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//! Mono Item Collection
//! ===========================
//!
//! This module is responsible for discovering all items that will contribute to
//! 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
//! specialized of the form described next, and consequently will don't 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 of 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 rustc::hir::{self, CodegenFnAttrFlags};
use rustc::hir::itemlikevisit::ItemLikeVisitor;
use rustc::hir::def_id::{DefId, LOCAL_CRATE};
use rustc::mir::interpret::{AllocId, ConstValue};
use rustc::middle::lang_items::{ExchangeMallocFnLangItem, StartFnLangItem};
use rustc::ty::subst::{InternalSubsts, SubstsRef};
use rustc::ty::{self, TypeFoldable, Ty, TyCtxt, GenericParamDefKind, Instance};
use rustc::ty::print::obsolete::DefPathBasedNames;
use rustc::ty::adjustment::{CustomCoerceUnsized, PointerCast};
use rustc::session::config::EntryFnType;
use rustc::mir::{self, Location, PlaceBase, Promoted, Static, StaticKind};
use rustc::mir::visit::Visitor as MirVisitor;
use rustc::mir::mono::{MonoItem, InstantiationMode};
use rustc::mir::interpret::{Scalar, GlobalId, GlobalAlloc, ErrorHandled};
use crate::monomorphize;
use rustc::util::nodemap::{FxHashSet, FxHashMap, DefIdMap};
use rustc::util::common::time;
use rustc_data_structures::bit_set::GrowableBitSet;
use rustc_data_structures::sync::{MTRef, MTLock, ParallelIterator, par_iter};
use std::iter;
#[derive(PartialEq, Eq, Hash, Clone, Copy, Debug)]
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<I>(&mut self,
source: MonoItem<'tcx>,
new_targets: I)
where I: Iterator<Item=(MonoItem<'tcx>, bool)> + ExactSizeIterator
{
assert!(!self.index.contains_key(&source));
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.enumerate() {
self.targets.push(target);
if inline {
self.inlines.insert(i + start_index);
}
}
let end_index = self.targets.len();
self.index.insert(source, (start_index, end_index));
}
// 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 roots = time(tcx.sess, "collecting roots", || {
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;
time(tcx.sess, "collecting mono items", || {
par_iter(roots).for_each(|root| {
let mut recursion_depths = DefIdMap::default();
collect_items_rec(tcx,
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.retain(|root| root.is_instantiable(tcx));
roots
}
// Collect all monomorphized items reachable from `starting_point`
fn collect_items_rec<'tcx>(
tcx: TyCtxt<'tcx>,
starting_point: 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.clone()) {
// We've been here already, no need to search again.
return;
}
debug!("BEGIN collect_items_rec({})", starting_point.to_string(tcx, true));
let mut neighbors = Vec::new();
let recursion_depth_reset;
match starting_point {
MonoItem::Static(def_id) => {
let instance = Instance::mono(tcx, def_id);
// Sanity check whether this ended up being collected accidentally
debug_assert!(should_monomorphize_locally(tcx, &instance));
let ty = instance.ty(tcx);
visit_drop_use(tcx, ty, true, &mut neighbors);
recursion_depth_reset = None;
let cid = GlobalId {
instance,
promoted: None,
};
let param_env = ty::ParamEnv::reveal_all();
if let Ok(val) = tcx.const_eval(param_env.and(cid)) {
collect_const(tcx, val, InternalSubsts::empty(), &mut neighbors);
}
}
MonoItem::Fn(instance) => {
// Sanity check whether this ended up being collected accidentally
debug_assert!(should_monomorphize_locally(tcx, &instance));
// Keep track of the monomorphization recursion depth
recursion_depth_reset = Some(check_recursion_limit(tcx,
instance,
recursion_depths));
check_type_length_limit(tcx, instance);
collect_neighbours(tcx, instance, &mut neighbors);
}
MonoItem::GlobalAsm(..) => {
recursion_depth_reset = None;
}
}
record_accesses(tcx, starting_point, &neighbors[..], 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.to_string(tcx, true));
}
fn record_accesses<'tcx>(
tcx: TyCtxt<'tcx>,
caller: MonoItem<'tcx>,
callees: &[MonoItem<'tcx>],
inlining_map: MTRef<'_, MTLock<InliningMap<'tcx>>>,
) {
let is_inlining_candidate = |mono_item: &MonoItem<'tcx>| {
mono_item.instantiation_mode(tcx) == InstantiationMode::LocalCopy
};
let accesses = callees.into_iter()
.map(|mono_item| {
(*mono_item, is_inlining_candidate(mono_item))
});
inlining_map.lock_mut().record_accesses(caller, accesses);
}
fn check_recursion_limit<'tcx>(
tcx: TyCtxt<'tcx>,
instance: Instance<'tcx>,
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 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 recursion_depth > *tcx.sess.recursion_limit.get() {
let error = format!("reached the recursion limit while instantiating `{}`",
instance);
if let Some(hir_id) = tcx.hir().as_local_hir_id(def_id) {
tcx.sess.span_fatal(tcx.hir().span(hir_id), &error);
} else {
tcx.sess.fatal(&error);
}
}
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.types().flat_map(|ty| ty.walk()).count();
let const_length = instance.substs.consts().flat_map(|ct| ct.ty.walk()).count();
debug!(" => type length={}, const length={}", type_length, const_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.
