compiler/rustc_middle/src/mir/mono.rs - toolchain/rustc - Git at Google

 use crate::dep_graph::{DepNode, WorkProduct, WorkProductId};
 use crate::ty::{subst::InternalSubsts, Instance, InstanceDef, SymbolName, TyCtxt};
 use rustc_attr::InlineAttr;
 use rustc_data_structures::base_n;
 use rustc_data_structures::fingerprint::Fingerprint;
 use rustc_data_structures::fx::FxHashMap;
 use rustc_data_structures::stable_hasher::{HashStable, StableHasher};
 use rustc_hir::def_id::{CrateNum, DefId, LOCAL_CRATE};
 use rustc_hir::ItemId;
 use rustc_index::vec::Idx;
 use rustc_query_system::ich::StableHashingContext;
 use rustc_session::config::OptLevel;
 use rustc_span::source_map::Span;
 use rustc_span::symbol::Symbol;
 use std::fmt;
 use std::hash::Hash;

 /// Describes how a monomorphization will be instantiated in object files.
 #[derive(PartialEq)]
 pub enum InstantiationMode {
     /// There will be exactly one instance of the given MonoItem. It will have
     /// external linkage so that it can be linked to from other codegen units.
     GloballyShared {
         /// In some compilation scenarios we may decide to take functions that
         /// are typically `LocalCopy` and instead move them to `GloballyShared`
         /// to avoid codegenning them a bunch of times. In this situation,
         /// however, our local copy may conflict with other crates also
         /// inlining the same function.
         ///
         /// This flag indicates that this situation is occurring, and informs
         /// symbol name calculation that some extra mangling is needed to
         /// avoid conflicts. Note that this may eventually go away entirely if
         /// ThinLTO enables us to *always* have a globally shared instance of a
         /// function within one crate's compilation.
         may_conflict: bool,
     },

     /// Each codegen unit containing a reference to the given MonoItem will
     /// have its own private copy of the function (with internal linkage).
     LocalCopy,
 }

 #[derive(PartialEq, Eq, Clone, Copy, Debug, Hash, HashStable)]
 pub enum MonoItem<'tcx> {
     Fn(Instance<'tcx>),
     Static(DefId),
     GlobalAsm(ItemId),
 }

 impl<'tcx> MonoItem<'tcx> {
     /// Returns `true` if the mono item is user-defined (i.e. not compiler-generated, like shims).
     pub fn is_user_defined(&self) -> bool {
         match *self {
             MonoItem::Fn(instance) => matches!(instance.def, InstanceDef::Item(..)),
             MonoItem::Static(..) | MonoItem::GlobalAsm(..) => true,
         }
     }

     pub fn size_estimate(&self, tcx: TyCtxt<'tcx>) -> usize {
         match *self {
             MonoItem::Fn(instance) => {
                 // Estimate the size of a function based on how many statements
                 // it contains.
                 tcx.instance_def_size_estimate(instance.def)
             }
             // Conservatively estimate the size of a static declaration
             // or assembly to be 1.
             MonoItem::Static(_) | MonoItem::GlobalAsm(_) => 1,
         }
     }

     pub fn is_generic_fn(&self) -> bool {
         match *self {
             MonoItem::Fn(ref instance) => instance.substs.non_erasable_generics().next().is_some(),
             MonoItem::Static(..) | MonoItem::GlobalAsm(..) => false,
         }
     }

     pub fn symbol_name(&self, tcx: TyCtxt<'tcx>) -> SymbolName<'tcx> {
         match *self {
             MonoItem::Fn(instance) => tcx.symbol_name(instance),
             MonoItem::Static(def_id) => tcx.symbol_name(Instance::mono(tcx, def_id)),
             MonoItem::GlobalAsm(item_id) => {
                 SymbolName::new(tcx, &format!("global_asm_{:?}", item_id.owner_id))
             }
         }
     }

     pub fn instantiation_mode(&self, tcx: TyCtxt<'tcx>) -> InstantiationMode {
         let generate_cgu_internal_copies = tcx
             .sess
             .opts
             .unstable_opts
             .inline_in_all_cgus
             .unwrap_or_else(|| tcx.sess.opts.optimize != OptLevel::No)
             && !tcx.sess.link_dead_code();

         match *self {
             MonoItem::Fn(ref instance) => {
                 let entry_def_id = tcx.entry_fn(()).map(|(id, _)| id);
                 // If this function isn't inlined or otherwise has an extern
                 // indicator, then we'll be creating a globally shared version.
                 if tcx.codegen_fn_attrs(instance.def_id()).contains_extern_indicator()
                     || !instance.def.generates_cgu_internal_copy(tcx)
                     || Some(instance.def_id()) == entry_def_id
                 {
                     return InstantiationMode::GloballyShared { may_conflict: false };
                 }

                 // At this point we don't have explicit linkage and we're an
                 // inlined function. If we're inlining into all CGUs then we'll
                 // be creating a local copy per CGU.
                 if generate_cgu_internal_copies {
                     return InstantiationMode::LocalCopy;
                 }

