src/librustc/ty/instance.rs

   1 use crate::hir::def::Namespace;
   2 use crate::hir::def_id::DefId;
   3 use crate::hir::CodegenFnAttrFlags;
   4 use crate::middle::lang_items::DropInPlaceFnLangItem;
   5 use crate::traits;
   6 use crate::ty::print::{FmtPrinter, Printer};
   7 use crate::ty::{self, SubstsRef, Ty, TyCtxt, TypeFoldable};
   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     pub fn ty(&self, tcx: TyCtxt<'tcx>) -> Ty<'tcx> {
  66         let ty = tcx.type_of(self.def.def_id());
  67         tcx.subst_and_normalize_erasing_regions(self.substs, ty::ParamEnv::reveal_all(), &ty)
  68     }
  69 }
  70
  71 impl<'tcx> InstanceDef<'tcx> {
  72     #[inline]
  73     pub fn def_id(&self) -> DefId {
  74         match *self {
  75             InstanceDef::Item(def_id)
  76             | InstanceDef::VtableShim(def_id)
  77             | InstanceDef::ReifyShim(def_id)
  78             | InstanceDef::FnPtrShim(def_id, _)
  79             | InstanceDef::Virtual(def_id, _)
  80             | InstanceDef::Intrinsic(def_id)
  81             | InstanceDef::ClosureOnceShim { call_once: def_id }
  82             | InstanceDef::DropGlue(def_id, _)
  83             | InstanceDef::CloneShim(def_id, _) => def_id,
  84         }
  85     }
  86
  87     #[inline]
  88     pub fn attrs(&self, tcx: TyCtxt<'tcx>) -> ty::Attributes<'tcx> {
  89         tcx.get_attrs(self.def_id())
  90     }
  91
  92     pub fn is_inline(&self, tcx: TyCtxt<'tcx>) -> bool {
  93         use crate::hir::map::DefPathData;
  94         let def_id = match *self {
  95             ty::InstanceDef::Item(def_id) => def_id,
  96             ty::InstanceDef::DropGlue(_, Some(_)) => return false,
  97             _ => return true,
  98         };
  99         match tcx.def_key(def_id).disambiguated_data.data {
 100             DefPathData::Ctor | DefPathData::ClosureExpr => true,
 101             _ => false,
 102         }
 103     }
 104
 105     pub fn requires_local(&self, tcx: TyCtxt<'tcx>) -> bool {
 106         if self.is_inline(tcx) {
 107             return true;
 108         }
 109         if let ty::InstanceDef::DropGlue(..) = *self {
 110             // Drop glue wants to be instantiated at every codegen
 111             // unit, but without an #[inline] hint. We should make this
 112             // available to normal end-users.
 113             return true;
 114         }
 115         tcx.codegen_fn_attrs(self.def_id()).requests_inline()
 116     }
 117
 118     pub fn requires_caller_location(&self, tcx: TyCtxt<'_>) -> bool {
 119         tcx.codegen_fn_attrs(self.def_id()).flags.contains(CodegenFnAttrFlags::TRACK_CALLER)
 120     }
 121 }
 122
 123 impl<'tcx> fmt::Display for Instance<'tcx> {
 124     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
 125         ty::tls::with(|tcx| {
 126             let substs = tcx.lift(&self.substs).expect("could not lift for printing");
 127             FmtPrinter::new(tcx, &mut *f, Namespace::ValueNS)
 128                 .print_def_path(self.def_id(), substs)?;
 129             Ok(())
 130         })?;
 131
 132         match self.def {
 133             InstanceDef::Item(_) => Ok(()),
 134             InstanceDef::VtableShim(_) => write!(f, " - shim(vtable)"),
 135             InstanceDef::ReifyShim(_) => write!(f, " - shim(reify)"),
 136             InstanceDef::Intrinsic(_) => write!(f, " - intrinsic"),
 137             InstanceDef::Virtual(_, num) => write!(f, " - virtual#{}", num),
 138             InstanceDef::FnPtrShim(_, ty) => write!(f, " - shim({:?})", ty),
 139             InstanceDef::ClosureOnceShim { .. } => write!(f, " - shim"),
 140             InstanceDef::DropGlue(_, ty) => write!(f, " - shim({:?})", ty),
 141             InstanceDef::CloneShim(_, ty) => write!(f, " - shim({:?})", ty),
 142         }
 143     }
 144 }
 145
 146 impl<'tcx> Instance<'tcx> {
 147     pub fn new(def_id: DefId, substs: SubstsRef<'tcx>) -> Instance<'tcx> {
 148         assert!(
 149             !substs.has_escaping_bound_vars(),
 150             "substs of instance {:?} not normalized for codegen: {:?}",
 151             def_id,
 152             substs
 153         );
 154         Instance { def: InstanceDef::Item(def_id), substs: substs }
 155     }
 156
 157     pub fn mono(tcx: TyCtxt<'tcx>, def_id: DefId) -> Instance<'tcx> {
 158         Instance::new(def_id, tcx.empty_substs_for_def_id(def_id))
 159     }
 160
 161     #[inline]
 162     pub fn def_id(&self) -> DefId {
 163         self.def.def_id()
 164     }
 165
 166     /// Resolves a `(def_id, substs)` pair to an (optional) instance -- most commonly,
 167     /// this is used to find the precise code that will run for a trait method invocation,
 168     /// if known.
