rustc_middle/mir/mono.rs
1use std::fmt;
2use std::hash::Hash;
3
4use rustc_ast::expand::autodiff_attrs::AutoDiffItem;
5use rustc_attr_data_structures::InlineAttr;
6use rustc_data_structures::base_n::{BaseNString, CASE_INSENSITIVE, ToBaseN};
7use rustc_data_structures::fingerprint::Fingerprint;
8use rustc_data_structures::fx::FxIndexMap;
9use rustc_data_structures::stable_hasher::{HashStable, StableHasher, ToStableHashKey};
10use rustc_data_structures::unord::UnordMap;
11use rustc_hashes::Hash128;
12use rustc_hir::ItemId;
13use rustc_hir::def_id::{CrateNum, DefId, DefIdSet, LOCAL_CRATE};
14use rustc_index::Idx;
15use rustc_macros::{HashStable, TyDecodable, TyEncodable};
16use rustc_query_system::ich::StableHashingContext;
17use rustc_session::config::OptLevel;
18use rustc_span::{Span, Symbol};
19use rustc_target::spec::SymbolVisibility;
20use tracing::debug;
21
22use crate::dep_graph::{DepNode, WorkProduct, WorkProductId};
23use crate::middle::codegen_fn_attrs::CodegenFnAttrFlags;
24use crate::ty::{self, GenericArgs, Instance, InstanceKind, SymbolName, Ty, TyCtxt};
25
26/// Describes how a monomorphization will be instantiated in object files.
27#[derive(PartialEq)]
28pub enum InstantiationMode {
29 /// There will be exactly one instance of the given MonoItem. It will have
30 /// external linkage so that it can be linked to from other codegen units.
31 GloballyShared {
32 /// In some compilation scenarios we may decide to take functions that
33 /// are typically `LocalCopy` and instead move them to `GloballyShared`
34 /// to avoid codegenning them a bunch of times. In this situation,
35 /// however, our local copy may conflict with other crates also
36 /// inlining the same function.
37 ///
38 /// This flag indicates that this situation is occurring, and informs
39 /// symbol name calculation that some extra mangling is needed to
40 /// avoid conflicts. Note that this may eventually go away entirely if
41 /// ThinLTO enables us to *always* have a globally shared instance of a
42 /// function within one crate's compilation.
43 may_conflict: bool,
44 },
45
46 /// Each codegen unit containing a reference to the given MonoItem will
47 /// have its own private copy of the function (with internal linkage).
48 LocalCopy,
49}
50
51#[derive(PartialEq, Eq, Clone, Copy, Debug, Hash, HashStable, TyEncodable, TyDecodable)]
52pub enum MonoItem<'tcx> {
53 Fn(Instance<'tcx>),
54 Static(DefId),
55 GlobalAsm(ItemId),
56}
57
58fn opt_incr_drop_glue_mode<'tcx>(tcx: TyCtxt<'tcx>, ty: Ty<'tcx>) -> InstantiationMode {
59 // Non-ADTs can't have a Drop impl. This case is mostly hit by closures whose captures require
60 // dropping.
61 let ty::Adt(adt_def, _) = ty.kind() else {
62 return InstantiationMode::LocalCopy;
63 };
64
65 // Types that don't have a direct Drop impl, but have fields that require dropping.
66 let Some(dtor) = adt_def.destructor(tcx) else {
67 // We use LocalCopy for drops of enums only; this code is inherited from
68 // https://github.com/rust-lang/rust/pull/67332 and the theory is that we get to optimize
69 // out code like drop_in_place(Option::None) before crate-local ThinLTO, which improves
70 // compile time. At the time of writing, simply removing this entire check does seem to
71 // regress incr-opt compile times. But it sure seems like a more sophisticated check could
72 // do better here.
73 if adt_def.is_enum() {
74 return InstantiationMode::LocalCopy;
75 } else {
76 return InstantiationMode::GloballyShared { may_conflict: true };
77 }
78 };
79
80 // We've gotten to a drop_in_place for a type that directly implements Drop.
81 // The drop glue is a wrapper for the Drop::drop impl, and we are an optimized build, so in an
82 // effort to coordinate with the mode that the actual impl will get, we make the glue also
83 // LocalCopy.
