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::hir::{self, CodegenFnAttrFlags};
180 use rustc::hir::itemlikevisit::ItemLikeVisitor;
181 use rustc::hir::def_id::{DefId, LOCAL_CRATE};
182 use rustc::mir::interpret::{AllocId, ConstValue};
183 use rustc::middle::lang_items::{ExchangeMallocFnLangItem, StartFnLangItem};
184 use rustc::ty::subst::{InternalSubsts, Subst, SubstsRef};
185 use rustc::ty::{self, TypeFoldable, Ty, TyCtxt, GenericParamDefKind, Instance};
186 use rustc::ty::print::obsolete::DefPathBasedNames;
187 use rustc::ty::adjustment::{CustomCoerceUnsized, PointerCast};
188 use rustc::session::config::EntryFnType;
189 use rustc::mir::{self, Location, PlaceBase, Static, StaticKind};
190 use rustc::mir::visit::Visitor as MirVisitor;
191 use rustc::mir::mono::{MonoItem, InstantiationMode};
192 use rustc::mir::interpret::{Scalar, GlobalId, GlobalAlloc, ErrorHandled};
193 use rustc::util::nodemap::{FxHashSet, FxHashMap, DefIdMap};
194 use rustc::util::common::time;
196 use rustc_index::bit_set::GrowableBitSet;
197 use rustc_data_structures::sync::{MTRef, MTLock, ParallelIterator, par_iter};
202 pub enum MonoItemCollectionMode {
207 /// Maps every mono item to all mono items it references in its
209 pub struct InliningMap<'tcx> {
210 // Maps a source mono item to the range of mono items
212 // The two numbers in the tuple are the start (inclusive) and
213 // end index (exclusive) within the `targets` vecs.
214 index: FxHashMap<MonoItem<'tcx>, (usize, usize)>,
215 targets: Vec<MonoItem<'tcx>>,
217 // Contains one bit per mono item in the `targets` field. That bit
218 // is true if that mono item needs to be inlined into every CGU.
219 inlines: GrowableBitSet<usize>,
222 impl<'tcx> InliningMap<'tcx> {
224 fn new() -> InliningMap<'tcx> {
226 index: FxHashMap::default(),
228 inlines: GrowableBitSet::with_capacity(1024),
232 fn record_accesses<I>(&mut self,
233 source: MonoItem<'tcx>,
235 where I: Iterator<Item=(MonoItem<'tcx>, bool)> + ExactSizeIterator
237 assert!(!self.index.contains_key(&source));
239 let start_index = self.targets.len();
240 let new_items_count = new_targets.len();
241 let new_items_count_total = new_items_count + self.targets.len();
243 self.targets.reserve(new_items_count);
244 self.inlines.ensure(new_items_count_total);
246 for (i, (target, inline)) in new_targets.enumerate() {
247 self.targets.push(target);
249 self.inlines.insert(i + start_index);
253 let end_index = self.targets.len();
254 self.index.insert(source, (start_index, end_index));
257 // Internally iterate over all items referenced by `source` which will be
258 // made available for inlining.
259 pub fn with_inlining_candidates<F>(&self, source: MonoItem<'tcx>, mut f: F)
260 where F: FnMut(MonoItem<'tcx>)
262 if let Some(&(start_index, end_index)) = self.index.get(&source) {
263 for (i, candidate) in self.targets[start_index .. end_index]
266 if self.inlines.contains(start_index + i) {
273 // Internally iterate over all items and the things each accesses.
274 pub fn iter_accesses<F>(&self, mut f: F)
275 where F: FnMut(MonoItem<'tcx>, &[MonoItem<'tcx>])
277 for (&accessor, &(start_index, end_index)) in &self.index {
278 f(accessor, &self.targets[start_index .. end_index])
283 pub fn collect_crate_mono_items(
285 mode: MonoItemCollectionMode,
286 ) -> (FxHashSet<MonoItem<'_>>, InliningMap<'_>) {
287 let _prof_timer = tcx.prof.generic_activity("monomorphization_collector");
289 let roots = time(tcx.sess, "collecting roots", || {
290 let _prof_timer = tcx.prof
291 .generic_activity("monomorphization_collector_root_collections");
292 collect_roots(tcx, mode)
295 debug!("building mono item graph, beginning at roots");
297 let mut visited = MTLock::new(FxHashSet::default());
298 let mut inlining_map = MTLock::new(InliningMap::new());
301 let _prof_timer = tcx.prof
302 .generic_activity("monomorphization_collector_graph_walk");
304 let visited: MTRef<'_, _> = &mut visited;
305 let inlining_map: MTRef<'_, _> = &mut inlining_map;
307 time(tcx.sess, "collecting mono items", || {
308 par_iter(roots).for_each(|root| {
309 let mut recursion_depths = DefIdMap::default();
310 collect_items_rec(tcx,
313 &mut recursion_depths,
319 (visited.into_inner(), inlining_map.into_inner())
322 // Find all non-generic items by walking the HIR. These items serve as roots to
323 // start monomorphizing from.
