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::link;
  13 use llvm::{ValueRef, get_params};
  14 use middle::def_id::DefId;
  15 use middle::infer;
  16 use middle::subst::{Subst, Substs};
  17 use middle::subst::VecPerParamSpace;
  18 use middle::subst;
  19 use middle::traits;
  20 use trans::base::*;
  21 use trans::build::*;
  22 use trans::callee::*;
  23 use trans::callee;
  24 use trans::cleanup;
  25 use trans::closure;
  26 use trans::common::*;
  27 use trans::consts;
  28 use trans::datum::*;
  29 use trans::debuginfo::DebugLoc;
  30 use trans::declare;
  31 use trans::expr;
  32 use trans::glue;
  33 use trans::machine;
  34 use trans::monomorphize;
  35 use trans::type_::Type;
  36 use trans::type_of::*;
  37 use middle::ty::{self, Ty, TypeFoldable};
  38 use middle::ty::MethodCall;
  39
  40 use syntax::ast;
  41 use syntax::attr;
  42 use syntax::codemap::DUMMY_SP;
  43
  44 use rustc_front::hir;
  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::Name,
  55                   impl_items: &[hir::ImplItem],
  56                   generics: &hir::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     // Both here and below with generic methods, be sure to recurse and look for
  64     // items that we need to translate.
  65     if !generics.ty_params.is_empty() {
  66         return;
  67     }
  68
  69     for impl_item in impl_items {
  70         match impl_item.node {
  71             hir::ImplItemKind::Method(ref sig, ref body) => {
  72                 if sig.generics.ty_params.is_empty() {
  73                     let trans_everywhere = attr::requests_inline(&impl_item.attrs);
  74                     for (ref ccx, is_origin) in ccx.maybe_iter(trans_everywhere) {
  75                         let llfn = get_item_val(ccx, impl_item.id);
  76                         let empty_substs = tcx.mk_substs(Substs::trans_empty());
  77                         trans_fn(ccx,
  78                                  &sig.decl,
  79                                  body,
  80                                  llfn,
  81                                  empty_substs,
  82                                  impl_item.id,
  83                                  &impl_item.attrs);
  84                         update_linkage(ccx,
  85                                        llfn,
  86                                        Some(impl_item.id),
  87                                        if is_origin { OriginalTranslation } else { InlinedCopy });
  88                     }
  89                 }
  90             }
  91             _ => {}
  92         }
  93     }
  94 }
  95
  96 pub fn trans_method_callee<'blk, 'tcx>(bcx: Block<'blk, 'tcx>,
  97                                        method_call: MethodCall,
  98                                        self_expr: Option<&hir::Expr>,
  99                                        arg_cleanup_scope: cleanup::ScopeId)
 100                                        -> Callee<'blk, 'tcx> {
 101     let _icx = push_ctxt("meth::trans_method_callee");
 102
 103     let method = bcx.tcx().tables.borrow().method_map[&method_call];
 104
 105     match bcx.tcx().impl_or_trait_item(method.def_id).container() {
 106         ty::ImplContainer(_) => {
 107             debug!("trans_method_callee: static, {:?}", method.def_id);
 108             let datum = callee::trans_fn_ref(bcx.ccx(),
 109                                              method.def_id,
 110                                              MethodCallKey(method_call),
 111                                              bcx.fcx.param_substs);
 112             Callee {
 113                 bcx: bcx,
 114                 data: Fn(datum.val),
 115                 ty: datum.ty
 116             }
 117         }
 118
 119         ty::TraitContainer(trait_def_id) => {
 120             let trait_substs = method.substs.clone().method_to_trait();
 121             let trait_substs = bcx.tcx().mk_substs(trait_substs);
 122             let trait_ref = ty::TraitRef::new(trait_def_id, trait_substs);
 123
 124             let trait_ref = ty::Binder(bcx.monomorphize(&trait_ref));
 125             let span = bcx.tcx().map.span(method_call.expr_id);
 126             debug!("method_call={:?} trait_ref={:?} trait_ref id={:?} substs={:?}",
 127                    method_call,
 128                    trait_ref,
 129                    trait_ref.0.def_id,