let type_length_limit = *tcx.sess.type_length_limit.get();
// We include the const length in the type length, as it's better
// to be overly conservative.
// FIXME(const_generics): we should instead uniformly walk through `substs`,
// ignoring lifetimes.
if type_length + const_length > type_length_limit {
// 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<MonoItem<'tcx>>,
param_substs: SubstsRef<'tcx>,
}
impl<'a, 'tcx> MirVisitor<'tcx> for MirNeighborCollector<'a, 'tcx> {
fn visit_rvalue(&mut self, rvalue: &mir::Rvalue<'tcx>, location: Location) {
debug!("visiting rvalue {:?}", *rvalue);
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.tcx.subst_and_normalize_erasing_regions(
self.param_substs,
ty::ParamEnv::reveal_all(),
&target_ty,
);
let source_ty = operand.ty(self.body, self.tcx);
let source_ty = self.tcx.subst_and_normalize_erasing_regions(
self.param_substs,
ty::ParamEnv::reveal_all(),
&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,
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.tcx.subst_and_normalize_erasing_regions(
self.param_substs,
ty::ParamEnv::reveal_all(),
&fn_ty,
);
visit_fn_use(self.tcx, fn_ty, false, &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.tcx.subst_and_normalize_erasing_regions(
self.param_substs,
ty::ParamEnv::reveal_all(),
&source_ty,
);
match source_ty.sty {
ty::Closure(def_id, substs) => {
let instance = Instance::resolve_closure(
self.tcx, def_id, substs, ty::ClosureKind::FnOnce);
if should_monomorphize_locally(self.tcx, &instance) {
self.output.push(create_fn_mono_item(instance));
}
}
_ => bug!(),
}
}
mir::Rvalue::NullaryOp(mir::NullOp::Box, _) => {
let tcx = self.tcx;
let exchange_malloc_fn_def_id = tcx
.lang_items()
.require(ExchangeMallocFnLangItem)
.unwrap_or_else(|e| tcx.sess.fatal(&e));
let instance = Instance::mono(tcx, exchange_malloc_fn_def_id);
if should_monomorphize_locally(tcx, &instance) {
self.output.push(create_fn_mono_item(instance));
}
}
_ => { /* not interesting */ }
}
self.super_rvalue(rvalue, location);
}
fn visit_const(&mut self, constant: &&'tcx ty::Const<'tcx>, location: Location) {
debug!("visiting const {:?} @ {:?}", *constant, location);
collect_const(self.tcx, *constant, self.param_substs, self.output);
self.super_const(constant);
}
fn visit_terminator_kind(&mut self,
kind: &mir::TerminatorKind<'tcx>,
location: Location) {
debug!("visiting terminator {:?} @ {:?}", kind, location);
let tcx = self.tcx;
match *kind {
mir::TerminatorKind::Call { ref func, .. } => {
let callee_ty = func.ty(self.body, tcx);
let callee_ty = tcx.subst_and_normalize_erasing_regions(
self.param_substs,
ty::ParamEnv::reveal_all(),
&callee_ty,
);
visit_fn_use(self.tcx, callee_ty, true, &mut self.output);
}
mir::TerminatorKind::Drop { ref location, .. } |
mir::TerminatorKind::DropAndReplace { ref location, .. } => {
let ty = location.ty(self.body, self.tcx).ty;
let ty = tcx.subst_and_normalize_erasing_regions(
self.param_substs,
ty::ParamEnv::reveal_all(),
&ty,
);
visit_drop_use(self.tcx, ty, true, self.output);
}
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::FalseEdges { .. } |
mir::TerminatorKind::FalseUnwind { .. } => bug!(),
}
self.super_terminator_kind(kind, location);
}
fn visit_place_base(&mut self,
place_base: &mir::PlaceBase<'tcx>,
_context: mir::visit::PlaceContext,
location: Location) {
match place_base {
PlaceBase::Static(box Static { kind: StaticKind::Static(def_id), .. }) => {
debug!("visiting static {:?} @ {:?}", def_id, location);
let tcx = self.tcx;
let instance = Instance::mono(tcx, *def_id);
if should_monomorphize_locally(tcx, &instance) {
self.output.push(MonoItem::Static(*def_id));
}
}
PlaceBase::Static(box Static { kind: StaticKind::Promoted(_), .. }) => {
// FIXME: should we handle promoteds here instead of eagerly in collect_neighbours?