324 fn collect_roots(tcx: TyCtxt<'_>, mode: MonoItemCollectionMode) -> Vec<MonoItem<'_>> {
325 debug!("collecting roots");
326 let mut roots = Vec::new();
329 let entry_fn = tcx.entry_fn(LOCAL_CRATE);
331 debug!("collect_roots: entry_fn = {:?}", entry_fn);
333 let mut visitor = RootCollector {
340 tcx.hir().krate().visit_all_item_likes(&mut visitor);
342 visitor.push_extra_entry_roots();
345 // We can only codegen items that are instantiable - items all of
346 // whose predicates hold. Luckily, items that aren't instantiable
347 // can't actually be used, so we can just skip codegenning them.
348 roots.retain(|root| root.is_instantiable(tcx));
353 // Collect all monomorphized items reachable from `starting_point`
354 fn collect_items_rec<'tcx>(
356 starting_point: MonoItem<'tcx>,
357 visited: MTRef<'_, MTLock<FxHashSet<MonoItem<'tcx>>>>,
358 recursion_depths: &mut DefIdMap<usize>,
359 inlining_map: MTRef<'_, MTLock<InliningMap<'tcx>>>,
361 if !visited.lock_mut().insert(starting_point.clone()) {
362 // We've been here already, no need to search again.
365 debug!("BEGIN collect_items_rec({})", starting_point.to_string(tcx, true));
367 let mut neighbors = Vec::new();
368 let recursion_depth_reset;
370 match starting_point {
371 MonoItem::Static(def_id) => {
372 let instance = Instance::mono(tcx, def_id);
374 // Sanity check whether this ended up being collected accidentally
375 debug_assert!(should_monomorphize_locally(tcx, &instance));
377 let ty = instance.ty(tcx);
378 visit_drop_use(tcx, ty, true, &mut neighbors);
380 recursion_depth_reset = None;
386 let param_env = ty::ParamEnv::reveal_all();
388 if let Ok(val) = tcx.const_eval(param_env.and(cid)) {
389 collect_const(tcx, val, InternalSubsts::empty(), &mut neighbors);
392 MonoItem::Fn(instance) => {
393 // Sanity check whether this ended up being collected accidentally
394 debug_assert!(should_monomorphize_locally(tcx, &instance));
396 // Keep track of the monomorphization recursion depth
397 recursion_depth_reset = Some(check_recursion_limit(tcx,
400 check_type_length_limit(tcx, instance);
402 collect_neighbours(tcx, instance, &mut neighbors);
404 MonoItem::GlobalAsm(..) => {
405 recursion_depth_reset = None;
409 record_accesses(tcx, starting_point, &neighbors[..], inlining_map);
411 for neighbour in neighbors {
412 collect_items_rec(tcx, neighbour, visited, recursion_depths, inlining_map);
415 if let Some((def_id, depth)) = recursion_depth_reset {
416 recursion_depths.insert(def_id, depth);
419 debug!("END collect_items_rec({})", starting_point.to_string(tcx, true));
422 fn record_accesses<'tcx>(
424 caller: MonoItem<'tcx>,
425 callees: &[MonoItem<'tcx>],
426 inlining_map: MTRef<'_, MTLock<InliningMap<'tcx>>>,
428 let is_inlining_candidate = |mono_item: &MonoItem<'tcx>| {
429 mono_item.instantiation_mode(tcx) == InstantiationMode::LocalCopy
432 let accesses = callees.into_iter()
434 (*mono_item, is_inlining_candidate(mono_item))
437 inlining_map.lock_mut().record_accesses(caller, accesses);
440 fn check_recursion_limit<'tcx>(
442 instance: Instance<'tcx>,
443 recursion_depths: &mut DefIdMap<usize>,
444 ) -> (DefId, usize) {
445 let def_id = instance.def_id();
446 let recursion_depth = recursion_depths.get(&def_id).cloned().unwrap_or(0);
447 debug!(" => recursion depth={}", recursion_depth);
449 let recursion_depth = if Some(def_id) == tcx.lang_items().drop_in_place_fn() {
450 // HACK: drop_in_place creates tight monomorphization loops. Give
457 // Code that needs to instantiate the same function recursively
458 // more than the recursion limit is assumed to be causing an
459 // infinite expansion.
