1 // Copyright 2014 The Rust Project Developers. See the COPYRIGHT
2 // file at the top-level directory of this distribution and at
3 // http://rust-lang.org/COPYRIGHT.
5 // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
6 // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
7 // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
8 // option. This file may not be copied, modified, or distributed
9 // except according to those terms.
11 //! Mono Item Collection
12 //! ===========================
14 //! This module is responsible for discovering all items that will contribute to
15 //! to code generation of the crate. The important part here is that it not only
16 //! needs to find syntax-level items (functions, structs, etc) but also all
17 //! their monomorphized instantiations. Every non-generic, non-const function
18 //! maps to one LLVM artifact. Every generic function can produce
19 //! from zero to N artifacts, depending on the sets of type arguments it
20 //! is instantiated with.
21 //! This also applies to generic items from other crates: A generic definition
22 //! in crate X might produce monomorphizations that are compiled into crate Y.
23 //! We also have to collect these here.
25 //! The following kinds of "mono items" are handled here:
33 //! The following things also result in LLVM artifacts, but are not collected
34 //! here, since we instantiate them locally on demand when needed in a given
44 //! Let's define some terms first:
46 //! - A "mono item" is something that results in a function or global in
47 //! the LLVM IR of a codegen unit. Mono items do not stand on their
48 //! own, they can reference other mono items. For example, if function
49 //! `foo()` calls function `bar()` then the mono item for `foo()`
50 //! references the mono item for function `bar()`. In general, the
51 //! definition for mono item A referencing a mono item B is that
52 //! the LLVM artifact produced for A references the LLVM artifact produced
55 //! - Mono items and the references between them form a directed graph,
56 //! where the mono items are the nodes and references form the edges.
57 //! Let's call this graph the "mono item graph".
59 //! - The mono item graph for a program contains all mono items
60 //! that are needed in order to produce the complete LLVM IR of the program.
62 //! The purpose of the algorithm implemented in this module is to build the
63 //! mono item graph for the current crate. It runs in two phases:
65 //! 1. Discover the roots of the graph by traversing the HIR of the crate.
66 //! 2. Starting from the roots, find neighboring nodes by inspecting the MIR
67 //! representation of the item corresponding to a given node, until no more
68 //! new nodes are found.
70 //! ### Discovering roots
72 //! The roots of the mono item graph correspond to the non-generic
73 //! syntactic items in the source code. We find them by walking the HIR of the
74 //! crate, and whenever we hit upon a function, method, or static item, we
75 //! create a mono item consisting of the items DefId and, since we only
76 //! consider non-generic items, an empty type-substitution set.
78 //! ### Finding neighbor nodes
79 //! Given a mono item node, we can discover neighbors by inspecting its
80 //! MIR. We walk the MIR and any time we hit upon something that signifies a
81 //! reference to another mono item, we have found a neighbor. Since the
82 //! mono item we are currently at is always monomorphic, we also know the
83 //! concrete type arguments of its neighbors, and so all neighbors again will be
84 //! monomorphic. The specific forms a reference to a neighboring node can take
85 //! in MIR are quite diverse. Here is an overview:
87 //! #### Calling Functions/Methods
88 //! The most obvious form of one mono item referencing another is a
89 //! function or method call (represented by a CALL terminator in MIR). But
90 //! calls are not the only thing that might introduce a reference between two
91 //! function mono items, and as we will see below, they are just a
92 //! specialized of the form described next, and consequently will don't get any
93 //! special treatment in the algorithm.
95 //! #### Taking a reference to a function or method
96 //! A function does not need to actually be called in order to be a neighbor of
97 //! another function. It suffices to just take a reference in order to introduce
98 //! an edge. Consider the following example:
101 //! fn print_val<T: Display>(x: T) {
102 //! println!("{}", x);
105 //! fn call_fn(f: &Fn(i32), x: i32) {
110 //! let print_i32 = print_val::<i32>;
111 //! call_fn(&print_i32, 0);
114 //! The MIR of none of these functions will contain an explicit call to
115 //! `print_val::<i32>`. Nonetheless, in order to mono this program, we need
116 //! an instance of this function. Thus, whenever we encounter a function or
117 //! method in operand position, we treat it as a neighbor of the current
118 //! mono item. Calls are just a special case of that.
121 //! In a way, closures are a simple case. Since every closure object needs to be
122 //! constructed somewhere, we can reliably discover them by observing
123 //! `RValue::Aggregate` expressions with `AggregateKind::Closure`. This is also
124 //! true for closures inlined from other crates.
127 //! Drop glue mono items are introduced by MIR drop-statements. The
128 //! generated mono item will again have drop-glue item neighbors if the
129 //! type to be dropped contains nested values that also need to be dropped. It
130 //! might also have a function item neighbor for the explicit `Drop::drop`
131 //! implementation of its type.
