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`, "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 { call_once: DefId },
  54
  55     /// `drop_in_place::<T>; None` for empty drop glue.
  56     DropGlue(DefId, Option<Ty<'tcx>>),
  57
  58     ///`<T as Clone>::clone` shim.
  59     CloneShim(DefId, Ty<'tcx>),
  60 }
  61
  62 impl<'tcx> Instance<'tcx> {
  63     pub fn ty(&self, tcx: TyCtxt<'tcx>) -> Ty<'tcx> {
  64         let ty = tcx.type_of(self.def.def_id());
  65         tcx.subst_and_normalize_erasing_regions(
  66             self.substs,
  67             ty::ParamEnv::reveal_all(),
  68             &ty,
  69         )
  70     }
  71 }
  72
  73 impl<'tcx> InstanceDef<'tcx> {
  74     #[inline]
  75     pub fn def_id(&self) -> DefId {
  76         match *self {
  77             InstanceDef::Item(def_id) |
  78             InstanceDef::VtableShim(def_id) |
  79             InstanceDef::ReifyShim(def_id) |
  80             InstanceDef::FnPtrShim(def_id, _) |
  81             InstanceDef::Virtual(def_id, _) |
  82             InstanceDef::Intrinsic(def_id, ) |
  83             InstanceDef::ClosureOnceShim { call_once: def_id } |
  84             InstanceDef::DropGlue(def_id, _) |
  85             InstanceDef::CloneShim(def_id, _) => def_id
  86         }
  87     }
  88
  89     #[inline]
  90     pub fn attrs(&self, tcx: TyCtxt<'tcx>) -> ty::Attributes<'tcx> {
  91         tcx.get_attrs(self.def_id())
  92     }
  93
  94     pub fn is_inline(&self, tcx: TyCtxt<'tcx>) -> bool {
  95         use crate::hir::map::DefPathData;
  96         let def_id = match *self {
  97             ty::InstanceDef::Item(def_id) => def_id,
  98             ty::InstanceDef::DropGlue(_, Some(_)) => return false,
  99             _ => return true
 100         };
 101         match tcx.def_key(def_id).disambiguated_data.data {
 102             DefPathData::Ctor | DefPathData::ClosureExpr => true,
 103             _ => false
 104         }
 105     }
 106
 107     pub fn requires_local(&self, tcx: TyCtxt<'tcx>) -> bool {
 108         if self.is_inline(tcx) {
 109             return true
 110         }
 111         if let ty::InstanceDef::DropGlue(..) = *self {
 112             // Drop glue wants to be instantiated at every codegen
 113             // unit, but without an #[inline] hint. We should make this
 114             // available to normal end-users.
 115             return true
 116         }
 117         tcx.codegen_fn_attrs(self.def_id()).requests_inline()
 118     }
 119
 120     pub fn requires_caller_location(&self, tcx: TyCtxt<'_>) -> bool {
 121         tcx.codegen_fn_attrs(self.def_id()).flags.contains(CodegenFnAttrFlags::TRACK_CALLER)
 122     }
 123 }
 124
 125 impl<'tcx> fmt::Display for Instance<'tcx> {
 126     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
 127         ty::tls::with(|tcx| {
 128             let substs = tcx.lift(&self.substs).expect("could not lift for printing");
 129             FmtPrinter::new(tcx, &mut *f, Namespace::ValueNS)
 130                 .print_def_path(self.def_id(), substs)?;
 131             Ok(())
 132         })?;
 133
 134         match self.def {
 135             InstanceDef::Item(_) => Ok(()),
 136             InstanceDef::VtableShim(_) => {
 137                 write!(f, " - shim(vtable)")
 138             }
 139             InstanceDef::ReifyShim(_) => {
 140                 write!(f, " - shim(reify)")
 141             }
 142             InstanceDef::Intrinsic(_) => {
 143                 write!(f, " - intrinsic")
 144             }
 145             InstanceDef::Virtual(_, num) => {
 146                 write!(f, " - virtual#{}", num)
 147             }
 148             InstanceDef::FnPtrShim(_, ty) => {
 149                 write!(f, " - shim({:?})", ty)
 150             }
 151             InstanceDef::ClosureOnceShim { .. } => {
 152                 write!(f, " - shim")
 153             }
 154             InstanceDef::DropGlue(_, ty) => {
 155                 write!(f, " - shim({:?})", ty)
 156             }
 157             InstanceDef::CloneShim(_, ty) => {
 158                 write!(f, " - shim({:?})", ty)
 159             }
 160         }
 161     }
 162 }
 163
 164 impl<'tcx> Instance<'tcx> {
 165     pub fn new(def_id: DefId, substs: SubstsRef<'tcx>)
 166                -> Instance<'tcx> {
 167         assert!(!substs.has_escaping_bound_vars(),
 168                 "substs of instance {:?} not normalized for codegen: {:?}",
 169                 def_id, substs);
 170         Instance { def: InstanceDef::Item(def_id), substs: substs }
 171     }
 172
 173     pub fn mono(tcx: TyCtxt<'tcx>, def_id: DefId) -> Instance<'tcx> {
 174         Instance::new(def_id, tcx.empty_substs_for_def_id(def_id))
 175     }
 176
 177     #[inline]
 178     pub fn def_id(&self) -> DefId {
 179         self.def.def_id()
 180     }
 181
 182     /// Resolves a `(def_id, substs)` pair to an (optional) instance -- most commonly,
 183     /// this is used to find the precise code that will run for a trait method invocation,
 184     /// if known.
