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 rustc::hir::{self, CodegenFnAttrFlags};
178 use rustc::hir::itemlikevisit::ItemLikeVisitor;
180 use rustc::hir::def_id::{DefId, LOCAL_CRATE};
181 use rustc::mir::interpret::{AllocId, ConstValue};
182 use rustc::middle::lang_items::{ExchangeMallocFnLangItem, StartFnLangItem};
183 use rustc::ty::subst::{InternalSubsts, Subst, SubstsRef};
184 use rustc::ty::{self, TypeFoldable, Ty, TyCtxt, GenericParamDefKind, Instance};
185 use rustc::ty::print::obsolete::DefPathBasedNames;
186 use rustc::ty::adjustment::{CustomCoerceUnsized, PointerCast};
187 use rustc::session::config::EntryFnType;
188 use rustc::mir::{self, Location, PlaceBase, Static, StaticKind};
189 use rustc::mir::visit::Visitor as MirVisitor;
190 use rustc::mir::mono::{MonoItem, InstantiationMode};
191 use rustc::mir::interpret::{Scalar, GlobalId, GlobalAlloc, ErrorHandled};
193 use crate::monomorphize;
194 use rustc::util::nodemap::{FxHashSet, FxHashMap, DefIdMap};
195 use rustc::util::common::time;
197 use rustc_index::bit_set::GrowableBitSet;
198 use rustc_data_structures::sync::{MTRef, MTLock, ParallelIterator, par_iter};
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> {
225 fn new() -> InliningMap<'tcx> {
227 index: FxHashMap::default(),
229 inlines: GrowableBitSet::with_capacity(1024),
233 fn record_accesses<I>(&mut self,
234 source: MonoItem<'tcx>,
236 where I: Iterator<Item=(MonoItem<'tcx>, bool)> + ExactSizeIterator
238 assert!(!self.index.contains_key(&source));
240 let start_index = self.targets.len();
241 let new_items_count = new_targets.len();
242 let new_items_count_total = new_items_count + self.targets.len();
244 self.targets.reserve(new_items_count);
245 self.inlines.ensure(new_items_count_total);
247 for (i, (target, inline)) in new_targets.enumerate() {
248 self.targets.push(target);
250 self.inlines.insert(i + start_index);
254 let end_index = self.targets.len();
255 self.index.insert(source, (start_index, end_index));
258 // Internally iterate over all items referenced by `source` which will be
259 // made available for inlining.
260 pub fn with_inlining_candidates<F>(&self, source: MonoItem<'tcx>, mut f: F)
261 where F: FnMut(MonoItem<'tcx>)
263 if let Some(&(start_index, end_index)) = self.index.get(&source) {
264 for (i, candidate) in self.targets[start_index .. end_index]
267 if self.inlines.contains(start_index + i) {
274 // Internally iterate over all items and the things each accesses.
275 pub fn iter_accesses<F>(&self, mut f: F)
276 where F: FnMut(MonoItem<'tcx>, &[MonoItem<'tcx>])
278 for (&accessor, &(start_index, end_index)) in &self.index {
279 f(accessor, &self.targets[start_index .. end_index])
284 pub fn collect_crate_mono_items(
286 mode: MonoItemCollectionMode,
287 ) -> (FxHashSet<MonoItem<'_>>, InliningMap<'_>) {
288 let _prof_timer = tcx.prof.generic_activity("monomorphization_collector");
290 let roots = time(tcx.sess, "collecting roots", || {
291 let _prof_timer = tcx.prof
292 .generic_activity("monomorphization_collector_root_collections");
293 collect_roots(tcx, mode)
296 debug!("building mono item graph, beginning at roots");
298 let mut visited = MTLock::new(FxHashSet::default());
299 let mut inlining_map = MTLock::new(InliningMap::new());
302 let _prof_timer = tcx.prof
303 .generic_activity("monomorphization_collector_graph_walk");
305 let visited: MTRef<'_, _> = &mut visited;
306 let inlining_map: MTRef<'_, _> = &mut inlining_map;
308 time(tcx.sess, "collecting mono items", || {
309 par_iter(roots).for_each(|root| {
310 let mut recursion_depths = DefIdMap::default();
311 collect_items_rec(tcx,
314 &mut recursion_depths,
320 (visited.into_inner(), inlining_map.into_inner())
323 // Find all non-generic items by walking the HIR. These items serve as roots to
324 // start monomorphizing from.