133 //! #### Unsizing Casts
134 //! A subtle way of introducing neighbor edges is by casting to a trait object.
135 //! Since the resulting fat-pointer contains a reference to a vtable, we need to
136 //! instantiate all object-save methods of the trait, as we need to store
137 //! pointers to these functions even if they never get called anywhere. This can
138 //! be seen as a special case of taking a function reference.
141 //! Since `Box` expression have special compiler support, no explicit calls to
142 //! `exchange_malloc()` and `exchange_free()` may show up in MIR, even if the
143 //! compiler will generate them. We have to observe `Rvalue::Box` expressions
144 //! and Box-typed drop-statements for that purpose.
147 //! Interaction with Cross-Crate Inlining
148 //! -------------------------------------
149 //! The binary of a crate will not only contain machine code for the items
150 //! defined in the source code of that crate. It will also contain monomorphic
151 //! instantiations of any extern generic functions and of functions marked with
153 //! The collection algorithm handles this more or less mono. If it is
154 //! about to create a mono item for something with an external `DefId`,
155 //! it will take a look if the MIR for that item is available, and if so just
156 //! proceed normally. If the MIR is not available, it assumes that the item is
157 //! just linked to and no node is created; which is exactly what we want, since
158 //! no machine code should be generated in the current crate for such an item.
160 //! Eager and Lazy Collection Mode
161 //! ------------------------------
162 //! Mono item collection can be performed in one of two modes:
164 //! - Lazy mode means that items will only be instantiated when actually
165 //! referenced. The goal is to produce the least amount of machine code
168 //! - Eager mode is meant to be used in conjunction with incremental compilation
169 //! where a stable set of mono items is more important than a minimal
170 //! one. Thus, eager mode will instantiate drop-glue for every drop-able type
171 //! in the crate, even of no drop call for that type exists (yet). It will
172 //! also instantiate default implementations of trait methods, something that
173 //! otherwise is only done on demand.
178 //! Some things are not yet fully implemented in the current version of this
181 //! ### Initializers of Constants and Statics
182 //! Since no MIR is constructed yet for initializer expressions of constants and
183 //! statics we cannot inspect these properly.
186 //! Ideally, no mono item should be generated for const fns unless there
187 //! is a call to them that cannot be evaluated at compile time. At the moment
188 //! this is not implemented however: a mono item will be produced
189 //! regardless of whether it is actually needed or not.
192 use rustc::hir::itemlikevisit::ItemLikeVisitor;
194 use rustc::hir::map as hir_map;
195 use rustc::hir::def_id::DefId;
196 use rustc::middle::const_val::ConstVal;
197 use rustc::middle::lang_items::{ExchangeMallocFnLangItem, StartFnLangItem};
199 use rustc::ty::subst::{Substs, Kind};
200 use rustc::ty::{self, TypeFoldable, Ty, TyCtxt};
201 use rustc::ty::adjustment::CustomCoerceUnsized;
202 use rustc::session::config;
203 use rustc::mir::{self, Location};
204 use rustc::mir::visit::Visitor as MirVisitor;
205 use rustc::mir::mono::MonoItem;
207 use monomorphize::{self, Instance};
208 use rustc::util::nodemap::{FxHashSet, FxHashMap, DefIdMap};
210 use monomorphize::item::{MonoItemExt, DefPathBasedNames, InstantiationMode};
212 use rustc_data_structures::bitvec::BitVector;
218 #[derive(PartialEq, Eq, Hash, Clone, Copy, Debug)]
219 pub enum MonoItemCollectionMode {
224 /// Maps every mono item to all mono items it references in its
226 pub struct InliningMap<'tcx> {
227 // Maps a source mono item to the range of mono items
229 // The two numbers in the tuple are the start (inclusive) and
230 // end index (exclusive) within the `targets` vecs.
231 index: FxHashMap<MonoItem<'tcx>, (usize, usize)>,
232 targets: Vec<MonoItem<'tcx>>,
234 // Contains one bit per mono item in the `targets` field. That bit
235 // is true if that mono item needs to be inlined into every CGU.
239 impl<'tcx> InliningMap<'tcx> {
241 fn new() -> InliningMap<'tcx> {
245 inlines: BitVector::new(1024),
249 fn record_accesses<I>(&mut self,
250 source: MonoItem<'tcx>,
252 where I: Iterator<Item=(MonoItem<'tcx>, bool)> + ExactSizeIterator
254 assert!(!self.index.contains_key(&source));
256 let start_index = self.targets.len();
257 let new_items_count = new_targets.len();
258 let new_items_count_total = new_items_count + self.targets.len();
260 self.targets.reserve(new_items_count);
261 self.inlines.grow(new_items_count_total);
263 for (i, (target, inline)) in new_targets.enumerate() {
264 self.targets.push(target);
266 self.inlines.insert(i + start_index);
270 let end_index = self.targets.len();
271 self.index.insert(source, (start_index, end_index));
274 // Internally iterate over all items referenced by `source` which will be
275 // made available for inlining.
