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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.
4 //
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.
10
11 //! Translation Item Collection
12 //! ===========================
13 //!
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.
24 //!
25 //! The following kinds of "translation items" are handled here:
26 //!
27 //! - Functions
28 //! - Methods
29 //! - Closures
30 //! - Statics
31 //! - Drop glue
32 //!
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
35 //! codegen unit:
36 //!
37 //! - Constants
38 //! - Vtables
39 //! - Object Shims
40 //!
41 //!
42 //! General Algorithm
43 //! -----------------
44 //! Let's define some terms first:
45 //!
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
53 //!   for B.
54 //!
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".
58 //!
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.
61 //!
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:
64 //!
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.
69 //!
70 //! ### Discovering roots
71 //!
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.
77 //!
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:
86 //!
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.
94 //!
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:
99 //!
100 //! ```rust
101 //! fn print_val<T: Display>(x: T) {
102 //!     println!("{}", x);
103 //! }
104 //!
105 //! fn call_fn(f: &Fn(i32), x: i32) {
106 //!     f(x);
107 //! }
108 //!
109 //! fn main() {
110 //!     let print_i32 = print_val::<i32>;
111 //!     call_fn(&print_i32, 0);
112 //! }
113 //! ```
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.
119 //!
120 //! #### Closures
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.
125 //!
126 //! #### Drop glue
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.
132 //!
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.
139 //!
140 //! #### Boxes
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.
145 //!
146 //!
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
152 //! #[inline].
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.
159 //!
160 //! Eager and Lazy Collection Mode
161 //! ------------------------------
162 //! Translation item collection can be performed in one of two modes:
163 //!
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
166 //!   possible.
167 //!
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.
174 //!
175 //!
176 //! Open Issues
177 //! -----------
178 //! Some things are not yet fully implemented in the current version of this
179 //! module.
180 //!
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.
184 //!
185 //! ### Const Fns
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.
190
191 use rustc::hir;
192 use rustc::hir::itemlikevisit::ItemLikeVisitor;
193
194 use rustc::hir::map as hir_map;
195 use rustc::hir::def_id::DefId;
196 use rustc::middle::lang_items::{BoxFreeFnLangItem, ExchangeMallocFnLangItem};
197 use rustc::traits;
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;
204
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::fulfill_obligation;
211 use glue::{self, DropGlueKind};
212 use monomorphize::{self, Instance};
213 use util::nodemap::{FxHashSet, FxHashMap, DefIdMap};
214
215 use trans_item::{TransItem, DefPathBasedNames, InstantiationMode};
216
217 use std::iter;
218
219 #[derive(PartialEq, Eq, Hash, Clone, Copy, Debug)]
220 pub enum TransItemCollectionMode {
221     Eager,
222     Lazy
223 }
224
225 /// Maps every translation item to all translation items it references in its
226 /// body.
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>>,
234 }
235
236 impl<'tcx> InliningMap<'tcx> {
237
238     fn new() -> InliningMap<'tcx> {
239         InliningMap {
240             index: FxHashMap(),
241             targets: Vec::new(),
242         }
243     }
244
245     fn record_inlining_canditates<I>(&mut self,
246                                      source: TransItem<'tcx>,
247                                      targets: I)
248         where I: Iterator<Item=TransItem<'tcx>>
249     {
250         assert!(!self.index.contains_key(&source));
251
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));
256     }
257
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)
263         {
264             for candidate in &self.targets[start_index .. end_index] {
265                 f(*candidate)
266             }
267         }
268     }
269 }
270
271 pub fn collect_crate_translation_items<'a, 'tcx>(scx: &SharedCrateContext<'a, 'tcx>,
272                                                  mode: TransItemCollectionMode)
273                                                  -> (FxHashSet<TransItem<'tcx>>,
274                                                      InliningMap<'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);
279
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();
284
285         for root in roots {
286             collect_items_rec(scx,
287                               root,
288                               &mut visited,
289                               &mut recursion_depths,
290                               &mut inlining_map);
291         }
292
293         (visited, inlining_map)
294     })
295 }
296
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();
304
305     {
306         let mut visitor = RootCollector {
307             scx: scx,
308             mode: mode,
309             output: &mut roots,
310         };
311
312         scx.tcx().hir.krate().visit_all_item_likes(&mut visitor);
313     }
314
315     roots
316 }
317
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.