325 fn collect_roots(tcx: TyCtxt<'_>, mode: MonoItemCollectionMode) -> Vec<MonoItem<'_>> {
326 debug!("collecting roots");
327 let mut roots = Vec::new();
330 let entry_fn = tcx.entry_fn(LOCAL_CRATE);
332 debug!("collect_roots: entry_fn = {:?}", entry_fn);
334 let mut visitor = RootCollector {
341 tcx.hir().krate().visit_all_item_likes(&mut visitor);
343 visitor.push_extra_entry_roots();
346 // We can only codegen items that are instantiable - items all of
347 // whose predicates hold. Luckily, items that aren't instantiable
348 // can't actually be used, so we can just skip codegenning them.
349 roots.retain(|root| root.is_instantiable(tcx));
354 // Collect all monomorphized items reachable from `starting_point`
355 fn collect_items_rec<'tcx>(
357 starting_point: MonoItem<'tcx>,
358 visited: MTRef<'_, MTLock<FxHashSet<MonoItem<'tcx>>>>,
359 recursion_depths: &mut DefIdMap<usize>,
360 inlining_map: MTRef<'_, MTLock<InliningMap<'tcx>>>,
362 if !visited.lock_mut().insert(starting_point.clone()) {
363 // We've been here already, no need to search again.
366 debug!("BEGIN collect_items_rec({})", starting_point.to_string(tcx, true));
368 let mut neighbors = Vec::new();
369 let recursion_depth_reset;
371 match starting_point {
372 MonoItem::Static(def_id) => {
373 let instance = Instance::mono(tcx, def_id);
375 // Sanity check whether this ended up being collected accidentally
376 debug_assert!(should_monomorphize_locally(tcx, &instance));
378 let ty = instance.ty(tcx);
379 visit_drop_use(tcx, ty, true, &mut neighbors);
381 recursion_depth_reset = None;
387 let param_env = ty::ParamEnv::reveal_all();
389 if let Ok(val) = tcx.const_eval(param_env.and(cid)) {
390 collect_const(tcx, val, InternalSubsts::empty(), &mut neighbors);
393 MonoItem::Fn(instance) => {
394 // Sanity check whether this ended up being collected accidentally
395 debug_assert!(should_monomorphize_locally(tcx, &instance));
397 // Keep track of the monomorphization recursion depth
398 recursion_depth_reset = Some(check_recursion_limit(tcx,
401 check_type_length_limit(tcx, instance);
403 collect_neighbours(tcx, instance, &mut neighbors);
405 MonoItem::GlobalAsm(..) => {
406 recursion_depth_reset = None;
410 record_accesses(tcx, starting_point, &neighbors[..], inlining_map);
412 for neighbour in neighbors {
413 collect_items_rec(tcx, neighbour, visited, recursion_depths, inlining_map);
416 if let Some((def_id, depth)) = recursion_depth_reset {
417 recursion_depths.insert(def_id, depth);
420 debug!("END collect_items_rec({})", starting_point.to_string(tcx, true));
423 fn record_accesses<'tcx>(
425 caller: MonoItem<'tcx>,
426 callees: &[MonoItem<'tcx>],
427 inlining_map: MTRef<'_, MTLock<InliningMap<'tcx>>>,
429 let is_inlining_candidate = |mono_item: &MonoItem<'tcx>| {
430 mono_item.instantiation_mode(tcx) == InstantiationMode::LocalCopy
433 let accesses = callees.into_iter()
435 (*mono_item, is_inlining_candidate(mono_item))
438 inlining_map.lock_mut().record_accesses(caller, accesses);
441 fn check_recursion_limit<'tcx>(
443 instance: Instance<'tcx>,
444 recursion_depths: &mut DefIdMap<usize>,
445 ) -> (DefId, usize) {
446 let def_id = instance.def_id();
447 let recursion_depth = recursion_depths.get(&def_id).cloned().unwrap_or(0);
448 debug!(" => recursion depth={}", recursion_depth);
450 let recursion_depth = if Some(def_id) == tcx.lang_items().drop_in_place_fn() {
451 // HACK: drop_in_place creates tight monomorphization loops. Give
458 // Code that needs to instantiate the same function recursively
459 // more than the recursion limit is assumed to be causing an
460 // infinite expansion.
461 if recursion_depth > *tcx.sess.recursion_limit.get() {
462 let error = format!("reached the recursion limit while instantiating `{}`",
464 if let Some(hir_id) = tcx.hir().as_local_hir_id(def_id) {
465 tcx.sess.span_fatal(tcx.hir().span(hir_id), &error);
467 tcx.sess.fatal(&error);
471 recursion_depths.insert(def_id, recursion_depth + 1);
473 (def_id, recursion_depth)
476 fn check_type_length_limit<'tcx>(tcx: TyCtxt<'tcx>, instance: Instance<'tcx>) {
477 let type_length = instance.substs.types().flat_map(|ty| ty.walk()).count();
478 let const_length = instance.substs.consts().flat_map(|ct| ct.ty.walk()).count();
479 debug!(" => type length={}, const length={}", type_length, const_length);
481 // Rust code can easily create exponentially-long types using only a
482 // polynomial recursion depth. Even with the default recursion
483 // depth, you can easily get cases that take >2^60 steps to run,
484 // which means that rustc basically hangs.
