1 //! Mono Item Collection
2 //! ====================
4 //! This module is responsible for discovering all items that will contribute to
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 //! specialized of the form described next, and consequently will don't 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 of 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::middle::codegen_fn_attrs::CodegenFnAttrFlags;
180 use rustc::middle::lang_items::{ExchangeMallocFnLangItem, StartFnLangItem};
181 use rustc::mir::interpret::{AllocId, ConstValue};
182 use rustc::mir::interpret::{ErrorHandled, GlobalAlloc, Scalar};
183 use rustc::mir::mono::{InstantiationMode, MonoItem};
184 use rustc::mir::visit::Visitor as MirVisitor;
185 use rustc::mir::{self, Local, Location};
186 use rustc::session::config::EntryFnType;
187 use rustc::ty::adjustment::{CustomCoerceUnsized, PointerCast};
188 use rustc::ty::print::obsolete::DefPathBasedNames;
189 use rustc::ty::subst::{InternalSubsts, SubstsRef};
190 use rustc::ty::{self, GenericParamDefKind, Instance, Ty, TyCtxt, TypeFoldable};
191 use rustc_data_structures::fx::{FxHashMap, FxHashSet};
192 use rustc_data_structures::sync::{par_iter, MTLock, MTRef, ParallelIterator};
193 use rustc_hir as hir;
194 use rustc_hir::def_id::{DefId, DefIdMap, LOCAL_CRATE};
195 use rustc_hir::itemlikevisit::ItemLikeVisitor;
196 use rustc_index::bit_set::GrowableBitSet;
197 use smallvec::SmallVec;
201 pub enum MonoItemCollectionMode {
206 /// Maps every mono item to all mono items it references in its
208 pub struct InliningMap<'tcx> {
209 // Maps a source mono item to the range of mono items
211 // The two numbers in the tuple are the start (inclusive) and
212 // end index (exclusive) within the `targets` vecs.
213 index: FxHashMap<MonoItem<'tcx>, (usize, usize)>,
214 targets: Vec<MonoItem<'tcx>>,
216 // Contains one bit per mono item in the `targets` field. That bit
217 // is true if that mono item needs to be inlined into every CGU.
218 inlines: GrowableBitSet<usize>,
221 impl<'tcx> InliningMap<'tcx> {
222 fn new() -> InliningMap<'tcx> {
224 index: FxHashMap::default(),
226 inlines: GrowableBitSet::with_capacity(1024),
230 fn record_accesses(&mut self, source: MonoItem<'tcx>, new_targets: &[(MonoItem<'tcx>, bool)]) {
231 let start_index = self.targets.len();
232 let new_items_count = new_targets.len();
233 let new_items_count_total = new_items_count + self.targets.len();
235 self.targets.reserve(new_items_count);
236 self.inlines.ensure(new_items_count_total);
238 for (i, (target, inline)) in new_targets.iter().enumerate() {
239 self.targets.push(*target);
241 self.inlines.insert(i + start_index);
245 let end_index = self.targets.len();
246 assert!(self.index.insert(source, (start_index, end_index)).is_none());
249 // Internally iterate over all items referenced by `source` which will be
250 // made available for inlining.
251 pub fn with_inlining_candidates<F>(&self, source: MonoItem<'tcx>, mut f: F)
253 F: FnMut(MonoItem<'tcx>),
255 if let Some(&(start_index, end_index)) = self.index.get(&source) {
256 for (i, candidate) in self.targets[start_index..end_index].iter().enumerate() {
257 if self.inlines.contains(start_index + i) {
264 // Internally iterate over all items and the things each accesses.
265 pub fn iter_accesses<F>(&self, mut f: F)
267 F: FnMut(MonoItem<'tcx>, &[MonoItem<'tcx>]),
269 for (&accessor, &(start_index, end_index)) in &self.index {
270 f(accessor, &self.targets[start_index..end_index])
275 pub fn collect_crate_mono_items(
277 mode: MonoItemCollectionMode,
278 ) -> (FxHashSet<MonoItem<'_>>, InliningMap<'_>) {
279 let _prof_timer = tcx.prof.generic_activity("monomorphization_collector");
282 tcx.sess.time("monomorphization_collector_root_collections", || collect_roots(tcx, mode));
284 debug!("building mono item graph, beginning at roots");
286 let mut visited = MTLock::new(FxHashSet::default());
287 let mut inlining_map = MTLock::new(InliningMap::new());
290 let visited: MTRef<'_, _> = &mut visited;
291 let inlining_map: MTRef<'_, _> = &mut inlining_map;
293 tcx.sess.time("monomorphization_collector_graph_walk", || {
294 par_iter(roots).for_each(|root| {
295 let mut recursion_depths = DefIdMap::default();
296 collect_items_rec(tcx, root, visited, &mut recursion_depths, inlining_map);
301 (visited.into_inner(), inlining_map.into_inner())
304 // Find all non-generic items by walking the HIR. These items serve as roots to
305 // start monomorphizing from.