276 pub fn with_inlining_candidates<F>(&self, source: MonoItem<'tcx>, mut f: F)
277 where F: FnMut(MonoItem<'tcx>)
279 if let Some(&(start_index, end_index)) = self.index.get(&source) {
280 for (i, candidate) in self.targets[start_index .. end_index]
283 if self.inlines.contains(start_index + i) {
290 // Internally iterate over all items and the things each accesses.
291 pub fn iter_accesses<F>(&self, mut f: F)
292 where F: FnMut(MonoItem<'tcx>, &[MonoItem<'tcx>])
294 for (&accessor, &(start_index, end_index)) in &self.index {
295 f(accessor, &self.targets[start_index .. end_index])
300 pub fn collect_crate_mono_items<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
301 mode: MonoItemCollectionMode)
302 -> (FxHashSet<MonoItem<'tcx>>,
304 let roots = collect_roots(tcx, mode);
306 debug!("Building mono item graph, beginning at roots");
307 let mut visited = FxHashSet();
308 let mut recursion_depths = DefIdMap();
309 let mut inlining_map = InliningMap::new();
312 collect_items_rec(tcx,
315 &mut recursion_depths,
319 (visited, inlining_map)
322 // Find all non-generic items by walking the HIR. These items serve as roots to
323 // start monomorphizing from.
324 fn collect_roots<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
325 mode: MonoItemCollectionMode)
326 -> Vec<MonoItem<'tcx>> {
327 debug!("Collecting roots");
328 let mut roots = Vec::new();
331 let entry_fn = tcx.sess.entry_fn.borrow().map(|(node_id, _)| {
332 tcx.hir.local_def_id(node_id)
335 debug!("collect_roots: entry_fn = {:?}", entry_fn);
337 let mut visitor = RootCollector {
344 tcx.hir.krate().visit_all_item_likes(&mut visitor);
347 // We can only translate items that are instantiable - items all of
348 // whose predicates hold. Luckily, items that aren't instantiable
349 // can't actually be used, so we can just skip translating them.
350 roots.retain(|root| root.is_instantiable(tcx));
355 // Collect all monomorphized items reachable from `starting_point`
356 fn collect_items_rec<'a, 'tcx: 'a>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
357 starting_point: MonoItem<'tcx>,
358 visited: &mut FxHashSet<MonoItem<'tcx>>,
359 recursion_depths: &mut DefIdMap<usize>,
360 inlining_map: &mut InliningMap<'tcx>) {
361 if !visited.insert(starting_point.clone()) {
362 // We've been here already, no need to search again.
365 debug!("BEGIN collect_items_rec({})", starting_point.to_string(tcx));
367 let mut neighbors = Vec::new();
368 let recursion_depth_reset;
370 match starting_point {
371 MonoItem::Static(node_id) => {
372 let def_id = tcx.hir.local_def_id(node_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;
383 collect_neighbours(tcx, instance, true, &mut neighbors);
385 MonoItem::Fn(instance) => {
386 // Sanity check whether this ended up being collected accidentally
387 debug_assert!(should_monomorphize_locally(tcx, &instance));
389 // Keep track of the monomorphization recursion depth
390 recursion_depth_reset = Some(check_recursion_limit(tcx,
393 check_type_length_limit(tcx, instance);
395 collect_neighbours(tcx, instance, false, &mut neighbors);
397 MonoItem::GlobalAsm(..) => {
398 recursion_depth_reset = None;
402 record_accesses(tcx, starting_point, &neighbors[..], inlining_map);
404 for neighbour in neighbors {
405 collect_items_rec(tcx, neighbour, visited, recursion_depths, inlining_map);
408 if let Some((def_id, depth)) = recursion_depth_reset {
409 recursion_depths.insert(def_id, depth);
412 debug!("END collect_items_rec({})", starting_point.to_string(tcx));
415 fn record_accesses<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
416 caller: MonoItem<'tcx>,
417 callees: &[MonoItem<'tcx>],
418 inlining_map: &mut InliningMap<'tcx>) {
419 let is_inlining_candidate = |mono_item: &MonoItem<'tcx>| {
420 mono_item.instantiation_mode(tcx) == InstantiationMode::LocalCopy
423 let accesses = callees.into_iter()
425 (*mono_item, is_inlining_candidate(mono_item))
428 inlining_map.record_accesses(caller, accesses);
431 fn check_recursion_limit<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
432 instance: Instance<'tcx>,
433 recursion_depths: &mut DefIdMap<usize>)
435 let def_id = instance.def_id();
436 let recursion_depth = recursion_depths.get(&def_id).cloned().unwrap_or(0);
437 debug!(" => recursion depth={}", recursion_depth);
439 let recursion_depth = if Some(def_id) == tcx.lang_items().drop_in_place_fn() {
440 // HACK: drop_in_place creates tight monomorphization loops. Give
447 // Code that needs to instantiate the same function recursively
448 // more than the recursion limit is assumed to be causing an
449 // infinite expansion.