486 // Bail out in these cases to avoid that bad user experience.
487 let type_length_limit = *tcx.sess.type_length_limit.get();
488 // We include the const length in the type length, as it's better
489 // to be overly conservative.
490 // FIXME(const_generics): we should instead uniformly walk through `substs`,
491 // ignoring lifetimes.
492 if type_length + const_length > type_length_limit {
493 // The instance name is already known to be too long for rustc.
494 // Show only the first and last 32 characters to avoid blasting
495 // the user's terminal with thousands of lines of type-name.
496 let shrink = |s: String, before: usize, after: usize| {
497 // An iterator of all byte positions including the end of the string.
498 let positions = || s.char_indices().map(|(i, _)| i).chain(iter::once(s.len()));
500 let shrunk = format!(
501 "{before}...{after}",
502 before = &s[..positions().nth(before).unwrap_or(s.len())],
503 after = &s[positions().rev().nth(after).unwrap_or(0)..],
506 // Only use the shrunk version if it's really shorter.
507 // This also avoids the case where before and after slices overlap.
508 if shrunk.len() < s.len() {
514 let msg = format!("reached the type-length limit while instantiating `{}`",
515 shrink(instance.to_string(), 32, 32));
516 let mut diag = tcx.sess.struct_span_fatal(tcx.def_span(instance.def_id()), &msg);
518 "consider adding a `#![type_length_limit=\"{}\"]` attribute to your crate",
521 tcx.sess.abort_if_errors();
525 struct MirNeighborCollector<'a, 'tcx> {
527 body: &'a mir::Body<'tcx>,
528 output: &'a mut Vec<MonoItem<'tcx>>,
529 param_substs: SubstsRef<'tcx>,
532 impl<'a, 'tcx> MirVisitor<'tcx> for MirNeighborCollector<'a, 'tcx> {
534 fn visit_rvalue(&mut self, rvalue: &mir::Rvalue<'tcx>, location: Location) {
535 debug!("visiting rvalue {:?}", *rvalue);
538 // When doing an cast from a regular pointer to a fat pointer, we
539 // have to instantiate all methods of the trait being cast to, so we
540 // can build the appropriate vtable.
542 mir::CastKind::Pointer(PointerCast::Unsize), ref operand, target_ty
544 let target_ty = self.tcx.subst_and_normalize_erasing_regions(
546 ty::ParamEnv::reveal_all(),
549 let source_ty = operand.ty(self.body, self.tcx);
550 let source_ty = self.tcx.subst_and_normalize_erasing_regions(
552 ty::ParamEnv::reveal_all(),
555 let (source_ty, target_ty) = find_vtable_types_for_unsizing(self.tcx,
558 // This could also be a different Unsize instruction, like
559 // from a fixed sized array to a slice. But we are only
560 // interested in things that produce a vtable.
561 if target_ty.is_trait() && !source_ty.is_trait() {
562 create_mono_items_for_vtable_methods(self.tcx,
569 mir::CastKind::Pointer(PointerCast::ReifyFnPointer), ref operand, _
571 let fn_ty = operand.ty(self.body, self.tcx);
572 let fn_ty = self.tcx.subst_and_normalize_erasing_regions(
574 ty::ParamEnv::reveal_all(),
577 visit_fn_use(self.tcx, fn_ty, false, &mut self.output);
580 mir::CastKind::Pointer(PointerCast::ClosureFnPointer(_)), ref operand, _
582 let source_ty = operand.ty(self.body, self.tcx);
583 let source_ty = self.tcx.subst_and_normalize_erasing_regions(
585 ty::ParamEnv::reveal_all(),
588 match source_ty.kind {
589 ty::Closure(def_id, substs) => {
590 let instance = Instance::resolve_closure(
592 substs, ty::ClosureKind::FnOnce);
593 if should_monomorphize_locally(self.tcx, &instance) {
594 self.output.push(create_fn_mono_item(instance));
600 mir::Rvalue::NullaryOp(mir::NullOp::Box, _) => {
602 let exchange_malloc_fn_def_id = tcx
604 .require(ExchangeMallocFnLangItem)
605 .unwrap_or_else(|e| tcx.sess.fatal(&e));
606 let instance = Instance::mono(tcx, exchange_malloc_fn_def_id);
607 if should_monomorphize_locally(tcx, &instance) {
608 self.output.push(create_fn_mono_item(instance));
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 collect_const(self.tcx, *constant, self.param_substs, self.output);
