1 //! Mono Item Collection
2 //! ====================
4 //! This module is responsible for discovering all items that will contribute
5 //! to code generation of the crate. The important part here is that it not only
6 //! needs to find syntax-level items (functions, structs, etc) but also all
7 //! their monomorphized instantiations. Every non-generic, non-const function
8 //! maps to one LLVM artifact. Every generic function can produce
9 //! from zero to N artifacts, depending on the sets of type arguments it
10 //! is instantiated with.
11 //! This also applies to generic items from other crates: A generic definition
12 //! in crate X might produce monomorphizations that are compiled into crate Y.
13 //! We also have to collect these here.
15 //! The following kinds of "mono items" are handled here:
23 //! The following things also result in LLVM artifacts, but are not collected
24 //! here, since we instantiate them locally on demand when needed in a given
34 //! Let's define some terms first:
36 //! - A "mono item" is something that results in a function or global in
37 //! the LLVM IR of a codegen unit. Mono items do not stand on their
38 //! own, they can reference other mono items. For example, if function
39 //! `foo()` calls function `bar()` then the mono item for `foo()`
40 //! references the mono item for function `bar()`. In general, the
41 //! definition for mono item A referencing a mono item B is that
42 //! the LLVM artifact produced for A references the LLVM artifact produced
45 //! - Mono items and the references between them form a directed graph,
46 //! where the mono items are the nodes and references form the edges.
47 //! Let's call this graph the "mono item graph".
49 //! - The mono item graph for a program contains all mono items
50 //! that are needed in order to produce the complete LLVM IR of the program.
52 //! The purpose of the algorithm implemented in this module is to build the
53 //! mono item graph for the current crate. It runs in two phases:
55 //! 1. Discover the roots of the graph by traversing the HIR of the crate.
56 //! 2. Starting from the roots, find neighboring nodes by inspecting the MIR
57 //! representation of the item corresponding to a given node, until no more
58 //! new nodes are found.
60 //! ### Discovering roots
62 //! The roots of the mono item graph correspond to the non-generic
63 //! syntactic items in the source code. We find them by walking the HIR of the
64 //! crate, and whenever we hit upon a function, method, or static item, we
65 //! create a mono item consisting of the items DefId and, since we only
66 //! consider non-generic items, an empty type-substitution set.
68 //! ### Finding neighbor nodes
69 //! Given a mono item node, we can discover neighbors by inspecting its
70 //! MIR. We walk the MIR and any time we hit upon something that signifies a
71 //! reference to another mono item, we have found a neighbor. Since the
72 //! mono item we are currently at is always monomorphic, we also know the
73 //! concrete type arguments of its neighbors, and so all neighbors again will be
74 //! monomorphic. The specific forms a reference to a neighboring node can take
75 //! in MIR are quite diverse. Here is an overview:
77 //! #### Calling Functions/Methods
78 //! The most obvious form of one mono item referencing another is a
79 //! function or method call (represented by a CALL terminator in MIR). But
80 //! calls are not the only thing that might introduce a reference between two
81 //! function mono items, and as we will see below, they are just a
82 //! specialization of the form described next, and consequently will not get any
83 //! special treatment in the algorithm.
85 //! #### Taking a reference to a function or method
86 //! A function does not need to actually be called in order to be a neighbor of
87 //! another function. It suffices to just take a reference in order to introduce
88 //! an edge. Consider the following example:
91 //! fn print_val<T: Display>(x: T) {
92 //! println!("{}", x);
95 //! fn call_fn(f: &Fn(i32), x: i32) {
100 //! let print_i32 = print_val::<i32>;
101 //! call_fn(&print_i32, 0);
104 //! The MIR of none of these functions will contain an explicit call to
105 //! `print_val::<i32>`. Nonetheless, in order to mono this program, we need
106 //! an instance of this function. Thus, whenever we encounter a function or
107 //! method in operand position, we treat it as a neighbor of the current
108 //! mono item. Calls are just a special case of that.
111 //! In a way, closures are a simple case. Since every closure object needs to be
112 //! constructed somewhere, we can reliably discover them by observing
113 //! `RValue::Aggregate` expressions with `AggregateKind::Closure`. This is also
114 //! true for closures inlined from other crates.
117 //! Drop glue mono items are introduced by MIR drop-statements. The
118 //! generated mono item will again have drop-glue item neighbors if the
119 //! type to be dropped contains nested values that also need to be dropped. It
120 //! might also have a function item neighbor for the explicit `Drop::drop`
121 //! implementation of its type.
123 //! #### Unsizing Casts
124 //! A subtle way of introducing neighbor edges is by casting to a trait object.
125 //! Since the resulting fat-pointer contains a reference to a vtable, we need to
126 //! instantiate all object-save methods of the trait, as we need to store
127 //! pointers to these functions even if they never get called anywhere. This can
128 //! be seen as a special case of taking a function reference.
131 //! Since `Box` expression have special compiler support, no explicit calls to
132 //! `exchange_malloc()` and `box_free()` may show up in MIR, even if the
133 //! compiler will generate them. We have to observe `Rvalue::Box` expressions
134 //! and Box-typed drop-statements for that purpose.
137 //! Interaction with Cross-Crate Inlining
138 //! -------------------------------------
139 //! The binary of a crate will not only contain machine code for the items
140 //! defined in the source code of that crate. It will also contain monomorphic
141 //! instantiations of any extern generic functions and of functions marked with
143 //! The collection algorithm handles this more or less mono. If it is
144 //! about to create a mono item for something with an external `DefId`,
145 //! it will take a look if the MIR for that item is available, and if so just
146 //! proceed normally. If the MIR is not available, it assumes that the item is
147 //! just linked to and no node is created; which is exactly what we want, since
148 //! no machine code should be generated in the current crate for such an item.
150 //! Eager and Lazy Collection Mode
151 //! ------------------------------
152 //! Mono item collection can be performed in one of two modes:
154 //! - Lazy mode means that items will only be instantiated when actually
155 //! referenced. The goal is to produce the least amount of machine code
158 //! - Eager mode is meant to be used in conjunction with incremental compilation
159 //! where a stable set of mono items is more important than a minimal
160 //! one. Thus, eager mode will instantiate drop-glue for every drop-able type
161 //! in the crate, even if no drop call for that type exists (yet). It will
162 //! also instantiate default implementations of trait methods, something that
163 //! otherwise is only done on demand.
