Cache "global" trait resolutions

src/librustc/middle/check_const.rs

@@ -285,7 +285,7 @@ impl<'a, 'tcx> CheckCrateVisitor<'a, 'tcx> {
     fn check_static_type(&self, e: &ast::Expr) {
         let ty = ty::node_id_to_type(self.tcx, e.id);
         let infcx = infer::new_infer_ctxt(self.tcx);
-        let mut fulfill_cx = traits::FulfillmentContext::new();
+        let mut fulfill_cx = traits::FulfillmentContext::new(false);
         let cause = traits::ObligationCause::new(e.span, e.id, traits::SharedStatic);
         fulfill_cx.register_builtin_bound(&infcx, ty, ty::BoundSync, cause);
         let env = ty::empty_parameter_environment(self.tcx);

src/librustc/middle/traits/fulfill.rs

@@ -28,6 +28,10 @@ use super::select::SelectionContext;
 use super::Unimplemented;
 use super::util::predicate_for_builtin_bound;
 
+pub struct FulfilledPredicates<'tcx> {
+    set: HashSet<ty::Predicate<'tcx>>
+}
+
 /// The fulfillment context is used to drive trait resolution.  It
 /// consists of a list of obligations that must be (eventually)
 /// satisfied. The job is to track which are satisfied, which yielded
@@ -44,7 +48,7 @@ pub struct FulfillmentContext<'tcx> {
     // than the `SelectionCache`: it avoids duplicate errors and
     // permits recursive obligations, which are often generated from
     // traits like `Send` et al.
-    duplicate_set: HashSet<ty::Predicate<'tcx>>,
+    duplicate_set: FulfilledPredicates<'tcx>,
 
     // A list of all obligations that have been registered with this
     // fulfillment context.
@@ -80,6 +84,8 @@ pub struct FulfillmentContext<'tcx> {
     // obligations (otherwise, it's easy to fail to walk to a
     // particular node-id).
     region_obligations: NodeMap<Vec<RegionObligation<'tcx>>>,
+
+    errors_will_be_reported: bool,
 }
 
 #[derive(Clone)]
@@ -90,12 +96,30 @@ pub struct RegionObligation<'tcx> {
 }
 
 impl<'tcx> FulfillmentContext<'tcx> {
-    pub fn new() -> FulfillmentContext<'tcx> {
+    /// Creates a new fulfillment context.
+    ///
+    /// `errors_will_be_reported` indicates whether ALL errors that
+    /// are generated by this fulfillment context will be reported to
+    /// the end user. This is used to inform caching, because it
+    /// allows us to conclude that traits that resolve successfully
+    /// will in fact always resolve successfully (in particular, it
+    /// guarantees that if some dependent obligation encounters a
+    /// problem, compilation will be aborted).  If you're not sure of
+    /// the right value here, pass `false`, as that is the more
+    /// conservative option.
+    ///
+    /// FIXME -- a better option would be to hold back on modifying
+    /// the global cache until we know that all dependent obligations
+    /// are also satisfied. In that case, we could actually remove
+    /// this boolean flag, and we'd also avoid the problem of squelching
+    /// duplicate errors that occur across fns.
+    pub fn new(errors_will_be_reported: bool) -> FulfillmentContext<'tcx> {
         FulfillmentContext {
-            duplicate_set: HashSet::new(),
+            duplicate_set: FulfilledPredicates::new(),
             predicates: Vec::new(),
             attempted_mark: 0,
             region_obligations: NodeMap(),
+            errors_will_be_reported: errors_will_be_reported,
         }
     }
 
@@ -165,7 +189,7 @@ impl<'tcx> FulfillmentContext<'tcx> {
 
         assert!(!obligation.has_escaping_regions());
 
-        if !self.duplicate_set.insert(obligation.predicate.clone()) {
+        if self.is_duplicate_or_add(infcx.tcx, &obligation.predicate) {
             debug!("register_predicate({}) -- already seen, skip", obligation.repr(infcx.tcx));
             return;
         }
@@ -231,6 +255,28 @@ impl<'tcx> FulfillmentContext<'tcx> {
         &self.predicates
     }
 
