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};
185 use rustc::ty::adjustment::CustomCoerceUnsized;
186 use rustc::session::config::EntryFnType;
187 use rustc::mir::{self, Location, Place, PlaceBase, Promoted, Static, StaticKind};
188 use rustc::mir::visit::Visitor as MirVisitor;
189 use rustc::mir::mono::MonoItem;
190 use rustc::mir::interpret::{Scalar, GlobalId, AllocKind, ErrorHandled};
192 use crate::monomorphize::{self, Instance};
193 use rustc::util::nodemap::{FxHashSet, FxHashMap, DefIdMap};
194 use rustc::util::common::time;
196 use crate::monomorphize::item::{MonoItemExt, DefPathBasedNames, InstantiationMode};
198 use rustc_data_structures::bit_set::GrowableBitSet;
199 use rustc_data_structures::sync::{MTRef, MTLock, ParallelIterator, par_iter};
203 #[derive(PartialEq, Eq, Hash, Clone, Copy, Debug)]
204 pub enum MonoItemCollectionMode {
209 /// Maps every mono item to all mono items it references in its
211 pub struct InliningMap<'tcx> {
212 // Maps a source mono item to the range of mono items
214 // The two numbers in the tuple are the start (inclusive) and
215 // end index (exclusive) within the `targets` vecs.
216 index: FxHashMap<MonoItem<'tcx>, (usize, usize)>,
217 targets: Vec<MonoItem<'tcx>>,
219 // Contains one bit per mono item in the `targets` field. That bit
220 // is true if that mono item needs to be inlined into every CGU.
221 inlines: GrowableBitSet<usize>,
224 impl<'tcx> InliningMap<'tcx> {
226 fn new() -> InliningMap<'tcx> {
228 index: FxHashMap::default(),
230 inlines: GrowableBitSet::with_capacity(1024),
234 fn record_accesses<I>(&mut self,
235 source: MonoItem<'tcx>,
237 where I: Iterator<Item=(MonoItem<'tcx>, bool)> + ExactSizeIterator
239 assert!(!self.index.contains_key(&source));
241 let start_index = self.targets.len();
242 let new_items_count = new_targets.len();
243 let new_items_count_total = new_items_count + self.targets.len();
245 self.targets.reserve(new_items_count);
246 self.inlines.ensure(new_items_count_total);
248 for (i, (target, inline)) in new_targets.enumerate() {
249 self.targets.push(target);
251 self.inlines.insert(i + start_index);
255 let end_index = self.targets.len();
256 self.index.insert(source, (start_index, end_index));
259 // Internally iterate over all items referenced by `source` which will be
260 // made available for inlining.
261 pub fn with_inlining_candidates<F>(&self, source: MonoItem<'tcx>, mut f: F)
262 where F: FnMut(MonoItem<'tcx>)
264 if let Some(&(start_index, end_index)) = self.index.get(&source) {
265 for (i, candidate) in self.targets[start_index .. end_index]
268 if self.inlines.contains(start_index + i) {
275 // Internally iterate over all items and the things each accesses.
276 pub fn iter_accesses<F>(&self, mut f: F)
277 where F: FnMut(MonoItem<'tcx>, &[MonoItem<'tcx>])
279 for (&accessor, &(start_index, end_index)) in &self.index {
280 f(accessor, &self.targets[start_index .. end_index])
285 pub fn collect_crate_mono_items<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
286 mode: MonoItemCollectionMode)
287 -> (FxHashSet<MonoItem<'tcx>>,
289 let roots = time(tcx.sess, "collecting roots", || {
290 collect_roots(tcx, mode)
293 debug!("Building mono item graph, beginning at roots");
295 let mut visited = MTLock::new(FxHashSet::default());
296 let mut inlining_map = MTLock::new(InliningMap::new());
299 let visited: MTRef<'_, _> = &mut visited;
300 let inlining_map: MTRef<'_, _> = &mut inlining_map;
302 time(tcx.sess, "collecting mono items", || {
303 par_iter(roots).for_each(|root| {
304 let mut recursion_depths = DefIdMap::default();
305 collect_items_rec(tcx,
308 &mut recursion_depths,
314 (visited.into_inner(), inlining_map.into_inner())
317 // Find all non-generic items by walking the HIR. These items serve as roots to
318 // start monomorphizing from.
