rustc_trans: simplify vtable and symbol handling.

Author: eddyb

src/librustc/traits/mod.rs

@@ -40,7 +40,7 @@ pub use self::select::{EvaluationCache, SelectionContext, SelectionCache};
 pub use self::select::{MethodMatchResult, MethodMatched, MethodAmbiguous, MethodDidNotMatch};
 pub use self::select::{MethodMatchedData}; // intentionally don't export variants
 pub use self::specialize::{OverlapError, specialization_graph, specializes, translate_substs};
-pub use self::specialize::{SpecializesCache};
+pub use self::specialize::{SpecializesCache, find_method};
 pub use self::util::elaborate_predicates;
 pub use self::util::supertraits;
 pub use self::util::Supertraits;
@@ -527,6 +527,88 @@ pub fn fully_normalize<'a, 'gcx, 'tcx, T>(infcx: &InferCtxt<'a, 'gcx, 'tcx>,
     Ok(resolved_value)
 }
 
+/// Normalizes the predicates and checks whether they hold.  If this
+/// returns false, then either normalize encountered an error or one
+/// of the predicates did not hold. Used when creating vtables to
+/// check for unsatisfiable methods.
+pub fn normalize_and_test_predicates<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
+                                               predicates: Vec<ty::Predicate<'tcx>>)
+                                               -> bool
+{
+    debug!("normalize_and_test_predicates(predicates={:?})",
+           predicates);
+
+    tcx.infer_ctxt(None, None, Reveal::All).enter(|infcx| {
+        let mut selcx = SelectionContext::new(&infcx);
+        let mut fulfill_cx = FulfillmentContext::new();
+        let cause = ObligationCause::dummy();
+        let Normalized { value: predicates, obligations } =
+            normalize(&mut selcx, cause.clone(), &predicates);
+        for obligation in obligations {
+            fulfill_cx.register_predicate_obligation(&infcx, obligation);
+        }
+        for predicate in predicates {
+            let obligation = Obligation::new(cause.clone(), predicate);
+            fulfill_cx.register_predicate_obligation(&infcx, obligation);
+        }
+
+        fulfill_cx.select_all_or_error(&infcx).is_ok()
+    })
+}
+
+/// Given a trait `trait_ref`, iterates the vtable entries
+/// that come from `trait_ref`, including its supertraits.
+#[inline] // FIXME(#35870) Avoid closures being unexported due to impl Trait.
+pub fn get_vtable_methods<'a, 'tcx>(
+    tcx: TyCtxt<'a, 'tcx, 'tcx>,
+    trait_ref: ty::PolyTraitRef<'tcx>)
+    -> impl Iterator<Item=Option<(DefId, &'tcx Substs<'tcx>)>> + 'a
+{
+    debug!("get_vtable_methods({:?})", trait_ref);
+
+    supertraits(tcx, trait_ref).flat_map(move |trait_ref| {
+        tcx.populate_implementations_for_trait_if_necessary(trait_ref.def_id());
+
+        let trait_item_def_ids = tcx.impl_or_trait_items(trait_ref.def_id());
+        let trait_methods = (0..trait_item_def_ids.len()).filter_map(move |i| {
+            match tcx.impl_or_trait_item(trait_item_def_ids[i]) {
+                ty::MethodTraitItem(m) => Some(m),
+                _ => None
+            }
+        });
+
+        // Now list each method's DefId and Substs (for within its trait).
+        // If the method can never be called from this object, produce None.
+        trait_methods.map(move |trait_method| {
+            debug!("get_vtable_methods: trait_method={:?}", trait_method);
+
+            // Some methods cannot be called on an object; skip those.
+            if !tcx.is_vtable_safe_method(trait_ref.def_id(), &trait_method) {
+                debug!("get_vtable_methods: not vtable safe");
+                return None;
+            }
+
+            // the method may have some early-bound lifetimes, add
+            // regions for those
+            let substs = Substs::for_item(tcx, trait_method.def_id,
+                                            |_, _| tcx.mk_region(ty::ReErased),
+                                            |def, _| trait_ref.substs().type_for_def(def));
+
+            // It's possible that the method relies on where clauses that
+            // do not hold for this particular set of type parameters.
+            // Note that this method could then never be called, so we
+            // do not want to try and trans it, in that case (see #23435).
+            let predicates = trait_method.predicates.instantiate_own(tcx, substs);
+            if !normalize_and_test_predicates(tcx, predicates.predicates) {
+                debug!("get_vtable_methods: predicates do not hold");
+                return None;
+            }
+
+            Some((trait_method.def_id, substs))
+        })
+    })
+}
+
 impl<'tcx,O> Obligation<'tcx,O> {
     pub fn new(cause: ObligationCause<'tcx>,
                trait_ref: O)

src/librustc/traits/specialize/mod.rs

@@ -26,9 +26,11 @@ use infer::{InferCtxt, TypeOrigin};
 use middle::region;
 use ty::subst::{Subst, Substs};
 use traits::{self, Reveal, ObligationCause, Normalized};
-use ty::{self, TyCtxt};
+use ty::{self, TyCtxt, TypeFoldable};
 use syntax_pos::DUMMY_SP;
 
