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, 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, Promoted, 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_data_structures::bit_set::GrowableBitSet;
198 use rustc_data_structures::sync::{MTRef, MTLock, ParallelIterator, par_iter};
202 #[derive(PartialEq, Eq, Hash, Clone, Copy, Debug)]
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 roots = time(tcx.sess, "collecting roots", || {
289 collect_roots(tcx, mode)
292 debug!("building mono item graph, beginning at roots");
294 let mut visited = MTLock::new(FxHashSet::default());
295 let mut inlining_map = MTLock::new(InliningMap::new());
298 let visited: MTRef<'_, _> = &mut visited;
299 let inlining_map: MTRef<'_, _> = &mut inlining_map;
301 time(tcx.sess, "collecting mono items", || {
302 par_iter(roots).for_each(|root| {
303 let mut recursion_depths = DefIdMap::default();
304 collect_items_rec(tcx,
307 &mut recursion_depths,
313 (visited.into_inner(), inlining_map.into_inner())
316 // Find all non-generic items by walking the HIR. These items serve as roots to
317 // start monomorphizing from.
318 fn collect_roots(tcx: TyCtxt<'_>, mode: MonoItemCollectionMode) -> Vec<MonoItem<'_>> {
319 debug!("collecting roots");
320 let mut roots = Vec::new();
323 let entry_fn = tcx.entry_fn(LOCAL_CRATE);
325 debug!("collect_roots: entry_fn = {:?}", entry_fn);
327 let mut visitor = RootCollector {
334 tcx.hir().krate().visit_all_item_likes(&mut visitor);
336 visitor.push_extra_entry_roots();
339 // We can only codegen items that are instantiable - items all of
340 // whose predicates hold. Luckily, items that aren't instantiable
341 // can't actually be used, so we can just skip codegenning them.
342 roots.retain(|root| root.is_instantiable(tcx));
347 // Collect all monomorphized items reachable from `starting_point`
348 fn collect_items_rec<'tcx>(
350 starting_point: MonoItem<'tcx>,
351 visited: MTRef<'_, MTLock<FxHashSet<MonoItem<'tcx>>>>,
352 recursion_depths: &mut DefIdMap<usize>,
353 inlining_map: MTRef<'_, MTLock<InliningMap<'tcx>>>,
355 if !visited.lock_mut().insert(starting_point.clone()) {
356 // We've been here already, no need to search again.
359 debug!("BEGIN collect_items_rec({})", starting_point.to_string(tcx, true));
361 let mut neighbors = Vec::new();
362 let recursion_depth_reset;
364 match starting_point {
365 MonoItem::Static(def_id) => {
366 let instance = Instance::mono(tcx, def_id);
368 // Sanity check whether this ended up being collected accidentally
369 debug_assert!(should_monomorphize_locally(tcx, &instance));
371 let ty = instance.ty(tcx);
372 visit_drop_use(tcx, ty, true, &mut neighbors);
374 recursion_depth_reset = None;
380 let param_env = ty::ParamEnv::reveal_all();
382 if let Ok(val) = tcx.const_eval(param_env.and(cid)) {
383 collect_const(tcx, val, InternalSubsts::empty(), &mut neighbors);
386 MonoItem::Fn(instance) => {
387 // Sanity check whether this ended up being collected accidentally
388 debug_assert!(should_monomorphize_locally(tcx, &instance));
390 // Keep track of the monomorphization recursion depth
391 recursion_depth_reset = Some(check_recursion_limit(tcx,
394 check_type_length_limit(tcx, instance);
396 collect_neighbours(tcx, instance, &mut neighbors);
398 MonoItem::GlobalAsm(..) => {
399 recursion_depth_reset = None;
403 record_accesses(tcx, starting_point, &neighbors[..], inlining_map);
405 for neighbour in neighbors {
406 collect_items_rec(tcx, neighbour, visited, recursion_depths, inlining_map);
409 if let Some((def_id, depth)) = recursion_depth_reset {
410 recursion_depths.insert(def_id, depth);
413 debug!("END collect_items_rec({})", starting_point.to_string(tcx, true));
416 fn record_accesses<'tcx>(
418 caller: MonoItem<'tcx>,
419 callees: &[MonoItem<'tcx>],
420 inlining_map: MTRef<'_, MTLock<InliningMap<'tcx>>>,
422 let is_inlining_candidate = |mono_item: &MonoItem<'tcx>| {
423 mono_item.instantiation_mode(tcx) == InstantiationMode::LocalCopy
426 let accesses = callees.into_iter()
428 (*mono_item, is_inlining_candidate(mono_item))
431 inlining_map.lock_mut().record_accesses(caller, accesses);
434 fn check_recursion_limit<'tcx>(
436 instance: Instance<'tcx>,
437 recursion_depths: &mut DefIdMap<usize>,
438 ) -> (DefId, usize) {
439 let def_id = instance.def_id();
440 let recursion_depth = recursion_depths.get(&def_id).cloned().unwrap_or(0);
441 debug!(" => recursion depth={}", recursion_depth);
443 let recursion_depth = if Some(def_id) == tcx.lang_items().drop_in_place_fn() {
444 // HACK: drop_in_place creates tight monomorphization loops. Give
451 // Code that needs to instantiate the same function recursively
452 // more than the recursion limit is assumed to be causing an
453 // infinite expansion.
