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 std::rc::Rc;
  12
  13 use arena::TypedArena;
  14 use back::link;
  15 use llvm::{ValueRef, get_params};
  16 use middle::def_id::DefId;
  17 use middle::infer;
  18 use middle::subst::{Subst, Substs};
  19 use middle::subst;
  20 use middle::traits;
  21 use trans::base::*;
  22 use trans::build::*;
  23 use trans::callee::{Callee, Virtual, ArgVals,
  24                     trans_fn_pointer_shim, trans_fn_ref_with_substs};
  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::type_::Type;
  35 use trans::type_of::*;
  36 use middle::ty::{self, Ty, TyCtxt};
  37
  38 use syntax::ast::{self, Name};
  39 use syntax::attr;
  40 use syntax::codemap::DUMMY_SP;
  41
  42 use rustc_front::hir;
  43
  44 // drop_glue pointer, size, align.
  45 const VTABLE_OFFSET: usize = 3;
  46
  47 /// The main "translation" pass for methods.  Generates code
  48 /// for non-monomorphized methods only.  Other methods will
  49 /// be generated once they are invoked with specific type parameters,
  50 /// see `trans::base::lval_static_fn()` or `trans::base::monomorphic_fn()`.
  51 pub fn trans_impl(ccx: &CrateContext,
  52                   name: ast::Name,
  53                   impl_items: &[hir::ImplItem],
  54                   generics: &hir::Generics,
  55                   id: ast::NodeId) {
  56     let _icx = push_ctxt("meth::trans_impl");
  57     let tcx = ccx.tcx();
  58
  59     debug!("trans_impl(name={}, id={})", name, id);
  60
  61     // Both here and below with generic methods, be sure to recurse and look for
  62     // items that we need to translate.
  63     if !generics.ty_params.is_empty() {
  64         return;
  65     }
  66
  67     for impl_item in impl_items {
  68         match impl_item.node {
  69             hir::ImplItemKind::Method(ref sig, ref body) => {
  70                 if sig.generics.ty_params.is_empty() {
  71                     let trans_everywhere = attr::requests_inline(&impl_item.attrs);
  72                     for (ref ccx, is_origin) in ccx.maybe_iter(trans_everywhere) {
  73                         let llfn = get_item_val(ccx, impl_item.id);
  74                         let empty_substs = tcx.mk_substs(Substs::trans_empty());
  75                         trans_fn(ccx,
  76                                  &sig.decl,
  77                                  body,
  78                                  llfn,
  79                                  empty_substs,
  80                                  impl_item.id,
  81                                  &impl_item.attrs);
  82                         update_linkage(ccx,
  83                                        llfn,
  84                                        Some(impl_item.id),
  85                                        if is_origin { OriginalTranslation } else { InlinedCopy });
  86                     }
  87                 }
  88             }
  89             _ => {}
  90         }
  91     }
  92 }
  93
  94 /// Compute the appropriate callee, give na method's ID, trait ID,
  95 /// substitutions and a Vtable for that trait.
  96 pub fn callee_for_trait_impl<'a, 'tcx>(ccx: &CrateContext<'a, 'tcx>,
  97                                        method_id: DefId,
  98                                        substs: &'tcx subst::Substs<'tcx>,
  99                                        trait_id: DefId,
 100                                        method_ty: Ty<'tcx>,
 101                                        vtable: traits::Vtable<'tcx, ()>)
 102                                        -> Callee<'tcx> {
 103     let _icx = push_ctxt("meth::callee_for_trait_impl");
 104     match vtable {
 105         traits::VtableImpl(vtable_impl) => {
 106             let impl_did = vtable_impl.impl_def_id;
 107             let mname = ccx.tcx().item_name(method_id);
 108             // create a concatenated set of substitutions which includes
 109             // those from the impl and those from the method:
 110             let impl_substs = vtable_impl.substs.with_method_from(&substs);
 111             let substs = ccx.tcx().mk_substs(impl_substs);
 112             let mth = get_impl_method(ccx.tcx(), impl_did, impl_substs, mname);
 113
 114             // Translate the function, bypassing Callee::def.
 115             // That is because default methods have the same ID as the
 116             // trait method used to look up the impl method that ended
 117             // up here, so calling Callee::def would infinitely recurse.