168 //! Some things are not yet fully implemented in the current version of this
172 //! Ideally, no mono item should be generated for const fns unless there
173 //! is a call to them that cannot be evaluated at compile time. At the moment
174 //! this is not implemented however: a mono item will be produced
175 //! regardless of whether it is actually needed or not.
177 use crate::monomorphize
;
179 use rustc_data_structures
::fx
::{FxHashMap, FxHashSet}
;
180 use rustc_data_structures
::sync
::{par_iter, MTLock, MTRef, ParallelIterator}
;
181 use rustc_errors
::{ErrorReported, FatalError}
;
182 use rustc_hir
as hir
;
183 use rustc_hir
::def_id
::{DefId, DefIdMap, LocalDefId, LOCAL_CRATE}
;
184 use rustc_hir
::itemlikevisit
::ItemLikeVisitor
;
185 use rustc_hir
::lang_items
::LangItem
;
186 use rustc_index
::bit_set
::GrowableBitSet
;
187 use rustc_middle
::middle
::codegen_fn_attrs
::CodegenFnAttrFlags
;
188 use rustc_middle
::mir
::interpret
::{AllocId, ConstValue}
;
189 use rustc_middle
::mir
::interpret
::{ErrorHandled, GlobalAlloc, Scalar}
;
190 use rustc_middle
::mir
::mono
::{InstantiationMode, MonoItem}
;
191 use rustc_middle
::mir
::visit
::Visitor
as MirVisitor
;
192 use rustc_middle
::mir
::{self, Local, Location}
;
193 use rustc_middle
::ty
::adjustment
::{CustomCoerceUnsized, PointerCast}
;
194 use rustc_middle
::ty
::subst
::{GenericArgKind, InternalSubsts}
;
195 use rustc_middle
::ty
::{self, GenericParamDefKind, Instance, Ty, TyCtxt, TypeFoldable}
;
196 use rustc_session
::config
::EntryFnType
;
197 use rustc_span
::source_map
::{dummy_spanned, respan, Span, Spanned, DUMMY_SP}
;
198 use smallvec
::SmallVec
;
201 use std
::path
::PathBuf
;
204 pub enum MonoItemCollectionMode
{
209 /// Maps every mono item to all mono items it references in its
211 pub struct InliningMap
<'tcx
> {
212 // Maps a source mono item to the range of mono items
214 // The range selects elements within the `targets` vecs.
215 index
: FxHashMap
<MonoItem
<'tcx
>, Range
<usize>>,
216 targets
: Vec
<MonoItem
<'tcx
>>,
218 // Contains one bit per mono item in the `targets` field. That bit
219 // is true if that mono item needs to be inlined into every CGU.
220 inlines
: GrowableBitSet
<usize>,
223 impl<'tcx
> InliningMap
<'tcx
> {
224 fn new() -> InliningMap
<'tcx
> {
226 index
: FxHashMap
::default(),
228 inlines
: GrowableBitSet
::with_capacity(1024),
232 fn record_accesses(&mut self, source
: MonoItem
<'tcx
>, new_targets
: &[(MonoItem
<'tcx
>, bool
)]) {
233 let start_index
= self.targets
.len();
234 let new_items_count
= new_targets
.len();
235 let new_items_count_total
= new_items_count
+ self.targets
.len();
237 self.targets
.reserve(new_items_count
);
238 self.inlines
.ensure(new_items_count_total
);
240 for (i
, (target
, inline
)) in new_targets
.iter().enumerate() {
241 self.targets
.push(*target
);
243 self.inlines
.insert(i
+ start_index
);
247 let end_index
= self.targets
.len();
248 assert
!(self.index
.insert(source
, start_index
..end_index
).is_none());
251 // Internally iterate over all items referenced by `source` which will be
252 // made available for inlining.
253 pub fn with_inlining_candidates
<F
>(&self, source
: MonoItem
<'tcx
>, mut f
: F
)
255 F
: FnMut(MonoItem
<'tcx
>),
257 if let Some(range
) = self.index
.get(&source
) {
258 for (i
, candidate
) in self.targets
[range
.clone()].iter().enumerate() {
259 if self.inlines
.contains(range
.start
+ i
) {
266 // Internally iterate over all items and the things each accesses.
267 pub fn iter_accesses
<F
>(&self, mut f
: F
)
269 F
: FnMut(MonoItem
<'tcx
>, &[MonoItem
<'tcx
>]),
271 for (&accessor
, range
) in &self.index
{
272 f(accessor
, &self.targets
[range
.clone()])
277 pub fn collect_crate_mono_items(
279 mode
: MonoItemCollectionMode
,
280 ) -> (FxHashSet
<MonoItem
<'_
>>, InliningMap
<'_
>) {
281 let _prof_timer
= tcx
.prof
.generic_activity("monomorphization_collector");
284 tcx
.sess
.time("monomorphization_collector_root_collections", || collect_roots(tcx
, mode
));
286 debug
!("building mono item graph, beginning at roots");
288 let mut visited
= MTLock
::new(FxHashSet
::default());
289 let mut inlining_map
= MTLock
::new(InliningMap
::new());
292 let visited
: MTRef
<'_
, _
> = &mut visited
;
293 let inlining_map
: MTRef
<'_
, _
> = &mut inlining_map
;
295 tcx
.sess
.time("monomorphization_collector_graph_walk", || {
296 par_iter(roots
).for_each(|root
| {
297 let mut recursion_depths
= DefIdMap
::default();
302 &mut recursion_depths
,
309 (visited
.into_inner(), inlining_map
.into_inner())
312 // Find all non-generic items by walking the HIR. These items serve as roots to
313 // start monomorphizing from.