454 if recursion_depth > *tcx.sess.recursion_limit.get() {
455 let error = format!("reached the recursion limit while instantiating `{}`",
457 if let Some(hir_id) = tcx.hir().as_local_hir_id(def_id) {
458 tcx.sess.span_fatal(tcx.hir().span(hir_id), &error);
460 tcx.sess.fatal(&error);
464 recursion_depths.insert(def_id, recursion_depth + 1);
466 (def_id, recursion_depth)
469 fn check_type_length_limit<'tcx>(tcx: TyCtxt<'tcx>, instance: Instance<'tcx>) {
470 let type_length = instance.substs.types().flat_map(|ty| ty.walk()).count();
471 let const_length = instance.substs.consts().flat_map(|ct| ct.ty.walk()).count();
472 debug!(" => type length={}, const length={}", type_length, const_length);
474 // Rust code can easily create exponentially-long types using only a
475 // polynomial recursion depth. Even with the default recursion
476 // depth, you can easily get cases that take >2^60 steps to run,
477 // which means that rustc basically hangs.
479 // Bail out in these cases to avoid that bad user experience.
480 let type_length_limit = *tcx.sess.type_length_limit.get();
481 // We include the const length in the type length, as it's better
482 // to be overly conservative.
483 // FIXME(const_generics): we should instead uniformly walk through `substs`,
484 // ignoring lifetimes.
485 if type_length + const_length > type_length_limit {
486 // The instance name is already known to be too long for rustc.
487 // Show only the first and last 32 characters to avoid blasting
488 // the user's terminal with thousands of lines of type-name.
489 let shrink = |s: String, before: usize, after: usize| {
490 // An iterator of all byte positions including the end of the string.
491 let positions = || s.char_indices().map(|(i, _)| i).chain(iter::once(s.len()));
493 let shrunk = format!(
494 "{before}...{after}",
495 before = &s[..positions().nth(before).unwrap_or(s.len())],
496 after = &s[positions().rev().nth(after).unwrap_or(0)..],
499 // Only use the shrunk version if it's really shorter.
500 // This also avoids the case where before and after slices overlap.
501 if shrunk.len() < s.len() {
507 let msg = format!("reached the type-length limit while instantiating `{}`",
508 shrink(instance.to_string(), 32, 32));
509 let mut diag = tcx.sess.struct_span_fatal(tcx.def_span(instance.def_id()), &msg);
511 "consider adding a `#![type_length_limit=\"{}\"]` attribute to your crate",
514 tcx.sess.abort_if_errors();
518 struct MirNeighborCollector<'a, 'tcx> {
520 body: &'a mir::Body<'tcx>,
521 output: &'a mut Vec<MonoItem<'tcx>>,
522 param_substs: SubstsRef<'tcx>,
525 impl<'a, 'tcx> MirVisitor<'tcx> for MirNeighborCollector<'a, 'tcx> {
527 fn visit_rvalue(&mut self, rvalue: &mir::Rvalue<'tcx>, location: Location) {
528 debug!("visiting rvalue {:?}", *rvalue);
531 // When doing an cast from a regular pointer to a fat pointer, we
532 // have to instantiate all methods of the trait being cast to, so we
533 // can build the appropriate vtable.
