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
182 //! Ideally, no mono item should be generated for const fns unless there
183 //! is a call to them that cannot be evaluated at compile time. At the moment
184 //! this is not implemented however: a mono item will be produced
185 //! regardless of whether it is actually needed or not.
187 use rustc::hir::{self, CodegenFnAttrFlags};
188 use rustc::hir::itemlikevisit::ItemLikeVisitor;
190 use rustc::hir::def_id::DefId;
191 use rustc::mir::interpret::{AllocId, ConstValue};
192 use rustc::middle::lang_items::{ExchangeMallocFnLangItem, StartFnLangItem};
193 use rustc::ty::subst::Substs;
194 use rustc::ty::{self, TypeFoldable, Ty, TyCtxt, GenericParamDefKind};
195 use rustc::ty::adjustment::CustomCoerceUnsized;
196 use rustc::session::config;
197 use rustc::mir::{self, Location, Promoted};
198 use rustc::mir::visit::Visitor as MirVisitor;
199 use rustc::mir::mono::MonoItem;
200 use rustc::mir::interpret::{Scalar, GlobalId, AllocType, ErrorHandled};
202 use monomorphize::{self, Instance};
203 use rustc::util::nodemap::{FxHashSet, FxHashMap, DefIdMap};
204 use rustc::util::common::time;
206 use monomorphize::item::{MonoItemExt, DefPathBasedNames, InstantiationMode};
208 use rustc_data_structures::bit_set::GrowableBitSet;
209 use rustc_data_structures::sync::{MTRef, MTLock, ParallelIterator, par_iter};
211 #[derive(PartialEq, Eq, Hash, Clone, Copy, Debug)]
212 pub enum MonoItemCollectionMode {
217 /// Maps every mono item to all mono items it references in its
219 pub struct InliningMap<'tcx> {
220 // Maps a source mono item to the range of mono items
222 // The two numbers in the tuple are the start (inclusive) and
223 // end index (exclusive) within the `targets` vecs.
224 index: FxHashMap<MonoItem<'tcx>, (usize, usize)>,
225 targets: Vec<MonoItem<'tcx>>,
227 // Contains one bit per mono item in the `targets` field. That bit
228 // is true if that mono item needs to be inlined into every CGU.
229 inlines: GrowableBitSet<usize>,
232 impl<'tcx> InliningMap<'tcx> {
234 fn new() -> InliningMap<'tcx> {
236 index: FxHashMap::default(),
238 inlines: GrowableBitSet::with_capacity(1024),
242 fn record_accesses<I>(&mut self,
243 source: MonoItem<'tcx>,
245 where I: Iterator<Item=(MonoItem<'tcx>, bool)> + ExactSizeIterator
247 assert!(!self.index.contains_key(&source));
249 let start_index = self.targets.len();
250 let new_items_count = new_targets.len();
251 let new_items_count_total = new_items_count + self.targets.len();
253 self.targets.reserve(new_items_count);
254 self.inlines.ensure(new_items_count_total);
256 for (i, (target, inline)) in new_targets.enumerate() {
257 self.targets.push(target);
259 self.inlines.insert(i + start_index);
263 let end_index = self.targets.len();
264 self.index.insert(source, (start_index, end_index));
267 // Internally iterate over all items referenced by `source` which will be
268 // made available for inlining.
269 pub fn with_inlining_candidates<F>(&self, source: MonoItem<'tcx>, mut f: F)
270 where F: FnMut(MonoItem<'tcx>)
272 if let Some(&(start_index, end_index)) = self.index.get(&source) {
273 for (i, candidate) in self.targets[start_index .. end_index]
276 if self.inlines.contains(start_index + i) {
283 // Internally iterate over all items and the things each accesses.
284 pub fn iter_accesses<F>(&self, mut f: F)
285 where F: FnMut(MonoItem<'tcx>, &[MonoItem<'tcx>])
287 for (&accessor, &(start_index, end_index)) in &self.index {
288 f(accessor, &self.targets[start_index .. end_index])
293 pub fn collect_crate_mono_items<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
294 mode: MonoItemCollectionMode)
295 -> (FxHashSet<MonoItem<'tcx>>,
297 let roots = time(tcx.sess, "collecting roots", || {
298 collect_roots(tcx, mode)
301 debug!("Building mono item graph, beginning at roots");
303 let mut visited = MTLock::new(FxHashSet::default());
304 let mut inlining_map = MTLock::new(InliningMap::new());
307 let visited: MTRef<'_, _> = &mut visited;
308 let inlining_map: MTRef<'_, _> = &mut inlining_map;
310 time(tcx.sess, "collecting mono items", || {
311 par_iter(roots).for_each(|root| {
312 let mut recursion_depths = DefIdMap::default();
313 collect_items_rec(tcx,
316 &mut recursion_depths,
322 (visited.into_inner(), inlining_map.into_inner())
325 // Find all non-generic items by walking the HIR. These items serve as roots to
326 // start monomorphizing from.