460 if recursion_depth > *tcx.sess.recursion_limit.get() {
461 let error = format!("reached the recursion limit while instantiating `{}`",
463 if let Some(hir_id) = tcx.hir().as_local_hir_id(def_id) {
464 tcx.sess.span_fatal(tcx.hir().span(hir_id), &error);
466 tcx.sess.fatal(&error);
470 recursion_depths.insert(def_id, recursion_depth + 1);
472 (def_id, recursion_depth)
475 fn check_type_length_limit<'tcx>(tcx: TyCtxt<'tcx>, instance: Instance<'tcx>) {
476 let type_length = instance.substs.types().flat_map(|ty| ty.walk()).count();
477 let const_length = instance.substs.consts().flat_map(|ct| ct.ty.walk()).count();
478 debug!(" => type length={}, const length={}", type_length, const_length);
480 // Rust code can easily create exponentially-long types using only a
481 // polynomial recursion depth. Even with the default recursion
482 // depth, you can easily get cases that take >2^60 steps to run,
483 // which means that rustc basically hangs.
485 // Bail out in these cases to avoid that bad user experience.
486 let type_length_limit = *tcx.sess.type_length_limit.get();
487 // We include the const length in the type length, as it's better
488 // to be overly conservative.
489 // FIXME(const_generics): we should instead uniformly walk through `substs`,
490 // ignoring lifetimes.
491 if type_length + const_length > type_length_limit {
492 // The instance name is already known to be too long for rustc.
493 // Show only the first and last 32 characters to avoid blasting
494 // the user's terminal with thousands of lines of type-name.
495 let shrink = |s: String, before: usize, after: usize| {
496 // An iterator of all byte positions including the end of the string.
497 let positions = || s.char_indices().map(|(i, _)| i).chain(iter::once(s.len()));
499 let shrunk = format!(
500 "{before}...{after}",
501 before = &s[..positions().nth(before).unwrap_or(s.len())],
502 after = &s[positions().rev().nth(after).unwrap_or(0)..],
505 // Only use the shrunk version if it's really shorter.
506 // This also avoids the case where before and after slices overlap.
507 if shrunk.len() < s.len() {
513 let msg = format!("reached the type-length limit while instantiating `{}`",
514 shrink(instance.to_string(), 32, 32));
515 let mut diag = tcx.sess.struct_span_fatal(tcx.def_span(instance.def_id()), &msg);
517 "consider adding a `#![type_length_limit=\"{}\"]` attribute to your crate",
520 tcx.sess.abort_if_errors();
524 struct MirNeighborCollector<'a, 'tcx> {
526 body: &'a mir::Body<'tcx>,
527 output: &'a mut Vec<MonoItem<'tcx>>,
528 param_substs: SubstsRef<'tcx>,
531 impl<'a, 'tcx> MirVisitor<'tcx> for MirNeighborCollector<'a, 'tcx> {
532 fn visit_rvalue(&mut self, rvalue: &mir::Rvalue<'tcx>, location: Location) {
533 debug!("visiting rvalue {:?}", *rvalue);
536 // When doing an cast from a regular pointer to a fat pointer, we
537 // have to instantiate all methods of the trait being cast to, so we
538 // can build the appropriate vtable.
540 mir::CastKind::Pointer(PointerCast::Unsize), ref operand, target_ty
542 let target_ty = self.tcx.subst_and_normalize_erasing_regions(
544 ty::ParamEnv::reveal_all(),
547 let source_ty = operand.ty(self.body, self.tcx);
548 let source_ty = self.tcx.subst_and_normalize_erasing_regions(
550 ty::ParamEnv::reveal_all(),
553 let (source_ty, target_ty) = find_vtable_types_for_unsizing(self.tcx,
556 // This could also be a different Unsize instruction, like
557 // from a fixed sized array to a slice. But we are only
558 // interested in things that produce a vtable.
