1 //! Partitioning Codegen Units for Incremental Compilation
2 //! ======================================================
4 //! The task of this module is to take the complete set of monomorphizations of
5 //! a crate and produce a set of codegen units from it, where a codegen unit
6 //! is a named set of (mono-item, linkage) pairs. That is, this module
7 //! decides which monomorphization appears in which codegen units with which
8 //! linkage. The following paragraphs describe some of the background on the
9 //! partitioning scheme.
11 //! The most important opportunity for saving on compilation time with
12 //! incremental compilation is to avoid re-codegenning and re-optimizing code.
13 //! Since the unit of codegen and optimization for LLVM is "modules" or, how
14 //! we call them "codegen units", the particulars of how much time can be saved
15 //! by incremental compilation are tightly linked to how the output program is
16 //! partitioned into these codegen units prior to passing it to LLVM --
17 //! especially because we have to treat codegen units as opaque entities once
18 //! they are created: There is no way for us to incrementally update an existing
19 //! LLVM module and so we have to build any such module from scratch if it was
20 //! affected by some change in the source code.
22 //! From that point of view it would make sense to maximize the number of
23 //! codegen units by, for example, putting each function into its own module.
24 //! That way only those modules would have to be re-compiled that were actually
25 //! affected by some change, minimizing the number of functions that could have
26 //! been re-used but just happened to be located in a module that is
29 //! However, since LLVM optimization does not work across module boundaries,
30 //! using such a highly granular partitioning would lead to very slow runtime
31 //! code since it would effectively prohibit inlining and other inter-procedure
32 //! optimizations. We want to avoid that as much as possible.
34 //! Thus we end up with a trade-off: The bigger the codegen units, the better
35 //! LLVM's optimizer can do its work, but also the smaller the compilation time
36 //! reduction we get from incremental compilation.
38 //! Ideally, we would create a partitioning such that there are few big codegen
39 //! units with few interdependencies between them. For now though, we use the
40 //! following heuristic to determine the partitioning:
42 //! - There are two codegen units for every source-level module:
43 //! - One for "stable", that is non-generic, code
44 //! - One for more "volatile" code, i.e., monomorphized instances of functions
45 //! defined in that module
47 //! In order to see why this heuristic makes sense, let's take a look at when a
48 //! codegen unit can get invalidated:
50 //! 1. The most straightforward case is when the BODY of a function or global
51 //! changes. Then any codegen unit containing the code for that item has to be
52 //! re-compiled. Note that this includes all codegen units where the function
55 //! 2. The next case is when the SIGNATURE of a function or global changes. In
56 //! this case, all codegen units containing a REFERENCE to that item have to be
57 //! re-compiled. This is a superset of case 1.
59 //! 3. The final and most subtle case is when a REFERENCE to a generic function
60 //! is added or removed somewhere. Even though the definition of the function
61 //! might be unchanged, a new REFERENCE might introduce a new monomorphized
62 //! instance of this function which has to be placed and compiled somewhere.
63 //! Conversely, when removing a REFERENCE, it might have been the last one with
64 //! that particular set of generic arguments and thus we have to remove it.
66 //! From the above we see that just using one codegen unit per source-level
67 //! module is not such a good idea, since just adding a REFERENCE to some
68 //! generic item somewhere else would invalidate everything within the module
69 //! containing the generic item. The heuristic above reduces this detrimental
70 //! side-effect of references a little by at least not touching the non-generic
71 //! code of the module.
73 //! A Note on Inlining
74 //! ------------------
75 //! As briefly mentioned above, in order for LLVM to be able to inline a
76 //! function call, the body of the function has to be available in the LLVM
77 //! module where the call is made. This has a few consequences for partitioning:
79 //! - The partitioning algorithm has to take care of placing functions into all
80 //! codegen units where they should be available for inlining. It also has to
81 //! decide on the correct linkage for these functions.
83 //! - The partitioning algorithm has to know which functions are likely to get
84 //! inlined, so it can distribute function instantiations accordingly. Since
85 //! there is no way of knowing for sure which functions LLVM will decide to
86 //! inline in the end, we apply a heuristic here: Only functions marked with
87 //! `#[inline]` are considered for inlining by the partitioner. The current
88 //! implementation will not try to determine if a function is likely to be
89 //! inlined by looking at the functions definition.
91 //! Note though that as a side-effect of creating a codegen units per
92 //! source-level module, functions from the same module will be available for
93 //! inlining, even when they are not marked `#[inline]`.