622 self.super_const(constant);
625 fn visit_terminator_kind(&mut self,
626 kind: &mir::TerminatorKind<'tcx>,
627 location: Location) {
628 debug!("visiting terminator {:?} @ {:?}", kind, location);
632 mir::TerminatorKind::Call { ref func, .. } => {
633 let callee_ty = func.ty(self.body, tcx);
634 let callee_ty = tcx.subst_and_normalize_erasing_regions(
636 ty::ParamEnv::reveal_all(),
639 visit_fn_use(self.tcx, callee_ty, true, &mut self.output);
641 mir::TerminatorKind::Drop { ref location, .. } |
642 mir::TerminatorKind::DropAndReplace { ref location, .. } => {
643 let ty = location.ty(self.body, self.tcx).ty;
644 let ty = tcx.subst_and_normalize_erasing_regions(
646 ty::ParamEnv::reveal_all(),
649 visit_drop_use(self.tcx, ty, true, self.output);
651 mir::TerminatorKind::Goto { .. } |
652 mir::TerminatorKind::SwitchInt { .. } |
653 mir::TerminatorKind::Resume |
654 mir::TerminatorKind::Abort |
655 mir::TerminatorKind::Return |
656 mir::TerminatorKind::Unreachable |
657 mir::TerminatorKind::Assert { .. } => {}
658 mir::TerminatorKind::GeneratorDrop |
659 mir::TerminatorKind::Yield { .. } |
660 mir::TerminatorKind::FalseEdges { .. } |
661 mir::TerminatorKind::FalseUnwind { .. } => bug!(),
664 self.super_terminator_kind(kind, location);
667 fn visit_place_base(&mut self,
668 place_base: &mir::PlaceBase<'tcx>,
669 _context: mir::visit::PlaceContext,
670 location: Location) {
672 PlaceBase::Static(box Static { kind: StaticKind::Static, def_id, .. }) => {
673 debug!("visiting static {:?} @ {:?}", def_id, location);
676 let instance = Instance::mono(tcx, *def_id);
677 if should_monomorphize_locally(tcx, &instance) {
678 self.output.push(MonoItem::Static(*def_id));
681 PlaceBase::Static(box Static {
682 kind: StaticKind::Promoted(promoted, substs),
686 let param_env = ty::ParamEnv::reveal_all();
688 instance: Instance::new(*def_id, substs.subst(self.tcx, self.param_substs)),
689 promoted: Some(*promoted),
691 match self.tcx.const_eval(param_env.and(cid)) {
692 Ok(val) => collect_const(self.tcx, val, substs, self.output),
693 Err(ErrorHandled::Reported) => {},
694 Err(ErrorHandled::TooGeneric) => {
695 let span = self.tcx.promoted_mir(*def_id)[*promoted].span;
696 span_bug!(span, "collection encountered polymorphic constant")
700 PlaceBase::Local(_) => {
701 // Locals have no relevance for collector
707 fn visit_drop_use<'tcx>(
710 is_direct_call: bool,
711 output: &mut Vec<MonoItem<'tcx>>,
713 let instance = Instance::resolve_drop_in_place(tcx, ty);
714 visit_instance_use(tcx, instance, is_direct_call, output);
717 fn visit_fn_use<'tcx>(
720 is_direct_call: bool,
721 output: &mut Vec<MonoItem<'tcx>>,
723 if let ty::FnDef(def_id, substs) = ty.kind {
724 let resolver = if is_direct_call {
725 ty::Instance::resolve
727 ty::Instance::resolve_for_fn_ptr
729 let instance = resolver(tcx, ty::ParamEnv::reveal_all(), def_id, substs).unwrap();
730 visit_instance_use(tcx, instance, is_direct_call, output);
734 fn visit_instance_use<'tcx>(
736 instance: ty::Instance<'tcx>,
737 is_direct_call: bool,
738 output: &mut Vec<MonoItem<'tcx>>,
740 debug!("visit_item_use({:?}, is_direct_call={:?})", instance, is_direct_call);
741 if !should_monomorphize_locally(tcx, &instance) {
746 ty::InstanceDef::Intrinsic(def_id) => {
748 bug!("intrinsic {:?} being reified", def_id);
751 ty::InstanceDef::VtableShim(..) |
752 ty::InstanceDef::ReifyShim(..) |
753 ty::InstanceDef::Virtual(..) |
754 ty::InstanceDef::DropGlue(_, None) => {
755 // don't need to emit shim if we are calling directly.
757 output.push(create_fn_mono_item(instance));
760 ty::InstanceDef::DropGlue(_, Some(_)) => {
761 output.push(create_fn_mono_item(instance));
763 ty::InstanceDef::ClosureOnceShim { .. } |
764 ty::InstanceDef::Item(..) |
765 ty::InstanceDef::FnPtrShim(..) |
766 ty::InstanceDef::CloneShim(..) => {
767 output.push(create_fn_mono_item(instance));
772 // Returns true if we should codegen an instance in the local crate.