+use syntax::ast;
+
 pub mod specialization_graph;
 
 /// Information pertinent to an overlapping impl error.
@@ -103,6 +105,41 @@ pub fn translate_substs<'a, 'gcx, 'tcx>(infcx: &InferCtxt<'a, 'gcx, 'tcx>,
     source_substs.rebase_onto(infcx.tcx, source_impl, target_substs)
 }
 
+/// Given a selected impl described by `impl_data`, returns the
+/// definition and substitions for the method with the name `name`,
+/// and trait method substitutions `substs`, in that impl, a less
+/// specialized impl, or the trait default, whichever applies.
+pub fn find_method<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
+                             name: ast::Name,
+                             substs: &'tcx Substs<'tcx>,
+                             impl_data: &super::VtableImplData<'tcx, ()>)
+                             -> (DefId, &'tcx Substs<'tcx>)
+{
+    assert!(!substs.needs_infer());
+
+    let trait_def_id = tcx.trait_id_of_impl(impl_data.impl_def_id).unwrap();
+    let trait_def = tcx.lookup_trait_def(trait_def_id);
+
+    match trait_def.ancestors(impl_data.impl_def_id).fn_defs(tcx, name).next() {
+        Some(node_item) => {
+            let substs = tcx.infer_ctxt(None, None, Reveal::All).enter(|infcx| {
+                let substs = substs.rebase_onto(tcx, trait_def_id, impl_data.substs);
+                let substs = translate_substs(&infcx, impl_data.impl_def_id,
+                                              substs, node_item.node);
+                tcx.lift(&substs).unwrap_or_else(|| {
+                    bug!("find_method: translate_substs \
+                          returned {:?} which contains inference types/regions",
+                         substs);
+                })
+            });
+            (node_item.item.def_id, substs)
+        }
+        None => {
+            bug!("method {:?} not found in {:?}", name, impl_data.impl_def_id)
+        }
+    }
+}
+
 /// Is impl1 a specialization of impl2?
 ///
 /// Specialization is determined by the sets of types to which the impls apply;

src/librustc_trans/back/symbol_names.rs

@@ -97,7 +97,7 @@
 //! virtually impossible. Thus, symbol hash generation exclusively relies on
 //! DefPaths which are much more robust in the face of changes to the code base.
 
-use common::{CrateContext, SharedCrateContext, gensym_name};
+use common::SharedCrateContext;
 use monomorphize::Instance;
 use util::sha2::{Digest, Sha256};
 
@@ -152,16 +152,17 @@ fn get_symbol_hash<'a, 'tcx>(scx: &SharedCrateContext<'a, 'tcx>,
     let mut hash_state = scx.symbol_hasher().borrow_mut();
     record_time(&tcx.sess.perf_stats.symbol_hash_time, || {
         hash_state.reset();
+        let mut hasher = Sha256Hasher(&mut hash_state);
 
-        let mut hasher = ty::util::TypeIdHasher::new(tcx, Sha256Hasher(&mut hash_state));
         // the main symbol name is not necessarily unique; hash in the
         // compiler's internal def-path, guaranteeing each symbol has a
         // truly unique path
-        hasher.hash(def_path.to_string(tcx));
+        def_path.deterministic_hash_to(tcx, &mut hasher);
 
         // Include the main item-type. Note that, in this case, the
         // assertions about `needs_subst` may not hold, but this item-type
         // ought to be the same for every reference anyway.
+        let mut hasher = ty::util::TypeIdHasher::new(tcx, hasher);
         assert!(!item_type.has_erasable_regions());
         hasher.visit_ty(item_type);
 
@@ -172,18 +173,15 @@ fn get_symbol_hash<'a, 'tcx>(scx: &SharedCrateContext<'a, 'tcx>,
             substs.visit_with(&mut hasher);
         }
     });
-    fn truncated_hash_result(symbol_hasher: &mut Sha256) -> String {
-        let output = symbol_hasher.result_bytes();
-        // 64 bits should be enough to avoid collisions.
-        output[.. 8].to_hex()
-    }
 
