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Diffstat (limited to 'compiler/rustc_middle/src/ty/instance.rs')
| -rw-r--r-- | compiler/rustc_middle/src/ty/instance.rs | 746 |
1 files changed, 746 insertions, 0 deletions
diff --git a/compiler/rustc_middle/src/ty/instance.rs b/compiler/rustc_middle/src/ty/instance.rs new file mode 100644 index 000000000..53218225d --- /dev/null +++ b/compiler/rustc_middle/src/ty/instance.rs @@ -0,0 +1,746 @@ +use crate::middle::codegen_fn_attrs::CodegenFnAttrFlags; +use crate::ty::print::{FmtPrinter, Printer}; +use crate::ty::subst::{InternalSubsts, Subst}; +use crate::ty::{ + self, EarlyBinder, SubstsRef, Ty, TyCtxt, TypeFoldable, TypeSuperFoldable, TypeVisitable, +}; +use rustc_errors::ErrorGuaranteed; +use rustc_hir::def::Namespace; +use rustc_hir::def_id::{CrateNum, DefId}; +use rustc_hir::lang_items::LangItem; +use rustc_macros::HashStable; +use rustc_middle::ty::normalize_erasing_regions::NormalizationError; +use rustc_span::Symbol; + +use std::fmt; + +/// A monomorphized `InstanceDef`. +/// +/// Monomorphization happens on-the-fly and no monomorphized MIR is ever created. Instead, this type +/// simply couples a potentially generic `InstanceDef` with some substs, and codegen and const eval +/// will do all required substitution as they run. +#[derive(Copy, Clone, PartialEq, Eq, Hash, Debug, TyEncodable, TyDecodable)] +#[derive(HashStable, Lift)] +pub struct Instance<'tcx> { + pub def: InstanceDef<'tcx>, + pub substs: SubstsRef<'tcx>, +} + +#[derive(Copy, Clone, PartialEq, Eq, PartialOrd, Ord, Hash, Debug)] +#[derive(TyEncodable, TyDecodable, HashStable, TypeFoldable, TypeVisitable)] +pub enum InstanceDef<'tcx> { + /// A user-defined callable item. + /// + /// This includes: + /// - `fn` items + /// - closures + /// - generators + Item(ty::WithOptConstParam<DefId>), + + /// An intrinsic `fn` item (with `"rust-intrinsic"` or `"platform-intrinsic"` ABI). + /// + /// Alongside `Virtual`, this is the only `InstanceDef` that does not have its own callable MIR. + /// Instead, codegen and const eval "magically" evaluate calls to intrinsics purely in the + /// caller. + Intrinsic(DefId), + + /// `<T as Trait>::method` where `method` receives unsizeable `self: Self` (part of the + /// `unsized_locals` feature). + /// + /// The generated shim will take `Self` via `*mut Self` - conceptually this is `&owned Self` - + /// and dereference the argument to call the original function. + VTableShim(DefId), + + /// `fn()` pointer where the function itself cannot be turned into a pointer. + /// + /// One example is `<dyn Trait as Trait>::fn`, where the shim contains + /// a virtual call, which codegen supports only via a direct call to the + /// `<dyn Trait as Trait>::fn` instance (an `InstanceDef::Virtual`). + /// + /// Another example is functions annotated with `#[track_caller]`, which + /// must have their implicit caller location argument populated for a call. + /// Because this is a required part of the function's ABI but can't be tracked + /// as a property of the function pointer, we use a single "caller location" + /// (the definition of the function itself). + ReifyShim(DefId), + + /// `<fn() as FnTrait>::call_*` (generated `FnTrait` implementation for `fn()` pointers). + /// + /// `DefId` is `FnTrait::call_*`. + FnPtrShim(DefId, Ty<'tcx>), + + /// Dynamic dispatch to `<dyn Trait as Trait>::fn`. + /// + /// This `InstanceDef` does not have