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 //! Translation 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 "translation 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 "translation item" is something that results in a function or global in
47 //! the LLVM IR of a codegen unit. Translation items do not stand on their
48 //! own, they can reference other translation items. For example, if function
49 //! `foo()` calls function `bar()` then the translation item for `foo()`
50 //! references the translation item for function `bar()`. In general, the
51 //! definition for translation item A referencing a translation item B is that
52 //! the LLVM artifact produced for A references the LLVM artifact produced
55 //! - Translation items and the references between them form a directed graph,
56 //! where the translation items are the nodes and references form the edges.
57 //! Let's call this graph the "translation item graph".
59 //! - The translation item graph for a program contains all translation 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 //! translation 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 translation 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 translation 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 translation 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 translation item, we have found a neighbor. Since the
82 //! translation 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 translation 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 translation 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 translate 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 //! translation 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 translation items are introduced by MIR drop-statements. The
128 //! generated translation 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 transparently. If it is
154 //! about to create a translation 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 //! Translation 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 translation 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 translation 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 translation 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};
199 use rustc::ty::subst::Substs;
200 use rustc::ty::{self, TypeFoldable, TyCtxt};
201 use rustc::ty::adjustment::CustomCoerceUnsized;
202 use rustc::mir::{self, Location};
203 use rustc::mir::visit::Visitor as MirVisitor;
205 use context::SharedCrateContext;
206 use common::{def_ty, instance_ty};
207 use monomorphize::{self, Instance};
208 use rustc::util::nodemap::{FxHashSet, FxHashMap, DefIdMap};
210 use trans_item::{TransItem, DefPathBasedNames, InstantiationMode};
212 use rustc_data_structures::bitvec::BitVector;
213 use back::symbol_export::ExportedSymbols;
215 #[derive(PartialEq, Eq, Hash, Clone, Copy, Debug)]
216 pub enum TransItemCollectionMode {
221 /// Maps every translation item to all translation items it references in its
223 pub struct InliningMap<'tcx> {
224 // Maps a source translation item to the range of translation items
226 // The two numbers in the tuple are the start (inclusive) and
227 // end index (exclusive) within the `targets` vecs.
228 index: FxHashMap<TransItem<'tcx>, (usize, usize)>,
229 targets: Vec<TransItem<'tcx>>,
231 // Contains one bit per translation item in the `targets` field. That bit
232 // is true if that translation item needs to be inlined into every CGU.
236 impl<'tcx> InliningMap<'tcx> {
238 fn new() -> InliningMap<'tcx> {
242 inlines: BitVector::new(1024),
246 fn record_accesses<I>(&mut self,
247 source: TransItem<'tcx>,
249 where I: Iterator<Item=(TransItem<'tcx>, bool)> + ExactSizeIterator
251 assert!(!self.index.contains_key(&source));
253 let start_index = self.targets.len();
254 let new_items_count = new_targets.len();
255 let new_items_count_total = new_items_count + self.targets.len();
257 self.targets.reserve(new_items_count);
258 self.inlines.grow(new_items_count_total);
260 for (i, (target, inline)) in new_targets.enumerate() {
261 self.targets.push(target);
263 self.inlines.insert(i + start_index);
267 let end_index = self.targets.len();
268 self.index.insert(source, (start_index, end_index));
271 // Internally iterate over all items referenced by `source` which will be
272 // made available for inlining.
273 pub fn with_inlining_candidates<F>(&self, source: TransItem<'tcx>, mut f: F)
274 where F: FnMut(TransItem<'tcx>)
276 if let Some(&(start_index, end_index)) = self.index.get(&source) {
277 for (i, candidate) in self.targets[start_index .. end_index]
280 if self.inlines.contains(start_index + i) {
287 // Internally iterate over all items and the things each accesses.
