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::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);
341 // Sanity check whether this ended up being collected accidentally
342 debug_assert!(should_trans_locally(scx.tcx(), def_id));
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)));
348 recursion_depth_reset = None;
350 collect_neighbours(scx, Instance::mono(scx, def_id), &mut neighbors);
352 TransItem::Fn(instance) => {
353 // Sanity check whether this ended up being collected accidentally
354 debug_assert!(should_trans_locally(scx.tcx(), instance.def));
356 // Keep track of the monomorphization recursion depth
357 recursion_depth_reset = Some(check_recursion_limit(scx.tcx(),
360 check_type_length_limit(scx.tcx(), instance);
362 collect_neighbours(scx, instance, &mut neighbors);
366 record_inlining_canditates(scx.tcx(), starting_point, &neighbors[..], inlining_map);
368 for neighbour in neighbors {
369 collect_items_rec(scx, neighbour, visited, recursion_depths, inlining_map);
372 if let Some((def_id, depth)) = recursion_depth_reset {
373 recursion_depths.insert(def_id, depth);
376 debug!("END collect_items_rec({})", starting_point.to_string(scx.tcx()));
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
387 let inlining_candidates = callees.into_iter()
389 .filter(is_inlining_candidate);
391 inlining_map.record_inlining_canditates(caller, inlining_candidates);
394 fn check_recursion_limit<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
395 instance: Instance<'tcx>,
396 recursion_depths: &mut DefIdMap<usize>)
398 let recursion_depth = recursion_depths.get(&instance.def)
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(instance.def) {
410 tcx.sess.span_fatal(tcx.hir.span(node_id), &error);
412 tcx.sess.fatal(&error);
416 recursion_depths.insert(instance.def, recursion_depth + 1);
418 (instance.def, 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) {
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 closure_trans_item =
497 create_fn_trans_item(self.scx,
501 self.output.push(closure_trans_item);
506 mir::Rvalue::Box(..) => {
507 let exchange_malloc_fn_def_id =
511 .require(ExchangeMallocFnLangItem)
512 .unwrap_or_else(|e| self.scx.sess().fatal(&e));
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,
522 self.output.push(exchange_malloc_fn_trans_item);
525 _ => { /* not interesting */ }
528 self.super_rvalue(rvalue, location);
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);
537 if let mir_visit::LvalueContext::Drop = context {
538 let ty = lvalue.ty(self.mir, self.scx.tcx())
539 .to_ty(self.scx.tcx());
541 let ty = monomorphize::apply_param_substs(self.scx,
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)));
549 self.super_lvalue(lvalue, context, location);
552 fn visit_operand(&mut self, operand: &mir::Operand<'tcx>, location: Location) {
553 debug!("visiting operand {:?}", *operand);
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))
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,
568 let instance = Instance::new(def_id, substs).resolve_const(self.scx);
569 collect_neighbours(self.scx, instance, self.output);
578 if let Some((callee_def_id, callee_substs)) = callee {
579 debug!(" => operand is callable");
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
585 // std::cmp::partial_cmp(0i32, 1i32)
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,
594 if let StaticDispatchResult::Dispatched {
595 def_id: callee_def_id,
596 substs: callee_substs,
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,
610 self.output.push(trans_item);
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));
626 self.super_operand(operand, location);
628 fn can_result_in_trans_item<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
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) {
640 ty::TyClosure(..) => {}
644 should_trans_locally(tcx, def_id)
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();
656 mir::TerminatorKind::Call {
657 func: mir::Operand::Constant(ref constant),
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,
669 let ty = glue::get_drop_glue_type(self.scx, operand_ty);
670 self.output.push(TransItem::DropGlue(DropGlueKind::Ty(ty)));
672 bug!("Has the drop_in_place() intrinsic's signature changed?")
675 _ => { /* Nothing to do. */ }
678 _ => { /* Nothing to do. */ }
681 self.super_terminator_kind(block, kind, location);
683 fn is_drop_in_place_intrinsic<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
685 bare_fn_ty: ty::PolyFnSig<'tcx>)
687 (bare_fn_ty.abi() == Abi::RustIntrinsic ||
688 bare_fn_ty.abi() == Abi::PlatformIntrinsic) &&
689 tcx.item_name(def_id) == "drop_in_place"
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>,
700 if let ty::TyFnDef(_, _, sig) = tcx.item_type(def_id).sty {
701 if let Some(adt_def) = 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.
710 if def_id.is_local() {
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
719 if !tcx.sess.cstore.is_item_mir_available(def_id) {
720 bug!("Cannot create local trans-item for {:?}", def_id)
727 fn find_drop_glue_neighbors<'a, 'tcx>(scx: &SharedCrateContext<'a, 'tcx>,
728 dg: DropGlueKind<'tcx>,
729 output: &mut Vec<TransItem<'tcx>>) {
731 DropGlueKind::Ty(ty) => ty,
732 DropGlueKind::TyContents(_) => {
733 // We already collected the neighbors of this item via the
734 // DropGlueKind::Ty variant.