326         return;
327     }
328     debug!("BEGIN collect_items_rec({})", starting_point.to_string(scx.tcx()));
329
330     let mut neighbors = Vec::new();
331     let recursion_depth_reset;
332
333     match starting_point {
334         TransItem::DropGlue(t) => {
335             find_drop_glue_neighbors(scx, t, &mut neighbors);
336             recursion_depth_reset = None;
337         }
338         TransItem::Static(node_id) => {
339             let def_id = scx.tcx().hir.local_def_id(node_id);
340
341             // Sanity check whether this ended up being collected accidentally
342             debug_assert!(should_trans_locally(scx.tcx(), def_id));
343
344             let ty = scx.tcx().item_type(def_id);
345             let ty = glue::get_drop_glue_type(scx, ty);
346             neighbors.push(TransItem::DropGlue(DropGlueKind::Ty(ty)));
347
348             recursion_depth_reset = None;
349
350             collect_neighbours(scx, Instance::mono(scx, def_id), &mut neighbors);
351         }
352         TransItem::Fn(instance) => {
353             // Sanity check whether this ended up being collected accidentally
354             debug_assert!(should_trans_locally(scx.tcx(), instance.def));
355
356             // Keep track of the monomorphization recursion depth
357             recursion_depth_reset = Some(check_recursion_limit(scx.tcx(),
358                                                                instance,
359                                                                recursion_depths));
360             check_type_length_limit(scx.tcx(), instance);
361
362             collect_neighbours(scx, instance, &mut neighbors);
363         }
364     }
365
366     record_inlining_canditates(scx.tcx(), starting_point, &neighbors[..], inlining_map);
367
368     for neighbour in neighbors {
369         collect_items_rec(scx, neighbour, visited, recursion_depths, inlining_map);
370     }
371
372     if let Some((def_id, depth)) = recursion_depth_reset {
373         recursion_depths.insert(def_id, depth);
374     }
375
376     debug!("END collect_items_rec({})", starting_point.to_string(scx.tcx()));
377 }
378
379 fn record_inlining_canditates<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
380                                         caller: TransItem<'tcx>,
381                                         callees: &[TransItem<'tcx>],
382                                         inlining_map: &mut InliningMap<'tcx>) {
383     let is_inlining_candidate = |trans_item: &TransItem<'tcx>| {
384         trans_item.instantiation_mode(tcx) == InstantiationMode::LocalCopy
385     };
386
387     let inlining_candidates = callees.into_iter()
388                                      .map(|x| *x)
389                                      .filter(is_inlining_candidate);
390
391     inlining_map.record_inlining_canditates(caller, inlining_candidates);
392 }
393
394 fn check_recursion_limit<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
395                                    instance: Instance<'tcx>,
396                                    recursion_depths: &mut DefIdMap<usize>)
397                                    -> (DefId, usize) {
398     let recursion_depth = recursion_depths.get(&instance.def)
399                                           .map(|x| *x)
400                                           .unwrap_or(0);
401     debug!(" => recursion depth={}", recursion_depth);
402
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 `{}`",
408                             instance);
409         if let Some(node_id) = tcx.hir.as_local_node_id(instance.def) {
410             tcx.sess.span_fatal(tcx.hir.span(node_id), &error);
411         } else {
412             tcx.sess.fatal(&error);
413         }
414     }
415
416     recursion_depths.insert(instance.def, recursion_depth + 1);
417
418     (instance.def, recursion_depth)
419 }
420
421 fn check_type_length_limit<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
422                                      instance: Instance<'tcx>)
423 {
424     let type_length = instance.substs.types().flat_map(|ty| ty.walk()).count();
425     debug!(" => type length={}", type_length);
426
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.
431     //
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}...`",
440                           instance_name);
441         let mut diag = if let Some(node_id) = tcx.hir.as_local_node_id(instance.def) {
442             tcx.sess.struct_span_fatal(tcx.hir.span(node_id), &msg)
443         } else {
444             tcx.sess.struct_fatal(&msg)
445         };
446
447         diag.note(&format!(
448             "consider adding a `#![type_length_limit=\"{}\"]` attribute to your crate",
449             type_length_limit*2));
450         diag.emit();
451         tcx.sess.abort_if_errors();
452     }
453 }
454
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>
460 }
461
462 impl<'a, 'tcx> MirVisitor<'tcx> for MirNeighborCollector<'a, 'tcx> {
463
464     fn visit_rvalue(&mut self, rvalue: &mir::Rvalue<'tcx>, location: Location) {
465         debug!("visiting rvalue {:?}", *rvalue);
466
467         match *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,
473                                                                  self.param_substs,
474                                                                  &target_ty);
475                 let source_ty = operand.ty(self.mir, self.scx.tcx());
476                 let source_ty = monomorphize::apply_param_substs(self.scx,
477                                                                  self.param_substs,
478                                                                  &source_ty);
479                 let (source_ty, target_ty) = find_vtable_types_for_unsizing(self.scx,
480                                                                             source_ty,
481                                                                             target_ty);
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,
487                                                           target_ty,
488                                                           source_ty,
489                                                           self.output);
490                 }
491             }
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 closure_trans_item =
497                             create_fn_trans_item(self.scx,
498                                                  def_id,
499                                                  substs.substs,
500                                                  self.param_substs);
501                         self.output.push(closure_trans_item);
502                     }
503                     _ => bug!(),
504                 }
505             }
506             mir::Rvalue::Box(..) => {
507                 let exchange_malloc_fn_def_id =
508                     self.scx
509                         .tcx()
510                         .lang_items
511                         .require(ExchangeMallocFnLangItem)
512                         .unwrap_or_else(|e| self.scx.sess().fatal(&e));
513
514                 if should_trans_locally(self.scx.tcx(), exchange_malloc_fn_def_id) {
515                     let empty_substs = self.scx.empty_substs_for_def_id(exchange_malloc_fn_def_id);
516                     let exchange_malloc_fn_trans_item =
517                         create_fn_trans_item(self.scx,
518                                              exchange_malloc_fn_def_id,
519                                              empty_substs,
520                                              self.param_substs);
521
522                     self.output.push(exchange_malloc_fn_trans_item);
523                 }
524             }
525             _ => { /* not interesting */ }
526         }
527
528         self.super_rvalue(rvalue, location);
529     }
530
531     fn visit_lvalue(&mut self,
532                     lvalue: &mir::Lvalue<'tcx>,
533                     context: mir_visit::LvalueContext<'tcx>,
534                     location: Location) {