319 fn collect_roots<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
320 mode: MonoItemCollectionMode)
321 -> Vec<MonoItem<'tcx>> {
322 debug!("Collecting roots");
323 let mut roots = Vec::new();
326 let entry_fn = tcx.entry_fn(LOCAL_CRATE);
328 debug!("collect_roots: entry_fn = {:?}", entry_fn);
330 let mut visitor = RootCollector {
337 tcx.hir().krate().visit_all_item_likes(&mut visitor);
339 visitor.push_extra_entry_roots();
342 // We can only codegen items that are instantiable - items all of
343 // whose predicates hold. Luckily, items that aren't instantiable
344 // can't actually be used, so we can just skip codegenning them.
345 roots.retain(|root| root.is_instantiable(tcx));
350 // Collect all monomorphized items reachable from `starting_point`
351 fn collect_items_rec<'a, 'tcx: 'a>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
352 starting_point: MonoItem<'tcx>,
353 visited: MTRef<'_, MTLock<FxHashSet<MonoItem<'tcx>>>>,
354 recursion_depths: &mut DefIdMap<usize>,
355 inlining_map: MTRef<'_, MTLock<InliningMap<'tcx>>>) {
356 if !visited.lock_mut().insert(starting_point.clone()) {
357 // We've been here already, no need to search again.
360 debug!("BEGIN collect_items_rec({})", starting_point.to_string(tcx, true));
362 let mut neighbors = Vec::new();
363 let recursion_depth_reset;
365 match starting_point {
366 MonoItem::Static(def_id) => {
367 let instance = Instance::mono(tcx, def_id);
369 // Sanity check whether this ended up being collected accidentally
370 debug_assert!(should_monomorphize_locally(tcx, &instance));
372 let ty = instance.ty(tcx);
373 visit_drop_use(tcx, ty, true, &mut neighbors);
375 recursion_depth_reset = None;
381 let param_env = ty::ParamEnv::reveal_all();
383 if let Ok(val) = tcx.const_eval(param_env.and(cid)) {
384 collect_const(tcx, val, InternalSubsts::empty(), &mut neighbors);
387 MonoItem::Fn(instance) => {
388 // Sanity check whether this ended up being collected accidentally
389 debug_assert!(should_monomorphize_locally(tcx, &instance));
391 // Keep track of the monomorphization recursion depth
392 recursion_depth_reset = Some(check_recursion_limit(tcx,
395 check_type_length_limit(tcx, instance);
397 collect_neighbours(tcx, instance, &mut neighbors);
399 MonoItem::GlobalAsm(..) => {
400 recursion_depth_reset = None;
404 record_accesses(tcx, starting_point, &neighbors[..], inlining_map);
406 for neighbour in neighbors {
407 collect_items_rec(tcx, neighbour, visited, recursion_depths, inlining_map);
410 if let Some((def_id, depth)) = recursion_depth_reset {
411 recursion_depths.insert(def_id, depth);
414 debug!("END collect_items_rec({})", starting_point.to_string(tcx, true));
417 fn record_accesses<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
418 caller: MonoItem<'tcx>,
419 callees: &[MonoItem<'tcx>],
420 inlining_map: MTRef<'_, MTLock<InliningMap<'tcx>>>) {
421 let is_inlining_candidate = |mono_item: &MonoItem<'tcx>| {
422 mono_item.instantiation_mode(tcx) == InstantiationMode::LocalCopy
425 let accesses = callees.into_iter()
427 (*mono_item, is_inlining_candidate(mono_item))
430 inlining_map.lock_mut().record_accesses(caller, accesses);
433 fn check_recursion_limit<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
434 instance: Instance<'tcx>,
435 recursion_depths: &mut DefIdMap<usize>)
437 let def_id = instance.def_id();
438 let recursion_depth = recursion_depths.get(&def_id).cloned().unwrap_or(0);
439 debug!(" => recursion depth={}", recursion_depth);
441 let recursion_depth = if Some(def_id) == tcx.lang_items().drop_in_place_fn() {
442 // HACK: drop_in_place creates tight monomorphization loops. Give
449 // Code that needs to instantiate the same function recursively
450 // more than the recursion limit is assumed to be causing an
451 // infinite expansion.
452 if recursion_depth > *tcx.sess.recursion_limit.get() {
453 let error = format!("reached the recursion limit while instantiating `{}`",
455 if let Some(hir_id) = tcx.hir().as_local_hir_id(def_id) {
456 tcx.sess.span_fatal(tcx.hir().span_by_hir_id(hir_id), &error);
458 tcx.sess.fatal(&error);
462 recursion_depths.insert(def_id, recursion_depth + 1);
464 (def_id, recursion_depth)
467 fn check_type_length_limit<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
468 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 if type_length + const_length > type_length_limit {
484 // The instance name is already known to be too long for rustc.