739 debug!("find_drop_glue_neighbors: {}", type_to_string(scx.tcx(), ty));
741 // Make sure the BoxFreeFn lang-item gets translated if there is a boxed value.
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,
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);
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(),
761 if let (Some(destructor_did), false) = (destructor_did, ty.is_box()) {
762 use rustc::ty::ToPolyTraitRef;
764 let drop_trait_def_id = scx.tcx()
769 let self_type_substs = scx.tcx().mk_substs_trait(ty, &[]);
771 let trait_ref = ty::TraitRef {
772 def_id: drop_trait_def_id,
773 substs: self_type_substs,
774 }.to_poly_trait_ref();
776 let substs = match fulfill_obligation(scx, DUMMY_SP, trait_ref) {
777 traits::VtableImpl(data) => data.substs,
781 if should_trans_locally(scx.tcx(), destructor_did) {
782 let trans_item = create_fn_trans_item(scx,
785 scx.tcx().intern_substs(&[]));
786 output.push(trans_item);
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)));
794 // Finally add the types of nested values
807 ty::TyDynamic(..) => {
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)));
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,
822 let field_type = glue::get_drop_glue_type(scx, field_type);
824 if scx.type_needs_drop(field_type) {
825 output.push(TransItem::DropGlue(DropGlueKind::Ty(field_type)));
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)));
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)));
844 ty::TyTuple(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)));
852 ty::TyProjection(_) |
857 bug!("encountered unexpected type");
862 fn do_static_dispatch<'a, 'tcx>(scx: &SharedCrateContext<'a, 'tcx>,
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),
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),
880 debug!(" => regular function");
881 // The function is not part of an impl or trait, no dispatching
883 StaticDispatchResult::Dispatched {
886 fn_once_adjustment: None,
891 enum StaticDispatchResult<'tcx> {
892 // The call could be resolved statically as going to the method with
893 // `def_id` and `substs`.
896 substs: &'tcx Substs<'tcx>,
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
901 fn_once_adjustment: Option<ty::Ty<'tcx>>,
903 // This goes to somewhere that we don't know at compile-time
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,
912 callee_substs: &'tcx Substs<'tcx>,
913 param_substs: &'tcx Substs<'tcx>)
914 -> StaticDispatchResult<'tcx> {
916 debug!("do_static_trait_method_dispatch(trait_method={}, \
918 callee_substs={:?}, \
920 def_id_to_string(scx.tcx(), trait_method.def_id),
921 def_id_to_string(scx.tcx(), trait_id),
925 let rcvr_substs = monomorphize::apply_param_substs(scx,
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));
931 // Now that we know which impl is being used, we can dispatch to
932 // the actual function:
934 traits::VtableImpl(impl_data) => {
935 let (def_id, substs) = traits::find_method(tcx,
939 StaticDispatchResult::Dispatched {
942 fn_once_adjustment: None,
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);
950 let needs_fn_once_adapter_shim =
951 match needs_fn_once_adapter_shim(actual_closure_kind,
952 trait_closure_kind) {
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))
964 StaticDispatchResult::Dispatched {
965 def_id: closure_def_id,
966 substs: closure_data.substs.substs,
967 fn_once_adjustment: fn_once_adjustment,
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)
978 StaticDispatchResult::Unknown
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
987 bug!("static call to invalid vtable: {:?}", vtbl)
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
996 /// For example, the source type might be `&SomeStruct` and the target type\
997 /// might be `&SomeTrait` in a cast like:
999 /// let src: &SomeStruct = ...;
1000 /// let target = src as &SomeTrait;
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.
1005 /// Things can get more complicated though because there's also the case where
1006 /// the unsized type occurs as a field:
1009 /// struct ComplexStruct<T: ?Sized> {
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:
1021 /// let src: &ComplexStruct<SomeStruct> = ...;
1022 /// let target = src as &ComplexStruct<SomeTrait>;
1024 /// Again, we want this `find_vtable_types_for_unsizing()` to provide the pair
1025 /// `(SomeStruct, SomeTrait)`.
