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;
  18 use middle::traits;
  19 use trans::base::*;
  20 use trans::build::*;
  21 use trans::callee::*;
  22 use trans::callee;
  23 use trans::cleanup;
  24 use trans::closure;
  25 use trans::common::*;
  26 use trans::consts;
  27 use trans::datum::*;
  28 use trans::debuginfo::DebugLoc;
  29 use trans::declare;
  30 use trans::expr;
  31 use trans::glue;
  32 use trans::machine;
  33 use trans::monomorphize;
  34 use trans::type_::Type;
  35 use trans::type_of::*;
  36 use middle::ty::{self, Ty};
  37 use middle::ty::MethodCall;
  38
  39 use syntax::ast;
  40 use syntax::attr;
  41 use syntax::codemap::DUMMY_SP;
  42
  43 use rustc_front::hir;
  44
  45 // drop_glue pointer, size, align.
  46 const VTABLE_OFFSET: usize = 3;
  47
  48 /// The main "translation" pass for methods.  Generates code
  49 /// for non-monomorphized methods only.  Other methods will
  50 /// be generated once they are invoked with specific type parameters,
  51 /// see `trans::base::lval_static_fn()` or `trans::base::monomorphic_fn()`.
  52 pub fn trans_impl(ccx: &CrateContext,
  53                   name: ast::Name,
  54                   impl_items: &[hir::ImplItem],
  55                   generics: &hir::Generics,
  56                   id: ast::NodeId) {
  57     let _icx = push_ctxt("meth::trans_impl");
  58     let tcx = ccx.tcx();
  59
  60     debug!("trans_impl(name={}, id={})", name, id);
  61
  62     // Both here and below with generic methods, be sure to recurse and look for
  63     // items that we need to translate.
  64     if !generics.ty_params.is_empty() {
  65         return;
  66     }
  67
  68     for impl_item in impl_items {
  69         match impl_item.node {
  70             hir::ImplItemKind::Method(ref sig, ref body) => {
  71                 if sig.generics.ty_params.is_empty() {
  72                     let trans_everywhere = attr::requests_inline(&impl_item.attrs);
  73                     for (ref ccx, is_origin) in ccx.maybe_iter(trans_everywhere) {
  74                         let llfn = get_item_val(ccx, impl_item.id);
  75                         let empty_substs = tcx.mk_substs(Substs::trans_empty());
  76                         trans_fn(ccx,
  77                                  &sig.decl,
  78                                  body,
  79                                  llfn,
  80                                  empty_substs,
  81                                  impl_item.id,
  82                                  &impl_item.attrs);
  83                         update_linkage(ccx,
  84                                        llfn,
  85                                        Some(impl_item.id),
  86                                        if is_origin { OriginalTranslation } else { InlinedCopy });
  87                     }
  88                 }
  89             }
  90             _ => {}
  91         }
  92     }
  93 }
  94
  95 pub fn trans_method_callee<'blk, 'tcx>(bcx: Block<'blk, 'tcx>,
  96                                        method_call: MethodCall,
  97                                        self_expr: Option<&hir::Expr>,
  98                                        arg_cleanup_scope: cleanup::ScopeId)
  99                                        -> Callee<'blk, 'tcx> {
 100     let _icx = push_ctxt("meth::trans_method_callee");
 101
 102     let method = bcx.tcx().tables.borrow().method_map[&method_call];
 103
 104     match bcx.tcx().impl_or_trait_item(method.def_id).container() {
 105         ty::ImplContainer(_) => {
 106             debug!("trans_method_callee: static, {:?}", method.def_id);
 107             let datum = callee::trans_fn_ref(bcx.ccx(),
 108                                              method.def_id,
 109                                              MethodCallKey(method_call),
 110                                              bcx.fcx.param_substs);
 111             Callee {
 112                 bcx: bcx,
 113                 data: Fn(datum.val),
 114                 ty: datum.ty
 115             }
 116         }
 117
 118         ty::TraitContainer(trait_def_id) => {
 119             let trait_ref = method.substs.to_trait_ref(bcx.tcx(), trait_def_id);
 120             let trait_ref = ty::Binder(bcx.monomorphize(&trait_ref));
 121             let span = bcx.tcx().map.span(method_call.expr_id);
 122             debug!("method_call={:?} trait_ref={:?} trait_ref id={:?} substs={:?}",
 123                    method_call,