 130                    trait_ref.0.substs);
 131             let origin = fulfill_obligation(bcx.ccx(),
 132                                             span,
 133                                             trait_ref.clone());
 134             debug!("origin = {:?}", origin);
 135             trans_monomorphized_callee(bcx,
 136                                        method_call,
 137                                        self_expr,
 138                                        trait_def_id,
 139                                        method.def_id,
 140                                        method.ty,
 141                                        origin,
 142                                        arg_cleanup_scope)
 143         }
 144     }
 145 }
 146
 147 pub fn trans_static_method_callee<'a, 'tcx>(ccx: &CrateContext<'a, 'tcx>,
 148                                             method_id: DefId,
 149                                             trait_id: DefId,
 150                                             expr_id: ast::NodeId,
 151                                             param_substs: &'tcx subst::Substs<'tcx>)
 152                                             -> Datum<'tcx, Rvalue>
 153 {
 154     let _icx = push_ctxt("meth::trans_static_method_callee");
 155     let tcx = ccx.tcx();
 156
 157     debug!("trans_static_method_callee(method_id={:?}, trait_id={}, \
 158             expr_id={})",
 159            method_id,
 160            tcx.item_path_str(trait_id),
 161            expr_id);
 162
 163     let mname = tcx.item_name(method_id);
 164
 165     debug!("trans_static_method_callee: method_id={:?}, expr_id={}, \
 166             name={}", method_id, expr_id, mname);
 167
 168     // Find the substitutions for the fn itself. This includes
 169     // type parameters that belong to the trait but also some that
 170     // belong to the method:
 171     let rcvr_substs = node_id_substs(ccx, ExprId(expr_id), param_substs);
 172     let subst::SeparateVecsPerParamSpace {
 173         types: rcvr_type,
 174         selfs: rcvr_self,
 175         fns: rcvr_method
 176     } = rcvr_substs.types.split();
 177
 178     // Lookup the precise impl being called. To do that, we need to
 179     // create a trait reference identifying the self type and other
 180     // input type parameters. To create that trait reference, we have
 181     // to pick apart the type parameters to identify just those that
 182     // pertain to the trait. This is easiest to explain by example:
 183     //
 184     //     trait Convert {
 185     //         fn from<U:Foo>(n: U) -> Option<Self>;
 186     //     }
 187     //     ...
 188     //     let f = <Vec<i32> as Convert>::from::<String>(...)
 189     //
 190     // Here, in this call, which I've written with explicit UFCS
 191     // notation, the set of type parameters will be:
 192     //
 193     //     rcvr_type: [] <-- nothing declared on the trait itself
 194     //     rcvr_self: [Vec<i32>] <-- the self type
 195     //     rcvr_method: [String] <-- method type parameter
 196     //
 197     // So we create a trait reference using the first two,
 198     // basically corresponding to `<Vec<i32> as Convert>`.
 199     // The remaining type parameters (`rcvr_method`) will be used below.
 200     let trait_substs =
 201         Substs::erased(VecPerParamSpace::new(rcvr_type,
 202                                              rcvr_self,
 203                                              Vec::new()));
 204     let trait_substs = tcx.mk_substs(trait_substs);
 205     debug!("trait_substs={:?}", trait_substs);
 206     let trait_ref = ty::Binder(ty::TraitRef::new(trait_id, trait_substs));
 207     let vtbl = fulfill_obligation(ccx,
 208                                   DUMMY_SP,
 209                                   trait_ref);
 210
 211     // Now that we know which impl is being used, we can dispatch to
 212     // the actual function:
 213     match vtbl {
 214         traits::VtableImpl(traits::VtableImplData {
 215             impl_def_id: impl_did,
 216             substs: impl_substs,
 217             nested: _ }) =>
 218         {
 219             assert!(!impl_substs.types.needs_infer());
 220
 221             // Create the substitutions that are in scope. This combines
 222             // the type parameters from the impl with those declared earlier.