84 if tcx.cross_crate_inlinable(dtor.did) {
85 InstantiationMode::LocalCopy
86 } else {
87 InstantiationMode::GloballyShared { may_conflict: true }
88 }
89}
90
91impl<'tcx> MonoItem<'tcx> {
92 /// Returns `true` if the mono item is user-defined (i.e. not compiler-generated, like shims).
93 pub fn is_user_defined(&self) -> bool {
94 match *self {
95 MonoItem::Fn(instance) => matches!(instance.def, InstanceKind::Item(..)),
96 MonoItem::Static(..) | MonoItem::GlobalAsm(..) => true,
97 }
98 }
99
100 // Note: if you change how item size estimates work, you might need to
101 // change NON_INCR_MIN_CGU_SIZE as well.
102 pub fn size_estimate(&self, tcx: TyCtxt<'tcx>) -> usize {
103 match *self {
104 MonoItem::Fn(instance) => tcx.size_estimate(instance),
105 // Conservatively estimate the size of a static declaration or
106 // assembly item to be 1.
107 MonoItem::Static(_) | MonoItem::GlobalAsm(_) => 1,
108 }
109 }
110
111 pub fn is_generic_fn(&self) -> bool {
112 match self {
113 MonoItem::Fn(instance) => instance.args.non_erasable_generics().next().is_some(),
114 MonoItem::Static(..) | MonoItem::GlobalAsm(..) => false,
115 }
116 }
117
118 pub fn symbol_name(&self, tcx: TyCtxt<'tcx>) -> SymbolName<'tcx> {
119 match *self {
120 MonoItem::Fn(instance) => tcx.symbol_name(instance),
121 MonoItem::Static(def_id) => tcx.symbol_name(Instance::mono(tcx, def_id)),
122 MonoItem::GlobalAsm(item_id) => {
123 SymbolName::new(tcx, &format!("global_asm_{:?}", item_id.owner_id))
124 }
125 }
126 }
127
128 pub fn instantiation_mode(&self, tcx: TyCtxt<'tcx>) -> InstantiationMode {
129 // The case handling here is written in the same style as cross_crate_inlinable, we first
130 // handle the cases where we must use a particular instantiation mode, then cascade down
131 // through a sequence of heuristics.
132
133 // The first thing we do is detect MonoItems which we must instantiate exactly once in the
134 // whole program.
135
136 // Statics and global_asm! must be instantiated exactly once.
137 let instance = match *self {
138 MonoItem::Fn(instance) => instance,
139 MonoItem::Static(..) | MonoItem::GlobalAsm(..) => {
140 return InstantiationMode::GloballyShared { may_conflict: false };
141 }
142 };
143
144 // Similarly, the executable entrypoint must be instantiated exactly once.
145 if let Some((entry_def_id, _)) = tcx.entry_fn(()) {
146 if instance.def_id() == entry_def_id {
147 return InstantiationMode::GloballyShared { may_conflict: false };
148 }
149 }
150
151 // If the function is #[naked] or contains any other attribute that requires exactly-once
152 // instantiation:
153 let codegen_fn_attrs = tcx.codegen_fn_attrs(instance.def_id());
154 if codegen_fn_attrs.contains_extern_indicator()
155 || codegen_fn_attrs.flags.contains(CodegenFnAttrFlags::NAKED)
156 {
157 return InstantiationMode::GloballyShared { may_conflict: false };
158 }
159
160 // This is technically a heuristic even though it's in the "not a heuristic" part of
161 // instantiation mode selection.
162 // It is surely possible to untangle this; the root problem is that the way we instantiate
163 // InstanceKind other than Item is very complicated.
164 //
165 // The fallback case is to give everything else GloballyShared at OptLevel::No and
166 // LocalCopy at all other opt levels. This is a good default, except for one specific build
167 // configuration: Optimized incremental builds.
168 // In the current compiler architecture there is a fundamental tension between
169 // optimizations (which want big CGUs with as many things LocalCopy as possible) and
170 // incrementality (which wants small CGUs with as many things GloballyShared as possible).
171 // The heuristics implemented here do better than a completely naive approach in the
172 // compiler benchmark suite, but there is no reason to believe they are optimal.