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)
1037 scx.tcx().struct_lockstep_tails(inner_source, inner_target)
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, .. })) => {
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())
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);
1057 let kind = custom_coerce_unsize_info(scx, source_ty, target_ty);
1059 let coerce_index = match kind {
1060 CustomCoerceUnsized::Struct(i) => i
1063 let source_fields = &source_adt_def.struct_variant().fields;
1064 let target_fields = &target_adt_def.struct_variant().fields;
1066 assert!(coerce_index < source_fields.len() &&
1067 source_fields.len() == target_fields.len());
1069 find_vtable_types_for_unsizing(scx,
1070 source_fields[coerce_index].ty(scx.tcx(),
1072 target_fields[coerce_index].ty(scx.tcx(),
1075 _ => bug!("find_vtable_types_for_unsizing: invalid coercion {:?} -> {:?}",
1081 fn create_fn_trans_item<'a, 'tcx>(scx: &SharedCrateContext<'a, 'tcx>,
1083 fn_substs: &'tcx Substs<'tcx>,
1084 param_substs: &'tcx Substs<'tcx>)
1085 -> TransItem<'tcx> {
1086 let tcx = scx.tcx();
1088 debug!("create_fn_trans_item(def_id={}, fn_substs={:?}, param_substs={:?})",
1089 def_id_to_string(tcx, def_id),
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,
1099 assert!(concrete_substs.is_normalized_for_trans(),
1100 "concrete_substs not normalized for trans: {:?}",
1102 TransItem::Fn(Instance::new(def_id, concrete_substs))
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());
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(&[]);
1119 assert!(!poly_trait_ref.has_escaping_regions());
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 {
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))
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);
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)));
1147 //=-----------------------------------------------------------------------------
1149 //=-----------------------------------------------------------------------------
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>>,
1157 impl<'b, 'a, 'v> ItemLikeVisitor<'v> for RootCollector<'b, 'a, 'v> {
1158 fn visit_item(&mut self, item: &'v hir::Item) {
1160 hir::ItemExternCrate(..) |
1162 hir::ItemForeignMod(..) |
1164 hir::ItemDefaultImpl(..) |
1165 hir::ItemTrait(..) |
1166 hir::ItemMod(..) => {
1167 // Nothing to do, just keep recursing...
1170 hir::ItemImpl(..) => {
1171 if self.mode == TransItemCollectionMode::Eager {
1172 create_trans_items_for_default_impls(self.scx,
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));
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)));
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));
1199 hir::ItemConst(..) => {
1200 // const items only generate translation items if they are
1201 // actually used somewhere. Just declaring them is insufficient.
1203 hir::ItemFn(.., ref generics, _) => {
1204 if !generics.is_type_parameterized() {
1205 let def_id = self.scx.tcx().hir.local_def_id(item.id);
1207 debug!("RootCollector: ItemFn({})",
1208 def_id_to_string(self.scx.tcx(), def_id));
1210 let instance = Instance::mono(self.scx, def_id);
1211 self.output.push(TransItem::Fn(instance));
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.
1222 fn visit_impl_item(&mut self, ii: &'v hir::ImplItem) {
1224 hir::ImplItemKind::Method(hir::MethodSig {
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) {
1232 node: hir::ItemImpl(_, _, ref generics, ..),
1235 generics.is_type_parameterized()
1242 if !generics.is_type_parameterized() && !is_impl_generic {
1243 let def_id = self.scx.tcx().hir.local_def_id(ii.id);
1245 debug!("RootCollector: MethodImplItem({})",
1246 def_id_to_string(self.scx.tcx(), def_id));
1248 let instance = Instance::mono(self.scx, def_id);
1249 self.output.push(TransItem::Fn(instance));
1252 _ => { /* Nothing to do here */ }
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();
1266 ref impl_item_refs) => {
1267 if generics.is_type_parameterized() {
1271 let impl_def_id = tcx.hir.local_def_id(item.id);
1273 debug!("create_trans_items_for_default_impls(item={})",
1274 def_id_to_string(tcx, impl_def_id));
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)
1282 for method in tcx.provided_trait_methods(trait_ref.def_id) {
1283 if overridden_methods.contains(&method.name) {
1287 if !tcx.item_generics(method.def_id).types.is_empty() {
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,
1301 let (def_id, substs) = traits::find_method(tcx,
1306 let predicates = tcx.item_predicates(def_id).predicates
1307 .subst(tcx, substs);
1308 if !traits::normalize_and_test_predicates(tcx, predicates) {
1312 if should_trans_locally(tcx, method.def_id) {
1313 let item = create_fn_trans_item(scx,
1316 tcx.erase_regions(&substs));
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>>)
1333 let mir = scx.tcx().item_mir(instance.def);
1335 let mut visitor = MirNeighborCollector {
1339 param_substs: instance.substs
1342 visitor.visit_mir(&mir);
1343 for promoted in &mir.promoted {
1344 visitor.mir = promoted;
1345 visitor.visit_mir(promoted);
1349 fn def_id_to_string<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
1352 let mut output = String::new();
1353 let printer = DefPathBasedNames::new(tcx, false, false);
1354 printer.push_def_path(def_id, &mut output);
1358 fn type_to_string<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
1361 let mut output = String::new();
1362 let printer = DefPathBasedNames::new(tcx, false, false);
1363 printer.push_type_name(ty, &mut output);