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::lang_items::{BoxFreeFnLangItem, ExchangeMallocFnLangItem};
198 use rustc::ty::subst::{Kind, Substs, Subst};
199 use rustc::ty::{self, TypeFoldable, TyCtxt};
200 use rustc::ty::adjustment::CustomCoerceUnsized;
201 use rustc::mir::{self, Location};
202 use rustc::mir::visit as mir_visit;
203 use rustc::mir::visit::Visitor as MirVisitor;
205 use syntax::abi::Abi;
206 use syntax_pos::DUMMY_SP;
207 use base::custom_coerce_unsize_info;
208 use callee::needs_fn_once_adapter_shim;
209 use context::SharedCrateContext;
210 use common::{def_ty, find_method, instance_ty, fulfill_obligation};
211 use glue::{self, DropGlueKind};
212 use monomorphize::{self, Instance};
213 use util::nodemap::{FxHashSet, FxHashMap, DefIdMap};
215 use trans_item::{TransItem, DefPathBasedNames, InstantiationMode};
219 #[derive(PartialEq, Eq, Hash, Clone, Copy, Debug)]
220 pub enum TransItemCollectionMode {
225 /// Maps every translation item to all translation items it references in its
227 pub struct InliningMap<'tcx> {
228 // Maps a source translation item to a range of target translation items
229 // that are potentially inlined by LLVM into the source.
230 // The two numbers in the tuple are the start (inclusive) and
231 // end index (exclusive) within the `targets` vecs.
232 index: FxHashMap<TransItem<'tcx>, (usize, usize)>,
233 targets: Vec<TransItem<'tcx>>,
236 impl<'tcx> InliningMap<'tcx> {
238 fn new() -> InliningMap<'tcx> {
245 fn record_inlining_canditates<I>(&mut self,
246 source: TransItem<'tcx>,
248 where I: Iterator<Item=TransItem<'tcx>>
250 assert!(!self.index.contains_key(&source));
252 let start_index = self.targets.len();
253 self.targets.extend(targets);
254 let end_index = self.targets.len();
255 self.index.insert(source, (start_index, end_index));
258 // Internally iterate over all items referenced by `source` which will be
259 // made available for inlining.
260 pub fn with_inlining_candidates<F>(&self, source: TransItem<'tcx>, mut f: F)
261 where F: FnMut(TransItem<'tcx>) {
262 if let Some(&(start_index, end_index)) = self.index.get(&source)
264 for candidate in &self.targets[start_index .. end_index] {
271 pub fn collect_crate_translation_items<'a, 'tcx>(scx: &SharedCrateContext<'a, 'tcx>,
272 mode: TransItemCollectionMode)
273 -> (FxHashSet<TransItem<'tcx>>,
275 // We are not tracking dependencies of this pass as it has to be re-executed
276 // every time no matter what.
277 scx.tcx().dep_graph.with_ignore(|| {
278 let roots = collect_roots(scx, mode);
280 debug!("Building translation item graph, beginning at roots");
281 let mut visited = FxHashSet();
282 let mut recursion_depths = DefIdMap();
283 let mut inlining_map = InliningMap::new();
286 collect_items_rec(scx,
289 &mut recursion_depths,
293 (visited, inlining_map)
297 // Find all non-generic items by walking the HIR. These items serve as roots to
298 // start monomorphizing from.
299 fn collect_roots<'a, 'tcx>(scx: &SharedCrateContext<'a, 'tcx>,
300 mode: TransItemCollectionMode)
301 -> Vec<TransItem<'tcx>> {
302 debug!("Collecting roots");
303 let mut roots = Vec::new();
306 let mut visitor = RootCollector {
312 scx.tcx().hir.krate().visit_all_item_likes(&mut visitor);
318 // Collect all monomorphized translation items reachable from `starting_point`
319 fn collect_items_rec<'a, 'tcx: 'a>(scx: &SharedCrateContext<'a, 'tcx>,
320 starting_point: TransItem<'tcx>,
321 visited: &mut FxHashSet<TransItem<'tcx>>,
322 recursion_depths: &mut DefIdMap<usize>,
323 inlining_map: &mut InliningMap<'tcx>) {
324 if !visited.insert(starting_point.clone()) {
325 // We've been here already, no need to search again.
