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 public 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 public function, method, or static item,
65 //! we create a mono item consisting of the items DefId and, since we only
66 //! consider non-generic items, an empty type-substitution set. (In eager
67 //! collection mode, during incremental compilation, all non-generic functions
68 //! are considered as roots, as well as when the `-Clink-dead-code` option is
69 //! specified. Functions marked `#[no_mangle]` and functions called by inlinable
70 //! functions also always act as roots.)
72 //! ### Finding neighbor nodes
73 //! Given a mono item node, we can discover neighbors by inspecting its
74 //! MIR. We walk the MIR and any time we hit upon something that signifies a
75 //! reference to another mono item, we have found a neighbor. Since the
76 //! mono item we are currently at is always monomorphic, we also know the
77 //! concrete type arguments of its neighbors, and so all neighbors again will be
78 //! monomorphic. The specific forms a reference to a neighboring node can take
79 //! in MIR are quite diverse. Here is an overview:
81 //! #### Calling Functions/Methods
82 //! The most obvious form of one mono item referencing another is a
83 //! function or method call (represented by a CALL terminator in MIR). But
84 //! calls are not the only thing that might introduce a reference between two
85 //! function mono items, and as we will see below, they are just a
86 //! specialization of the form described next, and consequently will not get any
87 //! special treatment in the algorithm.
89 //! #### Taking a reference to a function or method
90 //! A function does not need to actually be called in order to be a neighbor of
91 //! another function. It suffices to just take a reference in order to introduce
92 //! an edge. Consider the following example:
95 //! # use core::fmt::Display;
96 //! fn print_val<T: Display>(x: T) {
97 //! println!("{}", x);
100 //! fn call_fn(f: &dyn Fn(i32), x: i32) {
105 //! let print_i32 = print_val::<i32>;
106 //! call_fn(&print_i32, 0);
109 //! The MIR of none of these functions will contain an explicit call to
110 //! `print_val::<i32>`. Nonetheless, in order to mono this program, we need
111 //! an instance of this function. Thus, whenever we encounter a function or
112 //! method in operand position, we treat it as a neighbor of the current
113 //! mono item. Calls are just a special case of that.
116 //! In a way, closures are a simple case. Since every closure object needs to be
117 //! constructed somewhere, we can reliably discover them by observing
118 //! `RValue::Aggregate` expressions with `AggregateKind::Closure`. This is also
119 //! true for closures inlined from other crates.
122 //! Drop glue mono items are introduced by MIR drop-statements. The
123 //! generated mono item will again have drop-glue item neighbors if the
124 //! type to be dropped contains nested values that also need to be dropped. It
125 //! might also have a function item neighbor for the explicit `Drop::drop`
126 //! implementation of its type.
128 //! #### Unsizing Casts
129 //! A subtle way of introducing neighbor edges is by casting to a trait object.
130 //! Since the resulting fat-pointer contains a reference to a vtable, we need to
131 //! instantiate all object-save methods of the trait, as we need to store
132 //! pointers to these functions even if they never get called anywhere. This can
133 //! be seen as a special case of taking a function reference.
136 //! Since `Box` expression have special compiler support, no explicit calls to
137 //! `exchange_malloc()` and `box_free()` may show up in MIR, even if the
138 //! compiler will generate them. We have to observe `Rvalue::Box` expressions
139 //! and Box-typed drop-statements for that purpose.
142 //! Interaction with Cross-Crate Inlining
143 //! -------------------------------------
144 //! The binary of a crate will not only contain machine code for the items
145 //! defined in the source code of that crate. It will also contain monomorphic
146 //! instantiations of any extern generic functions and of functions marked with
148 //! The collection algorithm handles this more or less mono. If it is
149 //! about to create a mono item for something with an external `DefId`,
150 //! it will take a look if the MIR for that item is available, and if so just
151 //! proceed normally. If the MIR is not available, it assumes that the item is
152 //! just linked to and no node is created; which is exactly what we want, since
153 //! no machine code should be generated in the current crate for such an item.
155 //! Eager and Lazy Collection Mode
156 //! ------------------------------
157 //! Mono item collection can be performed in one of two modes:
159 //! - Lazy mode means that items will only be instantiated when actually
160 //! referenced. The goal is to produce the least amount of machine code
163 //! - Eager mode is meant to be used in conjunction with incremental compilation
164 //! where a stable set of mono items is more important than a minimal
165 //! one. Thus, eager mode will instantiate drop-glue for every drop-able type
166 //! in the crate, even if no drop call for that type exists (yet). It will
167 //! also instantiate default implementations of trait methods, something that
168 //! otherwise is only done on demand.
173 //! Some things are not yet fully implemented in the current version of this
177 //! Ideally, no mono item should be generated for const fns unless there
178 //! is a call to them that cannot be evaluated at compile time. At the moment
179 //! this is not implemented however: a mono item will be produced
180 //! regardless of whether it is actually needed or not.
182 use rustc_data_structures::fx::{FxHashMap, FxHashSet};
183 use rustc_data_structures::sync::{par_iter, MTLock, MTRef, ParallelIterator};
184 use rustc_hir as hir;
185 use rustc_hir::def::DefKind;
186 use rustc_hir::def_id::{DefId, DefIdMap, LocalDefId, LOCAL_CRATE};
187 use rustc_hir::lang_items::LangItem;
188 use rustc_index::bit_set::GrowableBitSet;
189 use rustc_middle::mir::interpret::{AllocId, ConstValue};
190 use rustc_middle::mir::interpret::{ErrorHandled, GlobalAlloc, Scalar};
191 use rustc_middle::mir::mono::{InstantiationMode, MonoItem};
192 use rustc_middle::mir::visit::Visitor as MirVisitor;
193 use rustc_middle::mir::{self, Local, Location};
194 use rustc_middle::ty::adjustment::{CustomCoerceUnsized, PointerCast};
195 use rustc_middle::ty::print::with_no_trimmed_paths;
196 use rustc_middle::ty::subst::{GenericArgKind, InternalSubsts};
197 use rustc_middle::ty::{self, GenericParamDefKind, Instance, Ty, TyCtxt, TypeFoldable, VtblEntry};
198 use rustc_middle::{middle::codegen_fn_attrs::CodegenFnAttrFlags, mir::visit::TyContext};
199 use rustc_session::config::EntryFnType;
200 use rustc_session::lint::builtin::LARGE_ASSIGNMENTS;
201 use rustc_session::Limit;
202 use rustc_span::source_map::{dummy_spanned, respan, Span, Spanned, DUMMY_SP};
203 use rustc_target::abi::Size;
204 use smallvec::SmallVec;
207 use std::path::PathBuf;
210 pub enum MonoItemCollectionMode {
215 /// Maps every mono item to all mono items it references in its
217 pub struct InliningMap<'tcx> {
218 // Maps a source mono item to the range of mono items
220 // The range selects elements within the `targets` vecs.