callable MIR. Calls to `Virtual` instances must be + /// codegen'd as virtual calls through the vtable. + /// + /// If this is reified to a `fn` pointer, a `ReifyShim` is used (see `ReifyShim` above for more + /// details on that). + Virtual(DefId, usize), + + /// `<[FnMut closure] as FnOnce>::call_once`. + /// + /// The `DefId` is the ID of the `call_once` method in `FnOnce`. + ClosureOnceShim { call_once: DefId, track_caller: bool }, + + /// `core::ptr::drop_in_place::<T>`. + /// + /// The `DefId` is for `core::ptr::drop_in_place`. + /// The `Option<Ty<'tcx>>` is either `Some(T)`, or `None` for empty drop + /// glue. + DropGlue(DefId, Option<Ty<'tcx>>), + + /// Compiler-generated `<T as Clone>::clone` implementation. + /// + /// For all types that automatically implement `Copy`, a trivial `Clone` impl is provided too. + /// Additionally, arrays, tuples, and closures get a `Clone` shim even if they aren't `Copy`. + /// + /// The `DefId` is for `Clone::clone`, the `Ty` is the type `T` with the builtin `Clone` impl. + CloneShim(DefId, Ty<'tcx>), +} + +impl<'tcx> Instance<'tcx> { + /// Returns the `Ty` corresponding to this `Instance`, with generic substitutions applied and + /// lifetimes erased, allowing a `ParamEnv` to be specified for use during normalization. + pub fn ty(&self, tcx: TyCtxt<'tcx>, param_env: ty::ParamEnv<'tcx>) -> Ty<'tcx> { + let ty = tcx.type_of(self.def.def_id()); + tcx.subst_and_normalize_erasing_regions(self.substs, param_env, ty) + } + + /// Finds a crate that contains a monomorphization of this instance that + /// can be linked to from the local crate. A return value of `None` means + /// no upstream crate provides such an exported monomorphization. + /// + /// This method already takes into account the global `-Zshare-generics` + /// setting, always returning `None` if `share-generics` is off. + pub fn upstream_monomorphization(&self, tcx: TyCtxt<'tcx>) -> Option<CrateNum> { + // If we are not in share generics mode, we don't link to upstream + // monomorphizations but always instantiate our own internal versions + // instead. + if !tcx.sess.opts.share_generics() { + return None; + } + + // If this is an item that is defined in the local crate, no upstream + // crate can know about it/provide a monomorphization. + if self.def_id().is_local() { + return None; + } + + // If this a non-generic instance, it cannot be a shared monomorphization. + self.substs.non_erasable_generics().next()?; + + match self.def { + InstanceDef::Item(def) => tcx + .upstream_monomorphizations_for(def.did) + .and_then(|monos| monos.get(&self.substs).cloned()), + InstanceDef::DropGlue(_, Some(_)) => tcx.upstream_drop_glue_for(self.substs), + _ => None, + } + } +} + +impl<'tcx> InstanceDef<'tcx> { + #[inline] + pub fn def_id(self) -> DefId { + match self { + InstanceDef::Item(def) => def.did, + InstanceDef::VTableShim(def_id) + | InstanceDef::ReifyShim(def_id) + | InstanceDef::FnPtrShim(def_id, _) + | InstanceDef::Virtual(def_id, _) + | InstanceDef::Intrinsic(def_id) + | InstanceDef::ClosureOnceShim { call_once: def_id, track_caller: _ } + | InstanceDef::DropGlue(def_id, _) + | InstanceDef::CloneShim(def_id, _) => def_id, + } + } + + /// Returns the `DefId` of instances which might not require codegen locally. + pub fn def_id_if_not_guaranteed_local_codegen(self) -> Option<DefId> { + match self { + ty::InstanceDef::Item(def) => Some(def.did), + ty::InstanceDef::DropGlue(def_id, Some(_)) => Some(def_id), + InstanceDef::VTableShim(..) + | InstanceDef::ReifyShim(..) + | InstanceDef::FnPtrShim(..) + | InstanceDef::Virtual(..) + | InstanceDef::Intrinsic(..) + | InstanceDef::ClosureOnceShim { .. } + | InstanceDef::DropGlue(..) + | InstanceDef::CloneShim(..) => None, + } + } + + #[inline] + pub fn with_opt_param(self) -> ty::WithOptConstParam<DefId> { + match self { + InstanceDef::Item(def) => def, + InstanceDef::VTableShim(def_id) + | InstanceDef::ReifyShim(def_id) + | InstanceDef::FnPtrShim(def_id, _) + | InstanceDef::Virtual(def_id, _) + | InstanceDef::Intrinsic(def_id) + | InstanceDef::ClosureOnceShim { call_once: def_id, track_caller: _ } + | InstanceDef::DropGlue(def_id, _) + | InstanceDef::CloneShim(def_id, _) => ty::WithOptConstParam::unknown(def_id), + } + } + + #[inline] + pub fn get_attrs(&self, tcx: TyCtxt<'tcx>, attr: Symbol) -> ty::Attributes<'tcx> { + tcx.get_attrs(self.def_id(), attr) + } + + /// Returns `true` if the LLVM version of this instance is unconditionally + /// marked with `inline`. This implies that a copy of this instance is + /// generated in every codegen unit. + /// Note that this is only a hint. See the documentation for + /// `generates_cgu_internal_copy` for more information. + pub fn requires_inline(&self, tcx: TyCtxt<'tcx>) -> bool { + use rustc_hir::definitions::DefPathData; + let def_id = match *self { + ty::InstanceDef::Item(def) => def.did, + ty::InstanceDef::DropGlue(_, Some(_)) => return false, + _ => return true, + }; + matches!( + tcx.def_key(def_id).disambiguated_data.data, + DefPathData::Ctor | DefPathData::ClosureExpr + ) + } + + /// Returns `true` if the machine code for this instance is instantiated in + /// each codegen unit that references it. + /// Note that this is only a hint! The compiler can globally decide to *not* + /// do this in order to speed up compilation. CGU-internal copies are + /// only exist to enable inlining. If inlining is not performed (e.g. at + /// `-Copt-level=0`) then the time for generating them is wasted and it's + /// better to create a single copy with external linkage. + pub fn generates_cgu_internal_copy(&self, tcx: TyCtxt<'tcx>) -> bool { + if self.requires_inline(tcx) { + return true; + } + if let ty::InstanceDef::DropGlue(.., Some(ty)) = *self { + // Drop glue generally wants to be instantiated at every codegen + // unit, but without an #[inline] hint. We should make this + // available to normal end-users. + if tcx.sess.opts.incremental.is_none() { + return true; + } + // When compiling with incremental, we can generate a *lot* of + // codegen units. Including drop glue into all of them has a + // considerable compile time cost. + // + // We include enums without destructors to allow, say, optimizing + // drops of `Option::None` before LTO. We also respect the intent of + // `#[inline]` on `Drop::drop` implementations. + return ty.ty_adt_def().map_or(true, |adt_def| { + adt_def.destructor(tcx).map_or_else( + || adt_def.is_enum(), + |dtor| tcx.codegen_fn_attrs(dtor.did).requests_inline(), + ) + }); + } + tcx.codegen_fn_attrs(self.def_id()).requests_inline() + } + + pub fn requires_caller_location(&self, tcx: TyCtxt<'_>) -> bool { + match *self { + InstanceDef::Item(ty::WithOptConstParam { did: def_id, .. }) + | InstanceDef::Virtual(def_id, _) => { + tcx.body_codegen_attrs(def_id).flags.contains(CodegenFnAttrFlags::TRACK_CALLER) + } + InstanceDef::ClosureOnceShim { call_once: _, track_caller } => track_caller, + _ => false, + } + } + + /// Returns `true` when the MIR body associated with this instance should be monomorphized + /// by its users (e.g. codegen or miri) by substituting the `substs` from `Instance` (see + /// `Instance::substs_for_mir_body`). + /// + /// Otherwise, returns `false` only for some kinds of shims where the construction of the MIR + /// body should perform necessary substitutions. + pub fn has_polymorphic_mir_body(&self) -> bool { + match *self { + InstanceDef::CloneShim(..) + | InstanceDef::FnPtrShim(..) + | InstanceDef::DropGlue(_, Some(_)) => false, + InstanceDef::ClosureOnceShim { .. } + | InstanceDef::DropGlue(..) + | InstanceDef::Item(_) + | InstanceDef::Intrinsic(..) + | InstanceDef::ReifyShim(..) + | InstanceDef::Virtual(..) + | InstanceDef::VTableShim(..) => true, + } + } +} + +impl<'tcx> fmt::Display for Instance<'tcx> { + fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { + ty::tls::with(|tcx| { + let substs = tcx.lift(self.substs).expect("could not lift for printing"); + let s = FmtPrinter::new(tcx, Namespace::ValueNS) + .print_def_path(self.def_id(), substs)? + .into_buffer(); + f.write_str(&s) + })?; + + match self.def { + InstanceDef::Item(_) => Ok(()), + InstanceDef::VTableShim(_) => write!(f, " - shim(vtable)"), + InstanceDef::ReifyShim(_) => write!(f, " - shim(reify)"), + InstanceDef::Intrinsic(_) => write!(f, " - intrinsic"), + InstanceDef::Virtual(_, num) => write!(f, " - virtual#{}", num), + InstanceDef::FnPtrShim(_, ty) => write!(f, " - shim({})", ty), + InstanceDef::ClosureOnceShim { .. } => write!(f, " - shim"), + InstanceDef::DropGlue(_, None) => write!(f, " - shim(None)"), + InstanceDef::DropGlue(_, Some(ty)) => write!(f, " - shim(Some({}))", ty), + InstanceDef::CloneShim(_, ty) => write!(f, " - shim({})", ty), + } + } +} + +impl<'tcx> Instance<'tcx> { + pub fn new(def_id: DefId, substs: SubstsRef<'tcx>) -> Instance<'tcx> { + assert!( + !substs.has_escaping_bound_vars(), + "substs of instance {:?} not normalized for codegen: {:?}", + def_id, + substs + ); + Instance { def: InstanceDef::Item(ty::WithOptConstParam::unknown(def_id)), substs } + } + + pub fn mono(tcx: TyCtxt<'tcx>, def_id: DefId) -> Instance<'tcx> { + let substs = InternalSubsts::for_item(tcx, def_id, |param, _| match param.kind { + ty::GenericParamDefKind::Lifetime => tcx.lifetimes.re_erased.into(), + ty::GenericParamDefKind::Type { .. } => { + bug!("Instance::mono: {:?} has type parameters", def_id) + } + ty::GenericParamDefKind::Const { .. } => { + bug!("Instance::mono: {:?} has const parameters", def_id) + } + }); + + Instance::new(def_id, substs) + } + + #[inline] + pub fn def_id(&self) -> DefId { + self.def.def_id() + } + + /// Resolves a `(def_id, substs)` pair to an (optional) instance -- most commonly, + /// this is used to find the precise code that will run for a trait method invocation, + /// if known. + /// + /// Returns `Ok(None)` if we cannot resolve `Instance` to a specific instance. + /// For example, in a context like this, + /// + /// ```ignore (illustrative) + /// fn foo<T: Debug>(t: T) { ... } + /// ``` + /// + /// trying to resolve `Debug::fmt` applied to `T` will yield `Ok(None)`, because we do not + /// know what code ought to run. (Note that this setting is also affected by the + /// `RevealMode` in the parameter environment.) + /// + /// Presuming that coherence and type-check have succeeded, if