535 mir::CastKind::Pointer(PointerCast::Unsize), ref operand, target_ty
537 let target_ty = self.tcx.subst_and_normalize_erasing_regions(
539 ty::ParamEnv::reveal_all(),
542 let source_ty = operand.ty(self.body, self.tcx);
543 let source_ty = self.tcx.subst_and_normalize_erasing_regions(
545 ty::ParamEnv::reveal_all(),
548 let (source_ty, target_ty) = find_vtable_types_for_unsizing(self.tcx,
551 // This could also be a different Unsize instruction, like
552 // from a fixed sized array to a slice. But we are only
553 // interested in things that produce a vtable.
554 if target_ty.is_trait() && !source_ty.is_trait() {
555 create_mono_items_for_vtable_methods(self.tcx,
562 mir::CastKind::Pointer(PointerCast::ReifyFnPointer), ref operand, _
564 let fn_ty = operand.ty(self.body, self.tcx);
565 let fn_ty = self.tcx.subst_and_normalize_erasing_regions(
567 ty::ParamEnv::reveal_all(),
570 visit_fn_use(self.tcx, fn_ty, false, &mut self.output);
573 mir::CastKind::Pointer(PointerCast::ClosureFnPointer(_)), ref operand, _
575 let source_ty = operand.ty(self.body, self.tcx);
576 let source_ty = self.tcx.subst_and_normalize_erasing_regions(
578 ty::ParamEnv::reveal_all(),
581 match source_ty.sty {
582 ty::Closure(def_id, substs) => {
583 let instance = Instance::resolve_closure(
584 self.tcx, def_id, substs, ty::ClosureKind::FnOnce);
585 if should_monomorphize_locally(self.tcx, &instance) {
586 self.output.push(create_fn_mono_item(instance));
592 mir::Rvalue::NullaryOp(mir::NullOp::Box, _) => {
594 let exchange_malloc_fn_def_id = tcx
596 .require(ExchangeMallocFnLangItem)
597 .unwrap_or_else(|e| tcx.sess.fatal(&e));
598 let instance = Instance::mono(tcx, exchange_malloc_fn_def_id);
599 if should_monomorphize_locally(tcx, &instance) {
600 self.output.push(create_fn_mono_item(instance));
603 _ => { /* not interesting */ }
606 self.super_rvalue(rvalue, location);
609 fn visit_const(&mut self, constant: &&'tcx ty::Const<'tcx>, location: Location) {
610 debug!("visiting const {:?} @ {:?}", *constant, location);
612 collect_const(self.tcx, *constant, self.param_substs, self.output);
614 self.super_const(constant);
617 fn visit_terminator_kind(&mut self,
618 kind: &mir::TerminatorKind<'tcx>,
619 location: Location) {
620 debug!("visiting terminator {:?} @ {:?}", kind, location);
624 mir::TerminatorKind::Call { ref func, .. } => {
625 let callee_ty = func.ty(self.body, tcx);
626 let callee_ty = tcx.subst_and_normalize_erasing_regions(
628 ty::ParamEnv::reveal_all(),
631 visit_fn_use(self.tcx, callee_ty, true, &mut self.output);
633 mir::TerminatorKind::Drop { ref location, .. } |
634 mir::TerminatorKind::DropAndReplace { ref location, .. } => {
635 let ty = location.ty(self.body, self.tcx).ty;
636 let ty = tcx.subst_and_normalize_erasing_regions(
638 ty::ParamEnv::reveal_all(),
641 visit_drop_use(self.tcx, ty, true, self.output);
643 mir::TerminatorKind::Goto { .. } |
644 mir::TerminatorKind::SwitchInt { .. } |
645 mir::TerminatorKind::Resume |
646 mir::TerminatorKind::Abort |
647 mir::TerminatorKind::Return |
648 mir::TerminatorKind::Unreachable |
649 mir::TerminatorKind::Assert { .. } => {}
650 mir::TerminatorKind::GeneratorDrop |
651 mir::TerminatorKind::Yield { .. } |
652 mir::TerminatorKind::FalseEdges { .. } |
653 mir::TerminatorKind::FalseUnwind { .. } => bug!(),
656 self.super_terminator_kind(kind, location);
659 fn visit_place_base(&mut self,
660 place_base: &mir::PlaceBase<'tcx>,
661 _context: mir::visit::PlaceContext,
662 location: Location) {
664 PlaceBase::Static(box Static { kind: StaticKind::Static(def_id), .. }) => {
665 debug!("visiting static {:?} @ {:?}", def_id, location);
668 let instance = Instance::mono(tcx, *def_id);
669 if should_monomorphize_locally(tcx, &instance) {
670 self.output.push(MonoItem::Static(*def_id));
673 PlaceBase::Static(box Static { kind: StaticKind::Promoted(_), .. }) => {
674 // FIXME: should we handle promoteds here instead of eagerly in collect_neighbours?