559 if target_ty.is_trait() && !source_ty.is_trait() {
560 create_mono_items_for_vtable_methods(self.tcx,
567 mir::CastKind::Pointer(PointerCast::ReifyFnPointer), ref operand, _
569 let fn_ty = operand.ty(self.body, self.tcx);
570 let fn_ty = self.tcx.subst_and_normalize_erasing_regions(
572 ty::ParamEnv::reveal_all(),
575 visit_fn_use(self.tcx, fn_ty, false, &mut self.output);
578 mir::CastKind::Pointer(PointerCast::ClosureFnPointer(_)), ref operand, _
580 let source_ty = operand.ty(self.body, self.tcx);
581 let source_ty = self.tcx.subst_and_normalize_erasing_regions(
583 ty::ParamEnv::reveal_all(),
586 match source_ty.kind {
587 ty::Closure(def_id, substs) => {
588 let instance = Instance::resolve_closure(
590 substs, ty::ClosureKind::FnOnce);
591 if should_monomorphize_locally(self.tcx, &instance) {
592 self.output.push(create_fn_mono_item(instance));
598 mir::Rvalue::NullaryOp(mir::NullOp::Box, _) => {
600 let exchange_malloc_fn_def_id = tcx
602 .require(ExchangeMallocFnLangItem)
603 .unwrap_or_else(|e| tcx.sess.fatal(&e));
604 let instance = Instance::mono(tcx, exchange_malloc_fn_def_id);
605 if should_monomorphize_locally(tcx, &instance) {
606 self.output.push(create_fn_mono_item(instance));
609 _ => { /* not interesting */ }
612 self.super_rvalue(rvalue, location);
615 fn visit_const(&mut self, constant: &&'tcx ty::Const<'tcx>, location: Location) {
616 debug!("visiting const {:?} @ {:?}", *constant, location);
618 collect_const(self.tcx, *constant, self.param_substs, self.output);
620 self.super_const(constant);
623 fn visit_terminator_kind(&mut self,
624 kind: &mir::TerminatorKind<'tcx>,
625 location: Location) {
626 debug!("visiting terminator {:?} @ {:?}", kind, location);
630 mir::TerminatorKind::Call { ref func, .. } => {
631 let callee_ty = func.ty(self.body, tcx);
632 let callee_ty = tcx.subst_and_normalize_erasing_regions(
634 ty::ParamEnv::reveal_all(),
637 visit_fn_use(self.tcx, callee_ty, true, &mut self.output);
639 mir::TerminatorKind::Drop { ref location, .. } |
640 mir::TerminatorKind::DropAndReplace { ref location, .. } => {
641 let ty = location.ty(self.body, self.tcx).ty;
642 let ty = tcx.subst_and_normalize_erasing_regions(
644 ty::ParamEnv::reveal_all(),
647 visit_drop_use(self.tcx, ty, true, self.output);
649 mir::TerminatorKind::Goto { .. } |
650 mir::TerminatorKind::SwitchInt { .. } |
651 mir::TerminatorKind::Resume |
652 mir::TerminatorKind::Abort |
653 mir::TerminatorKind::Return |
654 mir::TerminatorKind::Unreachable |
655 mir::TerminatorKind::Assert { .. } => {}
656 mir::TerminatorKind::GeneratorDrop |
657 mir::TerminatorKind::Yield { .. } |
658 mir::TerminatorKind::FalseEdges { .. } |
659 mir::TerminatorKind::FalseUnwind { .. } => bug!(),
662 self.super_terminator_kind(kind, location);
665 fn visit_place_base(&mut self,
666 place_base: &mir::PlaceBase<'tcx>,
667 _context: mir::visit::PlaceContext,
668 location: Location) {
670 PlaceBase::Static(box Static { kind: StaticKind::Static, def_id, .. }) => {
671 debug!("visiting static {:?} @ {:?}", def_id, location);
674 let instance = Instance::mono(tcx, *def_id);
675 if should_monomorphize_locally(tcx, &instance) {
676 self.output.push(MonoItem::Static(*def_id));
679 PlaceBase::Static(box Static {
680 kind: StaticKind::Promoted(promoted, substs),
684 let param_env = ty::ParamEnv::reveal_all();
686 instance: Instance::new(*def_id, substs.subst(self.tcx, self.param_substs)),
687 promoted: Some(*promoted),
689 match self.tcx.const_eval(param_env.and(cid)) {
690 Ok(val) => collect_const(self.tcx, val, substs, self.output),
691 Err(ErrorHandled::Reported) => {},
692 Err(ErrorHandled::TooGeneric) => {
693 let span = self.tcx.promoted_mir(*def_id)[*promoted].span;
694 span_bug!(span, "collection encountered polymorphic constant")
698 PlaceBase::Local(_) => {
699 // Locals have no relevance for collector.
705 fn visit_drop_use<'tcx>(
708 is_direct_call: bool,
709 output: &mut Vec<MonoItem<'tcx>>,
711 let instance = Instance::resolve_drop_in_place(tcx, ty);
712 visit_instance_use(tcx, instance, is_direct_call, output);
715 fn visit_fn_use<'tcx>(
718 is_direct_call: bool,
719 output: &mut Vec<MonoItem<'tcx>>,
721 if let ty::FnDef(def_id, substs) = ty.kind {
722 let resolver = if is_direct_call {
723 ty::Instance::resolve
725 ty::Instance::resolve_for_fn_ptr
727 let instance = resolver(tcx, ty::ParamEnv::reveal_all(), def_id, substs).unwrap();
728 visit_instance_use(tcx, instance, is_direct_call, output);
732 fn visit_instance_use<'tcx>(
734 instance: ty::Instance<'tcx>,
735 is_direct_call: bool,
736 output: &mut Vec<MonoItem<'tcx>>,
738 debug!("visit_item_use({:?}, is_direct_call={:?})", instance, is_direct_call);
739 if !should_monomorphize_locally(tcx, &instance) {
744 ty::InstanceDef::Intrinsic(def_id) => {
746 bug!("intrinsic {:?} being reified", def_id);
749 ty::InstanceDef::VtableShim(..) |
750 ty::InstanceDef::ReifyShim(..) |
751 ty::InstanceDef::Virtual(..) |
752 ty::InstanceDef::DropGlue(_, None) => {
753 // Don't need to emit shim if we are calling directly.