288 pub fn iter_accesses<F>(&self, mut f: F)
289 where F: FnMut(TransItem<'tcx>, &[TransItem<'tcx>])
291 for (&accessor, &(start_index, end_index)) in &self.index {
292 f(accessor, &self.targets[start_index .. end_index])
297 pub fn collect_crate_translation_items<'a, 'tcx>(scx: &SharedCrateContext<'a, 'tcx>,
298 exported_symbols: &ExportedSymbols,
299 mode: TransItemCollectionMode)
300 -> (FxHashSet<TransItem<'tcx>>,
302 // We are not tracking dependencies of this pass as it has to be re-executed
303 // every time no matter what.
304 scx.tcx().dep_graph.with_ignore(|| {
305 let roots = collect_roots(scx, exported_symbols, mode);
307 debug!("Building translation item graph, beginning at roots");
308 let mut visited = FxHashSet();
309 let mut recursion_depths = DefIdMap();
310 let mut inlining_map = InliningMap::new();
313 collect_items_rec(scx,
316 &mut recursion_depths,
320 (visited, inlining_map)
324 // Find all non-generic items by walking the HIR. These items serve as roots to
325 // start monomorphizing from.
326 fn collect_roots<'a, 'tcx>(scx: &SharedCrateContext<'a, 'tcx>,
327 exported_symbols: &ExportedSymbols,
328 mode: TransItemCollectionMode)
329 -> Vec<TransItem<'tcx>> {
330 debug!("Collecting roots");
331 let mut roots = Vec::new();
334 let mut visitor = RootCollector {
341 scx.tcx().hir.krate().visit_all_item_likes(&mut visitor);
344 // We can only translate items that are instantiable - items all of
345 // whose predicates hold. Luckily, items that aren't instantiable
346 // can't actually be used, so we can just skip translating them.
347 roots.retain(|root| root.is_instantiable(scx.tcx()));
352 // Collect all monomorphized translation items reachable from `starting_point`
353 fn collect_items_rec<'a, 'tcx: 'a>(scx: &SharedCrateContext<'a, 'tcx>,
354 starting_point: TransItem<'tcx>,
355 visited: &mut FxHashSet<TransItem<'tcx>>,
356 recursion_depths: &mut DefIdMap<usize>,
357 inlining_map: &mut InliningMap<'tcx>) {
358 if !visited.insert(starting_point.clone()) {
359 // We've been here already, no need to search again.
362 debug!("BEGIN collect_items_rec({})", starting_point.to_string(scx.tcx()));
364 let mut neighbors = Vec::new();
365 let recursion_depth_reset;
367 match starting_point {
368 TransItem::Static(node_id) => {
369 let def_id = scx.tcx().hir.local_def_id(node_id);
370 let instance = Instance::mono(scx.tcx(), def_id);
372 // Sanity check whether this ended up being collected accidentally
373 debug_assert!(should_trans_locally(scx.tcx(), &instance));
375 let ty = instance_ty(scx, &instance);
376 visit_drop_use(scx, ty, true, &mut neighbors);
378 recursion_depth_reset = None;
380 collect_neighbours(scx, instance, true, &mut neighbors);
382 TransItem::Fn(instance) => {
383 // Sanity check whether this ended up being collected accidentally
384 debug_assert!(should_trans_locally(scx.tcx(), &instance));
386 // Keep track of the monomorphization recursion depth
387 recursion_depth_reset = Some(check_recursion_limit(scx.tcx(),
390 check_type_length_limit(scx.tcx(), instance);
392 collect_neighbours(scx, instance, false, &mut neighbors);
394 TransItem::GlobalAsm(..) => {
395 recursion_depth_reset = None;
399 record_accesses(scx.tcx(), starting_point, &neighbors[..], inlining_map);
401 for neighbour in neighbors {
402 collect_items_rec(scx, neighbour, visited, recursion_depths, inlining_map);
405 if let Some((def_id, depth)) = recursion_depth_reset {
406 recursion_depths.insert(def_id, depth);
409 debug!("END collect_items_rec({})", starting_point.to_string(scx.tcx()));
412 fn record_accesses<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
413 caller: TransItem<'tcx>,
414 callees: &[TransItem<'tcx>],
415 inlining_map: &mut InliningMap<'tcx>) {
416 let is_inlining_candidate = |trans_item: &TransItem<'tcx>| {
417 trans_item.instantiation_mode(tcx) == InstantiationMode::LocalCopy
420 let accesses = callees.into_iter()
422 (*trans_item, is_inlining_candidate(trans_item))
425 inlining_map.record_accesses(caller, accesses);
428 fn check_recursion_limit<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
429 instance: Instance<'tcx>,
430 recursion_depths: &mut DefIdMap<usize>)
432 let def_id = instance.def_id();
433 let recursion_depth = recursion_depths.get(&def_id).cloned().unwrap_or(0);
434 debug!(" => recursion depth={}", recursion_depth);
436 let recursion_depth = if Some(def_id) == tcx.lang_items().drop_in_place_fn() {
437 // HACK: drop_in_place creates tight monomorphization loops. Give
444 // Code that needs to instantiate the same function recursively
445 // more than the recursion limit is assumed to be causing an
446 // infinite expansion.