535         debug!("visiting lvalue {:?}", *lvalue);
536
537         if let mir_visit::LvalueContext::Drop = context {
538             let ty = lvalue.ty(self.mir, self.scx.tcx())
539                            .to_ty(self.scx.tcx());
540
541             let ty = monomorphize::apply_param_substs(self.scx,
542                                                       self.param_substs,
543                                                       &ty);
544             assert!(ty.is_normalized_for_trans());
545             let ty = glue::get_drop_glue_type(self.scx, ty);
546             self.output.push(TransItem::DropGlue(DropGlueKind::Ty(ty)));
547         }
548
549         self.super_lvalue(lvalue, context, location);
550     }
551
552     fn visit_operand(&mut self, operand: &mir::Operand<'tcx>, location: Location) {
553         debug!("visiting operand {:?}", *operand);
554
555         let callee = match *operand {
556             mir::Operand::Constant(ref constant) => {
557                 if let ty::TyFnDef(def_id, substs, _) = constant.ty.sty {
558                     // This is something that can act as a callee, proceed
559                     Some((def_id, substs))
560                 } else {
561                     // This is not a callee, but we still have to look for
562                     // references to `const` items
563                     if let mir::Literal::Item { def_id, substs } = constant.literal {
564                         let substs = monomorphize::apply_param_substs(self.scx,
565                                                                       self.param_substs,
566                                                                       &substs);
567
568                         let instance = Instance::new(def_id, substs).resolve_const(self.scx);
569                         collect_neighbours(self.scx, instance, self.output);
570                     }
571
572                     None
573                 }
574             }
575             _ => None
576         };
577
578         if let Some((callee_def_id, callee_substs)) = callee {
579             debug!(" => operand is callable");
580
581             // `callee_def_id` might refer to a trait method instead of a
582             // concrete implementation, so we have to find the actual
583             // implementation. For example, the call might look like
584             //
585             // std::cmp::partial_cmp(0i32, 1i32)
586             //
587             // Calling do_static_dispatch() here will map the def_id of
588             // `std::cmp::partial_cmp` to the def_id of `i32::partial_cmp<i32>`
589             let dispatched = do_static_dispatch(self.scx,
590                                                 callee_def_id,
591                                                 callee_substs,
592                                                 self.param_substs);
593
594             if let StaticDispatchResult::Dispatched {
595                     def_id: callee_def_id,
596                     substs: callee_substs,
597                     fn_once_adjustment,
598                 } = dispatched {
599                 // if we have a concrete impl (which we might not have
600                 // in the case of something compiler generated like an
601                 // object shim or a closure that is handled differently),
602                 // we check if the callee is something that will actually
603                 // result in a translation item ...
604                 if can_result_in_trans_item(self.scx.tcx(), callee_def_id) {
605                     // ... and create one if it does.
606                     let trans_item = create_fn_trans_item(self.scx,
607                                                           callee_def_id,
608                                                           callee_substs,
609                                                           self.param_substs);
610                     self.output.push(trans_item);
611
612                     // This call will instantiate an FnOnce adapter, which drops
613                     // the closure environment. Therefore we need to make sure
614                     // that we collect the drop-glue for the environment type.
615                     if let Some(env_ty) = fn_once_adjustment {
616                         let env_ty = glue::get_drop_glue_type(self.scx, env_ty);
617                         if self.scx.type_needs_drop(env_ty) {
618                             let dg = DropGlueKind::Ty(env_ty);
619                             self.output.push(TransItem::DropGlue(dg));
620                         }
621                     }
622                 }
623             }
624         }
625
626         self.super_operand(operand, location);
627
628         fn can_result_in_trans_item<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
629                                               def_id: DefId)
630                                               -> bool {
631             match tcx.item_type(def_id).sty {
632                 ty::TyFnDef(def_id, _, _) => {
633                     // Some constructors also have type TyFnDef but they are
634                     // always instantiated inline and don't result in a
635                     // translation item. Same for FFI functions.
636                     if let Some(hir_map::NodeForeignItem(_)) = tcx.hir.get_if_local(def_id) {
637                         return false;
638                     }
639                 }
640                 ty::TyClosure(..) => {}
641                 _ => return false
642             }
643
644             should_trans_locally(tcx, def_id)
645         }
646     }
647
648     // This takes care of the "drop_in_place" intrinsic for which we otherwise
649     // we would not register drop-glues.
650     fn visit_terminator_kind(&mut self,
651                              block: mir::BasicBlock,
652                              kind: &mir::TerminatorKind<'tcx>,
653                              location: Location) {
654         let tcx = self.scx.tcx();
655         match *kind {
656             mir::TerminatorKind::Call {
657                 func: mir::Operand::Constant(ref constant),
658                 ref args,
659                 ..
660             } => {
661                 match constant.ty.sty {
662                     ty::TyFnDef(def_id, _, bare_fn_ty)
663                         if is_drop_in_place_intrinsic(tcx, def_id, bare_fn_ty) => {
664                         let operand_ty = args[0].ty(self.mir, tcx);
665                         if let ty::TyRawPtr(mt) = operand_ty.sty {
666                             let operand_ty = monomorphize::apply_param_substs(self.scx,
667                                                                               self.param_substs,
668                                                                               &mt.ty);
669                             let ty = glue::get_drop_glue_type(self.scx, operand_ty);
670                             self.output.push(TransItem::DropGlue(DropGlueKind::Ty(ty)));
671                         } else {
672                             bug!("Has the drop_in_place() intrinsic's signature changed?")
673                         }
674                     }
675                     _ => { /* Nothing to do. */ }
676                 }
677             }
678             _ => { /* Nothing to do. */ }
679         }
680
681         self.super_terminator_kind(block, kind, location);
682
683         fn is_drop_in_place_intrinsic<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
684                                                 def_id: DefId,
685                                                 bare_fn_ty: &ty::BareFnTy<'tcx>)
686                                                 -> bool {
687             (bare_fn_ty.abi == Abi::RustIntrinsic ||
688              bare_fn_ty.abi == Abi::PlatformIntrinsic) &&
689             tcx.item_name(def_id) == "drop_in_place"
690         }
691     }
692 }
693
694 // Returns true if we should translate an instance in the local crate.