 124                    trait_ref,
 125                    trait_ref.0.def_id,
 126                    trait_ref.0.substs);
 127             let origin = fulfill_obligation(bcx.ccx(), span, trait_ref);
 128             debug!("origin = {:?}", origin);
 129             trans_monomorphized_callee(bcx,
 130                                        method_call,
 131                                        self_expr,
 132                                        trait_def_id,
 133                                        method.def_id,
 134                                        method.ty,
 135                                        origin,
 136                                        arg_cleanup_scope)
 137         }
 138     }
 139 }
 140
 141 pub fn trans_static_method_callee<'a, 'tcx>(ccx: &CrateContext<'a, 'tcx>,
 142                                             method_id: DefId,
 143                                             trait_id: DefId,
 144                                             expr_id: ast::NodeId,
 145                                             param_substs: &'tcx subst::Substs<'tcx>)
 146                                             -> Datum<'tcx, Rvalue>
 147 {
 148     let _icx = push_ctxt("meth::trans_static_method_callee");
 149     let tcx = ccx.tcx();
 150
 151     debug!("trans_static_method_callee(method_id={:?}, trait_id={}, \
 152             expr_id={})",
 153            method_id,
 154            tcx.item_path_str(trait_id),
 155            expr_id);
 156
 157     let mname = tcx.item_name(method_id);
 158
 159     debug!("trans_static_method_callee: method_id={:?}, expr_id={}, \
 160             name={}", method_id, expr_id, mname);
 161
 162     // Find the substitutions for the fn itself. This includes
 163     // type parameters that belong to the trait but also some that
 164     // belong to the method:
 165     let rcvr_substs = node_id_substs(ccx, ExprId(expr_id), param_substs);
 166     debug!("rcvr_substs={:?}", rcvr_substs);
 167     let trait_ref = ty::Binder(rcvr_substs.to_trait_ref(tcx, trait_id));
 168     let vtbl = fulfill_obligation(ccx, DUMMY_SP, trait_ref);
 169
 170     // Now that we know which impl is being used, we can dispatch to
 171     // the actual function:
 172     match vtbl {
 173         traits::VtableImpl(traits::VtableImplData {
 174             impl_def_id: impl_did,
 175             substs: impl_substs,
 176             nested: _ }) =>
 177         {
 178             let callee_substs = impl_substs.with_method_from(&rcvr_substs);
 179             let mth = tcx.get_impl_method(impl_did, callee_substs, mname);
 180             trans_fn_ref_with_substs(ccx, mth.method.def_id, ExprId(expr_id),
 181                                      param_substs,
 182                                      mth.substs)
 183         }
 184         traits::VtableObject(ref data) => {
 185             let idx = traits::get_vtable_index_of_object_method(tcx, data, method_id);
 186             trans_object_shim(ccx,
 187                               data.upcast_trait_ref.clone(),
 188                               method_id,
 189                               idx)
 190         }
 191         _ => {
 192             // FIXME(#20847): handle at least VtableFnPointer
 193             tcx.sess.bug(&format!("static call to invalid vtable: {:?}",
 194                                  vtbl));
 195         }
 196     }
 197 }
 198
 199 fn trans_monomorphized_callee<'blk, 'tcx>(bcx: Block<'blk, 'tcx>,
 200                                           method_call: MethodCall,
 201                                           self_expr: Option<&hir::Expr>,
 202                                           trait_id: DefId,
 203                                           method_id: DefId,
 204                                           method_ty: Ty<'tcx>,
 205                                           vtable: traits::Vtable<'tcx, ()>,
 206                                           arg_cleanup_scope: cleanup::ScopeId)
 207                                           -> Callee<'blk, 'tcx> {
 208     let _icx = push_ctxt("meth::trans_monomorphized_callee");
 209     match vtable {
 210         traits::VtableImpl(vtable_impl) => {
 211             let ccx = bcx.ccx();
 212             let impl_did = vtable_impl.impl_def_id;
 213             let mname = match ccx.tcx().impl_or_trait_item(method_id) {
 214                 ty::MethodTraitItem(method) => method.name,
 215                 _ => {