755 output.push(create_fn_mono_item(instance));
758 ty::InstanceDef::DropGlue(_, Some(_)) => {
759 output.push(create_fn_mono_item(instance));
761 ty::InstanceDef::ClosureOnceShim { .. } |
762 ty::InstanceDef::Item(..) |
763 ty::InstanceDef::FnPtrShim(..) |
764 ty::InstanceDef::CloneShim(..) => {
765 output.push(create_fn_mono_item(instance));
770 // Returns `true` if we should codegen an instance in the local crate.
771 // Returns `false` if we can just link to the upstream crate and therefore don't
773 fn should_monomorphize_locally<'tcx>(tcx: TyCtxt<'tcx>, instance: &Instance<'tcx>) -> bool {
774 let def_id = match instance.def {
775 ty::InstanceDef::Item(def_id) => def_id,
776 ty::InstanceDef::VtableShim(..) |
777 ty::InstanceDef::ReifyShim(..) |
778 ty::InstanceDef::ClosureOnceShim { .. } |
779 ty::InstanceDef::Virtual(..) |
780 ty::InstanceDef::FnPtrShim(..) |
781 ty::InstanceDef::DropGlue(..) |
782 ty::InstanceDef::Intrinsic(_) |
783 ty::InstanceDef::CloneShim(..) => return true
786 if tcx.is_foreign_item(def_id) {
787 // We can always link to foreign items.
791 if def_id.is_local() {
792 // Local items cannot be referred to locally without monomorphizing them locally.
796 if tcx.is_reachable_non_generic(def_id) ||
797 is_available_upstream_generic(tcx, def_id, instance.substs) {
798 // We can link to the item in question, no instance needed
803 if !tcx.is_mir_available(def_id) {
804 bug!("cannot create local mono-item for {:?}", def_id)
808 fn is_available_upstream_generic<'tcx>(
811 substs: SubstsRef<'tcx>,
813 debug_assert!(!def_id.is_local());
815 // If we are not in share generics mode, we don't link to upstream
816 // monomorphizations but always instantiate our own internal versions
818 if !tcx.sess.opts.share_generics() {
822 // If this instance has non-erasable parameters, it cannot be a shared
823 // monomorphization. Non-generic instances are already handled above
824 // by `is_reachable_non_generic()`.
825 if substs.non_erasable_generics().next().is_none() {
829 // Take a look at the available monomorphizations listed in the metadata
830 // of upstream crates.
831 tcx.upstream_monomorphizations_for(def_id)
832 .map(|set| set.contains_key(substs))
837 /// For a given pair of source and target type that occur in an unsizing coercion,
838 /// this function finds the pair of types that determines the vtable linking
841 /// For example, the source type might be `&SomeStruct` and the target type\
842 /// might be `&SomeTrait` in a cast like:
844 /// let src: &SomeStruct = ...;
845 /// let target = src as &SomeTrait;
847 /// Then the output of this function would be (SomeStruct, SomeTrait) since for
848 /// constructing the `target` fat-pointer we need the vtable for that pair.
850 /// Things can get more complicated though because there's also the case where
851 /// the unsized type occurs as a field:
854 /// struct ComplexStruct<T: ?Sized> {
861 /// In this case, if `T` is sized, `&ComplexStruct<T>` is a thin pointer. If `T`
862 /// is unsized, `&SomeStruct` is a fat pointer, and the vtable it points to is
863 /// for the pair of `T` (which is a trait) and the concrete type that `T` was
864 /// originally coerced from:
866 /// let src: &ComplexStruct<SomeStruct> = ...;
867 /// let target = src as &ComplexStruct<SomeTrait>;
869 /// Again, we want this `find_vtable_types_for_unsizing()` to provide the pair
870 /// `(SomeStruct, SomeTrait)`.
872 /// Finally, there is also the case of custom unsizing coercions, e.g., for
873 /// smart pointers such as `Rc` and `Arc`.