447 if recursion_depth > tcx.sess.recursion_limit.get() {
448 let error = format!("reached the recursion limit while instantiating `{}`",
450 if let Some(node_id) = tcx.hir.as_local_node_id(def_id) {
451 tcx.sess.span_fatal(tcx.hir.span(node_id), &error);
453 tcx.sess.fatal(&error);
457 recursion_depths.insert(def_id, recursion_depth + 1);
459 (def_id, recursion_depth)
462 fn check_type_length_limit<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
463 instance: Instance<'tcx>)
465 let type_length = instance.substs.types().flat_map(|ty| ty.walk()).count();
466 debug!(" => type length={}", type_length);
468 // Rust code can easily create exponentially-long types using only a
469 // polynomial recursion depth. Even with the default recursion
470 // depth, you can easily get cases that take >2^60 steps to run,
471 // which means that rustc basically hangs.
473 // Bail out in these cases to avoid that bad user experience.
474 let type_length_limit = tcx.sess.type_length_limit.get();
475 if type_length > type_length_limit {
476 // The instance name is already known to be too long for rustc. Use
477 // `{:.64}` to avoid blasting the user's terminal with thousands of
478 // lines of type-name.
479 let instance_name = instance.to_string();
480 let msg = format!("reached the type-length limit while instantiating `{:.64}...`",
482 let mut diag = if let Some(node_id) = tcx.hir.as_local_node_id(instance.def_id()) {
483 tcx.sess.struct_span_fatal(tcx.hir.span(node_id), &msg)
485 tcx.sess.struct_fatal(&msg)
489 "consider adding a `#![type_length_limit=\"{}\"]` attribute to your crate",
490 type_length_limit*2));
492 tcx.sess.abort_if_errors();
496 struct MirNeighborCollector<'a, 'tcx: 'a> {
497 scx: &'a SharedCrateContext<'a, 'tcx>,
498 mir: &'a mir::Mir<'tcx>,
499 output: &'a mut Vec<TransItem<'tcx>>,
500 param_substs: &'tcx Substs<'tcx>,
504 impl<'a, 'tcx> MirVisitor<'tcx> for MirNeighborCollector<'a, 'tcx> {
506 fn visit_rvalue(&mut self, rvalue: &mir::Rvalue<'tcx>, location: Location) {
507 debug!("visiting rvalue {:?}", *rvalue);
510 // When doing an cast from a regular pointer to a fat pointer, we
511 // have to instantiate all methods of the trait being cast to, so we
512 // can build the appropriate vtable.
