src/librustc/mir/mono.rs

   1 use crate::hir::def_id::{DefId, CrateNum, LOCAL_CRATE};
   2 use crate::hir::HirId;
   3 use syntax::symbol::Symbol;
   4 use syntax::attr::InlineAttr;
   5 use syntax::source_map::Span;
   6 use crate::ty::{Instance, InstanceDef, TyCtxt, SymbolName, subst::InternalSubsts};
   7 use crate::util::nodemap::FxHashMap;
   8 use crate::ty::print::obsolete::DefPathBasedNames;
   9 use crate::dep_graph::{WorkProductId, DepNode, WorkProduct, DepConstructor};
  10 use rustc_data_structures::base_n;
  11 use rustc_data_structures::stable_hasher::{HashStable, StableHasher};
  12 use crate::ich::{Fingerprint, StableHashingContext, NodeIdHashingMode};
  13 use crate::session::config::OptLevel;
  14 use std::fmt;
  15 use std::hash::Hash;
  16
  17 /// Describes how a monomorphization will be instantiated in object files.
  18 #[derive(PartialEq)]
  19 pub enum InstantiationMode {
  20     /// There will be exactly one instance of the given MonoItem. It will have
  21     /// external linkage so that it can be linked to from other codegen units.
  22     GloballyShared {
  23         /// In some compilation scenarios we may decide to take functions that
  24         /// are typically `LocalCopy` and instead move them to `GloballyShared`
  25         /// to avoid codegenning them a bunch of times. In this situation,
  26         /// however, our local copy may conflict with other crates also
  27         /// inlining the same function.
  28         ///
  29         /// This flag indicates that this situation is occurring, and informs
  30         /// symbol name calculation that some extra mangling is needed to
  31         /// avoid conflicts. Note that this may eventually go away entirely if
  32         /// ThinLTO enables us to *always* have a globally shared instance of a
  33         /// function within one crate's compilation.
  34         may_conflict: bool,
  35     },
  36
  37     /// Each codegen unit containing a reference to the given MonoItem will
  38     /// have its own private copy of the function (with internal linkage).
  39     LocalCopy,
  40 }
  41
  42 #[derive(PartialEq, Eq, Clone, Copy, Debug, Hash)]
  43 pub enum MonoItem<'tcx> {
  44     Fn(Instance<'tcx>),
  45     Static(DefId),
  46     GlobalAsm(HirId),
  47 }
  48
  49 impl<'tcx> MonoItem<'tcx> {
  50     pub fn size_estimate(&self, tcx: TyCtxt<'tcx>) -> usize {
  51         match *self {
  52             MonoItem::Fn(instance) => {
  53                 // Estimate the size of a function based on how many statements
  54                 // it contains.
  55                 tcx.instance_def_size_estimate(instance.def)
  56             },
  57             // Conservatively estimate the size of a static declaration
  58             // or assembly to be 1.
  59             MonoItem::Static(_) |
  60             MonoItem::GlobalAsm(_) => 1,
  61         }
  62     }
  63
  64     pub fn is_generic_fn(&self) -> bool {
  65         match *self {
  66             MonoItem::Fn(ref instance) => {
  67                 instance.substs.non_erasable_generics().next().is_some()
  68             }
  69             MonoItem::Static(..) |
  70             MonoItem::GlobalAsm(..) => false,
  71         }
  72     }
  73
  74     pub fn symbol_name(&self, tcx: TyCtxt<'tcx>) -> SymbolName {
  75         match *self {
  76             MonoItem::Fn(instance) => tcx.symbol_name(instance),
  77             MonoItem::Static(def_id) => {
  78                 tcx.symbol_name(Instance::mono(tcx, def_id))
  79             }
  80             MonoItem::GlobalAsm(hir_id) => {
  81                 let def_id = tcx.hir().local_def_id(hir_id);
  82                 SymbolName {
  83                     name: Symbol::intern(&format!("global_asm_{:?}", def_id))
  84                 }
  85             }
  86         }
  87     }
  88
  89     pub fn instantiation_mode(&self, tcx: TyCtxt<'tcx>) -> InstantiationMode {
  90         let inline_in_all_cgus =
  91             tcx.sess.opts.debugging_opts.inline_in_all_cgus.unwrap_or_else(|| {
  92                 tcx.sess.opts.optimize != OptLevel::No
  93             }) && !tcx.sess.opts.cg.link_dead_code;
  94
  95         match *self {
  96             MonoItem::Fn(ref instance) => {
  97                 let entry_def_id = tcx.entry_fn(LOCAL_CRATE).map(|(id, _)| id);
  98                 // If this function isn't inlined or otherwise has explicit
  99                 // linkage, then we'll be creating a globally shared version.