450 if recursion_depth > tcx.sess.recursion_limit.get() {
451 let error = format!("reached the recursion limit while instantiating `{}`",
453 if let Some(node_id) = tcx.hir.as_local_node_id(def_id) {
454 tcx.sess.span_fatal(tcx.hir.span(node_id), &error);
456 tcx.sess.fatal(&error);
460 recursion_depths.insert(def_id, recursion_depth + 1);
462 (def_id, recursion_depth)
465 fn check_type_length_limit<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
466 instance: Instance<'tcx>)
468 let type_length = instance.substs.types().flat_map(|ty| ty.walk()).count();
469 debug!(" => type length={}", type_length);
471 // Rust code can easily create exponentially-long types using only a
472 // polynomial recursion depth. Even with the default recursion
473 // depth, you can easily get cases that take >2^60 steps to run,
474 // which means that rustc basically hangs.
476 // Bail out in these cases to avoid that bad user experience.
477 let type_length_limit = tcx.sess.type_length_limit.get();
478 if type_length > type_length_limit {
479 // The instance name is already known to be too long for rustc. Use
480 // `{:.64}` to avoid blasting the user's terminal with thousands of
481 // lines of type-name.
482 let instance_name = instance.to_string();
483 let msg = format!("reached the type-length limit while instantiating `{:.64}...`",
485 let mut diag = if let Some(node_id) = tcx.hir.as_local_node_id(instance.def_id()) {
486 tcx.sess.struct_span_fatal(tcx.hir.span(node_id), &msg)
488 tcx.sess.struct_fatal(&msg)
492 "consider adding a `#![type_length_limit=\"{}\"]` attribute to your crate",
493 type_length_limit*2));
495 tcx.sess.abort_if_errors();
499 struct MirNeighborCollector<'a, 'tcx: 'a> {
500 tcx: TyCtxt<'a, 'tcx, 'tcx>,
501 mir: &'a mir::Mir<'tcx>,
502 output: &'a mut Vec<MonoItem<'tcx>>,
503 param_substs: &'tcx Substs<'tcx>,
507 impl<'a, 'tcx> MirVisitor<'tcx> for MirNeighborCollector<'a, 'tcx> {
509 fn visit_rvalue(&mut self, rvalue: &mir::Rvalue<'tcx>, location: Location) {
510 debug!("visiting rvalue {:?}", *rvalue);
513 // When doing an cast from a regular pointer to a fat pointer, we
514 // have to instantiate all methods of the trait being cast to, so we
515 // can build the appropriate vtable.
516 mir::Rvalue::Cast(mir::CastKind::Unsize, ref operand, target_ty) => {
517 let target_ty = self.tcx.trans_apply_param_substs(self.param_substs,
519 let source_ty = operand.ty(self.mir, self.tcx);
520 let source_ty = self.tcx.trans_apply_param_substs(self.param_substs,
522 let (source_ty, target_ty) = find_vtable_types_for_unsizing(self.tcx,
525 // This could also be a different Unsize instruction, like
526 // from a fixed sized array to a slice. But we are only
527 // interested in things that produce a vtable.