 223             // To see what I mean, consider a possible impl:
 224             //
 225             //    impl<T> Convert for Vec<T> {
 226             //        fn from<U:Foo>(n: U) { ... }
 227             //    }
 228             //
 229             // Recall that we matched `<Vec<i32> as Convert>`. Trait
 230             // resolution will have given us a substitution
 231             // containing `impl_substs=[[T=i32],[],[]]` (the type
 232             // parameters defined on the impl). We combine
 233             // that with the `rcvr_method` from before, which tells us
 234             // the type parameters from the *method*, to yield
 235             // `callee_substs=[[T=i32],[],[U=String]]`.
 236             let subst::SeparateVecsPerParamSpace {
 237                 types: impl_type,
 238                 selfs: impl_self,
 239                 fns: _
 240             } = impl_substs.types.split();
 241             let callee_substs =
 242                 Substs::erased(VecPerParamSpace::new(impl_type,
 243                                                      impl_self,
 244                                                      rcvr_method));
 245
 246             let mth = tcx.get_impl_method(impl_did, callee_substs, mname);
 247             trans_fn_ref_with_substs(ccx, mth.method.def_id, ExprId(expr_id),
 248                                      param_substs,
 249                                      mth.substs)
 250         }
 251         traits::VtableObject(ref data) => {
 252             let idx = traits::get_vtable_index_of_object_method(tcx, data, method_id);
 253             trans_object_shim(ccx,
 254                               data.upcast_trait_ref.clone(),
 255                               method_id,
 256                               idx)
 257         }
 258         _ => {
 259             tcx.sess.bug(&format!("static call to invalid vtable: {:?}",
 260                                  vtbl));
 261         }
 262     }
 263 }
 264
 265 fn trans_monomorphized_callee<'blk, 'tcx>(bcx: Block<'blk, 'tcx>,
 266                                           method_call: MethodCall,
 267                                           self_expr: Option<&hir::Expr>,
 268                                           trait_id: DefId,
 269                                           method_id: DefId,
 270                                           method_ty: Ty<'tcx>,
 271                                           vtable: traits::Vtable<'tcx, ()>,
 272                                           arg_cleanup_scope: cleanup::ScopeId)
 273                                           -> Callee<'blk, 'tcx> {
 274     let _icx = push_ctxt("meth::trans_monomorphized_callee");
 275     match vtable {
 276         traits::VtableImpl(vtable_impl) => {
 277             let ccx = bcx.ccx();
 278             let impl_did = vtable_impl.impl_def_id;
 279             let mname = match ccx.tcx().impl_or_trait_item(method_id) {
 280                 ty::MethodTraitItem(method) => method.name,
 281                 _ => {
 282                     bcx.tcx().sess.bug("can't monomorphize a non-method trait \
 283                                         item")
 284                 }
 285             };
 286             // create a concatenated set of substitutions which includes
 287             // those from the impl and those from the method:
 288             let callee_substs =
 289                 combine_impl_and_methods_tps(
 290                     bcx, MethodCallKey(method_call), vtable_impl.substs);
 291
 292             let mth = bcx.tcx().get_impl_method(impl_did, callee_substs, mname);
 293             // translate the function
 294             let datum = trans_fn_ref_with_substs(bcx.ccx(),
 295                                                  mth.method.def_id,
 296                                                  MethodCallKey(method_call),
 297                                                  bcx.fcx.param_substs,
 298                                                  mth.substs);
 299
 300             Callee { bcx: bcx, data: Fn(datum.val), ty: datum.ty }
 301         }
 302         traits::VtableClosure(vtable_closure) => {
 303             // The substitutions should have no type parameters remaining
 304             // after passing through fulfill_obligation
 305             let trait_closure_kind = bcx.tcx().lang_items.fn_trait_kind(trait_id).unwrap();
