Auto merge of rust-lang#35761 - nikomatsakis:faster-trans-fulfill-obligation, r=eddyb

Cache projections in trans

This introduces a cache for the results of projection and normalization in trans. This is in addition to the existing cache that is per-inference-context. Trans is an easy place to put the cache because we are guaranteed not to have type parameters and also we don't expect any failures or inference variables, so there is no need to cache or follow-up on obligations that come along with.  (As evidenced by the fact that this particular code would panic if any error occurred.)

That said, I am not sure this is 100% the best place for it; I sort of wanted a cache like we have in the fulfillment context for global names; but that cache only triggers when all subsequent obligations are satisfied, and since projections don't have an entry in the obligation jungle there is no easy place to put it. I considered caching both the result and obligations globally, but haven't really tried implementing it. It might be a good next step.

Regardless, this cache seems to have no real effect on bootstrap time (maybe a slight improvement), but on [the futures.rs test case I was looking at](rust-lang-deprecated/rustc-benchmarks#6), it improves performance quite a bit:

| phase | before | after |
| ----- | ------ | ----- |
| collection | 0.79s | 0.46s |
| translation | 6.8s | 3.2s |
| total | 11.92s | 7.15s |

r? @arielb1

Author: bors

src/librustc/dep_graph/dep_node.rs

@@ -132,7 +132,7 @@ pub enum DepNode<D: Clone + Debug> {
     // which would yield an overly conservative dep-graph.
     TraitItems(D),
     ReprHints(D),
-    TraitSelect(D, Vec<D>),
+    TraitSelect(Vec<D>),
 }
 
 impl<D: Clone + Debug> DepNode<D> {
@@ -237,10 +237,9 @@ impl<D: Clone + Debug> DepNode<D> {
             TraitImpls(ref d) => op(d).map(TraitImpls),
             TraitItems(ref d) => op(d).map(TraitItems),
             ReprHints(ref d) => op(d).map(ReprHints),
-            TraitSelect(ref d, ref type_ds) => {
-                let d = try_opt!(op(d));
+            TraitSelect(ref type_ds) => {
                 let type_ds = try_opt!(type_ds.iter().map(|d| op(d)).collect());
-                Some(TraitSelect(d, type_ds))
+                Some(TraitSelect(type_ds))
             }
         }
     }

src/librustc/infer/mod.rs

@@ -136,13 +136,6 @@ pub struct InferCtxt<'a, 'gcx: 'a+'tcx, 'tcx: 'a> {
     // avoid reporting the same error twice.
     pub reported_trait_errors: RefCell<FnvHashSet<traits::TraitErrorKey<'tcx>>>,
 
-    // This is a temporary field used for toggling on normalization in the inference context,
-    // as we move towards the approach described here:
-    // https://internals.rust-lang.org/t/flattening-the-contexts-for-fun-and-profit/2293
-    // At a point sometime in the future normalization will be done by the typing context
-    // directly.
-    normalize: bool,
-
     // Sadly, the behavior of projection varies a bit depending on the
     // stage of compilation. The specifics are given in the
     // documentation for `Reveal`.
@@ -458,7 +451,6 @@ pub struct InferCtxtBuilder<'a, 'gcx: 'a+'tcx, 'tcx: 'a> {
     tables: Option<RefCell<ty::Tables<'tcx>>>,
     param_env: Option<ty::ParameterEnvironment<'gcx>>,
     projection_mode: Reveal,
-    normalize: bool
 }
 
 impl<'a, 'gcx, 'tcx> TyCtxt<'a, 'gcx, 'gcx> {
@@ -473,19 +465,6 @@ impl<'a, 'gcx, 'tcx> TyCtxt<'a, 'gcx, 'gcx> {
             tables: tables.map(RefCell::new),
             param_env: param_env,
             projection_mode: projection_mode,
-            normalize: false
-        }
-    }
-
-    pub fn normalizing_infer_ctxt(self, projection_mode: Reveal)
-                                  -> InferCtxtBuilder<'a, 'gcx, 'tcx> {
-        InferCtxtBuilder {
-            global_tcx: self,
-            arenas: ty::CtxtArenas::new(),
-            tables: None,
-            param_env: None,
-            projection_mode: projection_mode,
-            normalize: false
         }
     }
 