 100                 if self.explicit_linkage(tcx).is_some() ||
 101                     !instance.def.requires_local(tcx) ||
 102                     Some(instance.def_id()) == entry_def_id
 103                 {
 104                     return InstantiationMode::GloballyShared  { may_conflict: false }
 105                 }
 106
 107                 // At this point we don't have explicit linkage and we're an
 108                 // inlined function. If we're inlining into all CGUs then we'll
 109                 // be creating a local copy per CGU
 110                 if inline_in_all_cgus {
 111                     return InstantiationMode::LocalCopy
 112                 }
 113
 114                 // Finally, if this is `#[inline(always)]` we're sure to respect
 115                 // that with an inline copy per CGU, but otherwise we'll be
 116                 // creating one copy of this `#[inline]` function which may
 117                 // conflict with upstream crates as it could be an exported
 118                 // symbol.
 119                 match tcx.codegen_fn_attrs(instance.def_id()).inline {
 120                     InlineAttr::Always => InstantiationMode::LocalCopy,
 121                     _ => {
 122                         InstantiationMode::GloballyShared  { may_conflict: true }
 123                     }
 124                 }
 125             }
 126             MonoItem::Static(..) |
 127             MonoItem::GlobalAsm(..) => {
 128                 InstantiationMode::GloballyShared { may_conflict: false }
 129             }
 130         }
 131     }
 132
 133     pub fn explicit_linkage(&self, tcx: TyCtxt<'tcx>) -> Option<Linkage> {
 134         let def_id = match *self {
 135             MonoItem::Fn(ref instance) => instance.def_id(),
 136             MonoItem::Static(def_id) => def_id,
 137             MonoItem::GlobalAsm(..) => return None,
 138         };
 139
 140         let codegen_fn_attrs = tcx.codegen_fn_attrs(def_id);
 141         codegen_fn_attrs.linkage
 142     }
 143
 144     /// Returns `true` if this instance is instantiable - whether it has no unsatisfied
 145     /// predicates.
 146     ///
 147     /// In order to codegen an item, all of its predicates must hold, because
 148     /// otherwise the item does not make sense. Type-checking ensures that
 149     /// the predicates of every item that is *used by* a valid item *do*
 150     /// hold, so we can rely on that.
 151     ///
 152     /// However, we codegen collector roots (reachable items) and functions
 153     /// in vtables when they are seen, even if they are not used, and so they
 154     /// might not be instantiable. For example, a programmer can define this
 155     /// public function:
 156     ///
 157     ///     pub fn foo<'a>(s: &'a mut ()) where &'a mut (): Clone {
 158     ///         <&mut () as Clone>::clone(&s);
 159     ///     }
 160     ///
 161     /// That function can't be codegened, because the method `<&mut () as Clone>::clone`
 162     /// does not exist. Luckily for us, that function can't ever be used,
 163     /// because that would require for `&'a mut (): Clone` to hold, so we
 164     /// can just not emit any code, or even a linker reference for it.
 165     ///
 166     /// Similarly, if a vtable method has such a signature, and therefore can't
 167     /// be used, we can just not emit it and have a placeholder (a null pointer,
 168     /// which will never be accessed) in its place.
