src/librustc/ty/instance.rs

   1 use crate::middle::codegen_fn_attrs::CodegenFnAttrFlags;
   2 use crate::middle::lang_items::DropInPlaceFnLangItem;
   3 use crate::traits;
   4 use crate::ty::print::{FmtPrinter, Printer};
   5 use crate::ty::{self, SubstsRef, Ty, TyCtxt, TypeFoldable};
   6 use rustc_hir::def::Namespace;
   7 use rustc_hir::def_id::DefId;
   8 use rustc_macros::HashStable;
   9 use rustc_target::spec::abi::Abi;
  10
  11 use std::fmt;
  12
  13 #[derive(Copy, Clone, PartialEq, Eq, Hash, Debug, RustcEncodable, RustcDecodable)]
  14 #[derive(HashStable, Lift)]
  15 pub struct Instance<'tcx> {
  16     pub def: InstanceDef<'tcx>,
  17     pub substs: SubstsRef<'tcx>,
  18 }
  19
  20 #[derive(Copy, Clone, PartialEq, Eq, Hash, Debug, RustcEncodable, RustcDecodable, HashStable)]
  21 pub enum InstanceDef<'tcx> {
  22     Item(DefId),
  23     Intrinsic(DefId),
  24
  25     /// `<T as Trait>::method` where `method` receives unsizeable `self: Self`.
  26     VtableShim(DefId),
  27
  28     /// `fn()` pointer where the function itself cannot be turned into a pointer.
  29     ///
  30     /// One example is `<dyn Trait as Trait>::fn`, where the shim contains
  31     /// a virtual call, which codegen supports only via a direct call to the
  32     /// `<dyn Trait as Trait>::fn` instance (an `InstanceDef::Virtual`).
  33     ///
  34     /// Another example is functions annotated with `#[track_caller]`, which
  35     /// must have their implicit caller location argument populated for a call.
  36     /// Because this is a required part of the function's ABI but can't be tracked
  37     /// as a property of the function pointer, we use a single "caller location"
  38     /// (the definition of the function itself).
  39     ReifyShim(DefId),
  40
  41     /// `<fn() as FnTrait>::call_*`
  42     /// `DefId` is `FnTrait::call_*`.
  43     FnPtrShim(DefId, Ty<'tcx>),
  44
  45     /// `<dyn Trait as Trait>::fn`, "direct calls" of which are implicitly
  46     /// codegen'd as virtual calls.
  47     ///
  48     /// NB: if this is reified to a `fn` pointer, a `ReifyShim` is used
  49     /// (see `ReifyShim` above for more details on that).
  50     Virtual(DefId, usize),
  51
  52     /// `<[mut closure] as FnOnce>::call_once`
  53     ClosureOnceShim {
  54         call_once: DefId,
  55     },
  56
  57     /// `drop_in_place::<T>; None` for empty drop glue.
  58     DropGlue(DefId, Option<Ty<'tcx>>),
  59
  60     ///`<T as Clone>::clone` shim.
  61     CloneShim(DefId, Ty<'tcx>),
  62 }
  63
  64 impl<'tcx> Instance<'tcx> {
  65     /// Returns the `Ty` corresponding to this `Instance`,
  66     /// with generic substitutions applied and lifetimes erased.
  67     ///
  68     /// This method can only be called when the 'substs' for this Instance
  69     /// are fully monomorphic (no `ty::Param`'s are present).
  70     /// This is usually the case (e.g. during codegen).
  71     /// However, during constant evaluation, we may want
  72     /// to try to resolve a `Instance` using generic parameters
  73     /// (e.g. when we are attempting to to do const-propagation).
  74     /// In this case, `Instance.ty_env` should be used to provide
  75     /// the `ParamEnv` for our generic context.
  76     pub fn monomorphic_ty(&self, tcx: TyCtxt<'tcx>) -> Ty<'tcx> {
  77         let ty = tcx.type_of(self.def.def_id());
  78         // There shouldn't be any params - if there are, then
  79         // Instance.ty_env should have been used to provide the proper
  80         // ParamEnv
  81         if self.substs.has_param_types() {
  82             bug!("Instance.ty called for type {:?} with params in substs: {:?}", ty, self.substs);
  83         }
  84         tcx.subst_and_normalize_erasing_regions(self.substs, ty::ParamEnv::reveal_all(), &ty)
  85     }
  86
  87     /// Like `Instance.ty`, but allows a `ParamEnv` to be specified for use during
  88     /// normalization. This method is only really useful during constant evaluation,
  89     /// where we are dealing with potentially generic types.