96 use std::collections::hash_map::Entry;
98 use rustc_data_structures::fx::{FxHashMap, FxHashSet};
99 use rustc_data_structures::sync;
100 use rustc_hir::def::DefKind;
101 use rustc_hir::def_id::{CrateNum, DefId, DefIdSet, CRATE_DEF_INDEX, LOCAL_CRATE};
102 use rustc_middle::middle::codegen_fn_attrs::CodegenFnAttrFlags;
103 use rustc_middle::middle::exported_symbols::SymbolExportLevel;
104 use rustc_middle::mir::mono::{CodegenUnit, CodegenUnitNameBuilder, Linkage, Visibility};
105 use rustc_middle::mir::mono::{InstantiationMode, MonoItem};
106 use rustc_middle::ty::print::characteristic_def_id_of_type;
107 use rustc_middle::ty::query::Providers;
108 use rustc_middle::ty::{self, DefIdTree, InstanceDef, TyCtxt};
109 use rustc_span::symbol::{Symbol, SymbolStr};
111 use crate::monomorphize::collector::InliningMap;
112 use crate::monomorphize::collector::{self, MonoItemCollectionMode};
114 // Anything we can't find a proper codegen unit for goes into this.
115 fn fallback_cgu_name(name_builder: &mut CodegenUnitNameBuilder<'_>) -> Symbol {
116 name_builder.build_cgu_name(LOCAL_CRATE, &["fallback"], Some("cgu"))
119 pub fn partition<'tcx, I>(
122 max_cgu_count: usize,
123 inlining_map: &InliningMap<'tcx>,
124 ) -> Vec<CodegenUnit<'tcx>>
126 I: Iterator<Item = MonoItem<'tcx>>,
128 let _prof_timer = tcx.prof.generic_activity("cgu_partitioning");
130 // In the first step, we place all regular monomorphizations into their
131 // respective 'home' codegen unit. Regular monomorphizations are all
132 // functions and statics defined in the local crate.
133 let mut initial_partitioning = {
134 let _prof_timer = tcx.prof.generic_activity("cgu_partitioning_place_roots");
135 place_root_mono_items(tcx, mono_items)
138 initial_partitioning.codegen_units.iter_mut().for_each(|cgu| cgu.estimate_size(tcx));
140 debug_dump(tcx, "INITIAL PARTITIONING:", initial_partitioning.codegen_units.iter());
142 // Merge until we have at most `max_cgu_count` codegen units.
144 let _prof_timer = tcx.prof.generic_activity("cgu_partitioning_merge_cgus");
145 merge_codegen_units(tcx, &mut initial_partitioning, max_cgu_count);
146 debug_dump(tcx, "POST MERGING:", initial_partitioning.codegen_units.iter());
149 // In the next step, we use the inlining map to determine which additional
150 // monomorphizations have to go into each codegen unit. These additional
151 // monomorphizations can be drop-glue, functions from external crates, and
152 // local functions the definition of which is marked with `#[inline]`.
153 let mut post_inlining = {
154 let _prof_timer = tcx.prof.generic_activity("cgu_partitioning_place_inline_items");
155 place_inlined_mono_items(initial_partitioning, inlining_map)
158 post_inlining.codegen_units.iter_mut().for_each(|cgu| cgu.estimate_size(tcx));
160 debug_dump(tcx, "POST INLINING:", post_inlining.codegen_units.iter());
162 // Next we try to make as many symbols "internal" as possible, so LLVM has
163 // more freedom to optimize.
164 if !tcx.sess.opts.cg.link_dead_code {
165 let _prof_timer = tcx.prof.generic_activity("cgu_partitioning_internalize_symbols");
166 internalize_symbols(tcx, &mut post_inlining, inlining_map);
169 // Finally, sort by codegen unit name, so that we get deterministic results.
170 let PostInliningPartitioning {
171 codegen_units: mut result,
172 mono_item_placements: _,
173 internalization_candidates: _,
176 result.sort_by_cached_key(|cgu| cgu.name().as_str());
181 struct PreInliningPartitioning<'tcx> {
182 codegen_units: Vec<CodegenUnit<'tcx>>,
183 roots: FxHashSet<MonoItem<'tcx>>,
184 internalization_candidates: FxHashSet<MonoItem<'tcx>>,
187 /// For symbol internalization, we need to know whether a symbol/mono-item is
188 /// accessed from outside the codegen unit it is defined in. This type is used
189 /// to keep track of that.