485 // Show only the first and last 32 characters to avoid blasting
486 // the user's terminal with thousands of lines of type-name.
487 let shrink = |s: String, before: usize, after: usize| {
488 // An iterator of all byte positions including the end of the string.
489 let positions = || s.char_indices().map(|(i, _)| i).chain(iter::once(s.len()));
491 let shrunk = format!(
492 "{before}...{after}",
493 before = &s[..positions().nth(before).unwrap_or(s.len())],
494 after = &s[positions().rev().nth(after).unwrap_or(0)..],
497 // Only use the shrunk version if it's really shorter.
498 // This also avoids the case where before and after slices overlap.
499 if shrunk.len() < s.len() {
505 let msg = format!("reached the type-length limit while instantiating `{}`",
506 shrink(instance.to_string(), 32, 32));
507 let mut diag = tcx.sess.struct_span_fatal(tcx.def_span(instance.def_id()), &msg);
509 "consider adding a `#![type_length_limit=\"{}\"]` attribute to your crate",
512 tcx.sess.abort_if_errors();
516 struct MirNeighborCollector<'a, 'tcx: 'a> {
517 tcx: TyCtxt<'a, 'tcx, 'tcx>,
518 mir: &'a mir::Mir<'tcx>,
519 output: &'a mut Vec<MonoItem<'tcx>>,
520 param_substs: SubstsRef<'tcx>,
523 impl<'a, 'tcx> MirVisitor<'tcx> for MirNeighborCollector<'a, 'tcx> {
525 fn visit_rvalue(&mut self, rvalue: &mir::Rvalue<'tcx>, location: Location) {
526 debug!("visiting rvalue {:?}", *rvalue);
529 // When doing an cast from a regular pointer to a fat pointer, we
530 // have to instantiate all methods of the trait being cast to, so we
531 // can build the appropriate vtable.
532 mir::Rvalue::Cast(mir::CastKind::Unsize, ref operand, target_ty) => {
533 let target_ty = self.tcx.subst_and_normalize_erasing_regions(
535 ty::ParamEnv::reveal_all(),
538 let source_ty = operand.ty(self.mir, self.tcx);
539 let source_ty = self.tcx.subst_and_normalize_erasing_regions(
541 ty::ParamEnv::reveal_all(),
544 let (source_ty, target_ty) = find_vtable_types_for_unsizing(self.tcx,
547 // This could also be a different Unsize instruction, like
548 // from a fixed sized array to a slice. But we are only
549 // interested in things that produce a vtable.
550 if target_ty.is_trait() && !source_ty.is_trait() {
551 create_mono_items_for_vtable_methods(self.tcx,
557 mir::Rvalue::Cast(mir::CastKind::ReifyFnPointer, ref operand, _) => {
558 let fn_ty = operand.ty(self.mir, self.tcx);
559 let fn_ty = self.tcx.subst_and_normalize_erasing_regions(
561 ty::ParamEnv::reveal_all(),
564 visit_fn_use(self.tcx, fn_ty, false, &mut self.output);
566 mir::Rvalue::Cast(mir::CastKind::ClosureFnPointer, ref operand, _) => {
567 let source_ty = operand.ty(self.mir, self.tcx);
568 let source_ty = self.tcx.subst_and_normalize_erasing_regions(
570 ty::ParamEnv::reveal_all(),
573 match source_ty.sty {
574 ty::Closure(def_id, substs) => {
575 let instance = monomorphize::resolve_closure(
576 self.tcx, def_id, substs, ty::ClosureKind::FnOnce);
577 if should_monomorphize_locally(self.tcx, &instance) {
578 self.output.push(create_fn_mono_item(instance));
584 mir::Rvalue::NullaryOp(mir::NullOp::Box, _) => {
586 let exchange_malloc_fn_def_id = tcx
588 .require(ExchangeMallocFnLangItem)
589 .unwrap_or_else(|e| tcx.sess.fatal(&e));
590 let instance = Instance::mono(tcx, exchange_malloc_fn_def_id);
591 if should_monomorphize_locally(tcx, &instance) {
592 self.output.push(create_fn_mono_item(instance));
595 _ => { /* not interesting */ }
598 self.super_rvalue(rvalue, location);
601 fn visit_const(&mut self, constant: &&'tcx ty::Const<'tcx>, location: Location) {
