Auto merge of #42015 - nikomatsakis:chalk-trait-env-2, r=eddyb

remove interior mutability of type-flags

We were previously using the flags on `Ty<'tcx>` instances to do some ad-hoc caching schemes around things like `is_sized()`, `is_freeze()`, and `moves_by_default()`. This PR replaces those schemes with a proper query; the query key is based on the pair of a `(ParameterEnvironment<'tcx>, Ty<'tcx>)` pair. This is also intended to be a preliminary template for what trait-selection and projection will eventually look like.

I did some performance measurements. In the past, I observed a noticeable speedup (6%) for building rustc, but since I've rebased, the numbers appear to be more of a wash:

| Crate | Before | After | Percentage |
| --- | --- | --- | -- |
| syntax | 167s | 166s | 0.6% faster |
| rustc | 376s | 382s | 1.5% slower |

Some advantages of this new scheme:

- `is_sized` etc are proper queries
- we get caching across generic fns, so long as trait environment is identical
- dependency tracking is correct

Author: bors

src/librustc/dep_graph/dep_node.rs

@@ -108,6 +108,10 @@ pub enum DepNode<D: Clone + Debug> {
     SymbolName(D),
     SpecializationGraph(D),
     ObjectSafety(D),
+    IsCopy(D),
+    IsSized(D),
+    IsFreeze(D),
+    NeedsDrop(D),
 
     // The set of impls for a given trait. Ultimately, it would be
     // nice to get more fine-grained here (e.g., to include a
@@ -159,6 +163,7 @@ pub enum DepNode<D: Clone + Debug> {
     // not a hotspot.
     ProjectionCache { def_ids: Vec<D> },
 
+    ParamEnv(D),
     DescribeDef(D),
     DefSpan(D),
     Stability(D),
@@ -233,6 +238,10 @@ impl<D: Clone + Debug> DepNode<D> {
             // they are always absolute.
             WorkProduct(ref id) => Some(WorkProduct(id.clone())),
 
+            IsCopy(ref d) => op(d).map(IsCopy),
+            IsSized(ref d) => op(d).map(IsSized),
+            IsFreeze(ref d) => op(d).map(IsFreeze),
+            NeedsDrop(ref d) => op(d).map(NeedsDrop),
             Hir(ref d) => op(d).map(Hir),
             HirBody(ref d) => op(d).map(HirBody),
             MetaData(ref d) => op(d).map(MetaData),
@@ -284,6 +293,7 @@ impl<D: Clone + Debug> DepNode<D> {
                 let def_ids: Option<Vec<E>> = def_ids.iter().map(op).collect();
                 def_ids.map(|d| ProjectionCache { def_ids: d })
             }
+            ParamEnv(ref d) => op(d).map(ParamEnv),
             DescribeDef(ref d) => op(d).map(DescribeDef),
             DefSpan(ref d) => op(d).map(DefSpan),
             Stability(ref d) => op(d).map(Stability),

src/librustc/infer/mod.rs

@@ -161,7 +161,7 @@ pub struct InferCtxt<'a, 'gcx: 'a+'tcx, 'tcx: 'a> {
     // For region variables.
     region_vars: RegionVarBindings<'a, 'gcx, 'tcx>,
 
-    pub parameter_environment: ty::ParameterEnvironment<'gcx>,
+    pub param_env: ty::ParamEnv<'gcx>,
 
     /// Caches the results of trait selection. This cache is used
     /// for things that have to do with the parameters in scope.
@@ -406,41 +406,41 @@ pub trait InferEnv<'a, 'tcx> {
     fn to_parts(self, tcx: TyCtxt<'a, 'tcx, 'tcx>)
                 -> (Option<&'a ty::TypeckTables<'tcx>>,
                     Option<ty::TypeckTables<'tcx>>,
-                    Option<ty::ParameterEnvironment<'tcx>>);
+                    Option<ty::ParamEnv<'tcx>>);
 }
 
 impl<'a, 'tcx> InferEnv<'a, 'tcx> for () {
     fn to_parts(self, _: TyCtxt<'a, 'tcx, 'tcx>)
                 -> (Option<&'a ty::TypeckTables<'tcx>>,
                     Option<ty::TypeckTables<'tcx>>,
-                    Option<ty::ParameterEnvironment<'tcx>>) {
+                    Option<ty::ParamEnv<'tcx>>) {
         (None, None, None)
     }
 }
 
