src/librustc_trans/trans/meth.rs

   1 // Copyright 2012 The Rust Project Developers. See the COPYRIGHT
   2 // file at the top-level directory of this distribution and at
   3 // http://rust-lang.org/COPYRIGHT.
   4 //
   5 // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
   6 // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
   7 // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
   8 // option. This file may not be copied, modified, or distributed
   9 // except according to those terms.
  10
  11 use arena::TypedArena;
  12 use back::abi;
  13 use back::link;
  14 use llvm::{ValueRef, get_params};
  15 use metadata::csearch;
  16 use middle::subst::{Subst, Substs};
  17 use middle::subst::VecPerParamSpace;
  18 use middle::subst;
  19 use middle::traits;
  20 use rustc::ast_map;
  21 use trans::base::*;
  22 use trans::build::*;
  23 use trans::callee::*;
  24 use trans::callee;
  25 use trans::cleanup;
  26 use trans::closure;
  27 use trans::common::*;
  28 use trans::consts;
  29 use trans::datum::*;
  30 use trans::debuginfo::DebugLoc;
  31 use trans::declare;
  32 use trans::expr::SaveIn;
  33 use trans::expr;
  34 use trans::glue;
  35 use trans::machine;
  36 use trans::monomorphize;
  37 use trans::type_::Type;
  38 use trans::type_of::*;
  39 use middle::ty::{self, Ty, HasTypeFlags};
  40 use middle::ty::MethodCall;
  41
  42 use syntax::{ast, attr, visit};
  43 use syntax::codemap::DUMMY_SP;
  44 use syntax::ptr::P;
  45
  46 // drop_glue pointer, size, align.
  47 const VTABLE_OFFSET: usize = 3;
  48
  49 /// The main "translation" pass for methods.  Generates code
  50 /// for non-monomorphized methods only.  Other methods will
  51 /// be generated once they are invoked with specific type parameters,
  52 /// see `trans::base::lval_static_fn()` or `trans::base::monomorphic_fn()`.
  53 pub fn trans_impl(ccx: &CrateContext,
  54                   name: ast::Ident,
  55                   impl_items: &[P<ast::ImplItem>],
  56                   generics: &ast::Generics,
  57                   id: ast::NodeId) {
  58     let _icx = push_ctxt("meth::trans_impl");
  59     let tcx = ccx.tcx();
  60
  61     debug!("trans_impl(name={}, id={})", name, id);
  62
  63     let mut v = TransItemVisitor { ccx: ccx };
  64
  65     // Both here and below with generic methods, be sure to recurse and look for
  66     // items that we need to translate.
  67     if !generics.ty_params.is_empty() {
  68         for impl_item in impl_items {
  69             match impl_item.node {
  70                 ast::MethodImplItem(..) => {
  71                     visit::walk_impl_item(&mut v, impl_item);
  72                 }
  73                 _ => {}
  74             }
  75         }
  76         return;
  77     }
  78     for impl_item in impl_items {
  79         match impl_item.node {
  80             ast::MethodImplItem(ref sig, ref body) => {
  81                 if sig.generics.ty_params.is_empty() {
  82                     let trans_everywhere = attr::requests_inline(&impl_item.attrs);
  83                     for (ref ccx, is_origin) in ccx.maybe_iter(trans_everywhere) {
  84                         let llfn = get_item_val(ccx, impl_item.id);
  85                         let empty_substs = tcx.mk_substs(Substs::trans_empty());
  86                         trans_fn(ccx, &sig.decl, body, llfn,
  87                                  empty_substs, impl_item.id, &[]);
  88                         update_linkage(ccx,
  89                                        llfn,
  90                                        Some(impl_item.id),
  91                                        if is_origin { OriginalTranslation } else { InlinedCopy });
  92                     }
  93                 }
  94                 visit::walk_impl_item(&mut v, impl_item);
  95             }
  96             _ => {}
  97         }
  98     }
  99 }
 100
 101 pub fn trans_method_callee<'blk, 'tcx>(bcx: Block<'blk, 'tcx>,
 102                                        method_call: MethodCall,
 103                                        self_expr: Option<&ast::Expr>,
 104                                        arg_cleanup_scope: cleanup::ScopeId)
 105                                        -> Callee<'blk, 'tcx> {
 106     let _icx = push_ctxt("meth::trans_method_callee");
 107
 108     let method = bcx.tcx().tables.borrow().method_map[&method_call];
 109
 110     match bcx.tcx().impl_or_trait_item(method.def_id).container() {
 111         ty::ImplContainer(_) => {
 112             debug!("trans_method_callee: static, {:?}", method.def_id);
 113             let datum = callee::trans_fn_ref(bcx.ccx(),
