trans: Make common::fulfill_obligation only depend on SharedCrateContext.

Plus make it produce a nicer dependency graph via DepTrackingMap::memoize().

Author: michaelwoerister

src/librustc_trans/base.rs

@@ -678,7 +678,7 @@ pub fn custom_coerce_unsize_info<'ccx, 'tcx>(ccx: &CrateContext<'ccx, 'tcx>,
         substs: ccx.tcx().mk_substs(trait_substs)
     });
 
-    match fulfill_obligation(ccx, DUMMY_SP, trait_ref) {
+    match fulfill_obligation(ccx.shared(), DUMMY_SP, trait_ref) {
         traits::VtableImpl(traits::VtableImplData { impl_def_id, .. }) => {
             ccx.tcx().custom_coerce_unsized_kind(impl_def_id)
         }

src/librustc_trans/callee.rs

@@ -156,7 +156,7 @@ impl<'tcx> Callee<'tcx> {
         let trait_id = method_item.container().id();
         let trait_ref = ty::Binder(substs.to_trait_ref(tcx, trait_id));
         let trait_ref = infer::normalize_associated_type(tcx, &trait_ref);
-        match common::fulfill_obligation(ccx, DUMMY_SP, trait_ref) {
+        match common::fulfill_obligation(ccx.shared(), DUMMY_SP, trait_ref) {
             traits::VtableImpl(vtable_impl) => {
                 let impl_did = vtable_impl.impl_def_id;
                 let mname = tcx.item_name(def_id);

src/librustc_trans/collector.rs

@@ -701,7 +701,7 @@ fn find_drop_glue_neighbors<'a, 'tcx>(ccx: &CrateContext<'a, 'tcx>,
             substs: self_type_substs,
         }.to_poly_trait_ref();
 
-        let substs = match fulfill_obligation(ccx, DUMMY_SP, trait_ref) {
+        let substs = match fulfill_obligation(ccx.shared(), DUMMY_SP, trait_ref) {
             traits::VtableImpl(data) => data.substs,
             _ => bug!()
         };
@@ -844,7 +844,7 @@ fn do_static_trait_method_dispatch<'a, 'tcx>(ccx: &CrateContext<'a, 'tcx>,
                                                        callee_substs);
 
     let trait_ref = ty::Binder(rcvr_substs.to_trait_ref(tcx, trait_id));
-    let vtbl = fulfill_obligation(ccx, DUMMY_SP, trait_ref);
+    let vtbl = fulfill_obligation(ccx.shared(), DUMMY_SP, trait_ref);
 
     // Now that we know which impl is being used, we can dispatch to
     // the actual function:
@@ -999,7 +999,7 @@ fn create_trans_items_for_vtable_methods<'a, 'tcx>(ccx: &CrateContext<'a, 'tcx>,
 
         // Walk all methods of the trait, including those of its supertraits
         for trait_ref in traits::supertraits(ccx.tcx(), poly_trait_ref) {
-            let vtable = fulfill_obligation(ccx, DUMMY_SP, trait_ref);
+            let vtable = fulfill_obligation(ccx.shared(), DUMMY_SP, trait_ref);
             match vtable {
                 traits::VtableImpl(
                     traits::VtableImplData {

src/librustc_trans/common.rs

@@ -20,6 +20,7 @@ use rustc::cfg;
 use rustc::hir::def::Def;
 use rustc::hir::def_id::DefId;
 use rustc::infer;
+use rustc::util::common::MemoizationMap;
 use middle::lang_items::LangItem;
 use rustc::ty::subst::Substs;
 use abi::{Abi, FnType};
@@ -54,7 +55,7 @@ use syntax::codemap::{DUMMY_SP, Span};
 use syntax::parse::token::InternedString;
 use syntax::parse::token;
 
-pub use context::CrateContext;
+pub use context::{CrateContext, SharedCrateContext};
 
 /// Is the type's representation size known at compile time?
 pub fn type_is_sized<'tcx>(tcx: &TyCtxt<'tcx>, ty: Ty<'tcx>) -> bool {
@@ -1051,7 +1052,7 @@ pub fn expr_ty_adjusted<'blk, 'tcx>(bcx: &BlockS<'blk, 'tcx>, ex: &hir::Expr) ->
 /// Attempts to resolve an obligation. The result is a shallow vtable resolution -- meaning that we
 /// do not (necessarily) resolve all nested obligations on the impl. Note that type check should
 /// guarantee to us that all nested obligations *could be* resolved if we wanted to.
-pub fn fulfill_obligation<'a, 'tcx>(ccx: &CrateContext<'a, 'tcx>,
+pub fn fulfill_obligation<'a, 'tcx>(ccx: &SharedCrateContext<'a, 'tcx>,
                                     span: Span,
                                     trait_ref: ty::PolyTraitRef<'tcx>)
                                     -> traits::Vtable<'tcx, ()>
@@ -1061,68 +1062,63 @@ pub fn fulfill_obligation<'a, 'tcx>(ccx: &CrateContext<'a, 'tcx>,
     // Remove any references to regions; this helps improve caching.
     let trait_ref = tcx.erase_regions(&trait_ref);
 