328 debug!("BEGIN collect_items_rec({})", starting_point.to_string(scx.tcx()));
330 let mut neighbors = Vec::new();
331 let recursion_depth_reset;
333 match starting_point {
334 TransItem::DropGlue(t) => {
335 find_drop_glue_neighbors(scx, t, &mut neighbors);
336 recursion_depth_reset = None;
338 TransItem::Static(node_id) => {
339 let def_id = scx.tcx().hir.local_def_id(node_id);
340 let instance = Instance::mono(scx.tcx(), def_id);
342 // Sanity check whether this ended up being collected accidentally
343 debug_assert!(should_trans_locally(scx.tcx(), &instance));
345 let ty = instance_ty(scx, &instance);
346 let ty = glue::get_drop_glue_type(scx, ty);
347 neighbors.push(TransItem::DropGlue(DropGlueKind::Ty(ty)));
349 recursion_depth_reset = None;
351 collect_neighbours(scx, instance, &mut neighbors);
353 TransItem::Fn(instance) => {
354 // Sanity check whether this ended up being collected accidentally
355 debug_assert!(should_trans_locally(scx.tcx(), &instance));
357 // Keep track of the monomorphization recursion depth
358 recursion_depth_reset = Some(check_recursion_limit(scx.tcx(),
361 check_type_length_limit(scx.tcx(), instance);
363 collect_neighbours(scx, instance, &mut neighbors);
367 record_inlining_canditates(scx.tcx(), starting_point, &neighbors[..], inlining_map);
369 for neighbour in neighbors {
370 collect_items_rec(scx, neighbour, visited, recursion_depths, inlining_map);
373 if let Some((def_id, depth)) = recursion_depth_reset {
374 recursion_depths.insert(def_id, depth);
377 debug!("END collect_items_rec({})", starting_point.to_string(scx.tcx()));
380 fn record_inlining_canditates<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
381 caller: TransItem<'tcx>,
382 callees: &[TransItem<'tcx>],
383 inlining_map: &mut InliningMap<'tcx>) {
384 let is_inlining_candidate = |trans_item: &TransItem<'tcx>| {
385 trans_item.instantiation_mode(tcx) == InstantiationMode::LocalCopy
388 let inlining_candidates = callees.into_iter()
390 .filter(is_inlining_candidate);
392 inlining_map.record_inlining_canditates(caller, inlining_candidates);
395 fn check_recursion_limit<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
396 instance: Instance<'tcx>,
397 recursion_depths: &mut DefIdMap<usize>)
399 let def_id = instance.def_id();
400 let recursion_depth = recursion_depths.get(&def_id).cloned().unwrap_or(0);
401 debug!(" => recursion depth={}", recursion_depth);
403 // Code that needs to instantiate the same function recursively
404 // more than the recursion limit is assumed to be causing an
405 // infinite expansion.
406 if recursion_depth > tcx.sess.recursion_limit.get() {
407 let error = format!("reached the recursion limit while instantiating `{}`",
409 if let Some(node_id) = tcx.hir.as_local_node_id(def_id) {
410 tcx.sess.span_fatal(tcx.hir.span(node_id), &error);
412 tcx.sess.fatal(&error);
416 recursion_depths.insert(def_id, recursion_depth + 1);
418 (def_id, recursion_depth)
421 fn check_type_length_limit<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
422 instance: Instance<'tcx>)
424 let type_length = instance.substs.types().flat_map(|ty| ty.walk()).count();
425 debug!(" => type length={}", type_length);
427 // Rust code can easily create exponentially-long types using only a
428 // polynomial recursion depth. Even with the default recursion
429 // depth, you can easily get cases that take >2^60 steps to run,
430 // which means that rustc basically hangs.
432 // Bail out in these cases to avoid that bad user experience.
433 let type_length_limit = tcx.sess.type_length_limit.get();
434 if type_length > type_length_limit {
435 // The instance name is already known to be too long for rustc. Use
436 // `{:.64}` to avoid blasting the user's terminal with thousands of
437 // lines of type-name.
438 let instance_name = instance.to_string();
439 let msg = format!("reached the type-length limit while instantiating `{:.64}...`",
441 let mut diag = if let Some(node_id) = tcx.hir.as_local_node_id(instance.def_id()) {
442 tcx.sess.struct_span_fatal(tcx.hir.span(node_id), &msg)
444 tcx.sess.struct_fatal(&msg)
448 "consider adding a `#![type_length_limit=\"{}\"]` attribute to your crate",
449 type_length_limit*2));
451 tcx.sess.abort_if_errors();
455 struct MirNeighborCollector<'a, 'tcx: 'a> {
456 scx: &'a SharedCrateContext<'a, 'tcx>,
457 mir: &'a mir::Mir<'tcx>,
458 output: &'a mut Vec<TransItem<'tcx>>,
459 param_substs: &'tcx Substs<'tcx>
462 impl<'a, 'tcx> MirVisitor<'tcx> for MirNeighborCollector<'a, 'tcx> {
464 fn visit_rvalue(&mut self, rvalue: &mir::Rvalue<'tcx>, location: Location) {
465 debug!("visiting rvalue {:?}", *rvalue);
468 // When doing an cast from a regular pointer to a fat pointer, we
469 // have to instantiate all methods of the trait being cast to, so we
470 // can build the appropriate vtable.