676 PlaceBase::Local(_) => {
677 // Locals have no relevance for collector
683 fn visit_drop_use<'tcx>(
686 is_direct_call: bool,
687 output: &mut Vec<MonoItem<'tcx>>,
689 let instance = Instance::resolve_drop_in_place(tcx, ty);
690 visit_instance_use(tcx, instance, is_direct_call, output);
693 fn visit_fn_use<'tcx>(
696 is_direct_call: bool,
697 output: &mut Vec<MonoItem<'tcx>>,
699 if let ty::FnDef(def_id, substs) = ty.sty {
700 let instance = ty::Instance::resolve(tcx,
701 ty::ParamEnv::reveal_all(),
704 visit_instance_use(tcx, instance, is_direct_call, output);
708 fn visit_instance_use<'tcx>(
710 instance: ty::Instance<'tcx>,
711 is_direct_call: bool,
712 output: &mut Vec<MonoItem<'tcx>>,
714 debug!("visit_item_use({:?}, is_direct_call={:?})", instance, is_direct_call);
715 if !should_monomorphize_locally(tcx, &instance) {
720 ty::InstanceDef::Intrinsic(def_id) => {
722 bug!("intrinsic {:?} being reified", def_id);
725 ty::InstanceDef::VtableShim(..) |
726 ty::InstanceDef::Virtual(..) |
727 ty::InstanceDef::DropGlue(_, None) => {
728 // don't need to emit shim if we are calling directly.
730 output.push(create_fn_mono_item(instance));
733 ty::InstanceDef::DropGlue(_, Some(_)) => {
734 output.push(create_fn_mono_item(instance));
736 ty::InstanceDef::ClosureOnceShim { .. } |
737 ty::InstanceDef::Item(..) |
738 ty::InstanceDef::FnPtrShim(..) |
739 ty::InstanceDef::CloneShim(..) => {
740 output.push(create_fn_mono_item(instance));
745 // Returns true if we should codegen an instance in the local crate.
746 // Returns false if we can just link to the upstream crate and therefore don't
748 fn should_monomorphize_locally<'tcx>(tcx: TyCtxt<'tcx>, instance: &Instance<'tcx>) -> bool {
749 let def_id = match instance.def {
750 ty::InstanceDef::Item(def_id) => def_id,
751 ty::InstanceDef::VtableShim(..) |
752 ty::InstanceDef::ClosureOnceShim { .. } |
753 ty::InstanceDef::Virtual(..) |
754 ty::InstanceDef::FnPtrShim(..) |
755 ty::InstanceDef::DropGlue(..) |
756 ty::InstanceDef::Intrinsic(_) |
757 ty::InstanceDef::CloneShim(..) => return true
760 if tcx.is_foreign_item(def_id) {
761 // We can always link to foreign items
765 if def_id.is_local() {
766 // local items cannot be referred to locally without monomorphizing them locally
770 if tcx.is_reachable_non_generic(def_id) ||
771 is_available_upstream_generic(tcx, def_id, instance.substs) {
772 // We can link to the item in question, no instance needed
777 if !tcx.is_mir_available(def_id) {
778 bug!("Cannot create local mono-item for {:?}", def_id)
782 fn is_available_upstream_generic<'tcx>(
785 substs: SubstsRef<'tcx>,
787 debug_assert!(!def_id.is_local());
789 // If we are not in share generics mode, we don't link to upstream
790 // monomorphizations but always instantiate our own internal versions
792 if !tcx.sess.opts.share_generics() {
796 // If this instance has non-erasable parameters, it cannot be a shared
797 // monomorphization. Non-generic instances are already handled above
798 // by `is_reachable_non_generic()`
799 if substs.non_erasable_generics().next().is_none() {
803 // Take a look at the available monomorphizations listed in the metadata
804 // of upstream crates.