 185     ///
 186     /// Returns `None` if we cannot resolve `Instance` to a specific instance.
 187     /// For example, in a context like this,
 188     ///
 189     /// ```
 190     /// fn foo<T: Debug>(t: T) { ... }
 191     /// ```
 192     ///
 193     /// trying to resolve `Debug::fmt` applied to `T` will yield `None`, because we do not
 194     /// know what code ought to run. (Note that this setting is also affected by the
 195     /// `RevealMode` in the parameter environment.)
 196     ///
 197     /// Presuming that coherence and type-check have succeeded, if this method is invoked
 198     /// in a monomorphic context (i.e., like during codegen), then it is guaranteed to return
 199     /// `Some`.
 200     pub fn resolve(
 201         tcx: TyCtxt<'tcx>,
 202         param_env: ty::ParamEnv<'tcx>,
 203         def_id: DefId,
 204         substs: SubstsRef<'tcx>,
 205     ) -> Option<Instance<'tcx>> {
 206         debug!("resolve(def_id={:?}, substs={:?})", def_id, substs);
 207         let result = if let Some(trait_def_id) = tcx.trait_of_item(def_id) {
 208             debug!(" => associated item, attempting to find impl in param_env {:#?}", param_env);
 209             let item = tcx.associated_item(def_id);
 210             resolve_associated_item(tcx, &item, param_env, trait_def_id, substs)
 211         } else {
 212             let ty = tcx.type_of(def_id);
 213             let item_type = tcx.subst_and_normalize_erasing_regions(
 214                 substs,
 215                 param_env,
 216                 &ty,
 217             );
 218
 219             let def = match item_type.kind {
 220                 ty::FnDef(..) if {
 221                     let f = item_type.fn_sig(tcx);
 222                     f.abi() == Abi::RustIntrinsic ||
 223                         f.abi() == Abi::PlatformIntrinsic
 224                 } =>
 225                 {
 226                     debug!(" => intrinsic");
 227                     ty::InstanceDef::Intrinsic(def_id)
 228                 }
 229                 _ => {
 230                     if Some(def_id) == tcx.lang_items().drop_in_place_fn() {
 231                         let ty = substs.type_at(0);
 232                         if ty.needs_drop(tcx, ty::ParamEnv::reveal_all()) {
 233                             debug!(" => nontrivial drop glue");
 234                             ty::InstanceDef::DropGlue(def_id, Some(ty))
 235                         } else {
 236                             debug!(" => trivial drop glue");
 237                             ty::InstanceDef::DropGlue(def_id, None)
 238                         }
 239                     } else {
 240                         debug!(" => free item");
 241                         ty::InstanceDef::Item(def_id)
 242                     }
 243                 }
 244             };
 245             Some(Instance {
 246                 def: def,
 247                 substs: substs
 248             })
 249         };
 250         debug!("resolve(def_id={:?}, substs={:?}) = {:?}", def_id, substs, result);
 251         result
 252     }
 253
 254     pub fn resolve_for_fn_ptr(
 255         tcx: TyCtxt<'tcx>,
 256         param_env: ty::ParamEnv<'tcx>,
 257         def_id: DefId,
 258         substs: SubstsRef<'tcx>,
 259     ) -> Option<Instance<'tcx>> {
 260         debug!("resolve(def_id={:?}, substs={:?})", def_id, substs);
 261         Instance::resolve(tcx, param_env, def_id, substs).map(|mut resolved| {
 262             match resolved.def {
 263                 InstanceDef::Item(def_id) if resolved.def.requires_caller_location(tcx) => {
 264                     debug!(" => fn pointer created for function with #[track_caller]");
 265                     resolved.def = InstanceDef::ReifyShim(def_id);
 266                 }
 267                 InstanceDef::Virtual(def_id, _) => {