471 mir::Rvalue::Cast(mir::CastKind::Unsize, ref operand, target_ty) => {
472 let target_ty = monomorphize::apply_param_substs(self.scx,
475 let source_ty = operand.ty(self.mir, self.scx.tcx());
476 let source_ty = monomorphize::apply_param_substs(self.scx,
479 let (source_ty, target_ty) = find_vtable_types_for_unsizing(self.scx,
482 // This could also be a different Unsize instruction, like
483 // from a fixed sized array to a slice. But we are only
484 // interested in things that produce a vtable.
485 if target_ty.is_trait() && !source_ty.is_trait() {
486 create_trans_items_for_vtable_methods(self.scx,
492 mir::Rvalue::Cast(mir::CastKind::ClosureFnPointer, ref operand, _) => {
493 let source_ty = operand.ty(self.mir, self.scx.tcx());
494 match source_ty.sty {
495 ty::TyClosure(def_id, substs) => {
496 let substs = monomorphize::apply_param_substs(
497 self.scx, self.param_substs, &substs.substs);
498 self.output.push(create_fn_trans_item(
499 Instance::new(def_id, substs)
505 mir::Rvalue::Box(..) => {
506 let tcx = self.scx.tcx();
507 let exchange_malloc_fn_def_id = tcx
509 .require(ExchangeMallocFnLangItem)
510 .unwrap_or_else(|e| self.scx.sess().fatal(&e));
511 let instance = Instance::mono(tcx, exchange_malloc_fn_def_id);
512 if should_trans_locally(tcx, &instance) {
513 self.output.push(create_fn_trans_item(instance));
516 _ => { /* not interesting */ }
519 self.super_rvalue(rvalue, location);
522 fn visit_lvalue(&mut self,
523 lvalue: &mir::Lvalue<'tcx>,
524 context: mir_visit::LvalueContext<'tcx>,
525 location: Location) {
526 debug!("visiting lvalue {:?}", *lvalue);
528 if let mir_visit::LvalueContext::Drop = context {
529 let ty = lvalue.ty(self.mir, self.scx.tcx())
530 .to_ty(self.scx.tcx());
532 let ty = monomorphize::apply_param_substs(self.scx,
535 assert!(ty.is_normalized_for_trans());
536 let ty = glue::get_drop_glue_type(self.scx, ty);
537 self.output.push(TransItem::DropGlue(DropGlueKind::Ty(ty)));
540 self.super_lvalue(lvalue, context, location);
543 fn visit_operand(&mut self, operand: &mir::Operand<'tcx>, location: Location) {
544 debug!("visiting operand {:?}", *operand);
546 let callee = match *operand {
547 mir::Operand::Constant(ref constant) => {
548 if let ty::TyFnDef(def_id, substs, _) = constant.ty.sty {
549 // This is something that can act as a callee, proceed
550 Some((def_id, substs))
552 // This is not a callee, but we still have to look for
553 // references to `const` items
554 if let mir::Literal::Item { def_id, substs } = constant.literal {
555 let substs = monomorphize::apply_param_substs(self.scx,
558 let instance = monomorphize::resolve_const(self.scx, def_id, substs);
559 collect_neighbours(self.scx, instance, self.output);
568 if let Some((callee_def_id, callee_substs)) = callee {
569 debug!(" => operand is callable");
571 // `callee_def_id` might refer to a trait method instead of a
572 // concrete implementation, so we have to find the actual
573 // implementation. For example, the call might look like
575 // std::cmp::partial_cmp(0i32, 1i32)
577 // Calling do_static_dispatch() here will map the def_id of
578 // `std::cmp::partial_cmp` to the def_id of `i32::partial_cmp<i32>`
580 let callee_substs = monomorphize::apply_param_substs(self.scx,
583 let dispatched = do_static_dispatch(self.scx,
587 if let StaticDispatchResult::Dispatched {
588 instance, fn_once_adjustment
590 // if we have a concrete impl (which we might not have
591 // in the case of something compiler generated like an
592 // object shim or a closure that is handled differently),
593 // we check if the callee is something that will actually
594 // result in a translation item ...
