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Diffstat (limited to 'compiler/rustc_mir/src/monomorphize/collector.rs')
| -rw-r--r-- | compiler/rustc_mir/src/monomorphize/collector.rs | 1242 |
1 files changed, 1242 insertions, 0 deletions
diff --git a/compiler/rustc_mir/src/monomorphize/collector.rs b/compiler/rustc_mir/src/monomorphize/collector.rs new file mode 100644 index 00000000000..d379f4ef428 --- /dev/null +++ b/compiler/rustc_mir/src/monomorphize/collector.rs @@ -0,0 +1,1242 @@ +//! Mono Item Collection +//! ==================== +//! +//! This module is responsible for discovering all items that will contribute +//! to code generation of the crate. The important part here is that it not only +//! needs to find syntax-level items (functions, structs, etc) but also all +//! their monomorphized instantiations. Every non-generic, non-const function +//! maps to one LLVM artifact. Every generic function can produce +//! from zero to N artifacts, depending on the sets of type arguments it +//! is instantiated with. +//! This also applies to generic items from other crates: A generic definition +//! in crate X might produce monomorphizations that are compiled into crate Y. +//! We also have to collect these here. +//! +//! The following kinds of "mono items" are handled here: +//! +//! - Functions +//! - Methods +//! - Closures +//! - Statics +//! - Drop glue +//! +//! The following things also result in LLVM artifacts, but are not collected +//! here, since we instantiate them locally on demand when needed in a given +//! codegen unit: +//! +//! - Constants +//! - Vtables +//! - Object Shims +//! +//! +//! General Algorithm +//! ----------------- +//! Let's define some terms first: +//! +//! - A "mono item" is something that results in a function or global in +//! the LLVM IR of a codegen unit. Mono items do not stand on their +//! own, they can reference other mono items. For example, if function +//! `foo()` calls function `bar()` then the mono item for `foo()` +//! references the mono item for function `bar()`. In general, the +//! definition for mono item A referencing a mono item B is that +//! the LLVM artifact produced for A references the LLVM artifact produced +//! for B. +//! +//! - Mono items and the references between them form a directed graph, +//! where the mono items are the nodes and references form the edges. +//! Let's call this graph the "mono item graph". +//! +//! - The mono item graph for a program contains all mono items +//! that are needed in order to produce the complete LLVM IR of the program. +//! +//! The purpose of the algorithm implemented in this module is to build the +//! mono item graph for the current crate. It runs in two phases: +//! +//! 1. Discover the roots of the graph by traversing the HIR of the crate. +//! 2. Starting from the roots, find neighboring nodes by inspecting the MIR +//! representation of the item corresponding to a given node, until no more +//! new nodes are found. +//! +//! ### Discovering roots +//! +//! The roots of the mono item graph correspond to the non-generic +//! syntactic items in the source code. We find them by walking the HIR of the +//! crate, and whenever we hit upon a function, method, or static item, we +//! create a mono item consisting of the items DefId and, since we only +//! consider non-generic items, an empty type-substitution set. +//! +//! ### Finding neighbor nodes +//! Given a mono item node, we can discover neighbors by inspecting its +//! MIR. We walk the MIR and any time we hit upon something that signifies a +//! reference to another mono item, we have found a neighbor. Since the +//! mono item we are currently at is always monomorphic, we also know the +//! concrete type arguments of its neighbors, and so all neighbors again will be +//! monomorphic. The specific forms a reference to a neighboring node can take +//! in MIR are quite diverse. Here is an overview: +//! +//! #### Calling Functions/Methods +//! The most obvious form of one mono item referencing another is a +//! function or method call (represented by a CALL terminator in MIR). But +//! calls are not the only thing that might introduce a reference between two +//! function mono items, and as we will see below, they are just a +//! specialization of the form described next, and consequently will not get any +//! special treatment in the algorithm. +//! +//! #### Taking a reference to a function or method +//! A function does not need to actually be called in order to be a neighbor of +//! another function. It suffices to just take a reference in order to introduce +//! an edge. Consider the following example: +//! +//! ```rust +//! fn print_val<T: Display>(x: T) { +//! println!