librustc: Introduce a "quick reject" mechanism to quickly throw out

method candidates and prevent method lookup from being invoked at all
for overloaded operators.

40%-50% improvement in typechecking time.

Author: pcwalton

src/librustc/driver/config.rs

@@ -101,7 +101,7 @@ pub struct Options {
     /// An optional name to use as the crate for std during std injection,
     /// written `extern crate std = "name"`. Default to "std". Used by
     /// out-of-tree drivers.
-    pub alt_std_name: Option<String>
+    pub alt_std_name: Option<String>,
 }
 
 /// Some reasonable defaults
@@ -841,7 +841,7 @@ pub fn build_session_options(matches: &getopts::Matches) -> Options {
         color: color,
         externs: externs,
         crate_name: crate_name,
-        alt_std_name: None
+        alt_std_name: None,
     }
 }
 

src/librustc/middle/ty.rs

@@ -586,6 +586,11 @@ pub struct ctxt<'tcx> {
 
     /// Caches the representation hints for struct definitions.
     pub repr_hint_cache: RefCell<DefIdMap<Rc<Vec<attr::ReprAttr>>>>,
+
+    pub overloaded_operator_filter:
+        RefCell<HashMap<SimplifiedType,OverloadedOperatorFilter>>,
+
+    pub smart_pointers: RefCell<DefIdSet>,
 }
 
 pub enum tbox_flag {
@@ -1537,6 +1542,8 @@ pub fn mk_ctxt<'tcx>(s: Session,
         trait_associated_types: RefCell::new(DefIdMap::new()),
         selection_cache: traits::SelectionCache::new(),
         repr_hint_cache: RefCell::new(DefIdMap::new()),
+        overloaded_operator_filter: RefCell::new(HashMap::new()),
+        smart_pointers: RefCell::new(DefIdSet::new()),
    }
 }
 