@@ -506,7 +485,6 @@ impl<'a, 'gcx, 'tcx> TyCtxt<'a, 'gcx, 'gcx> {
             evaluation_cache: traits::EvaluationCache::new(),
             projection_cache: RefCell::new(traits::ProjectionCache::new()),
             reported_trait_errors: RefCell::new(FnvHashSet()),
-            normalize: false,
             projection_mode: Reveal::NotSpecializable,
             tainted_by_errors_flag: Cell::new(false),
             err_count_on_creation: self.sess.err_count(),
@@ -525,7 +503,6 @@ impl<'a, 'gcx, 'tcx> InferCtxtBuilder<'a, 'gcx, 'tcx> {
             ref tables,
             ref mut param_env,
             projection_mode,
-            normalize
         } = *self;
         let tables = if let Some(ref tables) = *tables {
             InferTables::Local(tables)
@@ -547,7 +524,6 @@ impl<'a, 'gcx, 'tcx> InferCtxtBuilder<'a, 'gcx, 'tcx> {
             selection_cache: traits::SelectionCache::new(),
             evaluation_cache: traits::EvaluationCache::new(),
             reported_trait_errors: RefCell::new(FnvHashSet()),
-            normalize: normalize,
             projection_mode: projection_mode,
             tainted_by_errors_flag: Cell::new(false),
             err_count_on_creation: tcx.sess.err_count(),
@@ -683,6 +659,15 @@ impl<'a, 'gcx, 'tcx> InferCtxt<'a, 'gcx, 'tcx> {
         self.drain_fulfillment_cx_or_panic(DUMMY_SP, &mut fulfill_cx, &result)
     }
 
+    /// Finishes processes any obligations that remain in the
+    /// fulfillment context, and then returns the result with all type
+    /// variables removed and regions erased. Because this is intended
+    /// for use after type-check has completed, if any errors occur,
+    /// it will panic. It is used during normalization and other cases
+    /// where processing the obligations in `fulfill_cx` may cause
+    /// type inference variables that appear in `result` to be
+    /// unified, and hence we need to process those obligations to get
+    /// the complete picture of the type.
     pub fn drain_fulfillment_cx_or_panic<T>(&self,
                                             span: Span,
                                             fulfill_cx: &mut traits::FulfillmentContext<'tcx>,
@@ -692,47 +677,28 @@ impl<'a, 'gcx, 'tcx> InferCtxt<'a, 'gcx, 'tcx> {
     {
         debug!("drain_fulfillment_cx_or_panic()");
 
-        let when = "resolving bounds after type-checking";
-        let v = match self.drain_fulfillment_cx(fulfill_cx, result) {
-            Ok(v) => v,
+        // In principle, we only need to do this so long as `result`
+        // contains unbound type parameters. It could be a slight
+        // optimization to stop iterating early.
+        match fulfill_cx.select_all_or_error(self) {
+            Ok(()) => { }
             Err(errors) => {
-                span_bug!(span, "Encountered errors `{:?}` {}", errors, when);
+                span_bug!(span, "Encountered errors `{:?}` resolving bounds after type-checking",
+                          errors);
             }
-        };
+        }
+
+        let result = self.resolve_type_vars_if_possible(result);
+        let result = self.tcx.erase_regions(&result);
 
-        match self.tcx.lift_to_global(&v) {
-            Some(v) => v,
+        match self.tcx.lift_to_global(&result) {
+            Some(result) => result,
             None => {
-                span_bug!(span, "Uninferred types/regions in `{:?}` {}", v, when);
+                span_bug!(span, "Uninferred types/regions in `{:?}`", result);
             }
         }
     }
 
-    /// Finishes processes any obligations that remain in the fulfillment
-    /// context, and then "freshens" and returns `result`. This is
-    /// primarily used during normalization and other cases where
-    /// processing the obligations in `fulfill_cx` may cause type
-    /// inference variables that appear in `result` to be unified, and
-    /// hence we need to process those obligations to get the complete
-    /// picture of the type.
-    pub fn drain_fulfillment_cx<T>(&self,
-                                   fulfill_cx: &mut traits::FulfillmentContext<'tcx>,
-                                   result: &T)
-                                   -> Result<T,Vec<traits::FulfillmentError<'tcx>>>
-        where T : TypeFoldable<'tcx>
-    {
-        debug!("drain_fulfillment_cx(result={:?})",
-               result);
-
-        // In principle, we only need to do this so long as `result`
-        // contains unbound type parameters. It could be a slight
-        // optimization to stop iterating early.
-        fulfill_cx.select_all_or_error(self)?;
-
-        let result = self.resolve_type_vars_if_possible(result);
-        Ok(self.tcx.erase_regions(&result))
-    }
-
     pub fn projection_mode(&self) -> Reveal {
         self.projection_mode
     }
@@ -1702,17 +1668,7 @@ impl<'a, 'gcx, 'tcx> InferCtxt<'a, 'gcx, 'tcx> {
         }
 
         let closure_ty = self.tcx.closure_type(def_id, substs);
-        if self.normalize {
-            let closure_ty = self.tcx.erase_regions(&closure_ty);
-
-            if !closure_ty.has_projection_types() {
-                return closure_ty;
-            }
-
-            self.normalize_projections_in(&closure_ty)
-        } else {
-            closure_ty
-        }
+        closure_ty
     }
 }
 

src/librustc/traits/specialize/mod.rs

@@ -147,7 +147,7 @@ pub fn specializes<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
                              .unwrap()
                              .subst(tcx, &penv.free_substs);
 