314 fn collect_roots(tcx
: TyCtxt
<'_
>, mode
: MonoItemCollectionMode
) -> Vec
<MonoItem
<'_
>> {
315 debug
!("collecting roots");
316 let mut roots
= Vec
::new();
319 let entry_fn
= tcx
.entry_fn(LOCAL_CRATE
);
321 debug
!("collect_roots: entry_fn = {:?}", entry_fn
);
323 let mut visitor
= RootCollector { tcx, mode, entry_fn, output: &mut roots }
;
325 tcx
.hir().krate().visit_all_item_likes(&mut visitor
);
327 visitor
.push_extra_entry_roots();
330 // We can only codegen items that are instantiable - items all of
331 // whose predicates hold. Luckily, items that aren't instantiable
332 // can't actually be used, so we can just skip codegenning them.
335 .filter_map(|root
| root
.node
.is_instantiable(tcx
).then_some(root
.node
))
339 // Collect all monomorphized items reachable from `starting_point`
340 fn collect_items_rec
<'tcx
>(
342 starting_point
: Spanned
<MonoItem
<'tcx
>>,
343 visited
: MTRef
<'_
, MTLock
<FxHashSet
<MonoItem
<'tcx
>>>>,
344 recursion_depths
: &mut DefIdMap
<usize>,
345 inlining_map
: MTRef
<'_
, MTLock
<InliningMap
<'tcx
>>>,
347 if !visited
.lock_mut().insert(starting_point
.node
) {
348 // We've been here already, no need to search again.
351 debug
!("BEGIN collect_items_rec({})", starting_point
.node
);
353 let mut neighbors
= Vec
::new();
354 let recursion_depth_reset
;
356 match starting_point
.node
{
357 MonoItem
::Static(def_id
) => {
358 let instance
= Instance
::mono(tcx
, def_id
);
360 // Sanity check whether this ended up being collected accidentally
361 debug_assert
!(should_codegen_locally(tcx
, &instance
));
363 let ty
= instance
.ty(tcx
, ty
::ParamEnv
::reveal_all());
364 visit_drop_use(tcx
, ty
, true, starting_point
.span
, &mut neighbors
);
366 recursion_depth_reset
= None
;
368 if let Ok(alloc
) = tcx
.eval_static_initializer(def_id
) {
369 for &((), id
) in alloc
.relocations().values() {
370 collect_miri(tcx
, id
, &mut neighbors
);
374 MonoItem
::Fn(instance
) => {
375 // Sanity check whether this ended up being collected accidentally
376 debug_assert
!(should_codegen_locally(tcx
, &instance
));
378 // Keep track of the monomorphization recursion depth
379 recursion_depth_reset
=
380 Some(check_recursion_limit(tcx
, instance
, starting_point
.span
, recursion_depths
));
381 check_type_length_limit(tcx
, instance
);
383 rustc_data_structures
::stack
::ensure_sufficient_stack(|| {
384 collect_neighbours(tcx
, instance
, &mut neighbors
);
387 MonoItem
::GlobalAsm(..) => {
388 recursion_depth_reset
= None
;
392 record_accesses(tcx
, starting_point
.node
, neighbors
.iter().map(|i
| &i
.node
), inlining_map
);
394 for neighbour
in neighbors
{
395 collect_items_rec(tcx
, neighbour
, visited
, recursion_depths
, inlining_map
);
398 if let Some((def_id
, depth
)) = recursion_depth_reset
{
399 recursion_depths
.insert(def_id
, depth
);
402 debug
!("END collect_items_rec({})", starting_point
.node
);
405 fn record_accesses
<'a
, 'tcx
: 'a
>(
407 caller
: MonoItem
<'tcx
>,
408 callees
: impl Iterator
<Item
= &'a MonoItem
<'tcx
>>,
409 inlining_map
: MTRef
<'_
, MTLock
<InliningMap
<'tcx
>>>,
411 let is_inlining_candidate
= |mono_item
: &MonoItem
<'tcx
>| {
412 mono_item
.instantiation_mode(tcx
) == InstantiationMode
::LocalCopy
415 // We collect this into a `SmallVec` to avoid calling `is_inlining_candidate` in the lock.
416 // FIXME: Call `is_inlining_candidate` when pushing to `neighbors` in `collect_items_rec`
417 // instead to avoid creating this `SmallVec`.
418 let accesses
: SmallVec
<[_
; 128]> =
419 callees
.map(|mono_item
| (*mono_item
, is_inlining_candidate(mono_item
))).collect();
421 inlining_map
.lock_mut().record_accesses(caller
, &accesses
);
424 /// Format instance name that is already known to be too long for rustc.
425 /// Show only the first and last 32 characters to avoid blasting
426 /// the user's terminal with thousands of lines of type-name.
428 /// If the type name is longer than before+after, it will be written to a file.
429 fn shrunk_instance_name(
431 instance
: &Instance
<'tcx
>,
434 ) -> (String
, Option
<PathBuf
>) {
435 let s
= instance
.to_string();
437 // Only use the shrunk version if it's really shorter.
438 // This also avoids the case where before and after slices overlap.
439 if s
.chars().nth(before
+ after
+ 1).is_some() {
440 // An iterator of all byte positions including the end of the string.
441 let positions
= || s
.char_indices().map(|(i
, _
)| i
).chain(iter
::once(s
.len()));
443 let shrunk
= format
!(
444 "{before}...{after}",
445 before
= &s
[..positions().nth(before
).unwrap_or(s
.len())],
446 after
= &s
[positions().rev().nth(after
).unwrap_or(0)..],
449 let path
= tcx
.output_filenames(LOCAL_CRATE
).temp_path_ext("long-type.txt", None
);
450 let written_to_path
= std
::fs
::write(&path
, s
).ok().map(|_
| path
);
452 (shrunk
, written_to_path
)
458 fn check_recursion_limit
<'tcx
>(
460 instance
: Instance
<'tcx
>,
462 recursion_depths
: &mut DefIdMap
<usize>,
463 ) -> (DefId
, usize) {
464 let def_id
= instance
.def_id();
465 let recursion_depth
= recursion_depths
.get(&def_id
).cloned().unwrap_or(0);
466 debug
!(" => recursion depth={}", recursion_depth
);
468 let adjusted_recursion_depth
= if Some(def_id
) == tcx
.lang_items().drop_in_place_fn() {
469 // HACK: drop_in_place creates tight monomorphization loops. Give
476 // Code that needs to instantiate the same function recursively
477 // more than the recursion limit is assumed to be causing an
478 // infinite expansion.