773 // Returns false if we can just link to the upstream crate and therefore don't
775 fn should_monomorphize_locally<'tcx>(tcx: TyCtxt<'tcx>, instance: &Instance<'tcx>) -> bool {
776 let def_id = match instance.def {
777 ty::InstanceDef::Item(def_id) => def_id,
778 ty::InstanceDef::VtableShim(..) |
779 ty::InstanceDef::ReifyShim(..) |
780 ty::InstanceDef::ClosureOnceShim { .. } |
781 ty::InstanceDef::Virtual(..) |
782 ty::InstanceDef::FnPtrShim(..) |
783 ty::InstanceDef::DropGlue(..) |
784 ty::InstanceDef::Intrinsic(_) |
785 ty::InstanceDef::CloneShim(..) => return true
788 if tcx.is_foreign_item(def_id) {
789 // We can always link to foreign items
793 if def_id.is_local() {
794 // local items cannot be referred to locally without monomorphizing them locally
798 if tcx.is_reachable_non_generic(def_id) ||
799 is_available_upstream_generic(tcx, def_id, instance.substs) {
800 // We can link to the item in question, no instance needed
805 if !tcx.is_mir_available(def_id) {
806 bug!("Cannot create local mono-item for {:?}", def_id)
810 fn is_available_upstream_generic<'tcx>(
813 substs: SubstsRef<'tcx>,
815 debug_assert!(!def_id.is_local());
817 // If we are not in share generics mode, we don't link to upstream
818 // monomorphizations but always instantiate our own internal versions
820 if !tcx.sess.opts.share_generics() {
824 // If this instance has non-erasable parameters, it cannot be a shared
825 // monomorphization. Non-generic instances are already handled above
826 // by `is_reachable_non_generic()`
827 if substs.non_erasable_generics().next().is_none() {
831 // Take a look at the available monomorphizations listed in the metadata
832 // of upstream crates.
833 tcx.upstream_monomorphizations_for(def_id)
834 .map(|set| set.contains_key(substs))
839 /// For given pair of source and target type that occur in an unsizing coercion,
840 /// this function finds the pair of types that determines the vtable linking
843 /// For example, the source type might be `&SomeStruct` and the target type\
844 /// might be `&SomeTrait` in a cast like:
846 /// let src: &SomeStruct = ...;
847 /// let target = src as &SomeTrait;
849 /// Then the output of this function would be (SomeStruct, SomeTrait) since for
850 /// constructing the `target` fat-pointer we need the vtable for that pair.
852 /// Things can get more complicated though because there's also the case where
853 /// the unsized type occurs as a field:
856 /// struct ComplexStruct<T: ?Sized> {
863 /// In this case, if `T` is sized, `&ComplexStruct<T>` is a thin pointer. If `T`
864 /// is unsized, `&SomeStruct` is a fat pointer, and the vtable it points to is
865 /// for the pair of `T` (which is a trait) and the concrete type that `T` was
866 /// originally coerced from:
868 /// let src: &ComplexStruct<SomeStruct> = ...;
869 /// let target = src as &ComplexStruct<SomeTrait>;
871 /// Again, we want this `find_vtable_types_for_unsizing()` to provide the pair
872 /// `(SomeStruct, SomeTrait)`.
874 /// Finally, there is also the case of custom unsizing coercions, e.g., for
875 /// smart pointers such as `Rc` and `Arc`.