 169     pub fn is_instantiable(&self, tcx: TyCtxt<'tcx>) -> bool {
 170         debug!("is_instantiable({:?})", self);
 171         let (def_id, substs) = match *self {
 172             MonoItem::Fn(ref instance) => (instance.def_id(), instance.substs),
 173             MonoItem::Static(def_id) => (def_id, InternalSubsts::empty()),
 174             // global asm never has predicates
 175             MonoItem::GlobalAsm(..) => return true
 176         };
 177
 178         tcx.substitute_normalize_and_test_predicates((def_id, &substs))
 179     }
 180
 181     pub fn to_string(&self, tcx: TyCtxt<'tcx>, debug: bool) -> String {
 182         return match *self {
 183             MonoItem::Fn(instance) => {
 184                 to_string_internal(tcx, "fn ", instance, debug)
 185             },
 186             MonoItem::Static(def_id) => {
 187                 let instance = Instance::new(def_id, tcx.intern_substs(&[]));
 188                 to_string_internal(tcx, "static ", instance, debug)
 189             },
 190             MonoItem::GlobalAsm(..) => {
 191                 "global_asm".to_string()
 192             }
 193         };
 194
 195         fn to_string_internal<'tcx>(
 196             tcx: TyCtxt<'tcx>,
 197             prefix: &str,
 198             instance: Instance<'tcx>,
 199             debug: bool,
 200         ) -> String {
 201             let mut result = String::with_capacity(32);
 202             result.push_str(prefix);
 203             let printer = DefPathBasedNames::new(tcx, false, false);
 204             printer.push_instance_as_string(instance, &mut result, debug);
 205             result
 206         }
 207     }
 208
 209     pub fn local_span(&self, tcx: TyCtxt<'tcx>) -> Option<Span> {
 210         match *self {
 211             MonoItem::Fn(Instance { def, .. }) => {
 212                 tcx.hir().as_local_hir_id(def.def_id())
 213             }
 214             MonoItem::Static(def_id) => {
 215                 tcx.hir().as_local_hir_id(def_id)
 216             }
 217             MonoItem::GlobalAsm(hir_id) => {
 218                 Some(hir_id)
 219             }
 220         }.map(|hir_id| tcx.hir().span(hir_id))
 221     }
 222 }
 223
 224 impl<'a, 'tcx> HashStable<StableHashingContext<'a>> for MonoItem<'tcx> {
 225     fn hash_stable(&self, hcx: &mut StableHashingContext<'a>, hasher: &mut StableHasher) {
 226         ::std::mem::discriminant(self).hash_stable(hcx, hasher);
 227
 228         match *self {
 229             MonoItem::Fn(ref instance) => {
 230                 instance.hash_stable(hcx, hasher);
 231             }
 232             MonoItem::Static(def_id) => {
 233                 def_id.hash_stable(hcx, hasher);
 234             }
 235             MonoItem::GlobalAsm(node_id) => {
 236                 hcx.with_node_id_hashing_mode(NodeIdHashingMode::HashDefPath, |hcx| {
 237                     node_id.hash_stable(hcx, hasher);
 238                 })
 239             }
 240         }
 241     }
 242 }
 243
 244 pub struct CodegenUnit<'tcx> {
 245     /// A name for this CGU. Incremental compilation requires that
 246     /// name be unique amongst **all** crates. Therefore, it should
 247     /// contain something unique to this crate (e.g., a module path)
 248     /// as well as the crate name and disambiguator.
 249     name: Symbol,
 250     items: FxHashMap<MonoItem<'tcx>, (Linkage, Visibility)>,
 251     size_estimate: Option<usize>,
 252 }
 253
 254 #[derive(Copy, Clone, PartialEq, Debug, RustcEncodable, RustcDecodable, HashStable)]
 255 pub enum Linkage {
 256     External,
 257     AvailableExternally,
 258     LinkOnceAny,
 259     LinkOnceODR,
 260     WeakAny,
 261     WeakODR,
 262     Appending,
 263     Internal,
 264     Private,
 265     ExternalWeak,
 266     Common,
 267 }
 268
 269 #[derive(Copy, Clone, PartialEq, Debug, HashStable)]
 270 pub enum Visibility {
 271     Default,
 272     Hidden,
 273     Protected,
 274 }
 275
 276 impl<'tcx> CodegenUnit<'tcx> {
 277     pub fn new(name: Symbol) -> CodegenUnit<'tcx> {
 278         CodegenUnit {
 279             name: name,
 280             items: Default::default(),
 281             size_estimate: None,
 282         }
 283     }
 284
 285     pub fn name(&self) -> Symbol {
 286         self.name
 287     }
 288
 289     pub fn set_name(&mut self, name: Symbol) {
 290         self.name = name;
 291     }
 292
 293     pub fn items(&self) -> &FxHashMap<MonoItem<'tcx>, (Linkage, Visibility)> {
 294         &self.items
 295     }
 296
 297     pub fn items_mut(&mut self)
 298         -> &mut FxHashMap<MonoItem<'tcx>, (Linkage, Visibility)>
 299     {
 300         &mut self.items
 301     }
 302
 303     pub fn mangle_name(human_readable_name: &str) -> String {
 304         // We generate a 80 bit hash from the name. This should be enough to
 305         // avoid collisions and is still reasonably short for filenames.
 306         let mut hasher = StableHasher::new();
 307         human_readable_name.hash(&mut hasher);
 308         let hash: u128 = hasher.finish();
 309         let hash = hash & ((1u128 << 80) - 1);
 310         base_n::encode(hash, base_n::CASE_INSENSITIVE)
 311     }
 312
 313     pub fn estimate_size(&mut self, tcx: TyCtxt<'tcx>) {
 314         // Estimate the size of a codegen unit as (approximately) the number of MIR
 315         // statements it corresponds to.