327 fn collect_roots<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
328 mode: MonoItemCollectionMode)
329 -> Vec<MonoItem<'tcx>> {
330 debug!("Collecting roots");
331 let mut roots = Vec::new();
334 let entry_fn = tcx.sess.entry_fn.borrow().map(|(node_id, _, _)| {
335 tcx.hir().local_def_id(node_id)
338 debug!("collect_roots: entry_fn = {:?}", entry_fn);
340 let mut visitor = RootCollector {
347 tcx.hir().krate().visit_all_item_likes(&mut visitor);
349 visitor.push_extra_entry_roots();
352 // We can only codegen items that are instantiable - items all of
353 // whose predicates hold. Luckily, items that aren't instantiable
354 // can't actually be used, so we can just skip codegenning them.
355 roots.retain(|root| root.is_instantiable(tcx));
360 // Collect all monomorphized items reachable from `starting_point`
361 fn collect_items_rec<'a, 'tcx: 'a>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
362 starting_point: MonoItem<'tcx>,
363 visited: MTRef<'_, MTLock<FxHashSet<MonoItem<'tcx>>>>,
364 recursion_depths: &mut DefIdMap<usize>,
365 inlining_map: MTRef<'_, MTLock<InliningMap<'tcx>>>) {
366 if !visited.lock_mut().insert(starting_point.clone()) {
367 // We've been here already, no need to search again.
370 debug!("BEGIN collect_items_rec({})", starting_point.to_string(tcx));
372 let mut neighbors = Vec::new();
373 let recursion_depth_reset;
375 match starting_point {
376 MonoItem::Static(def_id) => {
377 let instance = Instance::mono(tcx, def_id);
379 // Sanity check whether this ended up being collected accidentally
380 debug_assert!(should_monomorphize_locally(tcx, &instance));
382 let ty = instance.ty(tcx);
383 visit_drop_use(tcx, ty, true, &mut neighbors);
385 recursion_depth_reset = None;
391 let param_env = ty::ParamEnv::reveal_all();
393 if let Ok(val) = tcx.const_eval(param_env.and(cid)) {
394 collect_const(tcx, val, instance.substs, &mut neighbors);
397 MonoItem::Fn(instance) => {
398 // Sanity check whether this ended up being collected accidentally
399 debug_assert!(should_monomorphize_locally(tcx, &instance));
401 // Keep track of the monomorphization recursion depth
402 recursion_depth_reset = Some(check_recursion_limit(tcx,
405 check_type_length_limit(tcx, instance);
407 collect_neighbours(tcx, instance, &mut neighbors);
409 MonoItem::GlobalAsm(..) => {
410 recursion_depth_reset = None;
414 record_accesses(tcx, starting_point, &neighbors[..], inlining_map);
416 for neighbour in neighbors {
417 collect_items_rec(tcx, neighbour, visited, recursion_depths, inlining_map);
420 if let Some((def_id, depth)) = recursion_depth_reset {
421 recursion_depths.insert(def_id, depth);
424 debug!("END collect_items_rec({})", starting_point.to_string(tcx));
427 fn record_accesses<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
428 caller: MonoItem<'tcx>,
429 callees: &[MonoItem<'tcx>],
430 inlining_map: MTRef<'_, MTLock<InliningMap<'tcx>>>) {
431 let is_inlining_candidate = |mono_item: &MonoItem<'tcx>| {
432 mono_item.instantiation_mode(tcx) == InstantiationMode::LocalCopy
435 let accesses = callees.into_iter()
437 (*mono_item, is_inlining_candidate(mono_item))
440 inlining_map.lock_mut().record_accesses(caller, accesses);
443 fn check_recursion_limit<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
444 instance: Instance<'tcx>,
445 recursion_depths: &mut DefIdMap<usize>)
447 let def_id = instance.def_id();
448 let recursion_depth = recursion_depths.get(&def_id).cloned().unwrap_or(0);
449 debug!(" => recursion depth={}", recursion_depth);
451 let recursion_depth = if Some(def_id) == tcx.lang_items().drop_in_place_fn() {
452 // HACK: drop_in_place creates tight monomorphization loops. Give
459 // Code that needs to instantiate the same function recursively
460 // more than the recursion limit is assumed to be causing an
461 // infinite expansion.