190 #[derive(Clone, PartialEq, Eq, Debug)]
191 enum MonoItemPlacement {
192 SingleCgu { cgu_name: Symbol },
196 struct PostInliningPartitioning<'tcx> {
197 codegen_units: Vec<CodegenUnit<'tcx>>,
198 mono_item_placements: FxHashMap<MonoItem<'tcx>, MonoItemPlacement>,
199 internalization_candidates: FxHashSet<MonoItem<'tcx>>,
202 fn place_root_mono_items<'tcx, I>(tcx: TyCtxt<'tcx>, mono_items: I) -> PreInliningPartitioning<'tcx>
204 I: Iterator<Item = MonoItem<'tcx>>,
206 let mut roots = FxHashSet::default();
207 let mut codegen_units = FxHashMap::default();
208 let is_incremental_build = tcx.sess.opts.incremental.is_some();
209 let mut internalization_candidates = FxHashSet::default();
211 // Determine if monomorphizations instantiated in this crate will be made
212 // available to downstream crates. This depends on whether we are in
213 // share-generics mode and whether the current crate can even have
214 // downstream crates.
215 let export_generics = tcx.sess.opts.share_generics() && tcx.local_crate_exports_generics();
217 let cgu_name_builder = &mut CodegenUnitNameBuilder::new(tcx);
218 let cgu_name_cache = &mut FxHashMap::default();
220 for mono_item in mono_items {
221 match mono_item.instantiation_mode(tcx) {
222 InstantiationMode::GloballyShared { .. } => {}
223 InstantiationMode::LocalCopy => continue,
226 let characteristic_def_id = characteristic_def_id_of_mono_item(tcx, mono_item);
227 let is_volatile = is_incremental_build && mono_item.is_generic_fn();
229 let codegen_unit_name = match characteristic_def_id {
230 Some(def_id) => compute_codegen_unit_name(
237 None => fallback_cgu_name(cgu_name_builder),
240 let codegen_unit = codegen_units
241 .entry(codegen_unit_name)
242 .or_insert_with(|| CodegenUnit::new(codegen_unit_name));
244 let mut can_be_internalized = true;
245 let (linkage, visibility) = mono_item_linkage_and_visibility(
248 &mut can_be_internalized,
251 if visibility == Visibility::Hidden && can_be_internalized {
252 internalization_candidates.insert(mono_item);
255 codegen_unit.items_mut().insert(mono_item, (linkage, visibility));
256 roots.insert(mono_item);
259 // Always ensure we have at least one CGU; otherwise, if we have a
260 // crate with just types (for example), we could wind up with no CGU.
261 if codegen_units.is_empty() {
262 let codegen_unit_name = fallback_cgu_name(cgu_name_builder);
263 codegen_units.insert(codegen_unit_name, CodegenUnit::new(codegen_unit_name));
266 PreInliningPartitioning {
267 codegen_units: codegen_units.into_iter().map(|(_, codegen_unit)| codegen_unit).collect(),
269 internalization_candidates,
273 fn mono_item_linkage_and_visibility(
275 mono_item: &MonoItem<'tcx>,
276 can_be_internalized: &mut bool,
277 export_generics: bool,
278 ) -> (Linkage, Visibility) {
279 if let Some(explicit_linkage) = mono_item.explicit_linkage(tcx) {
280 return (explicit_linkage, Visibility::Default);
282 let vis = mono_item_visibility(tcx, mono_item, can_be_internalized, export_generics);
283 (Linkage::External, vis)
286 fn mono_item_visibility(
288 mono_item: &MonoItem<'tcx>,
289 can_be_internalized: &mut bool,
290 export_generics: bool,
292 let instance = match mono_item {
293 // This is pretty complicated; see below.
294 MonoItem::Fn(instance) => instance,
296 // Misc handling for generics and such, but otherwise:
297 MonoItem::Static(def_id) => {
298 return if tcx.is_reachable_non_generic(*def_id) {
299 *can_be_internalized = false;
300 default_visibility(tcx, *def_id, false)
305 MonoItem::GlobalAsm(hir_id) => {
306 let def_id = tcx.hir().local_def_id(*hir_id);
307 return if tcx.is_reachable_non_generic(def_id) {
308 *can_be_internalized = false;
309 default_visibility(tcx, def_id.to_def_id(), false)
316 let def_id = match instance.def {
317 InstanceDef::Item(def_id) | InstanceDef::DropGlue(def_id, Some(_)) => def_id,
319 // These are all compiler glue and such, never exported, always hidden.
320 InstanceDef::VtableShim(..)
321 | InstanceDef::ReifyShim(..)
322 | InstanceDef::FnPtrShim(..)
323 | InstanceDef::Virtual(..)
324 | InstanceDef::Intrinsic(..)
325 | InstanceDef::ClosureOnceShim { .. }
326 | InstanceDef::DropGlue(..)