+    fn is_duplicate_or_add(&mut self, tcx: &ty::ctxt<'tcx>,
+                           predicate: &ty::Predicate<'tcx>)
+                           -> bool {
+        // This is a kind of dirty hack to allow us to avoid "rederiving"
+        // things that we have already proven in other methods.
+        //
+        // The idea is that any predicate that doesn't involve type
+        // parameters and which only involves the 'static region (and
+        // no other regions) is universally solvable, since impls are global.
+        //
+        // This is particularly important since even if we have a
+        // cache hit in the selection context, we still wind up
+        // evaluating the 'nested obligations'.  This cache lets us
+        // skip those.
+
+        if self.errors_will_be_reported && predicate.is_global() {
+            tcx.fulfilled_predicates.borrow_mut().is_duplicate_or_add(predicate)
+        } else {
+            self.duplicate_set.is_duplicate_or_add(predicate)
+        }
+    }
+
     /// Attempts to select obligations using `selcx`. If `only_new_obligations` is true, then it
     /// only attempts to select obligations that haven't been seen before.
     fn select<'a>(&mut self,
@@ -442,3 +488,21 @@ fn register_region_obligation<'tcx>(tcx: &ty::ctxt<'tcx>,
         .push(region_obligation);
 
 }
+
+impl<'tcx> FulfilledPredicates<'tcx> {
+    pub fn new() -> FulfilledPredicates<'tcx> {
+        FulfilledPredicates {
+            set: HashSet::new()
+        }
+    }
+
+    pub fn is_duplicate(&self, p: &ty::Predicate<'tcx>) -> bool {
+        self.set.contains(p)
+    }
+
+    fn is_duplicate_or_add(&mut self, p: &ty::Predicate<'tcx>) -> bool {
+        !self.set.insert(p.clone())
+    }
+}
+
+

src/librustc/middle/traits/mod.rs

@@ -32,7 +32,7 @@ pub use self::error_reporting::suggest_new_overflow_limit;
 pub use self::coherence::orphan_check;
 pub use self::coherence::overlapping_impls;
 pub use self::coherence::OrphanCheckErr;
-pub use self::fulfill::{FulfillmentContext, RegionObligation};
+pub use self::fulfill::{FulfillmentContext, FulfilledPredicates, RegionObligation};
 pub use self::project::MismatchedProjectionTypes;
 pub use self::project::normalize;
 pub use self::project::Normalized;
@@ -315,7 +315,7 @@ pub fn evaluate_builtin_bound<'a,'tcx>(infcx: &InferCtxt<'a,'tcx>,
            ty.repr(infcx.tcx),
            bound);
 
-    let mut fulfill_cx = FulfillmentContext::new();
+    let mut fulfill_cx = FulfillmentContext::new(false);
 
     // We can use a dummy node-id here because we won't pay any mind
     // to region obligations that arise (there shouldn't really be any
@@ -414,9 +414,27 @@ pub fn normalize_param_env_or_error<'a,'tcx>(unnormalized_env: ty::ParameterEnvi
     debug!("normalize_param_env_or_error(unnormalized_env={})",
            unnormalized_env.repr(tcx));
 
+    let predicates: Vec<_> =
+        util::elaborate_predicates(tcx, unnormalized_env.caller_bounds.clone())
+        .filter(|p| !p.is_global()) // (*)
+        .collect();
+
+    // (*) Any predicate like `i32: Trait<u32>` or whatever doesn't
+    // need to be in the *environment* to be proven, so screen those
+    // out. This is important for the soundness of inter-fn
+    // caching. Note though that we should probably check that these
+    // predicates hold at the point where the environment is
+    // constructed, but I am not currently doing so out of laziness.
+    // -nmatsakis
+
+    debug!("normalize_param_env_or_error: elaborated-predicates={}",
+           predicates.repr(tcx));
+
+    let elaborated_env = unnormalized_env.with_caller_bounds(predicates);
+
     let infcx = infer::new_infer_ctxt(tcx);
-    let predicates = match fully_normalize(&infcx, &unnormalized_env, cause,
-                                           &unnormalized_env.caller_bounds) {
+    let predicates = match fully_normalize(&infcx, &elaborated_env, cause,
+                                           &elaborated_env.caller_bounds) {
         Ok(predicates) => predicates,
         Err(errors) => {
             report_fulfillment_errors(&infcx, &errors);
@@ -438,14 +456,11 @@ pub fn normalize_param_env_or_error<'a,'tcx>(unnormalized_env: ty::ParameterEnvi
             // all things considered.
             let err_msg = fixup_err_to_string(fixup_err);
             tcx.sess.span_err(span, &err_msg);
-            return unnormalized_env; // an unnormalized env is better than nothing
+            return elaborated_env; // an unnormalized env is better than nothing
         }
     };
 