 306             let llfn = closure::trans_closure_method(bcx.ccx(),
 307                                                      vtable_closure.closure_def_id,
 308                                                      vtable_closure.substs,
 309                                                      trait_closure_kind);
 310             Callee {
 311                 bcx: bcx,
 312                 data: Fn(llfn),
 313                 ty: monomorphize_type(bcx, method_ty)
 314             }
 315         }
 316         traits::VtableFnPointer(fn_ty) => {
 317             let trait_closure_kind = bcx.tcx().lang_items.fn_trait_kind(trait_id).unwrap();
 318             let llfn = trans_fn_pointer_shim(bcx.ccx(), trait_closure_kind, fn_ty);
 319             Callee {
 320                 bcx: bcx,
 321                 data: Fn(llfn),
 322                 ty: monomorphize_type(bcx, method_ty)
 323             }
 324         }
 325         traits::VtableObject(ref data) => {
 326             let idx = traits::get_vtable_index_of_object_method(bcx.tcx(), data, method_id);
 327             if let Some(self_expr) = self_expr {
 328                 if let ty::TyBareFn(_, ref fty) = monomorphize_type(bcx, method_ty).sty {
 329                     let ty = bcx.tcx().mk_fn(None, opaque_method_ty(bcx.tcx(), fty));
 330                     return trans_trait_callee(bcx, ty, idx, self_expr, arg_cleanup_scope);
 331                 }
 332             }
 333             let datum = trans_object_shim(bcx.ccx(),
 334                                           data.upcast_trait_ref.clone(),
 335                                           method_id,
 336                                           idx);
 337             Callee { bcx: bcx, data: Fn(datum.val), ty: datum.ty }
 338         }
 339         traits::VtableBuiltin(..) |
 340         traits::VtableDefaultImpl(..) |
 341         traits::VtableParam(..) => {
 342             bcx.sess().bug(
 343                 &format!("resolved vtable bad vtable {:?} in trans",
 344                         vtable));
 345         }
 346     }
 347 }
 348
 349  /// Creates a concatenated set of substitutions which includes those from the impl and those from
 350  /// the method.  This are some subtle complications here.  Statically, we have a list of type
 351  /// parameters like `[T0, T1, T2, M1, M2, M3]` where `Tn` are type parameters that appear on the
 352  /// receiver.  For example, if the receiver is a method parameter `A` with a bound like
 353  /// `trait<B,C,D>` then `Tn` would be `[B,C,D]`.
 354  ///
 355  /// The weird part is that the type `A` might now be bound to any other type, such as `foo<X>`.
 356  /// In that case, the vector we want is: `[X, M1, M2, M3]`.  Therefore, what we do now is to slice
 357  /// off the method type parameters and append them to the type parameters from the type that the
 358  /// receiver is mapped to.
 359 fn combine_impl_and_methods_tps<'blk, 'tcx>(bcx: Block<'blk, 'tcx>,
 360                                             node: ExprOrMethodCall,
 361                                             rcvr_substs: subst::Substs<'tcx>)
 362                                             -> subst::Substs<'tcx>
 363 {
 364     let ccx = bcx.ccx();
 365
 366     let node_substs = node_id_substs(ccx, node, bcx.fcx.param_substs);
 367
 368     debug!("rcvr_substs={:?}", rcvr_substs);
 369     debug!("node_substs={:?}", node_substs);
 370
 371     // Break apart the type parameters from the node and type
 372     // parameters from the receiver.
 373     let node_method = node_substs.types.split().fns;
 374     let subst::SeparateVecsPerParamSpace {
 375         types: rcvr_type,
 376         selfs: rcvr_self,
 377         fns: rcvr_method
 378     } = rcvr_substs.types.clone().split();
 379     assert!(rcvr_method.is_empty());
 380     subst::Substs {
 381         regions: subst::ErasedRegions,
 382         types: subst::VecPerParamSpace::new(rcvr_type, rcvr_self, node_method)
 383     }
 384 }
 385
 386 /// Create a method callee where the method is coming from a trait object (e.g., Box<Trait> type).
 387 /// In this case, we must pull the fn pointer out of the vtable that is packaged up with the
 388 /// object. Objects are represented as a pair, so we first evaluate the self expression and then
 389 /// extract the self data and vtable out of the pair.