462 if recursion_depth > *tcx.sess.recursion_limit.get() {
463 let error = format!("reached the recursion limit while instantiating `{}`",
465 if let Some(node_id) = tcx.hir().as_local_node_id(def_id) {
466 tcx.sess.span_fatal(tcx.hir().span(node_id), &error);
468 tcx.sess.fatal(&error);
472 recursion_depths.insert(def_id, recursion_depth + 1);
474 (def_id, recursion_depth)
477 fn check_type_length_limit<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
478 instance: Instance<'tcx>)
480 let type_length = instance.substs.types().flat_map(|ty| ty.walk()).count();
481 debug!(" => type length={}", type_length);
483 // Rust code can easily create exponentially-long types using only a
484 // polynomial recursion depth. Even with the default recursion
485 // depth, you can easily get cases that take >2^60 steps to run,
486 // which means that rustc basically hangs.
488 // Bail out in these cases to avoid that bad user experience.
489 let type_length_limit = *tcx.sess.type_length_limit.get();
490 if type_length > type_length_limit {
491 // The instance name is already known to be too long for rustc. Use
492 // `{:.64}` to avoid blasting the user's terminal with thousands of
493 // lines of type-name.
494 let instance_name = instance.to_string();
495 let msg = format!("reached the type-length limit while instantiating `{:.64}...`",
497 let mut diag = if let Some(node_id) = tcx.hir().as_local_node_id(instance.def_id()) {
498 tcx.sess.struct_span_fatal(tcx.hir().span(node_id), &msg)
500 tcx.sess.struct_fatal(&msg)
504 "consider adding a `#![type_length_limit=\"{}\"]` attribute to your crate",
505 type_length_limit*2));
507 tcx.sess.abort_if_errors();
511 struct MirNeighborCollector<'a, 'tcx: 'a> {
512 tcx: TyCtxt<'a, 'tcx, 'tcx>,
513 mir: &'a mir::Mir<'tcx>,
514 output: &'a mut Vec<MonoItem<'tcx>>,
515 param_substs: &'tcx Substs<'tcx>,
518 impl<'a, 'tcx> MirVisitor<'tcx> for MirNeighborCollector<'a, 'tcx> {
520 fn visit_rvalue(&mut self, rvalue: &mir::Rvalue<'tcx>, location: Location) {
521 debug!("visiting rvalue {:?}", *rvalue);
524 // When doing an cast from a regular pointer to a fat pointer, we
525 // have to instantiate all methods of the trait being cast to, so we
526 // can build the appropriate vtable.
527 mir::Rvalue::Cast(mir::CastKind::Unsize, ref operand, target_ty) => {
528 let target_ty = self.tcx.subst_and_normalize_erasing_regions(
530 ty::ParamEnv::reveal_all(),
533 let source_ty = operand.ty(self.mir, self.tcx);
534 let source_ty = self.tcx.subst_and_normalize_erasing_regions(
536 ty::ParamEnv::reveal_all(),
539 let (source_ty, target_ty) = find_vtable_types_for_unsizing(self.tcx,
542 // This could also be a different Unsize instruction, like
543 // from a fixed sized array to a slice. But we are only
544 // interested in things that produce a vtable.
545 if target_ty.is_trait() && !source_ty.is_trait() {
546 create_mono_items_for_vtable_methods(self.tcx,
552 mir::Rvalue::Cast(mir::CastKind::ReifyFnPointer, ref operand, _) => {
553 let fn_ty = operand.ty(self.mir, self.tcx);
554 let fn_ty = self.tcx.subst_and_normalize_erasing_regions(
556 ty::ParamEnv::reveal_all(),
559 visit_fn_use(self.tcx, fn_ty, false, &mut self.output);
561 mir::Rvalue::Cast(mir::CastKind::ClosureFnPointer, ref operand, _) => {
562 let source_ty = operand.ty(self.mir, self.tcx);
563 let source_ty = self.tcx.subst_and_normalize_erasing_regions(
565 ty::ParamEnv::reveal_all(),
568 match source_ty.sty {
569 ty::Closure(def_id, substs) => {
570 let instance = monomorphize::resolve_closure(
571 self.tcx, def_id, substs, ty::ClosureKind::FnOnce);
572 if should_monomorphize_locally(self.tcx, &instance) {
573 self.output.push(create_fn_mono_item(instance));
579 mir::Rvalue::NullaryOp(mir::NullOp::Box, _) => {
581 let exchange_malloc_fn_def_id = tcx
583 .require(ExchangeMallocFnLangItem)