-impl<'a, 'tcx> InferEnv<'a, 'tcx> for ty::ParameterEnvironment<'tcx> {
+impl<'a, 'tcx> InferEnv<'a, 'tcx> for ty::ParamEnv<'tcx> {
     fn to_parts(self, _: TyCtxt<'a, 'tcx, 'tcx>)
                 -> (Option<&'a ty::TypeckTables<'tcx>>,
                     Option<ty::TypeckTables<'tcx>>,
-                    Option<ty::ParameterEnvironment<'tcx>>) {
+                    Option<ty::ParamEnv<'tcx>>) {
         (None, None, Some(self))
     }
 }
 
-impl<'a, 'tcx> InferEnv<'a, 'tcx> for (&'a ty::TypeckTables<'tcx>, ty::ParameterEnvironment<'tcx>) {
+impl<'a, 'tcx> InferEnv<'a, 'tcx> for (&'a ty::TypeckTables<'tcx>, ty::ParamEnv<'tcx>) {
     fn to_parts(self, _: TyCtxt<'a, 'tcx, 'tcx>)
                 -> (Option<&'a ty::TypeckTables<'tcx>>,
                     Option<ty::TypeckTables<'tcx>>,
-                    Option<ty::ParameterEnvironment<'tcx>>) {
+                    Option<ty::ParamEnv<'tcx>>) {
         (Some(self.0), None, Some(self.1))
     }
 }
 
-impl<'a, 'tcx> InferEnv<'a, 'tcx> for (ty::TypeckTables<'tcx>, ty::ParameterEnvironment<'tcx>) {
+impl<'a, 'tcx> InferEnv<'a, 'tcx> for (ty::TypeckTables<'tcx>, ty::ParamEnv<'tcx>) {
     fn to_parts(self, _: TyCtxt<'a, 'tcx, 'tcx>)
                 -> (Option<&'a ty::TypeckTables<'tcx>>,
                     Option<ty::TypeckTables<'tcx>>,
-                    Option<ty::ParameterEnvironment<'tcx>>) {
+                    Option<ty::ParamEnv<'tcx>>) {
         (None, Some(self.0), Some(self.1))
     }
 }
@@ -449,11 +449,11 @@ impl<'a, 'tcx> InferEnv<'a, 'tcx> for hir::BodyId {
     fn to_parts(self, tcx: TyCtxt<'a, 'tcx, 'tcx>)
                 -> (Option<&'a ty::TypeckTables<'tcx>>,
                     Option<ty::TypeckTables<'tcx>>,
-                    Option<ty::ParameterEnvironment<'tcx>>) {
+                    Option<ty::ParamEnv<'tcx>>) {
         let def_id = tcx.hir.body_owner_def_id(self);
         (Some(tcx.typeck_tables_of(def_id)),
          None,
-         Some(tcx.parameter_environment(def_id)))
+         Some(tcx.param_env(def_id)))
     }
 }
 
@@ -465,7 +465,7 @@ pub struct InferCtxtBuilder<'a, 'gcx: 'a+'tcx, 'tcx: 'a> {
     arena: DroplessArena,
     fresh_tables: Option<RefCell<ty::TypeckTables<'tcx>>>,
     tables: Option<&'a ty::TypeckTables<'gcx>>,
-    param_env: Option<ty::ParameterEnvironment<'gcx>>,
+    param_env: Option<ty::ParamEnv<'gcx>>,
     projection_mode: Reveal,
 }
 