-    // First check the cache.
-    match ccx.trait_cache().borrow().get(&trait_ref) {
-        Some(vtable) => {
-            info!("Cache hit: {:?}", trait_ref);
-            return (*vtable).clone();
-        }
-        None => { }
-    }
-
-    debug!("trans fulfill_obligation: trait_ref={:?} def_id={:?}",
-           trait_ref, trait_ref.def_id());
-
-
-    // Do the initial selection for the obligation. This yields the
-    // shallow result we are looking for -- that is, what specific impl.
-    let infcx = infer::normalizing_infer_ctxt(tcx, &tcx.tables, ProjectionMode::Any);
-    let mut selcx = SelectionContext::new(&infcx);
-
-    let obligation =
-        traits::Obligation::new(traits::ObligationCause::misc(span, ast::DUMMY_NODE_ID),
-                                trait_ref.to_poly_trait_predicate());
-    let selection = match selcx.select(&obligation) {
-        Ok(Some(selection)) => selection,
-        Ok(None) => {
-            // Ambiguity can happen when monomorphizing during trans
-            // expands to some humongo type that never occurred
-            // statically -- this humongo type can then overflow,
-            // leading to an ambiguous result. So report this as an
-            // overflow bug, since I believe this is the only case
-            // where ambiguity can result.
-            debug!("Encountered ambiguity selecting `{:?}` during trans, \
-                    presuming due to overflow",
-                   trait_ref);
-            ccx.sess().span_fatal(
-                span,
-                "reached the recursion limit during monomorphization (selection ambiguity)");
-        }
-        Err(e) => {
-            span_bug!(
-                span,
-                "Encountered error `{:?}` selecting `{:?}` during trans",
-                e,
-                trait_ref)
-        }
-    };
-
-    // Currently, we use a fulfillment context to completely resolve
-    // all nested obligations. This is because they can inform the
-    // inference of the impl's type parameters.
-    let mut fulfill_cx = traits::FulfillmentContext::new();
-    let vtable = selection.map(|predicate| {
-        fulfill_cx.register_predicate_obligation(&infcx, predicate);
-    });
-    let vtable = infer::drain_fulfillment_cx_or_panic(
-        span, &infcx, &mut fulfill_cx, &vtable
-    );
+    ccx.trait_cache().memoize(trait_ref, || {
+        debug!("trans fulfill_obligation: trait_ref={:?} def_id={:?}",
+               trait_ref, trait_ref.def_id());
+
+        // Do the initial selection for the obligation. This yields the
+        // shallow result we are looking for -- that is, what specific impl.
+        let infcx = infer::normalizing_infer_ctxt(tcx,
+                                                  &tcx.tables,
+                                                  ProjectionMode::Any);
+        let mut selcx = SelectionContext::new(&infcx);
+
+        let obligation_cause = traits::ObligationCause::misc(span,
+                                                             ast::DUMMY_NODE_ID);
+        let obligation = traits::Obligation::new(obligation_cause,
+                                                 trait_ref.to_poly_trait_predicate());
+
+        let selection = match selcx.select(&obligation) {
+            Ok(Some(selection)) => selection,
+            Ok(None) => {
+                // Ambiguity can happen when monomorphizing during trans
+                // expands to some humongo type that never occurred
+                // statically -- this humongo type can then overflow,
+                // leading to an ambiguous result. So report this as an
+                // overflow bug, since I believe this is the only case
+                // where ambiguity can result.
+                debug!("Encountered ambiguity selecting `{:?}` during trans, \
+                        presuming due to overflow",
+                       trait_ref);
+                ccx.sess().span_fatal(
+                    span,
+                    "reached the recursion limit during monomorphization \
+                     (selection ambiguity)");
+            }
+            Err(e) => {
+                span_bug!(
+                    span,
+                    "Encountered error `{:?}` selecting `{:?}` during trans",
+                    e,
+                    trait_ref)
+            }
+        };
 