876 fn find_vtable_types_for_unsizing<'tcx>(
880 ) -> (Ty<'tcx>, Ty<'tcx>) {
881 let ptr_vtable = |inner_source: Ty<'tcx>, inner_target: Ty<'tcx>| {
882 let param_env = ty::ParamEnv::reveal_all();
883 let type_has_metadata = |ty: Ty<'tcx>| -> bool {
884 use syntax_pos::DUMMY_SP;
885 if ty.is_sized(tcx.at(DUMMY_SP), param_env) {
888 let tail = tcx.struct_tail_erasing_lifetimes(ty, param_env);
890 ty::Foreign(..) => false,
891 ty::Str | ty::Slice(..) | ty::Dynamic(..) => true,
892 _ => bug!("unexpected unsized tail: {:?}", tail),
895 if type_has_metadata(inner_source) {
896 (inner_source, inner_target)
898 tcx.struct_lockstep_tails_erasing_lifetimes(inner_source, inner_target, param_env)
902 match (&source_ty.kind, &target_ty.kind) {
906 &ty::RawPtr(ty::TypeAndMut { ty: b, .. })) |
907 (&ty::RawPtr(ty::TypeAndMut { ty: a, .. }),
908 &ty::RawPtr(ty::TypeAndMut { ty: b, .. })) => {
911 (&ty::Adt(def_a, _), &ty::Adt(def_b, _)) if def_a.is_box() && def_b.is_box() => {
912 ptr_vtable(source_ty.boxed_ty(), target_ty.boxed_ty())
915 (&ty::Adt(source_adt_def, source_substs),
916 &ty::Adt(target_adt_def, target_substs)) => {
917 assert_eq!(source_adt_def, target_adt_def);
920 monomorphize::custom_coerce_unsize_info(tcx, source_ty, target_ty);
922 let coerce_index = match kind {
923 CustomCoerceUnsized::Struct(i) => i
926 let source_fields = &source_adt_def.non_enum_variant().fields;
927 let target_fields = &target_adt_def.non_enum_variant().fields;
929 assert!(coerce_index < source_fields.len() &&
930 source_fields.len() == target_fields.len());
932 find_vtable_types_for_unsizing(tcx,
933 source_fields[coerce_index].ty(tcx,
935 target_fields[coerce_index].ty(tcx,
938 _ => bug!("find_vtable_types_for_unsizing: invalid coercion {:?} -> {:?}",
944 fn create_fn_mono_item(instance: Instance<'_>) -> MonoItem<'_> {
945 debug!("create_fn_mono_item(instance={})", instance);
946 MonoItem::Fn(instance)
949 /// Creates a `MonoItem` for each method that is referenced by the vtable for
950 /// the given trait/impl pair.
951 fn create_mono_items_for_vtable_methods<'tcx>(
955 output: &mut Vec<MonoItem<'tcx>>,
957 assert!(!trait_ty.needs_subst() && !trait_ty.has_escaping_bound_vars() &&
958 !impl_ty.needs_subst() && !impl_ty.has_escaping_bound_vars());
960 if let ty::Dynamic(ref trait_ty, ..) = trait_ty.kind {
961 if let Some(principal) = trait_ty.principal() {
962 let poly_trait_ref = principal.with_self_ty(tcx, impl_ty);
963 assert!(!poly_trait_ref.has_escaping_bound_vars());
965 // Walk all methods of the trait, including those of its supertraits
966 let methods = tcx.vtable_methods(poly_trait_ref);
967 let methods = methods.iter().cloned().filter_map(|method| method)
968 .map(|(def_id, substs)| ty::Instance::resolve_for_vtable(
970 ty::ParamEnv::reveal_all(),
973 .filter(|&instance| should_monomorphize_locally(tcx, &instance))
974 .map(|instance| create_fn_mono_item(instance));
975 output.extend(methods);
978 // Also add the destructor
979 visit_drop_use(tcx, impl_ty, false, output);
983 //=-----------------------------------------------------------------------------
985 //=-----------------------------------------------------------------------------
987 struct RootCollector<'a, 'tcx> {
989 mode: MonoItemCollectionMode,
990 output: &'a mut Vec<MonoItem<'tcx>>,
991 entry_fn: Option<(DefId, EntryFnType)>,
994 impl ItemLikeVisitor<'v> for RootCollector<'_, 'v> {
995 fn visit_item(&mut self, item: &'v hir::Item) {
997 hir::ItemKind::ExternCrate(..) |
998 hir::ItemKind::Use(..) |
999 hir::ItemKind::ForeignMod(..) |
1000 hir::ItemKind::TyAlias(..) |
1001 hir::ItemKind::Trait(..) |
1002 hir::ItemKind::TraitAlias(..) |
1003 hir::ItemKind::OpaqueTy(..) |
1004 hir::ItemKind::Mod(..) => {
1005 // Nothing to do, just keep recursing...
1008 hir::ItemKind::Impl(..) => {
1009 if self.mode == MonoItemCollectionMode::Eager {
1010 create_mono_items_for_default_impls(self.tcx,
1016 hir::ItemKind::Enum(_, ref generics) |
1017 hir::ItemKind::Struct(_, ref generics) |
1018 hir::ItemKind::Union(_, ref generics) => {
1019 if generics.params.is_empty() {
1020 if self.mode == MonoItemCollectionMode::Eager {
1021 let def_id = self.tcx.hir().local_def_id(item.hir_id);
1022 debug!("RootCollector: ADT drop-glue for {}",
1023 def_id_to_string(self.tcx, def_id));
1025 let ty = Instance::new(def_id, InternalSubsts::empty()).ty(self.tcx);
1026 visit_drop_use(self.tcx, ty, true, self.output);
1030 hir::ItemKind::GlobalAsm(..) => {
1031 debug!("RootCollector: ItemKind::GlobalAsm({})",
1032 def_id_to_string(self.tcx,
1033 self.tcx.hir().local_def_id(item.hir_id)));
1034 self.output.push(MonoItem::GlobalAsm(item.hir_id));
1036 hir::ItemKind::Static(..) => {
1037 let def_id = self.tcx.hir().local_def_id(item.hir_id);
1038 debug!("RootCollector: ItemKind::Static({})",
1039 def_id_to_string(self.tcx, def_id));
1040 self.output.push(MonoItem::Static(def_id));
1042 hir::ItemKind::Const(..) => {
1043 // const items only generate mono items if they are
1044 // actually used somewhere. Just declaring them is insufficient.