 118             Callee::ptr(trans_fn_ref_with_substs(ccx, mth.method.def_id,
 119                                                  Some(method_ty), mth.substs))
 120         }
 121         traits::VtableClosure(vtable_closure) => {
 122             // The substitutions should have no type parameters remaining
 123             // after passing through fulfill_obligation
 124             let trait_closure_kind = ccx.tcx().lang_items.fn_trait_kind(trait_id).unwrap();
 125             let llfn = closure::trans_closure_method(ccx,
 126                                                      vtable_closure.closure_def_id,
 127                                                      vtable_closure.substs,
 128                                                      trait_closure_kind);
 129             let fn_ptr_ty = match method_ty.sty {
 130                 ty::TyFnDef(_, _, fty) => ccx.tcx().mk_ty(ty::TyFnPtr(fty)),
 131                 _ => unreachable!("expected fn item type, found {}",
 132                                   method_ty)
 133             };
 134             Callee::ptr(immediate_rvalue(llfn, fn_ptr_ty))
 135         }
 136         traits::VtableFnPointer(fn_ty) => {
 137             let trait_closure_kind = ccx.tcx().lang_items.fn_trait_kind(trait_id).unwrap();
 138             let llfn = trans_fn_pointer_shim(ccx, trait_closure_kind, fn_ty);
 139             let fn_ptr_ty = match method_ty.sty {
 140                 ty::TyFnDef(_, _, fty) => ccx.tcx().mk_ty(ty::TyFnPtr(fty)),
 141                 _ => unreachable!("expected fn item type, found {}",
 142                                   method_ty)
 143             };
 144             Callee::ptr(immediate_rvalue(llfn, fn_ptr_ty))
 145         }
 146         traits::VtableObject(ref data) => {
 147             Callee {
 148                 data: Virtual(traits::get_vtable_index_of_object_method(
 149                     ccx.tcx(), data, method_id)),
 150                 ty: method_ty
 151             }
 152         }
 153         traits::VtableBuiltin(..) |
 154         traits::VtableDefaultImpl(..) |
 155         traits::VtableParam(..) => {
 156             ccx.sess().bug(
 157                 &format!("resolved vtable bad vtable {:?} in trans",
 158                         vtable));
 159         }
 160     }
 161 }
 162
 163 /// Extracts a method from a trait object's vtable, at the
 164 /// specified index, and casts it to the given type.
 165 pub fn get_virtual_method<'blk, 'tcx>(bcx: Block<'blk, 'tcx>,
 166                                       llvtable: ValueRef,
 167                                       vtable_index: usize,
 168                                       method_ty: Ty<'tcx>)
 169                                       -> Datum<'tcx, Rvalue> {
 170     let _icx = push_ctxt("meth::get_virtual_method");
 171     let ccx = bcx.ccx();
 172
 173     // Load the data pointer from the object.
 174     debug!("get_virtual_method(callee_ty={}, vtable_index={}, llvtable={})",
 175            method_ty,
 176            vtable_index,
 177            bcx.val_to_string(llvtable));
 178
 179     let mptr = Load(bcx, GEPi(bcx, llvtable, &[vtable_index + VTABLE_OFFSET]));
 180
 181     // Replace the self type (&Self or Box<Self>) with an opaque pointer.
 182     if let ty::TyFnDef(_, _, fty) = method_ty.sty {
 183         let opaque_ty = opaque_method_ty(ccx.tcx(), fty);
 184         immediate_rvalue(PointerCast(bcx, mptr, type_of(ccx, opaque_ty)), opaque_ty)
 185     } else {
 186         immediate_rvalue(mptr, method_ty)
 187     }
 188 }
 189
 190 /// Generate a shim function that allows an object type like `SomeTrait` to
 191 /// implement the type `SomeTrait`. Imagine a trait definition:
 192 ///
 193 ///    trait SomeTrait { fn get(&self) -> i32; ... }
 194 ///
 195 /// And a generic bit of code:
 196 ///
 197 ///    fn foo<T:SomeTrait>(t: &T) {
 198 ///        let x = SomeTrait::get;
 199 ///        x(t)
 200 ///    }
 201 ///
 202 /// What is the value of `x` when `foo` is invoked with `T=SomeTrait`?
