auto merge of #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. #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 #18674.

cc #18208

Author: bors

Diff for: 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;

Diff for: 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,
+    }
+}
+

Diff for: 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,

Diff for: 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>)

Diff for: 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)),
     }
 }