1 //! Mono Item Collection
2 //! ====================
4 //! This module is responsible for discovering all items that will contribute
5 //! to code generation of the crate. The important part here is that it not only
6 //! needs to find syntax-level items (functions, structs, etc) but also all
7 //! their monomorphized instantiations. Every non-generic, non-const function
8 //! maps to one LLVM artifact. Every generic function can produce
9 //! from zero to N artifacts, depending on the sets of type arguments it
10 //! is instantiated with.
11 //! This also applies to generic items from other crates: A generic definition
12 //! in crate X might produce monomorphizations that are compiled into crate Y.
13 //! We also have to collect these here.
15 //! The following kinds of "mono items" are handled here:
23 //! The following things also result in LLVM artifacts, but are not collected
24 //! here, since we instantiate them locally on demand when needed in a given
34 //! Let's define some terms first:
36 //! - A "mono item" is something that results in a function or global in
37 //! the LLVM IR of a codegen unit. Mono items do not stand on their
38 //! own, they can reference other mono items. For example, if function
39 //! `foo()` calls function `bar()` then the mono item for `foo()`
40 //! references the mono item for function `bar()`. In general, the
41 //! definition for mono item A referencing a mono item B is that
42 //! the LLVM artifact produced for A references the LLVM artifact produced
45 //! - Mono items and the references between them form a directed graph,
46 //! where the mono items are the nodes and references form the edges.
47 //! Let's call this graph the "mono item graph".
49 //! - The mono item graph for a program contains all mono items
50 //! that are needed in order to produce the complete LLVM IR of the program.
52 //! The purpose of the algorithm implemented in this module is to build the
53 //! mono item graph for the current crate. It runs in two phases:
55 //! 1. Discover the roots of the graph by traversing the HIR of the crate.
56 //! 2. Starting from the roots, find neighboring nodes by inspecting the MIR
57 //! representation of the item corresponding to a given node, until no more
58 //! new nodes are found.
60 //! ### Discovering roots
62 //! The roots of the mono item graph correspond to the non-generic
63 //! syntactic items in the source code. We find them by walking the HIR of the
64 //! crate, and whenever we hit upon a function, method, or static item, we
65 //! create a mono item consisting of the items DefId and, since we only
66 //! consider non-generic items, an empty type-substitution set.
68 //! ### Finding neighbor nodes
69 //! Given a mono item node, we can discover neighbors by inspecting its
70 //! MIR. We walk the MIR and any time we hit upon something that signifies a
71 //! reference to another mono item, we have found a neighbor. Since the
72 //! mono item we are currently at is always monomorphic, we also know the
73 //! concrete type arguments of its neighbors, and so all neighbors again will be
74 //! monomorphic. The specific forms a reference to a neighboring node can take
75 //! in MIR are quite diverse. Here is an overview:
77 //! #### Calling Functions/Methods
78 //! The most obvious form of one mono item referencing another is a
79 //! function or method call (represented by a CALL terminator in MIR). But
80 //! calls are not the only thing that might introduce a reference between two
81 //! function mono items, and as we will see below, they are just a
82 //! specialization of the form described next, and consequently will not get any
83 //! special treatment in the algorithm.
85 //! #### Taking a reference to a function or method
86 //! A function does not need to actually be called in order to be a neighbor of
87 //! another function. It suffices to just take a reference in order to introduce
88 //! an edge. Consider the following example:
91 //! fn print_val<T: Display>(x: T) {
92 //! println!("{}", x);
95 //! fn call_fn(f: &Fn(i32), x: i32) {
100 //! let print_i32 = print_val::<i32>;
101 //! call_fn(&print_i32, 0);
104 //! The MIR of none of these functions will contain an explicit call to
105 //! `print_val::<i32>`. Nonetheless, in order to mono this program, we need
106 //! an instance of this function. Thus, whenever we encounter a function or
107 //! method in operand position, we treat it as a neighbor of the current
108 //! mono item. Calls are just a special case of that.
111 //! In a way, closures are a simple case. Since every closure object needs to be
112 //! constructed somewhere, we can reliably discover them by observing
113 //! `RValue::Aggregate` expressions with `AggregateKind::Closure`. This is also
114 //! true for closures inlined from other crates.
117 //! Drop glue mono items are introduced by MIR drop-statements. The
118 //! generated mono item will again have drop-glue item neighbors if the
119 //! type to be dropped contains nested values that also need to be dropped. It
120 //! might also have a function item neighbor for the explicit `Drop::drop`
121 //! implementation of its type.
123 //! #### Unsizing Casts
124 //! A subtle way of introducing neighbor edges is by casting to a trait object.
125 //! Since the resulting fat-pointer contains a reference to a vtable, we need to
126 //! instantiate all object-save methods of the trait, as we need to store
127 //! pointers to these functions even if they never get called anywhere. This can
128 //! be seen as a special case of taking a function reference.
131 //! Since `Box` expression have special compiler support, no explicit calls to
132 //! `exchange_malloc()` and `box_free()` may show up in MIR, even if the
133 //! compiler will generate them. We have to observe `Rvalue::Box` expressions
134 //! and Box-typed drop-statements for that purpose.
137 //! Interaction with Cross-Crate Inlining
138 //! -------------------------------------
139 //! The binary of a crate will not only contain machine code for the items
140 //! defined in the source code of that crate. It will also contain monomorphic
141 //! instantiations of any extern generic functions and of functions marked with
143 //! The collection algorithm handles this more or less mono. If it is
144 //! about to create a mono item for something with an external `DefId`,
145 //! it will take a look if the MIR for that item is available, and if so just
146 //! proceed normally. If the MIR is not available, it assumes that the item is
147 //! just linked to and no node is created; which is exactly what we want, since
148 //! no machine code should be generated in the current crate for such an item.