 114                                              method.def_id,
 115                                              MethodCallKey(method_call),
 116                                              bcx.fcx.param_substs);
 117             Callee {
 118                 bcx: bcx,
 119                 data: Fn(datum.val),
 120                 ty: datum.ty
 121             }
 122         }
 123
 124         ty::TraitContainer(trait_def_id) => {
 125             let trait_substs = method.substs.clone().method_to_trait();
 126             let trait_substs = bcx.tcx().mk_substs(trait_substs);
 127             let trait_ref = ty::TraitRef::new(trait_def_id, trait_substs);
 128
 129             let trait_ref = ty::Binder(bcx.monomorphize(&trait_ref));
 130             let span = bcx.tcx().map.span(method_call.expr_id);
 131             debug!("method_call={:?} trait_ref={:?} trait_ref id={:?} substs={:?}",
 132                    method_call,
 133                    trait_ref,
 134                    trait_ref.0.def_id,
 135                    trait_ref.0.substs);
 136             let origin = fulfill_obligation(bcx.ccx(),
 137                                             span,
 138                                             trait_ref.clone());
 139             debug!("origin = {:?}", origin);
 140             trans_monomorphized_callee(bcx,
 141                                        method_call,
 142                                        self_expr,
 143                                        trait_def_id,
 144                                        method.def_id,
 145                                        method.ty,
 146                                        origin,
 147                                        arg_cleanup_scope)
 148         }
 149     }
 150 }
 151
 152 pub fn trans_static_method_callee<'a, 'tcx>(ccx: &CrateContext<'a, 'tcx>,
 153                                             method_id: ast::DefId,
 154                                             trait_id: ast::DefId,
 155                                             expr_id: ast::NodeId,
 156                                             param_substs: &'tcx subst::Substs<'tcx>)
 157                                             -> Datum<'tcx, Rvalue>
 158 {
 159     let _icx = push_ctxt("meth::trans_static_method_callee");
 160     let tcx = ccx.tcx();
 161
 162     debug!("trans_static_method_callee(method_id={:?}, trait_id={}, \
 163             expr_id={})",
 164            method_id,
 165            tcx.item_path_str(trait_id),
 166            expr_id);
 167
 168     let mname = if method_id.krate == ast::LOCAL_CRATE {
 169         match tcx.map.get(method_id.node) {
 170             ast_map::NodeTraitItem(trait_item) => trait_item.ident.name,
 171             _ => panic!("callee is not a trait method")
 172         }
 173     } else {
 174         csearch::get_item_path(tcx, method_id).last().unwrap().name()
 175     };
 176     debug!("trans_static_method_callee: method_id={:?}, expr_id={}, \
 177             name={}", method_id, expr_id, mname);
 178
 179     // Find the substitutions for the fn itself. This includes
 180     // type parameters that belong to the trait but also some that
 181     // belong to the method:
 182     let rcvr_substs = node_id_substs(ccx, ExprId(expr_id), param_substs);
 183     let subst::SeparateVecsPerParamSpace {
 184         types: rcvr_type,
 185         selfs: rcvr_self,
 186         fns: rcvr_method
 187     } = rcvr_substs.types.split();
 188
 189     // Lookup the precise impl being called. To do that, we need to
 190     // create a trait reference identifying the self type and other
 191     // input type parameters. To create that trait reference, we have
 192     // to pick apart the type parameters to identify just those that
 193     // pertain to the trait. This is easiest to explain by example:
 194     //
 195     //     trait Convert {
 196     //         fn from<U:Foo>(n: U) -> Option<Self>;
 197     //     }
 198     //     ...
 199     //     let f = <Vec<int> as Convert>::from::<String>(...)
 200     //
 201     // Here, in this call, which I've written with explicit UFCS
 202     // notation, the set of type parameters will be:
 203     //
 204     //     rcvr_type: [] <-- nothing declared on the trait itself
 205     //     rcvr_self: [Vec<int>] <-- the self type
 206     //     rcvr_method: [String] <-- method type parameter
 207     //
 208     // So we create a trait reference using the first two,
 209     // basically corresponding to `<Vec<int> as Convert>`.
 210     // The remaining type parameters (`rcvr_method`) will be used below.