513 mir::Rvalue::Cast(mir::CastKind::Unsize, ref operand, target_ty) => {
514 let target_ty = self.scx.tcx().trans_apply_param_substs(self.param_substs,
516 let source_ty = operand.ty(self.mir, self.scx.tcx());
517 let source_ty = self.scx.tcx().trans_apply_param_substs(self.param_substs,
519 let (source_ty, target_ty) = find_vtable_types_for_unsizing(self.scx,
522 // This could also be a different Unsize instruction, like
523 // from a fixed sized array to a slice. But we are only
524 // interested in things that produce a vtable.
525 if target_ty.is_trait() && !source_ty.is_trait() {
526 create_trans_items_for_vtable_methods(self.scx,
532 mir::Rvalue::Cast(mir::CastKind::ReifyFnPointer, ref operand, _) => {
533 let fn_ty = operand.ty(self.mir, self.scx.tcx());
534 let fn_ty = self.scx.tcx().trans_apply_param_substs(self.param_substs,
536 visit_fn_use(self.scx, fn_ty, false, &mut self.output);
538 mir::Rvalue::Cast(mir::CastKind::ClosureFnPointer, ref operand, _) => {
539 let source_ty = operand.ty(self.mir, self.scx.tcx());
540 let source_ty = self.scx.tcx().trans_apply_param_substs(self.param_substs,
542 match source_ty.sty {
543 ty::TyClosure(def_id, substs) => {
544 let instance = monomorphize::resolve_closure(
545 self.scx, def_id, substs, ty::ClosureKind::FnOnce);
546 self.output.push(create_fn_trans_item(instance));
551 mir::Rvalue::NullaryOp(mir::NullOp::Box, _) => {
552 let tcx = self.scx.tcx();
553 let exchange_malloc_fn_def_id = tcx
555 .require(ExchangeMallocFnLangItem)
556 .unwrap_or_else(|e| self.scx.sess().fatal(&e));
557 let instance = Instance::mono(tcx, exchange_malloc_fn_def_id);
558 if should_trans_locally(tcx, &instance) {
559 self.output.push(create_fn_trans_item(instance));
562 _ => { /* not interesting */ }
565 self.super_rvalue(rvalue, location);
568 fn visit_const(&mut self, constant: &&'tcx ty::Const<'tcx>, location: Location) {
569 debug!("visiting const {:?} @ {:?}", *constant, location);
571 if let ConstVal::Unevaluated(def_id, substs) = constant.val {
572 let substs = self.scx.tcx().trans_apply_param_substs(self.param_substs,
574 let instance = monomorphize::resolve(self.scx, def_id, substs);
575 collect_neighbours(self.scx, instance, true, self.output);
578 self.super_const(constant);
581 fn visit_terminator_kind(&mut self,
582 block: mir::BasicBlock,
583 kind: &mir::TerminatorKind<'tcx>,
584 location: Location) {
585 debug!("visiting terminator {:?} @ {:?}", kind, location);
587 let tcx = self.scx.tcx();
589 mir::TerminatorKind::Call { ref func, .. } => {
590 let callee_ty = func.ty(self.mir, tcx);
591 let callee_ty = tcx.trans_apply_param_substs(self.param_substs, &callee_ty);
593 let constness = match (self.const_context, &callee_ty.sty) {
594 (true, &ty::TyFnDef(def_id, substs)) if self.scx.tcx().is_const_fn(def_id) => {
595 let instance = monomorphize::resolve(self.scx, def_id, substs);
601 if let Some(const_fn_instance) = constness {
602 // If this is a const fn, called from a const context, we
603 // have to visit its body in order to find any fn reifications
605 collect_neighbours(self.scx,
610 visit_fn_use(self.scx, callee_ty, true, &mut self.output);
613 mir::TerminatorKind::Drop { ref location, .. } |
614 mir::TerminatorKind::DropAndReplace { ref location, .. } => {