                 // Finally, if this is `#[inline(always)]` we're sure to respect
                 // that with an inline copy per CGU, but otherwise we'll be
                 // creating one copy of this `#[inline]` function which may
                 // conflict with upstream crates as it could be an exported
                 // symbol.
                 match tcx.codegen_fn_attrs(instance.def_id()).inline {
                     InlineAttr::Always => InstantiationMode::LocalCopy,
                     _ => InstantiationMode::GloballyShared { may_conflict: true },
                 }
             }
             MonoItem::Static(..) | MonoItem::GlobalAsm(..) => {
                 InstantiationMode::GloballyShared { may_conflict: false }
             }
         }
     }

     pub fn explicit_linkage(&self, tcx: TyCtxt<'tcx>) -> Option<Linkage> {
         let def_id = match *self {
             MonoItem::Fn(ref instance) => instance.def_id(),
             MonoItem::Static(def_id) => def_id,
             MonoItem::GlobalAsm(..) => return None,
         };

         let codegen_fn_attrs = tcx.codegen_fn_attrs(def_id);
         codegen_fn_attrs.linkage
     }

     /// Returns `true` if this instance is instantiable - whether it has no unsatisfied
     /// predicates.
     ///
     /// In order to codegen an item, all of its predicates must hold, because
     /// otherwise the item does not make sense. Type-checking ensures that
     /// the predicates of every item that is *used by* a valid item *do*
     /// hold, so we can rely on that.
     ///
     /// However, we codegen collector roots (reachable items) and functions
     /// in vtables when they are seen, even if they are not used, and so they
     /// might not be instantiable. For example, a programmer can define this
     /// public function:
     ///
     ///     pub fn foo<'a>(s: &'a mut ()) where &'a mut (): Clone {
     ///         <&mut () as Clone>::clone(&s);
     ///     }
     ///
     /// That function can't be codegened, because the method `<&mut () as Clone>::clone`
     /// does not exist. Luckily for us, that function can't ever be used,
     /// because that would require for `&'a mut (): Clone` to hold, so we
     /// can just not emit any code, or even a linker reference for it.
     ///
     /// Similarly, if a vtable method has such a signature, and therefore can't
     /// be used, we can just not emit it and have a placeholder (a null pointer,
     /// which will never be accessed) in its place.
     pub fn is_instantiable(&self, tcx: TyCtxt<'tcx>) -> bool {
         debug!("is_instantiable({:?})", self);
         let (def_id, substs) = match *self {
             MonoItem::Fn(ref instance) => (instance.def_id(), instance.substs),
             MonoItem::Static(def_id) => (def_id, InternalSubsts::empty()),
             // global asm never has predicates
             MonoItem::GlobalAsm(..) => return true,
         };

         !tcx.subst_and_check_impossible_predicates((def_id, &substs))
     }

     pub fn local_span(&self, tcx: TyCtxt<'tcx>) -> Option<Span> {
         match *self {
             MonoItem::Fn(Instance { def, .. }) => def.def_id().as_local(),
             MonoItem::Static(def_id) => def_id.as_local(),
             MonoItem::GlobalAsm(item_id) => Some(item_id.owner_id.def_id),
         }
         .map(|def_id| tcx.def_span(def_id))
     }

     // Only used by rustc_codegen_cranelift
     pub fn codegen_dep_node(&self, tcx: TyCtxt<'tcx>) -> DepNode {
         crate::dep_graph::make_compile_mono_item(tcx, self)
     }

     /// Returns the item's `CrateNum`
     pub fn krate(&self) -> CrateNum {
         match self {
             MonoItem::Fn(ref instance) => instance.def_id().krate,
             MonoItem::Static(def_id) => def_id.krate,
             MonoItem::GlobalAsm(..) => LOCAL_CRATE,
         }
     }
 }

 impl<'tcx> fmt::Display for MonoItem<'tcx> {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
         match *self {
             MonoItem::Fn(instance) => write!(f, "fn {}", instance),
             MonoItem::Static(def_id) => {
                 write!(f, "static {}", Instance::new(def_id, InternalSubsts::empty()))
             }
             MonoItem::GlobalAsm(..) => write!(f, "global_asm"),
         }
     }
 }

 #[derive(Debug)]
 pub struct CodegenUnit<'tcx> {
     /// A name for this CGU. Incremental compilation requires that
     /// name be unique amongst **all** crates. Therefore, it should
     /// contain something unique to this crate (e.g., a module path)
     /// as well as the crate name and disambiguator.
     name: Symbol,
     items: FxHashMap<MonoItem<'tcx>, (Linkage, Visibility)>,
     size_estimate: Option<usize>,
     primary: bool,
     /// True if this is CGU is used to hold code coverage information for dead code,
     /// false otherwise.
     is_code_coverage_dead_code_cgu: bool,
 }