@@ -498,7 +498,7 @@ impl<'a, 'gcx, 'tcx> TyCtxt<'a, 'gcx, 'gcx> {
             int_unification_table: RefCell::new(UnificationTable::new()),
             float_unification_table: RefCell::new(UnificationTable::new()),
             region_vars: RegionVarBindings::new(self),
-            parameter_environment: param_env.unwrap(),
+            param_env: param_env.unwrap(),
             selection_cache: traits::SelectionCache::new(),
             evaluation_cache: traits::EvaluationCache::new(),
             projection_cache: RefCell::new(traits::ProjectionCache::new()),
@@ -526,9 +526,7 @@ impl<'a, 'gcx, 'tcx> InferCtxtBuilder<'a, 'gcx, 'tcx> {
         let tables = tables.map(InferTables::Interned).unwrap_or_else(|| {
             fresh_tables.as_ref().map_or(InferTables::Missing, InferTables::InProgress)
         });
-        let param_env = param_env.take().unwrap_or_else(|| {
-            global_tcx.empty_parameter_environment()
-        });
+        let param_env = param_env.take().unwrap_or_else(|| ty::ParamEnv::empty());
         global_tcx.enter_local(arena, |tcx| f(InferCtxt {
             tcx: tcx,
             tables: tables,
@@ -537,7 +535,7 @@ impl<'a, 'gcx, 'tcx> InferCtxtBuilder<'a, 'gcx, 'tcx> {
             int_unification_table: RefCell::new(UnificationTable::new()),
             float_unification_table: RefCell::new(UnificationTable::new()),
             region_vars: RegionVarBindings::new(tcx),
-            parameter_environment: param_env,
+            param_env: param_env,
             selection_cache: traits::SelectionCache::new(),
             evaluation_cache: traits::EvaluationCache::new(),
             reported_trait_errors: RefCell::new(FxHashSet()),
@@ -650,7 +648,7 @@ impl<'a, 'tcx> TyCtxt<'a, 'tcx, 'tcx> {
     }
 
     pub fn normalize_associated_type_in_env<T>(
-        self, value: &T, env: &'a ty::ParameterEnvironment<'tcx>
+        self, value: &T, env: ty::ParamEnv<'tcx>
     ) -> T
         where T: TransNormalize<'tcx>
     {
@@ -662,7 +660,7 @@ impl<'a, 'tcx> TyCtxt<'a, 'tcx, 'tcx> {
             return value;
         }
 
-        self.infer_ctxt(env.clone(), Reveal::All).enter(|infcx| {
+        self.infer_ctxt(env, Reveal::All).enter(|infcx| {
             value.trans_normalize(&infcx)
        })
     }
@@ -1674,8 +1672,8 @@ impl<'a, 'gcx, 'tcx> InferCtxt<'a, 'gcx, 'tcx> {
         self.tables.borrow().upvar_capture_map.get(&upvar_id).cloned()
     }
 
-    pub fn param_env(&self) -> &ty::ParameterEnvironment<'gcx> {
-        &self.parameter_environment
+    pub fn param_env(&self) -> ty::ParamEnv<'gcx> {
+        self.param_env
     }
 
     pub fn closure_kind(&self,

src/librustc/traits/README.md

@@ -418,16 +418,16 @@ before, and hence the cache lookup would succeed, yielding
 One subtle interaction is that the results of trait lookup will vary
 depending on what where clauses are in scope. Therefore, we actually
 have *two* caches, a local and a global cache. The local cache is
-attached to the `ParameterEnvironment` and the global cache attached
-to the `tcx`. We use the local cache whenever the result might depend
-on the where clauses that are in scope. The determination of which
-cache to use is done by the method `pick_candidate_cache` in
-`select.rs`. At the moment, we use a very simple, conservative rule:
-if there are any where-clauses in scope, then we use the local cache.
-We used to try and draw finer-grained distinctions, but that led to a
-serious of annoying and weird bugs like #22019 and #18290. This simple
-rule seems to be pretty clearly safe and also still retains a very
-high hit rate (~95% when compiling rustc).
+attached to the `ParamEnv` and the global cache attached to the
+`tcx`. We use the local cache whenever the result might depend on the
+where clauses that are in scope. The determination of which cache to
+use is done by the method `pick_candidate_cache` in `select.rs`. At
+the moment, we use a very simple, conservative rule: if there are any
+where-clauses in scope, then we use the local cache.  We used to try
+and draw finer-grained distinctions, but that led to a serious of
+annoying and weird bugs like #22019 and #18290. This simple rule seems
+to be pretty clearly safe and also still retains a very high hit rate
+(~95% when compiling rustc).
 