 211     let trait_substs =
 212         Substs::erased(VecPerParamSpace::new(rcvr_type,
 213                                              rcvr_self,
 214                                              Vec::new()));
 215     let trait_substs = tcx.mk_substs(trait_substs);
 216     debug!("trait_substs={:?}", trait_substs);
 217     let trait_ref = ty::Binder(ty::TraitRef::new(trait_id, trait_substs));
 218     let vtbl = fulfill_obligation(ccx,
 219                                   DUMMY_SP,
 220                                   trait_ref);
 221
 222     // Now that we know which impl is being used, we can dispatch to
 223     // the actual function:
 224     match vtbl {
 225         traits::VtableImpl(traits::VtableImplData {
 226             impl_def_id: impl_did,
 227             substs: impl_substs,
 228             nested: _ }) =>
 229         {
 230             assert!(!impl_substs.types.needs_infer());
 231
 232             // Create the substitutions that are in scope. This combines
 233             // the type parameters from the impl with those declared earlier.
 234             // To see what I mean, consider a possible impl:
 235             //
 236             //    impl<T> Convert for Vec<T> {
 237             //        fn from<U:Foo>(n: U) { ... }
 238             //    }
 239             //
 240             // Recall that we matched `<Vec<int> as Convert>`. Trait
 241             // resolution will have given us a substitution
 242             // containing `impl_substs=[[T=int],[],[]]` (the type
 243             // parameters defined on the impl). We combine
 244             // that with the `rcvr_method` from before, which tells us
 245             // the type parameters from the *method*, to yield
 246             // `callee_substs=[[T=int],[],[U=String]]`.
 247             let subst::SeparateVecsPerParamSpace {
 248                 types: impl_type,
 249                 selfs: impl_self,
 250                 fns: _
 251             } = impl_substs.types.split();
 252             let callee_substs =
 253                 Substs::erased(VecPerParamSpace::new(impl_type,
 254                                                      impl_self,
 255                                                      rcvr_method));
 256
 257             let mth_id = method_with_name(ccx, impl_did, mname);
 258             trans_fn_ref_with_substs(ccx, mth_id, ExprId(expr_id),
 259                                      param_substs,
 260                                      callee_substs)
 261         }
 262         traits::VtableObject(ref data) => {
 263             let idx = traits::get_vtable_index_of_object_method(tcx, data, method_id);
 264             trans_object_shim(ccx,
 265                               data.upcast_trait_ref.clone(),
 266                               method_id,
 267                               idx)
 268         }
 269         _ => {
 270             tcx.sess.bug(&format!("static call to invalid vtable: {:?}",
 271                                  vtbl));
 272         }
 273     }
 274 }
 275
 276 fn method_with_name(ccx: &CrateContext, impl_id: ast::DefId, name: ast::Name)
 277                     -> ast::DefId {
 278     match ccx.impl_method_cache().borrow().get(&(impl_id, name)).cloned() {
 279         Some(m) => return m,
 280         None => {}
 281     }
 282
 283     let impl_items = ccx.tcx().impl_items.borrow();
 284     let impl_items =
 285         impl_items.get(&impl_id)
 286                   .expect("could not find impl while translating");
 287     let meth_did = impl_items.iter()
 288                              .find(|&did| {
 289                                 ccx.tcx().impl_or_trait_item(did.def_id()).name() == name
 290                              }).expect("could not find method while \
 291                                         translating");
 292
 293     ccx.impl_method_cache().borrow_mut().insert((impl_id, name),
 294                                               meth_did.def_id());
 295     meth_did.def_id()
 296 }
 297
 298 fn trans_monomorphized_callee<'blk, 'tcx>(bcx: Block<'blk, 'tcx>,
 299                                           method_call: MethodCall,
 300                                           self_expr: Option<&ast::Expr>,
 301                                           trait_id: ast::DefId,
 302                                           method_id: ast::DefId,
 303                                           method_ty: Ty<'tcx>,
 304                                           vtable: traits::Vtable<'tcx, ()>,
 305                                           arg_cleanup_scope: cleanup::ScopeId)
 306                                           -> Callee<'blk, 'tcx> {
 307     let _icx = push_ctxt("meth::trans_monomorphized_callee");
 308     match vtable {
 309         traits::VtableImpl(vtable_impl) => {
 310             let ccx = bcx.ccx();
 311             let impl_did = vtable_impl.impl_def_id;
 312             let mname = match ccx.tcx().impl_or_trait_item(method_id) {
