auto merge of rust-lang#18694 : nikomatsakis/rust/issue-18208-method-dispatch-2, r=nrc

This is a pretty major refactoring of the method dispatch infrastructure. It is intended to avoid gross inefficiencies and enable caching and other optimizations (e.g. rust-lang#17995), though it itself doesn't seem to execute particularly faster yet. It also solves some cases where we were failing to resolve methods that we theoretically should have succeeded with.

Fixes rust-lang#18674.

cc rust-lang#18208

Author: bors

src/librustc/lib.rs

@@ -29,7 +29,7 @@ This API is completely unstable and subject to change.
       html_root_url = "http://doc.rust-lang.org/nightly/")]
 
 #![feature(default_type_params, globs, if_let, import_shadowing, macro_rules, phase, quote)]
-#![feature(slicing_syntax, struct_variant, unsafe_destructor)]
+#![feature(slicing_syntax, struct_variant, tuple_indexing, unsafe_destructor)]
 #![feature(rustc_diagnostic_macros)]
 
 extern crate arena;
@@ -87,6 +87,7 @@ pub mod middle {
     pub mod effect;
     pub mod entry;
     pub mod expr_use_visitor;
+    pub mod fast_reject;
     pub mod graph;
     pub mod intrinsicck;
     pub mod lang_items;

src/librustc/middle/fast_reject.rs

@@ -0,0 +1,105 @@
+// Copyright 2014 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+use middle::ty;
+use syntax::ast;
+
+use self::SimplifiedType::*;
+
+/** See `simplify_type */
+#[deriving(Clone, PartialEq, Eq, Hash)]
+pub enum SimplifiedType {
+    BoolSimplifiedType,
+    CharSimplifiedType,
+    IntSimplifiedType(ast::IntTy),
+    UintSimplifiedType(ast::UintTy),
+    FloatSimplifiedType(ast::FloatTy),
+    EnumSimplifiedType(ast::DefId),
+    StrSimplifiedType,
+    VecSimplifiedType,
+    PtrSimplifiedType,
+    TupleSimplifiedType(uint),
+    TraitSimplifiedType(ast::DefId),
+    StructSimplifiedType(ast::DefId),
+    UnboxedClosureSimplifiedType(ast::DefId),
+    FunctionSimplifiedType(uint),
+    ParameterSimplifiedType,
+}
+
+pub fn simplify_type(tcx: &ty::ctxt,
+                     ty: ty::t,
+                     can_simplify_params: bool)
+                     -> Option<SimplifiedType>
+{
+    /*!
+     * Tries to simplify a type by dropping type parameters, deref'ing
+     * away any reference types, etc. The idea is to get something
+     * simple that we can use to quickly decide if two types could
+     * unify during method lookup.
+     *
+     * If `can_simplify_params` is false, then we will fail to
+     * simplify type parameters entirely. This is useful when those
+     * type parameters would be instantiated with fresh type
+     * variables, since then we can't say much about whether two types
+     * would unify. Put another way, `can_simplify_params` should be
+     * true if type parameters appear free in `ty` and `false` if they
+     * are to be considered bound.
+     */
+
+    match ty::get(ty).sty {
+        ty::ty_bool => Some(BoolSimplifiedType),
+        ty::ty_char => Some(CharSimplifiedType),
+        ty::ty_int(int_type) => Some(IntSimplifiedType(int_type)),
+        ty::ty_uint(uint_type) => Some(UintSimplifiedType(uint_type)),
+        ty::ty_float(float_type) => Some(FloatSimplifiedType(float_type)),
+        ty::ty_enum(def_id, _) => Some(EnumSimplifiedType(def_id)),
+        ty::ty_str => Some(StrSimplifiedType),
+        ty::ty_vec(..) => Some(VecSimplifiedType),
+        ty::ty_ptr(_) => Some(PtrSimplifiedType),
+        ty::ty_trait(ref trait_info) => {
+            Some(TraitSimplifiedType(trait_info.principal.def_id))
+        }
+        ty::ty_struct(def_id, _) => {
+            Some(StructSimplifiedType(def_id))
+        }
+        ty::ty_rptr(_, mt) => {
+            // since we introduce auto-refs during method lookup, we
+            // just treat &T and T as equivalent from the point of
+            // view of possibly unifying
+            simplify_type(tcx, mt.ty, can_simplify_params)
+        }
+        ty::ty_uniq(_) => {
+            // treat like we would treat `Box`
+            let def_id = tcx.lang_items.owned_box().unwrap();
+            Some(StructSimplifiedType(def_id))
+        }
+        ty::ty_unboxed_closure(def_id, _, _) => {
+            Some(UnboxedClosureSimplifiedType(def_id))
+        }
+        ty::ty_tup(ref tys) => {
+            Some(TupleSimplifiedType(tys.len()))
+        }
+        ty::ty_closure(ref f) => {
+            Some(FunctionSimplifiedType(f.sig.inputs.len()))
+        }
+        ty::ty_bare_fn(ref f) => {
+            Some(FunctionSimplifiedType(f.sig.inputs.len()))
+        }
+        ty::ty_param(_) => {
+            if can_simplify_params {
+                Some(ParameterSimplifiedType)
+            } else {
+                None
+            }
+        }
+        ty::ty_open(_) | ty::ty_infer(_) | ty::ty_err => None,
+    }
+}
+

