add a per-param-env cache to impls_bound

There used to be only a global cache, which led to uncached calls to
trait selection when there were type parameters.

I'm running a check that there are no adverse performance effects.

Fixes #37106 (drop elaboration times are now ~half of borrow checking,
so might still be worthy of optimization, but not critical).

src/librustc/traits/select.rs

@@ -336,7 +336,7 @@ impl<'cx, 'gcx, 'tcx> SelectionContext<'cx, 'gcx, 'tcx> {
         self.infcx.tcx
     }
 
-    pub fn param_env(&self) -> &'cx ty::ParameterEnvironment<'tcx> {
+    pub fn param_env(&self) -> &'cx ty::ParameterEnvironment<'gcx> {
         self.infcx.param_env()
     }
 

src/librustc/ty/mod.rs

@@ -34,7 +34,7 @@ use util::nodemap::FnvHashMap;
 
 use serialize::{self, Encodable, Encoder};
 use std::borrow::Cow;
-use std::cell::Cell;
+use std::cell::{Cell, RefCell};
 use std::hash::{Hash, Hasher};
 use std::iter;
 use std::ops::Deref;
@@ -1220,6 +1220,12 @@ pub struct ParameterEnvironment<'tcx> {
     /// regions don't have this implicit scope and instead introduce
     /// relationships in the environment.
     pub free_id_outlive: CodeExtent,
+
+    /// A cache for `moves_by_default`.
+    pub is_copy_cache: RefCell<FnvHashMap<Ty<'tcx>, bool>>,
+
+    /// A cache for `type_is_sized`
+    pub is_sized_cache: RefCell<FnvHashMap<Ty<'tcx>, bool>>,
 }
 
 impl<'a, 'tcx> ParameterEnvironment<'tcx> {
@@ -1232,6 +1238,8 @@ impl<'a, 'tcx> ParameterEnvironment<'tcx> {
             implicit_region_bound: self.implicit_region_bound,
             caller_bounds: caller_bounds,
             free_id_outlive: self.free_id_outlive,
+            is_copy_cache: RefCell::new(FnvHashMap()),
+            is_sized_cache: RefCell::new(FnvHashMap()),
         }
     }
 
@@ -2773,7 +2781,9 @@ impl<'a, 'gcx, 'tcx> TyCtxt<'a, 'gcx, 'tcx> {
             free_substs: Substs::empty(self),
             caller_bounds: Vec::new(),
             implicit_region_bound: self.mk_region(ty::ReEmpty),
-            free_id_outlive: free_id_outlive
+            free_id_outlive: free_id_outlive,
+            is_copy_cache: RefCell::new(FnvHashMap()),
+            is_sized_cache: RefCell::new(FnvHashMap()),
         }
     }
 
@@ -2844,6 +2854,8 @@ impl<'a, 'gcx, 'tcx> TyCtxt<'a, 'gcx, 'tcx> {
             implicit_region_bound: tcx.mk_region(ty::ReScope(free_id_outlive)),
             caller_bounds: predicates,
             free_id_outlive: free_id_outlive,
+            is_copy_cache: RefCell::new(FnvHashMap()),
+            is_sized_cache: RefCell::new(FnvHashMap()),
         };
 
         let cause = traits::ObligationCause::misc(span, free_id_outlive.node_id(&self.region_maps));

src/librustc/ty/structural_impls.rs

@@ -901,23 +901,6 @@ impl<'tcx> TypeFoldable<'tcx> for ty::ClosureUpvar<'tcx> {
     }
 }
 
-impl<'tcx> TypeFoldable<'tcx> for ty::ParameterEnvironment<'tcx> {
-    fn super_fold_with<'gcx: 'tcx, F: TypeFolder<'gcx, 'tcx>>(&self, folder: &mut F) -> Self {
-        ty::ParameterEnvironment {
-            free_substs: self.free_substs.fold_with(folder),
-            implicit_region_bound: self.implicit_region_bound.fold_with(folder),
-            caller_bounds: self.caller_bounds.fold_with(folder),
-            free_id_outlive: self.free_id_outlive,
-        }
-    }
-
-    fn super_visit_with<V: TypeVisitor<'tcx>>(&self, visitor: &mut V) -> bool {
-        self.free_substs.visit_with(visitor) ||
-            self.implicit_region_bound.visit_with(visitor) ||
-            self.caller_bounds.visit_with(visitor)
-    }
-}
-
 impl<'tcx, T: TypeFoldable<'tcx>> TypeFoldable<'tcx> for ty::error::ExpectedFound<T> {
     fn super_fold_with<'gcx: 'tcx, F: TypeFolder<'gcx, 'tcx>>(&self, folder: &mut F) -> Self {
         ty::error::ExpectedFound {