874 fn find_vtable_types_for_unsizing<'tcx>(
878 ) -> (Ty<'tcx>, Ty<'tcx>) {
879 let ptr_vtable = |inner_source: Ty<'tcx>, inner_target: Ty<'tcx>| {
880 let param_env = ty::ParamEnv::reveal_all();
881 let type_has_metadata = |ty: Ty<'tcx>| -> bool {
882 use syntax_pos::DUMMY_SP;
883 if ty.is_sized(tcx.at(DUMMY_SP), param_env) {
886 let tail = tcx.struct_tail_erasing_lifetimes(ty, param_env);
888 ty::Foreign(..) => false,
889 ty::Str | ty::Slice(..) | ty::Dynamic(..) => true,
890 _ => bug!("unexpected unsized tail: {:?}", tail),
893 if type_has_metadata(inner_source) {
894 (inner_source, inner_target)
896 tcx.struct_lockstep_tails_erasing_lifetimes(inner_source, inner_target, param_env)
900 match (&source_ty.kind, &target_ty.kind) {
904 &ty::RawPtr(ty::TypeAndMut { ty: b, .. })) |
905 (&ty::RawPtr(ty::TypeAndMut { ty: a, .. }),
906 &ty::RawPtr(ty::TypeAndMut { ty: b, .. })) => {
909 (&ty::Adt(def_a, _), &ty::Adt(def_b, _)) if def_a.is_box() && def_b.is_box() => {
910 ptr_vtable(source_ty.boxed_ty(), target_ty.boxed_ty())
913 (&ty::Adt(source_adt_def, source_substs),
914 &ty::Adt(target_adt_def, target_substs)) => {
915 assert_eq!(source_adt_def, target_adt_def);
918 monomorphize::custom_coerce_unsize_info(tcx, source_ty, target_ty);
920 let coerce_index = match kind {
921 CustomCoerceUnsized::Struct(i) => i
924 let source_fields = &source_adt_def.non_enum_variant().fields;
925 let target_fields = &target_adt_def.non_enum_variant().fields;
927 assert!(coerce_index < source_fields.len() &&
928 source_fields.len() == target_fields.len());
930 find_vtable_types_for_unsizing(tcx,
931 source_fields[coerce_index].ty(tcx, source_substs),
932 target_fields[coerce_index].ty(tcx, target_substs)
935 _ => bug!("find_vtable_types_for_unsizing: invalid coercion {:?} -> {:?}",
941 fn create_fn_mono_item(instance: Instance<'_>) -> MonoItem<'_> {
942 debug!("create_fn_mono_item(instance={})", instance);
943 MonoItem::Fn(instance)
946 /// Creates a `MonoItem` for each method that is referenced by the vtable for
947 /// the given trait/impl pair.
948 fn create_mono_items_for_vtable_methods<'tcx>(
952 output: &mut Vec<MonoItem<'tcx>>,
954 assert!(!trait_ty.needs_subst() && !trait_ty.has_escaping_bound_vars() &&
955 !impl_ty.needs_subst() && !impl_ty.has_escaping_bound_vars());
957 if let ty::Dynamic(ref trait_ty, ..) = trait_ty.kind {
958 if let Some(principal) = trait_ty.principal() {
959 let poly_trait_ref = principal.with_self_ty(tcx, impl_ty);
960 assert!(!poly_trait_ref.has_escaping_bound_vars());
962 // Walk all methods of the trait, including those of its supertraits
963 let methods = tcx.vtable_methods(poly_trait_ref);
964 let methods = methods.iter().cloned().filter_map(|method| method)
965 .map(|(def_id, substs)| ty::Instance::resolve_for_vtable(
967 ty::ParamEnv::reveal_all(),
970 .filter(|&instance| should_monomorphize_locally(tcx, &instance))
971 .map(|instance| create_fn_mono_item(instance));
972 output.extend(methods);
975 // Also add the destructor.
976 visit_drop_use(tcx, impl_ty, false, output);
980 //=-----------------------------------------------------------------------------
982 //=-----------------------------------------------------------------------------
984 struct RootCollector<'a, 'tcx> {
986 mode: MonoItemCollectionMode,
987 output: &'a mut Vec<MonoItem<'tcx>>,
988 entry_fn: Option<(DefId, EntryFnType)>,
991 impl ItemLikeVisitor<'v> for RootCollector<'_, 'v> {
992 fn visit_item(&mut self, item: &'v hir::Item) {
994 hir::ItemKind::ExternCrate(..) |
995 hir::ItemKind::Use(..) |
996 hir::ItemKind::ForeignMod(..) |
997 hir::ItemKind::TyAlias(..) |
998 hir::ItemKind::Trait(..) |
999 hir::ItemKind::TraitAlias(..) |
1000 hir::ItemKind::OpaqueTy(..) |
1001 hir::ItemKind::Mod(..) => {
1002 // Nothing to do, just keep recursing.
1005 hir::ItemKind::Impl(..) => {
1006 if self.mode == MonoItemCollectionMode::Eager {
1007 create_mono_items_for_default_impls(self.tcx,
1013 hir::ItemKind::Enum(_, ref generics) |
1014 hir::ItemKind::Struct(_, ref generics) |
1015 hir::ItemKind::Union(_, ref generics) => {
1016 if generics.params.is_empty() {
1017 if self.mode == MonoItemCollectionMode::Eager {
1018 let def_id = self.tcx.hir().local_def_id(item.hir_id);
1019 debug!("RootCollector: ADT drop-glue for {}",
1020 def_id_to_string(self.tcx, def_id));
1022 let ty = Instance::new(def_id, InternalSubsts::empty()).ty(self.tcx);
1023 visit_drop_use(self.tcx, ty, true, self.output);
1027 hir::ItemKind::GlobalAsm(..) => {
1028 debug!("RootCollector: ItemKind::GlobalAsm({})",
1029 def_id_to_string(self.tcx,
1030 self.tcx.hir().local_def_id(item.hir_id)));
1031 self.output.push(MonoItem::GlobalAsm(item.hir_id));
1033 hir::ItemKind::Static(..) => {
1034 let def_id = self.tcx.hir().local_def_id(item.hir_id);
1035 debug!("RootCollector: ItemKind::Static({})",
1036 def_id_to_string(self.tcx, def_id));
1037 self.output.push(MonoItem::Static(def_id));
1039 hir::ItemKind::Const(..) => {
1040 // const items only generate mono items if they are
1041 // actually used somewhere. Just declaring them is insufficient.