306 fn collect_roots(tcx: TyCtxt<'_>, mode: MonoItemCollectionMode) -> Vec<MonoItem<'_>> {
307 debug!("collecting roots");
308 let mut roots = Vec::new();
311 let entry_fn = tcx.entry_fn(LOCAL_CRATE);
313 debug!("collect_roots: entry_fn = {:?}", entry_fn);
315 let mut visitor = RootCollector { tcx, mode, entry_fn, output: &mut roots };
317 tcx.hir().krate().visit_all_item_likes(&mut visitor);
319 visitor.push_extra_entry_roots();
322 // We can only codegen items that are instantiable - items all of
323 // whose predicates hold. Luckily, items that aren't instantiable
324 // can't actually be used, so we can just skip codegenning them.
325 roots.retain(|root| root.is_instantiable(tcx));
330 // Collect all monomorphized items reachable from `starting_point`
331 fn collect_items_rec<'tcx>(
333 starting_point: MonoItem<'tcx>,
334 visited: MTRef<'_, MTLock<FxHashSet<MonoItem<'tcx>>>>,
335 recursion_depths: &mut DefIdMap<usize>,
336 inlining_map: MTRef<'_, MTLock<InliningMap<'tcx>>>,
338 if !visited.lock_mut().insert(starting_point.clone()) {
339 // We've been here already, no need to search again.
342 debug!("BEGIN collect_items_rec({})", starting_point.to_string(tcx, true));
344 let mut neighbors = Vec::new();
345 let recursion_depth_reset;
347 match starting_point {
348 MonoItem::Static(def_id) => {
349 let instance = Instance::mono(tcx, def_id);
351 // Sanity check whether this ended up being collected accidentally
352 debug_assert!(should_monomorphize_locally(tcx, &instance));
354 let ty = instance.monomorphic_ty(tcx);
355 visit_drop_use(tcx, ty, true, &mut neighbors);
357 recursion_depth_reset = None;
359 if let Ok(val) = tcx.const_eval_poly(def_id) {
360 collect_const(tcx, val, InternalSubsts::empty(), &mut neighbors);
363 MonoItem::Fn(instance) => {
364 // Sanity check whether this ended up being collected accidentally
365 debug_assert!(should_monomorphize_locally(tcx, &instance));
367 // Keep track of the monomorphization recursion depth
368 recursion_depth_reset = Some(check_recursion_limit(tcx, instance, recursion_depths));
369 check_type_length_limit(tcx, instance);
371 collect_neighbours(tcx, instance, &mut neighbors);
373 MonoItem::GlobalAsm(..) => {
374 recursion_depth_reset = None;
378 record_accesses(tcx, starting_point, &neighbors[..], inlining_map);
380 for neighbour in neighbors {
381 collect_items_rec(tcx, neighbour, visited, recursion_depths, inlining_map);
384 if let Some((def_id, depth)) = recursion_depth_reset {
385 recursion_depths.insert(def_id, depth);
388 debug!("END collect_items_rec({})", starting_point.to_string(tcx, true));
391 fn record_accesses<'tcx>(
393 caller: MonoItem<'tcx>,
394 callees: &[MonoItem<'tcx>],
395 inlining_map: MTRef<'_, MTLock<InliningMap<'tcx>>>,
397 let is_inlining_candidate = |mono_item: &MonoItem<'tcx>| {
398 mono_item.instantiation_mode(tcx) == InstantiationMode::LocalCopy
401 // We collect this into a `SmallVec` to avoid calling `is_inlining_candidate` in the lock.
402 // FIXME: Call `is_inlining_candidate` when pushing to `neighbors` in `collect_items_rec`
403 // instead to avoid creating this `SmallVec`.
404 let accesses: SmallVec<[_; 128]> = callees
406 .map(|mono_item| (*mono_item, is_inlining_candidate(mono_item)))
409 inlining_map.lock_mut().record_accesses(caller, &accesses);
412 fn check_recursion_limit<'tcx>(
414 instance: Instance<'tcx>,
415 recursion_depths: &mut DefIdMap<usize>,
416 ) -> (DefId, usize) {
417 let def_id = instance.def_id();
418 let recursion_depth = recursion_depths.get(&def_id).cloned().unwrap_or(0);
419 debug!(" => recursion depth={}", recursion_depth);
421 let adjusted_recursion_depth = if Some(def_id) == tcx.lang_items().drop_in_place_fn() {
422 // HACK: drop_in_place creates tight monomorphization loops. Give
429 // Code that needs to instantiate the same function recursively
430 // more than the recursion limit is assumed to be causing an
431 // infinite expansion.