528 if target_ty.is_trait() && !source_ty.is_trait() {
529 create_mono_items_for_vtable_methods(self.tcx,
535 mir::Rvalue::Cast(mir::CastKind::ReifyFnPointer, ref operand, _) => {
536 let fn_ty = operand.ty(self.mir, self.tcx);
537 let fn_ty = self.tcx.trans_apply_param_substs(self.param_substs,
539 visit_fn_use(self.tcx, fn_ty, false, &mut self.output);
541 mir::Rvalue::Cast(mir::CastKind::ClosureFnPointer, ref operand, _) => {
542 let source_ty = operand.ty(self.mir, self.tcx);
543 let source_ty = self.tcx.trans_apply_param_substs(self.param_substs,
545 match source_ty.sty {
546 ty::TyClosure(def_id, substs) => {
547 let instance = monomorphize::resolve_closure(
548 self.tcx, def_id, substs, ty::ClosureKind::FnOnce);
549 self.output.push(create_fn_mono_item(instance));
554 mir::Rvalue::NullaryOp(mir::NullOp::Box, _) => {
556 let exchange_malloc_fn_def_id = tcx
558 .require(ExchangeMallocFnLangItem)
559 .unwrap_or_else(|e| tcx.sess.fatal(&e));
560 let instance = Instance::mono(tcx, exchange_malloc_fn_def_id);
561 if should_monomorphize_locally(tcx, &instance) {
562 self.output.push(create_fn_mono_item(instance));
565 _ => { /* not interesting */ }
568 self.super_rvalue(rvalue, location);
571 fn visit_const(&mut self, constant: &&'tcx ty::Const<'tcx>, location: Location) {
572 debug!("visiting const {:?} @ {:?}", *constant, location);
574 if let ConstVal::Unevaluated(def_id, substs) = constant.val {
575 let substs = self.tcx.trans_apply_param_substs(self.param_substs,
577 let instance = ty::Instance::resolve(self.tcx,
578 ty::ParamEnv::empty(traits::Reveal::All),
581 collect_neighbours(self.tcx, instance, true, self.output);
584 self.super_const(constant);
587 fn visit_terminator_kind(&mut self,
588 block: mir::BasicBlock,
589 kind: &mir::TerminatorKind<'tcx>,
590 location: Location) {
591 debug!("visiting terminator {:?} @ {:?}", kind, location);
595 mir::TerminatorKind::Call { ref func, .. } => {
596 let callee_ty = func.ty(self.mir, tcx);
597 let callee_ty = tcx.trans_apply_param_substs(self.param_substs, &callee_ty);
599 let constness = match (self.const_context, &callee_ty.sty) {
600 (true, &ty::TyFnDef(def_id, substs)) if self.tcx.is_const_fn(def_id) => {
602 ty::Instance::resolve(self.tcx,
603 ty::ParamEnv::empty(traits::Reveal::All),
611 if let Some(const_fn_instance) = constness {
612 // If this is a const fn, called from a const context, we
613 // have to visit its body in order to find any fn reifications
615 collect_neighbours(self.tcx,
620 visit_fn_use(self.tcx, callee_ty, true, &mut self.output);
623 mir::TerminatorKind::Drop { ref location, .. } |
624 mir::TerminatorKind::DropAndReplace { ref location, .. } => {
625 let ty = location.ty(self.mir, self.tcx)
627 let ty = tcx.trans_apply_param_substs(self.param_substs, &ty);
628 visit_drop_use(self.tcx, ty, true, self.output);
630 mir::TerminatorKind::Goto { .. } |
631 mir::TerminatorKind::SwitchInt { .. } |
632 mir::TerminatorKind::Resume |
633 mir::TerminatorKind::Abort |
634 mir::TerminatorKind::Return |
635 mir::TerminatorKind::Unreachable |
636 mir::TerminatorKind::Assert { .. } => {}
637 mir::TerminatorKind::GeneratorDrop |
638 mir::TerminatorKind::Yield { .. } |
639 mir::TerminatorKind::FalseEdges { .. } |
640 mir::TerminatorKind::FalseUnwind { .. } => bug!(),
643 self.super_terminator_kind(block, kind, location);
646 fn visit_static(&mut self,
647 static_: &mir::Static<'tcx>,
648 context: mir::visit::PlaceContext<'tcx>,
649 location: Location) {
650 debug!("visiting static {:?} @ {:?}", static_.def_id, location);
653 let instance = Instance::mono(tcx, static_.def_id);
654 if should_monomorphize_locally(tcx, &instance) {
655 let node_id = tcx.hir.as_local_node_id(static_.def_id).unwrap();
656 self.output.push(MonoItem::Static(node_id));
659 self.super_static(static_, context, location);
663 fn visit_drop_use<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
665 is_direct_call: bool,
666 output: &mut Vec<MonoItem<'tcx>>)
668 let instance = monomorphize::resolve_drop_in_place(tcx, ty);
669 visit_instance_use(tcx, instance, is_direct_call, output);
672 fn visit_fn_use<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
674 is_direct_call: bool,
675 output: &mut Vec<MonoItem<'tcx>>)
677 if let ty::TyFnDef(def_id, substs) = ty.sty {
678 let instance = ty::Instance::resolve(tcx,
679 ty::ParamEnv::empty(traits::Reveal::All),
682 visit_instance_use(tcx, instance, is_direct_call, output);
686 fn visit_instance_use<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
687 instance: ty::Instance<'tcx>,
688 is_direct_call: bool,
689 output: &mut Vec<MonoItem<'tcx>>)
691 debug!("visit_item_use({:?}, is_direct_call={:?})", instance, is_direct_call);
692 if !should_monomorphize_locally(tcx, &instance) {
697 ty::InstanceDef::Intrinsic(def_id) => {
699 bug!("intrinsic {:?} being reified", def_id);
702 ty::InstanceDef::Virtual(..) |
703 ty::InstanceDef::DropGlue(_, None) => {
704 // don't need to emit shim if we are calling directly.