595 if should_trans_locally(self.scx.tcx(), &instance) {
596 self.output.push(create_fn_trans_item(instance));
598 // This call will instantiate an FnOnce adapter, which drops
599 // the closure environment. Therefore we need to make sure
600 // that we collect the drop-glue for the environment type.
601 if let Some(env_ty) = fn_once_adjustment {
602 let env_ty = glue::get_drop_glue_type(self.scx, env_ty);
603 if self.scx.type_needs_drop(env_ty) {
604 let dg = DropGlueKind::Ty(env_ty);
605 self.output.push(TransItem::DropGlue(dg));
612 self.super_operand(operand, location);
615 // This takes care of the "drop_in_place" intrinsic for which we otherwise
616 // we would not register drop-glues.
617 fn visit_terminator_kind(&mut self,
618 block: mir::BasicBlock,
619 kind: &mir::TerminatorKind<'tcx>,
620 location: Location) {
621 let tcx = self.scx.tcx();
623 mir::TerminatorKind::Call {
624 func: mir::Operand::Constant(ref constant),
628 match constant.ty.sty {
629 ty::TyFnDef(def_id, _, bare_fn_ty)
630 if is_drop_in_place_intrinsic(tcx, def_id, bare_fn_ty) => {
631 let operand_ty = args[0].ty(self.mir, tcx);
632 if let ty::TyRawPtr(mt) = operand_ty.sty {
633 let operand_ty = monomorphize::apply_param_substs(self.scx,
636 let ty = glue::get_drop_glue_type(self.scx, operand_ty);
637 self.output.push(TransItem::DropGlue(DropGlueKind::Ty(ty)));
639 bug!("Has the drop_in_place() intrinsic's signature changed?")
642 _ => { /* Nothing to do. */ }
645 _ => { /* Nothing to do. */ }
648 self.super_terminator_kind(block, kind, location);
650 fn is_drop_in_place_intrinsic<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
652 bare_fn_ty: ty::PolyFnSig<'tcx>)
654 (bare_fn_ty.abi() == Abi::RustIntrinsic ||
655 bare_fn_ty.abi() == Abi::PlatformIntrinsic) &&
656 tcx.item_name(def_id) == "drop_in_place"
661 // Returns true if we should translate an instance in the local crate.
662 // Returns false if we can just link to the upstream crate and therefore don't
663 // need a translation item.
664 fn should_trans_locally<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>, instance: &Instance<'tcx>)
666 let def_id = match instance.def {
667 ty::InstanceDef::Item(def_id) => def_id,
668 ty::InstanceDef::FnPtrShim(..) => return true
670 match tcx.hir.get_if_local(def_id) {
671 Some(hir_map::NodeForeignItem(..)) => {
672 false // foreign items are linked against, not translated.
676 if tcx.sess.cstore.is_exported_symbol(def_id) ||
677 tcx.sess.cstore.is_foreign_item(def_id)
679 // We can link to the item in question, no instance needed
683 if !tcx.sess.cstore.is_item_mir_available(def_id) {
684 bug!("Cannot create local trans-item for {:?}", def_id)
692 fn find_drop_glue_neighbors<'a, 'tcx>(scx: &SharedCrateContext<'a, 'tcx>,
693 dg: DropGlueKind<'tcx>,
694 output: &mut Vec<TransItem<'tcx>>) {
696 DropGlueKind::Ty(ty) => ty,
697 DropGlueKind::TyContents(_) => {
698 // We already collected the neighbors of this item via the
699 // DropGlueKind::Ty variant.
704 debug!("find_drop_glue_neighbors: {}", type_to_string(scx.tcx(), ty));
706 // Make sure the BoxFreeFn lang-item gets translated if there is a boxed value.
709 let def_id = tcx.require_lang_item(BoxFreeFnLangItem);
710 let box_free_instance = Instance::new(
712 tcx.mk_substs(iter::once(Kind::from(ty.boxed_ty())))
714 if should_trans_locally(tcx, &box_free_instance) {
715 output.push(create_fn_trans_item(box_free_instance));
719 // If the type implements Drop, also add a translation item for the
720 // monomorphized Drop::drop() implementation.
721 let destructor = match ty.sty {
722 ty::TyAdt(def, _) => def.destructor(scx.tcx()),
726 if let (Some(destructor), false) = (destructor, ty.is_box()) {
727 use rustc::ty::ToPolyTraitRef;
729 let drop_trait_def_id = scx.tcx()
734 let self_type_substs = scx.tcx().mk_substs_trait(ty, &[]);
736 let trait_ref = ty::TraitRef {
737 def_id: drop_trait_def_id,
738 substs: self_type_substs,
739 }.to_poly_trait_ref();
741 let substs = match fulfill_obligation(scx, DUMMY_SP, trait_ref) {
742 traits::VtableImpl(data) => data.substs,
745 let instance = Instance::new(destructor.did, substs);
746 if should_trans_locally(scx.tcx(), &instance) {
747 output.push(create_fn_trans_item(instance));
750 // This type has a Drop implementation, we'll need the contents-only
751 // version of the glue too.