 203 /// The answer is that it is a shim function generated by this routine:
 204 ///
 205 ///    fn shim(t: &SomeTrait) -> i32 {
 206 ///        // ... call t.get() virtually ...
 207 ///    }
 208 ///
 209 /// In fact, all virtual calls can be thought of as normal trait calls
 210 /// that go through this shim function.
 211 pub fn trans_object_shim<'a, 'tcx>(ccx: &'a CrateContext<'a, 'tcx>,
 212                                    method_ty: Ty<'tcx>,
 213                                    vtable_index: usize)
 214                                    -> Datum<'tcx, Rvalue> {
 215     let _icx = push_ctxt("trans_object_shim");
 216     let tcx = ccx.tcx();
 217
 218     debug!("trans_object_shim(vtable_index={}, method_ty={:?})",
 219            vtable_index,
 220            method_ty);
 221
 222     let ret_ty = tcx.erase_late_bound_regions(&method_ty.fn_ret());
 223     let ret_ty = infer::normalize_associated_type(tcx, &ret_ty);
 224
 225     let shim_fn_ty = match method_ty.sty {
 226         ty::TyFnDef(_, _, fty) => tcx.mk_ty(ty::TyFnPtr(fty)),
 227         _ => unreachable!("expected fn item type, found {}", method_ty)
 228     };
 229
 230     //
 231     let function_name = link::mangle_internal_name_by_type_and_seq(ccx, shim_fn_ty, "object_shim");
 232     let llfn = declare::define_internal_rust_fn(ccx, &function_name, shim_fn_ty);
 233
 234     let empty_substs = tcx.mk_substs(Substs::trans_empty());
 235     let (block_arena, fcx): (TypedArena<_>, FunctionContext);
 236     block_arena = TypedArena::new();
 237     fcx = new_fn_ctxt(ccx,
 238                       llfn,
 239                       ast::DUMMY_NODE_ID,
 240                       false,
 241                       ret_ty,
 242                       empty_substs,
 243                       None,
 244                       &block_arena);
 245     let mut bcx = init_function(&fcx, false, ret_ty);
 246
 247     let llargs = get_params(fcx.llfn);
 248
 249     let self_idx = fcx.arg_offset();
 250     let llself = llargs[self_idx];
 251     let llvtable = llargs[self_idx + 1];
 252
 253     debug!("trans_object_shim: llself={}, llvtable={}",
 254            bcx.val_to_string(llself), bcx.val_to_string(llvtable));
 255
 256     assert!(!fcx.needs_ret_allocas);
 257
 258     let dest =
 259         fcx.llretslotptr.get().map(
 260             |_| expr::SaveIn(fcx.get_ret_slot(bcx, ret_ty, "ret_slot")));
 261
 262     debug!("trans_object_shim: method_offset_in_vtable={}",
 263            vtable_index);
 264
 265     let callee = Callee {
 266         data: Virtual(vtable_index),
 267         ty: method_ty
 268     };
 269     bcx = callee.call(bcx, DebugLoc::None, ArgVals(&llargs[self_idx..]), dest).bcx;
 270
 271     finish_fn(&fcx, bcx, ret_ty, DebugLoc::None);
 272
 273     immediate_rvalue(llfn, shim_fn_ty)
 274 }
 275
 276 /// Creates a returns a dynamic vtable for the given type and vtable origin.
 277 /// This is used only for objects.
 278 ///
 279 /// The `trait_ref` encodes the erased self type. Hence if we are
 280 /// making an object `Foo<Trait>` from a value of type `Foo<T>`, then
 281 /// `trait_ref` would map `T:Trait`.
 282 pub fn get_vtable<'a, 'tcx>(ccx: &CrateContext<'a, 'tcx>,
 283                             trait_ref: ty::PolyTraitRef<'tcx>)
 284                             -> ValueRef
 285 {
 286     let tcx = ccx.tcx();
 287     let _icx = push_ctxt("meth::get_vtable");
 288
 289     debug!("get_vtable(trait_ref={:?})", trait_ref);
 290
 291     // Check the cache.
 292     match ccx.vtables().borrow().get(&trait_ref) {
 293         Some(&val) => { return val }
 294         None => { }
 295     }
 296
 297     // Not in the cache. Build it.
 298     let methods = traits::supertraits(tcx, trait_ref.clone()).flat_map(|trait_ref| {
 299         let vtable = fulfill_obligation(ccx, DUMMY_SP, trait_ref.clone());
 300         match vtable {
 301             // Should default trait error here?