706 output.push(create_fn_mono_item(instance));
709 ty::InstanceDef::DropGlue(_, Some(_)) => {
710 output.push(create_fn_mono_item(instance));
712 ty::InstanceDef::ClosureOnceShim { .. } |
713 ty::InstanceDef::Item(..) |
714 ty::InstanceDef::FnPtrShim(..) |
715 ty::InstanceDef::CloneShim(..) => {
716 output.push(create_fn_mono_item(instance));
721 // Returns true if we should translate an instance in the local crate.
722 // Returns false if we can just link to the upstream crate and therefore don't
724 fn should_monomorphize_locally<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>, instance: &Instance<'tcx>)
726 let def_id = match instance.def {
727 ty::InstanceDef::Item(def_id) => def_id,
728 ty::InstanceDef::ClosureOnceShim { .. } |
729 ty::InstanceDef::Virtual(..) |
730 ty::InstanceDef::FnPtrShim(..) |
731 ty::InstanceDef::DropGlue(..) |
732 ty::InstanceDef::Intrinsic(_) |
733 ty::InstanceDef::CloneShim(..) => return true
735 match tcx.hir.get_if_local(def_id) {
736 Some(hir_map::NodeForeignItem(..)) => {
737 false // foreign items are linked against, not translated.
741 if tcx.is_exported_symbol(def_id) ||
742 tcx.is_foreign_item(def_id)
744 // We can link to the item in question, no instance needed
748 if !tcx.is_mir_available(def_id) {
749 bug!("Cannot create local mono-item for {:?}", def_id)
757 /// For given pair of source and target type that occur in an unsizing coercion,
758 /// this function finds the pair of types that determines the vtable linking
761 /// For example, the source type might be `&SomeStruct` and the target type\
762 /// might be `&SomeTrait` in a cast like:
764 /// let src: &SomeStruct = ...;
765 /// let target = src as &SomeTrait;
767 /// Then the output of this function would be (SomeStruct, SomeTrait) since for
768 /// constructing the `target` fat-pointer we need the vtable for that pair.
770 /// Things can get more complicated though because there's also the case where
771 /// the unsized type occurs as a field:
774 /// struct ComplexStruct<T: ?Sized> {
781 /// In this case, if `T` is sized, `&ComplexStruct<T>` is a thin pointer. If `T`
782 /// is unsized, `&SomeStruct` is a fat pointer, and the vtable it points to is
783 /// for the pair of `T` (which is a trait) and the concrete type that `T` was
784 /// originally coerced from:
786 /// let src: &ComplexStruct<SomeStruct> = ...;
787 /// let target = src as &ComplexStruct<SomeTrait>;
789 /// Again, we want this `find_vtable_types_for_unsizing()` to provide the pair
790 /// `(SomeStruct, SomeTrait)`.
792 /// Finally, there is also the case of custom unsizing coercions, e.g. for
793 /// smart pointers such as `Rc` and `Arc`.
794 fn find_vtable_types_for_unsizing<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
797 -> (Ty<'tcx>, Ty<'tcx>) {
798 let ptr_vtable = |inner_source: Ty<'tcx>, inner_target: Ty<'tcx>| {
799 let type_has_metadata = |ty: Ty<'tcx>| -> bool {
800 use syntax_pos::DUMMY_SP;
801 if ty.is_sized(tcx, ty::ParamEnv::empty(traits::Reveal::All), DUMMY_SP) {
804 let tail = tcx.struct_tail(ty);
806 ty::TyForeign(..) => false,
807 ty::TyStr | ty::TySlice(..) | ty::TyDynamic(..) => true,
808 _ => bug!("unexpected unsized tail: {:?}", tail.sty),
811 if type_has_metadata(inner_source) {
812 (inner_source, inner_target)
814 tcx.struct_lockstep_tails(inner_source, inner_target)
818 match (&source_ty.sty, &target_ty.sty) {
819 (&ty::TyRef(_, ty::TypeAndMut { ty: a, .. }),
820 &ty::TyRef(_, ty::TypeAndMut { ty: b, .. })) |
821 (&ty::TyRef(_, ty::TypeAndMut { ty: a, .. }),
822 &ty::TyRawPtr(ty::TypeAndMut { ty: b, .. })) |
823 (&ty::TyRawPtr(ty::TypeAndMut { ty: a, .. }),
824 &ty::TyRawPtr(ty::TypeAndMut { ty: b, .. })) => {
827 (&ty::TyAdt(def_a, _), &ty::TyAdt(def_b, _)) if def_a.is_box() && def_b.is_box() => {
828 ptr_vtable(source_ty.boxed_ty(), target_ty.boxed_ty())
831 (&ty::TyAdt(source_adt_def, source_substs),
832 &ty::TyAdt(target_adt_def, target_substs)) => {
833 assert_eq!(source_adt_def, target_adt_def);
836 monomorphize::custom_coerce_unsize_info(tcx, source_ty, target_ty);
838 let coerce_index = match kind {
839 CustomCoerceUnsized::Struct(i) => i
842 let source_fields = &source_adt_def.non_enum_variant().fields;
843 let target_fields = &target_adt_def.non_enum_variant().fields;
845 assert!(coerce_index < source_fields.len() &&
846 source_fields.len() == target_fields.len());
848 find_vtable_types_for_unsizing(tcx,
849 source_fields[coerce_index].ty(tcx,
851 target_fields[coerce_index].ty(tcx,
854 _ => bug!("find_vtable_types_for_unsizing: invalid coercion {:?} -> {:?}",
860 fn create_fn_mono_item<'a, 'tcx>(instance: Instance<'tcx>) -> MonoItem<'tcx> {
861 debug!("create_fn_mono_item(instance={})", instance);
862 MonoItem::Fn(instance)
865 /// Creates a `MonoItem` for each method that is referenced by the vtable for
866 /// the given trait/impl pair.