-    info!("Cache miss: {:?} => {:?}", trait_ref, vtable);
+        // Currently, we use a fulfillment context to completely resolve
+        // all nested obligations. This is because they can inform the
+        // inference of the impl's type parameters.
+        let mut fulfill_cx = traits::FulfillmentContext::new();
+        let vtable = selection.map(|predicate| {
+            fulfill_cx.register_predicate_obligation(&infcx, predicate);
+        });
+        let vtable = infer::drain_fulfillment_cx_or_panic(
+            span, &infcx, &mut fulfill_cx, &vtable
+        );
 
-    ccx.trait_cache().borrow_mut().insert(trait_ref, vtable.clone());
+        info!("Cache miss: {:?} => {:?}", trait_ref, vtable);
 
-    vtable
+        vtable
+    })
 }
 
 /// Normalizes the predicates and checks whether they hold.  If this

src/librustc_trans/context.rs

@@ -84,6 +84,7 @@ pub struct SharedCrateContext<'a, 'tcx: 'a> {
     use_dll_storage_attrs: bool,
 
     translation_items: RefCell<FnvHashMap<TransItem<'tcx>, TransItemState>>,
+    trait_cache: RefCell<DepTrackingMap<TraitSelectionCache<'tcx>>>,
 }
 
 /// The local portion of a `CrateContext`.  There is one `LocalCrateContext`
@@ -169,8 +170,6 @@ pub struct LocalCrateContext<'tcx> {
 
     /// Depth of the current type-of computation - used to bail out
     type_of_depth: Cell<usize>,
-
-    trait_cache: RefCell<DepTrackingMap<TraitSelectionCache<'tcx>>>,
 }
 
 // Implement DepTrackingMapConfig for `trait_cache`
@@ -423,6 +422,7 @@ impl<'b, 'tcx> SharedCrateContext<'b, 'tcx> {
             available_drop_glues: RefCell::new(FnvHashMap()),
             use_dll_storage_attrs: use_dll_storage_attrs,
             translation_items: RefCell::new(FnvHashMap()),
+            trait_cache: RefCell::new(DepTrackingMap::new(tcx.dep_graph.clone())),
         }
     }
 
@@ -446,6 +446,10 @@ impl<'b, 'tcx> SharedCrateContext<'b, 'tcx> {
         &self.item_symbols
     }
 
+    pub fn trait_cache(&self) -> &RefCell<DepTrackingMap<TraitSelectionCache<'tcx>>> {
+        &self.trait_cache
+    }
+
     pub fn link_meta<'a>(&'a self) -> &'a LinkMeta {
         &self.link_meta
     }
@@ -516,9 +520,6 @@ impl<'tcx> LocalCrateContext<'tcx> {
                 intrinsics: RefCell::new(FnvHashMap()),
                 n_llvm_insns: Cell::new(0),
                 type_of_depth: Cell::new(0),
-                trait_cache: RefCell::new(DepTrackingMap::new(shared.tcx
-                                                                    .dep_graph
-                                                                    .clone())),
             };
 
             let (int_type, opaque_vec_type, str_slice_ty, mut local_ccx) = {
@@ -805,10 +806,6 @@ impl<'b, 'tcx> CrateContext<'b, 'tcx> {
         self.local().n_llvm_insns.set(self.local().n_llvm_insns.get() + 1);
     }
 
-    pub fn trait_cache(&self) -> &RefCell<DepTrackingMap<TraitSelectionCache<'tcx>>> {
-        &self.local().trait_cache
-    }
-
     pub fn obj_size_bound(&self) -> u64 {
         self.tcx().data_layout.obj_size_bound()
     }

src/librustc_trans/glue.rs

@@ -364,7 +364,7 @@ fn trans_struct_drop<'blk, 'tcx>(bcx: Block<'blk, 'tcx>,
         def_id: tcx.lang_items.drop_trait().unwrap(),
         substs: tcx.mk_substs(Substs::empty().with_self_ty(t))
     });
-    let vtbl = match fulfill_obligation(bcx.ccx(), DUMMY_SP, trait_ref) {
+    let vtbl = match fulfill_obligation(bcx.ccx().shared(), DUMMY_SP, trait_ref) {
         traits::VtableImpl(data) => data,
         _ => bug!("dtor for {:?} is not an impl???", t)
     };

src/librustc_trans/meth.rs

@@ -144,7 +144,7 @@ pub fn get_vtable<'a, 'tcx>(ccx: &CrateContext<'a, 'tcx>,
 
     // Not in the cache. Build it.
     let methods = traits::supertraits(tcx, trait_ref.clone()).flat_map(|trait_ref| {
-        let vtable = fulfill_obligation(ccx, DUMMY_SP, trait_ref.clone());
+        let vtable = fulfill_obligation(ccx.shared(), DUMMY_SP, trait_ref.clone());
         match vtable {
             // Should default trait error here?
             traits::VtableDefaultImpl(_) |