 216                     bcx.tcx().sess.bug("can't monomorphize a non-method trait \
 217                                         item")
 218                 }
 219             };
 220             // create a concatenated set of substitutions which includes
 221             // those from the impl and those from the method:
 222             let meth_substs = node_id_substs(ccx,
 223                                              MethodCallKey(method_call),
 224                                              bcx.fcx.param_substs);
 225             let impl_substs = vtable_impl.substs.with_method_from(&meth_substs);
 226             let mth = bcx.tcx().get_impl_method(impl_did, impl_substs, mname);
 227             // translate the function
 228             let datum = trans_fn_ref_with_substs(bcx.ccx(),
 229                                                  mth.method.def_id,
 230                                                  MethodCallKey(method_call),
 231                                                  bcx.fcx.param_substs,
 232                                                  mth.substs);
 233
 234             Callee { bcx: bcx, data: Fn(datum.val), ty: datum.ty }
 235         }
 236         traits::VtableClosure(vtable_closure) => {
 237             // The substitutions should have no type parameters remaining
 238             // after passing through fulfill_obligation
 239             let trait_closure_kind = bcx.tcx().lang_items.fn_trait_kind(trait_id).unwrap();
 240             let llfn = closure::trans_closure_method(bcx.ccx(),
 241                                                      vtable_closure.closure_def_id,
 242                                                      vtable_closure.substs,
 243                                                      trait_closure_kind);
 244             Callee {
 245                 bcx: bcx,
 246                 data: Fn(llfn),
 247                 ty: monomorphize_type(bcx, method_ty)
 248             }
 249         }
 250         traits::VtableFnPointer(fn_ty) => {
 251             let trait_closure_kind = bcx.tcx().lang_items.fn_trait_kind(trait_id).unwrap();
 252             let llfn = trans_fn_pointer_shim(bcx.ccx(), trait_closure_kind, fn_ty);
 253             Callee {
 254                 bcx: bcx,
 255                 data: Fn(llfn),
 256                 ty: monomorphize_type(bcx, method_ty)
 257             }
 258         }
 259         traits::VtableObject(ref data) => {
 260             let idx = traits::get_vtable_index_of_object_method(bcx.tcx(), data, method_id);
 261             if let Some(self_expr) = self_expr {
 262                 if let ty::TyBareFn(_, ref fty) = monomorphize_type(bcx, method_ty).sty {
 263                     let ty = bcx.tcx().mk_fn(None, opaque_method_ty(bcx.tcx(), fty));
 264                     return trans_trait_callee(bcx, ty, idx, self_expr, arg_cleanup_scope);
 265                 }
 266             }
 267             let datum = trans_object_shim(bcx.ccx(),
 268                                           data.upcast_trait_ref.clone(),
 269                                           method_id,
 270                                           idx);
 271             Callee { bcx: bcx, data: Fn(datum.val), ty: datum.ty }
 272         }
 273         traits::VtableBuiltin(..) |
 274         traits::VtableDefaultImpl(..) |
 275         traits::VtableParam(..) => {
 276             bcx.sess().bug(
 277                 &format!("resolved vtable bad vtable {:?} in trans",
 278                         vtable));
 279         }
 280     }
 281 }
 282
 283 /// Create a method callee where the method is coming from a trait object (e.g., Box<Trait> type).
 284 /// In this case, we must pull the fn pointer out of the vtable that is packaged up with the
 285 /// object. Objects are represented as a pair, so we first evaluate the self expression and then
 286 /// extract the self data and vtable out of the pair.
 287 fn trans_trait_callee<'blk, 'tcx>(bcx: Block<'blk, 'tcx>,
 288                                   opaque_fn_ty: Ty<'tcx>,
 289                                   vtable_index: usize,
 290                                   self_expr: &hir::Expr,
 291                                   arg_cleanup_scope: cleanup::ScopeId)
 292                                   -> Callee<'blk, 'tcx> {
 293     let _icx = push_ctxt("meth::trans_trait_callee");
 294     let mut bcx = bcx;
 295
 296     // Translate self_datum and take ownership of the value by
 297     // converting to an rvalue.