  90     pub fn ty_env(&self, tcx: TyCtxt<'tcx>, param_env: ty::ParamEnv<'tcx>) -> Ty<'tcx> {
  91         let ty = tcx.type_of(self.def.def_id());
  92         tcx.subst_and_normalize_erasing_regions(self.substs, param_env, &ty)
  93     }
  94 }
  95
  96 impl<'tcx> InstanceDef<'tcx> {
  97     #[inline]
  98     pub fn def_id(&self) -> DefId {
  99         match *self {
 100             InstanceDef::Item(def_id)
 101             | InstanceDef::VtableShim(def_id)
 102             | InstanceDef::ReifyShim(def_id)
 103             | InstanceDef::FnPtrShim(def_id, _)
 104             | InstanceDef::Virtual(def_id, _)
 105             | InstanceDef::Intrinsic(def_id)
 106             | InstanceDef::ClosureOnceShim { call_once: def_id }
 107             | InstanceDef::DropGlue(def_id, _)
 108             | InstanceDef::CloneShim(def_id, _) => def_id,
 109         }
 110     }
 111
 112     #[inline]
 113     pub fn attrs(&self, tcx: TyCtxt<'tcx>) -> ty::Attributes<'tcx> {
 114         tcx.get_attrs(self.def_id())
 115     }
 116
 117     pub fn is_inline(&self, tcx: TyCtxt<'tcx>) -> bool {
 118         use crate::hir::map::DefPathData;
 119         let def_id = match *self {
 120             ty::InstanceDef::Item(def_id) => def_id,
 121             ty::InstanceDef::DropGlue(_, Some(_)) => return false,
 122             _ => return true,
 123         };
 124         match tcx.def_key(def_id).disambiguated_data.data {
 125             DefPathData::Ctor | DefPathData::ClosureExpr => true,
 126             _ => false,
 127         }
 128     }
 129
 130     pub fn requires_local(&self, tcx: TyCtxt<'tcx>) -> bool {
 131         if self.is_inline(tcx) {
 132             return true;
 133         }
 134         if let ty::InstanceDef::DropGlue(..) = *self {
 135             // Drop glue wants to be instantiated at every codegen
 136             // unit, but without an #[inline] hint. We should make this
 137             // available to normal end-users.
 138             return true;
 139         }
 140         tcx.codegen_fn_attrs(self.def_id()).requests_inline()
 141     }
 142
 143     pub fn requires_caller_location(&self, tcx: TyCtxt<'_>) -> bool {
 144         tcx.codegen_fn_attrs(self.def_id()).flags.contains(CodegenFnAttrFlags::TRACK_CALLER)
 145     }
 146 }
 147
 148 impl<'tcx> fmt::Display for Instance<'tcx> {
 149     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
 150         ty::tls::with(|tcx| {
 151             let substs = tcx.lift(&self.substs).expect("could not lift for printing");
 152             FmtPrinter::new(tcx, &mut *f, Namespace::ValueNS)
 153                 .print_def_path(self.def_id(), substs)?;
 154             Ok(())
 155         })?;
 156
 157         match self.def {
 158             InstanceDef::Item(_) => Ok(()),
 159             InstanceDef::VtableShim(_) => write!(f, " - shim(vtable)"),
 160             InstanceDef::ReifyShim(_) => write!(f, " - shim(reify)"),
 161             InstanceDef::Intrinsic(_) => write!(f, " - intrinsic"),
 162             InstanceDef::Virtual(_, num) => write!(f, " - virtual#{}", num),
 163             InstanceDef::FnPtrShim(_, ty) => write!(f, " - shim({:?})", ty),
 164             InstanceDef::ClosureOnceShim { .. } => write!(f, " - shim"),
 165             InstanceDef::DropGlue(_, ty) => write!(f, " - shim({:?})", ty),
 166             InstanceDef::CloneShim(_, ty) => write!(f, " - shim({:?})", ty),
 167         }
 168     }
 169 }
 170
 171 impl<'tcx> Instance<'tcx> {
 172     pub fn new(def_id: DefId, substs: SubstsRef<'tcx>) -> Instance<'tcx> {
 173         assert!(
 174             !substs.has_escaping_bound_vars(),
 175             "substs of instance {:?} not normalized for codegen: {:?}",
 176             def_id,
 177             substs
 178         );
 179         Instance { def: InstanceDef::Item(def_id), substs: substs }
 180     }
 181
 182     pub fn mono(tcx: TyCtxt<'tcx>, def_id: DefId) -> Instance<'tcx> {
 183         Instance::new(def_id, tcx.empty_substs_for_def_id(def_id))
 184     }
 185
 186     #[inline]
 187     pub fn def_id(&self) -> DefId {
 188         self.def.def_id()
 189     }
 190
 191     /// Resolves a `(def_id, substs)` pair to an (optional) instance -- most commonly,
 192     /// this is used to find the precise code that will run for a trait method invocation,
 193     /// if known.