327 | InstanceDef::CloneShim(..) => return Visibility::Hidden,
330 // The `start_fn` lang item is actually a monomorphized instance of a
331 // function in the standard library, used for the `main` function. We don't
332 // want to export it so we tag it with `Hidden` visibility but this symbol
333 // is only referenced from the actual `main` symbol which we unfortunately
334 // don't know anything about during partitioning/collection. As a result we
335 // forcibly keep this symbol out of the `internalization_candidates` set.
337 // FIXME: eventually we don't want to always force this symbol to have
338 // hidden visibility, it should indeed be a candidate for
339 // internalization, but we have to understand that it's referenced
340 // from the `main` symbol we'll generate later.
342 // This may be fixable with a new `InstanceDef` perhaps? Unsure!
343 if tcx.lang_items().start_fn() == Some(def_id) {
344 *can_be_internalized = false;
345 return Visibility::Hidden;
348 let is_generic = instance.substs.non_erasable_generics().next().is_some();
350 // Upstream `DefId` instances get different handling than local ones.
351 if !def_id.is_local() {
352 return if export_generics && is_generic {
353 // If it is a upstream monomorphization and we export generics, we must make
354 // it available to downstream crates.
355 *can_be_internalized = false;
356 default_visibility(tcx, def_id, true)
364 if tcx.is_unreachable_local_definition(def_id) {
365 // This instance cannot be used from another crate.
368 // This instance might be useful in a downstream crate.
369 *can_be_internalized = false;
370 default_visibility(tcx, def_id, true)
373 // We are not exporting generics or the definition is not reachable
374 // for downstream crates, we can internalize its instantiations.
378 // If this isn't a generic function then we mark this a `Default` if
379 // this is a reachable item, meaning that it's a symbol other crates may
380 // access when they link to us.
381 if tcx.is_reachable_non_generic(def_id) {
382 *can_be_internalized = false;
383 debug_assert!(!is_generic);
384 return default_visibility(tcx, def_id, false);
387 // If this isn't reachable then we're gonna tag this with `Hidden`
388 // visibility. In some situations though we'll want to prevent this
389 // symbol from being internalized.
391 // There's two categories of items here:
393 // * First is weak lang items. These are basically mechanisms for
394 // libcore to forward-reference symbols defined later in crates like
395 // the standard library or `#[panic_handler]` definitions. The
396 // definition of these weak lang items needs to be referenceable by
397 // libcore, so we're no longer a candidate for internalization.
398 // Removal of these functions can't be done by LLVM but rather must be
399 // done by the linker as it's a non-local decision.
401 // * Second is "std internal symbols". Currently this is primarily used
402 // for allocator symbols. Allocators are a little weird in their
403 // implementation, but the idea is that the compiler, at the last
404 // minute, defines an allocator with an injected object file. The
405 // `alloc` crate references these symbols (`__rust_alloc`) and the
406 // definition doesn't get hooked up until a linked crate artifact is
409 // The symbols synthesized by the compiler (`__rust_alloc`) are thin
410 // veneers around the actual implementation, some other symbol which
411 // implements the same ABI. These symbols (things like `__rg_alloc`,
412 // `__rdl_alloc`, `__rde_alloc`, etc), are all tagged with "std
413 // internal symbols".
415 // The std-internal symbols here **should not show up in a dll as an
416 // exported interface**, so they return `false` from
417 // `is_reachable_non_generic` above and we'll give them `Hidden`
418 // visibility below. Like the weak lang items, though, we can't let
419 // LLVM internalize them as this decision is left up to the linker to
420 // omit them, so prevent them from being internalized.
421 let attrs = tcx.codegen_fn_attrs(def_id);
422 if attrs.flags.contains(CodegenFnAttrFlags::RUSTC_STD_INTERNAL_SYMBOL) {
423 *can_be_internalized = false;
430 fn default_visibility(tcx: TyCtxt<'_>, id: DefId, is_generic: bool) -> Visibility {
431 if !tcx.sess.target.target.options.default_hidden_visibility {
432 return Visibility::Default;
435 // Generic functions never have export-level C.
437 return Visibility::Hidden;
440 // Things with export level C don't get instantiated in
441 // downstream crates.
443 return Visibility::Hidden;
446 // C-export level items remain at `Default`, all other internal
447 // items become `Hidden`.