 390 fn trans_trait_callee<'blk, 'tcx>(bcx: Block<'blk, 'tcx>,
 391                                   opaque_fn_ty: Ty<'tcx>,
 392                                   vtable_index: usize,
 393                                   self_expr: &hir::Expr,
 394                                   arg_cleanup_scope: cleanup::ScopeId)
 395                                   -> Callee<'blk, 'tcx> {
 396     let _icx = push_ctxt("meth::trans_trait_callee");
 397     let mut bcx = bcx;
 398
 399     // Translate self_datum and take ownership of the value by
 400     // converting to an rvalue.
 401     let self_datum = unpack_datum!(
 402         bcx, expr::trans(bcx, self_expr));
 403
 404     let llval = if bcx.fcx.type_needs_drop(self_datum.ty) {
 405         let self_datum = unpack_datum!(
 406             bcx, self_datum.to_rvalue_datum(bcx, "trait_callee"));
 407
 408         // Convert to by-ref since `trans_trait_callee_from_llval` wants it
 409         // that way.
 410         let self_datum = unpack_datum!(
 411             bcx, self_datum.to_ref_datum(bcx));
 412
 413         // Arrange cleanup in case something should go wrong before the
 414         // actual call occurs.
 415         self_datum.add_clean(bcx.fcx, arg_cleanup_scope)
 416     } else {
 417         // We don't have to do anything about cleanups for &Trait and &mut Trait.
 418         assert!(self_datum.kind.is_by_ref());
 419         self_datum.val
 420     };
 421
 422     let llself = Load(bcx, expr::get_dataptr(bcx, llval));
 423     let llvtable = Load(bcx, expr::get_meta(bcx, llval));
 424     trans_trait_callee_from_llval(bcx, opaque_fn_ty, vtable_index, llself, llvtable)
 425 }
 426
 427 /// Same as `trans_trait_callee()` above, except that it is given a by-ref pointer to the object
 428 /// pair.
 429 fn trans_trait_callee_from_llval<'blk, 'tcx>(bcx: Block<'blk, 'tcx>,
 430                                              opaque_fn_ty: Ty<'tcx>,
 431                                              vtable_index: usize,
 432                                              llself: ValueRef,
 433                                              llvtable: ValueRef)
 434                                              -> Callee<'blk, 'tcx> {
 435     let _icx = push_ctxt("meth::trans_trait_callee");
 436     let ccx = bcx.ccx();
 437
 438     // Load the data pointer from the object.
 439     debug!("trans_trait_callee_from_llval(callee_ty={}, vtable_index={}, llself={}, llvtable={})",
 440            opaque_fn_ty,
 441            vtable_index,
 442            bcx.val_to_string(llself),
 443            bcx.val_to_string(llvtable));
 444
 445     // Replace the self type (&Self or Box<Self>) with an opaque pointer.
 446     let mptr = Load(bcx, GEPi(bcx, llvtable, &[vtable_index + VTABLE_OFFSET]));
 447     let llcallee_ty = type_of_fn_from_ty(ccx, opaque_fn_ty);
 448
 449     Callee {
 450         bcx: bcx,
 451         data: TraitItem(MethodData {
 452             llfn: PointerCast(bcx, mptr, llcallee_ty.ptr_to()),
 453             llself: PointerCast(bcx, llself, Type::i8p(ccx)),
 454         }),
 455         ty: opaque_fn_ty
 456     }
 457 }
 458
 459 /// Generate a shim function that allows an object type like `SomeTrait` to
 460 /// implement the type `SomeTrait`. Imagine a trait definition:
 461 ///
 462 ///    trait SomeTrait { fn get(&self) -> i32; ... }
 463 ///
 464 /// And a generic bit of code:
 465 ///
 466 ///    fn foo<T:SomeTrait>(t: &T) {
 467 ///        let x = SomeTrait::get;
 468 ///        x(t)
 469 ///    }
 470 ///
 471 /// What is the value of `x` when `foo` is invoked with `T=SomeTrait`?
 472 /// The answer is that it is a shim function generated by this routine:
 473 ///
 474 ///    fn shim(t: &SomeTrait) -> i32 {
 475 ///        // ... call t.get() virtually ...
 476 ///    }
 477 ///
 478 /// In fact, all virtual calls can be thought of as normal trait calls
 479 /// that go through this shim function.