221 index: FxHashMap<MonoItem<'tcx>, Range<usize>>,
222 targets: Vec<MonoItem<'tcx>>,
224 // Contains one bit per mono item in the `targets` field. That bit
225 // is true if that mono item needs to be inlined into every CGU.
226 inlines: GrowableBitSet<usize>,
229 impl<'tcx> InliningMap<'tcx> {
230 fn new() -> InliningMap<'tcx> {
232 index: FxHashMap::default(),
234 inlines: GrowableBitSet::with_capacity(1024),
238 fn record_accesses(&mut self, source: MonoItem<'tcx>, new_targets: &[(MonoItem<'tcx>, bool)]) {
239 let start_index = self.targets.len();
240 let new_items_count = new_targets.len();
241 let new_items_count_total = new_items_count + self.targets.len();
243 self.targets.reserve(new_items_count);
244 self.inlines.ensure(new_items_count_total);
246 for (i, (target, inline)) in new_targets.iter().enumerate() {
247 self.targets.push(*target);
249 self.inlines.insert(i + start_index);
253 let end_index = self.targets.len();
254 assert!(self.index.insert(source, start_index..end_index).is_none());
257 // Internally iterate over all items referenced by `source` which will be
258 // made available for inlining.
259 pub fn with_inlining_candidates<F>(&self, source: MonoItem<'tcx>, mut f: F)
261 F: FnMut(MonoItem<'tcx>),
263 if let Some(range) = self.index.get(&source) {
264 for (i, candidate) in self.targets[range.clone()].iter().enumerate() {
265 if self.inlines.contains(range.start + i) {
272 // Internally iterate over all items and the things each accesses.
273 pub fn iter_accesses<F>(&self, mut f: F)
275 F: FnMut(MonoItem<'tcx>, &[MonoItem<'tcx>]),
277 for (&accessor, range) in &self.index {
278 f(accessor, &self.targets[range.clone()])
283 pub fn collect_crate_mono_items(
285 mode: MonoItemCollectionMode,
286 ) -> (FxHashSet<MonoItem<'_>>, InliningMap<'_>) {
287 let _prof_timer = tcx.prof.generic_activity("monomorphization_collector");
290 tcx.sess.time("monomorphization_collector_root_collections", || collect_roots(tcx, mode));
292 debug!("building mono item graph, beginning at roots");
294 let mut visited = MTLock::new(FxHashSet::default());
295 let mut inlining_map = MTLock::new(InliningMap::new());
296 let recursion_limit = tcx.recursion_limit();
299 let visited: MTRef<'_, _> = &mut visited;
300 let inlining_map: MTRef<'_, _> = &mut inlining_map;
302 tcx.sess.time("monomorphization_collector_graph_walk", || {
303 par_iter(roots).for_each(|root| {
304 let mut recursion_depths = DefIdMap::default();
309 &mut recursion_depths,
317 (visited.into_inner(), inlining_map.into_inner())
320 // Find all non-generic items by walking the HIR. These items serve as roots to
321 // start monomorphizing from.
322 fn collect_roots(tcx: TyCtxt<'_>, mode: MonoItemCollectionMode) -> Vec<MonoItem<'_>> {
323 debug!("collecting roots");
324 let mut roots = Vec::new();
327 let entry_fn = tcx.entry_fn(());
329 debug!("collect_roots: entry_fn = {:?}", entry_fn);
331 let mut collector = RootCollector { tcx, mode, entry_fn, output: &mut roots };
333 let crate_items = tcx.hir_crate_items(());
335 for id in crate_items.items() {
336 collector.process_item(id);
339 for id in crate_items.impl_items() {
340 collector.process_impl_item(id);
343 collector.push_extra_entry_roots();
346 // We can only codegen items that are instantiable - items all of
347 // whose predicates hold. Luckily, items that aren't instantiable
348 // can't actually be used, so we can just skip codegenning them.
351 .filter_map(|root| root.node.is_instantiable(tcx).then_some(root.node))
355 /// Collect all monomorphized items reachable from `starting_point`, and emit a note diagnostic if a
356 /// post-monorphization error is encountered during a collection step.
357 fn collect_items_rec<'tcx>(
359 starting_point: Spanned<MonoItem<'tcx>>,
360 visited: MTRef<'_, MTLock<FxHashSet<MonoItem<'tcx>>>>,
361 recursion_depths: &mut DefIdMap<usize>,
362 recursion_limit: Limit,
363 inlining_map: MTRef<'_, MTLock<InliningMap<'tcx>>>,
365 if !visited.lock_mut().insert(starting_point.node) {
366 // We've been here already, no need to search again.
369 debug!("BEGIN collect_items_rec({})", starting_point.node);
371 let mut neighbors = Vec::new();
372 let recursion_depth_reset;
375 // Post-monomorphization errors MVP
377 // We can encounter errors while monomorphizing an item, but we don't have a good way of
378 // showing a complete stack of spans ultimately leading to collecting the erroneous one yet.
379 // (It's also currently unclear exactly which diagnostics and information would be interesting
380 // to report in such cases)
382 // This leads to suboptimal error reporting: a post-monomorphization error (PME) will be
383 // shown with just a spanned piece of code causing the error, without information on where
384 // it was called from. This is especially obscure if the erroneous mono item is in a
385 // dependency. See for example issue #85155, where, before minimization, a PME happened two
386 // crates downstream from libcore's stdarch, without a way to know which dependency was the
389 // If such an error occurs in the current crate, its span will be enough to locate the
390 // source. If the cause is in another crate, the goal here is to quickly locate which mono
391 // item in the current crate is ultimately responsible for causing the error.