448 match tcx.reachable_non_generics(id.krate).get(&id) {
449 Some(SymbolExportLevel::C) => Visibility::Default,
450 _ => Visibility::Hidden,
454 fn merge_codegen_units<'tcx>(
456 initial_partitioning: &mut PreInliningPartitioning<'tcx>,
457 target_cgu_count: usize,
459 assert!(target_cgu_count >= 1);
460 let codegen_units = &mut initial_partitioning.codegen_units;
462 // Note that at this point in time the `codegen_units` here may not be in a
463 // deterministic order (but we know they're deterministically the same set).
464 // We want this merging to produce a deterministic ordering of codegen units
467 // Due to basically how we've implemented the merging below (merge the two
468 // smallest into each other) we're sure to start off with a deterministic
469 // order (sorted by name). This'll mean that if two cgus have the same size
470 // the stable sort below will keep everything nice and deterministic.
471 codegen_units.sort_by_cached_key(|cgu| cgu.name().as_str());
473 // This map keeps track of what got merged into what.
474 let mut cgu_contents: FxHashMap<Symbol, Vec<SymbolStr>> =
475 codegen_units.iter().map(|cgu| (cgu.name(), vec![cgu.name().as_str()])).collect();
477 // Merge the two smallest codegen units until the target size is reached.
478 while codegen_units.len() > target_cgu_count {
479 // Sort small cgus to the back
480 codegen_units.sort_by_cached_key(|cgu| cmp::Reverse(cgu.size_estimate()));
481 let mut smallest = codegen_units.pop().unwrap();
482 let second_smallest = codegen_units.last_mut().unwrap();
484 // Move the mono-items from `smallest` to `second_smallest`
485 second_smallest.modify_size_estimate(smallest.size_estimate());
486 for (k, v) in smallest.items_mut().drain() {
487 second_smallest.items_mut().insert(k, v);
490 // Record that `second_smallest` now contains all the stuff that was in
491 // `smallest` before.
492 let mut consumed_cgu_names = cgu_contents.remove(&smallest.name()).unwrap();
493 cgu_contents.get_mut(&second_smallest.name()).unwrap().extend(consumed_cgu_names.drain(..));
496 "CodegenUnit {} merged into CodegenUnit {}",
498 second_smallest.name()
502 let cgu_name_builder = &mut CodegenUnitNameBuilder::new(tcx);
504 if tcx.sess.opts.incremental.is_some() {
505 // If we are doing incremental compilation, we want CGU names to
506 // reflect the path of the source level module they correspond to.
507 // For CGUs that contain the code of multiple modules because of the
508 // merging done above, we use a concatenation of the names of
509 // all contained CGUs.
510 let new_cgu_names: FxHashMap<Symbol, String> = cgu_contents
512 // This `filter` makes sure we only update the name of CGUs that
513 // were actually modified by merging.
514 .filter(|(_, cgu_contents)| cgu_contents.len() > 1)
515 .map(|(current_cgu_name, cgu_contents)| {
516 let mut cgu_contents: Vec<&str> = cgu_contents.iter().map(|s| &s[..]).collect();
518 // Sort the names, so things are deterministic and easy to
522 (current_cgu_name, cgu_contents.join("--"))
526 for cgu in codegen_units.iter_mut() {
527 if let Some(new_cgu_name) = new_cgu_names.get(&cgu.name()) {
528 if tcx.sess.opts.debugging_opts.human_readable_cgu_names {
529 cgu.set_name(Symbol::intern(&new_cgu_name));
531 // If we don't require CGU names to be human-readable, we
532 // use a fixed length hash of the composite CGU name
534 let new_cgu_name = CodegenUnit::mangle_name(&new_cgu_name);
535 cgu.set_name(Symbol::intern(&new_cgu_name));
540 // If we are compiling non-incrementally we just generate simple CGU
541 // names containing an index.
542 for (index, cgu) in codegen_units.iter_mut().enumerate() {
543 cgu.set_name(numbered_codegen_unit_name(cgu_name_builder, index));
548 fn place_inlined_mono_items<'tcx>(
549 initial_partitioning: PreInliningPartitioning<'tcx>,
550 inlining_map: &InliningMap<'tcx>,
551 ) -> PostInliningPartitioning<'tcx> {
552 let mut new_partitioning = Vec::new();
553 let mut mono_item_placements = FxHashMap::default();
555 let PreInliningPartitioning { codegen_units: initial_cgus, roots, internalization_candidates } =
556 initial_partitioning;
558 let single_codegen_unit = initial_cgus.len() == 1;
560 for old_codegen_unit in initial_cgus {
561 // Collect all items that need to be available in this codegen unit.