 # Specialization
 

src/librustc/traits/mod.rs

@@ -437,9 +437,9 @@ pub fn type_known_to_meet_bound<'a, 'gcx, 'tcx>(infcx: &InferCtxt<'a, 'gcx, 'tcx
 /// Normalizes the parameter environment, reporting errors if they occur.
 pub fn normalize_param_env_or_error<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
                                               region_context: DefId,
-                                              unnormalized_env: ty::ParameterEnvironment<'tcx>,
+                                              unnormalized_env: ty::ParamEnv<'tcx>,
                                               cause: ObligationCause<'tcx>)
-                                              -> ty::ParameterEnvironment<'tcx>
+                                              -> ty::ParamEnv<'tcx>
 {
     // I'm not wild about reporting errors here; I'd prefer to
     // have the errors get reported at a defined place (e.g.,
@@ -477,15 +477,15 @@ pub fn normalize_param_env_or_error<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
     debug!("normalize_param_env_or_error: elaborated-predicates={:?}",
            predicates);
 
-    let elaborated_env = unnormalized_env.with_caller_bounds(tcx.intern_predicates(&predicates));
+    let elaborated_env = ty::ParamEnv::new(tcx.intern_predicates(&predicates));
 
     tcx.infer_ctxt(elaborated_env, Reveal::UserFacing).enter(|infcx| {
         let predicates = match fully_normalize(
                 &infcx, cause,
-                // You would really want to pass infcx.parameter_environment.caller_bounds here,
+                // You would really want to pass infcx.param_env.caller_bounds here,
                 // but that is an interned slice, and fully_normalize takes &T and returns T, so
                 // without further refactoring, a slice can't be used. Luckily, we still have the
-                // predicate vector from which we created the ParameterEnvironment in infcx, so we
+                // predicate vector from which we created the ParamEnv in infcx, so we
                 // can pass that instead. It's roundabout and a bit brittle, but this code path
                 // ought to be refactored anyway, and until then it saves us from having to copy.
                 &predicates,
@@ -494,7 +494,7 @@ pub fn normalize_param_env_or_error<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
             Err(errors) => {
                 infcx.report_fulfillment_errors(&errors);
                 // An unnormalized env is better than nothing.
-                return infcx.parameter_environment;
+                return infcx.param_env;
             }
         };
 
@@ -516,19 +516,19 @@ pub fn normalize_param_env_or_error<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
                 // all things considered.
                 tcx.sess.span_err(span, &fixup_err.to_string());
                 // An unnormalized env is better than nothing.
-                return infcx.parameter_environment;
+                return infcx.param_env;
             }
         };
 
         let predicates = match tcx.lift_to_global(&predicates) {
             Some(predicates) => predicates,
-            None => return infcx.parameter_environment
+            None => return infcx.param_env
         };
 
         debug!("normalize_param_env_or_error: resolved predicates={:?}",
             predicates);
 
-        infcx.parameter_environment.with_caller_bounds(tcx.intern_predicates(&predicates))
+        ty::ParamEnv::new(tcx.intern_predicates(&predicates))
     })
 }
 

src/librustc/traits/select.rs

@@ -315,7 +315,7 @@ impl<'cx, 'gcx, 'tcx> SelectionContext<'cx, 'gcx, 'tcx> {
         self.infcx.tcx
     }
 
-    pub fn param_env(&self) -> &'cx ty::ParameterEnvironment<'gcx> {
+    pub fn param_env(&self) -> ty::ParamEnv<'gcx> {
         self.infcx.param_env()
     }
 

src/librustc/traits/specialize/mod.rs

@@ -180,7 +180,7 @@ pub fn specializes<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
     }
 
     // create a parameter environment corresponding to a (skolemized) instantiation of impl1
-    let penv = tcx.parameter_environment(impl1_def_id);
+    let penv = tcx.param_env(impl1_def_id);
     let impl1_trait_ref = tcx.impl_trait_ref(impl1_def_id).unwrap();
 