 169     ///
 170     /// Returns `None` if we cannot resolve `Instance` to a specific instance.
 171     /// For example, in a context like this,
 172     ///
 173     /// ```
 174     /// fn foo<T: Debug>(t: T) { ... }
 175     /// ```
 176     ///
 177     /// trying to resolve `Debug::fmt` applied to `T` will yield `None`, because we do not
 178     /// know what code ought to run. (Note that this setting is also affected by the
 179     /// `RevealMode` in the parameter environment.)
 180     ///
 181     /// Presuming that coherence and type-check have succeeded, if this method is invoked
 182     /// in a monomorphic context (i.e., like during codegen), then it is guaranteed to return
 183     /// `Some`.
 184     pub fn resolve(
 185         tcx: TyCtxt<'tcx>,
 186         param_env: ty::ParamEnv<'tcx>,
 187         def_id: DefId,
 188         substs: SubstsRef<'tcx>,
 189     ) -> Option<Instance<'tcx>> {
 190         debug!("resolve(def_id={:?}, substs={:?})", def_id, substs);
 191         let result = if let Some(trait_def_id) = tcx.trait_of_item(def_id) {
 192             debug!(" => associated item, attempting to find impl in param_env {:#?}", param_env);
 193             let item = tcx.associated_item(def_id);
 194             resolve_associated_item(tcx, &item, param_env, trait_def_id, substs)
 195         } else {
 196             let ty = tcx.type_of(def_id);
 197             let item_type = tcx.subst_and_normalize_erasing_regions(substs, param_env, &ty);
 198
 199             let def = match item_type.kind {
 200                 ty::FnDef(..)
 201                     if {
 202                         let f = item_type.fn_sig(tcx);
 203                         f.abi() == Abi::RustIntrinsic || f.abi() == Abi::PlatformIntrinsic
 204                     } =>
 205                 {
 206                     debug!(" => intrinsic");
 207                     ty::InstanceDef::Intrinsic(def_id)
 208                 }
 209                 _ => {
 210                     if Some(def_id) == tcx.lang_items().drop_in_place_fn() {
 211                         let ty = substs.type_at(0);
 212                         if ty.needs_drop(tcx, ty::ParamEnv::reveal_all()) {
 213                             debug!(" => nontrivial drop glue");
 214                             ty::InstanceDef::DropGlue(def_id, Some(ty))
 215                         } else {
 216                             debug!(" => trivial drop glue");
 217                             ty::InstanceDef::DropGlue(def_id, None)
 218                         }
 219                     } else {
 220                         debug!(" => free item");
 221                         ty::InstanceDef::Item(def_id)
 222                     }
 223                 }
 224             };
 225             Some(Instance { def: def, substs: substs })
 226         };
 227         debug!("resolve(def_id={:?}, substs={:?}) = {:?}", def_id, substs, result);
 228         result
 229     }
 230
 231     pub fn resolve_for_fn_ptr(
 232         tcx: TyCtxt<'tcx>,
 233         param_env: ty::ParamEnv<'tcx>,
 234         def_id: DefId,
 235         substs: SubstsRef<'tcx>,
 236     ) -> Option<Instance<'tcx>> {
 237         debug!("resolve(def_id={:?}, substs={:?})", def_id, substs);
 238         Instance::resolve(tcx, param_env, def_id, substs).map(|mut resolved| {
 239             match resolved.def {
 240                 InstanceDef::Item(def_id) if resolved.def.requires_caller_location(tcx) => {
 241                     debug!(" => fn pointer created for function with #[track_caller]");
 242                     resolved.def = InstanceDef::ReifyShim(def_id);
 243                 }
 244                 InstanceDef::Virtual(def_id, _) => {