602 debug!("visiting const {:?} @ {:?}", *constant, location);
604 collect_const(self.tcx, **constant, self.param_substs, self.output);
606 self.super_const(constant);
609 fn visit_terminator_kind(&mut self,
610 block: mir::BasicBlock,
611 kind: &mir::TerminatorKind<'tcx>,
612 location: Location) {
613 debug!("visiting terminator {:?} @ {:?}", kind, location);
617 mir::TerminatorKind::Call { ref func, .. } => {
618 let callee_ty = func.ty(self.mir, tcx);
619 let callee_ty = tcx.subst_and_normalize_erasing_regions(
621 ty::ParamEnv::reveal_all(),
624 visit_fn_use(self.tcx, callee_ty, true, &mut self.output);
626 mir::TerminatorKind::Drop { ref location, .. } |
627 mir::TerminatorKind::DropAndReplace { ref location, .. } => {
628 let ty = location.ty(self.mir, self.tcx)
630 let ty = tcx.subst_and_normalize_erasing_regions(
632 ty::ParamEnv::reveal_all(),
635 visit_drop_use(self.tcx, ty, true, self.output);
637 mir::TerminatorKind::Goto { .. } |
638 mir::TerminatorKind::SwitchInt { .. } |
639 mir::TerminatorKind::Resume |
640 mir::TerminatorKind::Abort |
641 mir::TerminatorKind::Return |
642 mir::TerminatorKind::Unreachable |
643 mir::TerminatorKind::Assert { .. } => {}
644 mir::TerminatorKind::GeneratorDrop |
645 mir::TerminatorKind::Yield { .. } |
646 mir::TerminatorKind::FalseEdges { .. } |
647 mir::TerminatorKind::FalseUnwind { .. } => bug!(),
650 self.super_terminator_kind(block, kind, location);
653 fn visit_place(&mut self,
654 place: &mir::Place<'tcx>,
655 context: mir::visit::PlaceContext<'tcx>,
656 location: Location) {
659 PlaceBase::Static(box Static{ kind:StaticKind::Static(def_id), .. })
661 debug!("visiting static {:?} @ {:?}", def_id, location);
664 let instance = Instance::mono(tcx, *def_id);
665 if should_monomorphize_locally(tcx, &instance) {
666 self.output.push(MonoItem::Static(*def_id));
672 self.super_place(place, context, location);
676 fn visit_drop_use<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
678 is_direct_call: bool,
679 output: &mut Vec<MonoItem<'tcx>>)
681 let instance = monomorphize::resolve_drop_in_place(tcx, ty);
682 visit_instance_use(tcx, instance, is_direct_call, output);
685 fn visit_fn_use<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
687 is_direct_call: bool,
688 output: &mut Vec<MonoItem<'tcx>>)
690 if let ty::FnDef(def_id, substs) = ty.sty {
691 let instance = ty::Instance::resolve(tcx,
692 ty::ParamEnv::reveal_all(),
695 visit_instance_use(tcx, instance, is_direct_call, output);
699 fn visit_instance_use<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
700 instance: ty::Instance<'tcx>,
701 is_direct_call: bool,
702 output: &mut Vec<MonoItem<'tcx>>)
704 debug!("visit_item_use({:?}, is_direct_call={:?})", instance, is_direct_call);
705 if !should_monomorphize_locally(tcx, &instance) {
710 ty::InstanceDef::Intrinsic(def_id) => {
712 bug!("intrinsic {:?} being reified", def_id);
715 ty::InstanceDef::VtableShim(..) |
716 ty::InstanceDef::Virtual(..) |
717 ty::InstanceDef::DropGlue(_, None) => {
718 // don't need to emit shim if we are calling directly.
720 output.push(create_fn_mono_item(instance));
723 ty::InstanceDef::DropGlue(_, Some(_)) => {
724 output.push(create_fn_mono_item(instance));
726 ty::InstanceDef::ClosureOnceShim { .. } |
727 ty::InstanceDef::Item(..) |
728 ty::InstanceDef::FnPtrShim(..) |
729 ty::InstanceDef::CloneShim(..) => {
730 output.push(create_fn_mono_item(instance));
735 // Returns true if we should codegen an instance in the local crate.