-    format!("h{}", truncated_hash_result(&mut hash_state))
+    // 64 bits should be enough to avoid collisions.
+    let output = hash_state.result_bytes();
+    format!("h{}", output[..8].to_hex())
 }
 
 impl<'a, 'tcx> Instance<'tcx> {
     pub fn symbol_name(self, scx: &SharedCrateContext<'a, 'tcx>) -> String {
-        let Instance { def: def_id, ref substs } = self;
+        let Instance { def: def_id, substs } = self;
 
         debug!("symbol_name(def_id={:?}, substs={:?})",
                def_id, substs);
@@ -278,7 +276,7 @@ impl<'a, 'tcx> Instance<'tcx> {
             scx.tcx().push_item_path(&mut buffer, def_id);
         });
 
-        mangle(buffer.names.into_iter(), Some(&hash[..]))
+        mangle(buffer.names.into_iter(), &hash)
     }
 }
 
@@ -307,23 +305,7 @@ pub fn exported_name_from_type_and_prefix<'a, 'tcx>(scx: &SharedCrateContext<'a,
     };
     let hash = get_symbol_hash(scx, &empty_def_path, t, None);
     let path = [token::intern_and_get_ident(prefix)];
-    mangle(path.iter().cloned(), Some(&hash[..]))
-}
-
-/// Only symbols that are invisible outside their compilation unit should use a
-/// name generated by this function.
-pub fn internal_name_from_type_and_suffix<'a, 'tcx>(ccx: &CrateContext<'a, 'tcx>,
-                                                    t: Ty<'tcx>,
-                                                    suffix: &str)
-                                                    -> String {
-    let path = [token::intern(&t.to_string()).as_str(),
-                gensym_name(suffix).as_str()];
-    let def_path = DefPath {
-        data: vec![],
-        krate: LOCAL_CRATE,
-    };
-    let hash = get_symbol_hash(ccx.shared(), &def_path, t, None);
-    mangle(path.iter().cloned(), Some(&hash[..]))
+    mangle(path.iter().cloned(), &hash)
 }
 
 // Name sanitation. LLVM will happily accept identifiers with weird names, but
@@ -376,7 +358,7 @@ pub fn sanitize(s: &str) -> String {
     return result;
 }
 
-pub fn mangle<PI: Iterator<Item=InternedString>>(path: PI, hash: Option<&str>) -> String {
+fn mangle<PI: Iterator<Item=InternedString>>(path: PI, hash: &str) -> String {
     // Follow C++ namespace-mangling style, see
     // http://en.wikipedia.org/wiki/Name_mangling for more info.
     //
@@ -403,9 +385,7 @@ pub fn mangle<PI: Iterator<Item=InternedString>>(path: PI, hash: Option<&str>) -
         push(&mut n, &data);
     }
 
-    if let Some(s) = hash {
-        push(&mut n, s)
-    }
+    push(&mut n, hash);
 
     n.push('E'); // End name-sequence.
     n

src/librustc_trans/callee.rs

@@ -17,7 +17,6 @@
 pub use self::CalleeData::*;
 
 use arena::TypedArena;
-use back::symbol_names;
 use llvm::{self, ValueRef, get_params};
 use rustc::hir::def_id::DefId;
 use rustc::ty::subst::Substs;
@@ -133,34 +132,36 @@ impl<'tcx> Callee<'tcx> {
         let trait_ref = tcx.normalize_associated_type(&ty::Binder(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);
-                // create a concatenated set of substitutions which includes
-                // those from the impl and those from the method:
-                let mth = meth::get_impl_method(tcx, substs, impl_did, vtable_impl.substs, mname);
+                let name = tcx.item_name(def_id);
+                let (def_id, substs) = traits::find_method(tcx, name, substs, &vtable_impl);
 
                 // Translate the function, bypassing Callee::def.
                 // That is because default methods have the same ID as the
                 // trait method used to look up the impl method that ended
                 // up here, so calling Callee::def would infinitely recurse.
-                let (llfn, ty) = get_fn(ccx, mth.method.def_id, mth.substs);
+                let (llfn, ty) = get_fn(ccx, def_id, substs);
                 Callee::ptr(llfn, ty)
             }
             traits::VtableClosure(vtable_closure) => {
                 // The substitutions should have no type parameters remaining
                 // after passing through fulfill_obligation
                 let trait_closure_kind = tcx.lang_items.fn_trait_kind(trait_id).unwrap();
+                let instance = Instance::new(def_id, substs);
                 let llfn = closure::trans_closure_method(ccx,
                                                          vtable_closure.closure_def_id,
                                                          vtable_closure.substs,
+                                                         instance,
                                                          trait_closure_kind);
 