173 if let InstanceKind::DropGlue(_, Some(ty)) = instance.def {
174 if tcx.sess.opts.optimize == OptLevel::No {
175 return InstantiationMode::GloballyShared { may_conflict: false };
176 }
177 if tcx.sess.opts.incremental.is_none() {
178 return InstantiationMode::LocalCopy;
179 }
180 return opt_incr_drop_glue_mode(tcx, ty);
181 }
182
183 // We need to ensure that we do not decide the InstantiationMode of an exported symbol is
184 // LocalCopy. Since exported symbols are computed based on the output of
185 // cross_crate_inlinable, we are beholden to our previous decisions.
186 //
187 // Note that just like above, this check for requires_inline is technically a heuristic
188 // even though it's in the "not a heuristic" part of instantiation mode selection.
189 if !tcx.cross_crate_inlinable(instance.def_id()) && !instance.def.requires_inline(tcx) {
190 return InstantiationMode::GloballyShared { may_conflict: false };
191 }
192
193 // Beginning of heuristics. The handling of link-dead-code and inline(always) are QoL only,
194 // the compiler should not crash and linkage should work, but codegen may be undesirable.
195
196 // -Clink-dead-code was given an unfortunate name; the point of the flag is to assist
197 // coverage tools which rely on having every function in the program appear in the
198 // generated code. If we select LocalCopy, functions which are not used because they are
199 // missing test coverage will disappear from such coverage reports, defeating the point.
200 // Note that -Cinstrument-coverage does not require such assistance from us, only coverage
201 // tools implemented without compiler support ironically require a special compiler flag.
202 if tcx.sess.link_dead_code() {
203 return InstantiationMode::GloballyShared { may_conflict: true };
204 }
205
206 // To ensure that #[inline(always)] can be inlined as much as possible, especially in unoptimized
207 // builds, we always select LocalCopy.
208 if codegen_fn_attrs.inline.always() {
209 return InstantiationMode::LocalCopy;
210 }
211
212 // #[inline(never)] functions in general are poor candidates for inlining and thus since
213 // LocalCopy generally increases code size for the benefit of optimizations from inlining,
214 // we want to give them GloballyShared codegen.
215 // The slight problem is that generic functions need to always support cross-crate
216 // compilation, so all previous stages of the compiler are obligated to treat generic
217 // functions the same as those that unconditionally get LocalCopy codegen. It's only when
218 // we get here that we can at least not codegen a #[inline(never)] generic function in all
219 // of our CGUs.
220 if let InlineAttr::Never = tcx.codegen_fn_attrs(instance.def_id()).inline
221 && self.is_generic_fn()
222 {
223 return InstantiationMode::GloballyShared { may_conflict: true };
224 }
225
226 // The fallthrough case is to generate LocalCopy for all optimized builds, and
227 // GloballyShared with conflict prevention when optimizations are disabled.
228 match tcx.sess.opts.optimize {
229 OptLevel::No => InstantiationMode::GloballyShared { may_conflict: true },
230 _ => InstantiationMode::LocalCopy,
231 }
232 }
233
234 pub fn explicit_linkage(&self, tcx: TyCtxt<'tcx>) -> Option<Linkage> {
235 let def_id = match *self {
236 MonoItem::Fn(ref instance) => instance.def_id(),
237 MonoItem::Static(def_id) => def_id,
238 MonoItem::GlobalAsm(..) => return None,
239 };
240
241 let codegen_fn_attrs = tcx.codegen_fn_attrs(def_id);
242 codegen_fn_attrs.linkage
243 }
244
245 /// Returns `true` if this instance is instantiable - whether it has no unsatisfied
246 /// predicates.
247 ///
248 /// In order to codegen an item, all of its predicates must hold, because
249 /// otherwise the item does not make sense. Type-checking ensures that
250 /// the predicates of every item that is *used by* a valid item *do*
251 /// hold, so we can rely on that.
252 ///
253 /// However, we codegen collector roots (reachable items) and functions
254 /// in vtables when they are seen, even if they are not used, and so they
255 /// might not be instantiable. For example, a programmer can define this
256 /// public function:
257 ///
258 /// pub fn foo<'a>(s: &'a mut ()) where &'a mut (): Clone {
259 /// <&mut () as Clone>::clone(&s);
260 /// }
261 ///
262 /// That function can't be codegened, because the method `<&mut () as Clone>::clone`
263 /// does not exist. Luckily for us, that function can't ever be used,
264 /// because that would require for `&'a mut (): Clone` to hold, so we
265 /// can just not emit any code, or even a linker reference for it.
