1 use rustc::hir::def_id::LOCAL_CRATE;
2 use rustc::mir::mono::MonoItem;
3 use rustc::session::config::OptLevel;
4 use rustc::ty::{self, TyCtxt, Instance};
5 use rustc::ty::subst::InternalSubsts;
6 use rustc::ty::print::obsolete::DefPathBasedNames;
7 use syntax::attr::InlineAttr;
9 use rustc::mir::mono::Linkage;
10 use syntax_pos::symbol::InternedString;
11 use syntax::source_map::Span;
13 /// Describes how a monomorphization will be instantiated in object files.
14 #[derive(PartialEq, Eq, Clone, Copy, Debug, Hash)]
15 pub enum InstantiationMode {
16 /// There will be exactly one instance of the given MonoItem. It will have
17 /// external linkage so that it can be linked to from other codegen units.
19 /// In some compilation scenarios we may decide to take functions that
20 /// are typically `LocalCopy` and instead move them to `GloballyShared`
21 /// to avoid codegenning them a bunch of times. In this situation,
22 /// however, our local copy may conflict with other crates also
23 /// inlining the same function.
25 /// This flag indicates that this situation is occurring, and informs
26 /// symbol name calculation that some extra mangling is needed to
27 /// avoid conflicts. Note that this may eventually go away entirely if
28 /// ThinLTO enables us to *always* have a globally shared instance of a
29 /// function within one crate's compilation.
33 /// Each codegen unit containing a reference to the given MonoItem will
34 /// have its own private copy of the function (with internal linkage).
38 pub trait MonoItemExt<'tcx>: fmt::Debug {
39 fn as_mono_item(&self) -> &MonoItem<'tcx>;
41 fn is_generic_fn(&self) -> bool {
42 match *self.as_mono_item() {
43 MonoItem::Fn(ref instance) => {
44 instance.substs.non_erasable_generics().next().is_some()
46 MonoItem::Static(..) |
47 MonoItem::GlobalAsm(..) => false,
51 fn symbol_name(&self, tcx: TyCtxt<'tcx, 'tcx>) -> ty::SymbolName {
52 match *self.as_mono_item() {
53 MonoItem::Fn(instance) => tcx.symbol_name(instance),
54 MonoItem::Static(def_id) => {
55 tcx.symbol_name(Instance::mono(tcx, def_id))
57 MonoItem::GlobalAsm(hir_id) => {
58 let def_id = tcx.hir().local_def_id_from_hir_id(hir_id);
60 name: InternedString::intern(&format!("global_asm_{:?}", def_id))
65 fn instantiation_mode(&self,
66 tcx: TyCtxt<'tcx, 'tcx>)
67 -> InstantiationMode {
68 let inline_in_all_cgus =
69 tcx.sess.opts.debugging_opts.inline_in_all_cgus.unwrap_or_else(|| {
70 tcx.sess.opts.optimize != OptLevel::No
71 }) && !tcx.sess.opts.cg.link_dead_code;
73 match *self.as_mono_item() {
74 MonoItem::Fn(ref instance) => {
75 let entry_def_id = tcx.entry_fn(LOCAL_CRATE).map(|(id, _)| id);
76 // If this function isn't inlined or otherwise has explicit
77 // linkage, then we'll be creating a globally shared version.