 /// Specifies the linkage type for a `MonoItem`.
 ///
 /// See <https://llvm.org/docs/LangRef.html#linkage-types> for more details about these variants.
 #[derive(Copy, Clone, PartialEq, Debug, TyEncodable, TyDecodable, HashStable)]
 pub enum Linkage {
     External,
     AvailableExternally,
     LinkOnceAny,
     LinkOnceODR,
     WeakAny,
     WeakODR,
     Appending,
     Internal,
     Private,
     ExternalWeak,
     Common,
 }

 #[derive(Copy, Clone, PartialEq, Debug, HashStable)]
 pub enum Visibility {
     Default,
     Hidden,
     Protected,
 }

 impl<'tcx> CodegenUnit<'tcx> {
     #[inline]
     pub fn new(name: Symbol) -> CodegenUnit<'tcx> {
         CodegenUnit {
             name,
             items: Default::default(),
             size_estimate: None,
             primary: false,
             is_code_coverage_dead_code_cgu: false,
         }
     }

     pub fn name(&self) -> Symbol {
         self.name
     }

     pub fn set_name(&mut self, name: Symbol) {
         self.name = name;
     }

     pub fn is_primary(&self) -> bool {
         self.primary
     }

     pub fn make_primary(&mut self) {
         self.primary = true;
     }

     pub fn items(&self) -> &FxHashMap<MonoItem<'tcx>, (Linkage, Visibility)> {
         &self.items
     }

     pub fn items_mut(&mut self) -> &mut FxHashMap<MonoItem<'tcx>, (Linkage, Visibility)> {
         &mut self.items
     }

     pub fn is_code_coverage_dead_code_cgu(&self) -> bool {
         self.is_code_coverage_dead_code_cgu
     }

     /// Marks this CGU as the one used to contain code coverage information for dead code.
     pub fn make_code_coverage_dead_code_cgu(&mut self) {
         self.is_code_coverage_dead_code_cgu = true;
     }

     pub fn mangle_name(human_readable_name: &str) -> String {
         // We generate a 80 bit hash from the name. This should be enough to
         // avoid collisions and is still reasonably short for filenames.
         let mut hasher = StableHasher::new();
         human_readable_name.hash(&mut hasher);
         let hash: u128 = hasher.finish();
         let hash = hash & ((1u128 << 80) - 1);
         base_n::encode(hash, base_n::CASE_INSENSITIVE)
     }

     pub fn estimate_size(&mut self, tcx: TyCtxt<'tcx>) {
         // Estimate the size of a codegen unit as (approximately) the number of MIR
         // statements it corresponds to.
         self.size_estimate = Some(self.items.keys().map(|mi| mi.size_estimate(tcx)).sum());
     }

     #[inline]
     pub fn size_estimate(&self) -> usize {
         // Should only be called if `estimate_size` has previously been called.
         self.size_estimate.expect("estimate_size must be called before getting a size_estimate")
     }

     pub fn modify_size_estimate(&mut self, delta: usize) {
         assert!(self.size_estimate.is_some());
         if let Some(size_estimate) = self.size_estimate {
             self.size_estimate = Some(size_estimate + delta);
         }
     }

     pub fn contains_item(&self, item: &MonoItem<'tcx>) -> bool {
         self.items().contains_key(item)
     }

     pub fn work_product_id(&self) -> WorkProductId {
         WorkProductId::from_cgu_name(self.name().as_str())
     }

     pub fn previous_work_product(&self, tcx: TyCtxt<'_>) -> WorkProduct {
         let work_product_id = self.work_product_id();
         tcx.dep_graph
             .previous_work_product(&work_product_id)
             .unwrap_or_else(|| panic!("Could not find work-product for CGU `{}`", self.name()))
     }

     pub fn items_in_deterministic_order(
         &self,
         tcx: TyCtxt<'tcx>,
     ) -> Vec<(MonoItem<'tcx>, (Linkage, Visibility))> {
         // The codegen tests rely on items being process in the same order as
         // they appear in the file, so for local items, we sort by node_id first
         #[derive(PartialEq, Eq, PartialOrd, Ord)]
         pub struct ItemSortKey<'tcx>(Option<usize>, SymbolName<'tcx>);

         fn item_sort_key<'tcx>(tcx: TyCtxt<'tcx>, item: MonoItem<'tcx>) -> ItemSortKey<'tcx> {
             ItemSortKey(
                 match item {
                     MonoItem::Fn(ref instance) => {
                         match instance.def {
                             // We only want to take HirIds of user-defined
                             // instances into account. The others don't matter for
                             // the codegen tests and can even make item order
                             // unstable.
                             InstanceDef::Item(def) => def.did.as_local().map(Idx::index),
                             InstanceDef::VTableShim(..)
                             | InstanceDef::ReifyShim(..)
                             | InstanceDef::Intrinsic(..)
                             | InstanceDef::FnPtrShim(..)
                             | InstanceDef::Virtual(..)
                             | InstanceDef::ClosureOnceShim { .. }
                             | InstanceDef::DropGlue(..)
                             | InstanceDef::CloneShim(..) => None,
                         }
                     }
                     MonoItem::Static(def_id) => def_id.as_local().map(Idx::index),
                     MonoItem::GlobalAsm(item_id) => Some(item_id.owner_id.def_id.index()),
                 },
                 item.symbol_name(tcx),
             )
         }