266 ///
267 /// Similarly, if a vtable method has such a signature, and therefore can't
268 /// be used, we can just not emit it and have a placeholder (a null pointer,
269 /// which will never be accessed) in its place.
270 pub fn is_instantiable(&self, tcx: TyCtxt<'tcx>) -> bool {
271 debug!("is_instantiable({:?})", self);
272 let (def_id, args) = match *self {
273 MonoItem::Fn(ref instance) => (instance.def_id(), instance.args),
274 MonoItem::Static(def_id) => (def_id, GenericArgs::empty()),
275 // global asm never has predicates
276 MonoItem::GlobalAsm(..) => return true,
277 };
278
279 !tcx.instantiate_and_check_impossible_predicates((def_id, &args))
280 }
281
282 pub fn local_span(&self, tcx: TyCtxt<'tcx>) -> Option<Span> {
283 match *self {
284 MonoItem::Fn(Instance { def, .. }) => def.def_id().as_local(),
285 MonoItem::Static(def_id) => def_id.as_local(),
286 MonoItem::GlobalAsm(item_id) => Some(item_id.owner_id.def_id),
287 }
288 .map(|def_id| tcx.def_span(def_id))
289 }
290
291 // Only used by rustc_codegen_cranelift
292 pub fn codegen_dep_node(&self, tcx: TyCtxt<'tcx>) -> DepNode {
293 crate::dep_graph::make_compile_mono_item(tcx, self)
294 }
295
296 /// Returns the item's `CrateNum`
297 pub fn krate(&self) -> CrateNum {
298 match self {
299 MonoItem::Fn(instance) => instance.def_id().krate,
300 MonoItem::Static(def_id) => def_id.krate,
301 MonoItem::GlobalAsm(..) => LOCAL_CRATE,
302 }
303 }
304
305 /// Returns the item's `DefId`
306 pub fn def_id(&self) -> DefId {
307 match *self {
308 MonoItem::Fn(Instance { def, .. }) => def.def_id(),
309 MonoItem::Static(def_id) => def_id,
310 MonoItem::GlobalAsm(item_id) => item_id.owner_id.to_def_id(),
311 }
312 }
313}
314
315impl<'tcx> fmt::Display for MonoItem<'tcx> {
316 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
317 match *self {
318 MonoItem::Fn(instance) => write!(f, "fn {instance}"),
319 MonoItem::Static(def_id) => {
320 write!(f, "static {}", Instance::new(def_id, GenericArgs::empty()))
321 }
322 MonoItem::GlobalAsm(..) => write!(f, "global_asm"),
323 }
324 }
325}
326
327impl ToStableHashKey<StableHashingContext<'_>> for MonoItem<'_> {
328 type KeyType = Fingerprint;
329
330 fn to_stable_hash_key(&self, hcx: &StableHashingContext<'_>) -> Self::KeyType {
331 let mut hasher = StableHasher::new();
332 self.hash_stable(&mut hcx.clone(), &mut hasher);
333 hasher.finish()
334 }
335}
336
337#[derive(Debug, HashStable, Copy, Clone)]
338pub struct MonoItemPartitions<'tcx> {
339 pub codegen_units: &'tcx [CodegenUnit<'tcx>],
340 pub all_mono_items: &'tcx DefIdSet,
341 pub autodiff_items: &'tcx [AutoDiffItem],
342}
343
344#[derive(Debug, HashStable)]
345pub struct CodegenUnit<'tcx> {
346 /// A name for this CGU. Incremental compilation requires that
347 /// name be unique amongst **all** crates. Therefore, it should
348 /// contain something unique to this crate (e.g., a module path)
349 /// as well as the crate name and disambiguator.
350 name: Symbol,
351 items: FxIndexMap<MonoItem<'tcx>, MonoItemData>,
352 size_estimate: usize,
353 primary: bool,
354 /// True if this is CGU is used to hold code coverage information for dead code,
355 /// false otherwise.
356 is_code_coverage_dead_code_cgu: bool,
357}
358
359/// Auxiliary info about a `MonoItem`.