 268                     debug!(" => fn pointer created for virtual call");
 269                     resolved.def = InstanceDef::ReifyShim(def_id);
 270                 }
 271                 _ => {}
 272             }
 273
 274             resolved
 275         })
 276     }
 277
 278     pub fn resolve_for_vtable(
 279         tcx: TyCtxt<'tcx>,
 280         param_env: ty::ParamEnv<'tcx>,
 281         def_id: DefId,
 282         substs: SubstsRef<'tcx>,
 283     ) -> Option<Instance<'tcx>> {
 284         debug!("resolve(def_id={:?}, substs={:?})", def_id, substs);
 285         let fn_sig = tcx.fn_sig(def_id);
 286         let is_vtable_shim = fn_sig.inputs().skip_binder().len() > 0
 287             && fn_sig.input(0).skip_binder().is_param(0)
 288             && tcx.generics_of(def_id).has_self;
 289         if is_vtable_shim {
 290             debug!(" => associated item with unsizeable self: Self");
 291             Some(Instance {
 292                 def: InstanceDef::VtableShim(def_id),
 293                 substs,
 294             })
 295         } else {
 296             Instance::resolve(tcx, param_env, def_id, substs)
 297         }
 298     }
 299
 300     pub fn resolve_closure(
 301         tcx: TyCtxt<'tcx>,
 302         def_id: DefId,
 303         substs: ty::SubstsRef<'tcx>,
 304         requested_kind: ty::ClosureKind,
 305     ) -> Instance<'tcx> {
 306         let actual_kind = substs.as_closure().kind(def_id, tcx);
 307
 308         match needs_fn_once_adapter_shim(actual_kind, requested_kind) {
 309             Ok(true) => Instance::fn_once_adapter_instance(tcx, def_id, substs),
 310             _ => Instance::new(def_id, substs)
 311         }
 312     }
 313
 314     pub fn resolve_drop_in_place(tcx: TyCtxt<'tcx>, ty: Ty<'tcx>) -> ty::Instance<'tcx> {
 315         let def_id = tcx.require_lang_item(DropInPlaceFnLangItem, None);
 316         let substs = tcx.intern_substs(&[ty.into()]);
 317         Instance::resolve(tcx, ty::ParamEnv::reveal_all(), def_id, substs).unwrap()
 318     }
 319
 320     pub fn fn_once_adapter_instance(
 321         tcx: TyCtxt<'tcx>,
 322         closure_did: DefId,
 323         substs: ty::SubstsRef<'tcx>,
 324     ) -> Instance<'tcx> {
 325         debug!("fn_once_adapter_shim({:?}, {:?})",
 326                closure_did,
 327                substs);
 328         let fn_once = tcx.lang_items().fn_once_trait().unwrap();
 329         let call_once = tcx.associated_items(fn_once)
 330             .find(|it| it.kind == ty::AssocKind::Method)
 331             .unwrap().def_id;
 332         let def = ty::InstanceDef::ClosureOnceShim { call_once };
 333
 334         let self_ty = tcx.mk_closure(closure_did, substs);
 335
 336         let sig = substs.as_closure().sig(closure_did, tcx);
 337         let sig = tcx.normalize_erasing_late_bound_regions(ty::ParamEnv::reveal_all(), &sig);
 338         assert_eq!(sig.inputs().len(), 1);
 339         let substs = tcx.mk_substs_trait(self_ty, &[sig.inputs()[0].into()]);
 340
 341         debug!("fn_once_adapter_shim: self_ty={:?} sig={:?}", self_ty, sig);
 342         Instance { def, substs }
 343     }
 344
 345     pub fn is_vtable_shim(&self) -> bool {
 346         if let InstanceDef::VtableShim(..) = self.def {
 347             true
 348         } else {
 349             false
 350         }
 351     }
 352 }
 353
 354 fn resolve_associated_item<'tcx>(
 355     tcx: TyCtxt<'tcx>,
 356     trait_item: &ty::AssocItem,
 357     param_env: ty::ParamEnv<'tcx>,
 358     trait_id: DefId,
 359     rcvr_substs: SubstsRef<'tcx>,
 360 ) -> Option<Instance<'tcx>> {
 361     let def_id = trait_item.def_id;
 362     debug!("resolve_associated_item(trait_item={:?}, \
 363             param_env={:?}, \
 364             trait_id={:?}, \
 365             rcvr_substs={:?})",
 366             def_id, param_env, trait_id, rcvr_substs);
 367
 368     let trait_ref = ty::TraitRef::from_method(tcx, trait_id, rcvr_substs);