         let mut items: Vec<_> = self.items().iter().map(|(&i, &l)| (i, l)).collect();
         items.sort_by_cached_key(|&(i, _)| item_sort_key(tcx, i));
         items
     }

     pub fn codegen_dep_node(&self, tcx: TyCtxt<'tcx>) -> DepNode {
         crate::dep_graph::make_compile_codegen_unit(tcx, self.name())
     }
 }

 impl<'a, 'tcx> HashStable<StableHashingContext<'a>> for CodegenUnit<'tcx> {
     fn hash_stable(&self, hcx: &mut StableHashingContext<'a>, hasher: &mut StableHasher) {
         let CodegenUnit {
             ref items,
             name,
             // The size estimate is not relevant to the hash
             size_estimate: _,
             primary: _,
             is_code_coverage_dead_code_cgu,
         } = *self;

         name.hash_stable(hcx, hasher);
         is_code_coverage_dead_code_cgu.hash_stable(hcx, hasher);

         let mut items: Vec<(Fingerprint, _)> = items
             .iter()
             .map(|(mono_item, &attrs)| {
                 let mut hasher = StableHasher::new();
                 mono_item.hash_stable(hcx, &mut hasher);
                 let mono_item_fingerprint = hasher.finish();
                 (mono_item_fingerprint, attrs)
             })
             .collect();

         items.sort_unstable_by_key(|i| i.0);
         items.hash_stable(hcx, hasher);
     }
 }

 pub struct CodegenUnitNameBuilder<'tcx> {
     tcx: TyCtxt<'tcx>,
     cache: FxHashMap<CrateNum, String>,
 }

 impl<'tcx> CodegenUnitNameBuilder<'tcx> {
     pub fn new(tcx: TyCtxt<'tcx>) -> Self {
         CodegenUnitNameBuilder { tcx, cache: Default::default() }
     }

     /// CGU names should fulfill the following requirements:
     /// - They should be able to act as a file name on any kind of file system
     /// - They should not collide with other CGU names, even for different versions
     ///   of the same crate.
     ///
     /// Consequently, we don't use special characters except for '.' and '-' and we
     /// prefix each name with the crate-name and crate-disambiguator.
     ///
     /// This function will build CGU names of the form:
     ///
     /// ```text
     /// <crate-name>.<crate-disambiguator>[-in-<local-crate-id>](-<component>)*[.<special-suffix>]
     /// <local-crate-id> = <local-crate-name>.<local-crate-disambiguator>
     /// ```
     ///
     /// The '.' before `<special-suffix>` makes sure that names with a special
     /// suffix can never collide with a name built out of regular Rust
     /// identifiers (e.g., module paths).
     pub fn build_cgu_name<I, C, S>(
         &mut self,
         cnum: CrateNum,
         components: I,
         special_suffix: Option<S>,
     ) -> Symbol
     where
         I: IntoIterator<Item = C>,
         C: fmt::Display,
         S: fmt::Display,
     {
         let cgu_name = self.build_cgu_name_no_mangle(cnum, components, special_suffix);

         if self.tcx.sess.opts.unstable_opts.human_readable_cgu_names {
             cgu_name
         } else {
             Symbol::intern(&CodegenUnit::mangle_name(cgu_name.as_str()))
         }
     }

     /// Same as `CodegenUnit::build_cgu_name()` but will never mangle the
     /// resulting name.
     pub fn build_cgu_name_no_mangle<I, C, S>(
         &mut self,
         cnum: CrateNum,
         components: I,
         special_suffix: Option<S>,
     ) -> Symbol
     where
         I: IntoIterator<Item = C>,
         C: fmt::Display,
         S: fmt::Display,
     {
         use std::fmt::Write;

         let mut cgu_name = String::with_capacity(64);

         // Start out with the crate name and disambiguator
         let tcx = self.tcx;
         let crate_prefix = self.cache.entry(cnum).or_insert_with(|| {
             // Whenever the cnum is not LOCAL_CRATE we also mix in the
             // local crate's ID. Otherwise there can be collisions between CGUs
             // instantiating stuff for upstream crates.
             let local_crate_id = if cnum != LOCAL_CRATE {
                 let local_stable_crate_id = tcx.sess.local_stable_crate_id();
                 format!(
                     "-in-{}.{:08x}",
                     tcx.crate_name(LOCAL_CRATE),
                     local_stable_crate_id.to_u64() as u32,
                 )
             } else {
                 String::new()
             };

             let stable_crate_id = tcx.sess.local_stable_crate_id();
             format!(
                 "{}.{:08x}{}",
                 tcx.crate_name(cnum),
                 stable_crate_id.to_u64() as u32,
                 local_crate_id,
             )
         });

         write!(cgu_name, "{}", crate_prefix).unwrap();

         // Add the components
         for component in components {
             write!(cgu_name, "-{}", component).unwrap();
         }

         if let Some(special_suffix) = special_suffix {
             // We add a dot in here so it cannot clash with anything in a regular
             // Rust identifier
             write!(cgu_name, ".{}", special_suffix).unwrap();
         }