584 .unwrap_or_else(|e| tcx.sess.fatal(&e));
585 let instance = Instance::mono(tcx, exchange_malloc_fn_def_id);
586 if should_monomorphize_locally(tcx, &instance) {
587 self.output.push(create_fn_mono_item(instance));
590 _ => { /* not interesting */ }
593 self.super_rvalue(rvalue, location);
596 fn visit_const(&mut self, constant: &&'tcx ty::Const<'tcx>, location: Location) {
597 debug!("visiting const {:?} @ {:?}", *constant, location);
599 collect_const(self.tcx, constant, self.param_substs, self.output);
601 self.super_const(constant);
604 fn visit_terminator_kind(&mut self,
605 block: mir::BasicBlock,
606 kind: &mir::TerminatorKind<'tcx>,
607 location: Location) {
608 debug!("visiting terminator {:?} @ {:?}", kind, location);
612 mir::TerminatorKind::Call { ref func, .. } => {
613 let callee_ty = func.ty(self.mir, tcx);
614 let callee_ty = tcx.subst_and_normalize_erasing_regions(
616 ty::ParamEnv::reveal_all(),
619 visit_fn_use(self.tcx, callee_ty, true, &mut self.output);
621 mir::TerminatorKind::Drop { ref location, .. } |
622 mir::TerminatorKind::DropAndReplace { ref location, .. } => {
623 let ty = location.ty(self.mir, self.tcx)
625 let ty = tcx.subst_and_normalize_erasing_regions(
627 ty::ParamEnv::reveal_all(),
630 visit_drop_use(self.tcx, ty, true, self.output);
632 mir::TerminatorKind::Goto { .. } |
633 mir::TerminatorKind::SwitchInt { .. } |
634 mir::TerminatorKind::Resume |
635 mir::TerminatorKind::Abort |
636 mir::TerminatorKind::Return |
637 mir::TerminatorKind::Unreachable |
638 mir::TerminatorKind::Assert { .. } => {}
639 mir::TerminatorKind::GeneratorDrop |
640 mir::TerminatorKind::Yield { .. } |
641 mir::TerminatorKind::FalseEdges { .. } |
642 mir::TerminatorKind::FalseUnwind { .. } => bug!(),
645 self.super_terminator_kind(block, kind, location);
648 fn visit_static(&mut self,
649 static_: &mir::Static<'tcx>,
650 context: mir::visit::PlaceContext<'tcx>,
651 location: Location) {
652 debug!("visiting static {:?} @ {:?}", static_.def_id, location);
655 let instance = Instance::mono(tcx, static_.def_id);
656 if should_monomorphize_locally(tcx, &instance) {
657 self.output.push(MonoItem::Static(static_.def_id));
660 self.super_static(static_, context, location);
664 fn visit_drop_use<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
666 is_direct_call: bool,
667 output: &mut Vec<MonoItem<'tcx>>)
669 let instance = monomorphize::resolve_drop_in_place(tcx, ty);
670 visit_instance_use(tcx, instance, is_direct_call, output);
673 fn visit_fn_use<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
675 is_direct_call: bool,
676 output: &mut Vec<MonoItem<'tcx>>)
678 if let ty::FnDef(def_id, substs) = ty.sty {
679 let instance = ty::Instance::resolve(tcx,
680 ty::ParamEnv::reveal_all(),
683 visit_instance_use(tcx, instance, is_direct_call, output);
687 fn visit_instance_use<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
688 instance: ty::Instance<'tcx>,
689 is_direct_call: bool,
690 output: &mut Vec<MonoItem<'tcx>>)
692 debug!("visit_item_use({:?}, is_direct_call={:?})", instance, is_direct_call);
693 if !should_monomorphize_locally(tcx, &instance) {
698 ty::InstanceDef::Intrinsic(def_id) => {
700 bug!("intrinsic {:?} being reified", def_id);
703 ty::InstanceDef::VtableShim(..) |
704 ty::InstanceDef::Virtual(..) |
705 ty::InstanceDef::DropGlue(_, None) => {
706 // don't need to emit shim if we are calling directly.
708 output.push(create_fn_mono_item(instance));
711 ty::InstanceDef::DropGlue(_, Some(_)) => {
712 output.push(create_fn_mono_item(instance));
714 ty::InstanceDef::ClosureOnceShim { .. } |
715 ty::InstanceDef::Item(..) |
716 ty::InstanceDef::FnPtrShim(..) |
717 ty::InstanceDef::CloneShim(..) => {
718 output.push(create_fn_mono_item(instance));
723 // Returns true if we should codegen an instance in the local crate.