805 tcx.upstream_monomorphizations_for(def_id)
806 .map(|set| set.contains_key(substs))
811 /// For given pair of source and target type that occur in an unsizing coercion,
812 /// this function finds the pair of types that determines the vtable linking
815 /// For example, the source type might be `&SomeStruct` and the target type\
816 /// might be `&SomeTrait` in a cast like:
818 /// let src: &SomeStruct = ...;
819 /// let target = src as &SomeTrait;
821 /// Then the output of this function would be (SomeStruct, SomeTrait) since for
822 /// constructing the `target` fat-pointer we need the vtable for that pair.
824 /// Things can get more complicated though because there's also the case where
825 /// the unsized type occurs as a field:
828 /// struct ComplexStruct<T: ?Sized> {
835 /// In this case, if `T` is sized, `&ComplexStruct<T>` is a thin pointer. If `T`
836 /// is unsized, `&SomeStruct` is a fat pointer, and the vtable it points to is
837 /// for the pair of `T` (which is a trait) and the concrete type that `T` was
838 /// originally coerced from:
840 /// let src: &ComplexStruct<SomeStruct> = ...;
841 /// let target = src as &ComplexStruct<SomeTrait>;
843 /// Again, we want this `find_vtable_types_for_unsizing()` to provide the pair
844 /// `(SomeStruct, SomeTrait)`.
846 /// Finally, there is also the case of custom unsizing coercions, e.g., for
847 /// smart pointers such as `Rc` and `Arc`.
848 fn find_vtable_types_for_unsizing<'tcx>(
852 ) -> (Ty<'tcx>, Ty<'tcx>) {
853 let ptr_vtable = |inner_source: Ty<'tcx>, inner_target: Ty<'tcx>| {
854 let param_env = ty::ParamEnv::reveal_all();
855 let type_has_metadata = |ty: Ty<'tcx>| -> bool {
856 use syntax_pos::DUMMY_SP;
857 if ty.is_sized(tcx.at(DUMMY_SP), param_env) {
860 let tail = tcx.struct_tail_erasing_lifetimes(ty, param_env);
862 ty::Foreign(..) => false,
863 ty::Str | ty::Slice(..) | ty::Dynamic(..) => true,
864 _ => bug!("unexpected unsized tail: {:?}", tail),
867 if type_has_metadata(inner_source) {
868 (inner_source, inner_target)
870 tcx.struct_lockstep_tails_erasing_lifetimes(inner_source, inner_target, param_env)
874 match (&source_ty.sty, &target_ty.sty) {
878 &ty::RawPtr(ty::TypeAndMut { ty: b, .. })) |
879 (&ty::RawPtr(ty::TypeAndMut { ty: a, .. }),
880 &ty::RawPtr(ty::TypeAndMut { ty: b, .. })) => {
883 (&ty::Adt(def_a, _), &ty::Adt(def_b, _)) if def_a.is_box() && def_b.is_box() => {
884 ptr_vtable(source_ty.boxed_ty(), target_ty.boxed_ty())
887 (&ty::Adt(source_adt_def, source_substs),
888 &ty::Adt(target_adt_def, target_substs)) => {
889 assert_eq!(source_adt_def, target_adt_def);
892 monomorphize::custom_coerce_unsize_info(tcx, source_ty, target_ty);
894 let coerce_index = match kind {
895 CustomCoerceUnsized::Struct(i) => i
898 let source_fields = &source_adt_def.non_enum_variant().fields;
899 let target_fields = &target_adt_def.non_enum_variant().fields;
901 assert!(coerce_index < source_fields.len() &&
902 source_fields.len() == target_fields.len());
904 find_vtable_types_for_unsizing(tcx,
905 source_fields[coerce_index].ty(tcx,
907 target_fields[coerce_index].ty(tcx,
910 _ => bug!("find_vtable_types_for_unsizing: invalid coercion {:?} -> {:?}",
916 fn create_fn_mono_item(instance: Instance<'_>) -> MonoItem<'_> {
917 debug!("create_fn_mono_item(instance={})", instance);
918 MonoItem::Fn(instance)
921 /// Creates a `MonoItem` for each method that is referenced by the vtable for
922 /// the given trait/impl pair.
