make erase_regions use a query instead of an ad-hoc cache

Author: nikomatsakis

src/librustc/dep_graph/dep_node.rs

@@ -609,6 +609,7 @@ define_dep_nodes!( <'tcx>
     [] PostorderCnums,
     [] HasCloneClosures(CrateNum),
     [] HasCopyClosures(CrateNum),
+    [] EraseRegionsTy { ty: Ty<'tcx> },
 
     [] Freevars(DefId),
     [] MaybeUnusedTraitImport(DefId),

src/librustc/ty/context.rs

@@ -892,9 +892,6 @@ pub struct GlobalCtxt<'tcx> {
     // Internal cache for metadata decoding. No need to track deps on this.
     pub rcache: RefCell<FxHashMap<ty::CReaderCacheKey, Ty<'tcx>>>,
 
-    // FIXME dep tracking -- should be harmless enough
-    pub normalized_cache: RefCell<FxHashMap<Ty<'tcx>, Ty<'tcx>>>,
-
     /// Caches the results of trait selection. This cache is used
     /// for things that do not have to do with the parameters in scope.
     pub selection_cache: traits::SelectionCache<'tcx>,
@@ -1172,7 +1169,6 @@ impl<'a, 'gcx, 'tcx> TyCtxt<'a, 'gcx, 'tcx> {
             maps: maps::Maps::new(providers),
             mir_passes,
             rcache: RefCell::new(FxHashMap()),
-            normalized_cache: RefCell::new(FxHashMap()),
             selection_cache: traits::SelectionCache::new(),
             evaluation_cache: traits::EvaluationCache::new(),
             crate_name: Symbol::intern(crate_name),

src/librustc/ty/erase_regions.rs

@@ -0,0 +1,79 @@
+// Copyright 2017 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+use ty::{self, Ty, TyCtxt};
+use ty::fold::{TypeFolder, TypeFoldable};
+
+pub(super) fn provide(providers: &mut ty::maps::Providers) {
+    *providers = ty::maps::Providers {
+        erase_regions_ty,
+        ..*providers
+    };
+}
+
+fn erase_regions_ty<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>, ty: Ty<'tcx>) -> Ty<'tcx> {
+    // NB: use `super_fold_with` here. If we used `fold_with`, it
+    // could invoke the `erase_regions_ty` query recursively.
+    ty.super_fold_with(&mut RegionEraserVisitor { tcx })
+}
+
+impl<'a, 'gcx, 'tcx> TyCtxt<'a, 'gcx, 'tcx> {
+    /// Returns an equivalent value with all free regions removed (note
+    /// that late-bound regions remain, because they are important for
+    /// subtyping, but they are anonymized and normalized as well)..
+    pub fn erase_regions<T>(self, value: &T) -> T
+        where T : TypeFoldable<'tcx>
+    {
+        let value1 = value.fold_with(&mut RegionEraserVisitor { tcx: self });
+        debug!("erase_regions({:?}) = {:?}", value, value1);
+        value1
+    }
+}
+
+struct RegionEraserVisitor<'a, 'gcx: 'tcx, 'tcx: 'a> {
+    tcx: TyCtxt<'a, 'gcx, 'tcx>,
+}
+
+impl<'a, 'gcx, 'tcx> TypeFolder<'gcx, 'tcx> for RegionEraserVisitor<'a, 'gcx, 'tcx> {
+    fn tcx<'b>(&'b self) -> TyCtxt<'b, 'gcx, 'tcx> {
+        self.tcx
+    }
+
+    fn fold_ty(&mut self, ty: Ty<'tcx>) -> Ty<'tcx> {
+        if let Some(ty_lifted) = self.tcx.lift_to_global(&ty) {
+            self.tcx.erase_regions_ty(ty_lifted)
+        } else {
+            ty.super_fold_with(self)
+        }
+    }
+
+    fn fold_binder<T>(&mut self, t: &ty::Binder<T>) -> ty::Binder<T>
+        where T : TypeFoldable<'tcx>
+    {
+        let u = self.tcx.anonymize_late_bound_regions(t);
+        u.super_fold_with(self)
+    }
+
+    fn fold_region(&mut self, r: ty::Region<'tcx>) -> ty::Region<'tcx> {
+        // because late-bound regions affect subtyping, we can't
+        // erase the bound/free distinction, but we can replace
+        // all free regions with 'erased.
+        //
+        // Note that we *CAN* replace early-bound regions -- the
+        // type system never "sees" those, they get substituted
+        // away. In trans, they will always be erased to 'erased
+        // whenever a substitution occurs.
+        match *r {
+            ty::ReLateBound(..) => r,
+            _ => self.tcx.types.re_erased
+        }
+    }
+}
+

src/librustc/ty/fold.rs

@@ -444,67 +444,6 @@ impl<'a, 'gcx, 'tcx> TypeFolder<'gcx, 'tcx> for RegionReplacer<'a, 'gcx, 'tcx> {
     }
 }
 