         Symbol::intern(&cgu_name)
     }
 }
	use crate::dep_graph::{DepNode, WorkProduct, WorkProductId};
	use crate::ty::{subst::InternalSubsts, Instance, InstanceDef, SymbolName, TyCtxt};
	use rustc_attr::InlineAttr;
	use rustc_data_structures::base_n;
	use rustc_data_structures::fingerprint::Fingerprint;
	use rustc_data_structures::fx::FxHashMap;
	use rustc_data_structures::stable_hasher::{HashStable, StableHasher};
	use rustc_hir::def_id::{CrateNum, DefId, LOCAL_CRATE};
	use rustc_hir::ItemId;
	use rustc_index::vec::Idx;
	use rustc_query_system::ich::StableHashingContext;
	use rustc_session::config::OptLevel;
	use rustc_span::source_map::Span;
	use rustc_span::symbol::Symbol;
	use std::fmt;
	use std::hash::Hash;

	/// Describes how a monomorphization will be instantiated in object files.
	#[derive(PartialEq)]
	pub enum InstantiationMode {
	/// There will be exactly one instance of the given MonoItem. It will have
	/// external linkage so that it can be linked to from other codegen units.
	GloballyShared {
	/// In some compilation scenarios we may decide to take functions that
	/// are typically `LocalCopy` and instead move them to `GloballyShared`
	/// to avoid codegenning them a bunch of times. In this situation,
	/// however, our local copy may conflict with other crates also
	/// inlining the same function.
	///
	/// This flag indicates that this situation is occurring, and informs
	/// symbol name calculation that some extra mangling is needed to
	/// avoid conflicts. Note that this may eventually go away entirely if
	/// ThinLTO enables us to always have a globally shared instance of a
	/// function within one crate's compilation.
	may_conflict: bool,
	},

	/// Each codegen unit containing a reference to the given MonoItem will
	/// have its own private copy of the function (with internal linkage).
	LocalCopy,
	}

	#[derive(PartialEq, Eq, Clone, Copy, Debug, Hash, HashStable)]
	pub enum MonoItem<'tcx> {
	Fn(Instance<'tcx>),
	Static(DefId),
	GlobalAsm(ItemId),
	}

	impl<'tcx> MonoItem<'tcx> {
	/// Returns `true` if the mono item is user-defined (i.e. not compiler-generated, like shims).
	pub fn is_user_defined(&self) -> bool {
	match *self {
	MonoItem::Fn(instance) => matches!(instance.def, InstanceDef::Item(..)),
	MonoItem::Static(..) \| MonoItem::GlobalAsm(..) => true,
	}
	}

	pub fn size_estimate(&self, tcx: TyCtxt<'tcx>) -> usize {
	match *self {
	MonoItem::Fn(instance) => {
	// Estimate the size of a function based on how many statements
	// it contains.
	tcx.instance_def_size_estimate(instance.def)
	}
	// Conservatively estimate the size of a static declaration
	// or assembly to be 1.
	MonoItem::Static(_) \| MonoItem::GlobalAsm(_) => 1,
	}
	}

	pub fn is_generic_fn(&self) -> bool {
	match *self {
	MonoItem::Fn(ref instance) => instance.substs.non_erasable_generics().next().is_some(),
	MonoItem::Static(..) \| MonoItem::GlobalAsm(..) => false,
	}
	}

	pub fn symbol_name(&self, tcx: TyCtxt<'tcx>) -> SymbolName<'tcx> {
	match *self {
	MonoItem::Fn(instance) => tcx.symbol_name(instance),
	MonoItem::Static(def_id) => tcx.symbol_name(Instance::mono(tcx, def_id)),
	MonoItem::GlobalAsm(item_id) => {
	SymbolName::new(tcx, &format!("global_asm_{:?}", item_id.owner_id))
	}
	}
	}

	pub fn instantiation_mode(&self, tcx: TyCtxt<'tcx>) -> InstantiationMode {
	let generate_cgu_internal_copies = tcx
	.sess
	.opts
	.unstable_opts
	.inline_in_all_cgus
	.unwrap_or_else(\|\| tcx.sess.opts.optimize != OptLevel::No)
	&& !tcx.sess.link_dead_code();

	match *self {
	MonoItem::Fn(ref instance) => {
	let entry_def_id = tcx.entry_fn(()).map(\|(id, _)\| id);
	// If this function isn't inlined or otherwise has an extern
	// indicator, then we'll be creating a globally shared version.
	if tcx.codegen_fn_attrs(instance.def_id()).contains_extern_indicator()
	\|\| !instance.def.generates_cgu_internal_copy(tcx)
	\|\| Some(instance.def_id()) == entry_def_id
	{
	return InstantiationMode::GloballyShared { may_conflict: false };
	}

	// At this point we don't have explicit linkage and we're an
	// inlined function. If we're inlining into all CGUs then we'll
	// be creating a local copy per CGU.
	if generate_cgu_internal_copies {
	return InstantiationMode::LocalCopy;
	}