724 // Returns false if we can just link to the upstream crate and therefore don't
726 fn should_monomorphize_locally<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>, instance: &Instance<'tcx>)
728 let def_id = match instance.def {
729 ty::InstanceDef::Item(def_id) => def_id,
730 ty::InstanceDef::VtableShim(..) |
731 ty::InstanceDef::ClosureOnceShim { .. } |
732 ty::InstanceDef::Virtual(..) |
733 ty::InstanceDef::FnPtrShim(..) |
734 ty::InstanceDef::DropGlue(..) |
735 ty::InstanceDef::Intrinsic(_) |
736 ty::InstanceDef::CloneShim(..) => return true
739 if tcx.is_foreign_item(def_id) {
740 // We can always link to foreign items
744 if def_id.is_local() {
745 // local items cannot be referred to locally without monomorphizing them locally
749 if tcx.is_reachable_non_generic(def_id) ||
750 is_available_upstream_generic(tcx, def_id, instance.substs) {
751 // We can link to the item in question, no instance needed
756 if !tcx.is_mir_available(def_id) {
757 bug!("Cannot create local mono-item for {:?}", def_id)
761 fn is_available_upstream_generic<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
763 substs: &'tcx Substs<'tcx>)
765 debug_assert!(!def_id.is_local());
767 // If we are not in share generics mode, we don't link to upstream
768 // monomorphizations but always instantiate our own internal versions
770 if !tcx.sess.opts.share_generics() {
774 // If this instance has no type parameters, it cannot be a shared
775 // monomorphization. Non-generic instances are already handled above
776 // by `is_reachable_non_generic()`
777 if substs.types().next().is_none() {
781 // Take a look at the available monomorphizations listed in the metadata
782 // of upstream crates.
783 tcx.upstream_monomorphizations_for(def_id)
784 .map(|set| set.contains_key(substs))
789 /// For given pair of source and target type that occur in an unsizing coercion,
790 /// this function finds the pair of types that determines the vtable linking
793 /// For example, the source type might be `&SomeStruct` and the target type\
794 /// might be `&SomeTrait` in a cast like:
796 /// let src: &SomeStruct = ...;
797 /// let target = src as &SomeTrait;
799 /// Then the output of this function would be (SomeStruct, SomeTrait) since for
800 /// constructing the `target` fat-pointer we need the vtable for that pair.
802 /// Things can get more complicated though because there's also the case where
803 /// the unsized type occurs as a field:
806 /// struct ComplexStruct<T: ?Sized> {
813 /// In this case, if `T` is sized, `&ComplexStruct<T>` is a thin pointer. If `T`
814 /// is unsized, `&SomeStruct` is a fat pointer, and the vtable it points to is
815 /// for the pair of `T` (which is a trait) and the concrete type that `T` was
816 /// originally coerced from:
818 /// let src: &ComplexStruct<SomeStruct> = ...;
819 /// let target = src as &ComplexStruct<SomeTrait>;
821 /// Again, we want this `find_vtable_types_for_unsizing()` to provide the pair
822 /// `(SomeStruct, SomeTrait)`.
824 /// Finally, there is also the case of custom unsizing coercions, e.g., for
825 /// smart pointers such as `Rc` and `Arc`.
826 fn find_vtable_types_for_unsizing<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
829 -> (Ty<'tcx>, Ty<'tcx>) {
830 let ptr_vtable = |inner_source: Ty<'tcx>, inner_target: Ty<'tcx>| {
831 let type_has_metadata = |ty: Ty<'tcx>| -> bool {
832 use syntax_pos::DUMMY_SP;
833 if ty.is_sized(tcx.at(DUMMY_SP), ty::ParamEnv::reveal_all()) {
836 let tail = tcx.struct_tail(ty);
838 ty::Foreign(..) => false,
839 ty::Str | ty::Slice(..) | ty::Dynamic(..) => true,
840 _ => bug!("unexpected unsized tail: {:?}", tail.sty),
843 if type_has_metadata(inner_source) {
844 (inner_source, inner_target)
846 tcx.struct_lockstep_tails(inner_source, inner_target)
850 match (&source_ty.sty, &target_ty.sty) {
854 &ty::RawPtr(ty::TypeAndMut { ty: b, .. })) |
855 (&ty::RawPtr(ty::TypeAndMut { ty: a, .. }),
856 &ty::RawPtr(ty::TypeAndMut { ty: b, .. })) => {
859 (&ty::Adt(def_a, _), &ty::Adt(def_b, _)) if def_a.is_box() && def_b.is_box() => {
860 ptr_vtable(source_ty.boxed_ty(), target_ty.boxed_ty())
863 (&ty::Adt(source_adt_def, source_substs),
864 &ty::Adt(target_adt_def, target_substs)) => {
865 assert_eq!(source_adt_def, target_adt_def);
868 monomorphize::custom_coerce_unsize_info(tcx, source_ty, target_ty);
870 let coerce_index = match kind {
871 CustomCoerceUnsized::Struct(i) => i
874 let source_fields = &source_adt_def.non_enum_variant().fields;
875 let target_fields = &target_adt_def.non_enum_variant().fields;
877 assert!(coerce_index < source_fields.len() &&
878 source_fields.len() == target_fields.len());
880 find_vtable_types_for_unsizing(tcx,
881 source_fields[coerce_index].ty(tcx,
883 target_fields[coerce_index].ty(tcx,
886 _ => bug!("find_vtable_types_for_unsizing: invalid coercion {:?} -> {:?}",
892 fn create_fn_mono_item<'a, 'tcx>(instance: Instance<'tcx>) -> MonoItem<'tcx> {
893 debug!("create_fn_mono_item(instance={})", instance);
894 MonoItem::Fn(instance)
897 /// Creates a `MonoItem` for each method that is referenced by the vtable for
898 /// the given trait/impl pair.