432 if adjusted_recursion_depth > *tcx.sess.recursion_limit.get() {
433 let error = format!("reached the recursion limit while instantiating `{}`", instance);
434 if let Some(hir_id) = tcx.hir().as_local_hir_id(def_id) {
435 tcx.sess.span_fatal(tcx.hir().span(hir_id), &error);
437 tcx.sess.fatal(&error);
441 recursion_depths.insert(def_id, recursion_depth + 1);
443 (def_id, recursion_depth)
446 fn check_type_length_limit<'tcx>(tcx: TyCtxt<'tcx>, instance: Instance<'tcx>) {
447 let type_length = instance.substs.types().flat_map(|ty| ty.walk()).count();
448 let const_length = instance.substs.consts().flat_map(|ct| ct.ty.walk()).count();
449 debug!(" => type length={}, const length={}", type_length, const_length);
451 // Rust code can easily create exponentially-long types using only a
452 // polynomial recursion depth. Even with the default recursion
453 // depth, you can easily get cases that take >2^60 steps to run,
454 // which means that rustc basically hangs.
456 // Bail out in these cases to avoid that bad user experience.
457 let type_length_limit = *tcx.sess.type_length_limit.get();
458 // We include the const length in the type length, as it's better
459 // to be overly conservative.
460 // FIXME(const_generics): we should instead uniformly walk through `substs`,
461 // ignoring lifetimes.
462 if type_length + const_length > type_length_limit {
463 // The instance name is already known to be too long for rustc.
464 // Show only the first and last 32 characters to avoid blasting
465 // the user's terminal with thousands of lines of type-name.
466 let shrink = |s: String, before: usize, after: usize| {
467 // An iterator of all byte positions including the end of the string.
468 let positions = || s.char_indices().map(|(i, _)| i).chain(iter::once(s.len()));
470 let shrunk = format!(
471 "{before}...{after}",
472 before = &s[..positions().nth(before).unwrap_or(s.len())],
473 after = &s[positions().rev().nth(after).unwrap_or(0)..],
476 // Only use the shrunk version if it's really shorter.
477 // This also avoids the case where before and after slices overlap.
478 if shrunk.len() < s.len() { shrunk } else { s }
481 "reached the type-length limit while instantiating `{}`",
482 shrink(instance.to_string(), 32, 32)
484 let mut diag = tcx.sess.struct_span_fatal(tcx.def_span(instance.def_id()), &msg);
486 "consider adding a `#![type_length_limit=\"{}\"]` attribute to your crate",
490 tcx.sess.abort_if_errors();
494 struct MirNeighborCollector<'a, 'tcx> {
496 body: &'a mir::Body<'tcx>,
497 output: &'a mut Vec<MonoItem<'tcx>>,
498 param_substs: SubstsRef<'tcx>,
501 impl<'a, 'tcx> MirVisitor<'tcx> for MirNeighborCollector<'a, 'tcx> {
502 fn visit_rvalue(&mut self, rvalue: &mir::Rvalue<'tcx>, location: Location) {
503 debug!("visiting rvalue {:?}", *rvalue);
506 // When doing an cast from a regular pointer to a fat pointer, we
507 // have to instantiate all methods of the trait being cast to, so we
508 // can build the appropriate vtable.
510 mir::CastKind::Pointer(PointerCast::Unsize),
514 let target_ty = self.tcx.subst_and_normalize_erasing_regions(
516 ty::ParamEnv::reveal_all(),
519 let source_ty = operand.ty(self.body, self.tcx);
520 let source_ty = self.tcx.subst_and_normalize_erasing_regions(
522 ty::ParamEnv::reveal_all(),
525 let (source_ty, target_ty) =
526 find_vtable_types_for_unsizing(self.tcx, source_ty, target_ty);
527 // This could also be a different Unsize instruction, like
528 // from a fixed sized array to a slice. But we are only
529 // interested in things that produce a vtable.