("{}", x); +//! } +//! +//! fn call_fn(f: &Fn(i32), x: i32) { +//! f(x); +//! } +//! +//! fn main() { +//! let print_i32 = print_val::<i32>; +//! call_fn(&print_i32, 0); +//! } +//! ``` +//! The MIR of none of these functions will contain an explicit call to +//! `print_val::<i32>`. Nonetheless, in order to mono this program, we need +//! an instance of this function. Thus, whenever we encounter a function or +//! method in operand position, we treat it as a neighbor of the current +//! mono item. Calls are just a special case of that. +//! +//! #### Closures +//! In a way, closures are a simple case. Since every closure object needs to be +//! constructed somewhere, we can reliably discover them by observing +//! `RValue::Aggregate` expressions with `AggregateKind::Closure`. This is also +//! true for closures inlined from other crates. +//! +//! #### Drop glue +//! Drop glue mono items are introduced by MIR drop-statements. The +//! generated mono item will again have drop-glue item neighbors if the +//! type to be dropped contains nested values that also need to be dropped. It +//! might also have a function item neighbor for the explicit `Drop::drop` +//! implementation of its type. +//! +//! #### Unsizing Casts +//! A subtle way of introducing neighbor edges is by casting to a trait object. +//! Since the resulting fat-pointer contains a reference to a vtable, we need to +//! instantiate all object-save methods of the trait, as we need to store +//! pointers to these functions even if they never get called anywhere. This can +//! be seen as a special case of taking a function reference. +//! +//! #### Boxes +//! Since `Box` expression have special compiler support, no explicit calls to +//! `exchange_malloc()` and `box_free()` may show up in MIR, even if the +//! compiler will generate them. We have to observe `Rvalue::Box` expressions +//! and Box-typed drop-statements for that purpose. +//! +//! +//! Interaction with Cross-Crate Inlining +//! ------------------------------------- +//! The binary of a crate will not only contain machine code for the items +//! defined in the source code of that crate. It will also contain monomorphic +//! instantiations of any extern generic functions and of functions marked with +//! `#[inline]`. +//! The collection algorithm handles this more or less mono. If it is +//! about to create a mono item for something with an external `DefId`, +//! it will take a look if the MIR for that item is available, and if so just +//! proceed normally. If the MIR is not available, it assumes that the item is +//! just linked to and no node is created; which is exactly what we want, since +//! no machine code should be generated in the current crate for such an item. +//! +//! Eager and Lazy Collection Mode +//! ------------------------------ +//! Mono item collection can be performed in one of two modes: +//! +//! - Lazy mode means that items will only be instantiated when actually +//! referenced. The goal is to produce the least amount of machine code +//! possible. +//! +//! - Eager mode is meant to be used in conjunction with incremental compilation +//! where a stable set of mono items is more important than a minimal +//! one. Thus, eager mode will instantiate drop-glue for every drop-able type +//! in the crate, even if no drop call for that type exists (yet). It will +//! also instantiate default implementations of trait methods, something that +//! otherwise is only done on demand. +//! +//! +//! Open Issues +//! ----------- +//! Some things are not yet fully implemented in the current version of this +//! module. +//! +//! ### Const Fns +//! Ideally, no mono item should be generated for const fns unless there +//! is a call to them that cannot be evaluated at compile time. At the moment +//! this is not implemented however: a mono item will be produced +//! regardless of whether it is actually needed or not. + +use crate::monomorphize; + +use rustc_data_structures::fx::{FxHashMap, FxHashSet}; +use rustc_data_structures::sync::{par_iter, MTLock, MTRef, ParallelIterator}; +use rustc_errors::{ErrorReported, FatalError}; +use rustc_hir as hir; +use rustc_hir::def_id::{DefId, DefIdMap, LocalDefId, LOCAL_CRATE}; +use rustc_hir::itemlikevisit::ItemLikeVisitor; +use rustc_hir::lang_items::LangItem; +use rustc_index::bit_set::GrowableBitSet; +use rustc_middle::middle::codegen_fn_attrs::CodegenFnAttrFlags; +use rustc_middle::mir::interpret::{AllocId, ConstValue}; +use rustc_middle::mir::interpret::{ErrorHandled, GlobalAlloc, Scalar}; +use rustc_middle::mir::mono::{InstantiationMode, MonoItem}; +use rustc_middle::mir::visit::Visitor as MirVisitor; +use rustc_middle::mir::{self, Local, Location}; +use rustc_middle::ty::adjustment::{CustomCoerceUnsized, PointerCast}; +use rustc_middle::ty::print::obsolete::DefPathBasedNames; +use rustc_middle::ty::subst::{GenericArgKind, InternalSubsts}; +use rustc_middle::ty::{self, GenericParamDefKind, Instance, Ty, TyCtxt, TypeFoldable}; +use rustc_session::config::EntryFnType; +use rustc_span::source_map::{dummy_spanned, respan, Span, Spanned, DUMMY_SP}; +use smallvec::SmallVec; +use std::iter; + +#[derive(PartialEq)] +pub enum MonoItemCollectionMode { + Eager, + Lazy, +} + +/// Maps every mono item to all mono items it references in its +/// body. +pub struct InliningMap<'tcx> { + // Maps a source mono item to the range of mono items + // accessed by it. + // The two numbers in the tuple are the start (inclusive) and + // end index (exclusive) within the `targets` vecs. + index: FxHashMap<MonoItem<'tcx>, (usize, usize)>, + targets: Vec<MonoItem<'tcx>>, + + // Contains one bit per mono item in the `targets` field. That bit + // is true if that mono item needs to be inlined into every CGU. + inlines: GrowableBitSet<usize>, +} + +impl<'tcx> InliningMap<'tcx> { + fn new() -> InliningMap<'tcx> { + InliningMap { + index: FxHashMap::default(), + targets: Vec::new(), + inlines: GrowableBitSet::with_capacity(1024), + } + } + + fn record_accesses(&mut self, source: MonoItem<'tcx>, new_targets: &[(MonoItem<'tcx>, bool)]) { + let start_index = self.targets.len(); + let new_items_count = new_targets.len(); + let new_items_count_total = new_items_count + self.targets.len(); + + self.targets.reserve(new_items_count); + self.inlines.ensure(new_items_count_total); + + for (i, (target, inline)) in new_targets.iter().enumerate() { + self.targets.push(*target); + if *inline { + self.inlines.insert(i + start_index); + } + } + + let end_index = self.targets.len(); + assert!