 298     let self_datum = unpack_datum!(
 299         bcx, expr::trans(bcx, self_expr));
 300
 301     let llval = if bcx.fcx.type_needs_drop(self_datum.ty) {
 302         let self_datum = unpack_datum!(
 303             bcx, self_datum.to_rvalue_datum(bcx, "trait_callee"));
 304
 305         // Convert to by-ref since `trans_trait_callee_from_llval` wants it
 306         // that way.
 307         let self_datum = unpack_datum!(
 308             bcx, self_datum.to_ref_datum(bcx));
 309
 310         // Arrange cleanup in case something should go wrong before the
 311         // actual call occurs.
 312         self_datum.add_clean(bcx.fcx, arg_cleanup_scope)
 313     } else {
 314         // We don't have to do anything about cleanups for &Trait and &mut Trait.
 315         assert!(self_datum.kind.is_by_ref());
 316         self_datum.val
 317     };
 318
 319     let llself = Load(bcx, expr::get_dataptr(bcx, llval));
 320     let llvtable = Load(bcx, expr::get_meta(bcx, llval));
 321     trans_trait_callee_from_llval(bcx, opaque_fn_ty, vtable_index, llself, llvtable)
 322 }
 323
 324 /// Same as `trans_trait_callee()` above, except that it is given a by-ref pointer to the object
 325 /// pair.
 326 fn trans_trait_callee_from_llval<'blk, 'tcx>(bcx: Block<'blk, 'tcx>,
 327                                              opaque_fn_ty: Ty<'tcx>,
 328                                              vtable_index: usize,
 329                                              llself: ValueRef,
 330                                              llvtable: ValueRef)
 331                                              -> Callee<'blk, 'tcx> {
 332     let _icx = push_ctxt("meth::trans_trait_callee");
 333     let ccx = bcx.ccx();
 334
 335     // Load the data pointer from the object.
 336     debug!("trans_trait_callee_from_llval(callee_ty={}, vtable_index={}, llself={}, llvtable={})",
 337            opaque_fn_ty,
 338            vtable_index,
 339            bcx.val_to_string(llself),
 340            bcx.val_to_string(llvtable));
 341
 342     // Replace the self type (&Self or Box<Self>) with an opaque pointer.
 343     let mptr = Load(bcx, GEPi(bcx, llvtable, &[vtable_index + VTABLE_OFFSET]));
 344     let llcallee_ty = type_of_fn_from_ty(ccx, opaque_fn_ty);
 345
 346     Callee {
 347         bcx: bcx,
 348         data: TraitItem(MethodData {
 349             llfn: PointerCast(bcx, mptr, llcallee_ty.ptr_to()),
 350             llself: PointerCast(bcx, llself, Type::i8p(ccx)),
 351         }),
 352         ty: opaque_fn_ty
 353     }
 354 }
 355
 356 /// Generate a shim function that allows an object type like `SomeTrait` to
 357 /// implement the type `SomeTrait`. Imagine a trait definition:
 358 ///
 359 ///    trait SomeTrait { fn get(&self) -> i32; ... }
 360 ///
 361 /// And a generic bit of code:
 362 ///
 363 ///    fn foo<T:SomeTrait>(t: &T) {
 364 ///        let x = SomeTrait::get;
 365 ///        x(t)
 366 ///    }
 367 ///
 368 /// What is the value of `x` when `foo` is invoked with `T=SomeTrait`?
 369 /// The answer is that it is a shim function generated by this routine:
 370 ///
 371 ///    fn shim(t: &SomeTrait) -> i32 {
 372 ///        // ... call t.get() virtually ...
 373 ///    }
 374 ///
 375 /// In fact, all virtual calls can be thought of as normal trait calls
 376 /// that go through this shim function.