530 if target_ty.is_trait() && !source_ty.is_trait() {
531 create_mono_items_for_vtable_methods(
540 mir::CastKind::Pointer(PointerCast::ReifyFnPointer),
544 let fn_ty = operand.ty(self.body, self.tcx);
545 let fn_ty = self.tcx.subst_and_normalize_erasing_regions(
547 ty::ParamEnv::reveal_all(),
550 visit_fn_use(self.tcx, fn_ty, false, &mut self.output);
553 mir::CastKind::Pointer(PointerCast::ClosureFnPointer(_)),
557 let source_ty = operand.ty(self.body, self.tcx);
558 let source_ty = self.tcx.subst_and_normalize_erasing_regions(
560 ty::ParamEnv::reveal_all(),
563 match source_ty.kind {
564 ty::Closure(def_id, substs) => {
565 let instance = Instance::resolve_closure(
569 ty::ClosureKind::FnOnce,
571 if should_monomorphize_locally(self.tcx, &instance) {
572 self.output.push(create_fn_mono_item(instance));
578 mir::Rvalue::NullaryOp(mir::NullOp::Box, _) => {
580 let exchange_malloc_fn_def_id = tcx
582 .require(ExchangeMallocFnLangItem)
583 .unwrap_or_else(|e| tcx.sess.fatal(&e));
584 let instance = Instance::mono(tcx, exchange_malloc_fn_def_id);
585 if should_monomorphize_locally(tcx, &instance) {
586 self.output.push(create_fn_mono_item(instance));
589 _ => { /* not interesting */ }
592 self.super_rvalue(rvalue, location);
595 fn visit_const(&mut self, constant: &&'tcx ty::Const<'tcx>, location: Location) {
596 debug!("visiting const {:?} @ {:?}", *constant, location);
598 collect_const(self.tcx, *constant, self.param_substs, self.output);
600 self.super_const(constant);
603 fn visit_terminator_kind(&mut self, kind: &mir::TerminatorKind<'tcx>, location: Location) {
604 debug!("visiting terminator {:?} @ {:?}", kind, location);
608 mir::TerminatorKind::Call { ref func, .. } => {
609 let callee_ty = func.ty(self.body, tcx);
610 let callee_ty = tcx.subst_and_normalize_erasing_regions(
612 ty::ParamEnv::reveal_all(),
615 visit_fn_use(self.tcx, callee_ty, true, &mut self.output);
617 mir::TerminatorKind::Drop { ref location, .. }
618 | mir::TerminatorKind::DropAndReplace { ref location, .. } => {
619 let ty = location.ty(self.body, self.tcx).ty;
620 let ty = tcx.subst_and_normalize_erasing_regions(
622 ty::ParamEnv::reveal_all(),
625 visit_drop_use(self.tcx, ty, true, self.output);
627 mir::TerminatorKind::Goto { .. }
628 | mir::TerminatorKind::SwitchInt { .. }
629 | mir::TerminatorKind::Resume
630 | mir::TerminatorKind::Abort
631 | mir::TerminatorKind::Return
632 | mir::TerminatorKind::Unreachable
633 | mir::TerminatorKind::Assert { .. } => {}
634 mir::TerminatorKind::GeneratorDrop
635 | mir::TerminatorKind::Yield { .. }
636 | mir::TerminatorKind::FalseEdges { .. }
637 | mir::TerminatorKind::FalseUnwind { .. } => bug!(),
640 self.super_terminator_kind(kind, location);
645 _place_local: &Local,
646 _context: mir::visit::PlaceContext,
652 fn visit_drop_use<'tcx>(
655 is_direct_call: bool,
656 output: &mut Vec<MonoItem<'tcx>>,
658 let instance = Instance::resolve_drop_in_place(tcx, ty);
659 visit_instance_use(tcx, instance, is_direct_call, output);
662 fn visit_fn_use<'tcx>(
665 is_direct_call: bool,
666 output: &mut Vec<MonoItem<'tcx>>,
668 if let ty::FnDef(def_id, substs) = ty.kind {
670 if is_direct_call { ty::Instance::resolve } else { ty::Instance::resolve_for_fn_ptr };
671 let instance = resolver(tcx, ty::ParamEnv::reveal_all(), def_id, substs).unwrap();
672 visit_instance_use(tcx, instance, is_direct_call, output);
676 fn visit_instance_use<'tcx>(
678 instance: ty::Instance<'tcx>,
679 is_direct_call: bool,
680 output: &mut Vec<MonoItem<'tcx>>,
682 debug!("visit_item_use({:?}, is_direct_call={:?})", instance, is_direct_call);
683 if !should_monomorphize_locally(tcx, &instance) {
688 ty::InstanceDef::Virtual(..) | ty::InstanceDef::Intrinsic(_) => {
690 bug!("{:?} being reified", instance);
693 ty::InstanceDef::DropGlue(_, None) => {
694 // Don't need to emit noop drop glue if we are calling directly.
696 output.push(create_fn_mono_item(instance));
699 ty::InstanceDef::DropGlue(_, Some(_))
700 | ty::InstanceDef::VtableShim(..)
701 | ty::InstanceDef::ReifyShim(..)
702 | ty::InstanceDef::ClosureOnceShim { .. }
703 | ty::InstanceDef::Item(..)
704 | ty::InstanceDef::FnPtrShim(..)