 313                 ty::MethodTraitItem(method) => method.name,
 314                 _ => {
 315                     bcx.tcx().sess.bug("can't monomorphize a non-method trait \
 316                                         item")
 317                 }
 318             };
 319             let mth_id = method_with_name(bcx.ccx(), impl_did, mname);
 320
 321             // create a concatenated set of substitutions which includes
 322             // those from the impl and those from the method:
 323             let callee_substs =
 324                 combine_impl_and_methods_tps(
 325                     bcx, MethodCallKey(method_call), vtable_impl.substs);
 326
 327             // translate the function
 328             let datum = trans_fn_ref_with_substs(bcx.ccx(),
 329                                                  mth_id,
 330                                                  MethodCallKey(method_call),
 331                                                  bcx.fcx.param_substs,
 332                                                  callee_substs);
 333
 334             Callee { bcx: bcx, data: Fn(datum.val), ty: datum.ty }
 335         }
 336         traits::VtableClosure(vtable_closure) => {
 337             // The substitutions should have no type parameters remaining
 338             // after passing through fulfill_obligation
 339             let trait_closure_kind = bcx.tcx().lang_items.fn_trait_kind(trait_id).unwrap();
 340             let llfn = closure::trans_closure_method(bcx.ccx(),
 341                                                      vtable_closure.closure_def_id,
 342                                                      vtable_closure.substs,
 343                                                      trait_closure_kind);
 344             Callee {
 345                 bcx: bcx,
 346                 data: Fn(llfn),
 347                 ty: monomorphize_type(bcx, method_ty)
 348             }
 349         }
 350         traits::VtableFnPointer(fn_ty) => {
 351             let trait_closure_kind = bcx.tcx().lang_items.fn_trait_kind(trait_id).unwrap();
 352             let llfn = trans_fn_pointer_shim(bcx.ccx(), trait_closure_kind, fn_ty);
 353             Callee {
 354                 bcx: bcx,
 355                 data: Fn(llfn),
 356                 ty: monomorphize_type(bcx, method_ty)
 357             }
 358         }
 359         traits::VtableObject(ref data) => {
 360             let idx = traits::get_vtable_index_of_object_method(bcx.tcx(), data, method_id);
 361             if let Some(self_expr) = self_expr {
 362                 if let ty::TyBareFn(_, ref fty) = monomorphize_type(bcx, method_ty).sty {
 363                     let ty = bcx.tcx().mk_fn(None, opaque_method_ty(bcx.tcx(), fty));
 364                     return trans_trait_callee(bcx, ty, idx, self_expr, arg_cleanup_scope);
 365                 }
 366             }
 367             let datum = trans_object_shim(bcx.ccx(),
 368                                           data.upcast_trait_ref.clone(),
 369                                           method_id,
 370                                           idx);
 371             Callee { bcx: bcx, data: Fn(datum.val), ty: datum.ty }
 372         }
 373         traits::VtableBuiltin(..) |
 374         traits::VtableDefaultImpl(..) |
 375         traits::VtableParam(..) => {
 376             bcx.sess().bug(
 377                 &format!("resolved vtable bad vtable {:?} in trans",
 378                         vtable));
 379         }
 380     }
 381 }
 382
 383  /// Creates a concatenated set of substitutions which includes those from the impl and those from
 384  /// the method.  This are some subtle complications here.  Statically, we have a list of type
 385  /// parameters like `[T0, T1, T2, M1, M2, M3]` where `Tn` are type parameters that appear on the
 386  /// receiver.  For example, if the receiver is a method parameter `A` with a bound like
 387  /// `trait<B,C,D>` then `Tn` would be `[B,C,D]`.
 388  ///
 389  /// The weird part is that the type `A` might now be bound to any other type, such as `foo<X>`.
 390  /// In that case, the vector we want is: `[X, M1, M2, M3]`.  Therefore, what we do now is to slice
 391  /// off the method type parameters and append them to the type parameters from the type that the
 392  /// receiver is mapped to.
 393 fn combine_impl_and_methods_tps<'blk, 'tcx>(bcx: Block<'blk, 'tcx>,
 394                                             node: ExprOrMethodCall,
 395                                             rcvr_substs: subst::Substs<'tcx>)
 396                                             -> subst::Substs<'tcx>
 397 {
 398     let ccx = bcx.ccx();
 399
 400     let node_substs = node_id_substs(ccx, node, bcx.fcx.param_substs);
 401
 402     debug!("rcvr_substs={:?}", rcvr_substs);
 403     debug!("node_substs={:?}", node_substs);
 404
 405     // Break apart the type parameters from the node and type
 406     // parameters from the receiver.