-    let result = tcx.normalizing_infer_ctxt(Reveal::ExactMatch).enter(|mut infcx| {
+    let result = tcx.infer_ctxt(None, None, Reveal::ExactMatch).enter(|mut infcx| {
         // Normalize the trait reference, adding any obligations
         // that arise into the impl1 assumptions.
         let Normalized { value: impl1_trait_ref, obligations: normalization_obligations } = {
@@ -207,24 +207,27 @@ fn fulfill_implication<'a, 'gcx, 'tcx>(infcx: &InferCtxt<'a, 'gcx, 'tcx>,
     for oblig in obligations.into_iter() {
         fulfill_cx.register_predicate_obligation(&infcx, oblig);
     }
+    match fulfill_cx.select_all_or_error(infcx) {
+        Err(errors) => {
+            // no dice!
+            debug!("fulfill_implication: for impls on {:?} and {:?}, could not fulfill: {:?} given \
+                    {:?}",
+                   source_trait_ref,
+                   target_trait_ref,
+                   errors,
+                   infcx.parameter_environment.caller_bounds);
+            Err(())
+        }
 
-    if let Err(errors) = infcx.drain_fulfillment_cx(&mut fulfill_cx, &()) {
-        // no dice!
-        debug!("fulfill_implication: for impls on {:?} and {:?}, could not fulfill: {:?} given \
-                {:?}",
-               source_trait_ref,
-               target_trait_ref,
-               errors,
-               infcx.parameter_environment.caller_bounds);
-        Err(())
-    } else {
-        debug!("fulfill_implication: an impl for {:?} specializes {:?}",
-               source_trait_ref,
-               target_trait_ref);
+        Ok(()) => {
+            debug!("fulfill_implication: an impl for {:?} specializes {:?}",
+                   source_trait_ref,
+                   target_trait_ref);
 
-        // Now resolve the *substitution* we built for the target earlier, replacing
-        // the inference variables inside with whatever we got from fulfillment.
-        Ok(infcx.resolve_type_vars_if_possible(&target_substs))
+            // Now resolve the *substitution* we built for the target earlier, replacing
+            // the inference variables inside with whatever we got from fulfillment.
+            Ok(infcx.resolve_type_vars_if_possible(&target_substs))
+        }
     }
 }
 

src/librustc/ty/mod.rs

@@ -953,8 +953,9 @@ impl<'tcx> TraitPredicate<'tcx> {
                     _ =>
                         None
                 })
+                .chain(iter::once(self.def_id()))
                 .collect();
-        DepNode::TraitSelect(self.def_id(), def_ids)
+        DepNode::TraitSelect(def_ids)
     }
 
     pub fn input_types<'a>(&'a self) -> impl DoubleEndedIterator<Item=Ty<'tcx>> + 'a {

src/librustc_lint/types.rs

@@ -691,7 +691,7 @@ impl LateLintPass for VariantSizeDifferences {
         if let hir::ItemEnum(ref enum_definition, ref gens) = it.node {
             if gens.ty_params.is_empty() {  // sizes only make sense for non-generic types
                 let t = cx.tcx.node_id_to_type(it.id);
-                let layout = cx.tcx.normalizing_infer_ctxt(Reveal::All).enter(|infcx| {
+                let layout = cx.tcx.infer_ctxt(None, None, Reveal::All).enter(|infcx| {
                     let ty = cx.tcx.erase_regions(&t);
                     ty.layout(&infcx).unwrap_or_else(|e| {
                         bug!("failed to get layout for `{}`: {}", t, e)

src/librustc_trans/base.rs

@@ -1128,7 +1128,7 @@ pub fn trans_instance<'a, 'tcx>(ccx: &CrateContext<'a, 'tcx>, instance: Instance
 
     let fn_ty = ccx.tcx().lookup_item_type(instance.def).ty;
     let fn_ty = ccx.tcx().erase_regions(&fn_ty);
-    let fn_ty = monomorphize::apply_param_substs(ccx.tcx(), instance.substs, &fn_ty);
+    let fn_ty = monomorphize::apply_param_substs(ccx.shared(), instance.substs, &fn_ty);
 
     let sig = ccx.tcx().erase_late_bound_regions(fn_ty.fn_sig());
     let sig = ccx.tcx().normalize_associated_type(&sig);
@@ -1151,7 +1151,7 @@ pub fn trans_ctor_shim<'a, 'tcx>(ccx: &CrateContext<'a, 'tcx>,
     attributes::set_frame_pointer_elimination(ccx, llfndecl);
 