479 if !tcx
.sess
.recursion_limit().value_within_limit(adjusted_recursion_depth
) {
480 let (shrunk
, written_to_path
) = shrunk_instance_name(tcx
, &instance
, 32, 32);
481 let error
= format
!("reached the recursion limit while instantiating `{}`", shrunk
);
482 let mut err
= tcx
.sess
.struct_span_fatal(span
, &error
);
484 tcx
.def_span(def_id
),
485 &format
!("`{}` defined here", tcx
.def_path_str(def_id
)),
487 if let Some(path
) = written_to_path
{
488 err
.note(&format
!("the full type name has been written to '{}'", path
.display()));
494 recursion_depths
.insert(def_id
, recursion_depth
+ 1);
496 (def_id
, recursion_depth
)
499 fn check_type_length_limit
<'tcx
>(tcx
: TyCtxt
<'tcx
>, instance
: Instance
<'tcx
>) {
500 let type_length
= instance
503 .flat_map(|arg
| arg
.walk())
504 .filter(|arg
| match arg
.unpack() {
505 GenericArgKind
::Type(_
) | GenericArgKind
::Const(_
) => true,
506 GenericArgKind
::Lifetime(_
) => false,
509 debug
!(" => type length={}", type_length
);
511 // Rust code can easily create exponentially-long types using only a
512 // polynomial recursion depth. Even with the default recursion
513 // depth, you can easily get cases that take >2^60 steps to run,
514 // which means that rustc basically hangs.
516 // Bail out in these cases to avoid that bad user experience.
517 if !tcx
.sess
.type_length_limit().value_within_limit(type_length
) {
518 let (shrunk
, written_to_path
) = shrunk_instance_name(tcx
, &instance
, 32, 32);
519 let msg
= format
!("reached the type-length limit while instantiating `{}`", shrunk
);
520 let mut diag
= tcx
.sess
.struct_span_fatal(tcx
.def_span(instance
.def_id()), &msg
);
521 if let Some(path
) = written_to_path
{
522 diag
.note(&format
!("the full type name has been written to '{}'", path
.display()));
525 "consider adding a `#![type_length_limit=\"{}\"]` attribute to your crate",
529 tcx
.sess
.abort_if_errors();
533 struct MirNeighborCollector
<'a
, 'tcx
> {
535 body
: &'a mir
::Body
<'tcx
>,
536 output
: &'a
mut Vec
<Spanned
<MonoItem
<'tcx
>>>,
537 instance
: Instance
<'tcx
>,
540 impl<'a
, 'tcx
> MirNeighborCollector
<'a
, 'tcx
> {
541 pub fn monomorphize
<T
>(&self, value
: T
) -> T
543 T
: TypeFoldable
<'tcx
>,
545 debug
!("monomorphize: self.instance={:?}", self.instance
);
546 self.instance
.subst_mir_and_normalize_erasing_regions(
548 ty
::ParamEnv
::reveal_all(),
554 impl<'a
, 'tcx
> MirVisitor
<'tcx
> for MirNeighborCollector
<'a
, 'tcx
> {
555 fn visit_rvalue(&mut self, rvalue
: &mir
::Rvalue
<'tcx
>, location
: Location
) {
556 debug
!("visiting rvalue {:?}", *rvalue
);
558 let span
= self.body
.source_info(location
).span
;
561 // When doing an cast from a regular pointer to a fat pointer, we
562 // have to instantiate all methods of the trait being cast to, so we
563 // can build the appropriate vtable.
565 mir
::CastKind
::Pointer(PointerCast
::Unsize
),
569 let target_ty
= self.monomorphize(target_ty
);
570 let source_ty
= operand
.ty(self.body
, self.tcx
);
571 let source_ty
= self.monomorphize(source_ty
);
572 let (source_ty
, target_ty
) =
573 find_vtable_types_for_unsizing(self.tcx
, source_ty
, target_ty
);
574 // This could also be a different Unsize instruction, like
575 // from a fixed sized array to a slice. But we are only
576 // interested in things that produce a vtable.
577 if target_ty
.is_trait() && !source_ty
.is_trait() {
578 create_mono_items_for_vtable_methods(
588 mir
::CastKind
::Pointer(PointerCast
::ReifyFnPointer
),
592 let fn_ty
= operand
.ty(self.body
, self.tcx
);
593 let fn_ty
= self.monomorphize(fn_ty
);
594 visit_fn_use(self.tcx
, fn_ty
, false, span
, &mut self.output
);
597 mir
::CastKind
::Pointer(PointerCast
::ClosureFnPointer(_
)),
601 let source_ty
= operand
.ty(self.body
, self.tcx
);
602 let source_ty
= self.monomorphize(source_ty
);
603 match *source_ty
.kind() {
604 ty
::Closure(def_id
, substs
) => {
605 let instance
= Instance
::resolve_closure(
609 ty
::ClosureKind
::FnOnce
,
611 if should_codegen_locally(self.tcx
, &instance
) {
612 self.output
.push(create_fn_mono_item(self.tcx
, instance
, span
));
618 mir
::Rvalue
::NullaryOp(mir
::NullOp
::Box
, _
) => {
620 let exchange_malloc_fn_def_id
=
621 tcx
.require_lang_item(LangItem
::ExchangeMalloc
, None
);
622 let instance
= Instance
::mono(tcx
, exchange_malloc_fn_def_id
);
623 if should_codegen_locally(tcx
, &instance
) {
624 self.output
.push(create_fn_mono_item(self.tcx
, instance
, span
));
627 mir
::Rvalue
::ThreadLocalRef(def_id
) => {
628 assert
!(self.tcx
.is_thread_local_static(def_id
));
629 let instance
= Instance
::mono(self.tcx
, def_id
);
630 if should_codegen_locally(self.tcx
, &instance
) {
631 trace