78 if self.explicit_linkage(tcx).is_some() ||
79 !instance.def.requires_local(tcx) ||
80 Some(instance.def_id()) == entry_def_id
82 return InstantiationMode::GloballyShared { may_conflict: false }
85 // At this point we don't have explicit linkage and we're an
86 // inlined function. If we're inlining into all CGUs then we'll
87 // be creating a local copy per CGU
88 if inline_in_all_cgus {
89 return InstantiationMode::LocalCopy
92 // Finally, if this is `#[inline(always)]` we're sure to respect
93 // that with an inline copy per CGU, but otherwise we'll be
94 // creating one copy of this `#[inline]` function which may
95 // conflict with upstream crates as it could be an exported
97 match tcx.codegen_fn_attrs(instance.def_id()).inline {
98 InlineAttr::Always => InstantiationMode::LocalCopy,
100 InstantiationMode::GloballyShared { may_conflict: true }
104 MonoItem::Static(..) |
105 MonoItem::GlobalAsm(..) => {
106 InstantiationMode::GloballyShared { may_conflict: false }
111 fn explicit_linkage(&self, tcx: TyCtxt<'tcx, 'tcx>) -> Option<Linkage> {
112 let def_id = match *self.as_mono_item() {
113 MonoItem::Fn(ref instance) => instance.def_id(),
114 MonoItem::Static(def_id) => def_id,
115 MonoItem::GlobalAsm(..) => return None,
118 let codegen_fn_attrs = tcx.codegen_fn_attrs(def_id);
119 codegen_fn_attrs.linkage
122 /// Returns `true` if this instance is instantiable - whether it has no unsatisfied
125 /// In order to codegen an item, all of its predicates must hold, because
126 /// otherwise the item does not make sense. Type-checking ensures that
127 /// the predicates of every item that is *used by* a valid item *do*
128 /// hold, so we can rely on that.
130 /// However, we codegen collector roots (reachable items) and functions
131 /// in vtables when they are seen, even if they are not used, and so they
132 /// might not be instantiable. For example, a programmer can define this
135 /// pub fn foo<'a>(s: &'a mut ()) where &'a mut (): Clone {
136 /// <&mut () as Clone>::clone(&s);
139 /// That function can't be codegened, because the method `<&mut () as Clone>::clone`
140 /// does not exist. Luckily for us, that function can't ever be used,
141 /// because that would require for `&'a mut (): Clone` to hold, so we
142 /// can just not emit any code, or even a linker reference for it.
144 /// Similarly, if a vtable method has such a signature, and therefore can't
145 /// be used, we can just not emit it and have a placeholder (a null pointer,
146 /// which will never be accessed) in its place.
147 fn is_instantiable(&self, tcx: TyCtxt<'tcx, 'tcx>) -> bool {
148 debug!("is_instantiable({:?})", self);
149 let (def_id, substs) = match *self.as_mono_item() {
150 MonoItem::Fn(ref instance) => (instance.def_id(), instance.substs),
151 MonoItem::Static(def_id) => (def_id, InternalSubsts::empty()),
152 // global asm never has predicates
153 MonoItem::GlobalAsm(..) => return true
156 tcx.substitute_normalize_and_test_predicates((def_id, &substs))
159 fn to_string(&self, tcx: TyCtxt<'tcx, 'tcx>, debug: bool) -> String {
160 return match *self.as_mono_item() {
161 MonoItem::Fn(instance) => {
162 to_string_internal(tcx, "fn ", instance, debug)
164 MonoItem::Static(def_id) => {
165 let instance = Instance::new(def_id, tcx.intern_substs(&[]));
166 to_string_internal(tcx, "static ", instance, debug)
168 MonoItem::GlobalAsm(..) => {
169 "global_asm".to_string()
173 fn to_string_internal<'a, 'tcx>(tcx: TyCtxt<'tcx, 'tcx>,
175 instance: Instance<'tcx>,
178 let mut result = String::with_capacity(32);
179 result.push_str(prefix);
180 let printer = DefPathBasedNames::new(tcx, false, false);
181 printer.push_instance_as_string(instance, &mut result, debug);
186 fn local_span(&self, tcx: TyCtxt<'tcx, 'tcx>) -> Option<Span> {
187 match *self.as_mono_item() {
188 MonoItem::Fn(Instance { def, .. }) => {
189 tcx.hir().as_local_hir_id(def.def_id())
191 MonoItem::Static(def_id) => {
192 tcx.hir().as_local_hir_id(def_id)
194 MonoItem::GlobalAsm(hir_id) => {
197 }.map(|hir_id| tcx.hir().span_by_hir_id(hir_id))
201 impl MonoItemExt<'tcx> for MonoItem<'tcx> {
202 fn as_mono_item(&self) -> &MonoItem<'tcx> {