src/librustc/middle/traits/mod.rs

@@ -281,6 +281,16 @@ pub fn overlapping_impls(infcx: &InferCtxt,
     coherence::impl_can_satisfy(infcx, impl2_def_id, impl1_def_id)
 }
 
+pub fn impl_obligations(tcx: &ty::ctxt,
+                        cause: ObligationCause,
+                        impl_def_id: ast::DefId,
+                        impl_substs: &subst::Substs)
+                        -> subst::VecPerParamSpace<Obligation>
+{
+    let impl_generics = ty::lookup_item_type(tcx, impl_def_id).generics;
+    obligations_for_generics(tcx, cause, &impl_generics, impl_substs)
+}
+
 pub fn obligations_for_generics(tcx: &ty::ctxt,
                                 cause: ObligationCause,
                                 generics: &ty::Generics,

src/librustc/middle/traits/select.rs

@@ -27,11 +27,13 @@ use super::{VtableBuiltin, VtableImpl, VtableParam, VtableUnboxedClosure};
 use super::{VtableImplData, VtableParamData, VtableBuiltinData};
 use super::{util};
 
+use middle::fast_reject;
 use middle::mem_categorization::Typer;
 use middle::subst::{Subst, Substs, VecPerParamSpace};
 use middle::ty;
 use middle::typeck::check::regionmanip;
 use middle::typeck::infer;
+use middle::typeck::infer::LateBoundRegionConversionTime::*;
 use middle::typeck::infer::{InferCtxt, TypeSkolemizer};
 use middle::ty_fold::TypeFoldable;
 use std::cell::RefCell;
@@ -1714,7 +1716,8 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
                 closure_type.sig.binder_id,
                 &closure_type.sig,
                 |br| self.infcx.next_region_var(
-                         infer::LateBoundRegion(obligation.cause.span, br)));
+                         infer::LateBoundRegion(obligation.cause.span, br,
+                                                infer::FnCall)));
 
         let arguments_tuple = new_signature.inputs[0];
         let trait_ref = Rc::new(ty::TraitRef {
@@ -1766,12 +1769,20 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
                   obligation: &Obligation)
                   -> Result<Substs, ()>
     {
+        let impl_trait_ref = ty::impl_trait_ref(self.tcx(),
+                                                impl_def_id).unwrap();
+
+        // Before we create the substitutions and everything, first
+        // consider a "quick reject". This avoids creating more types
+        // and so forth that we need to.
+        if self.fast_reject_trait_refs(obligation, &*impl_trait_ref) {
+            return Err(());
+        }
+
         let impl_substs = util::fresh_substs_for_impl(self.infcx,
                                                       obligation.cause.span,
                                                       impl_def_id);
 