150 //! Eager and Lazy Collection Mode
151 //! ------------------------------
152 //! Mono item collection can be performed in one of two modes:
154 //! - Lazy mode means that items will only be instantiated when actually
155 //! referenced. The goal is to produce the least amount of machine code
158 //! - Eager mode is meant to be used in conjunction with incremental compilation
159 //! where a stable set of mono items is more important than a minimal
160 //! one. Thus, eager mode will instantiate drop-glue for every drop-able type
161 //! in the crate, even if no drop call for that type exists (yet). It will
162 //! also instantiate default implementations of trait methods, something that
163 //! otherwise is only done on demand.
168 //! Some things are not yet fully implemented in the current version of this
172 //! Ideally, no mono item should be generated for const fns unless there
173 //! is a call to them that cannot be evaluated at compile time. At the moment
174 //! this is not implemented however: a mono item will be produced
175 //! regardless of whether it is actually needed or not.
177 use crate::monomorphize;
179 use rustc_data_structures::fx::{FxHashMap, FxHashSet};
180 use rustc_data_structures::sync::{par_iter, MTLock, MTRef, ParallelIterator};
181 use rustc_errors::{ErrorReported, FatalError};
182 use rustc_hir as hir;
183 use rustc_hir::def_id::{DefId, DefIdMap, LocalDefId, LOCAL_CRATE};
184 use rustc_hir::itemlikevisit::ItemLikeVisitor;
185 use rustc_hir::lang_items::LangItem;
186 use rustc_index::bit_set::GrowableBitSet;
187 use rustc_middle::middle::codegen_fn_attrs::CodegenFnAttrFlags;
188 use rustc_middle::mir::interpret::{AllocId, ConstValue};
189 use rustc_middle::mir::interpret::{ErrorHandled, GlobalAlloc, Scalar};
190 use rustc_middle::mir::mono::{InstantiationMode, MonoItem};
191 use rustc_middle::mir::visit::Visitor as MirVisitor;
192 use rustc_middle::mir::{self, Local, Location};
193 use rustc_middle::ty::adjustment::{CustomCoerceUnsized, PointerCast};
194 use rustc_middle::ty::print::obsolete::DefPathBasedNames;
195 use rustc_middle::ty::subst::{GenericArgKind, InternalSubsts};
196 use rustc_middle::ty::{self, GenericParamDefKind, Instance, Ty, TyCtxt, TypeFoldable};
197 use rustc_session::config::EntryFnType;
198 use rustc_span::source_map::{dummy_spanned, respan, Span, Spanned, DUMMY_SP};
199 use smallvec::SmallVec;
203 pub enum MonoItemCollectionMode {
208 /// Maps every mono item to all mono items it references in its
210 pub struct InliningMap<'tcx> {
211 // Maps a source mono item to the range of mono items
213 // The two numbers in the tuple are the start (inclusive) and
214 // end index (exclusive) within the `targets` vecs.
215 index: FxHashMap<MonoItem<'tcx>, (usize, usize)>,
216 targets: Vec<MonoItem<'tcx>>,
218 // Contains one bit per mono item in the `targets` field. That bit
219 // is true if that mono item needs to be inlined into every CGU.
220 inlines: GrowableBitSet<usize>,
223 impl<'tcx> InliningMap<'tcx> {
224 fn new() -> InliningMap<'tcx> {
226 index: FxHashMap::default(),
228 inlines: GrowableBitSet::with_capacity(1024),
232 fn record_accesses(&mut self, source: MonoItem<'tcx>, new_targets: &[(MonoItem<'tcx>, bool)]) {
233 let start_index = self.targets.len();
234 let new_items_count = new_targets.len();
235 let new_items_count_total = new_items_count + self.targets.len();
237 self.targets.reserve(new_items_count);
238 self.inlines.ensure(new_items_count_total);
240 for (i, (target, inline)) in new_targets.iter().enumerate() {
241 self.targets.push(*target);
243 self.inlines.insert(i + start_index);
247 let end_index = self.targets.len();
248 assert!(self.index.insert(source, (start_index, end_index)).is_none());
251 // Internally iterate over all items referenced by `source` which will be
252 // made available for inlining.
253 pub fn with_inlining_candidates<F>(&self, source: MonoItem<'tcx>, mut f: F)
255 F: FnMut(MonoItem<'tcx>),
257 if let Some(&(start_index, end_index)) = self.index.get(&source) {
258 for (i, candidate) in self.targets[start_index..end_index].iter().enumerate() {
259 if self.inlines.contains(start_index + i) {
266 // Internally iterate over all items and the things each accesses.
267 pub fn iter_accesses<F>(&self, mut f: F)
269 F: FnMut(MonoItem<'tcx>, &[MonoItem<'tcx>]),
271 for (&accessor, &(start_index, end_index)) in &self.index {
272 f(accessor, &self.targets[start_index..end_index])
277 pub fn collect_crate_mono_items(
279 mode: MonoItemCollectionMode,
280 ) -> (FxHashSet<MonoItem<'_>>, InliningMap<'_>) {
281 let _prof_timer = tcx.prof.generic_activity("monomorphization_collector");
284 tcx.sess.time("monomorphization_collector_root_collections", || collect_roots(tcx, mode));
286 debug!("building mono item graph, beginning at roots");
288 let mut visited = MTLock::new(FxHashSet::default());
289 let mut inlining_map = MTLock::new(InliningMap::new());
292 let visited: MTRef<'_, _> = &mut visited;
293 let inlining_map: MTRef<'_, _> = &mut inlining_map;
295 tcx.sess.time("monomorphization_collector_graph_walk", || {
296 par_iter(roots).for_each(|root| {
297 let mut recursion_depths = DefIdMap::default();
302 &mut recursion_depths,
309 (visited.into_inner(), inlining_map.into_inner())
312 // Find all non-generic items by walking the HIR. These items serve as roots to
313 // start monomorphizing from.