615 let ty = location.ty(self.mir, self.scx.tcx())
616 .to_ty(self.scx.tcx());
617 let ty = tcx.trans_apply_param_substs(self.param_substs, &ty);
618 visit_drop_use(self.scx, ty, true, self.output);
620 mir::TerminatorKind::Goto { .. } |
621 mir::TerminatorKind::SwitchInt { .. } |
622 mir::TerminatorKind::Resume |
623 mir::TerminatorKind::Return |
624 mir::TerminatorKind::Unreachable |
625 mir::TerminatorKind::Assert { .. } => {}
626 mir::TerminatorKind::GeneratorDrop |
627 mir::TerminatorKind::Yield { .. } => bug!(),
630 self.super_terminator_kind(block, kind, location);
633 fn visit_static(&mut self,
634 static_: &mir::Static<'tcx>,
635 context: mir::visit::LvalueContext<'tcx>,
636 location: Location) {
637 debug!("visiting static {:?} @ {:?}", static_.def_id, location);
639 let tcx = self.scx.tcx();
640 let instance = Instance::mono(tcx, static_.def_id);
641 if should_trans_locally(tcx, &instance) {
642 let node_id = tcx.hir.as_local_node_id(static_.def_id).unwrap();
643 self.output.push(TransItem::Static(node_id));
646 self.super_static(static_, context, location);
650 fn visit_drop_use<'a, 'tcx>(scx: &SharedCrateContext<'a, 'tcx>,
652 is_direct_call: bool,
653 output: &mut Vec<TransItem<'tcx>>)
655 let instance = monomorphize::resolve_drop_in_place(scx, ty);
656 visit_instance_use(scx, instance, is_direct_call, output);
659 fn visit_fn_use<'a, 'tcx>(scx: &SharedCrateContext<'a, 'tcx>,
661 is_direct_call: bool,
662 output: &mut Vec<TransItem<'tcx>>)
664 if let ty::TyFnDef(def_id, substs) = ty.sty {
665 let instance = monomorphize::resolve(scx, def_id, substs);
666 visit_instance_use(scx, instance, is_direct_call, output);
670 fn visit_instance_use<'a, 'tcx>(scx: &SharedCrateContext<'a, 'tcx>,
671 instance: ty::Instance<'tcx>,
672 is_direct_call: bool,
673 output: &mut Vec<TransItem<'tcx>>)
675 debug!("visit_item_use({:?}, is_direct_call={:?})", instance, is_direct_call);
676 if !should_trans_locally(scx.tcx(), &instance) {
681 ty::InstanceDef::Intrinsic(def_id) => {
683 bug!("intrinsic {:?} being reified", def_id);
686 ty::InstanceDef::Virtual(..) |
687 ty::InstanceDef::DropGlue(_, None) => {
688 // don't need to emit shim if we are calling directly.
690 output.push(create_fn_trans_item(instance));
693 ty::InstanceDef::DropGlue(_, Some(_)) => {
694 output.push(create_fn_trans_item(instance));
696 ty::InstanceDef::ClosureOnceShim { .. } |
697 ty::InstanceDef::Item(..) |
698 ty::InstanceDef::FnPtrShim(..) |
699 ty::InstanceDef::CloneShim(..) => {
700 output.push(create_fn_trans_item(instance));
705 // Returns true if we should translate an instance in the local crate.
706 // Returns false if we can just link to the upstream crate and therefore don't
707 // need a translation item.
708 fn should_trans_locally<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>, instance: &Instance<'tcx>)
710 let def_id = match instance.def {
711 ty::InstanceDef::Item(def_id) => def_id,
712 ty::InstanceDef::ClosureOnceShim { .. } |
713 ty::InstanceDef::Virtual(..) |
714 ty::InstanceDef::FnPtrShim(..) |
715 ty::InstanceDef::DropGlue(..) |
716 ty::InstanceDef::Intrinsic(_) |
717 ty::InstanceDef::CloneShim(..) => return true
719 match tcx.hir.get_if_local(def_id) {
720 Some(hir_map::NodeForeignItem(..)) => {
721 false // foreign items are linked against, not translated.