1046 // but even just declaring them must collect the items they refer to
1047 let def_id = self.tcx.hir().local_def_id(item.hir_id);
1049 let instance = Instance::mono(self.tcx, def_id);
1050 let cid = GlobalId {
1054 let param_env = ty::ParamEnv::reveal_all();
1056 if let Ok(val) = self.tcx.const_eval(param_env.and(cid)) {
1057 collect_const(self.tcx, val, InternalSubsts::empty(), &mut self.output);
1060 hir::ItemKind::Fn(..) => {
1061 let def_id = self.tcx.hir().local_def_id(item.hir_id);
1062 self.push_if_root(def_id);
1067 fn visit_trait_item(&mut self, _: &'v hir::TraitItem) {
1068 // Even if there's a default body with no explicit generics,
1069 // it's still generic over some `Self: Trait`, so not a root.
1072 fn visit_impl_item(&mut self, ii: &'v hir::ImplItem) {
1074 hir::ImplItemKind::Method(hir::MethodSig { .. }, _) => {
1075 let def_id = self.tcx.hir().local_def_id(ii.hir_id);
1076 self.push_if_root(def_id);
1078 _ => { /* Nothing to do here */ }
1083 impl RootCollector<'_, 'v> {
1084 fn is_root(&self, def_id: DefId) -> bool {
1085 !item_requires_monomorphization(self.tcx, def_id) && match self.mode {
1086 MonoItemCollectionMode::Eager => {
1089 MonoItemCollectionMode::Lazy => {
1090 self.entry_fn.map(|(id, _)| id) == Some(def_id) ||
1091 self.tcx.is_reachable_non_generic(def_id) ||
1092 self.tcx.codegen_fn_attrs(def_id).flags.contains(
1093 CodegenFnAttrFlags::RUSTC_STD_INTERNAL_SYMBOL)
1098 /// If `def_id` represents a root, then push it onto the list of
1099 /// outputs. (Note that all roots must be monomorphic.)
1100 fn push_if_root(&mut self, def_id: DefId) {
1101 if self.is_root(def_id) {
1102 debug!("RootCollector::push_if_root: found root def_id={:?}", def_id);
1104 let instance = Instance::mono(self.tcx, def_id);
1105 self.output.push(create_fn_mono_item(instance));
1109 /// As a special case, when/if we encounter the
1110 /// `main()` function, we also have to generate a
1111 /// monomorphized copy of the start lang item based on
1112 /// the return type of `main`. This is not needed when
1113 /// the user writes their own `start` manually.
1114 fn push_extra_entry_roots(&mut self) {
1115 let main_def_id = match self.entry_fn {
1116 Some((def_id, EntryFnType::Main)) => def_id,
1120 let start_def_id = match self.tcx.lang_items().require(StartFnLangItem) {
1122 Err(err) => self.tcx.sess.fatal(&err),
1124 let main_ret_ty = self.tcx.fn_sig(main_def_id).output();
1126 // Given that `main()` has no arguments,
1127 // then its return type cannot have
1128 // late-bound regions, since late-bound
1129 // regions must appear in the argument
1131 let main_ret_ty = self.tcx.erase_regions(
1132 &main_ret_ty.no_bound_vars().unwrap(),
1135 let start_instance = Instance::resolve(
1137 ty::ParamEnv::reveal_all(),
1139 self.tcx.intern_substs(&[main_ret_ty.into()])
1142 self.output.push(create_fn_mono_item(start_instance));
1146 fn item_requires_monomorphization(tcx: TyCtxt<'_>, def_id: DefId) -> bool {
1147 let generics = tcx.generics_of(def_id);
1148 generics.requires_monomorphization(tcx)
1151 fn create_mono_items_for_default_impls<'tcx>(
1153 item: &'tcx hir::Item,
1154 output: &mut Vec<MonoItem<'tcx>>,
1157 hir::ItemKind::Impl(_, _, _, ref generics, .., ref impl_item_refs) => {
1158 for param in &generics.params {
1160 hir::GenericParamKind::Lifetime { .. } => {}
1161 hir::GenericParamKind::Type { .. } |
1162 hir::GenericParamKind::Const { .. } => {
1168 let impl_def_id = tcx.hir().local_def_id(item.hir_id);
1170 debug!("create_mono_items_for_default_impls(item={})",
1171 def_id_to_string(tcx, impl_def_id));