 245                     debug!(" => fn pointer created for virtual call");
 246                     resolved.def = InstanceDef::ReifyShim(def_id);
 247                 }
 248                 _ => {}
 249             }
 250
 251             resolved
 252         })
 253     }
 254
 255     pub fn resolve_for_vtable(
 256         tcx: TyCtxt<'tcx>,
 257         param_env: ty::ParamEnv<'tcx>,
 258         def_id: DefId,
 259         substs: SubstsRef<'tcx>,
 260     ) -> Option<Instance<'tcx>> {
 261         debug!("resolve(def_id={:?}, substs={:?})", def_id, substs);
 262         let fn_sig = tcx.fn_sig(def_id);
 263         let is_vtable_shim = fn_sig.inputs().skip_binder().len() > 0
 264             && fn_sig.input(0).skip_binder().is_param(0)
 265             && tcx.generics_of(def_id).has_self;
 266         if is_vtable_shim {
 267             debug!(" => associated item with unsizeable self: Self");
 268             Some(Instance { def: InstanceDef::VtableShim(def_id), substs })
 269         } else {
 270             Instance::resolve(tcx, param_env, def_id, substs)
 271         }
 272     }
 273
 274     pub fn resolve_closure(
 275         tcx: TyCtxt<'tcx>,
 276         def_id: DefId,
 277         substs: ty::SubstsRef<'tcx>,
 278         requested_kind: ty::ClosureKind,
 279     ) -> Instance<'tcx> {
 280         let actual_kind = substs.as_closure().kind(def_id, tcx);
 281
 282         match needs_fn_once_adapter_shim(actual_kind, requested_kind) {
 283             Ok(true) => Instance::fn_once_adapter_instance(tcx, def_id, substs),
 284             _ => Instance::new(def_id, substs),
 285         }
 286     }
 287
 288     pub fn resolve_drop_in_place(tcx: TyCtxt<'tcx>, ty: Ty<'tcx>) -> ty::Instance<'tcx> {
 289         let def_id = tcx.require_lang_item(DropInPlaceFnLangItem, None);
 290         let substs = tcx.intern_substs(&[ty.into()]);
 291         Instance::resolve(tcx, ty::ParamEnv::reveal_all(), def_id, substs).unwrap()
 292     }
 293
 294     pub fn fn_once_adapter_instance(
 295         tcx: TyCtxt<'tcx>,
 296         closure_did: DefId,
 297         substs: ty::SubstsRef<'tcx>,
 298     ) -> Instance<'tcx> {
 299         debug!("fn_once_adapter_shim({:?}, {:?})", closure_did, substs);
 300         let fn_once = tcx.lang_items().fn_once_trait().unwrap();
 301         let call_once = tcx
 302             .associated_items(fn_once)
 303             .find(|it| it.kind == ty::AssocKind::Method)
 304             .unwrap()
 305             .def_id;
 306         let def = ty::InstanceDef::ClosureOnceShim { call_once };
 307
 308         let self_ty = tcx.mk_closure(closure_did, substs);
 309
 310         let sig = substs.as_closure().sig(closure_did, tcx);
 311         let sig = tcx.normalize_erasing_late_bound_regions(ty::ParamEnv::reveal_all(), &sig);
 312         assert_eq!(sig.inputs().len(), 1);
 313         let substs = tcx.mk_substs_trait(self_ty, &[sig.inputs()[0].into()]);
 314
 315         debug!("fn_once_adapter_shim: self_ty={:?} sig={:?}", self_ty, sig);
 316         Instance { def, substs }
 317     }
 318
 319     pub fn is_vtable_shim(&self) -> bool {
 320         if let InstanceDef::VtableShim(..) = self.def { true } else { false }
 321     }
 322 }
 323
 324 fn resolve_associated_item<'tcx>(
 325     tcx: TyCtxt<'tcx>,
 326     trait_item: &ty::AssocItem,
 327     param_env: ty::ParamEnv<'tcx>,
 328     trait_id: DefId,
 329     rcvr_substs: SubstsRef<'tcx>,
 330 ) -> Option<Instance<'tcx>> {
 331     let def_id = trait_item.def_id;
 332     debug!(
 333         "resolve_associated_item(trait_item={:?}, \
 334             param_env={:?}, \
 335             trait_id={:?}, \
 336             rcvr_substs={:?})",
 337         def_id, param_env, trait_id, rcvr_substs
 338     );