     let ctor_ty = ccx.tcx().lookup_item_type(def_id).ty;
-    let ctor_ty = monomorphize::apply_param_substs(ccx.tcx(), substs, &ctor_ty);
+    let ctor_ty = monomorphize::apply_param_substs(ccx.shared(), substs, &ctor_ty);
 
     let sig = ccx.tcx().erase_late_bound_regions(&ctor_ty.fn_sig());
     let sig = ccx.tcx().normalize_associated_type(&sig);
@@ -1894,7 +1894,7 @@ fn collect_and_partition_translation_items<'a, 'tcx>(scx: &SharedCrateContext<'a
     };
 
     let codegen_units = time(time_passes, "codegen unit partitioning", || {
-        partitioning::partition(scx.tcx(),
+        partitioning::partition(scx,
                                 items.iter().cloned(),
                                 strategy,
                                 &inlining_map,

src/librustc_trans/callee.rs

@@ -28,7 +28,7 @@ use base;
 use base::*;
 use build::*;
 use closure;
-use common::{self, Block, Result, CrateContext, FunctionContext};
+use common::{self, Block, Result, CrateContext, FunctionContext, SharedCrateContext};
 use consts;
 use debuginfo::DebugLoc;
 use declare;
@@ -37,7 +37,7 @@ use monomorphize::{self, Instance};
 use trans_item::TransItem;
 use type_of;
 use Disr;
-use rustc::ty::{self, Ty, TyCtxt, TypeFoldable};
+use rustc::ty::{self, Ty, TypeFoldable};
 use rustc::hir;
 
 use syntax_pos::DUMMY_SP;
@@ -97,7 +97,7 @@ impl<'tcx> Callee<'tcx> {
             return Callee::trait_method(ccx, trait_id, def_id, substs);
         }
 
-        let fn_ty = def_ty(tcx, def_id, substs);
+        let fn_ty = def_ty(ccx.shared(), def_id, substs);
         if let ty::TyFnDef(_, _, f) = fn_ty.sty {
             if f.abi == Abi::RustIntrinsic || f.abi == Abi::PlatformIntrinsic {
                 return Callee {
@@ -155,20 +155,20 @@ impl<'tcx> Callee<'tcx> {
                                                          vtable_closure.substs,
                                                          trait_closure_kind);
 
-                let method_ty = def_ty(tcx, def_id, substs);
+                let method_ty = def_ty(ccx.shared(), def_id, substs);
                 Callee::ptr(llfn, method_ty)
             }
             traits::VtableFnPointer(vtable_fn_pointer) => {
                 let trait_closure_kind = tcx.lang_items.fn_trait_kind(trait_id).unwrap();
                 let llfn = trans_fn_pointer_shim(ccx, trait_closure_kind, vtable_fn_pointer.fn_ty);
 
-                let method_ty = def_ty(tcx, def_id, substs);
+                let method_ty = def_ty(ccx.shared(), def_id, substs);
                 Callee::ptr(llfn, method_ty)
             }
             traits::VtableObject(ref data) => {
                 Callee {
                     data: Virtual(tcx.get_vtable_index_of_object_method(data, def_id)),
-                    ty: def_ty(tcx, def_id, substs)
+                    ty: def_ty(ccx.shared(), def_id, substs)
                 }
             }
             vtable => {
@@ -244,12 +244,12 @@ impl<'tcx> Callee<'tcx> {
 }
 
 /// Given a DefId and some Substs, produces the monomorphic item type.
-fn def_ty<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
+fn def_ty<'a, 'tcx>(shared: &SharedCrateContext<'a, 'tcx>,
                     def_id: DefId,
                     substs: &'tcx Substs<'tcx>)
                     -> Ty<'tcx> {
-    let ty = tcx.lookup_item_type(def_id).ty;
-    monomorphize::apply_param_substs(tcx, substs, &ty)
+    let ty = shared.tcx().lookup_item_type(def_id).ty;
+    monomorphize::apply_param_substs(shared, substs, &ty)
 }
 
 /// Translates an adapter that implements the `Fn` trait for a fn
@@ -407,7 +407,7 @@ fn get_fn<'a, 'tcx>(ccx: &CrateContext<'a, 'tcx>,
     let substs = tcx.normalize_associated_type(&substs);
     let instance = Instance::new(def_id, substs);
     let item_ty = ccx.tcx().lookup_item_type(def_id).ty;
-    let fn_ty = monomorphize::apply_param_substs(ccx.tcx(), substs, &item_ty);
+    let fn_ty = monomorphize::apply_param_substs(ccx.shared(), substs, &item_ty);
 
     if let Some(&llfn) = ccx.instances().borrow().get(&instance) {
         return (llfn, fn_ty);