	// Finally, if this is `#[inline(always)]` we're sure to respect
	// that with an inline copy per CGU, but otherwise we'll be
	// creating one copy of this `#[inline]` function which may
	// conflict with upstream crates as it could be an exported
	// symbol.
	match tcx.codegen_fn_attrs(instance.def_id()).inline {
	InlineAttr::Always => InstantiationMode::LocalCopy,
	_ => InstantiationMode::GloballyShared { may_conflict: true },
	}
	}
	MonoItem::Static(..) \| MonoItem::GlobalAsm(..) => {
	InstantiationMode::GloballyShared { may_conflict: false }
	}
	}
	}

	pub fn explicit_linkage(&self, tcx: TyCtxt<'tcx>) -> Option<Linkage> {
	let def_id = match *self {
	MonoItem::Fn(ref instance) => instance.def_id(),
	MonoItem::Static(def_id) => def_id,
	MonoItem::GlobalAsm(..) => return None,
	};

	let codegen_fn_attrs = tcx.codegen_fn_attrs(def_id);
	codegen_fn_attrs.linkage
	}

	/// Returns `true` if this instance is instantiable - whether it has no unsatisfied
	/// predicates.
	///
	/// In order to codegen an item, all of its predicates must hold, because
	/// otherwise the item does not make sense. Type-checking ensures that
	/// the predicates of every item that is used by a valid item do
	/// hold, so we can rely on that.
	///
	/// However, we codegen collector roots (reachable items) and functions
	/// in vtables when they are seen, even if they are not used, and so they
	/// might not be instantiable. For example, a programmer can define this
	/// public function:
	///
	/// pub fn foo<'a>(s: &'a mut ()) where &'a mut (): Clone {
	/// <&mut () as Clone>::clone(&s);
	/// }
	///
	/// That function can't be codegened, because the method `<&mut () as Clone>::clone`
	/// does not exist. Luckily for us, that function can't ever be used,
	/// because that would require for `&'a mut (): Clone` to hold, so we
	/// can just not emit any code, or even a linker reference for it.
	///
	/// Similarly, if a vtable method has such a signature, and therefore can't
	/// be used, we can just not emit it and have a placeholder (a null pointer,
	/// which will never be accessed) in its place.
	pub fn is_instantiable(&self, tcx: TyCtxt<'tcx>) -> bool {
	debug!("is_instantiable({:?})", self);
	let (def_id, substs) = match *self {
	MonoItem::Fn(ref instance) => (instance.def_id(), instance.substs),
	MonoItem::Static(def_id) => (def_id, InternalSubsts::empty()),
	// global asm never has predicates
	MonoItem::GlobalAsm(..) => return true,
	};

	!tcx.subst_and_check_impossible_predicates((def_id, &substs))
	}

	pub fn local_span(&self, tcx: TyCtxt<'tcx>) -> Option<Span> {
	match *self {
	MonoItem::Fn(Instance { def, .. }) => def.def_id().as_local(),
	MonoItem::Static(def_id) => def_id.as_local(),
	MonoItem::GlobalAsm(item_id) => Some(item_id.owner_id.def_id),
	}
	.map(\|def_id\| tcx.def_span(def_id))
	}

	// Only used by rustc_codegen_cranelift
	pub fn codegen_dep_node(&self, tcx: TyCtxt<'tcx>) -> DepNode {
	crate::dep_graph::make_compile_mono_item(tcx, self)
	}

	/// Returns the item's `CrateNum`
	pub fn krate(&self) -> CrateNum {
	match self {
	MonoItem::Fn(ref instance) => instance.def_id().krate,
	MonoItem::Static(def_id) => def_id.krate,
	MonoItem::GlobalAsm(..) => LOCAL_CRATE,
	}
	}
	}

	impl<'tcx> fmt::Display for MonoItem<'tcx> {
	fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
	match *self {
	MonoItem::Fn(instance) => write!(f, "fn {}", instance),
	MonoItem::Static(def_id) => {
	write!(f, "static {}", Instance::new(def_id, InternalSubsts::empty()))
	}
	MonoItem::GlobalAsm(..) => write!(f, "global_asm"),
	}
	}
	}

	#[derive(Debug)]
	pub struct CodegenUnit<'tcx> {
	/// A name for this CGU. Incremental compilation requires that
	/// name be unique amongst all crates. Therefore, it should
	/// contain something unique to this crate (e.g., a module path)
	/// as well as the crate name and disambiguator.
	name: Symbol,
	items: FxHashMap<MonoItem<'tcx>, (Linkage, Visibility)>,
	size_estimate: Option<usize>,
	primary: bool,
	/// True if this is CGU is used to hold code coverage information for dead code,
	/// false otherwise.
	is_code_coverage_dead_code_cgu: bool,
	}

	/// Specifies the linkage type for a `MonoItem`.
	///
	/// See <https://llvm.org/docs/LangRef.html#linkage-types> for more details about these variants.
	#[derive(Copy, Clone, PartialEq, Debug, TyEncodable, TyDecodable, HashStable)]
	pub enum Linkage {
	External,
	AvailableExternally,
	LinkOnceAny,
	LinkOnceODR,
	WeakAny,
	WeakODR,
	Appending,
	Internal,
	Private,
	ExternalWeak,
	Common,
	}