 407     let node_method = node_substs.types.split().fns;
 408     let subst::SeparateVecsPerParamSpace {
 409         types: rcvr_type,
 410         selfs: rcvr_self,
 411         fns: rcvr_method
 412     } = rcvr_substs.types.clone().split();
 413     assert!(rcvr_method.is_empty());
 414     subst::Substs {
 415         regions: subst::ErasedRegions,
 416         types: subst::VecPerParamSpace::new(rcvr_type, rcvr_self, node_method)
 417     }
 418 }
 419
 420 /// Create a method callee where the method is coming from a trait object (e.g., Box<Trait> type).
 421 /// In this case, we must pull the fn pointer out of the vtable that is packaged up with the
 422 /// object. Objects are represented as a pair, so we first evaluate the self expression and then
 423 /// extract the self data and vtable out of the pair.
 424 fn trans_trait_callee<'blk, 'tcx>(bcx: Block<'blk, 'tcx>,
 425                                   opaque_fn_ty: Ty<'tcx>,
 426                                   vtable_index: usize,
 427                                   self_expr: &ast::Expr,
 428                                   arg_cleanup_scope: cleanup::ScopeId)
 429                                   -> Callee<'blk, 'tcx> {
 430     let _icx = push_ctxt("meth::trans_trait_callee");
 431     let mut bcx = bcx;
 432
 433     // Translate self_datum and take ownership of the value by
 434     // converting to an rvalue.
 435     let self_datum = unpack_datum!(
 436         bcx, expr::trans(bcx, self_expr));
 437
 438     let llval = if bcx.fcx.type_needs_drop(self_datum.ty) {
 439         let self_datum = unpack_datum!(
 440             bcx, self_datum.to_rvalue_datum(bcx, "trait_callee"));
 441
 442         // Convert to by-ref since `trans_trait_callee_from_llval` wants it
 443         // that way.
 444         let self_datum = unpack_datum!(
 445             bcx, self_datum.to_ref_datum(bcx));
 446
 447         // Arrange cleanup in case something should go wrong before the
 448         // actual call occurs.
 449         self_datum.add_clean(bcx.fcx, arg_cleanup_scope)
 450     } else {
 451         // We don't have to do anything about cleanups for &Trait and &mut Trait.
 452         assert!(self_datum.kind.is_by_ref());
 453         self_datum.val
 454     };
 455
 456     let llself = Load(bcx, GEPi(bcx, llval, &[0, abi::FAT_PTR_ADDR]));
 457     let llvtable = Load(bcx, GEPi(bcx, llval, &[0, abi::FAT_PTR_EXTRA]));
 458     trans_trait_callee_from_llval(bcx, opaque_fn_ty, vtable_index, llself, llvtable)
 459 }
 460
 461 /// Same as `trans_trait_callee()` above, except that it is given a by-ref pointer to the object
 462 /// pair.
 463 fn trans_trait_callee_from_llval<'blk, 'tcx>(bcx: Block<'blk, 'tcx>,
 464                                              opaque_fn_ty: Ty<'tcx>,
 465                                              vtable_index: usize,
 466                                              llself: ValueRef,
 467                                              llvtable: ValueRef)
 468                                              -> Callee<'blk, 'tcx> {
 469     let _icx = push_ctxt("meth::trans_trait_callee");
 470     let ccx = bcx.ccx();
 471
 472     // Load the data pointer from the object.
 473     debug!("trans_trait_callee_from_llval(callee_ty={}, vtable_index={}, llself={}, llvtable={})",
 474            opaque_fn_ty,
 475            vtable_index,
 476            bcx.val_to_string(llself),
 477            bcx.val_to_string(llvtable));
 478
 479     // Replace the self type (&Self or Box<Self>) with an opaque pointer.