 377 pub fn trans_object_shim<'a, 'tcx>(
 378     ccx: &'a CrateContext<'a, 'tcx>,
 379     upcast_trait_ref: ty::PolyTraitRef<'tcx>,
 380     method_id: DefId,
 381     vtable_index: usize)
 382     -> Datum<'tcx, Rvalue>
 383 {
 384     let _icx = push_ctxt("trans_object_shim");
 385     let tcx = ccx.tcx();
 386
 387     debug!("trans_object_shim(upcast_trait_ref={:?}, method_id={:?})",
 388            upcast_trait_ref,
 389            method_id);
 390
 391     // Upcast to the trait in question and extract out the substitutions.
 392     let upcast_trait_ref = tcx.erase_late_bound_regions(&upcast_trait_ref);
 393     let object_substs = upcast_trait_ref.substs.clone().erase_regions();
 394     debug!("trans_object_shim: object_substs={:?}", object_substs);
 395
 396     // Lookup the type of this method as declared in the trait and apply substitutions.
 397     let method_ty = match tcx.impl_or_trait_item(method_id) {
 398         ty::MethodTraitItem(method) => method,
 399         _ => {
 400             tcx.sess.bug("can't create a method shim for a non-method item")
 401         }
 402     };
 403     let fty = monomorphize::apply_param_substs(tcx, &object_substs, &method_ty.fty);
 404     let fty = tcx.mk_bare_fn(fty);
 405     let method_ty = opaque_method_ty(tcx, fty);
 406     debug!("trans_object_shim: fty={:?} method_ty={:?}", fty, method_ty);
 407
 408     //
 409     let shim_fn_ty = tcx.mk_fn(None, fty);
 410     let method_bare_fn_ty = tcx.mk_fn(None, method_ty);
 411     let function_name = link::mangle_internal_name_by_type_and_seq(ccx, shim_fn_ty, "object_shim");
 412     let llfn = declare::define_internal_rust_fn(ccx, &function_name, shim_fn_ty);
 413
 414     let sig = ccx.tcx().erase_late_bound_regions(&fty.sig);
 415     let sig = infer::normalize_associated_type(ccx.tcx(), &sig);
 416
 417     let empty_substs = tcx.mk_substs(Substs::trans_empty());
 418     let (block_arena, fcx): (TypedArena<_>, FunctionContext);
 419     block_arena = TypedArena::new();
 420     fcx = new_fn_ctxt(ccx,
 421                       llfn,
 422                       ast::DUMMY_NODE_ID,
 423                       false,
 424                       sig.output,
 425                       empty_substs,
 426                       None,
 427                       &block_arena);
 428     let mut bcx = init_function(&fcx, false, sig.output);
 429
 430     let llargs = get_params(fcx.llfn);
 431
 432     let self_idx = fcx.arg_offset();
 433     let llself = llargs[self_idx];
 434     let llvtable = llargs[self_idx + 1];
 435
 436     debug!("trans_object_shim: llself={}, llvtable={}",
 437            bcx.val_to_string(llself), bcx.val_to_string(llvtable));
 438
 439     assert!(!fcx.needs_ret_allocas);
 440
 441     let dest =
 442         fcx.llretslotptr.get().map(
 443             |_| expr::SaveIn(fcx.get_ret_slot(bcx, sig.output, "ret_slot")));
 444
 445     debug!("trans_object_shim: method_offset_in_vtable={}",
 446            vtable_index);
 447
 448     bcx = trans_call_inner(bcx,
 449                            DebugLoc::None,
 450                            |bcx, _| trans_trait_callee_from_llval(bcx,
 451                                                                   method_bare_fn_ty,
 452                                                                   vtable_index,
 453                                                                   llself, llvtable),
 454                            ArgVals(&llargs[(self_idx + 2)..]),
 455                            dest).bcx;
 456
 457     finish_fn(&fcx, bcx, sig.output, DebugLoc::None);
 458
 459     immediate_rvalue(llfn, shim_fn_ty)
 460 }
 461
 462 /// Creates a returns a dynamic vtable for the given type and vtable origin.
 463 /// This is used only for objects.
 464 ///
 465 /// The `trait_ref` encodes the erased self type. Hence if we are
 466 /// making an object `Foo<Trait>` from a value of type `Foo<T>`, then
 467 /// `trait_ref` would map `T:Trait`.