1043 // but even just declaring them must collect the items they refer to
1044 let def_id = self.tcx.hir().local_def_id(item.hir_id);
1046 let instance = Instance::mono(self.tcx, def_id);
1047 let cid = GlobalId {
1051 let param_env = ty::ParamEnv::reveal_all();
1053 if let Ok(val) = self.tcx.const_eval(param_env.and(cid)) {
1054 collect_const(self.tcx, val, InternalSubsts::empty(), &mut self.output);
1057 hir::ItemKind::Fn(..) => {
1058 let def_id = self.tcx.hir().local_def_id(item.hir_id);
1059 self.push_if_root(def_id);
1064 fn visit_trait_item(&mut self, _: &'v hir::TraitItem) {
1065 // Even if there's a default body with no explicit generics,
1066 // it's still generic over some `Self: Trait`, so not a root.
1069 fn visit_impl_item(&mut self, ii: &'v hir::ImplItem) {
1071 hir::ImplItemKind::Method(hir::FnSig { .. }, _) => {
1072 let def_id = self.tcx.hir().local_def_id(ii.hir_id);
1073 self.push_if_root(def_id);
1075 _ => { /* nothing to do here */ }
1080 impl RootCollector<'_, 'v> {
1081 fn is_root(&self, def_id: DefId) -> bool {
1082 !item_requires_monomorphization(self.tcx, def_id) && match self.mode {
1083 MonoItemCollectionMode::Eager => {
1086 MonoItemCollectionMode::Lazy => {
1087 self.entry_fn.map(|(id, _)| id) == Some(def_id) ||
1088 self.tcx.is_reachable_non_generic(def_id) ||
1089 self.tcx.codegen_fn_attrs(def_id).flags.contains(
1090 CodegenFnAttrFlags::RUSTC_STD_INTERNAL_SYMBOL)
1095 /// If `def_id` represents a root, pushes it onto the list of
1096 /// outputs. (Note that all roots must be monomorphic.)
1097 fn push_if_root(&mut self, def_id: DefId) {
1098 if self.is_root(def_id) {
1099 debug!("RootCollector::push_if_root: found root def_id={:?}", def_id);
1101 let instance = Instance::mono(self.tcx, def_id);
1102 self.output.push(create_fn_mono_item(instance));
1106 /// As a special case, when/if we encounter the
1107 /// `main()` function, we also have to generate a
1108 /// monomorphized copy of the start lang item based on
1109 /// the return type of `main`. This is not needed when
1110 /// the user writes their own `start` manually.
1111 fn push_extra_entry_roots(&mut self) {
1112 let main_def_id = match self.entry_fn {
1113 Some((def_id, EntryFnType::Main)) => def_id,
1117 let start_def_id = match self.tcx.lang_items().require(StartFnLangItem) {
1119 Err(err) => self.tcx.sess.fatal(&err),
1121 let main_ret_ty = self.tcx.fn_sig(main_def_id).output();
1123 // Given that `main()` has no arguments,
1124 // then its return type cannot have
1125 // late-bound regions, since late-bound
1126 // regions must appear in the argument
1128 let main_ret_ty = self.tcx.erase_regions(
1129 &main_ret_ty.no_bound_vars().unwrap(),
1132 let start_instance = Instance::resolve(
1134 ty::ParamEnv::reveal_all(),
1136 self.tcx.intern_substs(&[main_ret_ty.into()])
1139 self.output.push(create_fn_mono_item(start_instance));
1143 fn item_requires_monomorphization(tcx: TyCtxt<'_>, def_id: DefId) -> bool {
1144 let generics = tcx.generics_of(def_id);
1145 generics.requires_monomorphization(tcx)
1148 fn create_mono_items_for_default_impls<'tcx>(
1150 item: &'tcx hir::Item,
1151 output: &mut Vec<MonoItem<'tcx>>,
1154 hir::ItemKind::Impl(_, _, _, ref generics, .., ref impl_item_refs) => {
1155 for param in &generics.params {
1157 hir::GenericParamKind::Lifetime { .. } => {}
1158 hir::GenericParamKind::Type { .. } |
1159 hir::GenericParamKind::Const { .. } => {
1165 let impl_def_id = tcx.hir().local_def_id(item.hir_id);
1167 debug!("create_mono_items_for_default_impls(item={})",
1168 def_id_to_string(tcx, impl_def_id));
1170 if let Some(trait_ref) = tcx.impl_trait_ref(impl_def_id) {