736 // Returns false if we can just link to the upstream crate and therefore don't
738 fn should_monomorphize_locally<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>, instance: &Instance<'tcx>)
740 let def_id = match instance.def {
741 ty::InstanceDef::Item(def_id) => def_id,
742 ty::InstanceDef::VtableShim(..) |
743 ty::InstanceDef::ClosureOnceShim { .. } |
744 ty::InstanceDef::Virtual(..) |
745 ty::InstanceDef::FnPtrShim(..) |
746 ty::InstanceDef::DropGlue(..) |
747 ty::InstanceDef::Intrinsic(_) |
748 ty::InstanceDef::CloneShim(..) => return true
751 if tcx.is_foreign_item(def_id) {
752 // We can always link to foreign items
756 if def_id.is_local() {
757 // local items cannot be referred to locally without monomorphizing them locally
761 if tcx.is_reachable_non_generic(def_id) ||
762 is_available_upstream_generic(tcx, def_id, instance.substs) {
763 // We can link to the item in question, no instance needed
768 if !tcx.is_mir_available(def_id) {
769 bug!("Cannot create local mono-item for {:?}", def_id)
773 fn is_available_upstream_generic<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
775 substs: SubstsRef<'tcx>)
777 debug_assert!(!def_id.is_local());
779 // If we are not in share generics mode, we don't link to upstream
780 // monomorphizations but always instantiate our own internal versions
782 if !tcx.sess.opts.share_generics() {
786 // If this instance has non-erasable parameters, it cannot be a shared
787 // monomorphization. Non-generic instances are already handled above
788 // by `is_reachable_non_generic()`
789 if substs.non_erasable_generics().next().is_none() {
793 // Take a look at the available monomorphizations listed in the metadata
794 // of upstream crates.
795 tcx.upstream_monomorphizations_for(def_id)
796 .map(|set| set.contains_key(substs))
801 /// For given pair of source and target type that occur in an unsizing coercion,
802 /// this function finds the pair of types that determines the vtable linking
805 /// For example, the source type might be `&SomeStruct` and the target type\
806 /// might be `&SomeTrait` in a cast like:
808 /// let src: &SomeStruct = ...;
809 /// let target = src as &SomeTrait;
811 /// Then the output of this function would be (SomeStruct, SomeTrait) since for
812 /// constructing the `target` fat-pointer we need the vtable for that pair.
814 /// Things can get more complicated though because there's also the case where
815 /// the unsized type occurs as a field:
818 /// struct ComplexStruct<T: ?Sized> {
825 /// In this case, if `T` is sized, `&ComplexStruct<T>` is a thin pointer. If `T`
826 /// is unsized, `&SomeStruct` is a fat pointer, and the vtable it points to is
827 /// for the pair of `T` (which is a trait) and the concrete type that `T` was
828 /// originally coerced from:
830 /// let src: &ComplexStruct<SomeStruct> = ...;
831 /// let target = src as &ComplexStruct<SomeTrait>;
833 /// Again, we want this `find_vtable_types_for_unsizing()` to provide the pair
834 /// `(SomeStruct, SomeTrait)`.
836 /// Finally, there is also the case of custom unsizing coercions, e.g., for
837 /// smart pointers such as `Rc` and `Arc`.
838 fn find_vtable_types_for_unsizing<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
841 -> (Ty<'tcx>, Ty<'tcx>) {
842 let ptr_vtable = |inner_source: Ty<'tcx>, inner_target: Ty<'tcx>| {
843 let type_has_metadata = |ty: Ty<'tcx>| -> bool {
844 use syntax_pos::DUMMY_SP;
845 if ty.is_sized(tcx.at(DUMMY_SP), ty::ParamEnv::reveal_all()) {
848 let tail = tcx.struct_tail(ty);
850 ty::Foreign(..) => false,
851 ty::Str | ty::Slice(..) | ty::Dynamic(..) => true,
852 _ => bug!("unexpected unsized tail: {:?}", tail),
855 if type_has_metadata(inner_source) {
856 (inner_source, inner_target)
858 tcx.struct_lockstep_tails(inner_source, inner_target)
862 match (&source_ty.sty, &target_ty.sty) {
866 &ty::RawPtr(ty::TypeAndMut { ty: b, .. })) |
867 (&ty::RawPtr(ty::TypeAndMut { ty: a, .. }),
868 &ty::RawPtr(ty::TypeAndMut { ty: b, .. })) => {
871 (&ty::Adt(def_a, _), &ty::Adt(def_b, _)) if def_a.is_box() && def_b.is_box() => {
872 ptr_vtable(source_ty.boxed_ty(), target_ty.boxed_ty())
875 (&ty::Adt(source_adt_def, source_substs),
876 &ty::Adt(target_adt_def, target_substs)) => {
877 assert_eq!(source_adt_def, target_adt_def);
880 monomorphize::custom_coerce_unsize_info(tcx, source_ty, target_ty);
882 let coerce_index = match kind {
883 CustomCoerceUnsized::Struct(i) => i
886 let source_fields = &source_adt_def.non_enum_variant().fields;
887 let target_fields = &target_adt_def.non_enum_variant().fields;
889 assert!(coerce_index < source_fields.len() &&
890 source_fields.len() == target_fields.len());
892 find_vtable_types_for_unsizing(tcx,
893 source_fields[coerce_index].ty(tcx,
895 target_fields[coerce_index].ty(tcx,
898 _ => bug!("find_vtable_types_for_unsizing: invalid coercion {:?} -> {:?}",
904 fn create_fn_mono_item<'a, 'tcx>(instance: Instance<'tcx>) -> MonoItem<'tcx> {
905 debug!("create_fn_mono_item(instance={})", instance);
906 MonoItem::Fn(instance)
909 /// Creates a `MonoItem` for each method that is referenced by the vtable for
910 /// the given trait/impl pair.