 369     let vtbl = tcx.codegen_fulfill_obligation((param_env, ty::Binder::bind(trait_ref)));
 370
 371     // Now that we know which impl is being used, we can dispatch to
 372     // the actual function:
 373     match vtbl {
 374         traits::VtableImpl(impl_data) => {
 375             let (def_id, substs) = traits::find_associated_item(
 376                 tcx, param_env, trait_item, rcvr_substs, &impl_data);
 377             let substs = tcx.erase_regions(&substs);
 378             Some(ty::Instance::new(def_id, substs))
 379         }
 380         traits::VtableGenerator(generator_data) => {
 381             Some(Instance {
 382                 def: ty::InstanceDef::Item(generator_data.generator_def_id),
 383                 substs: generator_data.substs
 384             })
 385         }
 386         traits::VtableClosure(closure_data) => {
 387             let trait_closure_kind = tcx.lang_items().fn_trait_kind(trait_id).unwrap();
 388             Some(Instance::resolve_closure(tcx, closure_data.closure_def_id, closure_data.substs,
 389                                            trait_closure_kind))
 390         }
 391         traits::VtableFnPointer(ref data) => {
 392             Some(Instance {
 393                 def: ty::InstanceDef::FnPtrShim(trait_item.def_id, data.fn_ty),
 394                 substs: rcvr_substs
 395             })
 396         }
 397         traits::VtableObject(ref data) => {
 398             let index = tcx.get_vtable_index_of_object_method(data, def_id);
 399             Some(Instance {
 400                 def: ty::InstanceDef::Virtual(def_id, index),
 401                 substs: rcvr_substs
 402             })
 403         }
 404         traits::VtableBuiltin(..) => {
 405             if tcx.lang_items().clone_trait().is_some() {
 406                 Some(Instance {
 407                     def: ty::InstanceDef::CloneShim(def_id, trait_ref.self_ty()),
 408                     substs: rcvr_substs
 409                 })
 410             } else {
 411                 None
 412             }
 413         }
 414         traits::VtableAutoImpl(..) |
 415         traits::VtableParam(..) |
 416         traits::VtableTraitAlias(..) => None
 417     }
 418 }
 419
 420 fn needs_fn_once_adapter_shim(
 421     actual_closure_kind: ty::ClosureKind,
 422     trait_closure_kind: ty::ClosureKind,
 423 ) -> Result<bool, ()> {
 424     match (actual_closure_kind, trait_closure_kind) {
 425         (ty::ClosureKind::Fn, ty::ClosureKind::Fn) |
 426             (ty::ClosureKind::FnMut, ty::ClosureKind::FnMut) |
 427             (ty::ClosureKind::FnOnce, ty::ClosureKind::FnOnce) => {
 428                 // No adapter needed.
 429                 Ok(false)
 430             }
 431         (ty::ClosureKind::Fn, ty::ClosureKind::FnMut) => {
 432             // The closure fn `llfn` is a `fn(&self, ...)`.  We want a
 433             // `fn(&mut self, ...)`. In fact, at codegen time, these are
 434             // basically the same thing, so we can just return llfn.
 435             Ok(false)
 436         }
 437         (ty::ClosureKind::Fn, ty::ClosureKind::FnOnce) |
 438             (ty::ClosureKind::FnMut, ty::ClosureKind::FnOnce) => {
 439                 // The closure fn `llfn` is a `fn(&self, ...)` or `fn(&mut
 440                 // self, ...)`.  We want a `fn(self, ...)`. We can produce
 441                 // this by doing something like:
 442                 //
 443                 //     fn call_once(self, ...) { call_mut(&self, ...) }
 444                 //     fn call_once(mut self, ...) { call_mut(&mut self, ...) }
 445                 //
 446                 // These are both the same at codegen time.
 447                 Ok(true)
 448         }
 449         (ty::ClosureKind::FnMut, _) |
 450         (ty::ClosureKind::FnOnce, _) => Err(())
 451     }
 452 }