562 let mut reachable = FxHashSet::default();
563 for root in old_codegen_unit.items().keys() {
564 follow_inlining(*root, inlining_map, &mut reachable);
567 let mut new_codegen_unit = CodegenUnit::new(old_codegen_unit.name());
569 // Add all monomorphizations that are not already there.
570 for mono_item in reachable {
571 if let Some(linkage) = old_codegen_unit.items().get(&mono_item) {
572 // This is a root, just copy it over.
573 new_codegen_unit.items_mut().insert(mono_item, *linkage);
575 if roots.contains(&mono_item) {
577 "GloballyShared mono-item inlined into other CGU: \
583 // This is a CGU-private copy.
586 .insert(mono_item, (Linkage::Internal, Visibility::Default));
589 if !single_codegen_unit {
590 // If there is more than one codegen unit, we need to keep track
591 // in which codegen units each monomorphization is placed.
592 match mono_item_placements.entry(mono_item) {
593 Entry::Occupied(e) => {
594 let placement = e.into_mut();
595 debug_assert!(match *placement {
596 MonoItemPlacement::SingleCgu { cgu_name } => {
597 cgu_name != new_codegen_unit.name()
599 MonoItemPlacement::MultipleCgus => true,
601 *placement = MonoItemPlacement::MultipleCgus;
603 Entry::Vacant(e) => {
604 e.insert(MonoItemPlacement::SingleCgu {
605 cgu_name: new_codegen_unit.name(),
612 new_partitioning.push(new_codegen_unit);
615 return PostInliningPartitioning {
616 codegen_units: new_partitioning,
617 mono_item_placements,
618 internalization_candidates,
621 fn follow_inlining<'tcx>(
622 mono_item: MonoItem<'tcx>,
623 inlining_map: &InliningMap<'tcx>,
624 visited: &mut FxHashSet<MonoItem<'tcx>>,
626 if !visited.insert(mono_item) {
630 inlining_map.with_inlining_candidates(mono_item, |target| {
631 follow_inlining(target, inlining_map, visited);
636 fn internalize_symbols<'tcx>(
638 partitioning: &mut PostInliningPartitioning<'tcx>,
639 inlining_map: &InliningMap<'tcx>,
641 if partitioning.codegen_units.len() == 1 {
642 // Fast path for when there is only one codegen unit. In this case we
643 // can internalize all candidates, since there is nowhere else they
644 // could be accessed from.
645 for cgu in &mut partitioning.codegen_units {
646 for candidate in &partitioning.internalization_candidates {
647 cgu.items_mut().insert(*candidate, (Linkage::Internal, Visibility::Default));
654 // Build a map from every monomorphization to all the monomorphizations that
656 let mut accessor_map: FxHashMap<MonoItem<'tcx>, Vec<MonoItem<'tcx>>> = Default::default();
657 inlining_map.iter_accesses(|accessor, accessees| {
658 for accessee in accessees {
659 accessor_map.entry(*accessee).or_default().push(accessor);
663 let mono_item_placements = &partitioning.mono_item_placements;
665 // For each internalization candidates in each codegen unit, check if it is
666 // accessed from outside its defining codegen unit.
667 for cgu in &mut partitioning.codegen_units {
668 let home_cgu = MonoItemPlacement::SingleCgu { cgu_name: cgu.name() };
670 for (accessee, linkage_and_visibility) in cgu.items_mut() {
671 if !partitioning.internalization_candidates.contains(accessee) {
672 // This item is no candidate for internalizing, so skip it.
675 debug_assert_eq!(mono_item_placements[accessee], home_cgu);
677 if let Some(accessors) = accessor_map.get(accessee) {
680 .filter_map(|accessor| {
681 // Some accessors might not have been
682 // instantiated. We can safely ignore those.
683 mono_item_placements.get(accessor)
685 .any(|placement| *placement != home_cgu)
687 // Found an accessor from another CGU, so skip to the next
688 // item without marking this one as internal.
693 // If we got here, we did not find any accesses from other CGUs,
694 // so it's fine to make this monomorphization internal.
695 *linkage_and_visibility = (Linkage::Internal, Visibility::Default);
700 fn characteristic_def_id_of_mono_item<'tcx>(
702 mono_item: MonoItem<'tcx>,
705 MonoItem::Fn(instance) => {
706 let def_id = match instance.def {
707 ty::InstanceDef::Item(def_id) => def_id,
708 ty::InstanceDef::VtableShim(..)
709 | ty::InstanceDef::ReifyShim(..)
710 | ty::InstanceDef::FnPtrShim(..)
711 | ty::InstanceDef::ClosureOnceShim { .. }
712 | ty::InstanceDef::Intrinsic(..)