!("collecting thread-local static {:?}", def_id
);
632 self.output
.push(respan(span
, MonoItem
::Static(def_id
)));
635 _
=> { /* not interesting */ }
638 self.super_rvalue(rvalue
, location
);
641 fn visit_const(&mut self, constant
: &&'tcx ty
::Const
<'tcx
>, location
: Location
) {
642 debug
!("visiting const {:?} @ {:?}", *constant
, location
);
644 let substituted_constant
= self.monomorphize(*constant
);
645 let param_env
= ty
::ParamEnv
::reveal_all();
647 match substituted_constant
.val
{
648 ty
::ConstKind
::Value(val
) => collect_const_value(self.tcx
, val
, self.output
),
649 ty
::ConstKind
::Unevaluated(def
, substs
, promoted
) => {
650 match self.tcx
.const_eval_resolve(param_env
, def
, substs
, promoted
, None
) {
651 Ok(val
) => collect_const_value(self.tcx
, val
, self.output
),
652 Err(ErrorHandled
::Reported(ErrorReported
) | ErrorHandled
::Linted
) => {}
653 Err(ErrorHandled
::TooGeneric
) => span_bug
!(
654 self.body
.source_info(location
).span
,
655 "collection encountered polymorphic constant: {}",
663 self.super_const(constant
);
666 fn visit_terminator(&mut self, terminator
: &mir
::Terminator
<'tcx
>, location
: Location
) {
667 debug
!("visiting terminator {:?} @ {:?}", terminator
, location
);
668 let source
= self.body
.source_info(location
).span
;
671 match terminator
.kind
{
672 mir
::TerminatorKind
::Call { ref func, .. }
=> {
673 let callee_ty
= func
.ty(self.body
, tcx
);
674 let callee_ty
= self.monomorphize(callee_ty
);
675 visit_fn_use(self.tcx
, callee_ty
, true, source
, &mut self.output
);
677 mir
::TerminatorKind
::Drop { ref place, .. }
678 | mir
::TerminatorKind
::DropAndReplace { ref place, .. }
=> {
679 let ty
= place
.ty(self.body
, self.tcx
).ty
;
680 let ty
= self.monomorphize(ty
);
681 visit_drop_use(self.tcx
, ty
, true, source
, self.output
);
683 mir
::TerminatorKind
::InlineAsm { ref operands, .. }
=> {
686 mir
::InlineAsmOperand
::SymFn { ref value }
=> {
687 let fn_ty
= self.monomorphize(value
.literal
.ty());
688 visit_fn_use(self.tcx
, fn_ty
, false, source
, &mut self.output
);
690 mir
::InlineAsmOperand
::SymStatic { def_id }
=> {
691 let instance
= Instance
::mono(self.tcx
, def_id
);
692 if should_codegen_locally(self.tcx
, &instance
) {
693 trace
!("collecting asm sym static {:?}", def_id
);
694 self.output
.push(respan(source
, MonoItem
::Static(def_id
)));
701 mir
::TerminatorKind
::Goto { .. }
702 | mir
::TerminatorKind
::SwitchInt { .. }
703 | mir
::TerminatorKind
::Resume
704 | mir
::TerminatorKind
::Abort
705 | mir
::TerminatorKind
::Return
706 | mir
::TerminatorKind
::Unreachable
707 | mir
::TerminatorKind
::Assert { .. }
=> {}
708 mir
::TerminatorKind
::GeneratorDrop
709 | mir
::TerminatorKind
::Yield { .. }
710 | mir
::TerminatorKind
::FalseEdge { .. }
711 | mir
::TerminatorKind
::FalseUnwind { .. }
=> bug
!(),
714 self.super_terminator(terminator
, location
);
719 _place_local
: &Local
,
720 _context
: mir
::visit
::PlaceContext
,
726 fn visit_drop_use
<'tcx
>(
729 is_direct_call
: bool
,
731 output
: &mut Vec
<Spanned
<MonoItem
<'tcx
>>>,
733 let instance
= Instance
::resolve_drop_in_place(tcx
, ty
);
734 visit_instance_use(tcx
, instance
, is_direct_call
, source
, output
);
737 fn visit_fn_use
<'tcx
>(
740 is_direct_call
: bool
,
742 output
: &mut Vec
<Spanned
<MonoItem
<'tcx
>>>,
744 if let ty
::FnDef(def_id
, substs
) = *ty
.kind() {
745 let instance
= if is_direct_call
{
746 ty
::Instance
::resolve(tcx
, ty
::ParamEnv
::reveal_all(), def_id
, substs
).unwrap().unwrap()
748 ty
::Instance
::resolve_for_fn_ptr(tcx
, ty
::ParamEnv
::reveal_all(), def_id
, substs
)
751 visit_instance_use(tcx
, instance
, is_direct_call
, source
, output
);
755 fn visit_instance_use
<'tcx
>(
757 instance
: ty
::Instance
<'tcx
>,
758 is_direct_call
: bool
,
760 output
: &mut Vec
<Spanned
<MonoItem
<'tcx
>>>,
762 debug
!("visit_item_use({:?}, is_direct_call={:?})", instance
, is_direct_call
);
763 if !should_codegen_locally(tcx
, &instance
) {
768 ty
::InstanceDef
::Virtual(..) | ty
::InstanceDef
::Intrinsic(_
) => {
770 bug
!("{:?} being reified", instance
);
773 ty
::InstanceDef
::DropGlue(_
, None
) => {
774 // Don't need to emit noop drop glue if we are calling directly.
776 output
.push(create_fn_mono_item(tcx
, instance
, source
));
779 ty
::InstanceDef
::DropGlue(_
, Some(_
))
780 | ty
::InstanceDef
::VtableShim(..)
781 | ty
::InstanceDef
::ReifyShim(..)
782 | ty
::InstanceDef
::ClosureOnceShim { .. }
783 | ty
::InstanceDef
::Item(..)
784 | ty
::InstanceDef
::FnPtrShim(..)
785 | ty
::InstanceDef
::CloneShim(..) => {
786 output
.push(create_fn_mono_item(tcx
, instance
, source
));
791 // Returns `true` if we should codegen an instance in the local crate.