867 fn create_mono_items_for_vtable_methods<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
870 output: &mut Vec<MonoItem<'tcx>>) {
871 assert!(!trait_ty.needs_subst() && !trait_ty.has_escaping_regions() &&
872 !impl_ty.needs_subst() && !impl_ty.has_escaping_regions());
874 if let ty::TyDynamic(ref trait_ty, ..) = trait_ty.sty {
875 if let Some(principal) = trait_ty.principal() {
876 let poly_trait_ref = principal.with_self_ty(tcx, impl_ty);
877 assert!(!poly_trait_ref.has_escaping_regions());
879 // Walk all methods of the trait, including those of its supertraits
880 let methods = tcx.vtable_methods(poly_trait_ref);
881 let methods = methods.iter().cloned().filter_map(|method| method)
882 .map(|(def_id, substs)| ty::Instance::resolve(
884 ty::ParamEnv::empty(traits::Reveal::All),
887 .filter(|&instance| should_monomorphize_locally(tcx, &instance))
888 .map(|instance| create_fn_mono_item(instance));
889 output.extend(methods);
891 // Also add the destructor
892 visit_drop_use(tcx, impl_ty, false, output);
896 //=-----------------------------------------------------------------------------
898 //=-----------------------------------------------------------------------------
900 struct RootCollector<'b, 'a: 'b, 'tcx: 'a + 'b> {
901 tcx: TyCtxt<'a, 'tcx, 'tcx>,
902 mode: MonoItemCollectionMode,
903 output: &'b mut Vec<MonoItem<'tcx>>,
904 entry_fn: Option<DefId>,
907 impl<'b, 'a, 'v> ItemLikeVisitor<'v> for RootCollector<'b, 'a, 'v> {
908 fn visit_item(&mut self, item: &'v hir::Item) {
910 hir::ItemExternCrate(..) |
912 hir::ItemForeignMod(..) |
915 hir::ItemTraitAlias(..) |
916 hir::ItemMod(..) => {
917 // Nothing to do, just keep recursing...
920 hir::ItemImpl(..) => {
921 if self.mode == MonoItemCollectionMode::Eager {
922 create_mono_items_for_default_impls(self.tcx,
928 hir::ItemEnum(_, ref generics) |
929 hir::ItemStruct(_, ref generics) |
930 hir::ItemUnion(_, ref generics) => {
931 if generics.params.is_empty() {
932 if self.mode == MonoItemCollectionMode::Eager {
933 let def_id = self.tcx.hir.local_def_id(item.id);
934 debug!("RootCollector: ADT drop-glue for {}",
935 def_id_to_string(self.tcx, def_id));
937 let ty = Instance::new(def_id, Substs::empty()).ty(self.tcx);
938 visit_drop_use(self.tcx, ty, true, self.output);
942 hir::ItemGlobalAsm(..) => {
943 debug!("RootCollector: ItemGlobalAsm({})",
944 def_id_to_string(self.tcx,
945 self.tcx.hir.local_def_id(item.id)));
946 self.output.push(MonoItem::GlobalAsm(item.id));
948 hir::ItemStatic(..) => {
949 debug!("RootCollector: ItemStatic({})",
950 def_id_to_string(self.tcx,
951 self.tcx.hir.local_def_id(item.id)));
952 self.output.push(MonoItem::Static(item.id));
954 hir::ItemConst(..) => {
955 // const items only generate mono items if they are
956 // actually used somewhere. Just declaring them is insufficient.
959 let def_id = self.tcx.hir.local_def_id(item.id);
960 self.push_if_root(def_id);
965 fn visit_trait_item(&mut self, _: &'v hir::TraitItem) {
966 // Even if there's a default body with no explicit generics,
967 // it's still generic over some `Self: Trait`, so not a root.