 194     ///
 195     /// Returns `None` if we cannot resolve `Instance` to a specific instance.
 196     /// For example, in a context like this,
 197     ///
 198     /// ```
 199     /// fn foo<T: Debug>(t: T) { ... }
 200     /// ```
 201     ///
 202     /// trying to resolve `Debug::fmt` applied to `T` will yield `None`, because we do not
 203     /// know what code ought to run. (Note that this setting is also affected by the
 204     /// `RevealMode` in the parameter environment.)
 205     ///
 206     /// Presuming that coherence and type-check have succeeded, if this method is invoked
 207     /// in a monomorphic context (i.e., like during codegen), then it is guaranteed to return
 208     /// `Some`.
 209     pub fn resolve(
 210         tcx: TyCtxt<'tcx>,
 211         param_env: ty::ParamEnv<'tcx>,
 212         def_id: DefId,
 213         substs: SubstsRef<'tcx>,
 214     ) -> Option<Instance<'tcx>> {
 215         debug!("resolve(def_id={:?}, substs={:?})", def_id, substs);
 216         let result = if let Some(trait_def_id) = tcx.trait_of_item(def_id) {
 217             debug!(" => associated item, attempting to find impl in param_env {:#?}", param_env);
 218             let item = tcx.associated_item(def_id);
 219             resolve_associated_item(tcx, &item, param_env, trait_def_id, substs)
 220         } else {
 221             let ty = tcx.type_of(def_id);
 222             let item_type = tcx.subst_and_normalize_erasing_regions(substs, param_env, &ty);
 223
 224             let def = match item_type.kind {
 225                 ty::FnDef(..)
 226                     if {
 227                         let f = item_type.fn_sig(tcx);
 228                         f.abi() == Abi::RustIntrinsic || f.abi() == Abi::PlatformIntrinsic
 229                     } =>
 230                 {
 231                     debug!(" => intrinsic");
 232                     ty::InstanceDef::Intrinsic(def_id)
 233                 }
 234                 _ => {
 235                     if Some(def_id) == tcx.lang_items().drop_in_place_fn() {
 236                         let ty = substs.type_at(0);
 237                         if ty.needs_drop(tcx, ty::ParamEnv::reveal_all()) {
 238                             debug!(" => nontrivial drop glue");
 239                             ty::InstanceDef::DropGlue(def_id, Some(ty))
 240                         } else {
 241                             debug!(" => trivial drop glue");
 242                             ty::InstanceDef::DropGlue(def_id, None)
 243                         }
 244                     } else {
 245                         debug!(" => free item");
 246                         ty::InstanceDef::Item(def_id)
 247                     }
 248                 }
 249             };
 250             Some(Instance { def: def, substs: substs })
 251         };
 252         debug!("resolve(def_id={:?}, substs={:?}) = {:?}", def_id, substs, result);
 253         result
 254     }
 255
 256     pub fn resolve_for_fn_ptr(
 257         tcx: TyCtxt<'tcx>,
 258         param_env: ty::ParamEnv<'tcx>,
 259         def_id: DefId,
 260         substs: SubstsRef<'tcx>,
 261     ) -> Option<Instance<'tcx>> {
 262         debug!("resolve(def_id={:?}, substs={:?})", def_id, substs);
 263         Instance::resolve(tcx, param_env, def_id, substs).map(|mut resolved| {
 264             match resolved.def {
 265                 InstanceDef::Item(def_id) if resolved.def.requires_caller_location(tcx) => {
 266                     debug!(" => fn pointer created for function with #[track_caller]");
 267                     resolved.def = InstanceDef::ReifyShim(def_id);
 268                 }
 269                 InstanceDef::Virtual(def_id, _) => {
 270                     debug!(" => fn pointer created for virtual call");
 271                     resolved.def = InstanceDef::ReifyShim(def_id);
 272                 }
 273                 _ => {}
 274             }
 275
 276             resolved
 277         })
 278     }
 279
 280     pub fn resolve_for_vtable(
 281         tcx: TyCtxt<'tcx>,
 282         param_env: ty::ParamEnv<'tcx>,
 283         def_id: DefId,