792 // Returns `false` if we can just link to the upstream crate and therefore don't
794 fn should_codegen_locally
<'tcx
>(tcx
: TyCtxt
<'tcx
>, instance
: &Instance
<'tcx
>) -> bool
{
795 let def_id
= match instance
.def
{
796 ty
::InstanceDef
::Item(def
) => def
.did
,
797 ty
::InstanceDef
::DropGlue(def_id
, Some(_
)) => def_id
,
798 ty
::InstanceDef
::VtableShim(..)
799 | ty
::InstanceDef
::ReifyShim(..)
800 | ty
::InstanceDef
::ClosureOnceShim { .. }
801 | ty
::InstanceDef
::Virtual(..)
802 | ty
::InstanceDef
::FnPtrShim(..)
803 | ty
::InstanceDef
::DropGlue(..)
804 | ty
::InstanceDef
::Intrinsic(_
)
805 | ty
::InstanceDef
::CloneShim(..) => return true,
808 if tcx
.is_foreign_item(def_id
) {
809 // Foreign items are always linked against, there's no way of instantiating them.
813 if def_id
.is_local() {
814 // Local items cannot be referred to locally without monomorphizing them locally.
818 if tcx
.is_reachable_non_generic(def_id
)
819 || instance
.polymorphize(tcx
).upstream_monomorphization(tcx
).is_some()
821 // We can link to the item in question, no instance needed in this crate.
825 if !tcx
.is_mir_available(def_id
) {
826 bug
!("no MIR available for {:?}", def_id
);
832 /// For a given pair of source and target type that occur in an unsizing coercion,
833 /// this function finds the pair of types that determines the vtable linking
836 /// For example, the source type might be `&SomeStruct` and the target type\
837 /// might be `&SomeTrait` in a cast like:
839 /// let src: &SomeStruct = ...;
840 /// let target = src as &SomeTrait;
842 /// Then the output of this function would be (SomeStruct, SomeTrait) since for
843 /// constructing the `target` fat-pointer we need the vtable for that pair.
845 /// Things can get more complicated though because there's also the case where
846 /// the unsized type occurs as a field:
849 /// struct ComplexStruct<T: ?Sized> {
856 /// In this case, if `T` is sized, `&ComplexStruct<T>` is a thin pointer. If `T`
857 /// is unsized, `&SomeStruct` is a fat pointer, and the vtable it points to is
858 /// for the pair of `T` (which is a trait) and the concrete type that `T` was
859 /// originally coerced from:
861 /// let src: &ComplexStruct<SomeStruct> = ...;
862 /// let target = src as &ComplexStruct<SomeTrait>;
864 /// Again, we want this `find_vtable_types_for_unsizing()` to provide the pair
865 /// `(SomeStruct, SomeTrait)`.
867 /// Finally, there is also the case of custom unsizing coercions, e.g., for
868 /// smart pointers such as `Rc` and `Arc`.
869 fn find_vtable_types_for_unsizing
<'tcx
>(
873 ) -> (Ty
<'tcx
>, Ty
<'tcx
>) {
874 let ptr_vtable
= |inner_source
: Ty
<'tcx
>, inner_target
: Ty
<'tcx
>| {
875 let param_env
= ty
::ParamEnv
::reveal_all();
876 let type_has_metadata
= |ty
: Ty
<'tcx
>| -> bool
{
877 if ty
.is_sized(tcx
.at(DUMMY_SP
), param_env
) {
880 let tail
= tcx
.struct_tail_erasing_lifetimes(ty
, param_env
);
882 ty
::Foreign(..) => false,
883 ty
::Str
| ty
::Slice(..) | ty
::Dynamic(..) => true,
884 _
=> bug
!("unexpected unsized tail: {:?}", tail
),
887 if type_has_metadata(inner_source
) {
888 (inner_source
, inner_target
)
890 tcx
.struct_lockstep_tails_erasing_lifetimes(inner_source
, inner_target
, param_env
)
894 match (&source_ty
.kind(), &target_ty
.kind()) {
895 (&ty
::Ref(_
, a
, _
), &ty
::Ref(_
, b
, _
) | &ty
::RawPtr(ty
::TypeAndMut { ty: b, .. }
))
896 | (&ty
::RawPtr(ty
::TypeAndMut { ty: a, .. }
), &ty
::RawPtr(ty
::TypeAndMut { ty: b, .. }
)) => {
899 (&ty
::Adt(def_a
, _
), &ty
::Adt(def_b
, _
)) if def_a
.is_box() && def_b
.is_box() => {
900 ptr_vtable(source_ty
.boxed_ty(), target_ty
.boxed_ty())
903 (&ty
::Adt(source_adt_def
, source_substs
), &ty
::Adt(target_adt_def
, target_substs
)) => {
904 assert_eq
!(source_adt_def
, target_adt_def
);
906 let CustomCoerceUnsized
::Struct(coerce_index
) =
907 monomorphize
::custom_coerce_unsize_info(tcx
, source_ty
, target_ty
);
909 let source_fields
= &source_adt_def
.non_enum_variant().fields
;
910 let target_fields
= &target_adt_def
.non_enum_variant().fields
;
913 coerce_index
< source_fields
.len() && source_fields
.len() == target_fields
.len()
916 find_vtable_types_for_unsizing(
918 source_fields
[coerce_index
].ty(tcx
, source_substs
),
919 target_fields
[coerce_index
].ty(tcx
, target_substs
),
923 "find_vtable_types_for_unsizing: invalid coercion {:?} -> {:?}",
930 fn create_fn_mono_item
<'tcx
>(
932 instance
: Instance
<'tcx
>,
934 ) -> Spanned
<MonoItem
<'tcx
>> {
935 debug
!("create_fn_mono_item(instance={})", instance
);
936 respan(source
, MonoItem
::Fn(instance
.polymorphize(tcx
)))
939 /// Creates a `MonoItem` for each method that is referenced by the vtable for
940 /// the given trait/impl pair.