725 if tcx.is_exported_symbol(def_id) ||
726 tcx.is_foreign_item(def_id)
728 // We can link to the item in question, no instance needed
732 if !tcx.is_mir_available(def_id) {
733 bug!("Cannot create local trans-item for {:?}", def_id)
741 /// For given pair of source and target type that occur in an unsizing coercion,
742 /// this function finds the pair of types that determines the vtable linking
745 /// For example, the source type might be `&SomeStruct` and the target type\
746 /// might be `&SomeTrait` in a cast like:
748 /// let src: &SomeStruct = ...;
749 /// let target = src as &SomeTrait;
751 /// Then the output of this function would be (SomeStruct, SomeTrait) since for
752 /// constructing the `target` fat-pointer we need the vtable for that pair.
754 /// Things can get more complicated though because there's also the case where
755 /// the unsized type occurs as a field:
758 /// struct ComplexStruct<T: ?Sized> {
765 /// In this case, if `T` is sized, `&ComplexStruct<T>` is a thin pointer. If `T`
766 /// is unsized, `&SomeStruct` is a fat pointer, and the vtable it points to is
767 /// for the pair of `T` (which is a trait) and the concrete type that `T` was
768 /// originally coerced from:
770 /// let src: &ComplexStruct<SomeStruct> = ...;
771 /// let target = src as &ComplexStruct<SomeTrait>;
773 /// Again, we want this `find_vtable_types_for_unsizing()` to provide the pair
774 /// `(SomeStruct, SomeTrait)`.
776 /// Finally, there is also the case of custom unsizing coercions, e.g. for
777 /// smart pointers such as `Rc` and `Arc`.
778 fn find_vtable_types_for_unsizing<'a, 'tcx>(scx: &SharedCrateContext<'a, 'tcx>,
779 source_ty: ty::Ty<'tcx>,
780 target_ty: ty::Ty<'tcx>)
781 -> (ty::Ty<'tcx>, ty::Ty<'tcx>) {
782 let ptr_vtable = |inner_source: ty::Ty<'tcx>, inner_target: ty::Ty<'tcx>| {
783 if !scx.type_is_sized(inner_source) {
784 (inner_source, inner_target)
786 scx.tcx().struct_lockstep_tails(inner_source, inner_target)
789 match (&source_ty.sty, &target_ty.sty) {
790 (&ty::TyRef(_, ty::TypeAndMut { ty: a, .. }),
791 &ty::TyRef(_, ty::TypeAndMut { ty: b, .. })) |
792 (&ty::TyRef(_, ty::TypeAndMut { ty: a, .. }),
793 &ty::TyRawPtr(ty::TypeAndMut { ty: b, .. })) |
794 (&ty::TyRawPtr(ty::TypeAndMut { ty: a, .. }),
795 &ty::TyRawPtr(ty::TypeAndMut { ty: b, .. })) => {
798 (&ty::TyAdt(def_a, _), &ty::TyAdt(def_b, _)) if def_a.is_box() && def_b.is_box() => {
799 ptr_vtable(source_ty.boxed_ty(), target_ty.boxed_ty())
802 (&ty::TyAdt(source_adt_def, source_substs),
803 &ty::TyAdt(target_adt_def, target_substs)) => {
804 assert_eq!(source_adt_def, target_adt_def);
807 monomorphize::custom_coerce_unsize_info(scx, source_ty, target_ty);
809 let coerce_index = match kind {
810 CustomCoerceUnsized::Struct(i) => i
813 let source_fields = &source_adt_def.struct_variant().fields;
814 let target_fields = &target_adt_def.struct_variant().fields;
816 assert!(coerce_index < source_fields.len() &&
817 source_fields.len() == target_fields.len());
819 find_vtable_types_for_unsizing(scx,
820 source_fields[coerce_index].ty(scx.tcx(),
822 target_fields[coerce_index].ty(scx.tcx(),
825 _ => bug!("find_vtable_types_for_unsizing: invalid coercion {:?} -> {:?}",
831 fn create_fn_trans_item<'a, 'tcx>(instance: Instance<'tcx>) -> TransItem<'tcx> {
832 debug!("create_fn_trans_item(instance={})", instance);
833 TransItem::Fn(instance)
836 /// Creates a `TransItem` for each method that is referenced by the vtable for
837 /// the given trait/impl pair.