695 // Returns false if we can just link to the upstream crate and therefore don't
696 // need a translation item.
697 fn should_trans_locally<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
698                                   def_id: DefId)
699                                   -> bool {
700     if let ty::TyFnDef(_, _, f) = tcx.item_type(def_id).sty {
701         if let Some(adt_def) = f.sig.output().skip_binder().ty_adt_def() {
702             if adt_def.variants.iter().any(|v| def_id == v.did) {
703                 // HACK: ADT constructors are translated in-place and
704                 // do not have a trans-item.
705                 return false;
706             }
707         }
708     }
709
710     if def_id.is_local() {
711         true
712     } else {
713         if tcx.sess.cstore.is_exported_symbol(def_id) ||
714            tcx.sess.cstore.is_foreign_item(def_id) {
715             // We can link to the item in question, no instance needed in this
716             // crate
717             false
718         } else {
719             if !tcx.sess.cstore.is_item_mir_available(def_id) {
720                 bug!("Cannot create local trans-item for {:?}", def_id)
721             }
722             true
723         }
724     }
725 }
726
727 fn find_drop_glue_neighbors<'a, 'tcx>(scx: &SharedCrateContext<'a, 'tcx>,
728                                       dg: DropGlueKind<'tcx>,
729                                       output: &mut Vec<TransItem<'tcx>>) {
730     let ty = match dg {
731         DropGlueKind::Ty(ty) => ty,
732         DropGlueKind::TyContents(_) => {
733             // We already collected the neighbors of this item via the
734             // DropGlueKind::Ty variant.
735             return
736         }
737     };
738
739     debug!("find_drop_glue_neighbors: {}", type_to_string(scx.tcx(), ty));
740
741     // Make sure the BoxFreeFn lang-item gets translated if there is a boxed value.
742     if ty.is_box() {
743         let def_id = scx.tcx().require_lang_item(BoxFreeFnLangItem);
744         if should_trans_locally(scx.tcx(), def_id) {
745             let box_free_fn_trans_item =
746                 create_fn_trans_item(scx,
747                                      def_id,
748                                      scx.tcx().mk_substs(iter::once(Kind::from(ty.boxed_ty()))),
749                                      scx.tcx().intern_substs(&[]));
750             output.push(box_free_fn_trans_item);
751         }
752     }
753
754     // If the type implements Drop, also add a translation item for the
755     // monomorphized Drop::drop() implementation.
756     let destructor_did = match ty.sty {
757         ty::TyAdt(def, _) => def.destructor(),
758         _ => None
759     };
760
761     if let (Some(destructor_did), false) = (destructor_did, ty.is_box()) {
762         use rustc::ty::ToPolyTraitRef;
763
764         let drop_trait_def_id = scx.tcx()
765                                    .lang_items
766                                    .drop_trait()
767                                    .unwrap();
768
769         let self_type_substs = scx.tcx().mk_substs_trait(ty, &[]);
770
771         let trait_ref = ty::TraitRef {
772             def_id: drop_trait_def_id,
773             substs: self_type_substs,
774         }.to_poly_trait_ref();
775
776         let substs = match fulfill_obligation(scx, DUMMY_SP, trait_ref) {
777             traits::VtableImpl(data) => data.substs,
778             _ => bug!()
779         };
780
781         if should_trans_locally(scx.tcx(), destructor_did) {
782             let trans_item = create_fn_trans_item(scx,
783                                                   destructor_did,
784                                                   substs,
785                                                   scx.tcx().intern_substs(&[]));
786             output.push(trans_item);
787         }
788
789         // This type has a Drop implementation, we'll need the contents-only
790         // version of the glue too.
791         output.push(TransItem::DropGlue(DropGlueKind::TyContents(ty)));
792     }
793
794     // Finally add the types of nested values
795     match ty.sty {
796         ty::TyBool      |
797         ty::TyChar      |
798         ty::TyInt(_)    |
799         ty::TyUint(_)   |
800         ty::TyStr       |
801         ty::TyFloat(_)  |
802         ty::TyRawPtr(_) |
803         ty::TyRef(..)   |
804         ty::TyFnDef(..) |
805         ty::TyFnPtr(_)  |
806         ty::TyNever     |
807         ty::TyDynamic(..)  => {
808             /* nothing to do */
809         }
810         ty::TyAdt(def, _) if def.is_box() => {
811             let inner_type = glue::get_drop_glue_type(scx, ty.boxed_ty());
812             if scx.type_needs_drop(inner_type) {
813                 output.push(TransItem::DropGlue(DropGlueKind::Ty(inner_type)));
814             }
815         }
816         ty::TyAdt(def, substs) => {
817             for field in def.all_fields() {
818                 let field_type = scx.tcx().item_type(field.did);
819                 let field_type = monomorphize::apply_param_substs(scx,
820                                                                   substs,
821                                                                   &field_type);
822                 let field_type = glue::get_drop_glue_type(scx, field_type);
823
824                 if scx.type_needs_drop(field_type) {
825                     output.push(TransItem::DropGlue(DropGlueKind::Ty(field_type)));
826                 }
827             }
828         }
829         ty::TyClosure(def_id, substs) => {
830             for upvar_ty in substs.upvar_tys(def_id, scx.tcx()) {
831                 let upvar_ty = glue::get_drop_glue_type(scx, upvar_ty);
832                 if scx.type_needs_drop(upvar_ty) {
833                     output.push(TransItem::DropGlue(DropGlueKind::Ty(upvar_ty)));
834                 }
835             }
836         }
837         ty::TySlice(inner_type)    |
838         ty::TyArray(inner_type, _) => {
839             let inner_type = glue::get_drop_glue_type(scx, inner_type);
840             if scx.type_needs_drop(inner_type) {
841                 output.push(TransItem::DropGlue(DropGlueKind::Ty(inner_type)));