 316         self.size_estimate = Some(self.items.keys().map(|mi| mi.size_estimate(tcx)).sum());
 317     }
 318
 319     pub fn size_estimate(&self) -> usize {
 320         // Should only be called if `estimate_size` has previously been called.
 321         self.size_estimate.expect("estimate_size must be called before getting a size_estimate")
 322     }
 323
 324     pub fn modify_size_estimate(&mut self, delta: usize) {
 325         assert!(self.size_estimate.is_some());
 326         if let Some(size_estimate) = self.size_estimate {
 327             self.size_estimate = Some(size_estimate + delta);
 328         }
 329     }
 330
 331     pub fn contains_item(&self, item: &MonoItem<'tcx>) -> bool {
 332         self.items().contains_key(item)
 333     }
 334
 335     pub fn work_product_id(&self) -> WorkProductId {
 336         WorkProductId::from_cgu_name(&self.name().as_str())
 337     }
 338
 339     pub fn work_product(&self, tcx: TyCtxt<'_>) -> WorkProduct {
 340         let work_product_id = self.work_product_id();
 341         tcx.dep_graph
 342            .previous_work_product(&work_product_id)
 343            .unwrap_or_else(|| {
 344                 panic!("Could not find work-product for CGU `{}`", self.name())
 345             })
 346     }
 347
 348     pub fn items_in_deterministic_order(
 349         &self,
 350         tcx: TyCtxt<'tcx>,
 351     ) -> Vec<(MonoItem<'tcx>, (Linkage, Visibility))> {
 352         // The codegen tests rely on items being process in the same order as
 353         // they appear in the file, so for local items, we sort by node_id first
 354         #[derive(PartialEq, Eq, PartialOrd, Ord)]
 355         pub struct ItemSortKey(Option<HirId>, SymbolName);
 356
 357         fn item_sort_key<'tcx>(tcx: TyCtxt<'tcx>, item: MonoItem<'tcx>) -> ItemSortKey {
 358             ItemSortKey(match item {
 359                 MonoItem::Fn(ref instance) => {
 360                     match instance.def {
 361                         // We only want to take HirIds of user-defined
 362                         // instances into account. The others don't matter for
 363                         // the codegen tests and can even make item order
 364                         // unstable.
 365                         InstanceDef::Item(def_id) => {
 366                             tcx.hir().as_local_hir_id(def_id)
 367                         }
 368                         InstanceDef::VtableShim(..) |
 369                         InstanceDef::ReifyShim(..) |
 370                         InstanceDef::Intrinsic(..) |
 371                         InstanceDef::FnPtrShim(..) |
 372                         InstanceDef::Virtual(..) |
 373                         InstanceDef::ClosureOnceShim { .. } |
 374                         InstanceDef::DropGlue(..) |
 375                         InstanceDef::CloneShim(..) => {
 376                             None
 377                         }
 378                     }
 379                 }
 380                 MonoItem::Static(def_id) => {
 381                     tcx.hir().as_local_hir_id(def_id)
 382                 }
 383                 MonoItem::GlobalAsm(hir_id) => {
 384                     Some(hir_id)
 385                 }
 386             }, item.symbol_name(tcx))
 387         }
 388
 389         let mut items: Vec<_> = self.items().iter().map(|(&i, &l)| (i, l)).collect();
 390         items.sort_by_cached_key(|&(i, _)| item_sort_key(tcx, i));
 391         items
 392     }
 393
 394     pub fn codegen_dep_node(&self, tcx: TyCtxt<'tcx>) -> DepNode {
 395         DepNode::new(tcx, DepConstructor::CompileCodegenUnit(self.name().clone()))
 396     }
 397 }
 398
 399 impl<'a, 'tcx> HashStable<StableHashingContext<'a>> for CodegenUnit<'tcx> {
 400     fn hash_stable(&self, hcx: &mut StableHashingContext<'a>, hasher: &mut StableHasher) {
 401         let CodegenUnit {
 402             ref items,
 403             name,
 404             // The size estimate is not relevant to the hash
 405             size_estimate: _,
 406         } = *self;
 407
 408         name.hash_stable(hcx, hasher);
 409
 410         let mut items: Vec<(Fingerprint, _)> = items.iter().map(|(mono_item, &attrs)| {
 411             let mut hasher = StableHasher::new();
 412             mono_item.hash_stable(hcx, &mut hasher);
 413             let mono_item_fingerprint = hasher.finish();
 414             (mono_item_fingerprint, attrs)
 415         }).collect();
 416
 417         items.sort_unstable_by_key(|i| i.0);
 418         items.hash_stable(hcx, hasher);
 419     }
 420 }
 421
 422 pub struct CodegenUnitNameBuilder<'tcx> {
 423     tcx: TyCtxt<'tcx>,
 424     cache: FxHashMap<CrateNum, String>,
 425 }
 426
 427 impl CodegenUnitNameBuilder<'tcx> {
 428     pub fn new(tcx: TyCtxt<'tcx>) -> Self {
 429         CodegenUnitNameBuilder {
 430             tcx,
 431             cache: Default::default(),
 432         }
 433     }
 434
 435     /// CGU names should fulfill the following requirements:
 436     /// - They should be able to act as a file name on any kind of file system
 437     /// - They should not collide with other CGU names, even for different versions
 438     ///   of the same crate.