314 fn collect_roots(tcx: TyCtxt<'_>, mode: MonoItemCollectionMode) -> Vec<MonoItem<'_>> {
315 debug!("collecting roots");
316 let mut roots = Vec::new();
319 let entry_fn = tcx.entry_fn(LOCAL_CRATE);
321 debug!("collect_roots: entry_fn = {:?}", entry_fn);
323 let mut visitor = RootCollector { tcx, mode, entry_fn, output: &mut roots };
325 tcx.hir().krate().visit_all_item_likes(&mut visitor);
327 visitor.push_extra_entry_roots();
330 // We can only codegen items that are instantiable - items all of
331 // whose predicates hold. Luckily, items that aren't instantiable
332 // can't actually be used, so we can just skip codegenning them.
335 .filter_map(|root| root.node.is_instantiable(tcx).then_some(root.node))
339 // Collect all monomorphized items reachable from `starting_point`
340 fn collect_items_rec<'tcx>(
342 starting_point: Spanned<MonoItem<'tcx>>,
343 visited: MTRef<'_, MTLock<FxHashSet<MonoItem<'tcx>>>>,
344 recursion_depths: &mut DefIdMap<usize>,
345 inlining_map: MTRef<'_, MTLock<InliningMap<'tcx>>>,
347 if !visited.lock_mut().insert(starting_point.node) {
348 // We've been here already, no need to search again.
351 debug!("BEGIN collect_items_rec({})", starting_point.node.to_string(tcx, true));
353 let mut neighbors = Vec::new();
354 let recursion_depth_reset;
356 match starting_point.node {
357 MonoItem::Static(def_id) => {
358 let instance = Instance::mono(tcx, def_id);
360 // Sanity check whether this ended up being collected accidentally
361 debug_assert!(should_codegen_locally(tcx, &instance));
363 let ty = instance.ty(tcx, ty::ParamEnv::reveal_all());
364 visit_drop_use(tcx, ty, true, starting_point.span, &mut neighbors);
366 recursion_depth_reset = None;
368 if let Ok(val) = tcx.const_eval_poly(def_id) {
369 collect_const_value(tcx, val, &mut neighbors);
372 MonoItem::Fn(instance) => {
373 // Sanity check whether this ended up being collected accidentally
374 debug_assert!(should_codegen_locally(tcx, &instance));
376 // Keep track of the monomorphization recursion depth
377 recursion_depth_reset =
378 Some(check_recursion_limit(tcx, instance, starting_point.span, recursion_depths));
379 check_type_length_limit(tcx, instance);
381 rustc_data_structures::stack::ensure_sufficient_stack(|| {
382 collect_neighbours(tcx, instance, &mut neighbors);
385 MonoItem::GlobalAsm(..) => {
386 recursion_depth_reset = None;
390 record_accesses(tcx, starting_point.node, neighbors.iter().map(|i| &i.node), inlining_map);
392 for neighbour in neighbors {
393 collect_items_rec(tcx, neighbour, visited, recursion_depths, inlining_map);
396 if let Some((def_id, depth)) = recursion_depth_reset {
397 recursion_depths.insert(def_id, depth);
400 debug!("END collect_items_rec({})", starting_point.node.to_string(tcx, true));
403 fn record_accesses<'a, 'tcx: 'a>(
405 caller: MonoItem<'tcx>,
406 callees: impl Iterator<Item = &'a MonoItem<'tcx>>,
407 inlining_map: MTRef<'_, MTLock<InliningMap<'tcx>>>,
409 let is_inlining_candidate = |mono_item: &MonoItem<'tcx>| {
410 mono_item.instantiation_mode(tcx) == InstantiationMode::LocalCopy
413 // We collect this into a `SmallVec` to avoid calling `is_inlining_candidate` in the lock.
414 // FIXME: Call `is_inlining_candidate` when pushing to `neighbors` in `collect_items_rec`
415 // instead to avoid creating this `SmallVec`.
416 let accesses: SmallVec<[_; 128]> =
417 callees.map(|mono_item| (*mono_item, is_inlining_candidate(mono_item))).collect();
419 inlining_map.lock_mut().record_accesses(caller, &accesses);
422 fn check_recursion_limit<'tcx>(
424 instance: Instance<'tcx>,
426 recursion_depths: &mut DefIdMap<usize>,
427 ) -> (DefId, usize) {
428 let def_id = instance.def_id();
429 let recursion_depth = recursion_depths.get(&def_id).cloned().unwrap_or(0);
430 debug!(" => recursion depth={}", recursion_depth);
432 let adjusted_recursion_depth = if Some(def_id) == tcx.lang_items().drop_in_place_fn() {
433 // HACK: drop_in_place creates tight monomorphization loops. Give
440 // Code that needs to instantiate the same function recursively
441 // more than the recursion limit is assumed to be causing an
442 // infinite expansion.