713 | ty::InstanceDef::DropGlue(..)
714 | ty::InstanceDef::Virtual(..)
715 | ty::InstanceDef::CloneShim(..) => return None,
718 // If this is a method, we want to put it into the same module as
719 // its self-type. If the self-type does not provide a characteristic
720 // DefId, we use the location of the impl after all.
722 if tcx.trait_of_item(def_id).is_some() {
723 let self_ty = instance.substs.type_at(0);
724 // This is a default implementation of a trait method.
725 return characteristic_def_id_of_type(self_ty).or(Some(def_id));
728 if let Some(impl_def_id) = tcx.impl_of_method(def_id) {
729 if tcx.sess.opts.incremental.is_some()
730 && tcx.trait_id_of_impl(impl_def_id) == tcx.lang_items().drop_trait()
732 // Put `Drop::drop` into the same cgu as `drop_in_place`
733 // since `drop_in_place` is the only thing that can
737 // This is a method within an impl, find out what the self-type is:
738 let impl_self_ty = tcx.subst_and_normalize_erasing_regions(
740 ty::ParamEnv::reveal_all(),
741 &tcx.type_of(impl_def_id),
743 if let Some(def_id) = characteristic_def_id_of_type(impl_self_ty) {
750 MonoItem::Static(def_id) => Some(def_id),
751 MonoItem::GlobalAsm(hir_id) => Some(tcx.hir().local_def_id(hir_id).to_def_id()),
755 type CguNameCache = FxHashMap<(DefId, bool), Symbol>;
757 fn compute_codegen_unit_name(
759 name_builder: &mut CodegenUnitNameBuilder<'_>,
762 cache: &mut CguNameCache,
764 // Find the innermost module that is not nested within a function.
765 let mut current_def_id = def_id;
766 let mut cgu_def_id = None;
767 // Walk backwards from the item we want to find the module for.
769 if current_def_id.index == CRATE_DEF_INDEX {
770 if cgu_def_id.is_none() {
771 // If we have not found a module yet, take the crate root.
772 cgu_def_id = Some(DefId { krate: def_id.krate, index: CRATE_DEF_INDEX });
775 } else if tcx.def_kind(current_def_id) == DefKind::Mod {
776 if cgu_def_id.is_none() {
777 cgu_def_id = Some(current_def_id);
780 // If we encounter something that is not a module, throw away
781 // any module that we've found so far because we now know that
782 // it is nested within something else.
786 current_def_id = tcx.parent(current_def_id).unwrap();
789 let cgu_def_id = cgu_def_id.unwrap();
791 *cache.entry((cgu_def_id, volatile)).or_insert_with(|| {
792 let def_path = tcx.def_path(cgu_def_id);
794 let components = def_path.data.iter().map(|part| part.data.as_symbol());
796 let volatile_suffix = volatile.then_some("volatile");
798 name_builder.build_cgu_name(def_path.krate, components, volatile_suffix)
802 fn numbered_codegen_unit_name(
803 name_builder: &mut CodegenUnitNameBuilder<'_>,
806 name_builder.build_cgu_name_no_mangle(LOCAL_CRATE, &["cgu"], Some(index))
809 fn debug_dump<'a, 'tcx, I>(tcx: TyCtxt<'tcx>, label: &str, cgus: I)
811 I: Iterator<Item = &'a CodegenUnit<'tcx>>,
814 if cfg!(debug_assertions) {
817 debug!("CodegenUnit {} estimated size {} :", cgu.name(), cgu.size_estimate());
819 for (mono_item, linkage) in cgu.items() {
820 let symbol_name = mono_item.symbol_name(tcx).name.as_str();
821 let symbol_hash_start = symbol_name.rfind('h');
823 symbol_hash_start.map(|i| &symbol_name[i..]).unwrap_or("<no hash>");
826 " - {} [{:?}] [{}] estimated size {}",
827 mono_item.to_string(tcx, true),
830 mono_item.size_estimate(tcx)
839 #[inline(never)] // give this a place in the profiler
840 fn assert_symbols_are_distinct<'a, 'tcx, I>(tcx: TyCtxt<'tcx>, mono_items: I)
842 I: Iterator<Item = &'a MonoItem<'tcx>>,
845 let _prof_timer = tcx.prof.generic_activity("assert_symbols_are_distinct");
847 let mut symbols: Vec<_> =
848 mono_items.map(|mono_item| (mono_item, mono_item.symbol_name(tcx))).collect();
850 symbols.sort_by_key(|sym| sym.1);