752 output.push(TransItem::DropGlue(DropGlueKind::TyContents(ty)));
755 // Finally add the types of nested values
768 ty::TyDynamic(..) => {
771 ty::TyAdt(def, _) if def.is_box() => {
772 let inner_type = glue::get_drop_glue_type(scx, ty.boxed_ty());
773 if scx.type_needs_drop(inner_type) {
774 output.push(TransItem::DropGlue(DropGlueKind::Ty(inner_type)));
777 ty::TyAdt(def, substs) => {
778 for field in def.all_fields() {
779 let field_type = def_ty(scx, field.did, substs);
780 let field_type = glue::get_drop_glue_type(scx, field_type);
782 if scx.type_needs_drop(field_type) {
783 output.push(TransItem::DropGlue(DropGlueKind::Ty(field_type)));
787 ty::TyClosure(def_id, substs) => {
788 for upvar_ty in substs.upvar_tys(def_id, scx.tcx()) {
789 let upvar_ty = glue::get_drop_glue_type(scx, upvar_ty);
790 if scx.type_needs_drop(upvar_ty) {
791 output.push(TransItem::DropGlue(DropGlueKind::Ty(upvar_ty)));
795 ty::TySlice(inner_type) |
796 ty::TyArray(inner_type, _) => {
797 let inner_type = glue::get_drop_glue_type(scx, inner_type);
798 if scx.type_needs_drop(inner_type) {
799 output.push(TransItem::DropGlue(DropGlueKind::Ty(inner_type)));
802 ty::TyTuple(args, _) => {
804 let arg = glue::get_drop_glue_type(scx, arg);
805 if scx.type_needs_drop(arg) {
806 output.push(TransItem::DropGlue(DropGlueKind::Ty(arg)));
810 ty::TyProjection(_) |
815 bug!("encountered unexpected type");
820 enum StaticDispatchResult<'tcx> {
821 // The call could be resolved statically as going to the method with
824 instance: Instance<'tcx>,
825 // If this is a call to a closure that needs an FnOnce adjustment,
826 // this contains the new self type of the call (= type of the closure
828 fn_once_adjustment: Option<ty::Ty<'tcx>>,
830 // This goes to somewhere that we don't know at compile-time
834 fn do_static_dispatch<'a, 'tcx>(scx: &SharedCrateContext<'a, 'tcx>,
836 fn_substs: &'tcx Substs<'tcx>)
837 -> StaticDispatchResult<'tcx> {
838 debug!("do_static_dispatch(fn_def_id={}, fn_substs={:?})",
839 def_id_to_string(scx.tcx(), fn_def_id),
841 if let Some(trait_def_id) = scx.tcx().trait_of_item(fn_def_id) {
842 debug!(" => trait method, attempting to find impl");
843 do_static_trait_method_dispatch(scx,
844 &scx.tcx().associated_item(fn_def_id),
848 debug!(" => regular function");
849 // The function is not part of an impl or trait, no dispatching
851 StaticDispatchResult::Dispatched {
852 instance: Instance::new(fn_def_id, fn_substs),
853 fn_once_adjustment: None,
858 // Given a trait-method and substitution information, find out the actual
859 // implementation of the trait method.
860 fn do_static_trait_method_dispatch<'a, 'tcx>(scx: &SharedCrateContext<'a, 'tcx>,
861 trait_method: &ty::AssociatedItem,
863 rcvr_substs: &'tcx Substs<'tcx>)
864 -> StaticDispatchResult<'tcx> {
866 debug!("do_static_trait_method_dispatch(trait_method={}, \
869 def_id_to_string(scx.tcx(), trait_method.def_id),
870 def_id_to_string(scx.tcx(), trait_id),
873 let trait_ref = ty::TraitRef::from_method(tcx, trait_id, rcvr_substs);
874 let vtbl = fulfill_obligation(scx, DUMMY_SP, ty::Binder(trait_ref));
876 // Now that we know which impl is being used, we can dispatch to
877 // the actual function:
879 traits::VtableImpl(impl_data) => {
880 StaticDispatchResult::Dispatched {
881 instance: find_method(tcx, trait_method.name, rcvr_substs, &impl_data),
882 fn_once_adjustment: None,
885 traits::VtableClosure(closure_data) => {
886 let closure_def_id = closure_data.closure_def_id;
887 let trait_closure_kind = tcx.lang_items.fn_trait_kind(trait_id).unwrap();
888 let actual_closure_kind = tcx.closure_kind(closure_def_id);
890 let needs_fn_once_adapter_shim =
891 match needs_fn_once_adapter_shim(actual_closure_kind,
892 trait_closure_kind) {
897 let fn_once_adjustment = if needs_fn_once_adapter_shim {
898 Some(tcx.mk_closure_from_closure_substs(closure_def_id,
899 closure_data.substs))
904 StaticDispatchResult::Dispatched {
905 instance: Instance::new(closure_def_id, closure_data.substs.substs),
906 fn_once_adjustment: fn_once_adjustment,
909 traits::VtableFnPointer(ref data) => {
910 // If we know the destination of this fn-pointer, we'll have to make
911 // sure that this destination actually gets instantiated.