(self.index.insert(source, (start_index, end_index)).is_none()); + } + + // Internally iterate over all items referenced by `source` which will be + // made available for inlining. + pub fn with_inlining_candidates<F>(&self, source: MonoItem<'tcx>, mut f: F) + where + F: FnMut(MonoItem<'tcx>), + { + if let Some(&(start_index, end_index)) = self.index.get(&source) { + for (i, candidate) in self.targets[start_index..end_index].iter().enumerate() { + if self.inlines.contains(start_index + i) { + f(*candidate); + } + } + } + } + + // Internally iterate over all items and the things each accesses. + pub fn iter_accesses<F>(&self, mut f: F) + where + F: FnMut(MonoItem<'tcx>, &[MonoItem<'tcx>]), + { + for (&accessor, &(start_index, end_index)) in &self.index { + f(accessor, &self.targets[start_index..end_index]) + } + } +} + +pub fn collect_crate_mono_items( + tcx: TyCtxt<'_>, + mode: MonoItemCollectionMode, +) -> (FxHashSet<MonoItem<'_>>, InliningMap<'_>) { + let _prof_timer = tcx.prof.generic_activity("monomorphization_collector"); + + let roots = + tcx.sess.time("monomorphization_collector_root_collections", || collect_roots(tcx, mode)); + + debug!("building mono item graph, beginning at roots"); + + let mut visited = MTLock::new(FxHashSet::default()); + let mut inlining_map = MTLock::new(InliningMap::new()); + + { + let visited: MTRef<'_, _> = &mut visited; + let inlining_map: MTRef<'_, _> = &mut inlining_map; + + tcx.sess.time("monomorphization_collector_graph_walk", || { + par_iter(roots).for_each(|root| { + let mut recursion_depths = DefIdMap::default(); + collect_items_rec( + tcx, + dummy_spanned(root), + visited, + &mut recursion_depths, + inlining_map, + ); + }); + }); + } + + (visited.into_inner(), inlining_map.into_inner()) +} + +// Find all non-generic items by walking the HIR. These items serve as roots to +// start monomorphizing from. +fn collect_roots(tcx: TyCtxt<'_>, mode: MonoItemCollectionMode) -> Vec<MonoItem<'_>> { + debug!("collecting roots"); + let mut roots = Vec::new(); + + { + let entry_fn = tcx.entry_fn(LOCAL_CRATE); + + debug!("collect_roots: entry_fn = {:?}", entry_fn); + + let mut visitor = RootCollector { tcx, mode, entry_fn, output: &mut roots }; + + tcx.hir().krate().visit_all_item_likes(&mut visitor); + + visitor.push_extra_entry_roots(); + } + + // We can only codegen items that are instantiable - items all of + // whose predicates hold. Luckily, items that aren't instantiable + // can't actually be used, so we can just skip codegenning them. + roots + .into_iter() + .filter_map(|root| root.node.is_instantiable(tcx).then_some(root.node)) + .collect() +} + +// Collect all monomorphized items reachable from `starting_point` +fn collect_items_rec<'tcx>( + tcx: TyCtxt<'tcx>, + starting_point: Spanned<MonoItem<'tcx>>, + visited: MTRef<'_, MTLock<FxHashSet<MonoItem<'tcx>>>>, + recursion_depths: &mut DefIdMap<usize>, + inlining_map: MTRef<'_, MTLock<InliningMap<'tcx>>>, +) { + if !visited.lock_mut().insert(starting_point.node) { + // We've been here already, no need to search again. + return; + } + debug!("BEGIN collect_items_rec({})", starting_point.node.to_string(tcx, true)); + + let mut neighbors = Vec::new(); + let recursion_depth_reset; + + match starting_point.node { + MonoItem::Static(def_id) => { + let instance = Instance::mono(tcx, def_id); + + // Sanity check whether this ended up being collected accidentally + debug_assert!(should_codegen_locally(tcx, &instance)); + + let ty = instance.ty(tcx, ty::ParamEnv::reveal_all()); + visit_drop_use(tcx, ty, true, starting_point.span, &mut neighbors); + + recursion_depth_reset = None; + + if let Ok(val) = tcx.const_eval_poly(def_id) { + collect_const_value(tcx, val, &mut neighbors); + } + } + MonoItem::Fn(instance) => { + // Sanity check whether this ended up being collected accidentally + debug_assert!(should_codegen_locally(tcx, &instance)); + + // Keep track of the monomorphization recursion depth + recursion_depth_reset = + Some(check_recursion_limit(tcx, instance, starting_point.span, recursion_depths)); + check_type_length_limit(tcx, instance); + + rustc_data_structures::stack::ensure_sufficient_stack(|| { + collect_neighbours(tcx, instance, &mut neighbors); + }); + } + MonoItem::GlobalAsm(..) => { + recursion_depth_reset = None; + } + } + + record_accesses(tcx, starting_point.node, neighbors.iter().map(|i| &i.node), inlining_map); + + for neighbour in neighbors { + collect_items_rec(tcx, neighbour, visited, recursion_depths, inlining_map); + } + + if let Some((def_id, depth)) = recursion_depth_reset { + recursion_depths.insert(def_id, depth); + } + + debug!