842             }
843         }
844         ty::TyTuple(args, _) => {
845             for arg in args {
846                 let arg = glue::get_drop_glue_type(scx, arg);
847                 if scx.type_needs_drop(arg) {
848                     output.push(TransItem::DropGlue(DropGlueKind::Ty(arg)));
849                 }
850             }
851         }
852         ty::TyProjection(_) |
853         ty::TyParam(_)      |
854         ty::TyInfer(_)      |
855         ty::TyAnon(..)      |
856         ty::TyError         => {
857             bug!("encountered unexpected type");
858         }
859     }
860 }
861
862 fn do_static_dispatch<'a, 'tcx>(scx: &SharedCrateContext<'a, 'tcx>,
863                                 fn_def_id: DefId,
864                                 fn_substs: &'tcx Substs<'tcx>,
865                                 param_substs: &'tcx Substs<'tcx>)
866                                 -> StaticDispatchResult<'tcx> {
867     debug!("do_static_dispatch(fn_def_id={}, fn_substs={:?}, param_substs={:?})",
868            def_id_to_string(scx.tcx(), fn_def_id),
869            fn_substs,
870            param_substs);
871
872     if let Some(trait_def_id) = scx.tcx().trait_of_item(fn_def_id) {
873         debug!(" => trait method, attempting to find impl");
874         do_static_trait_method_dispatch(scx,
875                                         &scx.tcx().associated_item(fn_def_id),
876                                         trait_def_id,
877                                         fn_substs,
878                                         param_substs)
879     } else {
880         debug!(" => regular function");
881         // The function is not part of an impl or trait, no dispatching
882         // to be done
883         StaticDispatchResult::Dispatched {
884             def_id: fn_def_id,
885             substs: fn_substs,
886             fn_once_adjustment: None,
887         }
888     }
889 }
890
891 enum StaticDispatchResult<'tcx> {
892     // The call could be resolved statically as going to the method with
893     // `def_id` and `substs`.
894     Dispatched {
895         def_id: DefId,
896         substs: &'tcx Substs<'tcx>,
897
898         // If this is a call to a closure that needs an FnOnce adjustment,
899         // this contains the new self type of the call (= type of the closure
900         // environment)
901         fn_once_adjustment: Option<ty::Ty<'tcx>>,
902     },
903     // This goes to somewhere that we don't know at compile-time
904     Unknown
905 }
906
907 // Given a trait-method and substitution information, find out the actual
908 // implementation of the trait method.
909 fn do_static_trait_method_dispatch<'a, 'tcx>(scx: &SharedCrateContext<'a, 'tcx>,
910                                              trait_method: &ty::AssociatedItem,
911                                              trait_id: DefId,
912                                              callee_substs: &'tcx Substs<'tcx>,
913                                              param_substs: &'tcx Substs<'tcx>)
914                                              -> StaticDispatchResult<'tcx> {
915     let tcx = scx.tcx();
916     debug!("do_static_trait_method_dispatch(trait_method={}, \
917                                             trait_id={}, \
918                                             callee_substs={:?}, \
919                                             param_substs={:?}",
920            def_id_to_string(scx.tcx(), trait_method.def_id),
921            def_id_to_string(scx.tcx(), trait_id),
922            callee_substs,
923            param_substs);
924
925     let rcvr_substs = monomorphize::apply_param_substs(scx,
926                                                        param_substs,
927                                                        &callee_substs);
928     let trait_ref = ty::TraitRef::from_method(tcx, trait_id, rcvr_substs);
929     let vtbl = fulfill_obligation(scx, DUMMY_SP, ty::Binder(trait_ref));
930
931     // Now that we know which impl is being used, we can dispatch to
932     // the actual function:
933     match vtbl {
934         traits::VtableImpl(impl_data) => {
935             let (def_id, substs) = traits::find_method(tcx,
936                                                        trait_method.name,
937                                                        rcvr_substs,
938                                                        &impl_data);
939             StaticDispatchResult::Dispatched {
940                 def_id: def_id,
941                 substs: substs,
942                 fn_once_adjustment: None,
943             }
944         }
945         traits::VtableClosure(closure_data) => {
946             let closure_def_id = closure_data.closure_def_id;
947             let trait_closure_kind = tcx.lang_items.fn_trait_kind(trait_id).unwrap();
948             let actual_closure_kind = tcx.closure_kind(closure_def_id);
949
950             let needs_fn_once_adapter_shim =
951                 match needs_fn_once_adapter_shim(actual_closure_kind,
952                                                  trait_closure_kind) {
953                 Ok(true) => true,
954                 _ => false,
955             };
956
957             let fn_once_adjustment = if needs_fn_once_adapter_shim {
958                 Some(tcx.mk_closure_from_closure_substs(closure_def_id,
959                                                         closure_data.substs))
960             } else {
961                 None
962             };
963
964             StaticDispatchResult::Dispatched {
965                 def_id: closure_def_id,
966                 substs: closure_data.substs.substs,
967                 fn_once_adjustment: fn_once_adjustment,
968             }
969         }
970         traits::VtableFnPointer(ref data) => {
971             // If we know the destination of this fn-pointer, we'll have to make
972             // sure that this destination actually gets instantiated.
973             if let ty::TyFnDef(def_id, substs, _) = data.fn_ty.sty {
974                 // The destination of the pointer might be something that needs
975                 // further dispatching, such as a trait method, so we do that.