-    debug!("normalize_param_env_or_error: predicates={}",
-           predicates.repr(tcx));
-
-    unnormalized_env.with_caller_bounds(predicates)
+    elaborated_env.with_caller_bounds(predicates)
 }
 
 pub fn fully_normalize<'a,'tcx,T>(infcx: &InferCtxt<'a,'tcx>,
@@ -460,7 +475,7 @@ pub fn fully_normalize<'a,'tcx,T>(infcx: &InferCtxt<'a,'tcx>,
     debug!("normalize_param_env(value={})", value.repr(tcx));
 
     let mut selcx = &mut SelectionContext::new(infcx, closure_typer);
-    let mut fulfill_cx = FulfillmentContext::new();
+    let mut fulfill_cx = FulfillmentContext::new(false);
     let Normalized { value: normalized_value, obligations } =
         project::normalize(selcx, cause, value);
     debug!("normalize_param_env: normalized_value={} obligations={}",

src/librustc/middle/traits/project.rs

@@ -531,7 +531,7 @@ fn assemble_candidates_from_param_env<'cx,'tcx>(
     obligation_trait_ref: &ty::TraitRef<'tcx>,
     candidate_set: &mut ProjectionTyCandidateSet<'tcx>)
 {
-    let env_predicates = selcx.param_env().caller_bounds.clone();
+    let env_predicates = selcx.param_env().caller_bounds.iter().cloned();
     assemble_candidates_from_predicates(selcx, obligation, obligation_trait_ref,
                                         candidate_set, env_predicates);
 }
@@ -567,22 +567,25 @@ fn assemble_candidates_from_trait_def<'cx,'tcx>(
     // If so, extract what we know from the trait and try to come up with a good answer.
     let trait_predicates = ty::lookup_predicates(selcx.tcx(), trait_ref.def_id);
     let bounds = trait_predicates.instantiate(selcx.tcx(), trait_ref.substs);
+    let bounds = elaborate_predicates(selcx.tcx(), bounds.predicates.into_vec());
     assemble_candidates_from_predicates(selcx, obligation, obligation_trait_ref,
-                                        candidate_set, bounds.predicates.into_vec());
+                                        candidate_set, bounds)
 }
 
-fn assemble_candidates_from_predicates<'cx,'tcx>(
+fn assemble_candidates_from_predicates<'cx,'tcx,I>(
     selcx: &mut SelectionContext<'cx,'tcx>,
     obligation: &ProjectionTyObligation<'tcx>,
     obligation_trait_ref: &ty::TraitRef<'tcx>,
     candidate_set: &mut ProjectionTyCandidateSet<'tcx>,
-    env_predicates: Vec<ty::Predicate<'tcx>>)
+    env_predicates: I)
+    where I: Iterator<Item=ty::Predicate<'tcx>>
 {
-    debug!("assemble_candidates_from_predicates(obligation={}, env_predicates={})",
-           obligation.repr(selcx.tcx()),
-           env_predicates.repr(selcx.tcx()));
+    debug!("assemble_candidates_from_predicates(obligation={})",
+           obligation.repr(selcx.tcx()));
     let infcx = selcx.infcx();
-    for predicate in elaborate_predicates(selcx.tcx(), env_predicates) {
+    for predicate in env_predicates {
+        debug!("assemble_candidates_from_predicates: predicate={}",
+               predicate.repr(selcx.tcx()));
         match predicate {
             ty::Predicate::Projection(ref data) => {
                 let same_name = data.item_name() == obligation.predicate.item_name;
@@ -637,6 +640,7 @@ fn assemble_candidates_from_object_type<'cx,'tcx>(
     let env_predicates = projection_bounds.iter()
                                           .map(|p| p.as_predicate())
                                           .collect();
+    let env_predicates = elaborate_predicates(selcx.tcx(), env_predicates);
     assemble_candidates_from_predicates(selcx, obligation, obligation_trait_ref,
                                         candidate_set, env_predicates)
 }

src/librustc/middle/traits/select.rs

@@ -435,6 +435,14 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
         debug!("evaluate_predicate_recursively({})",
                obligation.repr(self.tcx()));
 
+        // Check the cache from the tcx of predicates that we know
+        // have been proven elsewhere. This cache only contains
+        // predicates that are global in scope and hence unaffected by
+        // the current environment.
+        if self.tcx().fulfilled_predicates.borrow().is_duplicate(&obligation.predicate) {
+            return EvaluatedToOk;
+        }
+
         match obligation.predicate {
             ty::Predicate::Trait(ref t) => {
                 assert!(!t.has_escaping_regions());
@@ -1075,14 +1083,10 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
         debug!("assemble_candidates_from_caller_bounds({})",
                stack.obligation.repr(self.tcx()));
 
-        let caller_trait_refs: Vec<_> =
-            self.param_env().caller_bounds.iter()
-            .filter_map(|o| o.to_opt_poly_trait_ref())
-            .collect();
-
         let all_bounds =
-            util::transitive_bounds(
-                self.tcx(), &caller_trait_refs[..]);
+            self.param_env().caller_bounds
+                            .iter()
+                            .filter_map(|o| o.to_opt_poly_trait_ref());
 
         let matching_bounds =
             all_bounds.filter(