                 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 instance = Instance::new(def_id, substs);
+                let llfn = trans_fn_pointer_shim(ccx, instance,
+                                                 trait_closure_kind,
+                                                 vtable_fn_pointer.fn_ty);
 
                 let method_ty = def_ty(ccx.shared(), def_id, substs);
                 Callee::ptr(llfn, method_ty)
@@ -217,9 +218,7 @@ impl<'tcx> Callee<'tcx> {
     pub fn reify<'a>(self, ccx: &CrateContext<'a, 'tcx>) -> ValueRef {
         match self.data {
             Fn(llfn) => llfn,
-            Virtual(idx) => {
-                meth::trans_object_shim(ccx, self.ty, idx)
-            }
+            Virtual(_) => meth::trans_object_shim(ccx, self),
             NamedTupleConstructor(disr) => match self.ty.sty {
                 ty::TyFnDef(def_id, substs, _) => {
                     let instance = Instance::new(def_id, substs);
@@ -264,8 +263,9 @@ fn def_ty<'a, 'tcx>(shared: &SharedCrateContext<'a, 'tcx>,
 /// ```
 ///
 /// but for the bare function type given.
-pub fn trans_fn_pointer_shim<'a, 'tcx>(
+fn trans_fn_pointer_shim<'a, 'tcx>(
     ccx: &'a CrateContext<'a, 'tcx>,
+    method_instance: Instance<'tcx>,
     closure_kind: ty::ClosureKind,
     bare_fn_ty: Ty<'tcx>)
     -> ValueRef
@@ -345,10 +345,7 @@ pub fn trans_fn_pointer_shim<'a, 'tcx>(
     debug!("tuple_fn_ty: {:?}", tuple_fn_ty);
 
     //
-    let function_name =
-        symbol_names::internal_name_from_type_and_suffix(ccx,
-                                                         bare_fn_ty,
-                                                         "fn_pointer_shim");
+    let function_name = method_instance.symbol_name(ccx.shared());
     let llfn = declare::define_internal_fn(ccx, &function_name, tuple_fn_ty);
     attributes::set_frame_pointer_elimination(ccx, llfn);
     //

src/librustc_trans/closure.rs

@@ -9,7 +9,6 @@
 // except according to those terms.
 
 use arena::TypedArena;
-use back::symbol_names;
 use llvm::{self, ValueRef, get_params};
 use rustc::hir::def_id::DefId;
 use abi::{Abi, FnType};
@@ -152,6 +151,7 @@ pub fn trans_closure_body_via_mir<'a, 'tcx>(ccx: &CrateContext<'a, 'tcx>,
 pub fn trans_closure_method<'a, 'tcx>(ccx: &'a CrateContext<'a, 'tcx>,
                                       closure_def_id: DefId,
                                       substs: ty::ClosureSubsts<'tcx>,
+                                      method_instance: Instance<'tcx>,
                                       trait_closure_kind: ty::ClosureKind)
                                       -> ValueRef
 {
@@ -199,7 +199,7 @@ pub fn trans_closure_method<'a, 'tcx>(ccx: &'a CrateContext<'a, 'tcx>,
             //     fn call_once(mut self, ...) { call_mut(&mut self, ...) }
             //
             // These are both the same at trans time.
-            trans_fn_once_adapter_shim(ccx, closure_def_id, substs, llfn)
+            trans_fn_once_adapter_shim(ccx, closure_def_id, substs, method_instance, llfn)
         }
         _ => {
             bug!("trans_closure_adapter_shim: cannot convert {:?} to {:?}",
@@ -213,6 +213,7 @@ fn trans_fn_once_adapter_shim<'a, 'tcx>(
     ccx: &'a CrateContext<'a, 'tcx>,
     closure_def_id: DefId,
     substs: ty::ClosureSubsts<'tcx>,
+    method_instance: Instance<'tcx>,
     llreffn: ValueRef)
     -> ValueRef
 {
@@ -255,8 +256,7 @@ fn trans_fn_once_adapter_shim<'a, 'tcx>(
     }));
 
     // Create the by-value helper.
-    let function_name =
-        symbol_names::internal_name_from_type_and_suffix(ccx, llonce_fn_ty, "once_shim");
+    let function_name = method_instance.symbol_name(ccx.shared());
     let lloncefn = declare::declare_fn(ccx, &function_name, llonce_fn_ty);
     attributes::set_frame_pointer_elimination(ccx, lloncefn);