912 if let ty::TyFnDef(def_id, substs, _) = data.fn_ty.sty {
913 // The destination of the pointer might be something that needs
914 // further dispatching, such as a trait method, so we do that.
915 do_static_dispatch(scx, def_id, substs)
917 StaticDispatchResult::Unknown
920 // Trait object shims are always instantiated in-place, and as they are
921 // just an ABI-adjusting indirect call they do not have any dependencies.
922 traits::VtableObject(..) => {
923 StaticDispatchResult::Unknown
926 bug!("static call to invalid vtable: {:?}", vtbl)
931 /// For given pair of source and target type that occur in an unsizing coercion,
932 /// this function finds the pair of types that determines the vtable linking
935 /// For example, the source type might be `&SomeStruct` and the target type\
936 /// might be `&SomeTrait` in a cast like:
938 /// let src: &SomeStruct = ...;
939 /// let target = src as &SomeTrait;
941 /// Then the output of this function would be (SomeStruct, SomeTrait) since for
942 /// constructing the `target` fat-pointer we need the vtable for that pair.
944 /// Things can get more complicated though because there's also the case where
945 /// the unsized type occurs as a field:
948 /// struct ComplexStruct<T: ?Sized> {
955 /// In this case, if `T` is sized, `&ComplexStruct<T>` is a thin pointer. If `T`
956 /// is unsized, `&SomeStruct` is a fat pointer, and the vtable it points to is
957 /// for the pair of `T` (which is a trait) and the concrete type that `T` was
958 /// originally coerced from:
960 /// let src: &ComplexStruct<SomeStruct> = ...;
961 /// let target = src as &ComplexStruct<SomeTrait>;
963 /// Again, we want this `find_vtable_types_for_unsizing()` to provide the pair
964 /// `(SomeStruct, SomeTrait)`.
966 /// Finally, there is also the case of custom unsizing coercions, e.g. for
967 /// smart pointers such as `Rc` and `Arc`.
968 fn find_vtable_types_for_unsizing<'a, 'tcx>(scx: &SharedCrateContext<'a, 'tcx>,
969 source_ty: ty::Ty<'tcx>,
970 target_ty: ty::Ty<'tcx>)
971 -> (ty::Ty<'tcx>, ty::Ty<'tcx>) {
972 let ptr_vtable = |inner_source: ty::Ty<'tcx>, inner_target: ty::Ty<'tcx>| {
973 if !scx.type_is_sized(inner_source) {
974 (inner_source, inner_target)
976 scx.tcx().struct_lockstep_tails(inner_source, inner_target)
979 match (&source_ty.sty, &target_ty.sty) {
980 (&ty::TyRef(_, ty::TypeAndMut { ty: a, .. }),
981 &ty::TyRef(_, ty::TypeAndMut { ty: b, .. })) |
982 (&ty::TyRef(_, ty::TypeAndMut { ty: a, .. }),
983 &ty::TyRawPtr(ty::TypeAndMut { ty: b, .. })) |
984 (&ty::TyRawPtr(ty::TypeAndMut { ty: a, .. }),
985 &ty::TyRawPtr(ty::TypeAndMut { ty: b, .. })) => {
988 (&ty::TyAdt(def_a, _), &ty::TyAdt(def_b, _)) if def_a.is_box() && def_b.is_box() => {
989 ptr_vtable(source_ty.boxed_ty(), target_ty.boxed_ty())
992 (&ty::TyAdt(source_adt_def, source_substs),
993 &ty::TyAdt(target_adt_def, target_substs)) => {
994 assert_eq!(source_adt_def, target_adt_def);
996 let kind = custom_coerce_unsize_info(scx, source_ty, target_ty);
998 let coerce_index = match kind {
999 CustomCoerceUnsized::Struct(i) => i
1002 let source_fields = &source_adt_def.struct_variant().fields;
1003 let target_fields = &target_adt_def.struct_variant().fields;
1005 assert!(coerce_index < source_fields.len() &&
1006 source_fields.len() == target_fields.len());
1008 find_vtable_types_for_unsizing(scx,
1009 source_fields[coerce_index].ty(scx.tcx(),
1011 target_fields[coerce_index].ty(scx.tcx(),
1014 _ => bug!("find_vtable_types_for_unsizing: invalid coercion {:?} -> {:?}",
1020 fn create_fn_trans_item<'a, 'tcx>(instance: Instance<'tcx>) -> TransItem<'tcx> {
1021 debug!("create_fn_trans_item(instance={})", instance);
1022 TransItem::Fn(instance)
1025 /// Creates a `TransItem` for each method that is referenced by the vtable for
1026 /// the given trait/impl pair.