}
PlaceBase::Local(_) => {
// Locals have no relevance for collector
}
}
}
}
fn visit_drop_use<'tcx>(
tcx: TyCtxt<'tcx>,
ty: Ty<'tcx>,
is_direct_call: bool,
output: &mut Vec<MonoItem<'tcx>>,
) {
let instance = Instance::resolve_drop_in_place(tcx, ty);
visit_instance_use(tcx, instance, is_direct_call, output);
}
fn visit_fn_use<'tcx>(
tcx: TyCtxt<'tcx>,
ty: Ty<'tcx>,
is_direct_call: bool,
output: &mut Vec<MonoItem<'tcx>>,
) {
if let ty::FnDef(def_id, substs) = ty.sty {
let instance = ty::Instance::resolve(tcx,
ty::ParamEnv::reveal_all(),
def_id,
substs).unwrap();
visit_instance_use(tcx, instance, is_direct_call, output);
}
}
fn visit_instance_use<'tcx>(
tcx: TyCtxt<'tcx>,
instance: ty::Instance<'tcx>,
is_direct_call: bool,
output: &mut Vec<MonoItem<'tcx>>,
) {
debug!("visit_item_use({:?}, is_direct_call={:?})", instance, is_direct_call);
if !should_monomorphize_locally(tcx, &instance) {
return
}
match instance.def {
ty::InstanceDef::Intrinsic(def_id) => {
if !is_direct_call {
bug!("intrinsic {:?} being reified", def_id);
}
}
ty::InstanceDef::VtableShim(..) |
ty::InstanceDef::Virtual(..) |
ty::InstanceDef::DropGlue(_, None) => {
// don't need to emit shim if we are calling directly.
if !is_direct_call {
output.push(create_fn_mono_item(instance));
}
}
ty::InstanceDef::DropGlue(_, Some(_)) => {
output.push(create_fn_mono_item(instance));
}
ty::InstanceDef::ClosureOnceShim { .. } |
ty::InstanceDef::Item(..) |
ty::InstanceDef::FnPtrShim(..) |
ty::InstanceDef::CloneShim(..) => {
output.push(create_fn_mono_item(instance));
}
}
}
// 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_monomorphize_locally<'tcx>(tcx: TyCtxt<'tcx>, instance: &Instance<'tcx>) -> bool {
let def_id = match instance.def {
ty::InstanceDef::Item(def_id) => def_id,
ty::InstanceDef::VtableShim(..) |
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) {
// We can always link to foreign items
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) ||
is_available_upstream_generic(tcx, def_id, instance.substs) {
// 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)
}
return true;
fn is_available_upstream_generic<'tcx>(
tcx: TyCtxt<'tcx>,
def_id: DefId,
substs: SubstsRef<'tcx>,
) -> bool {
debug_assert!(!def_id.is_local());
// If we are not in share generics mode, we don't link to upstream
// monomorphizations but always instantiate our own internal versions
// instead.
if !tcx.sess.opts.share_generics() {
return false
}
// If this instance has non-erasable parameters, it cannot be a shared
// monomorphization. Non-generic instances are already handled above
// by `is_reachable_non_generic()`
if substs.non_erasable_generics().next().is_none() {
return false
}
// Take a look at the available monomorphizations listed in the metadata
// of upstream crates.