 480     let mptr = Load(bcx, GEPi(bcx, llvtable, &[vtable_index + VTABLE_OFFSET]));
 481     let llcallee_ty = type_of_fn_from_ty(ccx, opaque_fn_ty);
 482
 483     Callee {
 484         bcx: bcx,
 485         data: TraitItem(MethodData {
 486             llfn: PointerCast(bcx, mptr, llcallee_ty.ptr_to()),
 487             llself: PointerCast(bcx, llself, Type::i8p(ccx)),
 488         }),
 489         ty: opaque_fn_ty
 490     }
 491 }
 492
 493 /// Generate a shim function that allows an object type like `SomeTrait` to
 494 /// implement the type `SomeTrait`. Imagine a trait definition:
 495 ///
 496 ///    trait SomeTrait { fn get(&self) -> int; ... }
 497 ///
 498 /// And a generic bit of code:
 499 ///
 500 ///    fn foo<T:SomeTrait>(t: &T) {
 501 ///        let x = SomeTrait::get;
 502 ///        x(t)
 503 ///    }
 504 ///
 505 /// What is the value of `x` when `foo` is invoked with `T=SomeTrait`?
 506 /// The answer is that it it is a shim function generate by this
 507 /// routine:
 508 ///
 509 ///    fn shim(t: &SomeTrait) -> int {
 510 ///        // ... call t.get() virtually ...
 511 ///    }
 512 ///
 513 /// In fact, all virtual calls can be thought of as normal trait calls
 514 /// that go through this shim function.
 515 fn trans_object_shim<'a, 'tcx>(
 516     ccx: &'a CrateContext<'a, 'tcx>,
 517     upcast_trait_ref: ty::PolyTraitRef<'tcx>,
 518     method_id: ast::DefId,
 519     vtable_index: usize)
 520     -> Datum<'tcx, Rvalue>
 521 {
 522     let _icx = push_ctxt("trans_object_shim");
 523     let tcx = ccx.tcx();
 524
 525     debug!("trans_object_shim(upcast_trait_ref={:?}, method_id={:?})",
 526            upcast_trait_ref,
 527            method_id);
 528
 529     // Upcast to the trait in question and extract out the substitutions.
 530     let upcast_trait_ref = tcx.erase_late_bound_regions(&upcast_trait_ref);
 531     let object_substs = upcast_trait_ref.substs.clone().erase_regions();
 532     debug!("trans_object_shim: object_substs={:?}", object_substs);
 533
 534     // Lookup the type of this method as declared in the trait and apply substitutions.
 535     let method_ty = match tcx.impl_or_trait_item(method_id) {
 536         ty::MethodTraitItem(method) => method,
 537         _ => {
 538             tcx.sess.bug("can't create a method shim for a non-method item")
 539         }
 540     };
 541     let fty = monomorphize::apply_param_substs(tcx, &object_substs, &method_ty.fty);
 542     let fty = tcx.mk_bare_fn(fty);
 543     let method_ty = opaque_method_ty(tcx, fty);
 544     debug!("trans_object_shim: fty={:?} method_ty={:?}", fty, method_ty);
 545
 546     //
 547     let shim_fn_ty = tcx.mk_fn(None, fty);
 548     let method_bare_fn_ty = tcx.mk_fn(None, method_ty);
 549     let function_name = link::mangle_internal_name_by_type_and_seq(ccx, shim_fn_ty, "object_shim");
 550     let llfn = declare::define_internal_rust_fn(ccx, &function_name, shim_fn_ty);
 551
 552     let sig = ccx.tcx().erase_late_bound_regions(&fty.sig);
 553
 554     let empty_substs = tcx.mk_substs(Substs::trans_empty());
 555     let (block_arena, fcx): (TypedArena<_>, FunctionContext);
 556     block_arena = TypedArena::new();
 557     fcx = new_fn_ctxt(ccx,
 558                       llfn,
 559                       ast::DUMMY_NODE_ID,
 560                       false,
 561                       sig.output,
 562                       empty_substs,
 563                       None,
 564                       &block_arena);
 565     let mut bcx = init_function(&fcx, false, sig.output);
 566
 567     let llargs = get_params(fcx.llfn);
 568
 569     let self_idx = fcx.arg_offset();
 570     let llself = llargs[self_idx];
 571     let llvtable = llargs[self_idx + 1];
 572
 573     debug!("trans_object_shim: llself={}, llvtable={}",
 574            bcx.val_to_string(llself), bcx.val_to_string(llvtable));
 575
 576     assert!(!fcx.needs_ret_allocas);
 577
 578     let dest =
 579         fcx.llretslotptr.get().map(
 580             |_| expr::SaveIn(fcx.get_ret_slot(bcx, sig.output, "ret_slot")));
 581
 582     debug!("trans_object_shim: method_offset_in_vtable={}",
 583            vtable_index);
 584
 585     bcx = trans_call_inner(bcx,
 586                            DebugLoc::None,
 587                            |bcx, _| trans_trait_callee_from_llval(bcx,
 588                                                                   method_bare_fn_ty,
 589                                                                   vtable_index,
 590                                                                   llself, llvtable),
 591                            ArgVals(&llargs[(self_idx + 2)..]),
 592                            dest).bcx;
 593
 594     finish_fn(&fcx, bcx, sig.output, DebugLoc::None);
 595
 596     immediate_rvalue(llfn, shim_fn_ty)
 597 }
 598
 599 /// Creates a returns a dynamic vtable for the given type and vtable origin.