911 fn create_mono_items_for_vtable_methods<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
914 output: &mut Vec<MonoItem<'tcx>>) {
915 assert!(!trait_ty.needs_subst() && !trait_ty.has_escaping_bound_vars() &&
916 !impl_ty.needs_subst() && !impl_ty.has_escaping_bound_vars());
918 if let ty::Dynamic(ref trait_ty, ..) = trait_ty.sty {
919 if let Some(principal) = trait_ty.principal() {
920 let poly_trait_ref = principal.with_self_ty(tcx, impl_ty);
921 assert!(!poly_trait_ref.has_escaping_bound_vars());
923 // Walk all methods of the trait, including those of its supertraits
924 let methods = tcx.vtable_methods(poly_trait_ref);
925 let methods = methods.iter().cloned().filter_map(|method| method)
926 .map(|(def_id, substs)| ty::Instance::resolve_for_vtable(
928 ty::ParamEnv::reveal_all(),
931 .filter(|&instance| should_monomorphize_locally(tcx, &instance))
932 .map(|instance| create_fn_mono_item(instance));
933 output.extend(methods);
936 // Also add the destructor
937 visit_drop_use(tcx, impl_ty, false, output);
941 //=-----------------------------------------------------------------------------
943 //=-----------------------------------------------------------------------------
945 struct RootCollector<'b, 'a: 'b, 'tcx: 'a + 'b> {
946 tcx: TyCtxt<'a, 'tcx, 'tcx>,
947 mode: MonoItemCollectionMode,
948 output: &'b mut Vec<MonoItem<'tcx>>,
949 entry_fn: Option<(DefId, EntryFnType)>,
952 impl<'b, 'a, 'v> ItemLikeVisitor<'v> for RootCollector<'b, 'a, 'v> {
953 fn visit_item(&mut self, item: &'v hir::Item) {
955 hir::ItemKind::ExternCrate(..) |
956 hir::ItemKind::Use(..) |
957 hir::ItemKind::ForeignMod(..) |
958 hir::ItemKind::Ty(..) |
959 hir::ItemKind::Trait(..) |
960 hir::ItemKind::TraitAlias(..) |
961 hir::ItemKind::Existential(..) |
962 hir::ItemKind::Mod(..) => {
963 // Nothing to do, just keep recursing...
966 hir::ItemKind::Impl(..) => {
967 if self.mode == MonoItemCollectionMode::Eager {
968 create_mono_items_for_default_impls(self.tcx,
974 hir::ItemKind::Enum(_, ref generics) |
975 hir::ItemKind::Struct(_, ref generics) |
976 hir::ItemKind::Union(_, ref generics) => {
977 if generics.params.is_empty() {
978 if self.mode == MonoItemCollectionMode::Eager {
979 let def_id = self.tcx.hir().local_def_id_from_hir_id(item.hir_id);
980 debug!("RootCollector: ADT drop-glue for {}",
981 def_id_to_string(self.tcx, def_id));
983 let ty = Instance::new(def_id, InternalSubsts::empty()).ty(self.tcx);
984 visit_drop_use(self.tcx, ty, true, self.output);
988 hir::ItemKind::GlobalAsm(..) => {
989 debug!("RootCollector: ItemKind::GlobalAsm({})",
990 def_id_to_string(self.tcx,
991 self.tcx.hir().local_def_id_from_hir_id(item.hir_id)));
992 self.output.push(MonoItem::GlobalAsm(item.hir_id));
994 hir::ItemKind::Static(..) => {
995 let def_id = self.tcx.hir().local_def_id_from_hir_id(item.hir_id);
996 debug!("RootCollector: ItemKind::Static({})",
997 def_id_to_string(self.tcx, def_id));
998 self.output.push(MonoItem::Static(def_id));
1000 hir::ItemKind::Const(..) => {
1001 // const items only generate mono items if they are
1002 // actually used somewhere. Just declaring them is insufficient.
