_body.map(|hir_id| DefId::local(hir_id.owner))
-                        ),
-                    );
-                }
-
-                // The trait/impl lifetime is in scope for the method's body.
-                self.root_body.unwrap().local_id
-            });
-
-        Scope { id: scope, data: ScopeData::CallSite }
-    }
-
-    /// Assuming that the provided region was defined within this `ScopeTree`,
-    /// returns the outermost `Scope` that the region outlives.
-    pub fn free_scope(&self, tcx: TyCtxt<'tcx>, fr: &ty::FreeRegion) -> Scope {
-        let param_owner = match fr.bound_region {
-            ty::BoundRegion::BrNamed(def_id, _) => tcx.parent(def_id).unwrap(),
-            _ => fr.scope,
-        };
-
-        // Ensure that the named late-bound lifetimes were defined
-        // on the same function that they ended up being freed in.
-        assert_eq!(param_owner, fr.scope);
-
-        let param_owner_id = tcx.hir().as_local_hir_id(param_owner).unwrap();
-        let body_id = tcx.hir().body_owned_by(param_owner_id);
-        Scope { id: tcx.hir().body(body_id).value.hir_id.local_id, data: ScopeData::CallSite }
-    }
-
-    /// Checks whether the given scope contains a `yield`. If so,
-    /// returns `Some((span, expr_count))` with the span of a yield we found and
-    /// the number of expressions and patterns appearing before the `yield` in the body + 1.
-    /// If there a are multiple yields in a scope, the one with the highest number is returned.
-    pub fn yield_in_scope(&self, scope: Scope) -> Option<YieldData> {
-        self.yield_in_scope.get(&scope).cloned()
-    }
-
-    /// Checks whether the given scope contains a `yield` and if that yield could execute
-    /// after `expr`. If so, it returns the span of that `yield`.
-    /// `scope` must be inside the body.
-    pub fn yield_in_scope_for_expr(
-        &self,
-        scope: Scope,
-        expr_hir_id: hir::HirId,
-        body: &'tcx hir::Body<'tcx>,
-    ) -> Option<Span> {
-        self.yield_in_scope(scope).and_then(|YieldData { span, expr_and_pat_count, .. }| {
-            let mut visitor =
-                ExprLocatorVisitor { hir_id: expr_hir_id, result: None, expr_and_pat_count: 0 };
-            visitor.visit_body(body);
-            if expr_and_pat_count >= visitor.result.unwrap() { Some(span) } else { None }
-        })
-    }
-
-    /// Gives the number of expressions visited in a body.
-    /// Used to sanity check visit_expr call count when
-    /// calculating generator interiors.
-    pub fn body_expr_count(&self, body_id: hir::BodyId) -> Option<usize> {
-        self.body_expr_count.get(&body_id).map(|r| *r)
-    }
-}
-
 /// Records the lifetime of a local variable as `cx.var_parent`
 fn record_var_lifetime(
     visitor: &mut RegionResolutionVisitor<'_>,
@@ -1505,32 +827,3 @@ fn region_scope_tree(tcx: TyCtxt<'_>, def_id: DefId) -> &ScopeTree {
 pub fn provide(providers: &mut Providers<'_>) {
     *providers = Providers { region_scope_tree, ..*providers };
 }
-
-impl<'a> HashStable<StableHashingContext<'a>> for ScopeTree {
-    fn hash_stable(&self, hcx: &mut StableHashingContext<'a>, hasher: &mut StableHasher) {
-        let ScopeTree {
-            root_body,
-            root_parent,
-            ref body_expr_count,
-            ref parent_map,
-            ref var_map,
-            ref destruction_scopes,
-            ref rvalue_scopes,
-            ref closure_tree,
-            ref yield_in_scope,
-        } = *self;
-
-        hcx.with_node_id_hashing_mode(NodeIdHashingMode::HashDefPath, |hcx| {
-            root_body.hash_stable(hcx, hasher);
-            root_parent.hash_stable(hcx, hasher);
-        });
-
-        body_expr_count.hash_stable(hcx, hasher);
-        parent_map.hash_stable(hcx, hasher);
-        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);
-    }
-}