1027 fn create_trans_items_for_vtable_methods<'a, 'tcx>(scx: &SharedCrateContext<'a, 'tcx>,
1028 trait_ty: ty::Ty<'tcx>,
1029 impl_ty: ty::Ty<'tcx>,
1030 output: &mut Vec<TransItem<'tcx>>) {
1031 assert!(!trait_ty.needs_subst() && !trait_ty.has_escaping_regions() &&
1032 !impl_ty.needs_subst() && !impl_ty.has_escaping_regions());
1034 if let ty::TyDynamic(ref trait_ty, ..) = trait_ty.sty {
1035 if let Some(principal) = trait_ty.principal() {
1036 let poly_trait_ref = principal.with_self_ty(scx.tcx(), impl_ty);
1037 assert!(!poly_trait_ref.has_escaping_regions());
1039 // Walk all methods of the trait, including those of its supertraits
1040 let methods = traits::get_vtable_methods(scx.tcx(), poly_trait_ref);
1041 let methods = methods.filter_map(|method| method)
1042 .filter_map(|(def_id, substs)| {
1043 if let StaticDispatchResult::Dispatched {
1045 // We already add the drop-glue for the closure env
1046 // unconditionally below.
1047 fn_once_adjustment: _ ,
1048 } = do_static_dispatch(scx, def_id, substs) {
1054 .filter(|&instance| should_trans_locally(scx.tcx(), &instance))
1055 .map(|instance| create_fn_trans_item(instance));
1056 output.extend(methods);
1058 // Also add the destructor
1059 let dg_type = glue::get_drop_glue_type(scx, impl_ty);
1060 output.push(TransItem::DropGlue(DropGlueKind::Ty(dg_type)));
1064 //=-----------------------------------------------------------------------------
1066 //=-----------------------------------------------------------------------------
1068 struct RootCollector<'b, 'a: 'b, 'tcx: 'a + 'b> {
1069 scx: &'b SharedCrateContext<'a, 'tcx>,
1070 mode: TransItemCollectionMode,
1071 output: &'b mut Vec<TransItem<'tcx>>,
1074 impl<'b, 'a, 'v> ItemLikeVisitor<'v> for RootCollector<'b, 'a, 'v> {
1075 fn visit_item(&mut self, item: &'v hir::Item) {
1077 hir::ItemExternCrate(..) |
1079 hir::ItemForeignMod(..) |
1081 hir::ItemDefaultImpl(..) |
1082 hir::ItemTrait(..) |
1083 hir::ItemMod(..) => {
1084 // Nothing to do, just keep recursing...
1087 hir::ItemImpl(..) => {
1088 if self.mode == TransItemCollectionMode::Eager {
1089 create_trans_items_for_default_impls(self.scx,
1095 hir::ItemEnum(_, ref generics) |
1096 hir::ItemStruct(_, ref generics) |
1097 hir::ItemUnion(_, ref generics) => {
1098 if !generics.is_parameterized() {
1099 if self.mode == TransItemCollectionMode::Eager {
1100 let def_id = self.scx.tcx().hir.local_def_id(item.id);
1101 debug!("RootCollector: ADT drop-glue for {}",
1102 def_id_to_string(self.scx.tcx(), def_id));
1104 let ty = def_ty(self.scx, def_id, Substs::empty());
1105 let ty = glue::get_drop_glue_type(self.scx, ty);
1106 self.output.push(TransItem::DropGlue(DropGlueKind::Ty(ty)));
1110 hir::ItemStatic(..) => {
1111 debug!("RootCollector: ItemStatic({})",
1112 def_id_to_string(self.scx.tcx(),
1113 self.scx.tcx().hir.local_def_id(item.id)));
1114 self.output.push(TransItem::Static(item.id));
1116 hir::ItemConst(..) => {
1117 // const items only generate translation items if they are
1118 // actually used somewhere. Just declaring them is insufficient.