360#[derive(Copy, Clone, PartialEq, Debug, HashStable)]
361pub struct MonoItemData {
362 /// A cached copy of the result of `MonoItem::instantiation_mode`, where
363 /// `GloballyShared` maps to `false` and `LocalCopy` maps to `true`.
364 pub inlined: bool,
365
366 pub linkage: Linkage,
367 pub visibility: Visibility,
368
369 /// A cached copy of the result of `MonoItem::size_estimate`.
370 pub size_estimate: usize,
371}
372
373/// Specifies the linkage type for a `MonoItem`.
374///
375/// See <https://llvm.org/docs/LangRef.html#linkage-types> for more details about these variants.
376#[derive(Copy, Clone, PartialEq, Debug, TyEncodable, TyDecodable, HashStable)]
377pub enum Linkage {
378 External,
379 AvailableExternally,
380 LinkOnceAny,
381 LinkOnceODR,
382 WeakAny,
383 WeakODR,
384 Internal,
385 ExternalWeak,
386 Common,
387}
388
389/// Specifies the symbol visibility with regards to dynamic linking.
390///
391/// Visibility doesn't have any effect when linkage is internal.
392///
393/// DSO means dynamic shared object, that is a dynamically linked executable or dylib.
394#[derive(Copy, Clone, PartialEq, Debug, HashStable)]
395pub enum Visibility {
396 /// Export the symbol from the DSO and apply overrides of the symbol by outside DSOs to within
397 /// the DSO if the object file format supports this.
398 Default,
399 /// Hide the symbol outside of the defining DSO even when external linkage is used to export it
400 /// from the object file.
401 Hidden,
402 /// Export the symbol from the DSO, but don't apply overrides of the symbol by outside DSOs to
403 /// within the DSO. Equivalent to default visibility with object file formats that don't support
404 /// overriding exported symbols by another DSO.
405 Protected,
406}
407
408impl From<SymbolVisibility> for Visibility {
409 fn from(value: SymbolVisibility) -> Self {
410 match value {
411 SymbolVisibility::Hidden => Visibility::Hidden,
412 SymbolVisibility::Protected => Visibility::Protected,
413 SymbolVisibility::Interposable => Visibility::Default,
414 }
415 }
416}
417
418impl<'tcx> CodegenUnit<'tcx> {
419 #[inline]
420 pub fn new(name: Symbol) -> CodegenUnit<'tcx> {
421 CodegenUnit {
422 name,
423 items: Default::default(),
424 size_estimate: 0,
425 primary: false,
426 is_code_coverage_dead_code_cgu: false,
427 }
428 }
429
430 pub fn name(&self) -> Symbol {
431 self.name
432 }
433
434 pub fn set_name(&mut self, name: Symbol) {
435 self.name = name;
436 }
437
438 pub fn is_primary(&self) -> bool {
439 self.primary
440 }
441
442 pub fn make_primary(&mut self) {
443 self.primary = true;
444 }
445
446 pub fn items(&self) -> &FxIndexMap<MonoItem<'tcx>, MonoItemData> {
447 &self.items
448 }
449
450 pub fn items_mut(&mut self) -> &mut FxIndexMap<MonoItem<'tcx>, MonoItemData> {
451 &mut self.items
452 }
453
454 pub fn is_code_coverage_dead_code_cgu(&self) -> bool {
455 self.is_code_coverage_dead_code_cgu
456 }
457
458 /// Marks this CGU as the one used to contain code coverage information for dead code.
459 pub fn make_code_coverage_dead_code_cgu(&mut self) {
460 self.is_code_coverage_dead_code_cgu = true;
461 }
462
463 pub fn mangle_name(human_readable_name: &str) -> BaseNString {
464 let mut hasher = StableHasher::new();
465 human_readable_name.hash(&mut hasher);
466 let hash: Hash128 = hasher.finish();
467 hash.as_u128().to_base_fixed_len(CASE_INSENSITIVE)
468 }
469
470 pub fn compute_size_estimate(&mut self) {
471 // The size of a codegen unit as the sum of the sizes of the items
472 // within it.
473 self.size_estimate = self.items.values().map(|data| data.size_estimate).sum();
474 }
475
476 /// Should only be called if [`compute_size_estimate`] has previously been called.