("END collect_items_rec({})", starting_point.node.to_string(tcx, true)); +} + +fn record_accesses<'a, 'tcx: 'a>( + tcx: TyCtxt<'tcx>, + caller: MonoItem<'tcx>, + callees: impl Iterator<Item = &'a MonoItem<'tcx>>, + inlining_map: MTRef<'_, MTLock<InliningMap<'tcx>>>, +) { + let is_inlining_candidate = |mono_item: &MonoItem<'tcx>| { + mono_item.instantiation_mode(tcx) == InstantiationMode::LocalCopy + }; + + // We collect this into a `SmallVec` to avoid calling `is_inlining_candidate` in the lock. + // FIXME: Call `is_inlining_candidate` when pushing to `neighbors` in `collect_items_rec` + // instead to avoid creating this `SmallVec`. + let accesses: SmallVec<[_; 128]> = + callees.map(|mono_item| (*mono_item, is_inlining_candidate(mono_item))).collect(); + + inlining_map.lock_mut().record_accesses(caller, &accesses); +} + +fn check_recursion_limit<'tcx>( + tcx: TyCtxt<'tcx>, + instance: Instance<'tcx>, + span: Span, + recursion_depths: &mut DefIdMap<usize>, +) -> (DefId, usize) { + let def_id = instance.def_id(); + let recursion_depth = recursion_depths.get(&def_id).cloned().unwrap_or(0); + debug!(" => recursion depth={}", recursion_depth); + + let adjusted_recursion_depth = if Some(def_id) == tcx.lang_items().drop_in_place_fn() { + // HACK: drop_in_place creates tight monomorphization loops. Give + // it more margin. + recursion_depth / 4 + } else { + recursion_depth + }; + + // Code that needs to instantiate the same function recursively + // more than the recursion limit is assumed to be causing an + // infinite expansion. + if !tcx.sess.recursion_limit().value_within_limit(adjusted_recursion_depth) { + let error = format!("reached the recursion limit while instantiating `{}`", instance); + let mut err = tcx.sess.struct_span_fatal(span, &error); + err.span_note( + tcx.def_span(def_id), + &format!("`{}` defined here", tcx.def_path_str(def_id)), + ); + err.emit(); + FatalError.raise(); + } + + recursion_depths.insert(def_id, recursion_depth + 1); + + (def_id, recursion_depth) +} + +fn check_type_length_limit<'tcx>(tcx: TyCtxt<'tcx>, instance: Instance<'tcx>) { + let type_length = instance + .substs + .iter() + .flat_map(|arg| arg.walk()) + .filter(|arg| match arg.unpack() { + GenericArgKind::Type(_) | GenericArgKind::Const(_) => true, + GenericArgKind::Lifetime(_) => false, + }) + .count(); + debug!(" => type length={}", type_length); + + // Rust code can easily create exponentially-long types using only a + // polynomial recursion depth. Even with the default recursion + // depth, you can easily get cases that take >2^60 steps to run, + // which means that rustc basically hangs. + // + // Bail out in these cases to avoid that bad user experience. + if !tcx.sess.type_length_limit().value_within_limit(type_length) { + // The instance name is already known to be too long for rustc. + // Show only the first and last 32 characters to avoid blasting + // the user's terminal with thousands of lines of type-name. + let shrink = |s: String, before: usize, after: usize| { + // An iterator of all byte positions including the end of the string. + let positions = || s.char_indices().map(|(i, _)| i).chain(iter::once(s.len())); + + let shrunk = format!( + "{before}...{after}", + before = &s[..positions().nth(before).unwrap_or(s.len())], + after = &s[positions().rev().nth(after).unwrap_or(0)..], + ); + + // Only use the shrunk version if it's really shorter. + // This also avoids the case where before and after slices overlap. + if shrunk.len() < s.len() { shrunk } else { s } + }; + let msg = format!( + "reached the type-length limit while instantiating `{}`", + shrink(instance.to_string(), 32, 32) + ); + let mut diag = tcx.sess.struct_span_fatal(tcx.def_span(instance.def_id()), &msg); + diag.note(&format!( + "consider adding a `#![type_length_limit=\"{}\"]` attribute to your crate", + type_length + )); + diag.emit(); + tcx.sess.abort_if_errors(); + } +} + +struct MirNeighborCollector<'a, 'tcx> { + tcx: TyCtxt<'tcx>, + body: &'a mir::Body<'tcx>, + output: &'a mut Vec<Spanned<MonoItem<'tcx>>>, + instance: Instance<'tcx>, +} + +impl<'a, 'tcx> MirNeighborCollector<'a, 'tcx> { + pub fn monomorphize<T>(&self, value: T) -> T + where + T: TypeFoldable<'tcx>, + { + debug!("monomorphize: self.instance={:?}", self.instance); + if let Some(substs) = self.instance.substs_for_mir_body() { + self.tcx.subst_and_normalize_erasing_regions(substs, ty::ParamEnv::reveal_all(), &value) + } else { + self.tcx.normalize_erasing_regions(ty::ParamEnv::reveal_all(), value) + } + } +} + +impl<'a, 'tcx> MirVisitor<'tcx> for MirNeighborCollector<'a, 'tcx> { + fn visit_rvalue(&mut self, rvalue: &mir::Rvalue<'tcx>, location: Location) { + debug!("visiting rvalue {:?