rust/src/librustc/mir/mono.rs

use crate::hir::def_id::{DefId, CrateNum, LOCAL_CRATE};
use crate::hir::HirId;
use syntax::symbol::InternedString;
use syntax::attr::InlineAttr;
use syntax::source_map::Span;
use crate::ty::{Instance, InstanceDef, TyCtxt, SymbolName, subst::InternalSubsts};
use crate::util::nodemap::FxHashMap;
use crate::ty::print::obsolete::DefPathBasedNames;
use crate::dep_graph::{WorkProductId, DepNode, WorkProduct, DepConstructor};
use rustc_data_structures::base_n;
use rustc_data_structures::stable_hasher::{HashStable, StableHasher};
use crate::ich::{Fingerprint, StableHashingContext, NodeIdHashingMode};
use crate::session::config::OptLevel;
use std::fmt;
use std::hash::Hash;

/// Describes how a monomorphization will be instantiated in object files.
#[derive(PartialEq, Eq, Clone, Copy, Debug, Hash)]
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)]
pub enum MonoItem<'tcx> {
    Fn(Instance<'tcx>),
    Static(DefId),
    GlobalAsm(HirId),
}

impl<'tcx> MonoItem<'tcx> {
    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 {
        match *self {
            MonoItem::Fn(instance) => tcx.symbol_name(instance),
            MonoItem::Static(def_id) => {
                tcx.symbol_name(Instance::mono(tcx, def_id))
            }
            MonoItem::GlobalAsm(hir_id) => {
                let def_id = tcx.hir().local_def_id(hir_id);
                SymbolName {
                    name: InternedString::intern(&format!("global_asm_{:?}", def_id))
                }
            }
        }
    }

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

        match *self {
            MonoItem::Fn(ref instance) => {
                let entry_def_id = tcx.entry_fn(LOCAL_CRATE).map(|(id, _)| id);
                // If this function isn't inlined or otherwise has explicit
                // linkage, then we'll be creating a globally shared version.
                if self.explicit_linkage(tcx).is_some() ||
                    !instance.def.requires_local(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 inline_in_all_cgus {
                    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.substitute_normalize_and_test_predicates((def_id, &substs))
    }

    pub fn to_string(&self, tcx: TyCtxt<'tcx>, debug: bool) -> String {
        return match *self {
            MonoItem::Fn(instance) => {
                to_string_internal(tcx, "fn ", instance, debug)
            },
            MonoItem::Static(def_id) => {
                let instance = Instance::new(def_id, tcx.intern_substs(&[]));
                to_string_internal(tcx, "static ", instance, debug)
            },
            MonoItem::GlobalAsm(..) => {
                "global_asm".to_string()
            }
        };

        fn to_string_internal<'tcx>(
            tcx: TyCtxt<'tcx>,
            prefix: &str,
            instance: Instance<'tcx>,
            debug: bool,
        ) -> String {
            let mut result = String::with_capacity(32);
            result.push_str(prefix);
            let printer = DefPathBasedNames::new(tcx, false, false);
            printer.push_instance_as_string(instance, &mut result, debug);
            result
        }
    }

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

impl<'a, 'tcx> HashStable<StableHashingContext<'a>> for MonoItem<'tcx> {
    fn hash_stable(&self, hcx: &mut StableHashingContext<'a>, hasher: &mut StableHasher) {
        ::std::mem::discriminant(self).hash_stable(hcx, hasher);

        match *self {
            MonoItem::Fn(ref instance) => {
                instance.hash_stable(hcx, hasher);
            }
            MonoItem::Static(def_id) => {
                def_id.hash_stable(hcx, hasher);
            }
            MonoItem::GlobalAsm(node_id) => {
                hcx.with_node_id_hashing_mode(NodeIdHashingMode::HashDefPath, |hcx| {
                    node_id.hash_stable(hcx, hasher);
                })
            }
        }
    }
}

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: InternedString,
    items: FxHashMap<MonoItem<'tcx>, (Linkage, Visibility)>,
    size_estimate: Option<usize>,
}

#[derive(Copy, Clone, PartialEq, Eq, Hash, Debug, RustcEncodable, RustcDecodable)]
pub enum Linkage {
    External,
    AvailableExternally,
    LinkOnceAny,
    LinkOnceODR,
    WeakAny,
    WeakODR,
    Appending,
    Internal,
    Private,
    ExternalWeak,
    Common,
}

impl_stable_hash_for!(enum self::Linkage {
    External,
    AvailableExternally,
    LinkOnceAny,
    LinkOnceODR,
    WeakAny,
    WeakODR,
    Appending,
    Internal,
    Private,
    ExternalWeak,
    Common
});

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

impl_stable_hash_for!(enum self::Visibility {
    Default,
    Hidden,
    Protected
});

impl<'tcx> CodegenUnit<'tcx> {
    pub fn new(name: InternedString) -> CodegenUnit<'tcx> {
        CodegenUnit {
            name: name,
            items: Default::default(),
            size_estimate: None,
        }
    }

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

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

    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 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());
    }

    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 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(Option<HirId>, SymbolName);

        fn item_sort_key<'tcx>(tcx: TyCtxt<'tcx>, item: MonoItem<'tcx>) -> ItemSortKey {
            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_id) => {
                            tcx.hir().as_local_hir_id(def_id)
                        }
                        InstanceDef::VtableShim(..) |
                        InstanceDef::ReifyShim(..) |
                        InstanceDef::Intrinsic(..) |
                        InstanceDef::FnPtrShim(..) |
                        InstanceDef::Virtual(..) |
                        InstanceDef::ClosureOnceShim { .. } |
                        InstanceDef::DropGlue(..) |
                        InstanceDef::CloneShim(..) => {
                            None
                        }
                    }
                }
                MonoItem::Static(def_id) => {
                    tcx.hir().as_local_hir_id(def_id)
                }
                MonoItem::GlobalAsm(hir_id) => {
                    Some(hir_id)
                }
            }, 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 {
        DepNode::new(tcx, DepConstructor::CompileCodegenUnit(self.name().clone()))
    }
}

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: _,
        } = *self;

        name.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 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:
    ///
    /// ```
    /// <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>)
                                   -> InternedString
        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.debugging_opts.human_readable_cgu_names {
            cgu_name
        } else {
            let cgu_name = &cgu_name.as_str()[..];
            InternedString::intern(&CodegenUnit::mangle_name(cgu_name))
        }
    }

    /// 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>)
                                             -> InternedString
        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_crate_disambiguator =
                    format!("{}", tcx.crate_disambiguator(LOCAL_CRATE));
                format!("-in-{}.{}",
                        tcx.crate_name(LOCAL_CRATE),
                        &local_crate_disambiguator[0 .. 8])
            } else {
                String::new()
            };

            let crate_disambiguator = tcx.crate_disambiguator(cnum).to_string();
            // Using a shortened disambiguator of about 40 bits
            format!("{}.{}{}",
                tcx.crate_name(cnum),
                &crate_disambiguator[0 .. 8],
                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();
        }

        InternedString::intern(&cgu_name[..])
    }
}