393 // To give at least _some_ context to the user: while collecting mono items, we check the
394 // error count. If it has changed, a PME occurred, and we trigger some diagnostics about the
395 // current step of mono items collection.
397 let error_count = tcx.sess.diagnostic().err_count();
399 match starting_point.node {
400 MonoItem::Static(def_id) => {
401 let instance = Instance::mono(tcx, def_id);
403 // Sanity check whether this ended up being collected accidentally
404 debug_assert!(should_codegen_locally(tcx, &instance));
406 let ty = instance.ty(tcx, ty::ParamEnv::reveal_all());
407 visit_drop_use(tcx, ty, true, starting_point.span, &mut neighbors);
409 recursion_depth_reset = None;
411 if let Ok(alloc) = tcx.eval_static_initializer(def_id) {
412 for &id in alloc.inner().relocations().values() {
413 collect_miri(tcx, id, &mut neighbors);
417 MonoItem::Fn(instance) => {
418 // Sanity check whether this ended up being collected accidentally
419 debug_assert!(should_codegen_locally(tcx, &instance));
421 // Keep track of the monomorphization recursion depth
422 recursion_depth_reset = Some(check_recursion_limit(
429 check_type_length_limit(tcx, instance);
431 rustc_data_structures::stack::ensure_sufficient_stack(|| {
432 collect_neighbours(tcx, instance, &mut neighbors);
435 MonoItem::GlobalAsm(item_id) => {
436 recursion_depth_reset = None;
438 let item = tcx.hir().item(item_id);
439 if let hir::ItemKind::GlobalAsm(asm) = item.kind {
440 for (op, op_sp) in asm.operands {
442 hir::InlineAsmOperand::Const { .. } => {
443 // Only constants which resolve to a plain integer
444 // are supported. Therefore the value should not
445 // depend on any other items.
447 hir::InlineAsmOperand::SymFn { anon_const } => {
448 let def_id = tcx.hir().body_owner_def_id(anon_const.body).to_def_id();
449 if let Ok(val) = tcx.const_eval_poly(def_id) {
450 rustc_data_structures::stack::ensure_sufficient_stack(|| {
451 collect_const_value(tcx, val, &mut neighbors);
455 hir::InlineAsmOperand::SymStatic { path: _, def_id } => {
456 let instance = Instance::mono(tcx, *def_id);
457 if should_codegen_locally(tcx, &instance) {
458 trace!("collecting static {:?}", def_id);
459 neighbors.push(dummy_spanned(MonoItem::Static(*def_id)));
462 hir::InlineAsmOperand::In { .. }
463 | hir::InlineAsmOperand::Out { .. }
464 | hir::InlineAsmOperand::InOut { .. }
465 | hir::InlineAsmOperand::SplitInOut { .. } => {
466 span_bug!(*op_sp, "invalid operand type for global_asm!")
471 span_bug!(item.span, "Mismatch between hir::Item type and MonoItem type")
476 // Check for PMEs and emit a diagnostic if one happened. To try to show relevant edges of the
477 // mono item graph where the PME diagnostics are currently the most problematic (e.g. ones
478 // involving a dependency, and the lack of context is confusing) in this MVP, we focus on
479 // diagnostics on edges crossing a crate boundary: the collected mono items which are not
480 // defined in the local crate.
481 if tcx.sess.diagnostic().err_count() > error_count
482 && starting_point.node.krate() != LOCAL_CRATE
483 && starting_point.node.is_user_defined()
485 let formatted_item = with_no_trimmed_paths!(starting_point.node.to_string());
486 tcx.sess.span_note_without_error(
488 &format!("the above error was encountered while instantiating `{}`", formatted_item),
492 record_accesses(tcx, starting_point.node, neighbors.iter().map(|i| &i.node), inlining_map);
494 for neighbour in neighbors {
495 collect_items_rec(tcx, neighbour, visited, recursion_depths, recursion_limit, inlining_map);
498 if let Some((def_id, depth)) = recursion_depth_reset {
499 recursion_depths.insert(def_id, depth);
502 debug!("END collect_items_rec({})", starting_point.node);
505 fn record_accesses<'a, 'tcx: 'a>(
507 caller: MonoItem<'tcx>,
508 callees: impl Iterator<Item = &'a MonoItem<'tcx>>,
509 inlining_map: MTRef<'_, MTLock<InliningMap<'tcx>>>,
511 let is_inlining_candidate = |mono_item: &MonoItem<'tcx>| {
512 mono_item.instantiation_mode(tcx) == InstantiationMode::LocalCopy
515 // We collect this into a `SmallVec` to avoid calling `is_inlining_candidate` in the lock.
516 // FIXME: Call `is_inlining_candidate` when pushing to `neighbors` in `collect_items_rec`
517 // instead to avoid creating this `SmallVec`.
518 let accesses: SmallVec<[_; 128]> =
519 callees.map(|mono_item| (*mono_item, is_inlining_candidate(mono_item))).collect();
521 inlining_map.lock_mut().record_accesses(caller, &accesses);
524 /// Format instance name that is already known to be too long for rustc.
525 /// Show only the first and last 32 characters to avoid blasting
526 /// the user's terminal with thousands of lines of type-name.
528 /// If the type name is longer than before+after, it will be written to a file.
529 fn shrunk_instance_name<'tcx>(
531 instance: &Instance<'tcx>,
534 ) -> (String, Option<PathBuf>) {
535 let s = instance.to_string();
537 // Only use the shrunk version if it's really shorter.
538 // This also avoids the case where before and after slices overlap.
539 if s.chars().nth(before + after + 1).is_some() {
540 // An iterator of all byte positions including the end of the string.