 339
 340     let trait_ref = ty::TraitRef::from_method(tcx, trait_id, rcvr_substs);
 341     let vtbl = tcx.codegen_fulfill_obligation((param_env, ty::Binder::bind(trait_ref)));
 342
 343     // Now that we know which impl is being used, we can dispatch to
 344     // the actual function:
 345     match vtbl {
 346         traits::VtableImpl(impl_data) => {
 347             let (def_id, substs) =
 348                 traits::find_associated_item(tcx, param_env, trait_item, rcvr_substs, &impl_data);
 349             let substs = tcx.erase_regions(&substs);
 350             Some(ty::Instance::new(def_id, substs))
 351         }
 352         traits::VtableGenerator(generator_data) => Some(Instance {
 353             def: ty::InstanceDef::Item(generator_data.generator_def_id),
 354             substs: generator_data.substs,
 355         }),
 356         traits::VtableClosure(closure_data) => {
 357             let trait_closure_kind = tcx.lang_items().fn_trait_kind(trait_id).unwrap();
 358             Some(Instance::resolve_closure(
 359                 tcx,
 360                 closure_data.closure_def_id,
 361                 closure_data.substs,
 362                 trait_closure_kind,
 363             ))
 364         }
 365         traits::VtableFnPointer(ref data) => Some(Instance {
 366             def: ty::InstanceDef::FnPtrShim(trait_item.def_id, data.fn_ty),
 367             substs: rcvr_substs,
 368         }),
 369         traits::VtableObject(ref data) => {
 370             let index = tcx.get_vtable_index_of_object_method(data, def_id);
 371             Some(Instance { def: ty::InstanceDef::Virtual(def_id, index), substs: rcvr_substs })
 372         }
 373         traits::VtableBuiltin(..) => {
 374             if tcx.lang_items().clone_trait().is_some() {
 375                 Some(Instance {
 376                     def: ty::InstanceDef::CloneShim(def_id, trait_ref.self_ty()),
 377                     substs: rcvr_substs,
 378                 })
 379             } else {
 380                 None
 381             }
 382         }
 383         traits::VtableAutoImpl(..) | traits::VtableParam(..) | traits::VtableTraitAlias(..) => None,
 384     }
 385 }
 386
 387 fn needs_fn_once_adapter_shim(
 388     actual_closure_kind: ty::ClosureKind,
 389     trait_closure_kind: ty::ClosureKind,
 390 ) -> Result<bool, ()> {
 391     match (actual_closure_kind, trait_closure_kind) {
 392         (ty::ClosureKind::Fn, ty::ClosureKind::Fn)
 393         | (ty::ClosureKind::FnMut, ty::ClosureKind::FnMut)
 394         | (ty::ClosureKind::FnOnce, ty::ClosureKind::FnOnce) => {
 395             // No adapter needed.
 396             Ok(false)
 397         }
 398         (ty::ClosureKind::Fn, ty::ClosureKind::FnMut) => {
 399             // The closure fn `llfn` is a `fn(&self, ...)`.  We want a
 400             // `fn(&mut self, ...)`. In fact, at codegen time, these are
 401             // basically the same thing, so we can just return llfn.
 402             Ok(false)
 403         }
 404         (ty::ClosureKind::Fn, ty::ClosureKind::FnOnce)
 405         | (ty::ClosureKind::FnMut, ty::ClosureKind::FnOnce) => {
 406             // The closure fn `llfn` is a `fn(&self, ...)` or `fn(&mut
 407             // self, ...)`.  We want a `fn(self, ...)`. We can produce
 408             // this by doing something like:
 409             //
 410             //     fn call_once(self, ...) { call_mut(&self, ...) }
 411             //     fn call_once(mut self, ...) { call_mut(&mut self, ...) }
 412             //
 413             // These are both the same at codegen time.
 414             Ok(true)
 415         }
 416         (ty::ClosureKind::FnMut, _) | (ty::ClosureKind::FnOnce, _) => Err(()),
 417     }
 418 }