this method is invoked + /// in a monomorphic context (i.e., like during codegen), then it is guaranteed to return + /// `Ok(Some(instance))`. + /// + /// Returns `Err(ErrorGuaranteed)` when the `Instance` resolution process + /// couldn't complete due to errors elsewhere - this is distinct + /// from `Ok(None)` to avoid misleading diagnostics when an error + /// has already been/will be emitted, for the original cause + pub fn resolve( + tcx: TyCtxt<'tcx>, + param_env: ty::ParamEnv<'tcx>, + def_id: DefId, + substs: SubstsRef<'tcx>, + ) -> Result<Option<Instance<'tcx>>, ErrorGuaranteed> { + Instance::resolve_opt_const_arg( + tcx, + param_env, + ty::WithOptConstParam::unknown(def_id), + substs, + ) + } + + // This should be kept up to date with `resolve`. + pub fn resolve_opt_const_arg( + tcx: TyCtxt<'tcx>, + param_env: ty::ParamEnv<'tcx>, + def: ty::WithOptConstParam<DefId>, + substs: SubstsRef<'tcx>, + ) -> Result<Option<Instance<'tcx>>, ErrorGuaranteed> { + // All regions in the result of this query are erased, so it's + // fine to erase all of the input regions. + + // HACK(eddyb) erase regions in `substs` first, so that `param_env.and(...)` + // below is more likely to ignore the bounds in scope (e.g. if the only + // generic parameters mentioned by `substs` were lifetime ones). + let substs = tcx.erase_regions(substs); + + // FIXME(eddyb) should this always use `param_env.with_reveal_all()`? + if let Some((did, param_did)) = def.as_const_arg() { + tcx.resolve_instance_of_const_arg( + tcx.erase_regions(param_env.and((did, param_did, substs))), + ) + } else { + tcx.resolve_instance(tcx.erase_regions(param_env.and((def.did, substs)))) + } + } + + pub fn resolve_for_fn_ptr( + tcx: TyCtxt<'tcx>, + param_env: ty::ParamEnv<'tcx>, + def_id: DefId, + substs: SubstsRef<'tcx>, + ) -> Option<Instance<'tcx>> { + debug!("resolve(def_id={:?}, substs={:?})", def_id, substs); + // Use either `resolve_closure` or `resolve_for_vtable` + assert!(!tcx.is_closure(def_id), "Called `resolve_for_fn_ptr` on closure: {:?}", def_id); + Instance::resolve(tcx, param_env, def_id, substs).ok().flatten().map(|mut resolved| { + match resolved.def { + InstanceDef::Item(def) if resolved.def.requires_caller_location(tcx) => { + debug!(" => fn pointer created for function with #[track_caller]"); + resolved.def = InstanceDef::ReifyShim(def.did); + } + InstanceDef::Virtual(def_id, _) => { + debug!(" => fn pointer created for virtual call"); + resolved.def = InstanceDef::ReifyShim(def_id); + } + _ => {} + } + + resolved + }) + } + + pub fn resolve_for_vtable( + tcx: TyCtxt<'tcx>, + param_env: ty::ParamEnv<'tcx>, + def_id: DefId, + substs: SubstsRef<'tcx>, + ) -> Option<Instance<'tcx>> { + debug!("resolve_for_vtable(def_id={:?}, substs={:?})", def_id, substs); + let fn_sig = tcx.fn_sig(def_id); + let is_vtable_shim = !fn_sig.inputs().skip_binder().is_empty() + && fn_sig.input(0).skip_binder().is_param(0) + && tcx.generics_of(def_id).has_self; + if is_vtable_shim { + debug!