541 let positions = || s.char_indices().map(|(i, _)| i).chain(iter::once(s.len()));
543 let shrunk = format!(
544 "{before}...{after}",
545 before = &s[..positions().nth(before).unwrap_or(s.len())],
546 after = &s[positions().rev().nth(after).unwrap_or(0)..],
549 let path = tcx.output_filenames(()).temp_path_ext("long-type.txt", None);
550 let written_to_path = std::fs::write(&path, s).ok().map(|_| path);
552 (shrunk, written_to_path)
558 fn check_recursion_limit<'tcx>(
560 instance: Instance<'tcx>,
562 recursion_depths: &mut DefIdMap<usize>,
563 recursion_limit: Limit,
564 ) -> (DefId, usize) {
565 let def_id = instance.def_id();
566 let recursion_depth = recursion_depths.get(&def_id).cloned().unwrap_or(0);
567 debug!(" => recursion depth={}", recursion_depth);
569 let adjusted_recursion_depth = if Some(def_id) == tcx.lang_items().drop_in_place_fn() {
570 // HACK: drop_in_place creates tight monomorphization loops. Give
577 // Code that needs to instantiate the same function recursively
578 // more than the recursion limit is assumed to be causing an
579 // infinite expansion.
580 if !recursion_limit.value_within_limit(adjusted_recursion_depth) {
581 let (shrunk, written_to_path) = shrunk_instance_name(tcx, &instance, 32, 32);
582 let error = format!("reached the recursion limit while instantiating `{}`", shrunk);
583 let mut err = tcx.sess.struct_span_fatal(span, &error);
585 tcx.def_span(def_id),
586 &format!("`{}` defined here", tcx.def_path_str(def_id)),
588 if let Some(path) = written_to_path {
589 err.note(&format!("the full type name has been written to '{}'", path.display()));
594 recursion_depths.insert(def_id, recursion_depth + 1);
596 (def_id, recursion_depth)
599 fn check_type_length_limit<'tcx>(tcx: TyCtxt<'tcx>, instance: Instance<'tcx>) {
600 let type_length = instance
603 .flat_map(|arg| arg.walk())
604 .filter(|arg| match arg.unpack() {
605 GenericArgKind::Type(_) | GenericArgKind::Const(_) => true,
606 GenericArgKind::Lifetime(_) => false,
609 debug!(" => type length={}", type_length);
611 // Rust code can easily create exponentially-long types using only a
612 // polynomial recursion depth. Even with the default recursion
613 // depth, you can easily get cases that take >2^60 steps to run,
614 // which means that rustc basically hangs.
616 // Bail out in these cases to avoid that bad user experience.
617 if !tcx.type_length_limit().value_within_limit(type_length) {
618 let (shrunk, written_to_path) = shrunk_instance_name(tcx, &instance, 32, 32);
619 let msg = format!("reached the type-length limit while instantiating `{}`", shrunk);
620 let mut diag = tcx.sess.struct_span_fatal(tcx.def_span(instance.def_id()), &msg);
621 if let Some(path) = written_to_path {
622 diag.note(&format!("the full type name has been written to '{}'", path.display()));
625 "consider adding a `#![type_length_limit=\"{}\"]` attribute to your crate",
632 struct MirNeighborCollector<'a, 'tcx> {
634 body: &'a mir::Body<'tcx>,
635 output: &'a mut Vec<Spanned<MonoItem<'tcx>>>,
636 instance: Instance<'tcx>,
639 impl<'a, 'tcx> MirNeighborCollector<'a, 'tcx> {
640 pub fn monomorphize<T>(&self, value: T) -> T
642 T: TypeFoldable<'tcx>,
644 debug!("monomorphize: self.instance={:?}", self.instance);
645 self.instance.subst_mir_and_normalize_erasing_regions(
647 ty::ParamEnv::reveal_all(),
653 impl<'a, 'tcx> MirVisitor<'tcx> for MirNeighborCollector<'a, 'tcx> {
654 fn visit_rvalue(&mut self, rvalue: &mir::Rvalue<'tcx>, location: Location) {
655 debug!("visiting rvalue {:?}", *rvalue);
657 let span = self.body.source_info(location).span;
660 // When doing an cast from a regular pointer to a fat pointer, we
661 // have to instantiate all methods of the trait being cast to, so we
662 // can build the appropriate vtable.
664 mir::CastKind::Pointer(PointerCast::Unsize),
668 let target_ty = self.monomorphize(target_ty);
669 let source_ty = operand.ty(self.body, self.tcx);
670 let source_ty = self.monomorphize(source_ty);
671 let (source_ty, target_ty) =
672 find_vtable_types_for_unsizing(self.tcx, source_ty, target_ty);
673 // This could also be a different Unsize instruction, like
674 // from a fixed sized array to a slice. But we are only
675 // interested in things that produce a vtable.
676 if target_ty.is_trait() && !source_ty.is_trait() {
677 create_mono_items_for_vtable_methods(
687 mir::CastKind::Pointer(PointerCast::ReifyFnPointer),
691 let fn_ty = operand.ty(self.body, self.tcx);
692 let fn_ty = self.monomorphize(fn_ty);
693 visit_fn_use(self.tcx, fn_ty, false, span, &mut self.output);
696 mir::CastKind::Pointer(PointerCast::ClosureFnPointer(_)),
700 let source_ty = operand.ty(self.body, self.tcx);
701 let source_ty = self.monomorphize(source_ty);
702 match *source_ty.kind() {
703 ty::Closure(def_id, substs) => {
704 let instance = Instance::resolve_closure(
708 ty::ClosureKind::FnOnce,
710 if should_codegen_locally(self.tcx, &instance) {
711 self.output.push(create_fn_mono_item(self.tcx, instance, span));
717 mir::Rvalue::ThreadLocalRef(def_id) => {
718 assert!(self.tcx.is_thread_local_static(def_id));
719 let instance = Instance::mono(self.tcx, def_id);
720 if should_codegen_locally(self.tcx, &instance) {
721 trace!("collecting thread-local static {:?}", def_id);
722 self.output.push(respan(span, MonoItem::Static(def_id)));
725 _ => { /* not interesting */ }
728 self.super_rvalue(rvalue, location);
731 /// This does not walk the constant, as it has been handled entirely here and trying
732 /// to walk it would attempt to evaluate the `ty::Const` inside, which doesn't necessarily
733 /// work, as some constants cannot be represented in the type system.