923 fn create_mono_items_for_vtable_methods<'tcx>(
927 output: &mut Vec<MonoItem<'tcx>>,
929 assert!(!trait_ty.needs_subst() && !trait_ty.has_escaping_bound_vars() &&
930 !impl_ty.needs_subst() && !impl_ty.has_escaping_bound_vars());
932 if let ty::Dynamic(ref trait_ty, ..) = trait_ty.sty {
933 if let Some(principal) = trait_ty.principal() {
934 let poly_trait_ref = principal.with_self_ty(tcx, impl_ty);
935 assert!(!poly_trait_ref.has_escaping_bound_vars());
937 // Walk all methods of the trait, including those of its supertraits
938 let methods = tcx.vtable_methods(poly_trait_ref);
939 let methods = methods.iter().cloned().filter_map(|method| method)
940 .map(|(def_id, substs)| ty::Instance::resolve_for_vtable(
942 ty::ParamEnv::reveal_all(),
945 .filter(|&instance| should_monomorphize_locally(tcx, &instance))
946 .map(|instance| create_fn_mono_item(instance));
947 output.extend(methods);
950 // Also add the destructor
951 visit_drop_use(tcx, impl_ty, false, output);
955 //=-----------------------------------------------------------------------------
957 //=-----------------------------------------------------------------------------
959 struct RootCollector<'a, 'tcx> {
961 mode: MonoItemCollectionMode,
962 output: &'a mut Vec<MonoItem<'tcx>>,
963 entry_fn: Option<(DefId, EntryFnType)>,
966 impl ItemLikeVisitor<'v> for RootCollector<'_, 'v> {
967 fn visit_item(&mut self, item: &'v hir::Item) {
969 hir::ItemKind::ExternCrate(..) |
970 hir::ItemKind::Use(..) |
971 hir::ItemKind::ForeignMod(..) |
972 hir::ItemKind::Ty(..) |
973 hir::ItemKind::Trait(..) |
974 hir::ItemKind::TraitAlias(..) |
975 hir::ItemKind::Existential(..) |
976 hir::ItemKind::Mod(..) => {
977 // Nothing to do, just keep recursing...
980 hir::ItemKind::Impl(..) => {
981 if self.mode == MonoItemCollectionMode::Eager {
982 create_mono_items_for_default_impls(self.tcx,
988 hir::ItemKind::Enum(_, ref generics) |
989 hir::ItemKind::Struct(_, ref generics) |
990 hir::ItemKind::Union(_, ref generics) => {
991 if generics.params.is_empty() {
992 if self.mode == MonoItemCollectionMode::Eager {
993 let def_id = self.tcx.hir().local_def_id(item.hir_id);
994 debug!("RootCollector: ADT drop-glue for {}",
995 def_id_to_string(self.tcx, def_id));
997 let ty = Instance::new(def_id, InternalSubsts::empty()).ty(self.tcx);
998 visit_drop_use(self.tcx, ty, true, self.output);
1002 hir::ItemKind::GlobalAsm(..) => {
1003 debug!("RootCollector: ItemKind::GlobalAsm({})",
1004 def_id_to_string(self.tcx,
1005 self.tcx.hir().local_def_id(item.hir_id)));
1006 self.output.push(MonoItem::GlobalAsm(item.hir_id));
1008 hir::ItemKind::Static(..) => {
1009 let def_id = self.tcx.hir().local_def_id(item.hir_id);
1010 debug!("RootCollector: ItemKind::Static({})",
1011 def_id_to_string(self.tcx, def_id));
1012 self.output.push(MonoItem::Static(def_id));
1014 hir::ItemKind::Const(..) => {
1015 // const items only generate mono items if they are
1016 // actually used somewhere. Just declaring them is insufficient.
1018 // but even just declaring them must collect the items they refer to
1019 let def_id = self.tcx.hir().local_def_id(item.hir_id);
1021 let instance = Instance::mono(self.tcx, def_id);
1022 let cid = GlobalId {
1026 let param_env = ty::ParamEnv::reveal_all();
1028 if let Ok(val) = self.tcx.const_eval(param_env.and(cid)) {
1029 collect_const(self.tcx, val, InternalSubsts::empty(), &mut self.output);
1032 hir::ItemKind::Fn(..) => {
1033 let def_id = self.tcx.hir().local_def_id(item.hir_id);
1034 self.push_if_root(def_id);
1039 fn visit_trait_item(&mut self, _: &'v hir::TraitItem) {
1040 // Even if there's a default body with no explicit generics,
1041 // it's still generic over some `Self: Trait`, so not a root.