976                 do_static_dispatch(scx, def_id, substs, param_substs)
977             } else {
978                 StaticDispatchResult::Unknown
979             }
980         }
981         // Trait object shims are always instantiated in-place, and as they are
982         // just an ABI-adjusting indirect call they do not have any dependencies.
983         traits::VtableObject(..) => {
984             StaticDispatchResult::Unknown
985         }
986         _ => {
987             bug!("static call to invalid vtable: {:?}", vtbl)
988         }
989     }
990 }
991
992 /// For given pair of source and target type that occur in an unsizing coercion,
993 /// this function finds the pair of types that determines the vtable linking
994 /// them.
995 ///
996 /// For example, the source type might be `&SomeStruct` and the target type\
997 /// might be `&SomeTrait` in a cast like:
998 ///
999 /// let src: &SomeStruct = ...;
1000 /// let target = src as &SomeTrait;
1001 ///
1002 /// Then the output of this function would be (SomeStruct, SomeTrait) since for
1003 /// constructing the `target` fat-pointer we need the vtable for that pair.
1004 ///
1005 /// Things can get more complicated though because there's also the case where
1006 /// the unsized type occurs as a field:
1007 ///
1008 /// ```rust
1009 /// struct ComplexStruct<T: ?Sized> {
1010 ///    a: u32,
1011 ///    b: f64,
1012 ///    c: T
1013 /// }
1014 /// ```
1015 ///
1016 /// In this case, if `T` is sized, `&ComplexStruct<T>` is a thin pointer. If `T`
1017 /// is unsized, `&SomeStruct` is a fat pointer, and the vtable it points to is
1018 /// for the pair of `T` (which is a trait) and the concrete type that `T` was
1019 /// originally coerced from:
1020 ///
1021 /// let src: &ComplexStruct<SomeStruct> = ...;
1022 /// let target = src as &ComplexStruct<SomeTrait>;
1023 ///
1024 /// Again, we want this `find_vtable_types_for_unsizing()` to provide the pair
1025 /// `(SomeStruct, SomeTrait)`.
1026 ///
1027 /// Finally, there is also the case of custom unsizing coercions, e.g. for
1028 /// smart pointers such as `Rc` and `Arc`.
1029 fn find_vtable_types_for_unsizing<'a, 'tcx>(scx: &SharedCrateContext<'a, 'tcx>,
1030                                             source_ty: ty::Ty<'tcx>,
1031                                             target_ty: ty::Ty<'tcx>)
1032                                             -> (ty::Ty<'tcx>, ty::Ty<'tcx>) {
1033     let ptr_vtable = |inner_source: ty::Ty<'tcx>, inner_target: ty::Ty<'tcx>| {
1034         if !scx.type_is_sized(inner_source) {
1035             (inner_source, inner_target)
1036         } else {
1037             scx.tcx().struct_lockstep_tails(inner_source, inner_target)
1038         }
1039     };
1040     match (&source_ty.sty, &target_ty.sty) {
1041         (&ty::TyRef(_, ty::TypeAndMut { ty: a, .. }),
1042          &ty::TyRef(_, ty::TypeAndMut { ty: b, .. })) |
1043         (&ty::TyRef(_, ty::TypeAndMut { ty: a, .. }),
1044          &ty::TyRawPtr(ty::TypeAndMut { ty: b, .. })) |
1045         (&ty::TyRawPtr(ty::TypeAndMut { ty: a, .. }),
1046          &ty::TyRawPtr(ty::TypeAndMut { ty: b, .. })) => {
1047             ptr_vtable(a, b)
1048         }
1049         (&ty::TyAdt(def_a, _), &ty::TyAdt(def_b, _)) if def_a.is_box() && def_b.is_box() => {
1050             ptr_vtable(source_ty.boxed_ty(), target_ty.boxed_ty())
1051         }
1052
1053         (&ty::TyAdt(source_adt_def, source_substs),
1054          &ty::TyAdt(target_adt_def, target_substs)) => {
1055             assert_eq!(source_adt_def, target_adt_def);
1056
1057             let kind = custom_coerce_unsize_info(scx, source_ty, target_ty);
1058
1059             let coerce_index = match kind {
1060                 CustomCoerceUnsized::Struct(i) => i
1061             };
1062
1063             let source_fields = &source_adt_def.struct_variant().fields;
1064             let target_fields = &target_adt_def.struct_variant().fields;
1065
1066             assert!(coerce_index < source_fields.len() &&
1067                     source_fields.len() == target_fields.len());
1068
1069             find_vtable_types_for_unsizing(scx,
1070                                            source_fields[coerce_index].ty(scx.tcx(),
1071                                                                           source_substs),
1072                                            target_fields[coerce_index].ty(scx.tcx(),
1073                                                                           target_substs))
1074         }
1075         _ => bug!("find_vtable_types_for_unsizing: invalid coercion {:?} -> {:?}",
1076                   source_ty,
1077                   target_ty)
1078     }
1079 }
1080
1081 fn create_fn_trans_item<'a, 'tcx>(scx: &SharedCrateContext<'a, 'tcx>,
1082                                   def_id: DefId,
1083                                   fn_substs: &'tcx Substs<'tcx>,
1084                                   param_substs: &'tcx Substs<'tcx>)
1085                                   -> TransItem<'tcx> {
1086     let tcx = scx.tcx();
1087
1088     debug!("create_fn_trans_item(def_id={}, fn_substs={:?}, param_substs={:?})",
1089             def_id_to_string(tcx, def_id),
1090             fn_substs,
1091             param_substs);
1092
1093     // We only get here, if fn_def_id either designates a local item or
1094     // an inlineable external item. Non-inlineable external items are
1095     // ignored because we don't want to generate any code for them.