 480 pub fn trans_object_shim<'a, 'tcx>(
 481     ccx: &'a CrateContext<'a, 'tcx>,
 482     upcast_trait_ref: ty::PolyTraitRef<'tcx>,
 483     method_id: DefId,
 484     vtable_index: usize)
 485     -> Datum<'tcx, Rvalue>
 486 {
 487     let _icx = push_ctxt("trans_object_shim");
 488     let tcx = ccx.tcx();
 489
 490     debug!("trans_object_shim(upcast_trait_ref={:?}, method_id={:?})",
 491            upcast_trait_ref,
 492            method_id);
 493
 494     // Upcast to the trait in question and extract out the substitutions.
 495     let upcast_trait_ref = tcx.erase_late_bound_regions(&upcast_trait_ref);
 496     let object_substs = upcast_trait_ref.substs.clone().erase_regions();
 497     debug!("trans_object_shim: object_substs={:?}", object_substs);
 498
 499     // Lookup the type of this method as declared in the trait and apply substitutions.
 500     let method_ty = match tcx.impl_or_trait_item(method_id) {
 501         ty::MethodTraitItem(method) => method,
 502         _ => {
 503             tcx.sess.bug("can't create a method shim for a non-method item")
 504         }
 505     };
 506     let fty = monomorphize::apply_param_substs(tcx, &object_substs, &method_ty.fty);
 507     let fty = tcx.mk_bare_fn(fty);
 508     let method_ty = opaque_method_ty(tcx, fty);
 509     debug!("trans_object_shim: fty={:?} method_ty={:?}", fty, method_ty);
 510
 511     //
 512     let shim_fn_ty = tcx.mk_fn(None, fty);
 513     let method_bare_fn_ty = tcx.mk_fn(None, method_ty);
 514     let function_name = link::mangle_internal_name_by_type_and_seq(ccx, shim_fn_ty, "object_shim");
 515     let llfn = declare::define_internal_rust_fn(ccx, &function_name, shim_fn_ty);
 516
 517     let sig = ccx.tcx().erase_late_bound_regions(&fty.sig);
 518     let sig = infer::normalize_associated_type(ccx.tcx(), &sig);
 519
 520     let empty_substs = tcx.mk_substs(Substs::trans_empty());
 521     let (block_arena, fcx): (TypedArena<_>, FunctionContext);
 522     block_arena = TypedArena::new();
 523     fcx = new_fn_ctxt(ccx,
 524                       llfn,
 525                       ast::DUMMY_NODE_ID,
 526                       false,
 527                       sig.output,
 528                       empty_substs,
 529                       None,
 530                       &block_arena);
 531     let mut bcx = init_function(&fcx, false, sig.output);
 532
 533     let llargs = get_params(fcx.llfn);
 534
 535     let self_idx = fcx.arg_offset();
 536     let llself = llargs[self_idx];
 537     let llvtable = llargs[self_idx + 1];
 538
 539     debug!("trans_object_shim: llself={}, llvtable={}",
 540            bcx.val_to_string(llself), bcx.val_to_string(llvtable));
 541
 542     assert!(!fcx.needs_ret_allocas);
 543
 544     let dest =
 545         fcx.llretslotptr.get().map(
 546             |_| expr::SaveIn(fcx.get_ret_slot(bcx, sig.output, "ret_slot")));
 547
 548     debug!("trans_object_shim: method_offset_in_vtable={}",
 549            vtable_index);
 550
 551     bcx = trans_call_inner(bcx,
 552                            DebugLoc::None,
 553                            |bcx, _| trans_trait_callee_from_llval(bcx,
 554                                                                   method_bare_fn_ty,
 555                                                                   vtable_index,
 556                                                                   llself, llvtable),
 557                            ArgVals(&llargs[(self_idx + 2)..]),
 558                            dest).bcx;
 559
 560     finish_fn(&fcx, bcx, sig.output, DebugLoc::None);
 561
 562     immediate_rvalue(llfn, shim_fn_ty)
 563 }
 564
 565 /// Creates a returns a dynamic vtable for the given type and vtable origin.
 566 /// This is used only for objects.