443 if !tcx.sess.recursion_limit().value_within_limit(adjusted_recursion_depth) {
444 let error = format!("reached the recursion limit while instantiating `{}`", instance);
445 let mut err = tcx.sess.struct_span_fatal(span, &error);
447 tcx.def_span(def_id),
448 &format!("`{}` defined here", tcx.def_path_str(def_id)),
454 recursion_depths.insert(def_id, recursion_depth + 1);
456 (def_id, recursion_depth)
459 fn check_type_length_limit<'tcx>(tcx: TyCtxt<'tcx>, instance: Instance<'tcx>) {
460 let type_length = instance
463 .flat_map(|arg| arg.walk())
464 .filter(|arg| match arg.unpack() {
465 GenericArgKind::Type(_) | GenericArgKind::Const(_) => true,
466 GenericArgKind::Lifetime(_) => false,
469 debug!(" => type length={}", type_length);
471 // Rust code can easily create exponentially-long types using only a
472 // polynomial recursion depth. Even with the default recursion
473 // depth, you can easily get cases that take >2^60 steps to run,
474 // which means that rustc basically hangs.
476 // Bail out in these cases to avoid that bad user experience.
477 if !tcx.sess.type_length_limit().value_within_limit(type_length) {
478 // The instance name is already known to be too long for rustc.
479 // Show only the first and last 32 characters to avoid blasting
480 // the user's terminal with thousands of lines of type-name.
481 let shrink = |s: String, before: usize, after: usize| {
482 // An iterator of all byte positions including the end of the string.
483 let positions = || s.char_indices().map(|(i, _)| i).chain(iter::once(s.len()));
485 let shrunk = format!(
486 "{before}...{after}",
487 before = &s[..positions().nth(before).unwrap_or(s.len())],
488 after = &s[positions().rev().nth(after).unwrap_or(0)..],
491 // Only use the shrunk version if it's really shorter.
492 // This also avoids the case where before and after slices overlap.
493 if shrunk.len() < s.len() { shrunk } else { s }
496 "reached the type-length limit while instantiating `{}`",
497 shrink(instance.to_string(), 32, 32)
499 let mut diag = tcx.sess.struct_span_fatal(tcx.def_span(instance.def_id()), &msg);
501 "consider adding a `#![type_length_limit=\"{}\"]` attribute to your crate",
505 tcx.sess.abort_if_errors();
509 struct MirNeighborCollector<'a, 'tcx> {
511 body: &'a mir::Body<'tcx>,
512 output: &'a mut Vec<Spanned<MonoItem<'tcx>>>,
513 instance: Instance<'tcx>,
516 impl<'a, 'tcx> MirNeighborCollector<'a, 'tcx> {
517 pub fn monomorphize<T>(&self, value: T) -> T
519 T: TypeFoldable<'tcx>,
521 debug!("monomorphize: self.instance={:?}", self.instance);
522 if let Some(substs) = self.instance.substs_for_mir_body() {
523 self.tcx.subst_and_normalize_erasing_regions(substs, ty::ParamEnv::reveal_all(), &value)
525 self.tcx.normalize_erasing_regions(ty::ParamEnv::reveal_all(), value)
530 impl<'a, 'tcx> MirVisitor<'tcx> for MirNeighborCollector<'a, 'tcx> {
531 fn visit_rvalue(&mut self, rvalue: &mir::Rvalue<'tcx>, location: Location) {
532 debug!("visiting rvalue {:?}", *rvalue);
534 let span = self.body.source_info(location).span;
537 // When doing an cast from a regular pointer to a fat pointer, we
538 // have to instantiate all methods of the trait being cast to, so we
539 // can build the appropriate vtable.
541 mir::CastKind::Pointer(PointerCast::Unsize),
545 let target_ty = self.monomorphize(target_ty);
546 let source_ty = operand.ty(self.body, self.tcx);
547 let source_ty = self.monomorphize(source_ty);
548 let (source_ty, target_ty) =
549 find_vtable_types_for_unsizing(self.tcx, source_ty, target_ty);
550 // This could also be a different Unsize instruction, like
551 // from a fixed sized array to a slice. But we are only
552 // interested in things that produce a vtable.
553 if target_ty.is_trait() && !source_ty.is_trait() {
554 create_mono_items_for_vtable_methods(
564 mir::CastKind::Pointer(PointerCast::ReifyFnPointer),
568 let fn_ty = operand.ty(self.body, self.tcx);
569 let fn_ty = self.monomorphize(fn_ty);
570 visit_fn_use(self.tcx, fn_ty, false, span, &mut self.output);
573 mir::CastKind::Pointer(PointerCast::ClosureFnPointer(_)),
577 let source_ty = operand.ty(self.body, self.tcx);
578 let source_ty = self.monomorphize(source_ty);
579 match source_ty.kind {
580 ty::Closure(def_id, substs) => {
581 let instance = Instance::resolve_closure(
585 ty::ClosureKind::FnOnce,
587 if should_codegen_locally(self.tcx, &instance) {
588 self.output.push(create_fn_mono_item(self.tcx, instance, span));
594 mir::Rvalue::NullaryOp(mir::NullOp::Box, _) => {
596 let exchange_malloc_fn_def_id =
597 tcx.require_lang_item(LangItem::ExchangeMalloc, None);
598 let instance = Instance::mono(tcx, exchange_malloc_fn_def_id);
599 if should_codegen_locally(tcx, &instance) {
600 self.output.push(create_fn_mono_item(self.tcx, instance, span));
603 mir::Rvalue::ThreadLocalRef(def_id) => {
604 assert!(self.tcx.is_thread_local_static(def_id));
605 let instance = Instance::mono(self.tcx, def_id);