 284         substs: SubstsRef<'tcx>,
 285     ) -> Option<Instance<'tcx>> {
 286         debug!("resolve(def_id={:?}, substs={:?})", def_id, substs);
 287         let fn_sig = tcx.fn_sig(def_id);
 288         let is_vtable_shim = fn_sig.inputs().skip_binder().len() > 0
 289             && fn_sig.input(0).skip_binder().is_param(0)
 290             && tcx.generics_of(def_id).has_self;
 291         if is_vtable_shim {
 292             debug!(" => associated item with unsizeable self: Self");
 293             Some(Instance { def: InstanceDef::VtableShim(def_id), substs })
 294         } else {
 295             Instance::resolve(tcx, param_env, def_id, substs)
 296         }
 297     }
 298
 299     pub fn resolve_closure(
 300         tcx: TyCtxt<'tcx>,
 301         def_id: DefId,
 302         substs: ty::SubstsRef<'tcx>,
 303         requested_kind: ty::ClosureKind,
 304     ) -> Instance<'tcx> {
 305         let actual_kind = substs.as_closure().kind(def_id, tcx);
 306
 307         match needs_fn_once_adapter_shim(actual_kind, requested_kind) {
 308             Ok(true) => Instance::fn_once_adapter_instance(tcx, def_id, substs),
 309             _ => Instance::new(def_id, substs),
 310         }
 311     }
 312
 313     pub fn resolve_drop_in_place(tcx: TyCtxt<'tcx>, ty: Ty<'tcx>) -> ty::Instance<'tcx> {
 314         let def_id = tcx.require_lang_item(DropInPlaceFnLangItem, None);
 315         let substs = tcx.intern_substs(&[ty.into()]);
 316         Instance::resolve(tcx, ty::ParamEnv::reveal_all(), def_id, substs).unwrap()
 317     }
 318
 319     pub fn fn_once_adapter_instance(
 320         tcx: TyCtxt<'tcx>,
 321         closure_did: DefId,
 322         substs: ty::SubstsRef<'tcx>,
 323     ) -> Instance<'tcx> {
 324         debug!("fn_once_adapter_shim({:?}, {:?})", closure_did, substs);
 325         let fn_once = tcx.lang_items().fn_once_trait().unwrap();
 326         let call_once = tcx
 327             .associated_items(fn_once)
 328             .find(|it| it.kind == ty::AssocKind::Method)
 329             .unwrap()
 330             .def_id;
 331         let def = ty::InstanceDef::ClosureOnceShim { call_once };
 332
 333         let self_ty = tcx.mk_closure(closure_did, substs);
 334
 335         let sig = substs.as_closure().sig(closure_did, tcx);
 336         let sig = tcx.normalize_erasing_late_bound_regions(ty::ParamEnv::reveal_all(), &sig);
 337         assert_eq!(sig.inputs().len(), 1);
 338         let substs = tcx.mk_substs_trait(self_ty, &[sig.inputs()[0].into()]);
 339
 340         debug!("fn_once_adapter_shim: self_ty={:?} sig={:?}", self_ty, sig);
 341         Instance { def, substs }
 342     }
 343
 344     pub fn is_vtable_shim(&self) -> bool {
 345         if let InstanceDef::VtableShim(..) = self.def { true } else { false }
 346     }
 347 }
 348
 349 fn resolve_associated_item<'tcx>(
 350     tcx: TyCtxt<'tcx>,
 351     trait_item: &ty::AssocItem,
 352     param_env: ty::ParamEnv<'tcx>,
 353     trait_id: DefId,
 354     rcvr_substs: SubstsRef<'tcx>,
 355 ) -> Option<Instance<'tcx>> {
 356     let def_id = trait_item.def_id;
 357     debug!(
 358         "resolve_associated_item(trait_item={:?}, \
 359             param_env={:?}, \
 360             trait_id={:?}, \
 361             rcvr_substs={:?})",
 362         def_id, param_env, trait_id, rcvr_substs
 363     );
 364
 365     let trait_ref = ty::TraitRef::from_method(tcx, trait_id, rcvr_substs);
 366     let vtbl = tcx.codegen_fulfill_obligation((param_env, ty::Binder::bind(trait_ref)));
 367
 368     // Now that we know which impl is being used, we can dispatch to
 369     // the actual function:
 370     match vtbl {
 371         traits::VtableImpl(impl_data) => {
 372             let (def_id, substs) =
 373                 traits::find_associated_item(tcx, param_env, trait_item, rcvr_substs, &impl_data);
 374
 375             let resolved_item = tcx.associated_item(def_id);
 376
 377             // Since this is a trait item, we need to see if the item is either a trait default item
 378             // or a specialization because we can't resolve those unless we can `Reveal::All`.