 468 pub fn get_vtable<'a, 'tcx>(ccx: &CrateContext<'a, 'tcx>,
 469                             trait_ref: ty::PolyTraitRef<'tcx>,
 470                             param_substs: &'tcx subst::Substs<'tcx>)
 471                             -> ValueRef
 472 {
 473     let tcx = ccx.tcx();
 474     let _icx = push_ctxt("meth::get_vtable");
 475
 476     debug!("get_vtable(trait_ref={:?})", trait_ref);
 477
 478     // Check the cache.
 479     match ccx.vtables().borrow().get(&trait_ref) {
 480         Some(&val) => { return val }
 481         None => { }
 482     }
 483
 484     // Not in the cache. Build it.
 485     let methods = traits::supertraits(tcx, trait_ref.clone()).flat_map(|trait_ref| {
 486         let vtable = fulfill_obligation(ccx, DUMMY_SP, trait_ref.clone());
 487         match vtable {
 488             // Should default trait error here?
 489             traits::VtableDefaultImpl(_) |
 490             traits::VtableBuiltin(_) => {
 491                 Vec::new().into_iter()
 492             }
 493             traits::VtableImpl(
 494                 traits::VtableImplData {
 495                     impl_def_id: id,
 496                     substs,
 497                     nested: _ }) => {
 498                 let nullptr = C_null(Type::nil(ccx).ptr_to());
 499                 get_vtable_methods(ccx, id, substs)
 500                     .into_iter()
 501                     .map(|opt_mth| {
 502                         match opt_mth {
 503                             Some(mth) => {
 504                                 trans_fn_ref_with_substs(ccx,
 505                                                          mth.method.def_id,
 506                                                          ExprId(0),
 507                                                          param_substs,
 508                                                          mth.substs).val
 509                             }
 510                             None => nullptr
 511                         }
 512                     })
 513                     .collect::<Vec<_>>()
 514                     .into_iter()
 515             }
 516             traits::VtableClosure(
 517                 traits::VtableClosureData {
 518                     closure_def_id,
 519                     substs,
 520                     nested: _ }) => {
 521                 let trait_closure_kind = tcx.lang_items.fn_trait_kind(trait_ref.def_id()).unwrap();
 522                 let llfn = closure::trans_closure_method(ccx,
 523                                                          closure_def_id,
 524                                                          substs,
 525                                                          trait_closure_kind);
 526                 vec![llfn].into_iter()
 527             }
 528             traits::VtableFnPointer(bare_fn_ty) => {
 529                 let trait_closure_kind = tcx.lang_items.fn_trait_kind(trait_ref.def_id()).unwrap();
 530                 vec![trans_fn_pointer_shim(ccx, trait_closure_kind, bare_fn_ty)].into_iter()
 531             }
 532             traits::VtableObject(ref data) => {
 533                 // this would imply that the Self type being erased is
 534                 // an object type; this cannot happen because we
 535                 // cannot cast an unsized type into a trait object
 536                 tcx.sess.bug(
 537                     &format!("cannot get vtable for an object type: {:?}",
 538                             data));
 539             }
 540             traits::VtableParam(..) => {
 541                 tcx.sess.bug(
 542                     &format!("resolved vtable for {:?} to bad vtable {:?} in trans",
 543                             trait_ref,
 544                             vtable));
 545             }
 546         }
 547     });
 548
 549     let size_ty = sizing_type_of(ccx, trait_ref.self_ty());
 550     let size = machine::llsize_of_alloc(ccx, size_ty);
 551     let align = align_of(ccx, trait_ref.self_ty());
 552
 553     let components: Vec<_> = vec![
 554         // Generate a destructor for the vtable.