 302             traits::VtableDefaultImpl(_) |
 303             traits::VtableBuiltin(_) => {
 304                 Vec::new().into_iter()
 305             }
 306             traits::VtableImpl(
 307                 traits::VtableImplData {
 308                     impl_def_id: id,
 309                     substs,
 310                     nested: _ }) => {
 311                 let nullptr = C_null(Type::nil(ccx).ptr_to());
 312                 get_vtable_methods(ccx, id, substs)
 313                     .into_iter()
 314                     .map(|opt_mth| {
 315                         match opt_mth {
 316                             Some(mth) => {
 317                                 trans_fn_ref_with_substs(ccx,
 318                                                          mth.method.def_id,
 319                                                          None,
 320                                                          mth.substs).val
 321                             }
 322                             None => nullptr
 323                         }
 324                     })
 325                     .collect::<Vec<_>>()
 326                     .into_iter()
 327             }
 328             traits::VtableClosure(
 329                 traits::VtableClosureData {
 330                     closure_def_id,
 331                     substs,
 332                     nested: _ }) => {
 333                 let trait_closure_kind = tcx.lang_items.fn_trait_kind(trait_ref.def_id()).unwrap();
 334                 let llfn = closure::trans_closure_method(ccx,
 335                                                          closure_def_id,
 336                                                          substs,
 337                                                          trait_closure_kind);
 338                 vec![llfn].into_iter()
 339             }
 340             traits::VtableFnPointer(bare_fn_ty) => {
 341                 let trait_closure_kind = tcx.lang_items.fn_trait_kind(trait_ref.def_id()).unwrap();
 342                 vec![trans_fn_pointer_shim(ccx, trait_closure_kind, bare_fn_ty)].into_iter()
 343             }
 344             traits::VtableObject(ref data) => {
 345                 // this would imply that the Self type being erased is
 346                 // an object type; this cannot happen because we
 347                 // cannot cast an unsized type into a trait object
 348                 tcx.sess.bug(
 349                     &format!("cannot get vtable for an object type: {:?}",
 350                             data));
 351             }
 352             traits::VtableParam(..) => {
 353                 tcx.sess.bug(
 354                     &format!("resolved vtable for {:?} to bad vtable {:?} in trans",
 355                             trait_ref,
 356                             vtable));
 357             }
 358         }
 359     });
 360
 361     let size_ty = sizing_type_of(ccx, trait_ref.self_ty());
 362     let size = machine::llsize_of_alloc(ccx, size_ty);
 363     let align = align_of(ccx, trait_ref.self_ty());
 364
 365     let components: Vec<_> = vec![
 366         // Generate a destructor for the vtable.
 367         glue::get_drop_glue(ccx, trait_ref.self_ty()),
 368         C_uint(ccx, size),
 369         C_uint(ccx, align)
 370     ].into_iter().chain(methods).collect();
 371
 372     let vtable_const = C_struct(ccx, &components, false);
 373     let align = machine::llalign_of_pref(ccx, val_ty(vtable_const));
 374     let vtable = consts::addr_of(ccx, vtable_const, align, "vtable");
 375
 376     ccx.vtables().borrow_mut().insert(trait_ref, vtable);
 377     vtable
 378 }
 379
 380 pub fn get_vtable_methods<'a, 'tcx>(ccx: &CrateContext<'a, 'tcx>,
 381                                     impl_id: DefId,
 382                                     substs: &'tcx subst::Substs<'tcx>)
 383                                     -> Vec<Option<ty::util::ImplMethod<'tcx>>>
 384 {
 385     let tcx = ccx.tcx();
 386
 387     debug!("get_vtable_methods(impl_id={:?}, substs={:?}", impl_id, substs);
 388
 389     let trt_id = match tcx.impl_trait_ref(impl_id) {
 390         Some(t_id) => t_id.def_id,
 391         None       => ccx.sess().bug("make_impl_vtable: don't know how to \
 392                                       make a vtable for a type impl!")
 393     };
 394
 395     tcx.populate_implementations_for_trait_if_necessary(trt_id);
 396
 397     let trait_item_def_ids = tcx.trait_item_def_ids(trt_id);
 398     trait_item_def_ids
 399         .iter()
 400
 401         // Filter out non-method items.