705 | ty::InstanceDef::CloneShim(..) => {
706 output.push(create_fn_mono_item(instance));
711 // Returns `true` if we should codegen an instance in the local crate.
712 // Returns `false` if we can just link to the upstream crate and therefore don't
714 fn should_monomorphize_locally<'tcx>(tcx: TyCtxt<'tcx>, instance: &Instance<'tcx>) -> bool {
715 let def_id = match instance.def {
716 ty::InstanceDef::Item(def_id) => def_id,
717 ty::InstanceDef::VtableShim(..)
718 | ty::InstanceDef::ReifyShim(..)
719 | ty::InstanceDef::ClosureOnceShim { .. }
720 | ty::InstanceDef::Virtual(..)
721 | ty::InstanceDef::FnPtrShim(..)
722 | ty::InstanceDef::DropGlue(..)
723 | ty::InstanceDef::Intrinsic(_)
724 | ty::InstanceDef::CloneShim(..) => return true,
727 if tcx.is_foreign_item(def_id) {
728 // We can always link to foreign items.
732 if def_id.is_local() {
733 // Local items cannot be referred to locally without monomorphizing them locally.
737 if tcx.is_reachable_non_generic(def_id)
738 || is_available_upstream_generic(tcx, def_id, instance.substs)
740 // We can link to the item in question, no instance needed
745 if !tcx.is_mir_available(def_id) {
746 bug!("cannot create local mono-item for {:?}", def_id)
750 fn is_available_upstream_generic<'tcx>(
753 substs: SubstsRef<'tcx>,
755 debug_assert!(!def_id.is_local());
757 // If we are not in share generics mode, we don't link to upstream
758 // monomorphizations but always instantiate our own internal versions
760 if !tcx.sess.opts.share_generics() {
764 // If this instance has non-erasable parameters, it cannot be a shared
765 // monomorphization. Non-generic instances are already handled above
766 // by `is_reachable_non_generic()`.
767 if substs.non_erasable_generics().next().is_none() {
771 // Take a look at the available monomorphizations listed in the metadata
772 // of upstream crates.
773 tcx.upstream_monomorphizations_for(def_id)
774 .map(|set| set.contains_key(substs))
779 /// For a given pair of source and target type that occur in an unsizing coercion,
780 /// this function finds the pair of types that determines the vtable linking
783 /// For example, the source type might be `&SomeStruct` and the target type\
784 /// might be `&SomeTrait` in a cast like:
786 /// let src: &SomeStruct = ...;
787 /// let target = src as &SomeTrait;
789 /// Then the output of this function would be (SomeStruct, SomeTrait) since for
790 /// constructing the `target` fat-pointer we need the vtable for that pair.
792 /// Things can get more complicated though because there's also the case where
793 /// the unsized type occurs as a field:
796 /// struct ComplexStruct<T: ?Sized> {
803 /// In this case, if `T` is sized, `&ComplexStruct<T>` is a thin pointer. If `T`
804 /// is unsized, `&SomeStruct` is a fat pointer, and the vtable it points to is
805 /// for the pair of `T` (which is a trait) and the concrete type that `T` was
806 /// originally coerced from:
808 /// let src: &ComplexStruct<SomeStruct> = ...;
809 /// let target = src as &ComplexStruct<SomeTrait>;
811 /// Again, we want this `find_vtable_types_for_unsizing()` to provide the pair
812 /// `(SomeStruct, SomeTrait)`.
814 /// Finally, there is also the case of custom unsizing coercions, e.g., for
815 /// smart pointers such as `Rc` and `Arc`.