852 for pair in symbols.windows(2) {
853 let sym1 = &pair[0].1;
854 let sym2 = &pair[1].1;
857 let mono_item1 = pair[0].0;
858 let mono_item2 = pair[1].0;
860 let span1 = mono_item1.local_span(tcx);
861 let span2 = mono_item2.local_span(tcx);
863 // Deterministically select one of the spans for error reporting
864 let span = match (span1, span2) {
865 (Some(span1), Some(span2)) => {
866 Some(if span1.lo().0 > span2.lo().0 { span1 } else { span2 })
868 (span1, span2) => span1.or(span2),
871 let error_message = format!("symbol `{}` is already defined", sym1);
873 if let Some(span) = span {
874 tcx.sess.span_fatal(span, &error_message)
876 tcx.sess.fatal(&error_message)
882 fn collect_and_partition_mono_items(
885 ) -> (&'tcx DefIdSet, &'tcx [CodegenUnit<'tcx>]) {
886 assert_eq!(cnum, LOCAL_CRATE);
888 let collection_mode = match tcx.sess.opts.debugging_opts.print_mono_items {
890 let mode_string = s.to_lowercase();
891 let mode_string = mode_string.trim();
892 if mode_string == "eager" {
893 MonoItemCollectionMode::Eager
895 if mode_string != "lazy" {
896 let message = format!(
897 "Unknown codegen-item collection mode '{}'. \
898 Falling back to 'lazy' mode.",
901 tcx.sess.warn(&message);
904 MonoItemCollectionMode::Lazy
908 if tcx.sess.opts.cg.link_dead_code {
909 MonoItemCollectionMode::Eager
911 MonoItemCollectionMode::Lazy
916 let (items, inlining_map) = collector::collect_crate_mono_items(tcx, collection_mode);
918 tcx.sess.abort_if_errors();
920 let (codegen_units, _) = tcx.sess.time("partition_and_assert_distinct_symbols", || {
923 &*tcx.arena.alloc_from_iter(partition(
925 items.iter().cloned(),
926 tcx.sess.codegen_units(),
930 || assert_symbols_are_distinct(tcx, items.iter()),
934 let mono_items: DefIdSet = items
936 .filter_map(|mono_item| match *mono_item {
937 MonoItem::Fn(ref instance) => Some(instance.def_id()),
938 MonoItem::Static(def_id) => Some(def_id),
943 if tcx.sess.opts.debugging_opts.print_mono_items.is_some() {
944 let mut item_to_cgus: FxHashMap<_, Vec<_>> = Default::default();
946 for cgu in codegen_units {
947 for (&mono_item, &linkage) in cgu.items() {
948 item_to_cgus.entry(mono_item).or_default().push((cgu.name(), linkage));
952 let mut item_keys: Vec<_> = items
955 let mut output = i.to_string(tcx, false);
956 output.push_str(" @@");
957 let mut empty = Vec::new();
958 let cgus = item_to_cgus.get_mut(i).unwrap_or(&mut empty);
959 cgus.sort_by_key(|(name, _)| *name);
961 for &(ref cgu_name, (linkage, _)) in cgus.iter() {
962 output.push_str(" ");
963 output.push_str(&cgu_name.as_str());
965 let linkage_abbrev = match linkage {
966 Linkage::External => "External",
967 Linkage::AvailableExternally => "Available",
968 Linkage::LinkOnceAny => "OnceAny",
969 Linkage::LinkOnceODR => "OnceODR",
970 Linkage::WeakAny => "WeakAny",
971 Linkage::WeakODR => "WeakODR",
972 Linkage::Appending => "Appending",
973 Linkage::Internal => "Internal",
974 Linkage::Private => "Private",
975 Linkage::ExternalWeak => "ExternalWeak",
976 Linkage::Common => "Common",
979 output.push_str("[");
980 output.push_str(linkage_abbrev);
981 output.push_str("]");
989 for item in item_keys {
990 println!("MONO_ITEM {}", item);
994 (tcx.arena.alloc(mono_items), codegen_units)
997 pub fn provide(providers: &mut Providers) {
998 providers.collect_and_partition_mono_items = collect_and_partition_mono_items;
1000 providers.is_codegened_item = |tcx, def_id| {
1001 let (all_mono_items, _) = tcx.collect_and_partition_mono_items(LOCAL_CRATE);
1002 all_mono_items.contains(&def_id)
1005 providers.codegen_unit = |tcx, name| {
1006 let (_, all) = tcx.collect_and_partition_mono_items(LOCAL_CRATE);
1008 .find(|cgu| cgu.name() == name)
1009 .unwrap_or_else(|| panic!("failed to find cgu with name {:?}", name))