1096     let concrete_substs = monomorphize::apply_param_substs(scx,
1097                                                            param_substs,
1098                                                            &fn_substs);
1099     assert!(concrete_substs.is_normalized_for_trans(),
1100             "concrete_substs not normalized for trans: {:?}",
1101             concrete_substs);
1102     TransItem::Fn(Instance::new(def_id, concrete_substs))
1103 }
1104
1105 /// Creates a `TransItem` for each method that is referenced by the vtable for
1106 /// the given trait/impl pair.
1107 fn create_trans_items_for_vtable_methods<'a, 'tcx>(scx: &SharedCrateContext<'a, 'tcx>,
1108                                                    trait_ty: ty::Ty<'tcx>,
1109                                                    impl_ty: ty::Ty<'tcx>,
1110                                                    output: &mut Vec<TransItem<'tcx>>) {
1111     assert!(!trait_ty.needs_subst() && !trait_ty.has_escaping_regions() &&
1112             !impl_ty.needs_subst() && !impl_ty.has_escaping_regions());
1113
1114     if let ty::TyDynamic(ref trait_ty, ..) = trait_ty.sty {
1115         if let Some(principal) = trait_ty.principal() {
1116             let poly_trait_ref = principal.with_self_ty(scx.tcx(), impl_ty);
1117             let param_substs = scx.tcx().intern_substs(&[]);
1118
1119             assert!(!poly_trait_ref.has_escaping_regions());
1120
1121             // Walk all methods of the trait, including those of its supertraits
1122             let methods = traits::get_vtable_methods(scx.tcx(), poly_trait_ref);
1123             let methods = methods.filter_map(|method| method)
1124                 .filter_map(|(def_id, substs)| {
1125                     if let StaticDispatchResult::Dispatched {
1126                         def_id,
1127                         substs,
1128                         // We already add the drop-glue for the closure env
1129                         // unconditionally below.
1130                         fn_once_adjustment: _ ,
1131                     } = do_static_dispatch(scx, def_id, substs, param_substs) {
1132                         Some((def_id, substs))
1133                     } else {
1134                         None
1135                     }
1136                 })
1137                 .filter(|&(def_id, _)| should_trans_locally(scx.tcx(), def_id))
1138                 .map(|(def_id, substs)| create_fn_trans_item(scx, def_id, substs, param_substs));
1139             output.extend(methods);
1140         }
1141         // Also add the destructor
1142         let dg_type = glue::get_drop_glue_type(scx, impl_ty);
1143         output.push(TransItem::DropGlue(DropGlueKind::Ty(dg_type)));
1144     }
1145 }
1146
1147 //=-----------------------------------------------------------------------------
1148 // Root Collection
1149 //=-----------------------------------------------------------------------------
1150
1151 struct RootCollector<'b, 'a: 'b, 'tcx: 'a + 'b> {
1152     scx: &'b SharedCrateContext<'a, 'tcx>,
1153     mode: TransItemCollectionMode,
1154     output: &'b mut Vec<TransItem<'tcx>>,
1155 }
1156
1157 impl<'b, 'a, 'v> ItemLikeVisitor<'v> for RootCollector<'b, 'a, 'v> {
1158     fn visit_item(&mut self, item: &'v hir::Item) {
1159         match item.node {
1160             hir::ItemExternCrate(..) |
1161             hir::ItemUse(..)         |
1162             hir::ItemForeignMod(..)  |
1163             hir::ItemTy(..)          |
1164             hir::ItemDefaultImpl(..) |
1165             hir::ItemTrait(..)       |
1166             hir::ItemMod(..)         => {
1167                 // Nothing to do, just keep recursing...
1168             }
1169
1170             hir::ItemImpl(..) => {
1171                 if self.mode == TransItemCollectionMode::Eager {
1172                     create_trans_items_for_default_impls(self.scx,
1173                                                          item,
1174                                                          self.output);
1175                 }
1176             }
1177
1178             hir::ItemEnum(_, ref generics) |
1179             hir::ItemStruct(_, ref generics) |
1180             hir::ItemUnion(_, ref generics) => {
1181                 if !generics.is_parameterized() {
1182                     if self.mode == TransItemCollectionMode::Eager {
1183                         let def_id = self.scx.tcx().hir.local_def_id(item.id);
1184                         debug!("RootCollector: ADT drop-glue for {}",
1185                                def_id_to_string(self.scx.tcx(), def_id));
1186
1187                         let ty = self.scx.tcx().item_type(def_id);
1188                         let ty = glue::get_drop_glue_type(self.scx, ty);
1189                         self.output.push(TransItem::DropGlue(DropGlueKind::Ty(ty)));
1190                     }
1191                 }
1192             }
1193             hir::ItemStatic(..) => {
1194                 debug!("RootCollector: ItemStatic({})",
1195                        def_id_to_string(self.scx.tcx(),
1196                                         self.scx.tcx().hir.local_def_id(item.id)));
1197                 self.output.push(TransItem::Static(item.id));
1198             }
1199             hir::ItemConst(..) => {
1200                 // const items only generate translation items if they are
1201                 // actually used somewhere. Just declaring them is insufficient.
1202             }
1203             hir::ItemFn(.., ref generics, _) => {
1204                 if !generics.is_type_parameterized() {
1205                     let def_id = self.scx.tcx().hir.local_def_id(item.id);
1206
1207                     debug!("RootCollector: ItemFn({})",
1208                            def_id_to_string(self.scx.tcx(), def_id));
1209
1210                     let instance = Instance::mono(self.scx, def_id);
1211                     self.output.push(TransItem::Fn(instance));
1212                 }
1213             }
1214         }
1215     }
1216
1217     fn visit_trait_item(&mut self, _: &'v hir::TraitItem) {
1218         // Even if there's a default body with no explicit generics,
1219         // it's still generic over some `Self: Trait`, so not a root.