}", *rvalue); + + let span = self.body.source_info(location).span; + + match *rvalue { + // When doing an cast from a regular pointer to a fat pointer, we + // have to instantiate all methods of the trait being cast to, so we + // can build the appropriate vtable. + mir::Rvalue::Cast( + mir::CastKind::Pointer(PointerCast::Unsize), + ref operand, + target_ty, + ) => { + let target_ty = self.monomorphize(target_ty); + let source_ty = operand.ty(self.body, self.tcx); + let source_ty = self.monomorphize(source_ty); + let (source_ty, target_ty) = + find_vtable_types_for_unsizing(self.tcx, source_ty, target_ty); + // This could also be a different Unsize instruction, like + // from a fixed sized array to a slice. But we are only + // interested in things that produce a vtable. + if target_ty.is_trait() && !source_ty.is_trait() { + create_mono_items_for_vtable_methods( + self.tcx, + target_ty, + source_ty, + span, + self.output, + ); + } + } + mir::Rvalue::Cast( + mir::CastKind::Pointer(PointerCast::ReifyFnPointer), + ref operand, + _, + ) => { + let fn_ty = operand.ty(self.body, self.tcx); + let fn_ty = self.monomorphize(fn_ty); + visit_fn_use(self.tcx, fn_ty, false, span, &mut self.output); + } + mir::Rvalue::Cast( + mir::CastKind::Pointer(PointerCast::ClosureFnPointer(_)), + ref operand, + _, + ) => { + let source_ty = operand.ty(self.body, self.tcx); + let source_ty = self.monomorphize(source_ty); + match source_ty.kind { + ty::Closure(def_id, substs) => { + let instance = Instance::resolve_closure( + self.tcx, + def_id, + substs, + ty::ClosureKind::FnOnce, + ); + if should_codegen_locally(self.tcx, &instance) { + self.output.push(create_fn_mono_item(self.tcx, instance, span)); + } + } + _ => bug!(), + } + } + mir::Rvalue::NullaryOp(mir::NullOp::Box, _) => { + let tcx = self.tcx; + let exchange_malloc_fn_def_id = + tcx.require_lang_item(LangItem::ExchangeMalloc, None); + let instance = Instance::mono(tcx, exchange_malloc_fn_def_id); + if should_codegen_locally(tcx, &instance) { + self.output.push(create_fn_mono_item(self.tcx, instance, span)); + } + } + mir::Rvalue::ThreadLocalRef(def_id) => { + assert!(self.tcx.is_thread_local_static(def_id)); + let instance = Instance::mono(self.tcx, def_id); + if should_codegen_locally(self.tcx, &instance) { + trace!("collecting thread-local static {:?}", def_id); + self.output.push(respan(span, MonoItem::Static(def_id))); + } + } + _ => { /* not interesting */ } + } + + self.super_rvalue(rvalue, location); + } + + fn visit_const(&mut self, constant: &&'tcx ty::Const<'tcx>, location: Location) { + debug!("visiting const {:?} @ {:?}", *constant, location); + + let substituted_constant = self.monomorphize(*constant); + let param_env = ty::ParamEnv::reveal_all(); + + match substituted_constant.val { + ty::ConstKind::Value(val) => collect_const_value(self.tcx, val, self.output), + ty::ConstKind::Unevaluated(def, substs, promoted) => { + match self.tcx.const_eval_resolve(param_env, def, substs, promoted, None) { + Ok(val) => collect_const_value(self.tcx, val, self.output), + Err(ErrorHandled::Reported(ErrorReported) | ErrorHandled::Linted) => {} + Err(ErrorHandled::TooGeneric) => span_bug!( + self.body.source_info(location).span, + "collection encountered polymorphic constant: {}", + substituted_constant + ), + } + } + _ => {} + } + + self.super_const(constant); + } + + fn visit_terminator(&mut self, terminator: &mir::Terminator<'tcx>, location: Location) { + debug!("visiting terminator {:?} @ {:?}", terminator, location); + let source = self.body.source_info(location).span; + + let tcx = self.tcx; + match terminator.kind { + mir::TerminatorKind::Call { ref func, .. } => { + let callee_ty = func.ty(self.body, tcx); + let callee_ty = self.monomorphize(callee_ty); + visit_fn_use(self.tcx, callee_ty, true, source, &mut self.output); + } + mir::TerminatorKind::Drop { ref place, .. } + | mir::TerminatorKind::DropAndReplace { ref place, .. } => { + let ty = place.ty(self.body, self.tcx).ty; + let ty = self.monomorphize(ty); + visit_drop_use(self.tcx, ty, true, source, self.output); + } + mir::TerminatorKind::InlineAsm { ref operands, .. } => { + for op in operands { + match *op { + mir::InlineAsmOperand::SymFn { ref value } => { + let fn_ty = self.monomorphize(value.literal.ty); + visit_fn_use(self.tcx, fn_ty, false, source, &mut self.output); + } + mir::InlineAsmOperand::SymStatic { def_id } => { + let instance = Instance::mono(self.tcx, def_id); + if should_codegen_locally(self.tcx, &instance) { + trace!("collecting asm sym static {:?}", def_id); + self.output.push(respan(source, MonoItem::Static(def_id))); + } + } + _ => {} + } + } + } + mir::TerminatorKind::Goto { .. } + | mir::TerminatorKind::SwitchInt { .. } + | mir::TerminatorKind::Resume + | mir::TerminatorKind::Abort + | mir::TerminatorKind::Return + | mir::TerminatorKind::Unreachable + | mir::TerminatorKind::Assert { .. } => {} + mir::TerminatorKind::GeneratorDrop + | mir::TerminatorKind::Yield { .. } + | mir::TerminatorKind::FalseEdge { .. } + | mir::TerminatorKind::FalseUnwind { .. } => bug!(), + } + + self.super_terminator(terminator, location); + } + + fn visit_local( + &mut self, + _place_local: &Local, + _context: mir::visit::PlaceContext, + _location: Location, + ) { + } +} + +fn visit_drop_use<'tcx>( + tcx: TyCtxt<'tcx>, + ty: Ty<'tcx>, + is_direct_call: bool, + source: Span, + output: &mut Vec<Spanned<MonoItem<'tcx>>>, +) { + let instance = Instance::resolve_drop_in_place(tcx, ty); + visit_instance_use(tcx, instance, is_direct_call, source, output); +} + +fn visit_fn_use<'tcx>( + tcx: TyCtxt<'tcx>, + ty: Ty<'tcx>, + is_direct_call: bool, + source: Span, + output: &mut Vec<Spanned<MonoItem<'tcx>>>, +) { + if let ty::FnDef(def_id, substs) = ty.kind { + let instance = if is_direct_call { + ty::Instance::resolve(tcx, ty::ParamEnv::reveal_all(), def_id, substs).unwrap().unwrap() + } else { + ty::Instance::resolve_for_fn_ptr(tcx, ty::ParamEnv::reveal_all(), def_id, substs) + .unwrap() + }; + visit_instance_use(tcx, instance, is_direct_call, source, output); + } +} + +fn visit_instance_use<'tcx>( + tcx: TyCtxt<'tcx>, + instance: ty::Instance<'tcx>, + is_direct_call: bool, + source: Span, + output: &mut Vec<Spanned<MonoItem<'tcx>>>, +) { + debug!