	#[derive(Copy, Clone, PartialEq, Debug, HashStable)]
	pub enum Visibility {
	Default,
	Hidden,
	Protected,
	}

	impl<'tcx> CodegenUnit<'tcx> {
	#[inline]
	pub fn new(name: Symbol) -> CodegenUnit<'tcx> {
	CodegenUnit {
	name,
	items: Default::default(),
	size_estimate: None,
	primary: false,
	is_code_coverage_dead_code_cgu: false,
	}
	}

	pub fn name(&self) -> Symbol {
	self.name
	}

	pub fn set_name(&mut self, name: Symbol) {
	self.name = name;
	}

	pub fn is_primary(&self) -> bool {
	self.primary
	}

	pub fn make_primary(&mut self) {
	self.primary = true;
	}

	pub fn items(&self) -> &FxHashMap<MonoItem<'tcx>, (Linkage, Visibility)> {
	&self.items
	}

	pub fn items_mut(&mut self) -> &mut FxHashMap<MonoItem<'tcx>, (Linkage, Visibility)> {
	&mut self.items
	}

	pub fn is_code_coverage_dead_code_cgu(&self) -> bool {
	self.is_code_coverage_dead_code_cgu
	}

	/// Marks this CGU as the one used to contain code coverage information for dead code.
	pub fn make_code_coverage_dead_code_cgu(&mut self) {
	self.is_code_coverage_dead_code_cgu = true;
	}

	pub fn mangle_name(human_readable_name: &str) -> String {
	// We generate a 80 bit hash from the name. This should be enough to
	// avoid collisions and is still reasonably short for filenames.
	let mut hasher = StableHasher::new();
	human_readable_name.hash(&mut hasher);
	let hash: u128 = hasher.finish();
	let hash = hash & ((1u128 << 80) - 1);
	base_n::encode(hash, base_n::CASE_INSENSITIVE)
	}

	pub fn estimate_size(&mut self, tcx: TyCtxt<'tcx>) {
	// Estimate the size of a codegen unit as (approximately) the number of MIR
	// statements it corresponds to.
	self.size_estimate = Some(self.items.keys().map(\|mi\| mi.size_estimate(tcx)).sum());
	}

	#[inline]
	pub fn size_estimate(&self) -> usize {
	// Should only be called if `estimate_size` has previously been called.
	self.size_estimate.expect("estimate_size must be called before getting a size_estimate")
	}

	pub fn modify_size_estimate(&mut self, delta: usize) {
	assert!(self.size_estimate.is_some());
	if let Some(size_estimate) = self.size_estimate {
	self.size_estimate = Some(size_estimate + delta);
	}
	}

	pub fn contains_item(&self, item: &MonoItem<'tcx>) -> bool {
	self.items().contains_key(item)
	}

	pub fn work_product_id(&self) -> WorkProductId {
	WorkProductId::from_cgu_name(self.name().as_str())
	}

	pub fn previous_work_product(&self, tcx: TyCtxt<'_>) -> WorkProduct {
	let work_product_id = self.work_product_id();
	tcx.dep_graph
	.previous_work_product(&work_product_id)
	.unwrap_or_else(\|\| panic!("Could not find work-product for CGU `{}`", self.name()))
	}

	pub fn items_in_deterministic_order(
	&self,
	tcx: TyCtxt<'tcx>,
	) -> Vec<(MonoItem<'tcx>, (Linkage, Visibility))> {
	// The codegen tests rely on items being process in the same order as
	// they appear in the file, so for local items, we sort by node_id first
	#[derive(PartialEq, Eq, PartialOrd, Ord)]
	pub struct ItemSortKey<'tcx>(Option<usize>, SymbolName<'tcx>);

	fn item_sort_key<'tcx>(tcx: TyCtxt<'tcx>, item: MonoItem<'tcx>) -> ItemSortKey<'tcx> {
	ItemSortKey(
	match item {
	MonoItem::Fn(ref instance) => {
	match instance.def {
	// We only want to take HirIds of user-defined
	// instances into account. The others don't matter for
	// the codegen tests and can even make item order
	// unstable.
	InstanceDef::Item(def) => def.did.as_local().map(Idx::index),
	InstanceDef::VTableShim(..)
	\| InstanceDef::ReifyShim(..)
	\| InstanceDef::Intrinsic(..)
	\| InstanceDef::FnPtrShim(..)
	\| InstanceDef::Virtual(..)
	\| InstanceDef::ClosureOnceShim { .. }
	\| InstanceDef::DropGlue(..)
	\| InstanceDef::CloneShim(..) => None,
	}
	}
	MonoItem::Static(def_id) => def_id.as_local().map(Idx::index),
	MonoItem::GlobalAsm(item_id) => Some(item_id.owner_id.def_id.index()),
	},
	item.symbol_name(tcx),
	)
	}