1044 fn visit_impl_item(&mut self, ii: &'v hir::ImplItem) {
1046 hir::ImplItemKind::Method(hir::MethodSig { .. }, _) => {
1047 let def_id = self.tcx.hir().local_def_id(ii.hir_id);
1048 self.push_if_root(def_id);
1050 _ => { /* Nothing to do here */ }
1055 impl RootCollector<'_, 'v> {
1056 fn is_root(&self, def_id: DefId) -> bool {
1057 !item_requires_monomorphization(self.tcx, def_id) && match self.mode {
1058 MonoItemCollectionMode::Eager => {
1061 MonoItemCollectionMode::Lazy => {
1062 self.entry_fn.map(|(id, _)| id) == Some(def_id) ||
1063 self.tcx.is_reachable_non_generic(def_id) ||
1064 self.tcx.codegen_fn_attrs(def_id).flags.contains(
1065 CodegenFnAttrFlags::RUSTC_STD_INTERNAL_SYMBOL)
1070 /// If `def_id` represents a root, then push it onto the list of
1071 /// outputs. (Note that all roots must be monomorphic.)
1072 fn push_if_root(&mut self, def_id: DefId) {
1073 if self.is_root(def_id) {
1074 debug!("RootCollector::push_if_root: found root def_id={:?}", def_id);
1076 let instance = Instance::mono(self.tcx, def_id);
1077 self.output.push(create_fn_mono_item(instance));
1081 /// As a special case, when/if we encounter the
1082 /// `main()` function, we also have to generate a
1083 /// monomorphized copy of the start lang item based on
1084 /// the return type of `main`. This is not needed when
1085 /// the user writes their own `start` manually.
1086 fn push_extra_entry_roots(&mut self) {
1087 let main_def_id = match self.entry_fn {
1088 Some((def_id, EntryFnType::Main)) => def_id,
1092 let start_def_id = match self.tcx.lang_items().require(StartFnLangItem) {
1094 Err(err) => self.tcx.sess.fatal(&err),
1096 let main_ret_ty = self.tcx.fn_sig(main_def_id).output();
1098 // Given that `main()` has no arguments,
1099 // then its return type cannot have
1100 // late-bound regions, since late-bound
1101 // regions must appear in the argument
1103 let main_ret_ty = self.tcx.erase_regions(
1104 &main_ret_ty.no_bound_vars().unwrap(),
1107 let start_instance = Instance::resolve(
1109 ty::ParamEnv::reveal_all(),
1111 self.tcx.intern_substs(&[main_ret_ty.into()])
1114 self.output.push(create_fn_mono_item(start_instance));
1118 fn item_requires_monomorphization(tcx: TyCtxt<'_>, def_id: DefId) -> bool {
1119 let generics = tcx.generics_of(def_id);
1120 generics.requires_monomorphization(tcx)
1123 fn create_mono_items_for_default_impls<'tcx>(
1125 item: &'tcx hir::Item,
1126 output: &mut Vec<MonoItem<'tcx>>,
1129 hir::ItemKind::Impl(_, _, _, ref generics, .., ref impl_item_refs) => {
1130 for param in &generics.params {
1132 hir::GenericParamKind::Lifetime { .. } => {}
1133 hir::GenericParamKind::Type { .. } |
1134 hir::GenericParamKind::Const { .. } => {
1140 let impl_def_id = tcx.hir().local_def_id(item.hir_id);
1142 debug!("create_mono_items_for_default_impls(item={})",
1143 def_id_to_string(tcx, impl_def_id));
1145 if let Some(trait_ref) = tcx.impl_trait_ref(impl_def_id) {
1146 let overridden_methods: FxHashSet<_> =
1147 impl_item_refs.iter()
1148 .map(|iiref| iiref.ident.modern())
1150 for method in tcx.provided_trait_methods(trait_ref.def_id) {
1151 if overridden_methods.contains(&method.ident.modern()) {
1155 if tcx.generics_of(method.def_id).own_requires_monomorphization() {
1159 let substs = InternalSubsts::for_item(tcx, method.def_id, |param, _| {
1161 GenericParamDefKind::Lifetime => tcx.lifetimes.re_erased.into(),