 567 ///
 568 /// The `trait_ref` encodes the erased self type. Hence if we are
 569 /// making an object `Foo<Trait>` from a value of type `Foo<T>`, then
 570 /// `trait_ref` would map `T:Trait`.
 571 pub fn get_vtable<'a, 'tcx>(ccx: &CrateContext<'a, 'tcx>,
 572                             trait_ref: ty::PolyTraitRef<'tcx>,
 573                             param_substs: &'tcx subst::Substs<'tcx>)
 574                             -> ValueRef
 575 {
 576     let tcx = ccx.tcx();
 577     let _icx = push_ctxt("meth::get_vtable");
 578
 579     debug!("get_vtable(trait_ref={:?})", trait_ref);
 580
 581     // Check the cache.
 582     match ccx.vtables().borrow().get(&trait_ref) {
 583         Some(&val) => { return val }
 584         None => { }
 585     }
 586
 587     // Not in the cache. Build it.
 588     let methods = traits::supertraits(tcx, trait_ref.clone()).flat_map(|trait_ref| {
 589         let vtable = fulfill_obligation(ccx, DUMMY_SP, trait_ref.clone());
 590         match vtable {
 591             // Should default trait error here?
 592             traits::VtableDefaultImpl(_) |
 593             traits::VtableBuiltin(_) => {
 594                 Vec::new().into_iter()
 595             }
 596             traits::VtableImpl(
 597                 traits::VtableImplData {
 598                     impl_def_id: id,
 599                     substs,
 600                     nested: _ }) => {
 601                 emit_vtable_methods(ccx, id, substs, param_substs).into_iter()
 602             }
 603             traits::VtableClosure(
 604                 traits::VtableClosureData {
 605                     closure_def_id,
 606                     substs,
 607                     nested: _ }) => {
 608                 let trait_closure_kind = tcx.lang_items.fn_trait_kind(trait_ref.def_id()).unwrap();
 609                 let llfn = closure::trans_closure_method(ccx,
 610                                                          closure_def_id,
 611                                                          substs,
 612                                                          trait_closure_kind);
 613                 vec![llfn].into_iter()
 614             }
 615             traits::VtableFnPointer(bare_fn_ty) => {
 616                 let trait_closure_kind = tcx.lang_items.fn_trait_kind(trait_ref.def_id()).unwrap();
 617                 vec![trans_fn_pointer_shim(ccx, trait_closure_kind, bare_fn_ty)].into_iter()
 618             }
 619             traits::VtableObject(ref data) => {
 620                 // this would imply that the Self type being erased is
 621                 // an object type; this cannot happen because we
 622                 // cannot cast an unsized type into a trait object
 623                 tcx.sess.bug(
 624                     &format!("cannot get vtable for an object type: {:?}",
 625                             data));
 626             }
 627             traits::VtableParam(..) => {
 628                 tcx.sess.bug(
 629                     &format!("resolved vtable for {:?} to bad vtable {:?} in trans",
 630                             trait_ref,
 631                             vtable));
 632             }
 633         }
 634     });
 635
 636     let size_ty = sizing_type_of(ccx, trait_ref.self_ty());
 637     let size = machine::llsize_of_alloc(ccx, size_ty);
 638     let align = align_of(ccx, trait_ref.self_ty());
 639
 640     let components: Vec<_> = vec![
 641         // Generate a destructor for the vtable.
 642         glue::get_drop_glue(ccx, trait_ref.self_ty()),
 643         C_uint(ccx, size),
 644         C_uint(ccx, align)
 645     ].into_iter().chain(methods).collect();
 646
 647     let vtable_const = C_struct(ccx, &components, false);
 648     let align = machine::llalign_of_pref(ccx, val_ty(vtable_const));
 649     let vtable = consts::addr_of(ccx, vtable_const, align, "vtable");
 650
 651     ccx.vtables().borrow_mut().insert(trait_ref, vtable);
 652     vtable
 653 }
 654
 655 fn emit_vtable_methods<'a, 'tcx>(ccx: &CrateContext<'a, 'tcx>,
 656                                  impl_id: DefId,
 657                                  substs: subst::Substs<'tcx>,
 658                                  param_substs: &'tcx subst::Substs<'tcx>)
 659                                  -> Vec<ValueRef>
 660 {
 661     let tcx = ccx.tcx();
 662
 663     debug!("emit_vtable_methods(impl_id={:?}, substs={:?}, param_substs={:?})",
 664            impl_id,
 665            substs,
 666            param_substs);
 667
 668     let trt_id = match tcx.impl_trait_ref(impl_id) {
 669         Some(t_id) => t_id.def_id,
 670         None       => ccx.sess().bug("make_impl_vtable: don't know how to \
 671                                       make a vtable for a type impl!")