734 fn visit_constant(&mut self, constant: &mir::Constant<'tcx>, location: Location) {
735 let literal = self.monomorphize(constant.literal);
736 let val = match literal {
737 mir::ConstantKind::Val(val, _) => val,
738 mir::ConstantKind::Ty(ct) => match ct.val() {
739 ty::ConstKind::Value(val) => val,
740 ty::ConstKind::Unevaluated(ct) => {
741 let param_env = ty::ParamEnv::reveal_all();
742 match self.tcx.const_eval_resolve(param_env, ct, None) {
743 // The `monomorphize` call should have evaluated that constant already.
745 Err(ErrorHandled::Reported(_) | ErrorHandled::Linted) => return,
746 Err(ErrorHandled::TooGeneric) => span_bug!(
747 self.body.source_info(location).span,
748 "collection encountered polymorphic constant: {:?}",
756 collect_const_value(self.tcx, val, self.output);
757 self.visit_ty(literal.ty(), TyContext::Location(location));
760 fn visit_const(&mut self, constant: ty::Const<'tcx>, location: Location) {
761 debug!("visiting const {:?} @ {:?}", constant, location);
763 let substituted_constant = self.monomorphize(constant);
764 let param_env = ty::ParamEnv::reveal_all();
766 match substituted_constant.val() {
767 ty::ConstKind::Value(val) => collect_const_value(self.tcx, val, self.output),
768 ty::ConstKind::Unevaluated(unevaluated) => {
769 match self.tcx.const_eval_resolve(param_env, unevaluated, None) {
770 // The `monomorphize` call should have evaluated that constant already.
771 Ok(val) => span_bug!(
772 self.body.source_info(location).span,
773 "collection encountered the unevaluated constant {} which evaluated to {:?}",
774 substituted_constant,
777 Err(ErrorHandled::Reported(_) | ErrorHandled::Linted) => {}
778 Err(ErrorHandled::TooGeneric) => span_bug!(
779 self.body.source_info(location).span,
780 "collection encountered polymorphic constant: {}",
788 self.super_const(constant);
791 fn visit_terminator(&mut self, terminator: &mir::Terminator<'tcx>, location: Location) {
792 debug!("visiting terminator {:?} @ {:?}", terminator, location);
793 let source = self.body.source_info(location).span;
796 match terminator.kind {
797 mir::TerminatorKind::Call { ref func, .. } => {
798 let callee_ty = func.ty(self.body, tcx);
799 let callee_ty = self.monomorphize(callee_ty);
800 visit_fn_use(self.tcx, callee_ty, true, source, &mut self.output);
802 mir::TerminatorKind::Drop { ref place, .. }
803 | mir::TerminatorKind::DropAndReplace { ref place, .. } => {
804 let ty = place.ty(self.body, self.tcx).ty;
805 let ty = self.monomorphize(ty);
806 visit_drop_use(self.tcx, ty, true, source, self.output);
808 mir::TerminatorKind::InlineAsm { ref operands, .. } => {
811 mir::InlineAsmOperand::SymFn { ref value } => {
812 let fn_ty = self.monomorphize(value.literal.ty());
813 visit_fn_use(self.tcx, fn_ty, false, source, &mut self.output);
815 mir::InlineAsmOperand::SymStatic { def_id } => {
816 let instance = Instance::mono(self.tcx, def_id);
817 if should_codegen_locally(self.tcx, &instance) {
818 trace!("collecting asm sym static {:?}", def_id);
819 self.output.push(respan(source, MonoItem::Static(def_id)));
826 mir::TerminatorKind::Assert { ref msg, .. } => {
827 let lang_item = match msg {
828 mir::AssertKind::BoundsCheck { .. } => LangItem::PanicBoundsCheck,
829 _ => LangItem::Panic,
831 let instance = Instance::mono(tcx, tcx.require_lang_item(lang_item, Some(source)));
832 if should_codegen_locally(tcx, &instance) {
833 self.output.push(create_fn_mono_item(tcx, instance, source));
836 mir::TerminatorKind::Abort { .. } => {
837 let instance = Instance::mono(
839 tcx.require_lang_item(LangItem::PanicNoUnwind, Some(source)),
841 if should_codegen_locally(tcx, &instance) {
842 self.output.push(create_fn_mono_item(tcx, instance, source));
845 mir::TerminatorKind::Goto { .. }
846 | mir::TerminatorKind::SwitchInt { .. }
847 | mir::TerminatorKind::Resume
848 | mir::TerminatorKind::Return
849 | mir::TerminatorKind::Unreachable => {}
850 mir::TerminatorKind::GeneratorDrop
851 | mir::TerminatorKind::Yield { .. }
852 | mir::TerminatorKind::FalseEdge { .. }
853 | mir::TerminatorKind::FalseUnwind { .. } => bug!(),
856 self.super_terminator(terminator, location);
859 fn visit_operand(&mut self, operand: &mir::Operand<'tcx>, location: Location) {
860 self.super_operand(operand, location);
861 let limit = self.tcx.move_size_limit().0;
865 let limit = Size::from_bytes(limit);
866 let ty = operand.ty(self.body, self.tcx);
867 let ty = self.monomorphize(ty);
868 let layout = self.tcx.layout_of(ty::ParamEnv::reveal_all().and(ty));
869 if let Ok(layout) = layout {
870 if layout.size > limit {
872 let source_info = self.body.source_info(location);
873 debug!(?source_info);
874 let lint_root = source_info.scope.lint_root(&self.body.source_scopes);
876 let Some(lint_root) = lint_root else {
877 // This happens when the issue is in a function from a foreign crate that
878 // we monomorphized in the current crate. We can't get a `HirId` for things
880 // FIXME: Find out where to report the lint on. Maybe simply crate-level lint root
881 // but correct span? This would make the lint at least accept crate-level lint attributes.