 600 /// This is used only for objects.
 601 ///
 602 /// The `trait_ref` encodes the erased self type. Hence if we are
 603 /// making an object `Foo<Trait>` from a value of type `Foo<T>`, then
 604 /// `trait_ref` would map `T:Trait`.
 605 pub fn get_vtable<'a, 'tcx>(ccx: &CrateContext<'a, 'tcx>,
 606                             trait_ref: ty::PolyTraitRef<'tcx>,
 607                             param_substs: &'tcx subst::Substs<'tcx>)
 608                             -> ValueRef
 609 {
 610     let tcx = ccx.tcx();
 611     let _icx = push_ctxt("meth::get_vtable");
 612
 613     debug!("get_vtable(trait_ref={:?})", trait_ref);
 614
 615     // Check the cache.
 616     match ccx.vtables().borrow().get(&trait_ref) {
 617         Some(&val) => { return val }
 618         None => { }
 619     }
 620
 621     // Not in the cache. Build it.
 622     let methods = traits::supertraits(tcx, trait_ref.clone()).flat_map(|trait_ref| {
 623         let vtable = fulfill_obligation(ccx, DUMMY_SP, trait_ref.clone());
 624         match vtable {
 625             // Should default trait error here?
 626             traits::VtableDefaultImpl(_) |
 627             traits::VtableBuiltin(_) => {
 628                 Vec::new().into_iter()
 629             }
 630             traits::VtableImpl(
 631                 traits::VtableImplData {
 632                     impl_def_id: id,
 633                     substs,
 634                     nested: _ }) => {
 635                 emit_vtable_methods(ccx, id, substs, param_substs).into_iter()
 636             }
 637             traits::VtableClosure(
 638                 traits::VtableClosureData {
 639                     closure_def_id,
 640                     substs,
 641                     nested: _ }) => {
 642                 let trait_closure_kind = tcx.lang_items.fn_trait_kind(trait_ref.def_id()).unwrap();
 643                 let llfn = closure::trans_closure_method(ccx,
 644                                                          closure_def_id,
 645                                                          substs,
 646                                                          trait_closure_kind);
 647                 vec![llfn].into_iter()
 648             }
 649             traits::VtableFnPointer(bare_fn_ty) => {
 650                 let trait_closure_kind = tcx.lang_items.fn_trait_kind(trait_ref.def_id()).unwrap();
 651                 vec![trans_fn_pointer_shim(ccx, trait_closure_kind, bare_fn_ty)].into_iter()
 652             }
 653             traits::VtableObject(ref data) => {
 654                 // this would imply that the Self type being erased is
 655                 // an object type; this cannot happen because we
 656                 // cannot cast an unsized type into a trait object
 657                 tcx.sess.bug(
 658                     &format!("cannot get vtable for an object type: {:?}",
 659                             data));
 660             }
 661             traits::VtableParam(..) => {
 662                 tcx.sess.bug(
 663                     &format!("resolved vtable for {:?} to bad vtable {:?} in trans",
 664                             trait_ref,
 665                             vtable));
 666             }
 667         }
 668     });
 669
 670     let size_ty = sizing_type_of(ccx, trait_ref.self_ty());
 671     let size = machine::llsize_of_alloc(ccx, size_ty);
 672     let align = align_of(ccx, trait_ref.self_ty());
 673
 674     let components: Vec<_> = vec![
 675         // Generate a destructor for the vtable.