(" => associated item with unsizeable self: Self"); + Some(Instance { def: InstanceDef::VTableShim(def_id), substs }) + } else { + Instance::resolve(tcx, param_env, def_id, substs).ok().flatten().map(|mut resolved| { + match resolved.def { + InstanceDef::Item(def) => { + // We need to generate a shim when we cannot guarantee that + // the caller of a trait object method will be aware of + // `#[track_caller]` - this ensures that the caller + // and callee ABI will always match. + // + // The shim is generated when all of these conditions are met: + // + // 1) The underlying method expects a caller location parameter + // in the ABI + if resolved.def.requires_caller_location(tcx) + // 2) The caller location parameter comes from having `#[track_caller]` + // on the implementation, and *not* on the trait method. + && !tcx.should_inherit_track_caller(def.did) + // If the method implementation comes from the trait definition itself + // (e.g. `trait Foo { #[track_caller] my_fn() { /* impl */ } }`), + // then we don't need to generate a shim. This check is needed because + // `should_inherit_track_caller` returns `false` if our method + // implementation comes from the trait block, and not an impl block + && !matches!( + tcx.opt_associated_item(def.did), + Some(ty::AssocItem { + container: ty::AssocItemContainer::TraitContainer, + .. + }) + ) + { + if tcx.is_closure(def.did) { + debug!(" => vtable fn pointer created for closure with #[track_caller]: {:?} for method {:?} {:?}", + def.did, def_id, substs); + + // Create a shim for the `FnOnce/FnMut/Fn` method we are calling + // - unlike functions, invoking a closure always goes through a + // trait. + resolved = Instance { def: InstanceDef::ReifyShim(def_id), substs }; + } else { + debug!( + " => vtable fn pointer created for function with #[track_caller]: {:?}", def.did + ); + resolved.def = InstanceDef::ReifyShim(def.did); + } + } + } + InstanceDef::Virtual(def_id, _) => { + debug!(" => vtable fn pointer created for virtual call"); + resolved.def = InstanceDef::ReifyShim(def_id); + } + _ => {} + } + + resolved + }) + } + } + + pub fn resolve_closure( + tcx: TyCtxt<'tcx>, + def_id: DefId, + substs: ty::SubstsRef<'tcx>, + requested_kind: ty::ClosureKind, + ) -> Option<Instance<'tcx>> { + let actual_kind = substs.as_closure().kind(); + + match needs_fn_once_adapter_shim(actual_kind, requested_kind) { + Ok(true) => Instance::fn_once_adapter_instance(tcx, def_id, substs), + _ => Some(Instance::new(def_id, substs)), + } + } + + pub fn resolve_drop_in_place(tcx: TyCtxt<'tcx>, ty: Ty<'tcx>) -> ty::Instance<'tcx> { + let def_id = tcx.require_lang_item(LangItem::DropInPlace, None); + let substs = tcx.intern_substs(&[ty.into()]); + Instance::resolve(tcx, ty::ParamEnv::reveal_all(), def_id, substs).unwrap().unwrap() + } + + pub fn fn_once_adapter_instance( + tcx: TyCtxt<'tcx>, + closure_did: DefId, + substs: ty::SubstsRef<'tcx>, + ) -> Option<Instance<'tcx>> { + debug!("fn_once_adapter_shim({:?}, {:?})", closure_did, substs); + let fn_once = tcx.require_lang_item(LangItem::FnOnce, None); + let call_once = tcx + .associated_items(fn_once) + .in_definition_order() + .find(|it| it.kind == ty::AssocKind::Fn) + .unwrap() + .def_id; + let track_caller = + tcx.codegen_fn_attrs(closure_did).flags.contains(CodegenFnAttrFlags::TRACK_CALLER); + let def = ty::InstanceDef::ClosureOnceShim { call_once, track_caller }; + + let self_ty = tcx.mk_closure(closure_did, substs); + + let sig = substs.as_closure().sig(); + let sig = + tcx.try_normalize_erasing_late_bound_regions(ty::ParamEnv::reveal_all(), sig).ok()?; + assert_eq!(sig.inputs().len(), 1); + let substs = tcx.mk_substs_trait(self_ty, &[sig.inputs()[0].into()]); + + debug!("fn_once_adapter_shim: self_ty={:?} sig={:?