1004 // but even just declaring them must collect the items they refer to
1005 let def_id = self.tcx.hir().local_def_id_from_hir_id(item.hir_id);
1007 let instance = Instance::mono(self.tcx, def_id);
1008 let cid = GlobalId {
1012 let param_env = ty::ParamEnv::reveal_all();
1014 if let Ok(val) = self.tcx.const_eval(param_env.and(cid)) {
1015 collect_const(self.tcx, val, InternalSubsts::empty(), &mut self.output);
1018 hir::ItemKind::Fn(..) => {
1019 let def_id = self.tcx.hir().local_def_id_from_hir_id(item.hir_id);
1020 self.push_if_root(def_id);
1025 fn visit_trait_item(&mut self, _: &'v hir::TraitItem) {
1026 // Even if there's a default body with no explicit generics,
1027 // it's still generic over some `Self: Trait`, so not a root.
1030 fn visit_impl_item(&mut self, ii: &'v hir::ImplItem) {
1032 hir::ImplItemKind::Method(hir::MethodSig { .. }, _) => {
1033 let def_id = self.tcx.hir().local_def_id_from_hir_id(ii.hir_id);
1034 self.push_if_root(def_id);
1036 _ => { /* Nothing to do here */ }
1041 impl<'b, 'a, 'v> RootCollector<'b, 'a, 'v> {
1042 fn is_root(&self, def_id: DefId) -> bool {
1043 !item_has_type_parameters(self.tcx, def_id) && match self.mode {
1044 MonoItemCollectionMode::Eager => {
1047 MonoItemCollectionMode::Lazy => {
1048 self.entry_fn.map(|(id, _)| id) == Some(def_id) ||
1049 self.tcx.is_reachable_non_generic(def_id) ||
1050 self.tcx.codegen_fn_attrs(def_id).flags.contains(
1051 CodegenFnAttrFlags::RUSTC_STD_INTERNAL_SYMBOL)
1056 /// If `def_id` represents a root, then push it onto the list of
1057 /// outputs. (Note that all roots must be monomorphic.)
1058 fn push_if_root(&mut self, def_id: DefId) {
1059 if self.is_root(def_id) {
1060 debug!("RootCollector::push_if_root: found root def_id={:?}", def_id);
1062 let instance = Instance::mono(self.tcx, def_id);
1063 self.output.push(create_fn_mono_item(instance));
1067 /// As a special case, when/if we encounter the
1068 /// `main()` function, we also have to generate a
1069 /// monomorphized copy of the start lang item based on
1070 /// the return type of `main`. This is not needed when
1071 /// the user writes their own `start` manually.
1072 fn push_extra_entry_roots(&mut self) {
1073 let main_def_id = match self.entry_fn {
1074 Some((def_id, EntryFnType::Main)) => def_id,
1078 let start_def_id = match self.tcx.lang_items().require(StartFnLangItem) {
1080 Err(err) => self.tcx.sess.fatal(&err),
1082 let main_ret_ty = self.tcx.fn_sig(main_def_id).output();
1084 // Given that `main()` has no arguments,
1085 // then its return type cannot have
1086 // late-bound regions, since late-bound
1087 // regions must appear in the argument
1089 let main_ret_ty = self.tcx.erase_regions(
1090 &main_ret_ty.no_bound_vars().unwrap(),
1093 let start_instance = Instance::resolve(
1095 ty::ParamEnv::reveal_all(),
1097 self.tcx.intern_substs(&[main_ret_ty.into()])
1100 self.output.push(create_fn_mono_item(start_instance));
1104 fn item_has_type_parameters<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>, def_id: DefId) -> bool {
1105 let generics = tcx.generics_of(def_id);
1106 generics.requires_monomorphization(tcx)
1109 fn create_mono_items_for_default_impls<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
1110 item: &'tcx hir::Item,
1111 output: &mut Vec<MonoItem<'tcx>>) {
1113 hir::ItemKind::Impl(_, _, _, ref generics, .., ref impl_item_refs) => {
1114 for param in &generics.params {
1116 hir::GenericParamKind::Lifetime { .. } => {}
1117 hir::GenericParamKind::Type { .. } |
1118 hir::GenericParamKind::Const { .. } => {
1124 let impl_def_id = tcx.hir().local_def_id_from_hir_id(item.hir_id);
1126 debug!("create_mono_items_for_default_impls(item={})",
1127 def_id_to_string(tcx, impl_def_id));
1129 if let Some(trait_ref) = tcx.impl_trait_ref(impl_def_id) {
1130 let overridden_methods: FxHashSet<_> =