884 self.tcx.struct_span_lint_hir(
889 let mut err = lint.build(&format!("moving {} bytes", layout.size.bytes()));
890 err.span_label(source_info.span, "value moved from here");
891 err.note(&format!(r#"The current maximum size is {}, but it can be customized with the move_size_limit attribute: `#![move_size_limit = "..."]`"#, limit.bytes()));
901 _place_local: &Local,
902 _context: mir::visit::PlaceContext,
908 fn visit_drop_use<'tcx>(
911 is_direct_call: bool,
913 output: &mut Vec<Spanned<MonoItem<'tcx>>>,
915 let instance = Instance::resolve_drop_in_place(tcx, ty);
916 visit_instance_use(tcx, instance, is_direct_call, source, output);
919 fn visit_fn_use<'tcx>(
922 is_direct_call: bool,
924 output: &mut Vec<Spanned<MonoItem<'tcx>>>,
926 if let ty::FnDef(def_id, substs) = *ty.kind() {
927 let instance = if is_direct_call {
928 ty::Instance::resolve(tcx, ty::ParamEnv::reveal_all(), def_id, substs).unwrap().unwrap()
930 ty::Instance::resolve_for_fn_ptr(tcx, ty::ParamEnv::reveal_all(), def_id, substs)
933 visit_instance_use(tcx, instance, is_direct_call, source, output);
937 fn visit_instance_use<'tcx>(
939 instance: ty::Instance<'tcx>,
940 is_direct_call: bool,
942 output: &mut Vec<Spanned<MonoItem<'tcx>>>,
944 debug!("visit_item_use({:?}, is_direct_call={:?})", instance, is_direct_call);
945 if !should_codegen_locally(tcx, &instance) {
950 ty::InstanceDef::Virtual(..) | ty::InstanceDef::Intrinsic(_) => {
952 bug!("{:?} being reified", instance);
955 ty::InstanceDef::DropGlue(_, None) => {
956 // Don't need to emit noop drop glue if we are calling directly.
958 output.push(create_fn_mono_item(tcx, instance, source));
961 ty::InstanceDef::DropGlue(_, Some(_))
962 | ty::InstanceDef::VtableShim(..)
963 | ty::InstanceDef::ReifyShim(..)
964 | ty::InstanceDef::ClosureOnceShim { .. }
965 | ty::InstanceDef::Item(..)
966 | ty::InstanceDef::FnPtrShim(..)
967 | ty::InstanceDef::CloneShim(..) => {
968 output.push(create_fn_mono_item(tcx, instance, source));
973 /// Returns `true` if we should codegen an instance in the local crate, or returns `false` if we
974 /// can just link to the upstream crate and therefore don't need a mono item.
975 fn should_codegen_locally<'tcx>(tcx: TyCtxt<'tcx>, instance: &Instance<'tcx>) -> bool {
976 let Some(def_id) = instance.def.def_id_if_not_guaranteed_local_codegen() else {
980 if tcx.is_foreign_item(def_id) {
981 // Foreign items are always linked against, there's no way of instantiating them.
985 if def_id.is_local() {
986 // Local items cannot be referred to locally without monomorphizing them locally.
990 if tcx.is_reachable_non_generic(def_id)
991 || instance.polymorphize(tcx).upstream_monomorphization(tcx).is_some()
993 // We can link to the item in question, no instance needed in this crate.
997 if !tcx.is_mir_available(def_id) {
998 bug!("no MIR available for {:?}", def_id);
1004 /// For a given pair of source and target type that occur in an unsizing coercion,
1005 /// this function finds the pair of types that determines the vtable linking
1008 /// For example, the source type might be `&SomeStruct` and the target type
1009 /// might be `&SomeTrait` in a cast like:
1011 /// let src: &SomeStruct = ...;
1012 /// let target = src as &SomeTrait;
1014 /// Then the output of this function would be (SomeStruct, SomeTrait) since for
1015 /// constructing the `target` fat-pointer we need the vtable for that pair.
1017 /// Things can get more complicated though because there's also the case where
1018 /// the unsized type occurs as a field:
1021 /// struct ComplexStruct<T: ?Sized> {
1028 /// In this case, if `T` is sized, `&ComplexStruct<T>` is a thin pointer. If `T`
1029 /// is unsized, `&SomeStruct` is a fat pointer, and the vtable it points to is
1030 /// for the pair of `T` (which is a trait) and the concrete type that `T` was
1031 /// originally coerced from:
1033 /// let src: &ComplexStruct<SomeStruct> = ...;
1034 /// let target = src as &ComplexStruct<SomeTrait>;
1036 /// Again, we want this `find_vtable_types_for_unsizing()` to provide the pair
1037 /// `(SomeStruct, SomeTrait)`.
1039 /// Finally, there is also the case of custom unsizing coercions, e.g., for
1040 /// smart pointers such as `Rc` and `Arc`.