("visit_item_use({:?}, is_direct_call={:?})", instance, is_direct_call); + if !should_codegen_locally(tcx, &instance) { + return; + } + + match instance.def { + ty::InstanceDef::Virtual(..) | ty::InstanceDef::Intrinsic(_) => { + if !is_direct_call { + bug!("{:?} being reified", instance); + } + } + ty::InstanceDef::DropGlue(_, None) => { + // Don't need to emit noop drop glue if we are calling directly. + if !is_direct_call { + output.push(create_fn_mono_item(tcx, instance, source)); + } + } + ty::InstanceDef::DropGlue(_, Some(_)) + | ty::InstanceDef::VtableShim(..) + | ty::InstanceDef::ReifyShim(..) + | ty::InstanceDef::ClosureOnceShim { .. } + | ty::InstanceDef::Item(..) + | ty::InstanceDef::FnPtrShim(..) + | ty::InstanceDef::CloneShim(..) => { + output.push(create_fn_mono_item(tcx, instance, source)); + } + } +} + +// Returns `true` if we should codegen an instance in the local crate. +// Returns `false` if we can just link to the upstream crate and therefore don't +// need a mono item. +fn should_codegen_locally<'tcx>(tcx: TyCtxt<'tcx>, instance: &Instance<'tcx>) -> bool { + let def_id = match instance.def { + ty::InstanceDef::Item(def) => def.did, + ty::InstanceDef::DropGlue(def_id, Some(_)) => def_id, + ty::InstanceDef::VtableShim(..) + | ty::InstanceDef::ReifyShim(..) + | ty::InstanceDef::ClosureOnceShim { .. } + | ty::InstanceDef::Virtual(..) + | ty::InstanceDef::FnPtrShim(..) + | ty::InstanceDef::DropGlue(..) + | ty::InstanceDef::Intrinsic(_) + | ty::InstanceDef::CloneShim(..) => return true, + }; + + if tcx.is_foreign_item(def_id) { + // Foreign items are always linked against, there's no way of instantiating them. + return false; + } + + if def_id.is_local() { + // Local items cannot be referred to locally without monomorphizing them locally. + return true; + } + + if tcx.is_reachable_non_generic(def_id) + || instance.polymorphize(tcx).upstream_monomorphization(tcx).is_some() + { + // We can link to the item in question, no instance needed in this crate. + return false; + } + + if !tcx.is_mir_available(def_id) { + bug!("cannot create local mono-item for {:?}", def_id) + } + + true +} + +/// For a given pair of source and target type that occur in an unsizing coercion, +/// this function finds the pair of types that determines the vtable linking +/// them. +/// +/// For example, the source type might be `&SomeStruct` and the target type\ +/// might be `&SomeTrait` in a cast like: +/// +/// let src: &SomeStruct = ...; +/// let target = src as &SomeTrait; +/// +/// Then the output of this function would be (SomeStruct, SomeTrait) since for +/// constructing the `target` fat-pointer we need the vtable for that pair. +/// +/// Things can get more complicated though because there's also the case where +/// the unsized type occurs as a field: +/// +/// ```rust +/// struct ComplexStruct<T: ?Sized> { +/// a: u32, +/// b: f64, +/// c: T +/// } +/// ``` +/// +/// In this case, if `T` is sized, `&ComplexStruct<T>` is a thin pointer. If `T` +/// is unsized, `&SomeStruct` is a fat pointer, and the vtable it points to is +/// for the pair of `T` (which is a trait) and the concrete type that `T` was +/// originally coerced from: +/// +/// let src: &ComplexStruct<SomeStruct> = ...; +/// let target = src as &ComplexStruct<SomeTrait>; +/// +/// Again, we want this `find_vtable_types_for_unsizing()` to provide the pair +/// `(SomeStruct, SomeTrait)`. +/// +/// Finally, there is also the case of custom unsizing coercions, e.g., for +/// smart pointers such as `Rc` and `Arc`. +fn find_vtable_types_for_unsizing<'tcx>( + tcx: TyCtxt<'tcx>, + source_ty: Ty<'tcx>, + target_ty: Ty<'tcx>, +) -> (Ty<'tcx>, Ty<'tcx>) { + let ptr_vtable = |inner_source: Ty<'tcx>, inner_target: Ty<'tcx>| { + let param_env = ty::ParamEnv::reveal_all(); + let type_has_metadata = |ty: Ty<'tcx>| -> bool { + if ty.is_sized(tcx.at(DUMMY_SP), param_env) { + return false; + } + let tail = tcx.struct_tail_erasing_lifetimes(ty, param_env); + match tail.kind { + ty::Foreign(..) => false, + ty::Str | ty::Slice(..) | ty::Dynamic(..) => true, + _ => bug!("unexpected unsized tail: {:?}", tail), + } + }; + if type_has_metadata(inner_source) { + (inner_source, inner_target) + } else { + tcx.struct_lockstep_tails_erasing_lifetimes(inner_source, inner_target, param_env) + } + }; + + match (&source_ty.kind, &target_ty.kind) { + (&ty::Ref(_, a, _), &ty::Ref(_, b, _) | &ty::RawPtr(ty::TypeAndMut { ty: b, .. })) + | (&ty::RawPtr(ty::TypeAndMut { ty: a, .. }), &ty::RawPtr(ty::TypeAndMut { ty: b, .. })) => { + ptr_vtable(a, b) + } + (&ty::Adt(def_a, _), &ty::Adt(def_b, _)) if def_a.is_box() && def_b.is_box() => { + ptr_vtable(source_ty.boxed_ty(), target_ty.boxed_ty()) + } + + (&ty::Adt(source_adt_def, source_substs), &ty::Adt(target_adt_def, target_substs)) => { + assert_eq!(source_adt_def, target_adt_def); + + let CustomCoerceUnsized::Struct(coerce_index) = + monomorphize::custom_coerce_unsize_info(tcx, source_ty, target_ty); + + let source_fields = &source_adt_def.non_enum_variant().fields; + let target_fields = &target_adt_def.non_enum_variant().fields; + + assert!