1220     }
1221
1222     fn visit_impl_item(&mut self, ii: &'v hir::ImplItem) {
1223         match ii.node {
1224             hir::ImplItemKind::Method(hir::MethodSig {
1225                 ref generics,
1226                 ..
1227             }, _) => {
1228                 let hir_map = &self.scx.tcx().hir;
1229                 let parent_node_id = hir_map.get_parent_node(ii.id);
1230                 let is_impl_generic = match hir_map.expect_item(parent_node_id) {
1231                     &hir::Item {
1232                         node: hir::ItemImpl(_, _, ref generics, ..),
1233                         ..
1234                     } => {
1235                         generics.is_type_parameterized()
1236                     }
1237                     _ => {
1238                         bug!()
1239                     }
1240                 };
1241
1242                 if !generics.is_type_parameterized() && !is_impl_generic {
1243                     let def_id = self.scx.tcx().hir.local_def_id(ii.id);
1244
1245                     debug!("RootCollector: MethodImplItem({})",
1246                            def_id_to_string(self.scx.tcx(), def_id));
1247
1248                     let instance = Instance::mono(self.scx, def_id);
1249                     self.output.push(TransItem::Fn(instance));
1250                 }
1251             }
1252             _ => { /* Nothing to do here */ }
1253         }
1254     }
1255 }
1256
1257 fn create_trans_items_for_default_impls<'a, 'tcx>(scx: &SharedCrateContext<'a, 'tcx>,
1258                                                   item: &'tcx hir::Item,
1259                                                   output: &mut Vec<TransItem<'tcx>>) {
1260     let tcx = scx.tcx();
1261     match item.node {
1262         hir::ItemImpl(_,
1263                       _,
1264                       ref generics,
1265                       ..,
1266                       ref impl_item_refs) => {
1267             if generics.is_type_parameterized() {
1268                 return
1269             }
1270
1271             let impl_def_id = tcx.hir.local_def_id(item.id);
1272
1273             debug!("create_trans_items_for_default_impls(item={})",
1274                    def_id_to_string(tcx, impl_def_id));
1275
1276             if let Some(trait_ref) = tcx.impl_trait_ref(impl_def_id) {
1277                 let callee_substs = tcx.erase_regions(&trait_ref.substs);
1278                 let overridden_methods: FxHashSet<_> =
1279                     impl_item_refs.iter()
1280                                   .map(|iiref| iiref.name)
1281                                   .collect();
1282                 for method in tcx.provided_trait_methods(trait_ref.def_id) {
1283                     if overridden_methods.contains(&method.name) {
1284                         continue;
1285                     }
1286
1287                     if !tcx.item_generics(method.def_id).types.is_empty() {
1288                         continue;
1289                     }
1290
1291                     // The substitutions we have are on the impl, so we grab
1292                     // the method type from the impl to substitute into.
1293                     let impl_substs = Substs::for_item(tcx, impl_def_id,
1294                                                        |_, _| tcx.mk_region(ty::ReErased),
1295                                                        |_, _| tcx.types.err);
1296                     let impl_data = traits::VtableImplData {
1297                         impl_def_id: impl_def_id,
1298                         substs: impl_substs,
1299                         nested: vec![]
1300                     };
1301                     let (def_id, substs) = traits::find_method(tcx,
1302                                                                method.name,
1303                                                                callee_substs,
1304                                                                &impl_data);
1305
1306                     let predicates = tcx.item_predicates(def_id).predicates
1307                                         .subst(tcx, substs);
1308                     if !traits::normalize_and_test_predicates(tcx, predicates) {
1309                         continue;
1310                     }
1311
1312                     if should_trans_locally(tcx, method.def_id) {
1313                         let item = create_fn_trans_item(scx,
1314                                                         method.def_id,
1315                                                         callee_substs,
1316                                                         tcx.erase_regions(&substs));
1317                         output.push(item);
1318                     }
1319                 }
1320             }
1321         }
1322         _ => {
1323             bug!()
1324         }
1325     }
1326 }
1327
1328 /// Scan the MIR in order to find function calls, closures, and drop-glue
1329 fn collect_neighbours<'a, 'tcx>(scx: &SharedCrateContext<'a, 'tcx>,
1330                                 instance: Instance<'tcx>,
1331                                 output: &mut Vec<TransItem<'tcx>>)
1332 {
1333     let mir = scx.tcx().item_mir(instance.def);
1334
1335     let mut visitor = MirNeighborCollector {
1336         scx: scx,
1337         mir: &mir,
1338         output: output,
1339         param_substs: instance.substs
1340     };
1341
1342     visitor.visit_mir(&mir);
1343     for promoted in &mir.promoted {
1344         visitor.mir = promoted;
1345         visitor.visit_mir(promoted);
1346     }
1347 }
1348
1349 fn def_id_to_string<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
1350                               def_id: DefId)
1351                               -> String {
1352     let mut output = String::new();
1353     let printer = DefPathBasedNames::new(tcx, false, false);
1354     printer.push_def_path(def_id, &mut output);
1355     output
1356 }
1357
1358 fn type_to_string<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
1359                             ty: ty::Ty<'tcx>)
1360                             -> String {
1361     let mut output = String::new();
1362     let printer = DefPathBasedNames::new(tcx, false, false);
1363     printer.push_type_name(ty, &mut output);
1364     output
1365 }