838 fn create_trans_items_for_vtable_methods<'a, 'tcx>(scx: &SharedCrateContext<'a, 'tcx>,
839 trait_ty: ty::Ty<'tcx>,
840 impl_ty: ty::Ty<'tcx>,
841 output: &mut Vec<TransItem<'tcx>>) {
842 assert!(!trait_ty.needs_subst() && !trait_ty.has_escaping_regions() &&
843 !impl_ty.needs_subst() && !impl_ty.has_escaping_regions());
845 if let ty::TyDynamic(ref trait_ty, ..) = trait_ty.sty {
846 if let Some(principal) = trait_ty.principal() {
847 let poly_trait_ref = principal.with_self_ty(scx.tcx(), impl_ty);
848 assert!(!poly_trait_ref.has_escaping_regions());
850 // Walk all methods of the trait, including those of its supertraits
851 let methods = traits::get_vtable_methods(scx.tcx(), poly_trait_ref);
852 let methods = methods.filter_map(|method| method)
853 .map(|(def_id, substs)| monomorphize::resolve(scx, def_id, substs))
854 .filter(|&instance| should_trans_locally(scx.tcx(), &instance))
855 .map(|instance| create_fn_trans_item(instance));
856 output.extend(methods);
858 // Also add the destructor
859 visit_drop_use(scx, impl_ty, false, output);
863 //=-----------------------------------------------------------------------------
865 //=-----------------------------------------------------------------------------
867 struct RootCollector<'b, 'a: 'b, 'tcx: 'a + 'b> {
868 scx: &'b SharedCrateContext<'a, 'tcx>,
869 exported_symbols: &'b ExportedSymbols,
870 mode: TransItemCollectionMode,
871 output: &'b mut Vec<TransItem<'tcx>>,
874 impl<'b, 'a, 'v> ItemLikeVisitor<'v> for RootCollector<'b, 'a, 'v> {
875 fn visit_item(&mut self, item: &'v hir::Item) {
877 hir::ItemExternCrate(..) |
879 hir::ItemForeignMod(..) |
881 hir::ItemDefaultImpl(..) |
883 hir::ItemMod(..) => {
884 // Nothing to do, just keep recursing...
887 hir::ItemImpl(..) => {
888 if self.mode == TransItemCollectionMode::Eager {
889 create_trans_items_for_default_impls(self.scx,
895 hir::ItemEnum(_, ref generics) |
896 hir::ItemStruct(_, ref generics) |
897 hir::ItemUnion(_, ref generics) => {
898 if !generics.is_parameterized() {
899 if self.mode == TransItemCollectionMode::Eager {
900 let def_id = self.scx.tcx().hir.local_def_id(item.id);
901 debug!("RootCollector: ADT drop-glue for {}",
902 def_id_to_string(self.scx.tcx(), def_id));
904 let ty = def_ty(self.scx, def_id, Substs::empty());
905 visit_drop_use(self.scx, ty, true, self.output);
909 hir::ItemGlobalAsm(..) => {
910 debug!("RootCollector: ItemGlobalAsm({})",
911 def_id_to_string(self.scx.tcx(),
912 self.scx.tcx().hir.local_def_id(item.id)));
913 self.output.push(TransItem::GlobalAsm(item.id));
915 hir::ItemStatic(..) => {
916 debug!("RootCollector: ItemStatic({})",
917 def_id_to_string(self.scx.tcx(),
918 self.scx.tcx().hir.local_def_id(item.id)));
919 self.output.push(TransItem::Static(item.id));
921 hir::ItemConst(..) => {
922 // const items only generate translation items if they are
923 // actually used somewhere. Just declaring them is insufficient.