@@ -5598,3 +5605,186 @@ pub fn with_freevars<T>(tcx: &ty::ctxt, fid: ast::NodeId, f: |&[Freevar]| -> T)
         Some(d) => f(d.as_slice())
     }
 }
+
+pub enum AllowDerefableFlag<'a> {
+    AllowDerefable,
+    DisallowDerefable(&'a ParameterEnvironment),
+}
+
+#[deriving(Clone, PartialEq, Eq, Hash)]
+pub enum SimplifiedType {
+    NilSimplifiedType,
+    BoolSimplifiedType,
+    CharSimplifiedType,
+    IntSimplifiedType(ast::IntTy),
+    UintSimplifiedType(ast::UintTy),
+    FloatSimplifiedType(ast::FloatTy),
+    EnumSimplifiedType(DefId),
+    StrSimplifiedType,
+    VecSimplifiedType,
+    PtrSimplifiedType,
+    TupleSimplifiedType(uint),
+    TraitSimplifiedType(DefId),
+    StructSimplifiedType(DefId),
+    UnboxedClosureSimplifiedType(DefId),
+    FunctionSimplifiedType(uint),
+    ParameterSimplifiedType,
+}
+
+impl SimplifiedType {
+    pub fn from_type(tcx: &ctxt,
+                     ty: ty::t,
+                     can_simplify_params: bool,
+                     allow_derefable: AllowDerefableFlag)
+                     -> Option<SimplifiedType> {
+        let simplified_type = match get(ty).sty {
+            ty_nil => Some(NilSimplifiedType),
+            ty_bool => Some(BoolSimplifiedType),
+            ty_char => Some(CharSimplifiedType),
+            ty_int(int_type) => Some(IntSimplifiedType(int_type)),
+            ty_uint(uint_type) => Some(UintSimplifiedType(uint_type)),
+            ty_float(float_type) => Some(FloatSimplifiedType(float_type)),
+            ty_enum(def_id, _) => Some(EnumSimplifiedType(def_id)),
+            ty_str => Some(StrSimplifiedType),
+            ty_trait(ref trait_info) => {
+                Some(TraitSimplifiedType(trait_info.def_id))
+            }
+            ty_struct(def_id, _) => {
+                Some(StructSimplifiedType(def_id))
+            }
+            ty_unboxed_closure(def_id, _) => {
+                Some(UnboxedClosureSimplifiedType(def_id))
+            }
+            ty_vec(..) => Some(VecSimplifiedType),
+            ty_ptr(_) => Some(PtrSimplifiedType),
+            ty_rptr(_, ref mt) => {
+                SimplifiedType::from_type(tcx,
+                                          mt.ty,
+                                          can_simplify_params,
+                                          allow_derefable)
+            }
+            ty_uniq(ref ty) => {
+                SimplifiedType::from_type(tcx,
+                                          *ty,
+                                          can_simplify_params,
+                                          allow_derefable)
+            }
+            ty_tup(ref tys) => Some(TupleSimplifiedType(tys.len())),
+            ty_closure(ref f) => {
+                Some(FunctionSimplifiedType(f.sig.inputs.len()))
+            }
+            ty_bare_fn(ref f) => {
+                Some(FunctionSimplifiedType(f.sig.inputs.len()))
+            }
+            ty_param(_) if can_simplify_params => {
+                Some(ParameterSimplifiedType)
+            }
+            ty_bot | ty_param(_) | ty_open(_) | ty_infer(_) | ty_err => None,
+        };
+
+        let simplified_type = match simplified_type {
+            None => return None,
+            Some(simplified_type) => simplified_type,
+        };
+
+        match allow_derefable {
+            AllowDerefable => {}
+            DisallowDerefable(param_env) => {
+                match tcx.overloaded_operator_filter
+                         .borrow()
+                         .find(&simplified_type) {
+                    Some(ref flags) if flags.contains(
+                            DEREF_OVERLOADED_OPERATOR_FILTER) => {
+                        return None
+                    }
+                    Some(_) | None => {}
+                }
+
+                match get(ty).sty {
+                    ty_param(ref param_ty) => {
+                        let bounds = &param_env.bounds
+                                               .get(param_ty.space,
+                                                    param_ty.idx)
+                                               .trait_bounds;
+                        for bound in bounds.iter() {
+                            let bad = Some(bound.def_id) ==
+                                    tcx.lang_items.deref_trait() ||
+                                    Some(bound.def_id) ==
+                                    tcx.lang_items.deref_mut_trait();
+                            debug!("for param {} bound {} deref {} bad {}",
+                                   param_ty.repr(tcx),
+                                   bound.repr(tcx),
+                                   tcx.lang_items.deref_trait(),
+                                   bad);
+                            if bad {
+                                return None
+                            }
+                        }
+                    }
+                    _ => {}
+                }
+            }
+        }
+
+        Some(simplified_type)
+    }
+}
+
+pub enum MethodLookupKey {
+    SimplifiedTypeLookupKey(SimplifiedType),
+    SmartPointerLookupKey(ast::DefId, SimplifiedType),
+}
+
+impl MethodLookupKey {
+    pub fn from_type(tcx: &ctxt, ty: ty::t, param_env: &ParameterEnvironment)
+                     -> Option<MethodLookupKey> {
+        match get(ty).sty {
+            ty_struct(def_id, ref substs) => {
+                if tcx.smart_pointers.borrow().contains(&def_id) {
+                    let simplified_referent = SimplifiedType::from_type(
+                        tcx,
+                        *substs.types.get(subst::TypeSpace, 0),
+                        true,
+                        DisallowDerefable(param_env));
+                    match simplified_referent {
+                        None => return None,
+                        Some(simplified_referent) => {
+                            return Some(SmartPointerLookupKey(
+                                    def_id,
+                                    simplified_referent))
+                        }
+                    }
+                }
+            }
+            _ => {}
+        }
+
+        match SimplifiedType::from_type(tcx,
+                                        ty,
+                                        true,
+                                        DisallowDerefable(param_env)) {
+            None => None,
+            Some(simplified_type) => {
+                Some(SimplifiedTypeLookupKey(simplified_type))
+            }
+        }
+    }
+
+    pub fn might_match(&self, other: &SimplifiedType) -> bool {
+        match *self {
+            SimplifiedTypeLookupKey(ref this) => *this == *other,
+            SmartPointerLookupKey(def_id, ref this) => {
+                *this == *other || StructSimplifiedType(def_id) == *other
+            }
+        }
+    }
+}
+
+bitflags! {
+    flags OverloadedOperatorFilter: u8 {
+        const INDEX_OVERLOADED_OPERATOR_FILTER = 0x01,
+        const DEREF_OVERLOADED_OPERATOR_FILTER = 0x02,
+        const CALL_OVERLOADED_OPERATOR_FILTER = 0x04
+    }
+}
+

src/librustc/middle/typeck/check/method.rs

@@ -161,7 +161,15 @@ pub fn lookup<'a, 'tcx>(
     lcx.push_inherent_candidates(self_ty);
     debug!("searching extension candidates");
     lcx.push_bound_candidates(self_ty, None);
-    lcx.push_extension_candidates(expr.id);
+
+    let method_lookup_key = MethodLookupKey::from_type(fcx.tcx(),
+                                                       self_ty,
+                                                       &fcx.inh.param_env);
+    if method_lookup_key.is_none() {
+        debug!("couldn't simplify {}", lcx.ty_to_string(self_ty));
+    }
+    lcx.push_extension_candidates(expr.id, &method_lookup_key);
+
     lcx.search(self_ty)
 }
 