-///////////////////////////////////////////////////////////////////////////
-// Region eraser
-
-impl<'a, 'gcx, 'tcx> TyCtxt<'a, 'gcx, 'tcx> {
-    /// Returns an equivalent value with all free regions removed (note
-    /// that late-bound regions remain, because they are important for
-    /// subtyping, but they are anonymized and normalized as well)..
-    pub fn erase_regions<T>(self, value: &T) -> T
-        where T : TypeFoldable<'tcx>
-    {
-        let value1 = value.fold_with(&mut RegionEraser(self));
-        debug!("erase_regions({:?}) = {:?}",
-               value, value1);
-        return value1;
-
-        struct RegionEraser<'a, 'gcx: 'a+'tcx, 'tcx: 'a>(TyCtxt<'a, 'gcx, 'tcx>);
-
-        impl<'a, 'gcx, 'tcx> TypeFolder<'gcx, 'tcx> for RegionEraser<'a, 'gcx, 'tcx> {
-            fn tcx<'b>(&'b self) -> TyCtxt<'b, 'gcx, 'tcx> { self.0 }
-
-            fn fold_ty(&mut self, ty: Ty<'tcx>) -> Ty<'tcx> {
-                if let Some(u) = self.tcx().normalized_cache.borrow().get(&ty).cloned() {
-                    return u;
-                }
-
-                // FIXME(eddyb) should local contexts have a cache too?
-                if let Some(ty_lifted) = self.tcx().lift_to_global(&ty) {
-                    let tcx = self.tcx().global_tcx();
-                    let t_norm = ty_lifted.super_fold_with(&mut RegionEraser(tcx));
-                    tcx.normalized_cache.borrow_mut().insert(ty_lifted, t_norm);
-                    t_norm
-                } else {
-                    ty.super_fold_with(self)
-                }
-            }
-
-            fn fold_binder<T>(&mut self, t: &ty::Binder<T>) -> ty::Binder<T>
-                where T : TypeFoldable<'tcx>
-            {
-                let u = self.tcx().anonymize_late_bound_regions(t);
-                u.super_fold_with(self)
-            }
-
-            fn fold_region(&mut self, r: ty::Region<'tcx>) -> ty::Region<'tcx> {
-                // because late-bound regions affect subtyping, we can't
-                // erase the bound/free distinction, but we can replace
-                // all free regions with 'erased.
-                //
-                // Note that we *CAN* replace early-bound regions -- the
-                // type system never "sees" those, they get substituted
-                // away. In trans, they will always be erased to 'erased
-                // whenever a substitution occurs.
-                match *r {
-                    ty::ReLateBound(..) => r,
-                    _ => self.tcx().types.re_erased
-                }
-            }
-        }
-    }
-}
-
 ///////////////////////////////////////////////////////////////////////////
 // Region shifter
 //

src/librustc/ty/maps/config.rs

@@ -75,6 +75,12 @@ impl<'tcx> QueryDescription for queries::super_predicates_of<'tcx> {
     }
 }
 
+impl<'tcx> QueryDescription for queries::erase_regions_ty<'tcx> {
+    fn describe(_tcx: TyCtxt, ty: Ty<'tcx>) -> String {
+        format!("erasing regions from `{:?}`", ty)
+    }
+}
+
 impl<'tcx> QueryDescription for queries::type_param_predicates<'tcx> {
     fn describe(tcx: TyCtxt, (_, def_id): (DefId, DefId)) -> String {
         let id = tcx.hir.as_local_node_id(def_id).unwrap();

src/librustc/ty/maps/mod.rs

@@ -341,12 +341,21 @@ define_maps! { <'tcx>
 
     [] fn has_copy_closures: HasCopyClosures(CrateNum) -> bool,
     [] fn has_clone_closures: HasCloneClosures(CrateNum) -> bool,
+
+    // Erases regions from `ty` to yield a new type.
+    // Normally you would just use `tcx.erase_regions(&value)`,
+    // however, which uses this query as a kind of cache.
+    [] fn erase_regions_ty: erase_regions_ty(Ty<'tcx>) -> Ty<'tcx>,
 }
 
 //////////////////////////////////////////////////////////////////////
 // These functions are little shims used to find the dep-node for a
 // given query when there is not a *direct* mapping:
 
+fn erase_regions_ty<'tcx>(ty: Ty<'tcx>) -> DepConstructor<'tcx> {
+    DepConstructor::EraseRegionsTy { ty }
+}
+
 fn type_param_predicates<'tcx>((item_id, param_id): (DefId, DefId)) -> DepConstructor<'tcx> {
     DepConstructor::TypeParamPredicates {
         item_id,

src/librustc/ty/maps/plumbing.rs

@@ -701,6 +701,7 @@ pub fn force_from_dep_node<'a, 'gcx, 'lcx>(tcx: TyCtxt<'a, 'gcx, 'lcx>,
         DepKind::CompileCodegenUnit |
         DepKind::FulfillObligation |
         DepKind::VtableMethods |
+        DepKind::EraseRegionsTy |
 
         // These are just odd
         DepKind::Null |
@@ -773,6 +774,7 @@ pub fn force_from_dep_node<'a, 'gcx, 'lcx>(tcx: TyCtxt<'a, 'gcx, 'lcx>,
         DepKind::ConstIsRvaluePromotableToStatic => {
             force!(const_is_rvalue_promotable_to_static, def_id!());
         }
+        DepKind::RvaluePromotableMap => { force!(rvalue_promotable_map, def_id!()); }
         DepKind::ImplParent => { force!(impl_parent, def_id!()); }
         DepKind::TraitOfItem => { force!(trait_of_item, def_id!()); }
         DepKind::IsExportedSymbol => { force!(is_exported_symbol, def_id!()); }

src/librustc/ty/mod.rs

@@ -90,6 +90,7 @@ pub mod adjustment;
 pub mod binding;
 pub mod cast;
 pub mod error;
+mod erase_regions;
 pub mod fast_reject;
 pub mod fold;
 pub mod inhabitedness;
@@ -2575,6 +2576,7 @@ fn original_crate_name<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
 pub fn provide(providers: &mut ty::maps::Providers) {
     util::provide(providers);
     context::provide(providers);
+    erase_regions::provide(providers);
     *providers = ty::maps::Providers {
         associated_item,
         associated_item_def_ids,