}", self_ty, sig); + Some(Instance { def, substs }) + } + + /// Depending on the kind of `InstanceDef`, the MIR body associated with an + /// instance is expressed in terms of the generic parameters of `self.def_id()`, and in other + /// cases the MIR body is expressed in terms of the types found in the substitution array. + /// In the former case, we want to substitute those generic types and replace them with the + /// values from the substs when monomorphizing the function body. But in the latter case, we + /// don't want to do that substitution, since it has already been done effectively. + /// + /// This function returns `Some(substs)` in the former case and `None` otherwise -- i.e., if + /// this function returns `None`, then the MIR body does not require substitution during + /// codegen. + fn substs_for_mir_body(&self) -> Option<SubstsRef<'tcx>> { + if self.def.has_polymorphic_mir_body() { Some(self.substs) } else { None } + } + + pub fn subst_mir<T>(&self, tcx: TyCtxt<'tcx>, v: &T) -> T + where + T: TypeFoldable<'tcx> + Copy, + { + if let Some(substs) = self.substs_for_mir_body() { + EarlyBinder(*v).subst(tcx, substs) + } else { + *v + } + } + + #[inline(always)] + pub fn subst_mir_and_normalize_erasing_regions<T>( + &self, + tcx: TyCtxt<'tcx>, + param_env: ty::ParamEnv<'tcx>, + v: T, + ) -> T + where + T: TypeFoldable<'tcx> + Clone, + { + if let Some(substs) = self.substs_for_mir_body() { + tcx.subst_and_normalize_erasing_regions(substs, param_env, v) + } else { + tcx.normalize_erasing_regions(param_env, v) + } + } + + #[inline(always)] + pub fn try_subst_mir_and_normalize_erasing_regions<T>( + &self, + tcx: TyCtxt<'tcx>, + param_env: ty::ParamEnv<'tcx>, + v: T, + ) -> Result<T, NormalizationError<'tcx>> + where + T: TypeFoldable<'tcx> + Clone, + { + if let Some(substs) = self.substs_for_mir_body() { + tcx.try_subst_and_normalize_erasing_regions(substs, param_env, v) + } else { + tcx.try_normalize_erasing_regions(param_env, v) + } + } + + /// Returns a new `Instance` where generic parameters in `instance.substs` are replaced by + /// identity parameters if they are determined to be unused in `instance.def`. + pub fn polymorphize(self, tcx: TyCtxt<'tcx>) -> Self { + debug!("polymorphize: running polymorphization analysis"); + if !tcx.sess.opts.unstable_opts.polymorphize { + return self; + } + + let polymorphized_substs = polymorphize(tcx, self.def, self.substs); + debug!("polymorphize: self={:?} polymorphized_substs={:?}", self, polymorphized_substs); + Self { def: self.def, substs: polymorphized_substs } + } +} + +fn polymorphize<'tcx>( + tcx: TyCtxt<'tcx>, + instance: ty::InstanceDef<'tcx>, + substs: SubstsRef<'tcx>, +) -> SubstsRef<'tcx> { + debug!("polymorphize({:?}, {:?})", instance, substs); + let unused = tcx.unused_generic_params(instance); + debug!("polymorphize: unused={:?}", unused); + + // If this is a closure or generator then we need to handle the case where another closure + // from the function is captured as an upvar and hasn't been polymorphized. In this case, + // the unpolymorphized upvar closure would result in a polymorphized closure producing + // multiple mono items (and eventually symbol clashes). + let def_id = instance.def_id(); + let upvars_ty = if tcx.is_closure(def_id) { + Some(substs.as_closure().tupled_upvars_ty()) + } else if tcx.type_of(def_id).is_generator() { + Some(substs.as_generator().tupled_upvars_ty()) + } else { + None + }; + let has_upvars = upvars_ty.map_or(false, |ty| !ty.tuple_fields().is_empty()); + debug!("polymorphize: upvars_ty={:?