@@ -197,7 +205,14 @@ pub fn lookup_in_trait<'a, 'tcx>(
            self_ty.repr(fcx.tcx()), self_expr.map(|e| e.repr(fcx.tcx())));
 
     lcx.push_bound_candidates(self_ty, Some(trait_did));
-    lcx.push_extension_candidate(trait_did);
+
+    let method_lookup_key = MethodLookupKey::from_type(fcx.tcx(),
+                                                       self_ty,
+                                                       &fcx.inh.param_env);
+    if method_lookup_key.is_none() {
+        debug!("couldn't simplify {}", lcx.ty_to_string(self_ty));
+    }
+    lcx.push_extension_candidate(trait_did, &method_lookup_key);
     lcx.search(self_ty)
 }
 
@@ -484,7 +499,9 @@ impl<'a, 'tcx> LookupContext<'a, 'tcx> {
         });
     }
 
-    fn push_extension_candidate(&mut self, trait_did: DefId) {
+    fn push_extension_candidate(&mut self,
+                                trait_did: DefId,
+                                method_lookup_key: &Option<MethodLookupKey>) {
         ty::populate_implementations_for_trait_if_necessary(self.tcx(), trait_did);
 
         // Look for explicit implementations.
@@ -494,12 +511,16 @@ impl<'a, 'tcx> LookupContext<'a, 'tcx> {
                 let items = impl_items.get(impl_did);
                 self.push_candidates_from_impl(*impl_did,
                                                items.as_slice(),
+                                               method_lookup_key,
                                                true);
             }
         }
     }
 
-    fn push_extension_candidates(&mut self, expr_id: ast::NodeId) {
+    fn push_extension_candidates(
+            &mut self,
+            expr_id: ast::NodeId,
+            method_lookup_key: &Option<MethodLookupKey>) {
         // If the method being called is associated with a trait, then
         // find all the impls of that trait.  Each of those are
         // candidates.
@@ -512,7 +533,7 @@ impl<'a, 'tcx> LookupContext<'a, 'tcx> {
                        } else {
                            "(external)".to_string()
                        });
-                self.push_extension_candidate(*trait_did);
+                self.push_extension_candidate(*trait_did, method_lookup_key);
             }
         }
     }
@@ -775,6 +796,7 @@ impl<'a, 'tcx> LookupContext<'a, 'tcx> {
                 let items = impl_items.get(impl_did);
                 self.push_candidates_from_impl(*impl_did,
                                                items.as_slice(),
+                                               &None,
                                                false);
             }
         }
@@ -783,6 +805,7 @@ impl<'a, 'tcx> LookupContext<'a, 'tcx> {
     fn push_candidates_from_impl(&mut self,
                                  impl_did: DefId,
                                  impl_items: &[ImplOrTraitItemId],
+                                 method_lookup_key: &Option<MethodLookupKey>,
                                  is_extension: bool) {
         let did = if self.report_statics == ReportStaticMethods {
             // we only want to report each base trait once
@@ -798,6 +821,38 @@ impl<'a, 'tcx> LookupContext<'a, 'tcx> {
             return; // already visited
         }
 
+        // See if we can quickly reject...
+        match *method_lookup_key {
+            Some(ref method_lookup_key) => {
+                let impl_type = ty::lookup_item_type(self.tcx(), impl_did);
+                let simplified_impl_type =
+                    SimplifiedType::from_type(self.tcx(),
+                                              impl_type.ty,
+                                              false,
+                                              ty::AllowDerefable);
+                match simplified_impl_type {
+                    Some(ref simplified_impl_type) => {
+                        if !method_lookup_key.might_match(
+                                simplified_impl_type) {
+                            debug!("quick reject succeeded");
+                            return
+                        }
+                        debug!("quick reject failed: could possibly unify");
+                    }
+                    None => {
+                        debug!("quick reject failed: impl type {} was \
+                                unsimplifiable",
+                               self.ty_to_string(impl_type.ty));
+                    }
+                }
+            }
+            None => {
+                if is_extension {
+                    debug!("quick reject failed: callee is unsimplifiable");
+                }
+            }
+        }
+
         debug!("push_candidates_from_impl: {} {}",
                token::get_name(self.m_name),
                impl_items.iter()