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