606 if should_codegen_locally(self.tcx, &instance) {
607 trace!("collecting thread-local static {:?}", def_id);
608 self.output.push(respan(span, MonoItem::Static(def_id)));
611 _ => { /* not interesting */ }
614 self.super_rvalue(rvalue, location);
617 fn visit_const(&mut self, constant: &&'tcx ty::Const<'tcx>, location: Location) {
618 debug!("visiting const {:?} @ {:?}", *constant, location);
620 let substituted_constant = self.monomorphize(*constant);
621 let param_env = ty::ParamEnv::reveal_all();
623 match substituted_constant.val {
624 ty::ConstKind::Value(val) => collect_const_value(self.tcx, val, self.output),
625 ty::ConstKind::Unevaluated(def, substs, promoted) => {
626 match self.tcx.const_eval_resolve(param_env, def, substs, promoted, None) {
627 Ok(val) => collect_const_value(self.tcx, val, self.output),
628 Err(ErrorHandled::Reported(ErrorReported) | ErrorHandled::Linted) => {}
629 Err(ErrorHandled::TooGeneric) => span_bug!(
630 self.body.source_info(location).span,
631 "collection encountered polymorphic constant: {}",
639 self.super_const(constant);
642 fn visit_terminator(&mut self, terminator: &mir::Terminator<'tcx>, location: Location) {
643 debug!("visiting terminator {:?} @ {:?}", terminator, location);
644 let source = self.body.source_info(location).span;
647 match terminator.kind {
648 mir::TerminatorKind::Call { ref func, .. } => {
649 let callee_ty = func.ty(self.body, tcx);
650 let callee_ty = self.monomorphize(callee_ty);
651 visit_fn_use(self.tcx, callee_ty, true, source, &mut self.output);
653 mir::TerminatorKind::Drop { ref place, .. }
654 | mir::TerminatorKind::DropAndReplace { ref place, .. } => {
655 let ty = place.ty(self.body, self.tcx).ty;
656 let ty = self.monomorphize(ty);
657 visit_drop_use(self.tcx, ty, true, source, self.output);
659 mir::TerminatorKind::InlineAsm { ref operands, .. } => {
662 mir::InlineAsmOperand::SymFn { ref value } => {
663 let fn_ty = self.monomorphize(value.literal.ty);
664 visit_fn_use(self.tcx, fn_ty, false, source, &mut self.output);
666 mir::InlineAsmOperand::SymStatic { def_id } => {
667 let instance = Instance::mono(self.tcx, def_id);
668 if should_codegen_locally(self.tcx, &instance) {
669 trace!("collecting asm sym static {:?}", def_id);
670 self.output.push(respan(source, MonoItem::Static(def_id)));
677 mir::TerminatorKind::Goto { .. }
678 | mir::TerminatorKind::SwitchInt { .. }
679 | mir::TerminatorKind::Resume
680 | mir::TerminatorKind::Abort
681 | mir::TerminatorKind::Return
682 | mir::TerminatorKind::Unreachable
683 | mir::TerminatorKind::Assert { .. } => {}
684 mir::TerminatorKind::GeneratorDrop
685 | mir::TerminatorKind::Yield { .. }
686 | mir::TerminatorKind::FalseEdge { .. }
687 | mir::TerminatorKind::FalseUnwind { .. } => bug!(),
690 self.super_terminator(terminator, location);
695 _place_local: &Local,
696 _context: mir::visit::PlaceContext,
702 fn visit_drop_use<'tcx>(
705 is_direct_call: bool,
707 output: &mut Vec<Spanned<MonoItem<'tcx>>>,
709 let instance = Instance::resolve_drop_in_place(tcx, ty);
710 visit_instance_use(tcx, instance, is_direct_call, source, output);
713 fn visit_fn_use<'tcx>(
716 is_direct_call: bool,
718 output: &mut Vec<Spanned<MonoItem<'tcx>>>,
720 if let ty::FnDef(def_id, substs) = ty.kind {
721 let instance = if is_direct_call {
722 ty::Instance::resolve(tcx, ty::ParamEnv::reveal_all(), def_id, substs).unwrap().unwrap()
724 ty::Instance::resolve_for_fn_ptr(tcx, ty::ParamEnv::reveal_all(), def_id, substs)
727 visit_instance_use(tcx, instance, is_direct_call, source, output);
731 fn visit_instance_use<'tcx>(
733 instance: ty::Instance<'tcx>,
734 is_direct_call: bool,
736 output: &mut Vec<Spanned<MonoItem<'tcx>>>,
738 debug!("visit_item_use({:?}, is_direct_call={:?})", instance, is_direct_call);
739 if !should_codegen_locally(tcx, &instance) {
744 ty::InstanceDef::Virtual(..) | ty::InstanceDef::Intrinsic(_) => {
746 bug!("{:?} being reified", instance);
749 ty::InstanceDef::DropGlue(_, None) => {
750 // Don't need to emit noop drop glue if we are calling directly.
752 output.push(create_fn_mono_item(tcx, instance, source));
755 ty::InstanceDef::DropGlue(_, Some(_))
756 | ty::InstanceDef::VtableShim(..)
757 | ty::InstanceDef::ReifyShim(..)
758 | ty::InstanceDef::ClosureOnceShim { .. }
759 | ty::InstanceDef::Item(..)
760 | ty::InstanceDef::FnPtrShim(..)
761 | ty::InstanceDef::CloneShim(..) => {
762 output.push(create_fn_mono_item(tcx, instance, source));
767 // Returns `true` if we should codegen an instance in the local crate.
768 // Returns `false` if we can just link to the upstream crate and therefore don't
770 fn should_codegen_locally<'tcx>(tcx: TyCtxt<'tcx>, instance: &Instance<'tcx>) -> bool {
771 let def_id = match instance.def {
772 ty::InstanceDef::Item(def) => def.did,
773 ty::InstanceDef::DropGlue(def_id, Some(_)) => def_id,
774 ty::InstanceDef::VtableShim(..)
775 | ty::InstanceDef::ReifyShim(..)