 402         .filter_map(|item_def_id| {
 403             match *item_def_id {
 404                 ty::MethodTraitItemId(def_id) => Some(def_id),
 405                 _ => None,
 406             }
 407         })
 408
 409         // Now produce pointers for each remaining method. If the
 410         // method could never be called from this object, just supply
 411         // null.
 412         .map(|trait_method_def_id| {
 413             debug!("get_vtable_methods: trait_method_def_id={:?}",
 414                    trait_method_def_id);
 415
 416             let trait_method_type = match tcx.impl_or_trait_item(trait_method_def_id) {
 417                 ty::MethodTraitItem(m) => m,
 418                 _ => ccx.sess().bug("should be a method, not other assoc item"),
 419             };
 420             let name = trait_method_type.name;
 421
 422             // Some methods cannot be called on an object; skip those.
 423             if !traits::is_vtable_safe_method(tcx, trt_id, &trait_method_type) {
 424                 debug!("get_vtable_methods: not vtable safe");
 425                 return None;
 426             }
 427
 428             debug!("get_vtable_methods: trait_method_type={:?}",
 429                    trait_method_type);
 430
 431             // The substitutions we have are on the impl, so we grab
 432             // the method type from the impl to substitute into.
 433             let mth = get_impl_method(tcx, impl_id, substs.clone(), name);
 434
 435             debug!("get_vtable_methods: mth={:?}", mth);
 436
 437             // If this is a default method, it's possible that it
 438             // relies on where clauses that do not hold for this
 439             // particular set of type parameters. Note that this
 440             // method could then never be called, so we do not want to
 441             // try and trans it, in that case. Issue #23435.
 442             if mth.is_provided {
 443                 let predicates = mth.method.predicates.predicates.subst(tcx, mth.substs);
 444                 if !normalize_and_test_predicates(ccx, predicates.into_vec()) {
 445                     debug!("get_vtable_methods: predicates do not hold");
 446                     return None;
 447                 }
 448             }
 449
 450             Some(mth)
 451         })
 452         .collect()
 453 }
 454
 455 /// Replace the self type (&Self or Box<Self>) with an opaque pointer.
 456 fn opaque_method_ty<'tcx>(tcx: &TyCtxt<'tcx>, method_ty: &ty::BareFnTy<'tcx>)
 457                           -> Ty<'tcx> {
 458     let mut inputs = method_ty.sig.0.inputs.clone();
 459     inputs[0] = tcx.mk_mut_ptr(tcx.mk_mach_int(ast::IntTy::I8));
 460
 461     tcx.mk_fn_ptr(ty::BareFnTy {
 462         unsafety: method_ty.unsafety,
 463         abi: method_ty.abi,
 464         sig: ty::Binder(ty::FnSig {
 465             inputs: inputs,
 466             output: method_ty.sig.0.output,
 467             variadic: method_ty.sig.0.variadic,
 468         }),
 469     })
 470 }
 471
 472 #[derive(Debug)]
 473 pub struct ImplMethod<'tcx> {
 474     pub method: Rc<ty::Method<'tcx>>,
 475     pub substs: Substs<'tcx>,
 476     pub is_provided: bool
 477 }
 478
 479 /// Locates the applicable definition of a method, given its name.
 480 pub fn get_impl_method<'tcx>(tcx: &ty::ctxt<'tcx>,
 481                              impl_def_id: DefId,
 482                              substs: Substs<'tcx>,
 483                              name: Name)
 484                              -> ImplMethod<'tcx>
 485 {
 486     assert!(!substs.types.needs_infer());
 487
 488     traits::get_impl_item_or_default(tcx, impl_def_id, |cand| {
 489         if let &ty::MethodTraitItem(ref meth) = cand {
 490             if meth.name == name {
 491                 return Some(meth.clone())
 492             }
 493         }
 494         None
 495     }).map(|(meth, source)| {
 496         ImplMethod {
 497             method: meth,
 498             substs: source.translate_substs(tcx, substs),
 499             is_provided: source.is_from_trait(),
 500         }
 501     }).unwrap_or_else(|| {
 502         tcx.sess.bug(&format!("method {:?} not found in {:?}",
 503                               name, impl_def_id))
 504     })
 505 }