1173 if let Some(trait_ref) = tcx.impl_trait_ref(impl_def_id) {
1174 let param_env = ty::ParamEnv::reveal_all();
1175 let trait_ref = tcx.normalize_erasing_regions(
1179 let overridden_methods: FxHashSet<_> =
1180 impl_item_refs.iter()
1181 .map(|iiref| iiref.ident.modern())
1183 for method in tcx.provided_trait_methods(trait_ref.def_id) {
1184 if overridden_methods.contains(&method.ident.modern()) {
1188 if tcx.generics_of(method.def_id).own_requires_monomorphization() {
1192 let substs = InternalSubsts::for_item(tcx, method.def_id, |param, _| {
1194 GenericParamDefKind::Lifetime => tcx.lifetimes.re_erased.into(),
1195 GenericParamDefKind::Type { .. } |
1196 GenericParamDefKind::Const => {
1197 trait_ref.substs[param.index as usize]
1201 let instance = ty::Instance::resolve(tcx,
1206 let mono_item = create_fn_mono_item(instance);
1207 if mono_item.is_instantiable(tcx)
1208 && should_monomorphize_locally(tcx, &instance) {
1209 output.push(mono_item);
1220 /// Scan the miri alloc in order to find function calls, closures, and drop-glue
1221 fn collect_miri<'tcx>(tcx: TyCtxt<'tcx>, alloc_id: AllocId, output: &mut Vec<MonoItem<'tcx>>) {
1222 let alloc_kind = tcx.alloc_map.lock().get(alloc_id);
1224 Some(GlobalAlloc::Static(def_id)) => {
1225 let instance = Instance::mono(tcx, def_id);
1226 if should_monomorphize_locally(tcx, &instance) {
1227 trace!("collecting static {:?}", def_id);
1228 output.push(MonoItem::Static(def_id));
1231 Some(GlobalAlloc::Memory(alloc)) => {
1232 trace!("collecting {:?} with {:#?}", alloc_id, alloc);
1233 for &((), inner) in alloc.relocations().values() {
1234 collect_miri(tcx, inner, output);
1237 Some(GlobalAlloc::Function(fn_instance)) => {
1238 if should_monomorphize_locally(tcx, &fn_instance) {
1239 trace!("collecting {:?} with {:#?}", alloc_id, fn_instance);
1240 output.push(create_fn_mono_item(fn_instance));
1243 None => bug!("alloc id without corresponding allocation: {}", alloc_id),
1247 /// Scan the MIR in order to find function calls, closures, and drop-glue
1248 fn collect_neighbours<'tcx>(
1250 instance: Instance<'tcx>,
1251 output: &mut Vec<MonoItem<'tcx>>,
1253 debug!("collect_neighbours: {:?}", instance.def_id());
1254 let body = tcx.instance_mir(instance.def);
1256 MirNeighborCollector {
1260 param_substs: instance.substs,
1261 }.visit_body(&body);
1264 fn def_id_to_string(tcx: TyCtxt<'_>, def_id: DefId) -> String {
1265 let mut output = String::new();
1266 let printer = DefPathBasedNames::new(tcx, false, false);
1267 printer.push_def_path(def_id, &mut output);
1271 fn collect_const<'tcx>(
1273 constant: &'tcx ty::Const<'tcx>,
1274 param_substs: SubstsRef<'tcx>,
1275 output: &mut Vec<MonoItem<'tcx>>,
1277 debug!("visiting const {:?}", constant);
1279 let param_env = ty::ParamEnv::reveal_all();
1280 let substituted_constant = tcx.subst_and_normalize_erasing_regions(
1286 match substituted_constant.val {
1287 ConstValue::Scalar(Scalar::Ptr(ptr)) =>
1288 collect_miri(tcx, ptr.alloc_id, output),
1289 ConstValue::Slice { data: alloc, start: _, end: _ } |
1290 ConstValue::ByRef { alloc, .. } => {
1291 for &((), id) in alloc.relocations().values() {
1292 collect_miri(tcx, id, output);
1295 ConstValue::Unevaluated(def_id, substs) => {
1296 let instance = ty::Instance::resolve(tcx,
1301 let cid = GlobalId {
1305 match tcx.const_eval(param_env.and(cid)) {
1306 Ok(val) => collect_const(tcx, val, param_substs, output),
1307 Err(ErrorHandled::Reported) => {},
1308 Err(ErrorHandled::TooGeneric) => span_bug!(
1309 tcx.def_span(def_id), "collection encountered polymorphic constant",