     // Create a infcx, taking the predicates of impl1 as assumptions:
@@ -250,7 +250,7 @@ fn fulfill_implication<'a, 'gcx, 'tcx>(infcx: &InferCtxt<'a, 'gcx, 'tcx>,
                        source_trait_ref,
                        target_trait_ref,
                        errors,
-                       infcx.parameter_environment.caller_bounds);
+                       infcx.param_env.caller_bounds);
                 Err(())
             }
 

src/librustc/ty/context.rs

@@ -138,7 +138,7 @@ impl<'gcx: 'tcx, 'tcx> CtxtInterners<'tcx> {
             let flags = super::flags::FlagComputation::for_sty(&st);
             let ty_struct = TyS {
                 sty: st,
-                flags: Cell::new(flags.flags),
+                flags: flags.flags,
                 region_depth: flags.depth,
             };
 
@@ -978,8 +978,8 @@ macro_rules! sty_debug_print {
                         ty::TyError => /* unimportant */ continue,
                         $(ty::$variant(..) => &mut $variant,)*
                     };
-                    let region = t.flags.get().intersects(ty::TypeFlags::HAS_RE_INFER);
-                    let ty = t.flags.get().intersects(ty::TypeFlags::HAS_TY_INFER);
+                    let region = t.flags.intersects(ty::TypeFlags::HAS_RE_INFER);
+                    let ty = t.flags.intersects(ty::TypeFlags::HAS_TY_INFER);
 
                     variant.total += 1;
                     total.total += 1;

src/librustc/ty/flags.rs

@@ -167,7 +167,7 @@ impl FlagComputation {
     }
 
     fn add_ty(&mut self, ty: Ty) {
-        self.add_flags(ty.flags.get());
+        self.add_flags(ty.flags);
         self.add_depth(ty.region_depth);
     }
 

src/librustc/ty/fold.rs

@@ -625,9 +625,8 @@ struct HasTypeFlagsVisitor {
 
 impl<'tcx> TypeVisitor<'tcx> for HasTypeFlagsVisitor {
     fn visit_ty(&mut self, t: Ty) -> bool {
-        let flags = t.flags.get();
-        debug!("HasTypeFlagsVisitor: t={:?} t.flags={:?} self.flags={:?}", t, flags, self.flags);
-        flags.intersects(self.flags)
+        debug!("HasTypeFlagsVisitor: t={:?} t.flags={:?} self.flags={:?}", t, t.flags, self.flags);
+        t.flags.intersects(self.flags)
     }
 
     fn visit_region(&mut self, r: ty::Region<'tcx>) -> bool {

src/librustc/ty/layout.rs

@@ -1079,7 +1079,7 @@ impl<'a, 'gcx, 'tcx> Layout {
         let ptr_layout = |pointee: Ty<'gcx>| {
             let non_zero = !ty.is_unsafe_ptr();
             let pointee = infcx.normalize_projections(pointee);
-            if pointee.is_sized(tcx, &infcx.parameter_environment, DUMMY_SP) {
+            if pointee.is_sized(tcx, infcx.param_env, DUMMY_SP) {
                 Ok(Scalar { value: Pointer, non_zero: non_zero })
             } else {
                 let unsized_part = tcx.struct_tail(pointee);
@@ -1268,11 +1268,11 @@ impl<'a, 'gcx, 'tcx> Layout {
                     let kind = if def.is_enum() || def.variants[0].fields.len() == 0{
                         StructKind::AlwaysSizedUnivariant
                     } else {
-                        let param_env = tcx.parameter_environment(def.did);
+                        let param_env = tcx.param_env(def.did);
                         let fields = &def.variants[0].fields;
                         let last_field = &fields[fields.len()-1];
                         let always_sized = tcx.type_of(last_field.did)
-                          .is_sized(tcx, &param_env, DUMMY_SP);
+                          .is_sized(tcx, param_env, DUMMY_SP);
                         if !always_sized { StructKind::MaybeUnsizedUnivariant }
                         else { StructKind::AlwaysSizedUnivariant }
                     };