 439     ///
 440     /// Consequently, we don't use special characters except for '.' and '-' and we
 441     /// prefix each name with the crate-name and crate-disambiguator.
 442     ///
 443     /// This function will build CGU names of the form:
 444     ///
 445     /// ```
 446     /// <crate-name>.<crate-disambiguator>[-in-<local-crate-id>](-<component>)*[.<special-suffix>]
 447     /// <local-crate-id> = <local-crate-name>.<local-crate-disambiguator>
 448     /// ```
 449     ///
 450     /// The '.' before `<special-suffix>` makes sure that names with a special
 451     /// suffix can never collide with a name built out of regular Rust
 452     /// identifiers (e.g., module paths).
 453     pub fn build_cgu_name<I, C, S>(&mut self,
 454                                    cnum: CrateNum,
 455                                    components: I,
 456                                    special_suffix: Option<S>)
 457                                    -> Symbol
 458         where I: IntoIterator<Item=C>,
 459               C: fmt::Display,
 460               S: fmt::Display,
 461     {
 462         let cgu_name = self.build_cgu_name_no_mangle(cnum,
 463                                                      components,
 464                                                      special_suffix);
 465
 466         if self.tcx.sess.opts.debugging_opts.human_readable_cgu_names {
 467             cgu_name
 468         } else {
 469             let cgu_name = &cgu_name.as_str();
 470             Symbol::intern(&CodegenUnit::mangle_name(cgu_name))
 471         }
 472     }
 473
 474     /// Same as `CodegenUnit::build_cgu_name()` but will never mangle the
 475     /// resulting name.
 476     pub fn build_cgu_name_no_mangle<I, C, S>(&mut self,
 477                                              cnum: CrateNum,
 478                                              components: I,
 479                                              special_suffix: Option<S>)
 480                                              -> Symbol
 481         where I: IntoIterator<Item=C>,
 482               C: fmt::Display,
 483               S: fmt::Display,
 484     {
 485         use std::fmt::Write;
 486
 487         let mut cgu_name = String::with_capacity(64);
 488
 489         // Start out with the crate name and disambiguator
 490         let tcx = self.tcx;
 491         let crate_prefix = self.cache.entry(cnum).or_insert_with(|| {
 492             // Whenever the cnum is not LOCAL_CRATE we also mix in the
 493             // local crate's ID. Otherwise there can be collisions between CGUs
 494             // instantiating stuff for upstream crates.
 495             let local_crate_id = if cnum != LOCAL_CRATE {
 496                 let local_crate_disambiguator =
 497                     format!("{}", tcx.crate_disambiguator(LOCAL_CRATE));
 498                 format!("-in-{}.{}",
 499                         tcx.crate_name(LOCAL_CRATE),
 500                         &local_crate_disambiguator[0 .. 8])
 501             } else {
 502                 String::new()
 503             };
 504
 505             let crate_disambiguator = tcx.crate_disambiguator(cnum).to_string();
 506             // Using a shortened disambiguator of about 40 bits
 507             format!("{}.{}{}",
 508                 tcx.crate_name(cnum),
 509                 &crate_disambiguator[0 .. 8],
 510                 local_crate_id)
 511         });
 512
 513         write!(cgu_name, "{}", crate_prefix).unwrap();
 514
 515         // Add the components
 516         for component in components {
 517             write!(cgu_name, "-{}", component).unwrap();
 518         }
 519
 520         if let Some(special_suffix) = special_suffix {
 521             // We add a dot in here so it cannot clash with anything in a regular
 522             // Rust identifier
 523             write!(cgu_name, ".{}", special_suffix).unwrap();
 524         }
 525
 526         Symbol::intern(&cgu_name[..])
 527     }
 528 }