816 fn find_vtable_types_for_unsizing<'tcx>(
820 ) -> (Ty<'tcx>, Ty<'tcx>) {
821 let ptr_vtable = |inner_source: Ty<'tcx>, inner_target: Ty<'tcx>| {
822 let param_env = ty::ParamEnv::reveal_all();
823 let type_has_metadata = |ty: Ty<'tcx>| -> bool {
824 use rustc_span::DUMMY_SP;
825 if ty.is_sized(tcx.at(DUMMY_SP), param_env) {
828 let tail = tcx.struct_tail_erasing_lifetimes(ty, param_env);
830 ty::Foreign(..) => false,
831 ty::Str | ty::Slice(..) | ty::Dynamic(..) => true,
832 _ => bug!("unexpected unsized tail: {:?}", tail),
835 if type_has_metadata(inner_source) {
836 (inner_source, inner_target)
838 tcx.struct_lockstep_tails_erasing_lifetimes(inner_source, inner_target, param_env)
842 match (&source_ty.kind, &target_ty.kind) {
843 (&ty::Ref(_, a, _), &ty::Ref(_, b, _))
844 | (&ty::Ref(_, a, _), &ty::RawPtr(ty::TypeAndMut { ty: b, .. }))
845 | (&ty::RawPtr(ty::TypeAndMut { ty: a, .. }), &ty::RawPtr(ty::TypeAndMut { ty: b, .. })) => {
848 (&ty::Adt(def_a, _), &ty::Adt(def_b, _)) if def_a.is_box() && def_b.is_box() => {
849 ptr_vtable(source_ty.boxed_ty(), target_ty.boxed_ty())
852 (&ty::Adt(source_adt_def, source_substs), &ty::Adt(target_adt_def, target_substs)) => {
853 assert_eq!(source_adt_def, target_adt_def);
855 let kind = monomorphize::custom_coerce_unsize_info(tcx, source_ty, target_ty);
857 let coerce_index = match kind {
858 CustomCoerceUnsized::Struct(i) => i,
861 let source_fields = &source_adt_def.non_enum_variant().fields;
862 let target_fields = &target_adt_def.non_enum_variant().fields;
865 coerce_index < source_fields.len() && source_fields.len() == target_fields.len()
868 find_vtable_types_for_unsizing(
870 source_fields[coerce_index].ty(tcx, source_substs),
871 target_fields[coerce_index].ty(tcx, target_substs),
875 "find_vtable_types_for_unsizing: invalid coercion {:?} -> {:?}",
882 fn create_fn_mono_item(instance: Instance<'_>) -> MonoItem<'_> {
883 debug!("create_fn_mono_item(instance={})", instance);
884 MonoItem::Fn(instance)
887 /// Creates a `MonoItem` for each method that is referenced by the vtable for
888 /// the given trait/impl pair.
889 fn create_mono_items_for_vtable_methods<'tcx>(
893 output: &mut Vec<MonoItem<'tcx>>,
896 !trait_ty.needs_subst()
897 && !trait_ty.has_escaping_bound_vars()
898 && !impl_ty.needs_subst()
899 && !impl_ty.has_escaping_bound_vars()
902 if let ty::Dynamic(ref trait_ty, ..) = trait_ty.kind {
903 if let Some(principal) = trait_ty.principal() {
904 let poly_trait_ref = principal.with_self_ty(tcx, impl_ty);
905 assert!(!poly_trait_ref.has_escaping_bound_vars());
907 // Walk all methods of the trait, including those of its supertraits
908 let methods = tcx.vtable_methods(poly_trait_ref);
909 let methods = methods
912 .filter_map(|method| method)
913 .map(|(def_id, substs)| {
914 ty::Instance::resolve_for_vtable(
916 ty::ParamEnv::reveal_all(),
922 .filter(|&instance| should_monomorphize_locally(tcx, &instance))
923 .map(|instance| create_fn_mono_item(instance));
924 output.extend(methods);
927 // Also add the destructor.
928 visit_drop_use(tcx, impl_ty, false, output);
932 //=-----------------------------------------------------------------------------
934 //=-----------------------------------------------------------------------------
936 struct RootCollector<'a, 'tcx> {
938 mode: MonoItemCollectionMode,
939 output: &'a mut Vec<MonoItem<'tcx>>,
940 entry_fn: Option<(DefId, EntryFnType)>,
943 impl ItemLikeVisitor<'v> for RootCollector<'_, 'v> {
944 fn visit_item(&mut self, item: &'v hir::Item<'v>) {
946 hir::ItemKind::ExternCrate(..)
947 | hir::ItemKind::Use(..)
948 | hir::ItemKind::ForeignMod(..)
949 | hir::ItemKind::TyAlias(..)
950 | hir::ItemKind::Trait(..)
951 | hir::ItemKind::TraitAlias(..)
952 | hir::ItemKind::OpaqueTy(..)
953 | hir::ItemKind::Mod(..) => {
954 // Nothing to do, just keep recursing.
957 hir::ItemKind::Impl(..) => {
958 if self.mode == MonoItemCollectionMode::Eager {
959 create_mono_items_for_default_impls(self.tcx, item, self.output);
963 hir::ItemKind::Enum(_, ref generics)
964 | hir::ItemKind::Struct(_, ref generics)
965 | hir::ItemKind::Union(_, ref generics) => {
966 if generics.params.is_empty() {
967 if self.mode == MonoItemCollectionMode::Eager {
968 let def_id = self.tcx.hir().local_def_id(item.hir_id);
970 "RootCollector: ADT drop-glue for {}",
971 def_id_to_string(self.tcx, def_id)
975 Instance::new(def_id, InternalSubsts::empty()).monomorphic_ty(self.tcx);
976 visit_drop_use(self.tcx, ty, true, self.output);
980 hir::ItemKind::GlobalAsm(..) => {
982 "RootCollector: ItemKind::GlobalAsm({})",
983 def_id_to_string(self.tcx, self.tcx.hir().local_def_id(item.hir_id))
985 self.output.push(MonoItem::GlobalAsm(item.hir_id));
987 hir::ItemKind::Static(..) => {
988 let def_id = self.tcx.hir().local_def_id(item.hir_id);
989 debug!("RootCollector: ItemKind::Static({})", def_id_to_string(self.tcx, def_id));
990 self.output.push(MonoItem::Static(def_id));
992 hir::ItemKind::Const(..) => {
993 // const items only generate mono items if they are
994 // actually used somewhere. Just declaring them is insufficient.