 555         glue::get_drop_glue(ccx, trait_ref.self_ty()),
 556         C_uint(ccx, size),
 557         C_uint(ccx, align)
 558     ].into_iter().chain(methods).collect();
 559
 560     let vtable_const = C_struct(ccx, &components, false);
 561     let align = machine::llalign_of_pref(ccx, val_ty(vtable_const));
 562     let vtable = consts::addr_of(ccx, vtable_const, align, "vtable");
 563
 564     ccx.vtables().borrow_mut().insert(trait_ref, vtable);
 565     vtable
 566 }
 567
 568 pub fn get_vtable_methods<'a, 'tcx>(ccx: &CrateContext<'a, 'tcx>,
 569                                     impl_id: DefId,
 570                                     substs: subst::Substs<'tcx>)
 571                                     -> Vec<Option<ty::util::ImplMethod<'tcx>>>
 572 {
 573     let tcx = ccx.tcx();
 574
 575     debug!("get_vtable_methods(impl_id={:?}, substs={:?}", impl_id, substs);
 576
 577     let trt_id = match tcx.impl_trait_ref(impl_id) {
 578         Some(t_id) => t_id.def_id,
 579         None       => ccx.sess().bug("make_impl_vtable: don't know how to \
 580                                       make a vtable for a type impl!")
 581     };
 582
 583     tcx.populate_implementations_for_trait_if_necessary(trt_id);
 584
 585     let trait_item_def_ids = tcx.trait_item_def_ids(trt_id);
 586     trait_item_def_ids
 587         .iter()
 588
 589         // Filter out non-method items.
 590         .filter_map(|item_def_id| {
 591             match *item_def_id {
 592                 ty::MethodTraitItemId(def_id) => Some(def_id),
 593                 _ => None,
 594             }
 595         })
 596
 597         // Now produce pointers for each remaining method. If the
 598         // method could never be called from this object, just supply
 599         // null.
 600         .map(|trait_method_def_id| {
 601             debug!("get_vtable_methods: trait_method_def_id={:?}",
 602                    trait_method_def_id);
 603
 604             let trait_method_type = match tcx.impl_or_trait_item(trait_method_def_id) {
 605                 ty::MethodTraitItem(m) => m,
 606                 _ => ccx.sess().bug("should be a method, not other assoc item"),
 607             };
 608             let name = trait_method_type.name;
 609
 610             // Some methods cannot be called on an object; skip those.
 611             if !traits::is_vtable_safe_method(tcx, trt_id, &trait_method_type) {
 612                 debug!("get_vtable_methods: not vtable safe");
 613                 return None;
 614             }
 615
 616             debug!("get_vtable_methods: trait_method_type={:?}",
 617                    trait_method_type);
 618
 619             // The substitutions we have are on the impl, so we grab
 620             // the method type from the impl to substitute into.
 621             let mth = tcx.get_impl_method(impl_id, substs.clone(), name);
 622
 623             debug!("get_vtable_methods: mth={:?}", mth);
 624
 625             // If this is a default method, it's possible that it
 626             // relies on where clauses that do not hold for this
 627             // particular set of type parameters. Note that this
 628             // method could then never be called, so we do not want to
 629             // try and trans it, in that case. Issue #23435.
 630             if mth.is_provided {
 631                 let predicates = mth.method.predicates.predicates.subst(tcx, &mth.substs);
 632                 if !normalize_and_test_predicates(ccx, predicates.into_vec()) {
 633                     debug!("get_vtable_methods: predicates do not hold");
 634                     return None;
 635                 }
 636             }
 637
 638             Some(mth)
 639         })
 640         .collect()
 641 }
 642
 643 /// Replace the self type (&Self or Box<Self>) with an opaque pointer.
 644 fn opaque_method_ty<'tcx>(tcx: &ty::ctxt<'tcx>, method_ty: &ty::BareFnTy<'tcx>)
 645                           -> &'tcx ty::BareFnTy<'tcx> {
 646     let mut inputs = method_ty.sig.0.inputs.clone();
 647     inputs[0] = tcx.mk_mut_ptr(tcx.mk_mach_int(ast::IntTy::I8));
 648
 649     tcx.mk_bare_fn(ty::BareFnTy {
 650         unsafety: method_ty.unsafety,
 651         abi: method_ty.abi,
 652         sig: ty::Binder(ty::FnSig {
 653             inputs: inputs,
 654             output: method_ty.sig.0.output,
 655             variadic: method_ty.sig.0.variadic,
 656         }),
 657     })
 658 }