1041 fn find_vtable_types_for_unsizing<'tcx>(
1043 source_ty: Ty<'tcx>,
1044 target_ty: Ty<'tcx>,
1045 ) -> (Ty<'tcx>, Ty<'tcx>) {
1046 let ptr_vtable = |inner_source: Ty<'tcx>, inner_target: Ty<'tcx>| {
1047 let param_env = ty::ParamEnv::reveal_all();
1048 let type_has_metadata = |ty: Ty<'tcx>| -> bool {
1049 if ty.is_sized(tcx.at(DUMMY_SP), param_env) {
1052 let tail = tcx.struct_tail_erasing_lifetimes(ty, param_env);
1054 ty::Foreign(..) => false,
1055 ty::Str | ty::Slice(..) | ty::Dynamic(..) => true,
1056 _ => bug!("unexpected unsized tail: {:?}", tail),
1059 if type_has_metadata(inner_source) {
1060 (inner_source, inner_target)
1062 tcx.struct_lockstep_tails_erasing_lifetimes(inner_source, inner_target, param_env)
1066 match (&source_ty.kind(), &target_ty.kind()) {
1067 (&ty::Ref(_, a, _), &ty::Ref(_, b, _) | &ty::RawPtr(ty::TypeAndMut { ty: b, .. }))
1068 | (&ty::RawPtr(ty::TypeAndMut { ty: a, .. }), &ty::RawPtr(ty::TypeAndMut { ty: b, .. })) => {
1071 (&ty::Adt(def_a, _), &ty::Adt(def_b, _)) if def_a.is_box() && def_b.is_box() => {
1072 ptr_vtable(source_ty.boxed_ty(), target_ty.boxed_ty())
1075 (&ty::Adt(source_adt_def, source_substs), &ty::Adt(target_adt_def, target_substs)) => {
1076 assert_eq!(source_adt_def, target_adt_def);
1078 let CustomCoerceUnsized::Struct(coerce_index) =
1079 crate::custom_coerce_unsize_info(tcx, source_ty, target_ty);
1081 let source_fields = &source_adt_def.non_enum_variant().fields;
1082 let target_fields = &target_adt_def.non_enum_variant().fields;
1085 coerce_index < source_fields.len() && source_fields.len() == target_fields.len()
1088 find_vtable_types_for_unsizing(
1090 source_fields[coerce_index].ty(tcx, source_substs),
1091 target_fields[coerce_index].ty(tcx, target_substs),
1095 "find_vtable_types_for_unsizing: invalid coercion {:?} -> {:?}",
1102 fn create_fn_mono_item<'tcx>(
1104 instance: Instance<'tcx>,
1106 ) -> Spanned<MonoItem<'tcx>> {
1107 debug!("create_fn_mono_item(instance={})", instance);
1109 let def_id = instance.def_id();
1110 if tcx.sess.opts.debugging_opts.profile_closures && def_id.is_local() && tcx.is_closure(def_id)
1112 crate::util::dump_closure_profile(tcx, instance);
1115 respan(source, MonoItem::Fn(instance.polymorphize(tcx)))
1118 /// Creates a `MonoItem` for each method that is referenced by the vtable for
1119 /// the given trait/impl pair.
1120 fn create_mono_items_for_vtable_methods<'tcx>(
1125 output: &mut Vec<Spanned<MonoItem<'tcx>>>,
1127 assert!(!trait_ty.has_escaping_bound_vars() && !impl_ty.has_escaping_bound_vars());
1129 if let ty::Dynamic(ref trait_ty, ..) = trait_ty.kind() {
1130 if let Some(principal) = trait_ty.principal() {
1131 let poly_trait_ref = principal.with_self_ty(tcx, impl_ty);
1132 assert!(!poly_trait_ref.has_escaping_bound_vars());
1134 // Walk all methods of the trait, including those of its supertraits
1135 let entries = tcx.vtable_entries(poly_trait_ref);
1136 let methods = entries
1138 .filter_map(|entry| match entry {
1139 VtblEntry::MetadataDropInPlace
1140 | VtblEntry::MetadataSize
1141 | VtblEntry::MetadataAlign
1142 | VtblEntry::Vacant => None,
1143 VtblEntry::TraitVPtr(_) => {
1144 // all super trait items already covered, so skip them.
1147 VtblEntry::Method(instance) => {
1148 Some(*instance).filter(|instance| should_codegen_locally(tcx, instance))
1151 .map(|item| create_fn_mono_item(tcx, item, source));
1152 output.extend(methods);
1155 // Also add the destructor.
1156 visit_drop_use(tcx, impl_ty, false, source, output);
1160 //=-----------------------------------------------------------------------------
1162 //=-----------------------------------------------------------------------------
1164 struct RootCollector<'a, 'tcx> {
1166 mode: MonoItemCollectionMode,
1167 output: &'a mut Vec<Spanned<MonoItem<'tcx>>>,
1168 entry_fn: Option<(DefId, EntryFnType)>,
1171 impl<'v> RootCollector<'_, 'v> {
1172 fn process_item(&mut self, id: hir::ItemId) {
1173 match self.tcx.hir().def_kind(id.def_id) {
1174 DefKind::Enum | DefKind::Struct | DefKind::Union => {
1175 let item = self.tcx.hir().item(id);
1177 hir::ItemKind::Enum(_, ref generics)
1178 | hir::ItemKind::Struct(_, ref generics)
1179 | hir::ItemKind::Union(_, ref generics) => {
1180 if generics.params.is_empty() {
1181 if self.mode == MonoItemCollectionMode::Eager {
1183 "RootCollector: ADT drop-glue for {}",
1184 self.tcx.def_path_str(item.def_id.to_def_id())
1188 Instance::new(item.def_id.to_def_id(), InternalSubsts::empty())
1189 .ty(self.tcx, ty::ParamEnv::reveal_all());
1190 visit_drop_use(self.tcx, ty, true, DUMMY_SP, self.output);
1197 DefKind::GlobalAsm => {
1199 "RootCollector: ItemKind::GlobalAsm({})",
1200 self.tcx.def_path_str(id.def_id.to_def_id())
1202 self.output.push(dummy_spanned(MonoItem::GlobalAsm(id)));
1204 DefKind::Static(..) => {
1206 "RootCollector: ItemKind::Static({})",
1207 self.tcx.def_path_str(id.def_id.to_def_id())
1209 self.output.push(dummy_spanned(MonoItem::Static(id.def_id.to_def_id())));
1212 // const items only generate mono items if they are
1213 // actually used somewhere. Just declaring them is insufficient.
1215 // but even just declaring them must collect the items they refer to
1216 if let Ok(val) = self.tcx.const_eval_poly(id.def_id.to_def_id()) {
1217 collect_const_value(self.tcx, val, &mut self.output);
1221 if self.mode == MonoItemCollectionMode::Eager {
1222 let item = self.tcx.hir().item(id);
1223 create_mono_items_for_default_impls(self.tcx, item, self.output);
1227 self.push_if_root(id.def_id);
1233 fn process_impl_item(&mut self, id: hir::ImplItemId) {
1234 if matches!(self.tcx.hir().def_kind(id.def_id), DefKind::AssocFn) {
1235 self.push_if_root(id.def_id);
1239 fn is_root(&self, def_id: LocalDefId) -> bool {
1240 !item_requires_monomorphization(self.tcx, def_id)
1241 && match self.mode {
1242 MonoItemCollectionMode::Eager => true,
1243 MonoItemCollectionMode::Lazy => {
1244 self.entry_fn.and_then(|(id, _)| id.as_local()) == Some(def_id)
1245 || self.tcx.is_reachable_non_generic(def_id)
1248 .codegen_fn_attrs(def_id)
1250 .contains(CodegenFnAttrFlags::RUSTC_STD_INTERNAL_SYMBOL)
1255 /// If `def_id` represents a root, pushes it onto the list of
1256 /// outputs. (Note that all roots must be monomorphic.)