996 // but even just declaring them must collect the items they refer to
997 let def_id = self.tcx.hir().local_def_id(item.hir_id);
999 if let Ok(val) = self.tcx.const_eval_poly(def_id) {
1000 collect_const(self.tcx, val, InternalSubsts::empty(), &mut self.output);
1003 hir::ItemKind::Fn(..) => {
1004 let def_id = self.tcx.hir().local_def_id(item.hir_id);
1005 self.push_if_root(def_id);
1010 fn visit_trait_item(&mut self, _: &'v hir::TraitItem<'v>) {
1011 // Even if there's a default body with no explicit generics,
1012 // it's still generic over some `Self: Trait`, so not a root.
1015 fn visit_impl_item(&mut self, ii: &'v hir::ImplItem<'v>) {
1017 hir::ImplItemKind::Method(hir::FnSig { .. }, _) => {
1018 let def_id = self.tcx.hir().local_def_id(ii.hir_id);
1019 self.push_if_root(def_id);
1021 _ => { /* nothing to do here */ }
1026 impl RootCollector<'_, 'v> {
1027 fn is_root(&self, def_id: DefId) -> bool {
1028 !item_requires_monomorphization(self.tcx, def_id)
1029 && match self.mode {
1030 MonoItemCollectionMode::Eager => true,
1031 MonoItemCollectionMode::Lazy => {
1032 self.entry_fn.map(|(id, _)| id) == Some(def_id)
1033 || self.tcx.is_reachable_non_generic(def_id)
1036 .codegen_fn_attrs(def_id)
1038 .contains(CodegenFnAttrFlags::RUSTC_STD_INTERNAL_SYMBOL)
1043 /// If `def_id` represents a root, pushes it onto the list of
1044 /// outputs. (Note that all roots must be monomorphic.)
1045 fn push_if_root(&mut self, def_id: DefId) {
1046 if self.is_root(def_id) {
1047 debug!("RootCollector::push_if_root: found root def_id={:?}", def_id);
1049 let instance = Instance::mono(self.tcx, def_id);
1050 self.output.push(create_fn_mono_item(instance));
1054 /// As a special case, when/if we encounter the
1055 /// `main()` function, we also have to generate a
1056 /// monomorphized copy of the start lang item based on
1057 /// the return type of `main`. This is not needed when
1058 /// the user writes their own `start` manually.
1059 fn push_extra_entry_roots(&mut self) {
1060 let main_def_id = match self.entry_fn {
1061 Some((def_id, EntryFnType::Main)) => def_id,
1065 let start_def_id = match self.tcx.lang_items().require(StartFnLangItem) {
1067 Err(err) => self.tcx.sess.fatal(&err),
1069 let main_ret_ty = self.tcx.fn_sig(main_def_id).output();
1071 // Given that `main()` has no arguments,
1072 // then its return type cannot have
1073 // late-bound regions, since late-bound
1074 // regions must appear in the argument
1076 let main_ret_ty = self.tcx.erase_regions(&main_ret_ty.no_bound_vars().unwrap());
1078 let start_instance = Instance::resolve(
1080 ty::ParamEnv::reveal_all(),
1082 self.tcx.intern_substs(&[main_ret_ty.into()]),
1086 self.output.push(create_fn_mono_item(start_instance));
1090 fn item_requires_monomorphization(tcx: TyCtxt<'_>, def_id: DefId) -> bool {
1091 let generics = tcx.generics_of(def_id);
1092 generics.requires_monomorphization(tcx)
1095 fn create_mono_items_for_default_impls<'tcx>(
1097 item: &'tcx hir::Item<'tcx>,
1098 output: &mut Vec<MonoItem<'tcx>>,
1101 hir::ItemKind::Impl(_, _, _, ref generics, .., ref impl_item_refs) => {
1102 for param in generics.params {
1104 hir::GenericParamKind::Lifetime { .. } => {}
1105 hir::GenericParamKind::Type { .. } | hir::GenericParamKind::Const { .. } => {
1111 let impl_def_id = tcx.hir().local_def_id(item.hir_id);
1114 "create_mono_items_for_default_impls(item={})",
1115 def_id_to_string(tcx, impl_def_id)
1118 if let Some(trait_ref) = tcx.impl_trait_ref(impl_def_id) {
1119 let param_env = ty::ParamEnv::reveal_all();
1120 let trait_ref = tcx.normalize_erasing_regions(param_env, trait_ref);
1121 let overridden_methods: FxHashSet<_> =
1122 impl_item_refs.iter().map(|iiref| iiref.ident.modern()).collect();
1123 for method in tcx.provided_trait_methods(trait_ref.def_id) {
1124 if overridden_methods.contains(&method.ident.modern()) {
1128 if tcx.generics_of(method.def_id).own_requires_monomorphization() {
1133 InternalSubsts::for_item(tcx, method.def_id, |param, _| match param.kind {
1134 GenericParamDefKind::Lifetime => tcx.lifetimes.re_erased.into(),
1135 GenericParamDefKind::Type { .. } | GenericParamDefKind::Const => {
1136 trait_ref.substs[param.index as usize]
1140 ty::Instance::resolve(tcx, param_env, method.def_id, substs).unwrap();
1142 let mono_item = create_fn_mono_item(instance);
1143 if mono_item.is_instantiable(tcx) && should_monomorphize_locally(tcx, &instance)
1145 output.push(mono_item);
1154 /// Scans the miri alloc in order to find function calls, closures, and drop-glue.