( + coerce_index < source_fields.len() && source_fields.len() == target_fields.len() + ); + + find_vtable_types_for_unsizing( + tcx, + source_fields[coerce_index].ty(tcx, source_substs), + target_fields[coerce_index].ty(tcx, target_substs), + ) + } + _ => bug!( + "find_vtable_types_for_unsizing: invalid coercion {:?} -> {:?}", + source_ty, + target_ty + ), + } +} + +fn create_fn_mono_item<'tcx>( + tcx: TyCtxt<'tcx>, + instance: Instance<'tcx>, + source: Span, +) -> Spanned<MonoItem<'tcx>> { + debug!("create_fn_mono_item(instance={})", instance); + respan(source, MonoItem::Fn(instance.polymorphize(tcx))) +} + +/// Creates a `MonoItem` for each method that is referenced by the vtable for +/// the given trait/impl pair. +fn create_mono_items_for_vtable_methods<'tcx>( + tcx: TyCtxt<'tcx>, + trait_ty: Ty<'tcx>, + impl_ty: Ty<'tcx>, + source: Span, + output: &mut Vec<Spanned<MonoItem<'tcx>>>, +) { + assert!(!trait_ty.has_escaping_bound_vars() && !impl_ty.has_escaping_bound_vars()); + + if let ty::Dynamic(ref trait_ty, ..) = trait_ty.kind { + if let Some(principal) = trait_ty.principal() { + let poly_trait_ref = principal.with_self_ty(tcx, impl_ty); + assert!(!poly_trait_ref.has_escaping_bound_vars()); + + // Walk all methods of the trait, including those of its supertraits + let methods = tcx.vtable_methods(poly_trait_ref); + let methods = methods + .iter() + .cloned() + .filter_map(|method| method) + .map(|(def_id, substs)| { + ty::Instance::resolve_for_vtable( + tcx, + ty::ParamEnv::reveal_all(), + def_id, + substs, + ) + .unwrap() + }) + .filter(|&instance| should_codegen_locally(tcx, &instance)) + .map(|item| create_fn_mono_item(tcx, item, source)); + output.extend(methods); + } + + // Also add the destructor. + visit_drop_use(tcx, impl_ty, false, source, output); + } +} + +//=----------------------------------------------------------------------------- +// Root Collection +//=----------------------------------------------------------------------------- + +struct RootCollector<'a, 'tcx> { + tcx: TyCtxt<'tcx>, + mode: MonoItemCollectionMode, + output: &'a mut Vec<Spanned<MonoItem<'tcx>>>, + entry_fn: Option<(LocalDefId, EntryFnType)>, +} + +impl ItemLikeVisitor<'v> for RootCollector<'_, 'v> { + fn visit_item(&mut self, item: &'v hir::Item<'v>) { + match item.kind { + hir::ItemKind::ExternCrate(..) + | hir::ItemKind::Use(..) + | hir::ItemKind::ForeignMod(..) + | hir::ItemKind::TyAlias(..) + | hir::ItemKind::Trait(..) + | hir::ItemKind::TraitAlias(..) + | hir::ItemKind::OpaqueTy(..) + | hir::ItemKind::Mod(..) => { + // Nothing to do, just keep recursing. + } + + hir::ItemKind::Impl { .. } => { + if self.mode == MonoItemCollectionMode::Eager { + create_mono_items_for_default_impls(self.tcx, item, self.output); + } + } + + hir::ItemKind::Enum(_, ref generics) + | hir::ItemKind::Struct(_, ref generics) + | hir::ItemKind::Union(_, ref generics) => { + if generics.params.is_empty() { + if self.mode == MonoItemCollectionMode::Eager { + let def_id = self.tcx.hir().local_def_id(item.hir_id); + debug!( + "RootCollector: ADT drop-glue for {}", + def_id_to_string(self.tcx, def_id) + ); + + let ty = Instance::new(def_id.to_def_id(), InternalSubsts::empty()) + .ty(self.tcx, ty::ParamEnv::reveal_all()); + visit_drop_use(self.tcx, ty, true, DUMMY_SP, self.output); + } + } + } + hir::ItemKind::GlobalAsm(..) => { + debug!( + "RootCollector: ItemKind::GlobalAsm({})", + def_id_to_string(self.tcx, self.tcx.hir().local_def_id(item.hir_id)) + ); + self.output.push(dummy_spanned(MonoItem::GlobalAsm(item.hir_id))); + } + hir::ItemKind::Static(..) => { + let def_id = self.tcx.hir().local_def_id(item.hir_id); + debug!("RootCollector: ItemKind::Static({})", def_id_to_string(self.tcx, def_id)); + self.output.push(dummy_spanned(MonoItem::Static(def_id.to_def_id()))); + } + hir::ItemKind::Const(..) => { + // const items only generate mono items if they are + // actually used somewhere. Just declaring them is insufficient. + + // but even just declaring them must collect the items they refer to + let def_id = self.tcx.hir().local_def_id(item.hir_id); + + if let Ok(val) = self.tcx.const_eval_poly(def_id.to_def_id()) { + collect_const_value(self.tcx, val, &mut self.output); + } + } + hir::ItemKind::Fn(..) => { + let def_id = self.tcx.hir().local_def_id(item.hir_id); + self.push_if_root(def_id); + } + } + } + + fn visit_trait_item(&mut self, _: &'v hir::TraitItem<'v>) { + // Even if there's a default body with no explicit generics, + // it's still generic over some `Self: Trait`, so not a root. + } + + fn visit_impl_item(&mut self, ii: &'v hir::ImplItem<'v>) { + if let hir::ImplItemKind::Fn(hir::FnSig { .. }, _) = ii.kind { + let def_id = self.tcx.hir().local_def_id(ii.hir_id); + self.push_if_root(def_id); + } + } +} + +impl RootCollector<'_, 'v> { + fn is_root(&self, def_id: LocalDefId) -> bool { + !item_requires_monomorphization(self.tcx, def_id) + && match self.mode { + MonoItemCollectionMode::Eager => true, + MonoItemCollectionMode::Lazy => { + self.entry_fn.map(|(id, _)| id) == Some(def_id) + || self.tcx.is_reachable_non_generic(def_id) + || self + .tcx + .codegen_fn_attrs(def_id) + .flags + .contains(CodegenFnAttrFlags::RUSTC_STD_INTERNAL_SYMBOL) + } + } + } + + /// If `def_id` represents a root, pushes it onto the list of + /// outputs. (Note that all roots must be monomorphic.) + fn push_if_root(&mut self, def_id: LocalDefId) { + if self.is_root(def_id) { + debug!