899 fn create_mono_items_for_vtable_methods<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
902 output: &mut Vec<MonoItem<'tcx>>) {
903 assert!(!trait_ty.needs_subst() && !trait_ty.has_escaping_bound_vars() &&
904 !impl_ty.needs_subst() && !impl_ty.has_escaping_bound_vars());
906 if let ty::Dynamic(ref trait_ty, ..) = trait_ty.sty {
907 let poly_trait_ref = trait_ty.principal().with_self_ty(tcx, impl_ty);
908 assert!(!poly_trait_ref.has_escaping_bound_vars());
910 // Walk all methods of the trait, including those of its supertraits
911 let methods = tcx.vtable_methods(poly_trait_ref);
912 let methods = methods.iter().cloned().filter_map(|method| method)
913 .map(|(def_id, substs)| ty::Instance::resolve_for_vtable(
915 ty::ParamEnv::reveal_all(),
918 .filter(|&instance| should_monomorphize_locally(tcx, &instance))
919 .map(|instance| create_fn_mono_item(instance));
920 output.extend(methods);
921 // Also add the destructor
922 visit_drop_use(tcx, impl_ty, false, output);
926 //=-----------------------------------------------------------------------------
928 //=-----------------------------------------------------------------------------
930 struct RootCollector<'b, 'a: 'b, 'tcx: 'a + 'b> {
931 tcx: TyCtxt<'a, 'tcx, 'tcx>,
932 mode: MonoItemCollectionMode,
933 output: &'b mut Vec<MonoItem<'tcx>>,
934 entry_fn: Option<DefId>,
937 impl<'b, 'a, 'v> ItemLikeVisitor<'v> for RootCollector<'b, 'a, 'v> {
938 fn visit_item(&mut self, item: &'v hir::Item) {
940 hir::ItemKind::ExternCrate(..) |
941 hir::ItemKind::Use(..) |
942 hir::ItemKind::ForeignMod(..) |
943 hir::ItemKind::Ty(..) |
944 hir::ItemKind::Trait(..) |
945 hir::ItemKind::TraitAlias(..) |
946 hir::ItemKind::Existential(..) |
947 hir::ItemKind::Mod(..) => {
948 // Nothing to do, just keep recursing...
951 hir::ItemKind::Impl(..) => {
952 if self.mode == MonoItemCollectionMode::Eager {
953 create_mono_items_for_default_impls(self.tcx,
959 hir::ItemKind::Enum(_, ref generics) |
960 hir::ItemKind::Struct(_, ref generics) |
961 hir::ItemKind::Union(_, ref generics) => {
962 if generics.params.is_empty() {
963 if self.mode == MonoItemCollectionMode::Eager {
964 let def_id = self.tcx.hir().local_def_id(item.id);
965 debug!("RootCollector: ADT drop-glue for {}",
966 def_id_to_string(self.tcx, def_id));
968 let ty = Instance::new(def_id, Substs::empty()).ty(self.tcx);
969 visit_drop_use(self.tcx, ty, true, self.output);
973 hir::ItemKind::GlobalAsm(..) => {
974 debug!("RootCollector: ItemKind::GlobalAsm({})",
975 def_id_to_string(self.tcx,
976 self.tcx.hir().local_def_id(item.id)));
977 self.output.push(MonoItem::GlobalAsm(item.id));
979 hir::ItemKind::Static(..) => {
980 let def_id = self.tcx.hir().local_def_id(item.id);
981 debug!("RootCollector: ItemKind::Static({})",
982 def_id_to_string(self.tcx, def_id));
983 self.output.push(MonoItem::Static(def_id));
985 hir::ItemKind::Const(..) => {
986 // const items only generate mono items if they are
987 // actually used somewhere. Just declaring them is insufficient.