477 ///
478 /// [`compute_size_estimate`]: Self::compute_size_estimate
479 #[inline]
480 pub fn size_estimate(&self) -> usize {
481 // Items are never zero-sized, so if we have items the estimate must be
482 // non-zero, unless we forgot to call `compute_size_estimate` first.
483 assert!(self.items.is_empty() || self.size_estimate != 0);
484 self.size_estimate
485 }
486
487 pub fn contains_item(&self, item: &MonoItem<'tcx>) -> bool {
488 self.items().contains_key(item)
489 }
490
491 pub fn work_product_id(&self) -> WorkProductId {
492 WorkProductId::from_cgu_name(self.name().as_str())
493 }
494
495 pub fn previous_work_product(&self, tcx: TyCtxt<'_>) -> WorkProduct {
496 let work_product_id = self.work_product_id();
497 tcx.dep_graph
498 .previous_work_product(&work_product_id)
499 .unwrap_or_else(|| panic!("Could not find work-product for CGU `{}`", self.name()))
500 }
501
502 pub fn items_in_deterministic_order(
503 &self,
504 tcx: TyCtxt<'tcx>,
505 ) -> Vec<(MonoItem<'tcx>, MonoItemData)> {
506 // The codegen tests rely on items being process in the same order as
507 // they appear in the file, so for local items, we sort by node_id first
508 #[derive(PartialEq, Eq, PartialOrd, Ord)]
509 struct ItemSortKey<'tcx>(Option<usize>, SymbolName<'tcx>);
510
511 fn item_sort_key<'tcx>(tcx: TyCtxt<'tcx>, item: MonoItem<'tcx>) -> ItemSortKey<'tcx> {
512 ItemSortKey(
513 match item {
514 MonoItem::Fn(ref instance) => {
515 match instance.def {
516 // We only want to take HirIds of user-defined
517 // instances into account. The others don't matter for
518 // the codegen tests and can even make item order
519 // unstable.
520 InstanceKind::Item(def) => def.as_local().map(Idx::index),
521 InstanceKind::VTableShim(..)
522 | InstanceKind::ReifyShim(..)
523 | InstanceKind::Intrinsic(..)
524 | InstanceKind::FnPtrShim(..)
525 | InstanceKind::Virtual(..)
526 | InstanceKind::ClosureOnceShim { .. }
527 | InstanceKind::ConstructCoroutineInClosureShim { .. }
528 | InstanceKind::DropGlue(..)
529 | InstanceKind::CloneShim(..)
530 | InstanceKind::ThreadLocalShim(..)
531 | InstanceKind::FnPtrAddrShim(..)
532 | InstanceKind::AsyncDropGlueCtorShim(..) => None,
533 }
534 }
535 MonoItem::Static(def_id) => def_id.as_local().map(Idx::index),
536 MonoItem::GlobalAsm(item_id) => Some(item_id.owner_id.def_id.index()),
537 },
538 item.symbol_name(tcx),
539 )
540 }
541
542 let mut items: Vec<_> = self.items().iter().map(|(&i, &data)| (i, data)).collect();
543 items.sort_by_cached_key(|&(i, _)| item_sort_key(tcx, i));
544 items
545 }
546
547 pub fn codegen_dep_node(&self, tcx: TyCtxt<'tcx>) -> DepNode {
548 crate::dep_graph::make_compile_codegen_unit(tcx, self.name())
549 }
550}
551
552impl ToStableHashKey<StableHashingContext<'_>> for CodegenUnit<'_> {
553 type KeyType = String;
554
555 fn to_stable_hash_key(&self, _: &StableHashingContext<'_>) -> Self::KeyType {
556 // Codegen unit names are conceptually required to be stable across
557 // compilation session so that object file names match up.
558 self.name.to_string()
559 }
560}
561
562pub struct CodegenUnitNameBuilder<'tcx> {
563 tcx: TyCtxt<'tcx>,
564 cache: UnordMap<CrateNum, String>,
565}
566
567impl<'tcx> CodegenUnitNameBuilder<'tcx> {
568 pub fn new(tcx: TyCtxt<'tcx>) -> Self {
569 CodegenUnitNameBuilder { tcx, cache: Default::default() }
570 }
571
572 /// CGU names should fulfill the following requirements:
573 /// - They should be able to act as a file name on any kind of file system
574 /// - They should not collide with other CGU names, even for different versions
575 /// of the same crate.