1162 GenericParamDefKind::Type { .. } |
1163 GenericParamDefKind::Const => {
1164 trait_ref.substs[param.index as usize]
1169 let instance = ty::Instance::resolve(tcx,
1170 ty::ParamEnv::reveal_all(),
1174 let mono_item = create_fn_mono_item(instance);
1175 if mono_item.is_instantiable(tcx)
1176 && should_monomorphize_locally(tcx, &instance) {
1177 output.push(mono_item);
1188 /// Scan the miri alloc in order to find function calls, closures, and drop-glue
1189 fn collect_miri<'tcx>(tcx: TyCtxt<'tcx>, alloc_id: AllocId, output: &mut Vec<MonoItem<'tcx>>) {
1190 let alloc_kind = tcx.alloc_map.lock().get(alloc_id);
1192 Some(GlobalAlloc::Static(def_id)) => {
1193 let instance = Instance::mono(tcx, def_id);
1194 if should_monomorphize_locally(tcx, &instance) {
1195 trace!("collecting static {:?}", def_id);
1196 output.push(MonoItem::Static(def_id));
1199 Some(GlobalAlloc::Memory(alloc)) => {
1200 trace!("collecting {:?} with {:#?}", alloc_id, alloc);
1201 for &((), inner) in alloc.relocations.values() {
1202 collect_miri(tcx, inner, output);
1205 Some(GlobalAlloc::Function(fn_instance)) => {
1206 if should_monomorphize_locally(tcx, &fn_instance) {
1207 trace!("collecting {:?} with {:#?}", alloc_id, fn_instance);
1208 output.push(create_fn_mono_item(fn_instance));
1211 None => bug!("alloc id without corresponding allocation: {}", alloc_id),
1215 /// Scan the MIR in order to find function calls, closures, and drop-glue
1216 fn collect_neighbours<'tcx>(
1218 instance: Instance<'tcx>,
1219 output: &mut Vec<MonoItem<'tcx>>,
1221 let body = tcx.instance_mir(instance.def);
1223 MirNeighborCollector {
1227 param_substs: instance.substs,
1228 }.visit_body(&body);
1229 let param_env = ty::ParamEnv::reveal_all();
1230 for i in 0..body.promoted.len() {
1231 use rustc_data_structures::indexed_vec::Idx;
1232 let i = Promoted::new(i);
1233 let cid = GlobalId {
1237 match tcx.const_eval(param_env.and(cid)) {
1238 Ok(val) => collect_const(tcx, val, instance.substs, output),
1239 Err(ErrorHandled::Reported) => {},
1240 Err(ErrorHandled::TooGeneric) => span_bug!(
1241 body.promoted[i].span, "collection encountered polymorphic constant",
1247 fn def_id_to_string(tcx: TyCtxt<'_>, def_id: DefId) -> String {
1248 let mut output = String::new();
1249 let printer = DefPathBasedNames::new(tcx, false, false);
1250 printer.push_def_path(def_id, &mut output);
1254 fn collect_const<'tcx>(
1256 constant: &'tcx ty::Const<'tcx>,
1257 param_substs: SubstsRef<'tcx>,
1258 output: &mut Vec<MonoItem<'tcx>>,
1260 debug!("visiting const {:?}", constant);
1262 match constant.val {
1263 ConstValue::Scalar(Scalar::Ptr(ptr)) =>
1264 collect_miri(tcx, ptr.alloc_id, output),
1265 ConstValue::Slice { data: alloc, start: _, end: _ } |
1266 ConstValue::ByRef { alloc, .. } => {
1267 for &((), id) in alloc.relocations.values() {
1268 collect_miri(tcx, id, output);
1271 ConstValue::Unevaluated(def_id, substs) => {
1272 let param_env = ty::ParamEnv::reveal_all();
1273 let substs = tcx.subst_and_normalize_erasing_regions(
1278 let instance = ty::Instance::resolve(tcx,
1283 let cid = GlobalId {
1287 match tcx.const_eval(param_env.and(cid)) {
1288 Ok(val) => collect_const(tcx, val, param_substs, output),
1289 Err(ErrorHandled::Reported) => {},
1290 Err(ErrorHandled::TooGeneric) => span_bug!(
1291 tcx.def_span(def_id), "collection encountered polymorphic constant",