src/librustc/ty/util.rs

@@ -20,9 +20,11 @@ use ty::{Disr, ParameterEnvironment};
 use ty::fold::TypeVisitor;
 use ty::layout::{Layout, LayoutError};
 use ty::TypeVariants::*;
+use util::nodemap::FnvHashMap;
 
 use rustc_const_math::{ConstInt, ConstIsize, ConstUsize};
 
+use std::cell::RefCell;
 use std::cmp;
 use std::hash::{Hash, Hasher};
 use std::collections::hash_map::DefaultHasher;
@@ -579,11 +581,24 @@ impl<'a, 'gcx, 'tcx, H: Hasher> TypeVisitor<'tcx> for TypeIdHasher<'a, 'gcx, 'tc
 impl<'a, 'tcx> ty::TyS<'tcx> {
     fn impls_bound(&'tcx self, tcx: TyCtxt<'a, 'tcx, 'tcx>,
                    param_env: &ParameterEnvironment<'tcx>,
-                   bound: ty::BuiltinBound, span: Span) -> bool
+                   bound: ty::BuiltinBound,
+                   cache: &RefCell<FnvHashMap<Ty<'tcx>, bool>>,
+                   span: Span) -> bool
     {
-        tcx.infer_ctxt(None, Some(param_env.clone()), Reveal::ExactMatch).enter(|infcx| {
-            traits::type_known_to_meet_builtin_bound(&infcx, self, bound, span)
-        })
+        if self.has_param_types() || self.has_self_ty() {
+            if let Some(result) = cache.borrow().get(self) {
+                return *result;
+            }
+        }
+        let result =
+            tcx.infer_ctxt(None, Some(param_env.clone()), Reveal::ExactMatch)
+            .enter(|infcx| {
+                traits::type_known_to_meet_builtin_bound(&infcx, self, bound, span)
+            });
+        if self.has_param_types() || self.has_self_ty() {
+            cache.borrow_mut().insert(self, result);
+        }
+        return result;
     }
 
     // FIXME (@jroesch): I made this public to use it, not sure if should be private
@@ -610,7 +625,9 @@ impl<'a, 'tcx> ty::TyS<'tcx> {
             TyArray(..) | TySlice(..) | TyTrait(..) | TyTuple(..) |
             TyClosure(..) | TyAdt(..) | TyAnon(..) |
             TyProjection(..) | TyParam(..) | TyInfer(..) | TyError => None
-        }.unwrap_or_else(|| !self.impls_bound(tcx, param_env, ty::BoundCopy, span));
+        }.unwrap_or_else(|| {
+            !self.impls_bound(tcx, param_env, ty::BoundCopy, &param_env.is_copy_cache, span)
+        });
 
         if !self.has_param_types() && !self.has_self_ty() {
             self.flags.set(self.flags.get() | if result {
@@ -650,7 +667,9 @@ impl<'a, 'tcx> ty::TyS<'tcx> {
 
             TyAdt(..) | TyProjection(..) | TyParam(..) |
             TyInfer(..) | TyAnon(..) | TyError => None
-        }.unwrap_or_else(|| self.impls_bound(tcx, param_env, ty::BoundSized, span));
+        }.unwrap_or_else(|| {
+            self.impls_bound(tcx, param_env, ty::BoundSized, &param_env.is_sized_cache, span)
+        });
 
         if !self.has_param_types() && !self.has_self_ty() {
             self.flags.set(self.flags.get() | if result {

src/librustc_typeck/check/mod.rs

@@ -1458,7 +1458,7 @@ impl<'a, 'gcx, 'tcx> FnCtxt<'a, 'gcx, 'tcx> {
         }
     }
 
-    pub fn param_env(&self) -> &ty::ParameterEnvironment<'tcx> {
+    pub fn param_env(&self) -> &ty::ParameterEnvironment<'gcx> {
         &self.parameter_environment
     }