576 ///
577 /// Consequently, we don't use special characters except for '.' and '-' and we
578 /// prefix each name with the crate-name and crate-disambiguator.
579 ///
580 /// This function will build CGU names of the form:
581 ///
582 /// ```text
583 /// <crate-name>.<crate-disambiguator>[-in-<local-crate-id>](-<component>)*[.<special-suffix>]
584 /// <local-crate-id> = <local-crate-name>.<local-crate-disambiguator>
585 /// ```
586 ///
587 /// The '.' before `<special-suffix>` makes sure that names with a special
588 /// suffix can never collide with a name built out of regular Rust
589 /// identifiers (e.g., module paths).
590 pub fn build_cgu_name<I, C, S>(
591 &mut self,
592 cnum: CrateNum,
593 components: I,
594 special_suffix: Option<S>,
595 ) -> Symbol
596 where
597 I: IntoIterator<Item = C>,
598 C: fmt::Display,
599 S: fmt::Display,
600 {
601 let cgu_name = self.build_cgu_name_no_mangle(cnum, components, special_suffix);
602
603 if self.tcx.sess.opts.unstable_opts.human_readable_cgu_names {
604 cgu_name
605 } else {
606 Symbol::intern(&CodegenUnit::mangle_name(cgu_name.as_str()))
607 }
608 }
609
610 /// Same as `CodegenUnit::build_cgu_name()` but will never mangle the
611 /// resulting name.
612 pub fn build_cgu_name_no_mangle<I, C, S>(
613 &mut self,
614 cnum: CrateNum,
615 components: I,
616 special_suffix: Option<S>,
617 ) -> Symbol
618 where
619 I: IntoIterator<Item = C>,
620 C: fmt::Display,
621 S: fmt::Display,
622 {
623 use std::fmt::Write;
624
625 let mut cgu_name = String::with_capacity(64);
626
627 // Start out with the crate name and disambiguator
628 let tcx = self.tcx;
629 let crate_prefix = self.cache.entry(cnum).or_insert_with(|| {
630 // Whenever the cnum is not LOCAL_CRATE we also mix in the
631 // local crate's ID. Otherwise there can be collisions between CGUs
632 // instantiating stuff for upstream crates.
633 let local_crate_id = if cnum != LOCAL_CRATE {
634 let local_stable_crate_id = tcx.stable_crate_id(LOCAL_CRATE);
635 format!("-in-{}.{:08x}", tcx.crate_name(LOCAL_CRATE), local_stable_crate_id)
636 } else {
637 String::new()
638 };
639
640 let stable_crate_id = tcx.stable_crate_id(LOCAL_CRATE);
641 format!("{}.{:08x}{}", tcx.crate_name(cnum), stable_crate_id, local_crate_id)
642 });
643
644 write!(cgu_name, "{crate_prefix}").unwrap();
645
646 // Add the components
647 for component in components {
648 write!(cgu_name, "-{component}").unwrap();
649 }
650
651 if let Some(special_suffix) = special_suffix {
652 // We add a dot in here so it cannot clash with anything in a regular
653 // Rust identifier
654 write!(cgu_name, ".{special_suffix}").unwrap();
655 }
656
657 Symbol::intern(&cgu_name)
658 }
659}
660
661/// See module-level docs of `rustc_monomorphize::collector` on some context for "mentioned" items.
662#[derive(Copy, Clone, Debug, PartialEq, Eq, Hash, HashStable)]
663pub enum CollectionMode {
664 /// Collect items that are used, i.e., actually needed for codegen.
665 ///
666 /// Which items are used can depend on optimization levels, as MIR optimizations can remove
667 /// uses.
668 UsedItems,
669 /// Collect items that are mentioned. The goal of this mode is that it is independent of
670 /// optimizations: the set of "mentioned" items is computed before optimizations are run.
671 ///
672 /// The exact contents of this set are *not* a stable guarantee. (For instance, it is currently
673 /// computed after drop-elaboration. If we ever do some optimizations even in debug builds, we
674 /// might decide to run them before computing mentioned items.) The key property of this set is
675 /// that it is optimization-independent.
676 MentionedItems,
677}