 379             // NOTE: This should be kept in sync with the similar code in
 380             // `rustc::traits::project::assemble_candidates_from_impls()`.
 381             let eligible = if !resolved_item.defaultness.is_default() {
 382                 true
 383             } else if param_env.reveal == traits::Reveal::All {
 384                 !trait_ref.needs_subst()
 385             } else {
 386                 false
 387             };
 388
 389             if !eligible {
 390                 return None;
 391             }
 392
 393             let substs = tcx.erase_regions(&substs);
 394             Some(ty::Instance::new(def_id, substs))
 395         }
 396         traits::VtableGenerator(generator_data) => Some(Instance {
 397             def: ty::InstanceDef::Item(generator_data.generator_def_id),
 398             substs: generator_data.substs,
 399         }),
 400         traits::VtableClosure(closure_data) => {
 401             let trait_closure_kind = tcx.lang_items().fn_trait_kind(trait_id).unwrap();
 402             Some(Instance::resolve_closure(
 403                 tcx,
 404                 closure_data.closure_def_id,
 405                 closure_data.substs,
 406                 trait_closure_kind,
 407             ))
 408         }
 409         traits::VtableFnPointer(ref data) => Some(Instance {
 410             def: ty::InstanceDef::FnPtrShim(trait_item.def_id, data.fn_ty),
 411             substs: rcvr_substs,
 412         }),
 413         traits::VtableObject(ref data) => {
 414             let index = traits::get_vtable_index_of_object_method(tcx, data, def_id);
 415             Some(Instance { def: ty::InstanceDef::Virtual(def_id, index), substs: rcvr_substs })
 416         }
 417         traits::VtableBuiltin(..) => {
 418             if tcx.lang_items().clone_trait().is_some() {
 419                 Some(Instance {
 420                     def: ty::InstanceDef::CloneShim(def_id, trait_ref.self_ty()),
 421                     substs: rcvr_substs,
 422                 })
 423             } else {
 424                 None
 425             }
 426         }
 427         traits::VtableAutoImpl(..) | traits::VtableParam(..) | traits::VtableTraitAlias(..) => None,
 428     }
 429 }
 430
 431 fn needs_fn_once_adapter_shim(
 432     actual_closure_kind: ty::ClosureKind,
 433     trait_closure_kind: ty::ClosureKind,
 434 ) -> Result<bool, ()> {
 435     match (actual_closure_kind, trait_closure_kind) {
 436         (ty::ClosureKind::Fn, ty::ClosureKind::Fn)
 437         | (ty::ClosureKind::FnMut, ty::ClosureKind::FnMut)
 438         | (ty::ClosureKind::FnOnce, ty::ClosureKind::FnOnce) => {
 439             // No adapter needed.
 440             Ok(false)
 441         }
 442         (ty::ClosureKind::Fn, ty::ClosureKind::FnMut) => {
 443             // The closure fn `llfn` is a `fn(&self, ...)`.  We want a
 444             // `fn(&mut self, ...)`. In fact, at codegen time, these are
 445             // basically the same thing, so we can just return llfn.
 446             Ok(false)
 447         }
 448         (ty::ClosureKind::Fn, ty::ClosureKind::FnOnce)
 449         | (ty::ClosureKind::FnMut, ty::ClosureKind::FnOnce) => {
 450             // The closure fn `llfn` is a `fn(&self, ...)` or `fn(&mut
 451             // self, ...)`.  We want a `fn(self, ...)`. We can produce
 452             // this by doing something like:
 453             //
 454             //     fn call_once(self, ...) { call_mut(&self, ...) }
 455             //     fn call_once(mut self, ...) { call_mut(&mut self, ...) }
 456             //
 457             // These are both the same at codegen time.
 458             Ok(true)
 459         }
 460         (ty::ClosureKind::FnMut, _) | (ty::ClosureKind::FnOnce, _) => Err(()),
 461     }
 462 }