1131 impl_item_refs.iter()
1132 .map(|iiref| iiref.ident.modern())
1134 for method in tcx.provided_trait_methods(trait_ref.def_id) {
1135 if overridden_methods.contains(&method.ident.modern()) {
1139 let counts = tcx.generics_of(method.def_id).own_counts();
1140 if counts.types + counts.consts != 0 {
1144 let substs = InternalSubsts::for_item(tcx, method.def_id, |param, _| {
1146 GenericParamDefKind::Lifetime => tcx.types.re_erased.into(),
1147 GenericParamDefKind::Type { .. } |
1148 GenericParamDefKind::Const => {
1149 trait_ref.substs[param.index as usize]
1154 let instance = ty::Instance::resolve(tcx,
1155 ty::ParamEnv::reveal_all(),
1159 let mono_item = create_fn_mono_item(instance);
1160 if mono_item.is_instantiable(tcx)
1161 && should_monomorphize_locally(tcx, &instance) {
1162 output.push(mono_item);
1173 /// Scan the miri alloc in order to find function calls, closures, and drop-glue
1174 fn collect_miri<'a, 'tcx>(
1175 tcx: TyCtxt<'a, 'tcx, 'tcx>,
1177 output: &mut Vec<MonoItem<'tcx>>,
1179 let alloc_kind = tcx.alloc_map.lock().get(alloc_id);
1181 Some(AllocKind::Static(did)) => {
1182 let instance = Instance::mono(tcx, did);
1183 if should_monomorphize_locally(tcx, &instance) {
1184 trace!("collecting static {:?}", did);
1185 output.push(MonoItem::Static(did));
1188 Some(AllocKind::Memory(alloc)) => {
1189 trace!("collecting {:?} with {:#?}", alloc_id, alloc);
1190 for &((), inner) in alloc.relocations.values() {
1191 collect_miri(tcx, inner, output);
1194 Some(AllocKind::Function(fn_instance)) => {
1195 if should_monomorphize_locally(tcx, &fn_instance) {
1196 trace!("collecting {:?} with {:#?}", alloc_id, fn_instance);
1197 output.push(create_fn_mono_item(fn_instance));
1200 None => bug!("alloc id without corresponding allocation: {}", alloc_id),
1204 /// Scan the MIR in order to find function calls, closures, and drop-glue
1205 fn collect_neighbours<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
1206 instance: Instance<'tcx>,
1207 output: &mut Vec<MonoItem<'tcx>>)
1209 let mir = tcx.instance_mir(instance.def);
1211 MirNeighborCollector {
1215 param_substs: instance.substs,
1217 let param_env = ty::ParamEnv::reveal_all();
1218 for i in 0..mir.promoted.len() {
1219 use rustc_data_structures::indexed_vec::Idx;
1220 let i = Promoted::new(i);
1221 let cid = GlobalId {
1225 match tcx.const_eval(param_env.and(cid)) {
1226 Ok(val) => collect_const(tcx, val, instance.substs, output),
1227 Err(ErrorHandled::Reported) => {},
1228 Err(ErrorHandled::TooGeneric) => span_bug!(
1229 mir.promoted[i].span, "collection encountered polymorphic constant",
1235 fn def_id_to_string<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
1238 let mut output = String::new();
1239 let printer = DefPathBasedNames::new(tcx, false, false);
1240 printer.push_def_path(def_id, &mut output);
1244 fn collect_const<'a, 'tcx>(
1245 tcx: TyCtxt<'a, 'tcx, 'tcx>,
1246 constant: ty::Const<'tcx>,
1247 param_substs: SubstsRef<'tcx>,
1248 output: &mut Vec<MonoItem<'tcx>>,
1250 debug!("visiting const {:?}", constant);
1252 match constant.val {
1253 ConstValue::Slice(Scalar::Ptr(ptr), _) |
1254 ConstValue::Scalar(Scalar::Ptr(ptr)) =>
1255 collect_miri(tcx, ptr.alloc_id, output),
1256 ConstValue::ByRef(_ptr, alloc) => {
1257 for &((), id) in alloc.relocations.values() {
1258 collect_miri(tcx, id, output);
1261 ConstValue::Unevaluated(did, substs) => {
1262 let param_env = ty::ParamEnv::reveal_all();
1263 let substs = tcx.subst_and_normalize_erasing_regions(
1268 let instance = ty::Instance::resolve(tcx,
1273 let cid = GlobalId {
1277 match tcx.const_eval(param_env.and(cid)) {
1278 Ok(val) => collect_const(tcx, val, param_substs, output),
1279 Err(ErrorHandled::Reported) => {},
1280 Err(ErrorHandled::TooGeneric) => span_bug!(
1281 tcx.def_span(did), "collection encountered polymorphic constant",