776 | ty::InstanceDef::ClosureOnceShim { .. }
777 | ty::InstanceDef::Virtual(..)
778 | ty::InstanceDef::FnPtrShim(..)
779 | ty::InstanceDef::DropGlue(..)
780 | ty::InstanceDef::Intrinsic(_)
781 | ty::InstanceDef::CloneShim(..) => return true,
784 if tcx.is_foreign_item(def_id) {
785 // Foreign items are always linked against, there's no way of instantiating them.
789 if def_id.is_local() {
790 // Local items cannot be referred to locally without monomorphizing them locally.
794 if tcx.is_reachable_non_generic(def_id)
795 || instance.polymorphize(tcx).upstream_monomorphization(tcx).is_some()
797 // We can link to the item in question, no instance needed in this crate.
801 if !tcx.is_mir_available(def_id) {
802 bug!("cannot create local mono-item for {:?}", def_id)
808 /// For a given pair of source and target type that occur in an unsizing coercion,
809 /// this function finds the pair of types that determines the vtable linking
812 /// For example, the source type might be `&SomeStruct` and the target type\
813 /// might be `&SomeTrait` in a cast like:
815 /// let src: &SomeStruct = ...;
816 /// let target = src as &SomeTrait;
818 /// Then the output of this function would be (SomeStruct, SomeTrait) since for
819 /// constructing the `target` fat-pointer we need the vtable for that pair.
821 /// Things can get more complicated though because there's also the case where
822 /// the unsized type occurs as a field:
825 /// struct ComplexStruct<T: ?Sized> {
832 /// In this case, if `T` is sized, `&ComplexStruct<T>` is a thin pointer. If `T`
833 /// is unsized, `&SomeStruct` is a fat pointer, and the vtable it points to is
834 /// for the pair of `T` (which is a trait) and the concrete type that `T` was
835 /// originally coerced from:
837 /// let src: &ComplexStruct<SomeStruct> = ...;
838 /// let target = src as &ComplexStruct<SomeTrait>;
840 /// Again, we want this `find_vtable_types_for_unsizing()` to provide the pair
841 /// `(SomeStruct, SomeTrait)`.
843 /// Finally, there is also the case of custom unsizing coercions, e.g., for
844 /// smart pointers such as `Rc` and `Arc`.
845 fn find_vtable_types_for_unsizing<'tcx>(
849 ) -> (Ty<'tcx>, Ty<'tcx>) {
850 let ptr_vtable = |inner_source: Ty<'tcx>, inner_target: Ty<'tcx>| {
851 let param_env = ty::ParamEnv::reveal_all();
852 let type_has_metadata = |ty: Ty<'tcx>| -> bool {
853 if ty.is_sized(tcx.at(DUMMY_SP), param_env) {
856 let tail = tcx.struct_tail_erasing_lifetimes(ty, param_env);
858 ty::Foreign(..) => false,
859 ty::Str | ty::Slice(..) | ty::Dynamic(..) => true,
860 _ => bug!("unexpected unsized tail: {:?}", tail),
863 if type_has_metadata(inner_source) {
864 (inner_source, inner_target)
866 tcx.struct_lockstep_tails_erasing_lifetimes(inner_source, inner_target, param_env)
870 match (&source_ty.kind, &target_ty.kind) {
871 (&ty::Ref(_, a, _), &ty::Ref(_, b, _) | &ty::RawPtr(ty::TypeAndMut { ty: b, .. }))
872 | (&ty::RawPtr(ty::TypeAndMut { ty: a, .. }), &ty::RawPtr(ty::TypeAndMut { ty: b, .. })) => {
875 (&ty::Adt(def_a, _), &ty::Adt(def_b, _)) if def_a.is_box() && def_b.is_box() => {
876 ptr_vtable(source_ty.boxed_ty(), target_ty.boxed_ty())
879 (&ty::Adt(source_adt_def, source_substs), &ty::Adt(target_adt_def, target_substs)) => {
880 assert_eq!(source_adt_def, target_adt_def);
882 let CustomCoerceUnsized::Struct(coerce_index) =
883 monomorphize::custom_coerce_unsize_info(tcx, source_ty, target_ty);
885 let source_fields = &source_adt_def.non_enum_variant().fields;
886 let target_fields = &target_adt_def.non_enum_variant().fields;
889 coerce_index < source_fields.len() && source_fields.len() == target_fields.len()
892 find_vtable_types_for_unsizing(
894 source_fields[coerce_index].ty(tcx, source_substs),
895 target_fields[coerce_index].ty(tcx, target_substs),
899 "find_vtable_types_for_unsizing: invalid coercion {:?} -> {:?}",
906 fn create_fn_mono_item<'tcx>(
908 instance: Instance<'tcx>,
910 ) -> Spanned<MonoItem<'tcx>> {
911 debug!("create_fn_mono_item(instance={})", instance);
912 respan(source, MonoItem::Fn(instance.polymorphize(tcx)))
915 /// Creates a `MonoItem` for each method that is referenced by the vtable for
916 /// the given trait/impl pair.
917 fn create_mono_items_for_vtable_methods<'tcx>(
922 output: &mut Vec<Spanned<MonoItem<'tcx>>>,
924 assert!(!trait_ty.has_escaping_bound_vars() && !impl_ty.has_escaping_bound_vars());
926 if let ty::Dynamic(ref trait_ty, ..) = trait_ty.kind {
927 if let Some(principal) = trait_ty.principal() {
928 let poly_trait_ref = principal.with_self_ty(tcx, impl_ty);
929 assert!(!poly_trait_ref.has_escaping_bound_vars());
931 // Walk all methods of the trait, including those of its supertraits
932 let methods = tcx.vtable_methods(poly_trait_ref);
933 let methods = methods
936 .filter_map(|method| method)
937 .map(|(def_id, substs)| {
938 ty::Instance::resolve_for_vtable(
940 ty::ParamEnv::reveal_all(),
946 .filter(|&instance| should_codegen_locally(tcx, &instance))
947 .map(|item| create_fn_mono_item(tcx, item, source));
948 output.extend(methods);
951 // Also add the destructor.