1155 fn collect_miri<'tcx>(tcx: TyCtxt<'tcx>, alloc_id: AllocId, output: &mut Vec<MonoItem<'tcx>>) {
1156 let alloc_kind = tcx.alloc_map.lock().get(alloc_id);
1158 Some(GlobalAlloc::Static(def_id)) => {
1159 let instance = Instance::mono(tcx, def_id);
1160 if should_monomorphize_locally(tcx, &instance) {
1161 trace!("collecting static {:?}", def_id);
1162 output.push(MonoItem::Static(def_id));
1165 Some(GlobalAlloc::Memory(alloc)) => {
1166 trace!("collecting {:?} with {:#?}", alloc_id, alloc);
1167 for &((), inner) in alloc.relocations().values() {
1168 collect_miri(tcx, inner, output);
1171 Some(GlobalAlloc::Function(fn_instance)) => {
1172 if should_monomorphize_locally(tcx, &fn_instance) {
1173 trace!("collecting {:?} with {:#?}", alloc_id, fn_instance);
1174 output.push(create_fn_mono_item(fn_instance));
1177 None => bug!("alloc id without corresponding allocation: {}", alloc_id),
1181 /// Scans the MIR in order to find function calls, closures, and drop-glue.
1182 fn collect_neighbours<'tcx>(
1184 instance: Instance<'tcx>,
1185 output: &mut Vec<MonoItem<'tcx>>,
1187 debug!("collect_neighbours: {:?}", instance.def_id());
1188 let body = tcx.instance_mir(instance.def);
1190 MirNeighborCollector { tcx, body: &body, output, param_substs: instance.substs }
1194 fn def_id_to_string(tcx: TyCtxt<'_>, def_id: DefId) -> String {
1195 let mut output = String::new();
1196 let printer = DefPathBasedNames::new(tcx, false, false);
1197 printer.push_def_path(def_id, &mut output);
1201 fn collect_const<'tcx>(
1203 constant: &'tcx ty::Const<'tcx>,
1204 param_substs: SubstsRef<'tcx>,
1205 output: &mut Vec<MonoItem<'tcx>>,
1207 debug!("visiting const {:?}", constant);
1209 let param_env = ty::ParamEnv::reveal_all();
1210 let substituted_constant =
1211 tcx.subst_and_normalize_erasing_regions(param_substs, param_env, &constant);
1213 match substituted_constant.val {
1214 ty::ConstKind::Value(ConstValue::Scalar(Scalar::Ptr(ptr))) => {
1215 collect_miri(tcx, ptr.alloc_id, output)
1217 ty::ConstKind::Value(ConstValue::Slice { data: alloc, start: _, end: _ })
1218 | ty::ConstKind::Value(ConstValue::ByRef { alloc, .. }) => {
1219 for &((), id) in alloc.relocations().values() {
1220 collect_miri(tcx, id, output);
1223 ty::ConstKind::Unevaluated(def_id, substs, promoted) => {
1224 match tcx.const_eval_resolve(param_env, def_id, substs, promoted, None) {
1225 Ok(val) => collect_const(tcx, val, param_substs, output),
1226 Err(ErrorHandled::Reported) => {}
1227 Err(ErrorHandled::TooGeneric) => {
1228 span_bug!(tcx.def_span(def_id), "collection encountered polymorphic constant",)