941 fn create_mono_items_for_vtable_methods
<'tcx
>(
946 output
: &mut Vec
<Spanned
<MonoItem
<'tcx
>>>,
948 assert
!(!trait_ty
.has_escaping_bound_vars() && !impl_ty
.has_escaping_bound_vars());
950 if let ty
::Dynamic(ref trait_ty
, ..) = trait_ty
.kind() {
951 if let Some(principal
) = trait_ty
.principal() {
952 let poly_trait_ref
= principal
.with_self_ty(tcx
, impl_ty
);
953 assert
!(!poly_trait_ref
.has_escaping_bound_vars());
955 // Walk all methods of the trait, including those of its supertraits
956 let methods
= tcx
.vtable_methods(poly_trait_ref
);
957 let methods
= methods
960 .filter_map(|method
| method
)
961 .map(|(def_id
, substs
)| {
962 ty
::Instance
::resolve_for_vtable(
964 ty
::ParamEnv
::reveal_all(),
970 .filter(|&instance
| should_codegen_locally(tcx
, &instance
))
971 .map(|item
| create_fn_mono_item(tcx
, item
, source
));
972 output
.extend(methods
);
975 // Also add the destructor.
976 visit_drop_use(tcx
, impl_ty
, false, source
, output
);
980 //=-----------------------------------------------------------------------------
982 //=-----------------------------------------------------------------------------
984 struct RootCollector
<'a
, 'tcx
> {
986 mode
: MonoItemCollectionMode
,
987 output
: &'a
mut Vec
<Spanned
<MonoItem
<'tcx
>>>,
988 entry_fn
: Option
<(LocalDefId
, EntryFnType
)>,
991 impl ItemLikeVisitor
<'v
> for RootCollector
<'_
, 'v
> {
992 fn visit_item(&mut self, item
: &'v hir
::Item
<'v
>) {
994 hir
::ItemKind
::ExternCrate(..)
995 | hir
::ItemKind
::Use(..)
996 | hir
::ItemKind
::ForeignMod { .. }
997 | hir
::ItemKind
::TyAlias(..)
998 | hir
::ItemKind
::Trait(..)
999 | hir
::ItemKind
::TraitAlias(..)
1000 | hir
::ItemKind
::OpaqueTy(..)
1001 | hir
::ItemKind
::Mod(..) => {
1002 // Nothing to do, just keep recursing.
1005 hir
::ItemKind
::Impl { .. }
=> {
1006 if self.mode
== MonoItemCollectionMode
::Eager
{
1007 create_mono_items_for_default_impls(self.tcx
, item
, self.output
);
1011 hir
::ItemKind
::Enum(_
, ref generics
)
1012 | hir
::ItemKind
::Struct(_
, ref generics
)
1013 | hir
::ItemKind
::Union(_
, ref generics
) => {
1014 if generics
.params
.is_empty() {
1015 if self.mode
== MonoItemCollectionMode
::Eager
{
1017 "RootCollector: ADT drop-glue for {}",
1018 self.tcx
.def_path_str(item
.def_id
.to_def_id())
1021 let ty
= Instance
::new(item
.def_id
.to_def_id(), InternalSubsts
::empty())
1022 .ty(self.tcx
, ty
::ParamEnv
::reveal_all());
1023 visit_drop_use(self.tcx
, ty
, true, DUMMY_SP
, self.output
);
1027 hir
::ItemKind
::GlobalAsm(..) => {
1029 "RootCollector: ItemKind::GlobalAsm({})",
1030 self.tcx
.def_path_str(item
.def_id
.to_def_id())
1032 self.output
.push(dummy_spanned(MonoItem
::GlobalAsm(item
.item_id())));
1034 hir
::ItemKind
::Static(..) => {
1036 "RootCollector: ItemKind::Static({})",
1037 self.tcx
.def_path_str(item
.def_id
.to_def_id())
1039 self.output
.push(dummy_spanned(MonoItem
::Static(item
.def_id
.to_def_id())));
1041 hir
::ItemKind
::Const(..) => {
1042 // const items only generate mono items if they are
1043 // actually used somewhere. Just declaring them is insufficient.
1045 // but even just declaring them must collect the items they refer to
1046 if let Ok(val
) = self.tcx
.const_eval_poly(item
.def_id
.to_def_id()) {
1047 collect_const_value(self.tcx
, val
, &mut self.output
);
1050 hir
::ItemKind
::Fn(..) => {
1051 self.push_if_root(item
.def_id
);
1056 fn visit_trait_item(&mut self, _
: &'v hir
::TraitItem
<'v
>) {
1057 // Even if there's a default body with no explicit generics,
1058 // it's still generic over some `Self: Trait`, so not a root.
1061 fn visit_impl_item(&mut self, ii
: &'v hir
::ImplItem
<'v
>) {
1062 if let hir
::ImplItemKind
::Fn(hir
::FnSig { .. }
, _
) = ii
.kind
{
1063 self.push_if_root(ii
.def_id
);
1067 fn visit_foreign_item(&mut self, _foreign_item
: &'v hir
::ForeignItem
<'v
>) {}
1070 impl RootCollector
<'_
, 'v
> {
1071 fn is_root(&self, def_id
: LocalDefId
) -> bool
{
1072 !item_requires_monomorphization(self.tcx
, def_id
)
1073 && match self.mode
{
1074 MonoItemCollectionMode
::Eager
=> true,
1075 MonoItemCollectionMode
::Lazy
=> {
1076 self.entry_fn
.map(|(id
, _
)| id
) == Some(def_id
)
1077 || self.tcx
.is_reachable_non_generic(def_id
)
1080 .codegen_fn_attrs(def_id
)
1082 .contains(CodegenFnAttrFlags
::RUSTC_STD_INTERNAL_SYMBOL
)
1087 /// If `def_id` represents a root, pushes it onto the list of
1088 /// outputs. (Note that all roots must be monomorphic.)
1089 fn push_if_root(&mut self, def_id
: LocalDefId
) {
1090 if self.is_root(def_id
) {
1091 debug
!("RootCollector::push_if_root: found root def_id={:?}", def_id
);
1093 let instance
= Instance
::mono(self.tcx
, def_id
.to_def_id());
1094 self.output
.push(create_fn_mono_item(self.tcx
, instance
, DUMMY_SP
));
1098 /// As a special case, when/if we encounter the
1099 /// `main()` function, we also have to generate a
1100 /// monomorphized copy of the start lang item based on
1101 /// the return type of `main`. This is not needed when
1102 /// the user writes their own `start` manually.