-        let impl_trait_ref = ty::impl_trait_ref(self.tcx(),
-                                                impl_def_id).unwrap();
         let impl_trait_ref = impl_trait_ref.subst(self.tcx(),
                                                   &impl_substs);
 
@@ -1781,6 +1792,29 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
         }
     }
 
+    fn fast_reject_trait_refs(&mut self,
+                              obligation: &Obligation,
+                              impl_trait_ref: &ty::TraitRef)
+                              -> bool
+    {
+        // We can avoid creating type variables and doing the full
+        // substitution if we find that any of the input types, when
+        // simplified, do not match.
+
+        obligation.trait_ref.input_types().iter()
+            .zip(impl_trait_ref.input_types().iter())
+            .any(|(&obligation_ty, &impl_ty)| {
+                let simplified_obligation_ty =
+                    fast_reject::simplify_type(self.tcx(), obligation_ty, true);
+                let simplified_impl_ty =
+                    fast_reject::simplify_type(self.tcx(), impl_ty, false);
+
+                simplified_obligation_ty.is_some() &&
+                    simplified_impl_ty.is_some() &&
+                    simplified_obligation_ty != simplified_impl_ty
+            })
+    }
+
     fn match_trait_refs(&mut self,
                         obligation: &Obligation,
                         trait_ref: Rc<ty::TraitRef>)

src/librustc/middle/ty.rs

@@ -3491,43 +3491,45 @@ pub fn adjust_ty(cx: &ctxt,
                         }
                     }
 
-                    match adj.autoref {
-                        None => adjusted_ty,
-                        Some(ref autoref) => adjust_for_autoref(cx, span, adjusted_ty, autoref)
-                    }
+                    adjust_ty_for_autoref(cx, span, adjusted_ty, adj.autoref.as_ref())
                 }
             }
         }
         None => unadjusted_ty
     };
+}
 
-    fn adjust_for_autoref(cx: &ctxt,
-                          span: Span,
-                          ty: ty::t,
-                          autoref: &AutoRef) -> ty::t{
-        match *autoref {
-            AutoPtr(r, m, ref a) => {
-                let adjusted_ty = match a {
-                    &Some(box ref a) => adjust_for_autoref(cx, span, ty, a),
-                    &None => ty
-                };
-                mk_rptr(cx, r, mt {
-                    ty: adjusted_ty,
-                    mutbl: m
-                })
-            }
+pub fn adjust_ty_for_autoref(cx: &ctxt,
+                             span: Span,
+                             ty: ty::t,
+                             autoref: Option<&AutoRef>)
+                             -> ty::t
+{
+    match autoref {
+        None => ty,
 
-            AutoUnsafe(m, ref a) => {
-                let adjusted_ty = match a {
-                    &Some(box ref a) => adjust_for_autoref(cx, span, ty, a),
-                    &None => ty
-                };
-                mk_ptr(cx, mt {ty: adjusted_ty, mutbl: m})
-            }
+        Some(&AutoPtr(r, m, ref a)) => {
+            let adjusted_ty = match a {
+                &Some(box ref a) => adjust_ty_for_autoref(cx, span, ty, Some(a)),
+                &None => ty
+            };
+            mk_rptr(cx, r, mt {
+                ty: adjusted_ty,
+                mutbl: m
+            })
+        }
 
-            AutoUnsize(ref k) => unsize_ty(cx, ty, k, span),
-            AutoUnsizeUniq(ref k) => ty::mk_uniq(cx, unsize_ty(cx, ty, k, span)),
+        Some(&AutoUnsafe(m, ref a)) => {
+            let adjusted_ty = match a {
+                &Some(box ref a) => adjust_ty_for_autoref(cx, span, ty, Some(a)),
+                &None => ty
+            };
+            mk_ptr(cx, mt {ty: adjusted_ty, mutbl: m})
         }
+
+        Some(&AutoUnsize(ref k)) => unsize_ty(cx, ty, k, span),
+
+        Some(&AutoUnsizeUniq(ref k)) => ty::mk_uniq(cx, unsize_ty(cx, ty, k, span)),
     }
 }