970 fn visit_impl_item(&mut self, ii: &'v hir::ImplItem) {
972 hir::ImplItemKind::Method(hir::MethodSig { .. }, _) => {
973 let def_id = self.tcx.hir.local_def_id(ii.id);
974 self.push_if_root(def_id);
976 _ => { /* Nothing to do here */ }
981 impl<'b, 'a, 'v> RootCollector<'b, 'a, 'v> {
982 fn is_root(&self, def_id: DefId) -> bool {
983 !item_has_type_parameters(self.tcx, def_id) && match self.mode {
984 MonoItemCollectionMode::Eager => {
987 MonoItemCollectionMode::Lazy => {
988 self.entry_fn == Some(def_id) ||
989 self.tcx.is_exported_symbol(def_id) ||
990 attr::contains_name(&self.tcx.get_attrs(def_id),
991 "rustc_std_internal_symbol")
996 /// If `def_id` represents a root, then push it onto the list of
997 /// outputs. (Note that all roots must be monomorphic.)
998 fn push_if_root(&mut self, def_id: DefId) {
999 if self.is_root(def_id) {
1000 debug!("RootCollector::push_if_root: found root def_id={:?}", def_id);
1002 let instance = Instance::mono(self.tcx, def_id);
1003 self.output.push(create_fn_mono_item(instance));
1005 self.push_extra_entry_roots(def_id);
1009 /// As a special case, when/if we encounter the
1010 /// `main()` function, we also have to generate a
1011 /// monomorphized copy of the start lang item based on
1012 /// the return type of `main`. This is not needed when
1013 /// the user writes their own `start` manually.
1014 fn push_extra_entry_roots(&mut self, def_id: DefId) {
1015 if self.entry_fn != Some(def_id) {
1019 if self.tcx.sess.entry_type.get() != Some(config::EntryMain) {
1023 let start_def_id = match self.tcx.lang_items().require(StartFnLangItem) {
1025 Err(err) => self.tcx.sess.fatal(&err),
1027 let main_ret_ty = self.tcx.fn_sig(def_id).output();
1029 // Given that `main()` has no arguments,
1030 // then its return type cannot have
1031 // late-bound regions, since late-bound
1032 // regions must appear in the argument
1034 let main_ret_ty = main_ret_ty.no_late_bound_regions().unwrap();
1036 let start_instance = Instance::resolve(
1038 ty::ParamEnv::empty(traits::Reveal::All),
1040 self.tcx.mk_substs(iter::once(Kind::from(main_ret_ty)))
1043 self.output.push(create_fn_mono_item(start_instance));
1047 fn item_has_type_parameters<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>, def_id: DefId) -> bool {
1048 let generics = tcx.generics_of(def_id);
1049 generics.parent_types as usize + generics.types.len() > 0
1052 fn create_mono_items_for_default_impls<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
1053 item: &'tcx hir::Item,
1054 output: &mut Vec<MonoItem<'tcx>>) {
1061 ref impl_item_refs) => {
1062 if generics.is_type_parameterized() {
1066 let impl_def_id = tcx.hir.local_def_id(item.id);
1068 debug!("create_mono_items_for_default_impls(item={})",
1069 def_id_to_string(tcx, impl_def_id));
1071 if let Some(trait_ref) = tcx.impl_trait_ref(impl_def_id) {
1072 let callee_substs = tcx.erase_regions(&trait_ref.substs);
1073 let overridden_methods: FxHashSet<_> =
1074 impl_item_refs.iter()
1075 .map(|iiref| iiref.name)
1077 for method in tcx.provided_trait_methods(trait_ref.def_id) {
1078 if overridden_methods.contains(&method.name) {
1082 if !tcx.generics_of(method.def_id).types.is_empty() {
1086 let instance = ty::Instance::resolve(tcx,
1087 ty::ParamEnv::empty(traits::Reveal::All),
1089 callee_substs).unwrap();
1091 let mono_item = create_fn_mono_item(instance);
1092 if mono_item.is_instantiable(tcx)
1093 && should_monomorphize_locally(tcx, &instance) {
1094 output.push(mono_item);
1105 /// Scan the MIR in order to find function calls, closures, and drop-glue
1106 fn collect_neighbours<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
1107 instance: Instance<'tcx>,
1108 const_context: bool,
1109 output: &mut Vec<MonoItem<'tcx>>)
1111 let mir = tcx.instance_mir(instance.def);
1113 let mut visitor = MirNeighborCollector {
1117 param_substs: instance.substs,
1121 visitor.visit_mir(&mir);
1122 for promoted in &mir.promoted {
1123 visitor.mir = promoted;
1124 visitor.visit_mir(promoted);
1128 fn def_id_to_string<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
1131 let mut output = String::new();
1132 let printer = DefPathBasedNames::new(tcx, false, false);
1133 printer.push_def_path(def_id, &mut output);