src/librustc/ty/instance.rs

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