	let mut items: Vec<_> = self.items().iter().map(\|(&i, &l)\| (i, l)).collect();
	items.sort_by_cached_key(\|&(i, _)\| item_sort_key(tcx, i));
	items
	}

	pub fn codegen_dep_node(&self, tcx: TyCtxt<'tcx>) -> DepNode {
	crate::dep_graph::make_compile_codegen_unit(tcx, self.name())
	}
	}

	impl<'a, 'tcx> HashStable<StableHashingContext<'a>> for CodegenUnit<'tcx> {
	fn hash_stable(&self, hcx: &mut StableHashingContext<'a>, hasher: &mut StableHasher) {
	let CodegenUnit {
	ref items,
	name,
	// The size estimate is not relevant to the hash
	size_estimate: _,
	primary: _,
	is_code_coverage_dead_code_cgu,
	} = *self;

	name.hash_stable(hcx, hasher);
	is_code_coverage_dead_code_cgu.hash_stable(hcx, hasher);

	let mut items: Vec<(Fingerprint, _)> = items
	.iter()
	.map(\|(mono_item, &attrs)\| {
	let mut hasher = StableHasher::new();
	mono_item.hash_stable(hcx, &mut hasher);
	let mono_item_fingerprint = hasher.finish();
	(mono_item_fingerprint, attrs)
	})
	.collect();

	items.sort_unstable_by_key(\|i\| i.0);
	items.hash_stable(hcx, hasher);
	}
	}

	pub struct CodegenUnitNameBuilder<'tcx> {
	tcx: TyCtxt<'tcx>,
	cache: FxHashMap<CrateNum, String>,
	}

	impl<'tcx> CodegenUnitNameBuilder<'tcx> {
	pub fn new(tcx: TyCtxt<'tcx>) -> Self {
	CodegenUnitNameBuilder { tcx, cache: Default::default() }
	}

	/// CGU names should fulfill the following requirements:
	/// - They should be able to act as a file name on any kind of file system
	/// - They should not collide with other CGU names, even for different versions
	/// of the same crate.
	///
	/// Consequently, we don't use special characters except for '.' and '-' and we
	/// prefix each name with the crate-name and crate-disambiguator.
	///
	/// This function will build CGU names of the form:
	///
	/// ```text
	/// <crate-name>.<crate-disambiguator>[-in-<local-crate-id>](-<component>)*[.<special-suffix>]
	/// <local-crate-id> = <local-crate-name>.<local-crate-disambiguator>
	/// ```
	///
	/// The '.' before `<special-suffix>` makes sure that names with a special
	/// suffix can never collide with a name built out of regular Rust
	/// identifiers (e.g., module paths).
	pub fn build_cgu_name<I, C, S>(
	&mut self,
	cnum: CrateNum,
	components: I,
	special_suffix: Option<S>,
	) -> Symbol
	where
	I: IntoIterator<Item = C>,
	C: fmt::Display,
	S: fmt::Display,
	{
	let cgu_name = self.build_cgu_name_no_mangle(cnum, components, special_suffix);

	if self.tcx.sess.opts.unstable_opts.human_readable_cgu_names {
	cgu_name
	} else {
	Symbol::intern(&CodegenUnit::mangle_name(cgu_name.as_str()))
	}
	}

	/// Same as `CodegenUnit::build_cgu_name()` but will never mangle the
	/// resulting name.
	pub fn build_cgu_name_no_mangle<I, C, S>(
	&mut self,
	cnum: CrateNum,
	components: I,
	special_suffix: Option<S>,
	) -> Symbol
	where
	I: IntoIterator<Item = C>,
	C: fmt::Display,
	S: fmt::Display,
	{
	use std::fmt::Write;

	let mut cgu_name = String::with_capacity(64);

	// Start out with the crate name and disambiguator
	let tcx = self.tcx;
	let crate_prefix = self.cache.entry(cnum).or_insert_with(\|\| {
	// Whenever the cnum is not LOCAL_CRATE we also mix in the
	// local crate's ID. Otherwise there can be collisions between CGUs
	// instantiating stuff for upstream crates.
	let local_crate_id = if cnum != LOCAL_CRATE {
	let local_stable_crate_id = tcx.sess.local_stable_crate_id();
	format!(
	"-in-{}.{:08x}",
	tcx.crate_name(LOCAL_CRATE),
	local_stable_crate_id.to_u64() as u32,
	)
	} else {
	String::new()
	};

	let stable_crate_id = tcx.sess.local_stable_crate_id();
	format!(
	"{}.{:08x}{}",
	tcx.crate_name(cnum),
	stable_crate_id.to_u64() as u32,
	local_crate_id,
	)
	});

	write!(cgu_name, "{}", crate_prefix).unwrap();

	// Add the components
	for component in components {
	write!(cgu_name, "-{}", component).unwrap();
	}

	if let Some(special_suffix) = special_suffix {
	// We add a dot in here so it cannot clash with anything in a regular
	// Rust identifier
	write!(cgu_name, ".{}", special_suffix).unwrap();
	}

	Symbol::intern(&cgu_name)
	}
	}