952 visit_drop_use(tcx, impl_ty, false, source, output);
956 //=-----------------------------------------------------------------------------
958 //=-----------------------------------------------------------------------------
960 struct RootCollector<'a, 'tcx> {
962 mode: MonoItemCollectionMode,
963 output: &'a mut Vec<Spanned<MonoItem<'tcx>>>,
964 entry_fn: Option<(LocalDefId, EntryFnType)>,
967 impl ItemLikeVisitor<'v> for RootCollector<'_, 'v> {
968 fn visit_item(&mut self, item: &'v hir::Item<'v>) {
970 hir::ItemKind::ExternCrate(..)
971 | hir::ItemKind::Use(..)
972 | hir::ItemKind::ForeignMod(..)
973 | hir::ItemKind::TyAlias(..)
974 | hir::ItemKind::Trait(..)
975 | hir::ItemKind::TraitAlias(..)
976 | hir::ItemKind::OpaqueTy(..)
977 | hir::ItemKind::Mod(..) => {
978 // Nothing to do, just keep recursing.
981 hir::ItemKind::Impl { .. } => {
982 if self.mode == MonoItemCollectionMode::Eager {
983 create_mono_items_for_default_impls(self.tcx, item, self.output);
987 hir::ItemKind::Enum(_, ref generics)
988 | hir::ItemKind::Struct(_, ref generics)
989 | hir::ItemKind::Union(_, ref generics) => {
990 if generics.params.is_empty() {
991 if self.mode == MonoItemCollectionMode::Eager {
992 let def_id = self.tcx.hir().local_def_id(item.hir_id);
994 "RootCollector: ADT drop-glue for {}",
995 def_id_to_string(self.tcx, def_id)
998 let ty = Instance::new(def_id.to_def_id(), InternalSubsts::empty())
999 .ty(self.tcx, ty::ParamEnv::reveal_all());
1000 visit_drop_use(self.tcx, ty, true, DUMMY_SP, self.output);
1004 hir::ItemKind::GlobalAsm(..) => {
1006 "RootCollector: ItemKind::GlobalAsm({})",
1007 def_id_to_string(self.tcx, self.tcx.hir().local_def_id(item.hir_id))
1009 self.output.push(dummy_spanned(MonoItem::GlobalAsm(item.hir_id)));
1011 hir::ItemKind::Static(..) => {
1012 let def_id = self.tcx.hir().local_def_id(item.hir_id);
1013 debug!("RootCollector: ItemKind::Static({})", def_id_to_string(self.tcx, def_id));
1014 self.output.push(dummy_spanned(MonoItem::Static(def_id.to_def_id())));
1016 hir::ItemKind::Const(..) => {
1017 // const items only generate mono items if they are
1018 // actually used somewhere. Just declaring them is insufficient.
1020 // but even just declaring them must collect the items they refer to
1021 let def_id = self.tcx.hir().local_def_id(item.hir_id);
1023 if let Ok(val) = self.tcx.const_eval_poly(def_id.to_def_id()) {
1024 collect_const_value(self.tcx, val, &mut self.output);
1027 hir::ItemKind::Fn(..) => {
1028 let def_id = self.tcx.hir().local_def_id(item.hir_id);
1029 self.push_if_root(def_id);
1034 fn visit_trait_item(&mut self, _: &'v hir::TraitItem<'v>) {
1035 // Even if there's a default body with no explicit generics,
1036 // it's still generic over some `Self: Trait`, so not a root.
1039 fn visit_impl_item(&mut self, ii: &'v hir::ImplItem<'v>) {
1040 if let hir::ImplItemKind::Fn(hir::FnSig { .. }, _) = ii.kind {
1041 let def_id = self.tcx.hir().local_def_id(ii.hir_id);
1042 self.push_if_root(def_id);
1047 impl RootCollector<'_, 'v> {
1048 fn is_root(&self, def_id: LocalDefId) -> bool {
1049 !item_requires_monomorphization(self.tcx, def_id)
1050 && match self.mode {
1051 MonoItemCollectionMode::Eager => true,
1052 MonoItemCollectionMode::Lazy => {
1053 self.entry_fn.map(|(id, _)| id) == Some(def_id)
1054 || self.tcx.is_reachable_non_generic(def_id)
1057 .codegen_fn_attrs(def_id)
1059 .contains(CodegenFnAttrFlags::RUSTC_STD_INTERNAL_SYMBOL)
1064 /// If `def_id` represents a root, pushes it onto the list of
1065 /// outputs. (Note that all roots must be monomorphic.)
1066 fn push_if_root(&mut self, def_id: LocalDefId) {
1067 if self.is_root(def_id) {
1068 debug!("RootCollector::push_if_root: found root def_id={:?}", def_id);
1070 let instance = Instance::mono(self.tcx, def_id.to_def_id());
1071 self.output.push(create_fn_mono_item(self.tcx, instance, DUMMY_SP));
1075 /// As a special case, when/if we encounter the
1076 /// `main()` function, we also have to generate a
1077 /// monomorphized copy of the start lang item based on
1078 /// the return type of `main`. This is not needed when
1079 /// the user writes their own `start` manually.