} has_upvars={:?}", upvars_ty, has_upvars); + + struct PolymorphizationFolder<'tcx> { + tcx: TyCtxt<'tcx>, + } + + impl<'tcx> ty::TypeFolder<'tcx> for PolymorphizationFolder<'tcx> { + fn tcx<'a>(&'a self) -> TyCtxt<'tcx> { + self.tcx + } + + fn fold_ty(&mut self, ty: Ty<'tcx>) -> Ty<'tcx> { + debug!("fold_ty: ty={:?}", ty); + match *ty.kind() { + ty::Closure(def_id, substs) => { + let polymorphized_substs = polymorphize( + self.tcx, + ty::InstanceDef::Item(ty::WithOptConstParam::unknown(def_id)), + substs, + ); + if substs == polymorphized_substs { + ty + } else { + self.tcx.mk_closure(def_id, polymorphized_substs) + } + } + ty::Generator(def_id, substs, movability) => { + let polymorphized_substs = polymorphize( + self.tcx, + ty::InstanceDef::Item(ty::WithOptConstParam::unknown(def_id)), + substs, + ); + if substs == polymorphized_substs { + ty + } else { + self.tcx.mk_generator(def_id, polymorphized_substs, movability) + } + } + _ => ty.super_fold_with(self), + } + } + } + + InternalSubsts::for_item(tcx, def_id, |param, _| { + let is_unused = unused.contains(param.index).unwrap_or(false); + debug!("polymorphize: param={:?} is_unused={:?}", param, is_unused); + match param.kind { + // Upvar case: If parameter is a type parameter.. + ty::GenericParamDefKind::Type { .. } if + // ..and has upvars.. + has_upvars && + // ..and this param has the same type as the tupled upvars.. + upvars_ty == Some(substs[param.index as usize].expect_ty()) => { + // ..then double-check that polymorphization marked it used.. + debug_assert!(!is_unused); + // ..and polymorphize any closures/generators captured as upvars. + let upvars_ty = upvars_ty.unwrap(); + let polymorphized_upvars_ty = upvars_ty.fold_with( + &mut PolymorphizationFolder { tcx }); + debug!("polymorphize: polymorphized_upvars_ty={:?}", polymorphized_upvars_ty); + ty::GenericArg::from(polymorphized_upvars_ty) + }, + + // Simple case: If parameter is a const or type parameter.. + ty::GenericParamDefKind::Const { .. } | ty::GenericParamDefKind::Type { .. } if + // ..and is within range and unused.. + unused.contains(param.index).unwrap_or(false) => + // ..then use the identity for this parameter. + tcx.mk_param_from_def(param), + + // Otherwise, use the parameter as before. + _ => substs[param.index as usize], + } + }) +} + +fn needs_fn_once_adapter_shim( + actual_closure_kind: ty::ClosureKind, + trait_closure_kind: ty::ClosureKind, +) -> Result<bool, ()> { + match (actual_closure_kind, trait_closure_kind) { + (ty::ClosureKind::Fn, ty::ClosureKind::Fn) + | (ty::ClosureKind::FnMut, ty::ClosureKind::FnMut) + | (ty::ClosureKind::FnOnce, ty::ClosureKind::FnOnce) => { + // No adapter needed. + Ok(false) + } + (ty::ClosureKind::Fn, ty::ClosureKind::FnMut) => { + // The closure fn `llfn` is a `fn(&self, ...)`. We want a + // `fn(&mut self, ...)`. In fact, at codegen time, these are + // basically the same thing, so we can just return llfn. + Ok(false) + } + (ty::ClosureKind::Fn | ty::ClosureKind::FnMut, ty::ClosureKind::FnOnce) => { + // The closure fn `llfn` is a `fn(&self, ...)` or `fn(&mut + // self, ...)`. We want a `fn(self, ...)`. We can produce + // this by doing something like: + // + // fn call_once(self, ...) { call_mut(&self, ...) } + // fn call_once(mut self, ...) { call_mut(&mut self, ...) } + // + // These are both the same at codegen time. + Ok(true) + } + (ty::ClosureKind::FnMut | ty::ClosureKind::FnOnce, _) => Err(()), + } +} |