1257 fn push_if_root(&mut self, def_id: LocalDefId) {
1258 if self.is_root(def_id) {
1259 debug!("RootCollector::push_if_root: found root def_id={:?}", def_id);
1261 let instance = Instance::mono(self.tcx, def_id.to_def_id());
1262 self.output.push(create_fn_mono_item(self.tcx, instance, DUMMY_SP));
1266 /// As a special case, when/if we encounter the
1267 /// `main()` function, we also have to generate a
1268 /// monomorphized copy of the start lang item based on
1269 /// the return type of `main`. This is not needed when
1270 /// the user writes their own `start` manually.
1271 fn push_extra_entry_roots(&mut self) {
1272 let Some((main_def_id, EntryFnType::Main)) = self.entry_fn else {
1276 let start_def_id = match self.tcx.lang_items().require(LangItem::Start) {
1278 Err(err) => self.tcx.sess.fatal(&err),
1280 let main_ret_ty = self.tcx.fn_sig(main_def_id).output();
1282 // Given that `main()` has no arguments,
1283 // then its return type cannot have
1284 // late-bound regions, since late-bound
1285 // regions must appear in the argument
1287 let main_ret_ty = self.tcx.normalize_erasing_regions(
1288 ty::ParamEnv::reveal_all(),
1289 main_ret_ty.no_bound_vars().unwrap(),
1292 let start_instance = Instance::resolve(
1294 ty::ParamEnv::reveal_all(),
1296 self.tcx.intern_substs(&[main_ret_ty.into()]),
1301 self.output.push(create_fn_mono_item(self.tcx, start_instance, DUMMY_SP));
1305 fn item_requires_monomorphization(tcx: TyCtxt<'_>, def_id: LocalDefId) -> bool {
1306 let generics = tcx.generics_of(def_id);
1307 generics.requires_monomorphization(tcx)
1310 fn create_mono_items_for_default_impls<'tcx>(
1312 item: &'tcx hir::Item<'tcx>,
1313 output: &mut Vec<Spanned<MonoItem<'tcx>>>,
1316 hir::ItemKind::Impl(ref impl_) => {
1317 for param in impl_.generics.params {
1319 hir::GenericParamKind::Lifetime { .. } => {}
1320 hir::GenericParamKind::Type { .. } | hir::GenericParamKind::Const { .. } => {
1327 "create_mono_items_for_default_impls(item={})",
1328 tcx.def_path_str(item.def_id.to_def_id())
1331 if let Some(trait_ref) = tcx.impl_trait_ref(item.def_id) {
1332 let param_env = ty::ParamEnv::reveal_all();
1333 let trait_ref = tcx.normalize_erasing_regions(param_env, trait_ref);
1334 let overridden_methods = tcx.impl_item_implementor_ids(item.def_id);
1335 for method in tcx.provided_trait_methods(trait_ref.def_id) {
1336 if overridden_methods.contains_key(&method.def_id) {
1340 if tcx.generics_of(method.def_id).own_requires_monomorphization() {
1345 InternalSubsts::for_item(tcx, method.def_id, |param, _| match param.kind {
1346 GenericParamDefKind::Lifetime => tcx.lifetimes.re_erased.into(),
1347 GenericParamDefKind::Type { .. }
1348 | GenericParamDefKind::Const { .. } => {
1349 trait_ref.substs[param.index as usize]
1352 let instance = ty::Instance::resolve(tcx, param_env, method.def_id, substs)
1356 let mono_item = create_fn_mono_item(tcx, instance, DUMMY_SP);
1357 if mono_item.node.is_instantiable(tcx) && should_codegen_locally(tcx, &instance)
1359 output.push(mono_item);
1368 /// Scans the miri alloc in order to find function calls, closures, and drop-glue.
1369 fn collect_miri<'tcx>(
1372 output: &mut Vec<Spanned<MonoItem<'tcx>>>,
1374 match tcx.global_alloc(alloc_id) {
1375 GlobalAlloc::Static(def_id) => {
1376 assert!(!tcx.is_thread_local_static(def_id));
1377 let instance = Instance::mono(tcx, def_id);
1378 if should_codegen_locally(tcx, &instance) {
1379 trace!("collecting static {:?}", def_id);
1380 output.push(dummy_spanned(MonoItem::Static(def_id)));
1383 GlobalAlloc::Memory(alloc) => {
1384 trace!("collecting {:?} with {:#?}", alloc_id, alloc);
1385 for &inner in alloc.inner().relocations().values() {
1386 rustc_data_structures::stack::ensure_sufficient_stack(|| {
1387 collect_miri(tcx, inner, output);
1391 GlobalAlloc::Function(fn_instance) => {
1392 if should_codegen_locally(tcx, &fn_instance) {
1393 trace!("collecting {:?} with {:#?}", alloc_id, fn_instance);
1394 output.push(create_fn_mono_item(tcx, fn_instance, DUMMY_SP));
1400 /// Scans the MIR in order to find function calls, closures, and drop-glue.
1401 fn collect_neighbours<'tcx>(
1403 instance: Instance<'tcx>,
1404 output: &mut Vec<Spanned<MonoItem<'tcx>>>,
1406 debug!("collect_neighbours: {:?}", instance.def_id());
1407 let body = tcx.instance_mir(instance.def);
1409 MirNeighborCollector { tcx, body: &body, output, instance }.visit_body(&body);
1412 fn collect_const_value<'tcx>(
1414 value: ConstValue<'tcx>,
1415 output: &mut Vec<Spanned<MonoItem<'tcx>>>,
1418 ConstValue::Scalar(Scalar::Ptr(ptr, _size)) => collect_miri(tcx, ptr.provenance, output),
1419 ConstValue::Slice { data: alloc, start: _, end: _ } | ConstValue::ByRef { alloc, .. } => {
1420 for &id in alloc.inner().relocations().values() {
1421 collect_miri(tcx, id, output);