989 // but even just declaring them must collect the items they refer to
990 let def_id = self.tcx.hir().local_def_id(item.id);
992 let instance = Instance::mono(self.tcx, def_id);
997 let param_env = ty::ParamEnv::reveal_all();
999 if let Ok(val) = self.tcx.const_eval(param_env.and(cid)) {
1000 collect_const(self.tcx, val, instance.substs, &mut self.output);
1003 hir::ItemKind::Fn(..) => {
1004 let def_id = self.tcx.hir().local_def_id(item.id);
1005 self.push_if_root(def_id);
1010 fn visit_trait_item(&mut self, _: &'v hir::TraitItem) {
1011 // Even if there's a default body with no explicit generics,
1012 // it's still generic over some `Self: Trait`, so not a root.
1015 fn visit_impl_item(&mut self, ii: &'v hir::ImplItem) {
1017 hir::ImplItemKind::Method(hir::MethodSig { .. }, _) => {
1018 let def_id = self.tcx.hir().local_def_id(ii.id);
1019 self.push_if_root(def_id);
1021 _ => { /* Nothing to do here */ }
1026 impl<'b, 'a, 'v> RootCollector<'b, 'a, 'v> {
1027 fn is_root(&self, def_id: DefId) -> bool {
1028 !item_has_type_parameters(self.tcx, def_id) && match self.mode {
1029 MonoItemCollectionMode::Eager => {
1032 MonoItemCollectionMode::Lazy => {
1033 self.entry_fn == Some(def_id) ||
1034 self.tcx.is_reachable_non_generic(def_id) ||
1035 self.tcx.codegen_fn_attrs(def_id).flags.contains(
1036 CodegenFnAttrFlags::RUSTC_STD_INTERNAL_SYMBOL)
1041 /// If `def_id` represents a root, then push it onto the list of
1042 /// outputs. (Note that all roots must be monomorphic.)
1043 fn push_if_root(&mut self, def_id: DefId) {
1044 if self.is_root(def_id) {
1045 debug!("RootCollector::push_if_root: found root def_id={:?}", def_id);
1047 let instance = Instance::mono(self.tcx, def_id);
1048 self.output.push(create_fn_mono_item(instance));
1052 /// As a special case, when/if we encounter the
1053 /// `main()` function, we also have to generate a
1054 /// monomorphized copy of the start lang item based on
1055 /// the return type of `main`. This is not needed when
1056 /// the user writes their own `start` manually.
1057 fn push_extra_entry_roots(&mut self) {
1058 if self.tcx.sess.entry_fn.get().map(|e| e.2) != Some(config::EntryFnType::Main) {
1062 let main_def_id = if let Some(def_id) = self.entry_fn {
1068 let start_def_id = match self.tcx.lang_items().require(StartFnLangItem) {
1070 Err(err) => self.tcx.sess.fatal(&err),
1072 let main_ret_ty = self.tcx.fn_sig(main_def_id).output();
1074 // Given that `main()` has no arguments,
1075 // then its return type cannot have
1076 // late-bound regions, since late-bound
1077 // regions must appear in the argument
1079 let main_ret_ty = self.tcx.erase_regions(
1080 &main_ret_ty.no_bound_vars().unwrap(),
1083 let start_instance = Instance::resolve(
1085 ty::ParamEnv::reveal_all(),
1087 self.tcx.intern_substs(&[main_ret_ty.into()])
1090 self.output.push(create_fn_mono_item(start_instance));
1094 fn item_has_type_parameters<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>, def_id: DefId) -> bool {
1095 let generics = tcx.generics_of(def_id);
1096 generics.requires_monomorphization(tcx)
1099 fn create_mono_items_for_default_impls<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
1100 item: &'tcx hir::Item,
1101 output: &mut Vec<MonoItem<'tcx>>) {
1103 hir::ItemKind::Impl(_, _, _, ref generics, .., ref impl_item_refs) => {
1104 for param in &generics.params {
1106 hir::GenericParamKind::Lifetime { .. } => {}
1107 hir::GenericParamKind::Type { .. } => return,
1111 let impl_def_id = tcx.hir().local_def_id(item.id);
1113 debug!("create_mono_items_for_default_impls(item={})",
1114 def_id_to_string(tcx, impl_def_id));
1116 if let Some(trait_ref) = tcx.impl_trait_ref(impl_def_id) {
1117 let overridden_methods: FxHashSet<_> =
1118 impl_item_refs.iter()
1119 .map(|iiref| iiref.ident.modern())
1121 for method in tcx.provided_trait_methods(trait_ref.def_id) {