 676         glue::get_drop_glue(ccx, trait_ref.self_ty()),
 677         C_uint(ccx, size),
 678         C_uint(ccx, align)
 679     ].into_iter().chain(methods).collect();
 680
 681     let vtable = consts::addr_of(ccx, C_struct(ccx, &components, false), "vtable");
 682
 683     ccx.vtables().borrow_mut().insert(trait_ref, vtable);
 684     vtable
 685 }
 686
 687 fn emit_vtable_methods<'a, 'tcx>(ccx: &CrateContext<'a, 'tcx>,
 688                                  impl_id: ast::DefId,
 689                                  substs: subst::Substs<'tcx>,
 690                                  param_substs: &'tcx subst::Substs<'tcx>)
 691                                  -> Vec<ValueRef>
 692 {
 693     let tcx = ccx.tcx();
 694
 695     debug!("emit_vtable_methods(impl_id={:?}, substs={:?}, param_substs={:?})",
 696            impl_id,
 697            substs,
 698            param_substs);
 699
 700     let trt_id = match tcx.impl_trait_ref(impl_id) {
 701         Some(t_id) => t_id.def_id,
 702         None       => ccx.sess().bug("make_impl_vtable: don't know how to \
 703                                       make a vtable for a type impl!")
 704     };
 705
 706     tcx.populate_implementations_for_trait_if_necessary(trt_id);
 707
 708     let nullptr = C_null(Type::nil(ccx).ptr_to());
 709     let trait_item_def_ids = tcx.trait_item_def_ids(trt_id);
 710     trait_item_def_ids
 711         .iter()
 712
 713         // Filter out non-method items.
 714         .filter_map(|item_def_id| {
 715             match *item_def_id {
 716                 ty::MethodTraitItemId(def_id) => Some(def_id),
 717                 _ => None,
 718             }
 719         })
 720
 721         // Now produce pointers for each remaining method. If the
 722         // method could never be called from this object, just supply
 723         // null.
 724         .map(|trait_method_def_id| {
 725             debug!("emit_vtable_methods: trait_method_def_id={:?}",
 726                    trait_method_def_id);
 727
 728             let trait_method_type = match tcx.impl_or_trait_item(trait_method_def_id) {
 729                 ty::MethodTraitItem(m) => m,
 730                 _ => ccx.sess().bug("should be a method, not other assoc item"),
 731             };
 732             let name = trait_method_type.name;
 733
 734             // Some methods cannot be called on an object; skip those.
 735             if !traits::is_vtable_safe_method(tcx, trt_id, &trait_method_type) {
 736                 debug!("emit_vtable_methods: not vtable safe");
 737                 return nullptr;
 738             }
 739
 740             debug!("emit_vtable_methods: trait_method_type={:?}",
 741                    trait_method_type);
 742
 743             // The substitutions we have are on the impl, so we grab
 744             // the method type from the impl to substitute into.
 745             let impl_method_def_id = method_with_name(ccx, impl_id, name);
 746             let impl_method_type = match tcx.impl_or_trait_item(impl_method_def_id) {
 747                 ty::MethodTraitItem(m) => m,
 748                 _ => ccx.sess().bug("should be a method, not other assoc item"),
 749             };
 750
 751             debug!("emit_vtable_methods: impl_method_type={:?}",
 752                    impl_method_type);
 753
 754             // If this is a default method, it's possible that it
 755             // relies on where clauses that do not hold for this
 756             // particular set of type parameters. Note that this
 757             // method could then never be called, so we do not want to
 758             // try and trans it, in that case. Issue #23435.
 759             if tcx.provided_source(impl_method_def_id).is_some() {
 760                 let predicates = impl_method_type.predicates.predicates.subst(tcx, &substs);
 761                 if !normalize_and_test_predicates(ccx, predicates.into_vec()) {
 762                     debug!("emit_vtable_methods: predicates do not hold");
 763                     return nullptr;
 764                 }
 765             }
 766
 767             trans_fn_ref_with_substs(ccx,
 768                                      impl_method_def_id,
 769                                      ExprId(0),
 770                                      param_substs,
 771                                      substs.clone()).val
 772         })
 773         .collect()
 774 }
 775
 776 /// Replace the self type (&Self or Box<Self>) with an opaque pointer.
 777 fn opaque_method_ty<'tcx>(tcx: &ty::ctxt<'tcx>, method_ty: &ty::BareFnTy<'tcx>)
 778                           -> &'tcx ty::BareFnTy<'tcx> {
 779     let mut inputs = method_ty.sig.0.inputs.clone();
 780     inputs[0] = tcx.mk_mut_ptr(tcx.mk_mach_int(ast::TyI8));
 781
 782     tcx.mk_bare_fn(ty::BareFnTy {
 783         unsafety: method_ty.unsafety,
 784         abi: method_ty.abi,
 785         sig: ty::Binder(ty::FnSig {
 786             inputs: inputs,
 787             output: method_ty.sig.0.output,
 788             variadic: method_ty.sig.0.variadic,
 789         }),
 790     })
 791 }