1120 hir::ItemFn(.., ref generics, _) => {
1121 if !generics.is_type_parameterized() {
1122 let def_id = self.scx.tcx().hir.local_def_id(item.id);
1124 debug!("RootCollector: ItemFn({})",
1125 def_id_to_string(self.scx.tcx(), def_id));
1127 let instance = Instance::mono(self.scx.tcx(), def_id);
1128 self.output.push(TransItem::Fn(instance));
1134 fn visit_trait_item(&mut self, _: &'v hir::TraitItem) {
1135 // Even if there's a default body with no explicit generics,
1136 // it's still generic over some `Self: Trait`, so not a root.
1139 fn visit_impl_item(&mut self, ii: &'v hir::ImplItem) {
1141 hir::ImplItemKind::Method(hir::MethodSig {
1145 let hir_map = &self.scx.tcx().hir;
1146 let parent_node_id = hir_map.get_parent_node(ii.id);
1147 let is_impl_generic = match hir_map.expect_item(parent_node_id) {
1149 node: hir::ItemImpl(_, _, ref generics, ..),
1152 generics.is_type_parameterized()
1159 if !generics.is_type_parameterized() && !is_impl_generic {
1160 let def_id = self.scx.tcx().hir.local_def_id(ii.id);
1162 debug!("RootCollector: MethodImplItem({})",
1163 def_id_to_string(self.scx.tcx(), def_id));
1165 let instance = Instance::mono(self.scx.tcx(), def_id);
1166 self.output.push(TransItem::Fn(instance));
1169 _ => { /* Nothing to do here */ }
1174 fn create_trans_items_for_default_impls<'a, 'tcx>(scx: &SharedCrateContext<'a, 'tcx>,
1175 item: &'tcx hir::Item,
1176 output: &mut Vec<TransItem<'tcx>>) {
1177 let tcx = scx.tcx();
1183 ref impl_item_refs) => {
1184 if generics.is_type_parameterized() {
1188 let impl_def_id = tcx.hir.local_def_id(item.id);
1190 debug!("create_trans_items_for_default_impls(item={})",
1191 def_id_to_string(tcx, impl_def_id));
1193 if let Some(trait_ref) = tcx.impl_trait_ref(impl_def_id) {
1194 let callee_substs = tcx.erase_regions(&trait_ref.substs);
1195 let overridden_methods: FxHashSet<_> =
1196 impl_item_refs.iter()
1197 .map(|iiref| iiref.name)
1199 for method in tcx.provided_trait_methods(trait_ref.def_id) {
1200 if overridden_methods.contains(&method.name) {
1204 if !tcx.item_generics(method.def_id).types.is_empty() {
1208 // The substitutions we have are on the impl, so we grab
1209 // the method type from the impl to substitute into.
1210 let impl_substs = tcx.empty_substs_for_def_id(impl_def_id);
1211 let impl_data = traits::VtableImplData {
1212 impl_def_id: impl_def_id,
1213 substs: impl_substs,
1216 let instance = find_method(tcx, method.name, callee_substs, &impl_data);
1218 let predicates = tcx.item_predicates(instance.def_id()).predicates
1219 .subst(tcx, impl_substs);
1220 if !traits::normalize_and_test_predicates(tcx, predicates) {
1224 if should_trans_locally(tcx, &instance) {
1225 output.push(create_fn_trans_item(instance));
1236 /// Scan the MIR in order to find function calls, closures, and drop-glue
1237 fn collect_neighbours<'a, 'tcx>(scx: &SharedCrateContext<'a, 'tcx>,
1238 instance: Instance<'tcx>,
1239 output: &mut Vec<TransItem<'tcx>>)
1241 let mir = scx.tcx().instance_mir(instance.def);
1243 let mut visitor = MirNeighborCollector {
1247 param_substs: instance.substs
1250 visitor.visit_mir(&mir);
1251 for promoted in &mir.promoted {
1252 visitor.mir = promoted;
1253 visitor.visit_mir(promoted);
1257 fn def_id_to_string<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
1260 let mut output = String::new();
1261 let printer = DefPathBasedNames::new(tcx, false, false);
1262 printer.push_def_path(def_id, &mut output);
1266 fn type_to_string<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
1269 let mut output = String::new();
1270 let printer = DefPathBasedNames::new(tcx, false, false);
1271 printer.push_type_name(ty, &mut output);