 672     };
 673
 674     tcx.populate_implementations_for_trait_if_necessary(trt_id);
 675
 676     let nullptr = C_null(Type::nil(ccx).ptr_to());
 677     let trait_item_def_ids = tcx.trait_item_def_ids(trt_id);
 678     trait_item_def_ids
 679         .iter()
 680
 681         // Filter out non-method items.
 682         .filter_map(|item_def_id| {
 683             match *item_def_id {
 684                 ty::MethodTraitItemId(def_id) => Some(def_id),
 685                 _ => None,
 686             }
 687         })
 688
 689         // Now produce pointers for each remaining method. If the
 690         // method could never be called from this object, just supply
 691         // null.
 692         .map(|trait_method_def_id| {
 693             debug!("emit_vtable_methods: trait_method_def_id={:?}",
 694                    trait_method_def_id);
 695
 696             let trait_method_type = match tcx.impl_or_trait_item(trait_method_def_id) {
 697                 ty::MethodTraitItem(m) => m,
 698                 _ => ccx.sess().bug("should be a method, not other assoc item"),
 699             };
 700             let name = trait_method_type.name;
 701
 702             // Some methods cannot be called on an object; skip those.
 703             if !traits::is_vtable_safe_method(tcx, trt_id, &trait_method_type) {
 704                 debug!("emit_vtable_methods: not vtable safe");
 705                 return nullptr;
 706             }
 707
 708             debug!("emit_vtable_methods: trait_method_type={:?}",
 709                    trait_method_type);
 710
 711             // The substitutions we have are on the impl, so we grab
 712             // the method type from the impl to substitute into.
 713             let mth = tcx.get_impl_method(impl_id, substs.clone(), name);
 714
 715             debug!("emit_vtable_methods: mth={:?}", mth);
 716
 717             // If this is a default method, it's possible that it
 718             // relies on where clauses that do not hold for this
 719             // particular set of type parameters. Note that this
 720             // method could then never be called, so we do not want to
 721             // try and trans it, in that case. Issue #23435.
 722             if mth.is_provided {
 723                 let predicates = mth.method.predicates.predicates.subst(tcx, &mth.substs);
 724                 if !normalize_and_test_predicates(ccx, predicates.into_vec()) {
 725                     debug!("emit_vtable_methods: predicates do not hold");
 726                     return nullptr;
 727                 }
 728             }
 729
 730             trans_fn_ref_with_substs(ccx,
 731                                      mth.method.def_id,
 732                                      ExprId(0),
 733                                      param_substs,
 734                                      mth.substs).val
 735         })
 736         .collect()
 737 }
 738
 739 /// Replace the self type (&Self or Box<Self>) with an opaque pointer.
 740 fn opaque_method_ty<'tcx>(tcx: &ty::ctxt<'tcx>, method_ty: &ty::BareFnTy<'tcx>)
 741                           -> &'tcx ty::BareFnTy<'tcx> {
 742     let mut inputs = method_ty.sig.0.inputs.clone();
 743     inputs[0] = tcx.mk_mut_ptr(tcx.mk_mach_int(ast::TyI8));
 744
 745     tcx.mk_bare_fn(ty::BareFnTy {
 746         unsafety: method_ty.unsafety,
 747         abi: method_ty.abi,
 748         sig: ty::Binder(ty::FnSig {
 749             inputs: inputs,
 750             output: method_ty.sig.0.output,
 751             variadic: method_ty.sig.0.variadic,
 752         }),
 753     })
 754 }