1122 if overridden_methods.contains(&method.ident.modern()) {
1126 if tcx.generics_of(method.def_id).own_counts().types != 0 {
1130 let substs = Substs::for_item(tcx, method.def_id, |param, _| {
1132 GenericParamDefKind::Lifetime => tcx.types.re_erased.into(),
1133 GenericParamDefKind::Type {..} => {
1134 trait_ref.substs[param.index as usize]
1139 let instance = ty::Instance::resolve(tcx,
1140 ty::ParamEnv::reveal_all(),
1144 let mono_item = create_fn_mono_item(instance);
1145 if mono_item.is_instantiable(tcx)
1146 && should_monomorphize_locally(tcx, &instance) {
1147 output.push(mono_item);
1158 /// Scan the miri alloc in order to find function calls, closures, and drop-glue
1159 fn collect_miri<'a, 'tcx>(
1160 tcx: TyCtxt<'a, 'tcx, 'tcx>,
1162 output: &mut Vec<MonoItem<'tcx>>,
1164 let alloc_type = tcx.alloc_map.lock().get(alloc_id);
1166 Some(AllocType::Static(did)) => {
1167 let instance = Instance::mono(tcx, did);
1168 if should_monomorphize_locally(tcx, &instance) {
1169 trace!("collecting static {:?}", did);
1170 output.push(MonoItem::Static(did));
1173 Some(AllocType::Memory(alloc)) => {
1174 trace!("collecting {:?} with {:#?}", alloc_id, alloc);
1175 for &((), inner) in alloc.relocations.values() {
1176 collect_miri(tcx, inner, output);
1179 Some(AllocType::Function(fn_instance)) => {
1180 if should_monomorphize_locally(tcx, &fn_instance) {
1181 trace!("collecting {:?} with {:#?}", alloc_id, fn_instance);
1182 output.push(create_fn_mono_item(fn_instance));
1185 None => bug!("alloc id without corresponding allocation: {}", alloc_id),
1189 /// Scan the MIR in order to find function calls, closures, and drop-glue
1190 fn collect_neighbours<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
1191 instance: Instance<'tcx>,
1192 output: &mut Vec<MonoItem<'tcx>>)
1194 let mir = tcx.instance_mir(instance.def);
1196 MirNeighborCollector {
1200 param_substs: instance.substs,
1202 let param_env = ty::ParamEnv::reveal_all();
1203 for i in 0..mir.promoted.len() {
1204 use rustc_data_structures::indexed_vec::Idx;
1205 let i = Promoted::new(i);
1206 let cid = GlobalId {
1210 match tcx.const_eval(param_env.and(cid)) {
1211 Ok(val) => collect_const(tcx, val, instance.substs, output),
1212 Err(ErrorHandled::Reported) => {},
1213 Err(ErrorHandled::TooGeneric) => span_bug!(
1214 mir.promoted[i].span, "collection encountered polymorphic constant",
1220 fn def_id_to_string<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
1223 let mut output = String::new();
1224 let printer = DefPathBasedNames::new(tcx, false, false);
1225 printer.push_def_path(def_id, &mut output);
1229 fn collect_const<'a, 'tcx>(
1230 tcx: TyCtxt<'a, 'tcx, 'tcx>,
1231 constant: &ty::Const<'tcx>,
1232 param_substs: &'tcx Substs<'tcx>,
1233 output: &mut Vec<MonoItem<'tcx>>,
1235 debug!("visiting const {:?}", *constant);
1237 let val = match constant.val {
1238 ConstValue::Unevaluated(def_id, substs) => {
1239 let param_env = ty::ParamEnv::reveal_all();
1240 let substs = tcx.subst_and_normalize_erasing_regions(
1245 let instance = ty::Instance::resolve(tcx,
1250 let cid = GlobalId {
1254 match tcx.const_eval(param_env.and(cid)) {
1256 Err(ErrorHandled::Reported) => return,
1257 Err(ErrorHandled::TooGeneric) => span_bug!(
1258 tcx.def_span(def_id), "collection encountered polymorphic constant",
1265 ConstValue::Unevaluated(..) => bug!("const eval yielded unevaluated const"),
1266 ConstValue::ScalarPair(Scalar::Ptr(a), Scalar::Ptr(b)) => {
1267 collect_miri(tcx, a.alloc_id, output);
1268 collect_miri(tcx, b.alloc_id, output);
1270 ConstValue::ScalarPair(_, Scalar::Ptr(ptr)) |
1271 ConstValue::ScalarPair(Scalar::Ptr(ptr), _) |
1272 ConstValue::Scalar(Scalar::Ptr(ptr)) =>
1273 collect_miri(tcx, ptr.alloc_id, output),
1274 ConstValue::ByRef(_id, alloc, _offset) => {
1275 for &((), id) in alloc.relocations.values() {
1276 collect_miri(tcx, id, output);