1080 fn push_extra_entry_roots(&mut self) {
1081 let main_def_id = match self.entry_fn {
1082 Some((def_id, EntryFnType::Main)) => def_id,
1086 let start_def_id = match self.tcx.lang_items().require(LangItem::Start) {
1088 Err(err) => self.tcx.sess.fatal(&err),
1090 let main_ret_ty = self.tcx.fn_sig(main_def_id).output();
1092 // Given that `main()` has no arguments,
1093 // then its return type cannot have
1094 // late-bound regions, since late-bound
1095 // regions must appear in the argument
1097 let main_ret_ty = self.tcx.erase_regions(&main_ret_ty.no_bound_vars().unwrap());
1099 let start_instance = Instance::resolve(
1101 ty::ParamEnv::reveal_all(),
1103 self.tcx.intern_substs(&[main_ret_ty.into()]),
1108 self.output.push(create_fn_mono_item(self.tcx, start_instance, DUMMY_SP));
1112 fn item_requires_monomorphization(tcx: TyCtxt<'_>, def_id: LocalDefId) -> bool {
1113 let generics = tcx.generics_of(def_id);
1114 generics.requires_monomorphization(tcx)
1117 fn create_mono_items_for_default_impls<'tcx>(
1119 item: &'tcx hir::Item<'tcx>,
1120 output: &mut Vec<Spanned<MonoItem<'tcx>>>,
1123 hir::ItemKind::Impl { ref generics, ref items, .. } => {
1124 for param in generics.params {
1126 hir::GenericParamKind::Lifetime { .. } => {}
1127 hir::GenericParamKind::Type { .. } | hir::GenericParamKind::Const { .. } => {
1133 let impl_def_id = tcx.hir().local_def_id(item.hir_id);
1136 "create_mono_items_for_default_impls(item={})",
1137 def_id_to_string(tcx, impl_def_id)
1140 if let Some(trait_ref) = tcx.impl_trait_ref(impl_def_id) {
1141 let param_env = ty::ParamEnv::reveal_all();
1142 let trait_ref = tcx.normalize_erasing_regions(param_env, trait_ref);
1143 let overridden_methods: FxHashSet<_> =
1144 items.iter().map(|iiref| iiref.ident.normalize_to_macros_2_0()).collect();
1145 for method in tcx.provided_trait_methods(trait_ref.def_id) {
1146 if overridden_methods.contains(&method.ident.normalize_to_macros_2_0()) {
1150 if tcx.generics_of(method.def_id).own_requires_monomorphization() {
1155 InternalSubsts::for_item(tcx, method.def_id, |param, _| match param.kind {
1156 GenericParamDefKind::Lifetime => tcx.lifetimes.re_erased.into(),
1157 GenericParamDefKind::Type { .. } | GenericParamDefKind::Const => {
1158 trait_ref.substs[param.index as usize]
1161 let instance = ty::Instance::resolve(tcx, param_env, method.def_id, substs)
1165 let mono_item = create_fn_mono_item(tcx, instance, DUMMY_SP);
1166 if mono_item.node.is_instantiable(tcx) && should_codegen_locally(tcx, &instance)
1168 output.push(mono_item);
1177 /// Scans the miri alloc in order to find function calls, closures, and drop-glue.
1178 fn collect_miri<'tcx>(
1181 output: &mut Vec<Spanned<MonoItem<'tcx>>>,
1183 match tcx.global_alloc(alloc_id) {
1184 GlobalAlloc::Static(def_id) => {
1185 assert!(!tcx.is_thread_local_static(def_id));
1186 let instance = Instance::mono(tcx, def_id);
1187 if should_codegen_locally(tcx, &instance) {
1188 trace!("collecting static {:?}", def_id);
1189 output.push(dummy_spanned(MonoItem::Static(def_id)));
1192 GlobalAlloc::Memory(alloc) => {
1193 trace!("collecting {:?} with {:#?}", alloc_id, alloc);
1194 for &((), inner) in alloc.relocations().values() {
1195 rustc_data_structures::stack::ensure_sufficient_stack(|| {
1196 collect_miri(tcx, inner, output);
1200 GlobalAlloc::Function(fn_instance) => {
1201 if should_codegen_locally(tcx, &fn_instance) {
1202 trace!("collecting {:?} with {:#?}", alloc_id, fn_instance);
1203 output.push(create_fn_mono_item(tcx, fn_instance, DUMMY_SP));
1209 /// Scans the MIR in order to find function calls, closures, and drop-glue.
1210 fn collect_neighbours<'tcx>(
1212 instance: Instance<'tcx>,
1213 output: &mut Vec<Spanned<MonoItem<'tcx>>>,
1215 debug!("collect_neighbours: {:?}", instance.def_id());
1216 let body = tcx.instance_mir(instance.def);
1218 MirNeighborCollector { tcx, body: &body, output, instance }.visit_body(&body);
1221 fn def_id_to_string(tcx: TyCtxt<'_>, def_id: LocalDefId) -> String {
1222 let mut output = String::new();
1223 let printer = DefPathBasedNames::new(tcx, false, false);
1224 printer.push_def_path(def_id.to_def_id(), &mut output);
1228 fn collect_const_value<'tcx>(
1230 value: ConstValue<'tcx>,
1231 output: &mut Vec<Spanned<MonoItem<'tcx>>>,
1234 ConstValue::Scalar(Scalar::Ptr(ptr)) => collect_miri(tcx, ptr.alloc_id, output),
1235 ConstValue::Slice { data: alloc, start: _, end: _ } | ConstValue::ByRef { alloc, .. } => {
1236 for &((), id) in alloc.relocations().values() {
1237 collect_miri(tcx, id, output);