("RootCollector::push_if_root: found root def_id={:?}", def_id); + + let instance = Instance::mono(self.tcx, def_id.to_def_id()); + self.output.push(create_fn_mono_item(self.tcx, instance, DUMMY_SP)); + } + } + + /// As a special case, when/if we encounter the + /// `main()` function, we also have to generate a + /// monomorphized copy of the start lang item based on + /// the return type of `main`. This is not needed when + /// the user writes their own `start` manually. + fn push_extra_entry_roots(&mut self) { + let main_def_id = match self.entry_fn { + Some((def_id, EntryFnType::Main)) => def_id, + _ => return, + }; + + let start_def_id = match self.tcx.lang_items().require(LangItem::Start) { + Ok(s) => s, + Err(err) => self.tcx.sess.fatal(&err), + }; + let main_ret_ty = self.tcx.fn_sig(main_def_id).output(); + + // Given that `main()` has no arguments, + // then its return type cannot have + // late-bound regions, since late-bound + // regions must appear in the argument + // listing. + let main_ret_ty = self.tcx.erase_regions(&main_ret_ty.no_bound_vars().unwrap()); + + let start_instance = Instance::resolve( + self.tcx, + ty::ParamEnv::reveal_all(), + start_def_id, + self.tcx.intern_substs(&[main_ret_ty.into()]), + ) + .unwrap() + .unwrap(); + + self.output.push(create_fn_mono_item(self.tcx, start_instance, DUMMY_SP)); + } +} + +fn item_requires_monomorphization(tcx: TyCtxt<'_>, def_id: LocalDefId) -> bool { + let generics = tcx.generics_of(def_id); + generics.requires_monomorphization(tcx) +} + +fn create_mono_items_for_default_impls<'tcx>( + tcx: TyCtxt<'tcx>, + item: &'tcx hir::Item<'tcx>, + output: &mut Vec<Spanned<MonoItem<'tcx>>>, +) { + match item.kind { + hir::ItemKind::Impl { ref generics, ref items, .. } => { + for param in generics.params { + match param.kind { + hir::GenericParamKind::Lifetime { .. } => {} + hir::GenericParamKind::Type { .. } | hir::GenericParamKind::Const { .. } => { + return; + } + } + } + + let impl_def_id = tcx.hir().local_def_id(item.hir_id); + + debug!( + "create_mono_items_for_default_impls(item={})", + def_id_to_string(tcx, impl_def_id) + ); + + if let Some(trait_ref) = tcx.impl_trait_ref(impl_def_id) { + let param_env = ty::ParamEnv::reveal_all(); + let trait_ref = tcx.normalize_erasing_regions(param_env, trait_ref); + let overridden_methods: FxHashSet<_> = + items.iter().map(|iiref| iiref.ident.normalize_to_macros_2_0()).collect(); + for method in tcx.provided_trait_methods(trait_ref.def_id) { + if overridden_methods.contains(&method.ident.normalize_to_macros_2_0()) { + continue; + } + + if tcx.generics_of(method.def_id).own_requires_monomorphization() { + continue; + } + + let substs = + InternalSubsts::for_item(tcx, method.def_id, |param, _| match param.kind { + GenericParamDefKind::Lifetime => tcx.lifetimes.re_erased.into(), + GenericParamDefKind::Type { .. } | GenericParamDefKind::Const => { + trait_ref.substs[param.index as usize] + } + }); + let instance = ty::Instance::resolve(tcx, param_env, method.def_id, substs) + .unwrap() + .unwrap(); + + let mono_item = create_fn_mono_item(tcx, instance, DUMMY_SP); + if mono_item.node.is_instantiable(tcx) && should_codegen_locally(tcx, &instance) + { + output.push(mono_item); + } + } + } + } + _ => bug!(), + } +} + +/// Scans the miri alloc in order to find function calls, closures, and drop-glue. +fn collect_miri<'tcx>( + tcx: TyCtxt<'tcx>, + alloc_id: AllocId, + output: &mut Vec<Spanned<MonoItem<'tcx>>>, +) { + match tcx.global_alloc(alloc_id) { + GlobalAlloc::Static(def_id) => { + assert!(!tcx.is_thread_local_static(def_id)); + let instance = Instance::mono(tcx, def_id); + if should_codegen_locally(tcx, &instance) { + trace!("collecting static {:?}", def_id); + output.push(dummy_spanned(MonoItem::Static(def_id))); + } + } + GlobalAlloc::Memory(alloc) => { + trace!("collecting {:?} with {:#?}", alloc_id, alloc); + for &((), inner) in alloc.relocations().values() { + rustc_data_structures::stack::ensure_sufficient_stack(|| { + collect_miri(tcx, inner, output); + }); + } + } + GlobalAlloc::Function(fn_instance) => { + if should_codegen_locally(tcx, &fn_instance) { + trace!("collecting {:?} with {:#?}", alloc_id, fn_instance); + output.push(create_fn_mono_item(tcx, fn_instance, DUMMY_SP)); + } + } + } +} + +/// Scans the MIR in order to find function calls, closures, and drop-glue. +fn collect_neighbours<'tcx>( + tcx: TyCtxt<'tcx>, + instance: Instance<'tcx>, + output: &mut Vec<Spanned<MonoItem<'tcx>>>, +) { + debug!("collect_neighbours: {:?}", instance.def_id()); + let body = tcx.instance_mir(instance.def); + + MirNeighborCollector { tcx, body: &body, output, instance }.visit_body(&body); +} + +fn def_id_to_string(tcx: TyCtxt<'_>, def_id: LocalDefId) -> String { + let mut output = String::new(); + let printer = DefPathBasedNames::new(tcx, false, false); + printer.push_def_path(def_id.to_def_id(), &mut output); + output +} + +fn collect_const_value<'tcx>( + tcx: TyCtxt<'tcx>, + value: ConstValue<'tcx>, + output: &mut Vec<Spanned<MonoItem<'tcx>>>, +) { + match value { + ConstValue::Scalar(Scalar::Ptr(ptr)) => collect_miri(tcx, ptr.alloc_id, output), + ConstValue::Slice { data: alloc, start: _, end: _ } | ConstValue::ByRef { alloc, .. } => { + for &((), id) in alloc.relocations().values() { + collect_miri(tcx, id, output); + } + } + _ => {} + } +} |