1171 let param_env = ty::ParamEnv::reveal_all();
1172 let trait_ref = tcx.normalize_erasing_regions(
1176 let overridden_methods: FxHashSet<_> =
1177 impl_item_refs.iter()
1178 .map(|iiref| iiref.ident.modern())
1180 for method in tcx.provided_trait_methods(trait_ref.def_id) {
1181 if overridden_methods.contains(&method.ident.modern()) {
1185 if tcx.generics_of(method.def_id).own_requires_monomorphization() {
1189 let substs = InternalSubsts::for_item(tcx, method.def_id, |param, _| {
1191 GenericParamDefKind::Lifetime => tcx.lifetimes.re_erased.into(),
1192 GenericParamDefKind::Type { .. } |
1193 GenericParamDefKind::Const => {
1194 trait_ref.substs[param.index as usize]
1198 let instance = ty::Instance::resolve(tcx,
1203 let mono_item = create_fn_mono_item(instance);
1204 if mono_item.is_instantiable(tcx)
1205 && should_monomorphize_locally(tcx, &instance) {
1206 output.push(mono_item);
1217 /// Scans the miri alloc in order to find function calls, closures, and drop-glue.
1218 fn collect_miri<'tcx>(tcx: TyCtxt<'tcx>, alloc_id: AllocId, output: &mut Vec<MonoItem<'tcx>>) {
1219 let alloc_kind = tcx.alloc_map.lock().get(alloc_id);
1221 Some(GlobalAlloc::Static(def_id)) => {
1222 let instance = Instance::mono(tcx, def_id);
1223 if should_monomorphize_locally(tcx, &instance) {
1224 trace!("collecting static {:?}", def_id);
1225 output.push(MonoItem::Static(def_id));
1228 Some(GlobalAlloc::Memory(alloc)) => {
1229 trace!("collecting {:?} with {:#?}", alloc_id, alloc);
1230 for &((), inner) in alloc.relocations().values() {
1231 collect_miri(tcx, inner, output);
1234 Some(GlobalAlloc::Function(fn_instance)) => {
1235 if should_monomorphize_locally(tcx, &fn_instance) {
1236 trace!("collecting {:?} with {:#?}", alloc_id, fn_instance);
1237 output.push(create_fn_mono_item(fn_instance));
1240 None => bug!("alloc id without corresponding allocation: {}", alloc_id),
1244 /// Scans the MIR in order to find function calls, closures, and drop-glue.
1245 fn collect_neighbours<'tcx>(
1247 instance: Instance<'tcx>,
1248 output: &mut Vec<MonoItem<'tcx>>,
1250 debug!("collect_neighbours: {:?}", instance.def_id());
1251 let body = tcx.instance_mir(instance.def);
1253 MirNeighborCollector {
1257 param_substs: instance.substs,
1258 }.visit_body(&body);
1261 fn def_id_to_string(tcx: TyCtxt<'_>, def_id: DefId) -> String {
1262 let mut output = String::new();
1263 let printer = DefPathBasedNames::new(tcx, false, false);
1264 printer.push_def_path(def_id, &mut output);
1268 fn collect_const<'tcx>(
1270 constant: &'tcx ty::Const<'tcx>,
1271 param_substs: SubstsRef<'tcx>,
1272 output: &mut Vec<MonoItem<'tcx>>,
1274 debug!("visiting const {:?}", constant);
1276 let param_env = ty::ParamEnv::reveal_all();
1277 let substituted_constant = tcx.subst_and_normalize_erasing_regions(
1283 match substituted_constant.val {
1284 ty::ConstKind::Value(ConstValue::Scalar(Scalar::Ptr(ptr))) =>
1285 collect_miri(tcx, ptr.alloc_id, output),
1286 ty::ConstKind::Value(ConstValue::Slice { data: alloc, start: _, end: _ }) |
1287 ty::ConstKind::Value(ConstValue::ByRef { alloc, .. }) => {
1288 for &((), id) in alloc.relocations().values() {
1289 collect_miri(tcx, id, output);
1292 ty::ConstKind::Unevaluated(def_id, substs) => {
1293 let instance = ty::Instance::resolve(tcx,
1298 let cid = GlobalId {
1302 match tcx.const_eval(param_env.and(cid)) {
1303 Ok(val) => collect_const(tcx, val, param_substs, output),
1304 Err(ErrorHandled::Reported) => {},
1305 Err(ErrorHandled::TooGeneric) => span_bug!(
1306 tcx.def_span(def_id), "collection encountered polymorphic constant",