926 let tcx = self.scx.tcx();
927 let def_id = tcx.hir.local_def_id(item.id);
929 if (self.mode == TransItemCollectionMode::Eager ||
930 !tcx.is_const_fn(def_id) ||
931 self.exported_symbols.local_exports().contains(&item.id)) &&
932 !item_has_type_parameters(tcx, def_id) {
934 debug!("RootCollector: ItemFn({})",
935 def_id_to_string(tcx, def_id));
937 let instance = Instance::mono(tcx, def_id);
938 self.output.push(TransItem::Fn(instance));
944 fn visit_trait_item(&mut self, _: &'v hir::TraitItem) {
945 // Even if there's a default body with no explicit generics,
946 // it's still generic over some `Self: Trait`, so not a root.
949 fn visit_impl_item(&mut self, ii: &'v hir::ImplItem) {
951 hir::ImplItemKind::Method(hir::MethodSig { .. }, _) => {
952 let tcx = self.scx.tcx();
953 let def_id = tcx.hir.local_def_id(ii.id);
955 if (self.mode == TransItemCollectionMode::Eager ||
956 !tcx.is_const_fn(def_id) ||
957 self.exported_symbols.local_exports().contains(&ii.id)) &&
958 !item_has_type_parameters(tcx, def_id) {
959 debug!("RootCollector: MethodImplItem({})",
960 def_id_to_string(tcx, def_id));
962 let instance = Instance::mono(tcx, def_id);
963 self.output.push(TransItem::Fn(instance));
966 _ => { /* Nothing to do here */ }
971 fn item_has_type_parameters<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>, def_id: DefId) -> bool {
972 let generics = tcx.generics_of(def_id);
973 generics.parent_types as usize + generics.types.len() > 0
976 fn create_trans_items_for_default_impls<'a, 'tcx>(scx: &SharedCrateContext<'a, 'tcx>,
977 item: &'tcx hir::Item,
978 output: &mut Vec<TransItem<'tcx>>) {
986 ref impl_item_refs) => {
987 if generics.is_type_parameterized() {
991 let impl_def_id = tcx.hir.local_def_id(item.id);
993 debug!("create_trans_items_for_default_impls(item={})",
994 def_id_to_string(tcx, impl_def_id));
996 if let Some(trait_ref) = tcx.impl_trait_ref(impl_def_id) {
997 let callee_substs = tcx.erase_regions(&trait_ref.substs);
998 let overridden_methods: FxHashSet<_> =
999 impl_item_refs.iter()
1000 .map(|iiref| iiref.name)
1002 for method in tcx.provided_trait_methods(trait_ref.def_id) {
1003 if overridden_methods.contains(&method.name) {
1007 if !tcx.generics_of(method.def_id).types.is_empty() {
1012 monomorphize::resolve(scx, method.def_id, callee_substs);
1014 let trans_item = create_fn_trans_item(instance);
1015 if trans_item.is_instantiable(tcx) && should_trans_locally(tcx, &instance) {
1016 output.push(trans_item);
1027 /// Scan the MIR in order to find function calls, closures, and drop-glue
1028 fn collect_neighbours<'a, 'tcx>(scx: &SharedCrateContext<'a, 'tcx>,
1029 instance: Instance<'tcx>,
1030 const_context: bool,
1031 output: &mut Vec<TransItem<'tcx>>)
1033 let mir = scx.tcx().instance_mir(instance.def);
1035 let mut visitor = MirNeighborCollector {
1039 param_substs: instance.substs,
1043 visitor.visit_mir(&mir);
1044 for promoted in &mir.promoted {
1045 visitor.mir = promoted;
1046 visitor.visit_mir(promoted);
1050 fn def_id_to_string<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
1053 let mut output = String::new();
1054 let printer = DefPathBasedNames::new(tcx, false, false);
1055 printer.push_def_path(def_id, &mut output);