1103 fn push_extra_entry_roots(&mut self) {
1104 let main_def_id
= match self.entry_fn
{
1105 Some((def_id
, EntryFnType
::Main
)) => def_id
,
1109 let start_def_id
= match self.tcx
.lang_items().require(LangItem
::Start
) {
1111 Err(err
) => self.tcx
.sess
.fatal(&err
),
1113 let main_ret_ty
= self.tcx
.fn_sig(main_def_id
).output();
1115 // Given that `main()` has no arguments,
1116 // then its return type cannot have
1117 // late-bound regions, since late-bound
1118 // regions must appear in the argument
1120 let main_ret_ty
= self.tcx
.erase_regions(main_ret_ty
.no_bound_vars().unwrap());
1122 let start_instance
= Instance
::resolve(
1124 ty
::ParamEnv
::reveal_all(),
1126 self.tcx
.intern_substs(&[main_ret_ty
.into()]),
1131 self.output
.push(create_fn_mono_item(self.tcx
, start_instance
, DUMMY_SP
));
1135 fn item_requires_monomorphization(tcx
: TyCtxt
<'_
>, def_id
: LocalDefId
) -> bool
{
1136 let generics
= tcx
.generics_of(def_id
);
1137 generics
.requires_monomorphization(tcx
)
1140 fn create_mono_items_for_default_impls
<'tcx
>(
1142 item
: &'tcx hir
::Item
<'tcx
>,
1143 output
: &mut Vec
<Spanned
<MonoItem
<'tcx
>>>,
1146 hir
::ItemKind
::Impl(ref impl_
) => {
1147 for param
in impl_
.generics
.params
{
1149 hir
::GenericParamKind
::Lifetime { .. }
=> {}
1150 hir
::GenericParamKind
::Type { .. }
| hir
::GenericParamKind
::Const { .. }
=> {
1157 "create_mono_items_for_default_impls(item={})",
1158 tcx
.def_path_str(item
.def_id
.to_def_id())
1161 if let Some(trait_ref
) = tcx
.impl_trait_ref(item
.def_id
) {
1162 let param_env
= ty
::ParamEnv
::reveal_all();
1163 let trait_ref
= tcx
.normalize_erasing_regions(param_env
, trait_ref
);
1164 let overridden_methods
: FxHashSet
<_
> =
1165 impl_
.items
.iter().map(|iiref
| iiref
.ident
.normalize_to_macros_2_0()).collect();
1166 for method
in tcx
.provided_trait_methods(trait_ref
.def_id
) {
1167 if overridden_methods
.contains(&method
.ident
.normalize_to_macros_2_0()) {
1171 if tcx
.generics_of(method
.def_id
).own_requires_monomorphization() {
1176 InternalSubsts
::for_item(tcx
, method
.def_id
, |param
, _
| match param
.kind
{
1177 GenericParamDefKind
::Lifetime
=> tcx
.lifetimes
.re_erased
.into(),
1178 GenericParamDefKind
::Type { .. }
| GenericParamDefKind
::Const
=> {
1179 trait_ref
.substs
[param
.index
as usize]
1182 let instance
= ty
::Instance
::resolve(tcx
, param_env
, method
.def_id
, substs
)
1186 let mono_item
= create_fn_mono_item(tcx
, instance
, DUMMY_SP
);
1187 if mono_item
.node
.is_instantiable(tcx
) && should_codegen_locally(tcx
, &instance
)
1189 output
.push(mono_item
);
1198 /// Scans the miri alloc in order to find function calls, closures, and drop-glue.
1199 fn collect_miri
<'tcx
>(
1202 output
: &mut Vec
<Spanned
<MonoItem
<'tcx
>>>,
1204 match tcx
.global_alloc(alloc_id
) {
1205 GlobalAlloc
::Static(def_id
) => {
1206 assert
!(!tcx
.is_thread_local_static(def_id
));
1207 let instance
= Instance
::mono(tcx
, def_id
);
1208 if should_codegen_locally(tcx
, &instance
) {
1209 trace
!("collecting static {:?}", def_id
);
1210 output
.push(dummy_spanned(MonoItem
::Static(def_id
)));
1213 GlobalAlloc
::Memory(alloc
) => {
1214 trace
!("collecting {:?} with {:#?}", alloc_id
, alloc
);
1215 for &((), inner
) in alloc
.relocations().values() {
1216 rustc_data_structures
::stack
::ensure_sufficient_stack(|| {
1217 collect_miri(tcx
, inner
, output
);
1221 GlobalAlloc
::Function(fn_instance
) => {
1222 if should_codegen_locally(tcx
, &fn_instance
) {
1223 trace
!("collecting {:?} with {:#?}", alloc_id
, fn_instance
);
1224 output
.push(create_fn_mono_item(tcx
, fn_instance
, DUMMY_SP
));
1230 /// Scans the MIR in order to find function calls, closures, and drop-glue.
1231 fn collect_neighbours
<'tcx
>(
1233 instance
: Instance
<'tcx
>,
1234 output
: &mut Vec
<Spanned
<MonoItem
<'tcx
>>>,
1236 debug
!("collect_neighbours: {:?}", instance
.def_id());
1237 let body
= tcx
.instance_mir(instance
.def
);
1239 MirNeighborCollector { tcx, body: &body, output, instance }
.visit_body(&body
);
1242 fn collect_const_value
<'tcx
>(
1244 value
: ConstValue
<'tcx
>,
1245 output
: &mut Vec
<Spanned
<MonoItem
<'tcx
>>>,
1248 ConstValue
::Scalar(Scalar
::Ptr(ptr
)) => collect_miri(tcx
, ptr
.alloc_id
, output
),
1249 ConstValue
::Slice { data: alloc, start: _, end: _ }
| ConstValue
::ByRef { alloc, .. }
=> {
1250 for &((), id
) in alloc
.relocations().values() {
1251 collect_miri(tcx
, id
, output
);