tcx.upstream_monomorphizations_for(def_id)
.map(|set| set.contains_key(substs))
.unwrap_or(false)
}
}
/// For 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 {
use syntax_pos::DUMMY_SP;
if ty.is_sized(tcx.at(DUMMY_SP), param_env) {
return false;
}
let tail = tcx.struct_tail_erasing_lifetimes(ty, param_env);
match tail.sty {
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.sty, &target_ty.sty) {
(&ty::Ref(_, a, _),
&ty::Ref(_, b, _)) |
(&ty::Ref(_, a, _),
&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 kind =
monomorphize::custom_coerce_unsize_info(tcx, source_ty, target_ty);
let coerce_index = match kind {
CustomCoerceUnsized::Struct(i) => i
};
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(instance: Instance<'_>) -> MonoItem<'_> {
debug!("create_fn_mono_item(instance={})", instance);
MonoItem::Fn(instance)
}
/// 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>,
output: &mut Vec<MonoItem<'tcx>>,
) {
assert!(!trait_ty.needs_subst() && !trait_ty.has_escaping_bound_vars() &&
!impl_ty.needs_subst() && !impl_ty.has_escaping_bound_vars());
if let ty::Dynamic(ref trait_ty, ..) = trait_ty.sty {
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_monomorphize_locally(tcx, &instance))
.map(|instance| create_fn_mono_item(instance));
output.extend(methods);
}
// Also add the destructor
visit_drop_use(tcx, impl_ty, false, output);
}
}
//=-----------------------------------------------------------------------------
// Root Collection
//=-----------------------------------------------------------------------------
struct RootCollector<'a, 'tcx> {
tcx: TyCtxt<'tcx>,
mode: MonoItemCollectionMode,
output: &'a mut Vec<MonoItem<'tcx>>,
entry_fn: Option<(DefId, EntryFnType)>,
}
impl ItemLikeVisitor<'v> for RootCollector<'_, 'v> {
fn visit_item(&mut self, item: &'v hir::Item) {
match item.node {
hir::ItemKind::ExternCrate(..) |
hir::ItemKind::Use(..) |
hir::ItemKind::ForeignMod(..) |
hir::ItemKind::Ty(..) |
hir::ItemKind::Trait(..) |
hir::ItemKind::TraitAlias(..) |
hir::ItemKind::Existential(..) |
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, InternalSubsts::empty()).ty(self.tcx);
visit_drop_use(self.tcx, ty, true, 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(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(MonoItem::Static(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);
let instance = Instance::mono(self.tcx, def_id);
let cid = GlobalId {
instance,
promoted: None,
};
let param_env = ty::ParamEnv::reveal_all();
if let Ok(val) = self.tcx.const_eval(param_env.and(cid)) {
collect_const(self.tcx, val, InternalSubsts::empty(), &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) {
// 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) {
match ii.node {
hir::ImplItemKind::Method(hir::MethodSig { .. }, _) => {
let def_id = self.tcx.hir().local_def_id(ii.hir_id);
self.push_if_root(def_id);
}
_ => { /* Nothing to do here */ }
}
}
}
impl RootCollector<'_, 'v> {
fn is_root(&self, def_id: DefId) -> 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, then push it onto the list of
/// outputs. (Note that all roots must be monomorphic.)
fn push_if_root(&mut self, def_id: DefId) {
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);
self.output.push(create_fn_mono_item(instance));
}
}
/// 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(StartFnLangItem) {
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();
self.output.push(create_fn_mono_item(start_instance));
}
}
fn item_requires_monomorphization(tcx: TyCtxt<'_>, def_id: DefId) -> 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,
output: &mut Vec<MonoItem<'tcx>>,
) {
match item.node {
hir::ItemKind::Impl(_, _, _, ref generics, .., ref impl_item_refs) => {
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<_> =
impl_item_refs.iter()
.map(|iiref| iiref.ident.modern())
.collect();
for method in tcx.provided_trait_methods(trait_ref.def_id) {
if overridden_methods.contains(&method.ident.modern()) {
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();
let mono_item = create_fn_mono_item(instance);
if mono_item.is_instantiable(tcx)
&& should_monomorphize_locally(tcx, &instance) {
output.push(mono_item);
}
}
}
}
_ => {
bug!()
}
}
}
/// Scan 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<MonoItem<'tcx>>) {
let alloc_kind = tcx.alloc_map.lock().get(alloc_id);
match alloc_kind {
Some(GlobalAlloc::Static(def_id)) => {
let instance = Instance::mono(tcx, def_id);
if should_monomorphize_locally(tcx, &instance) {
trace!("collecting static {:?}", def_id);
output.push(MonoItem::Static(def_id));
}
}
Some(GlobalAlloc::Memory(alloc)) => {
trace!("collecting {:?} with {:#?}", alloc_id, alloc);
for &((), inner) in alloc.relocations.values() {
collect_miri(tcx, inner, output);
}
},
Some(GlobalAlloc::Function(fn_instance)) => {
if should_monomorphize_locally(tcx, &fn_instance) {
trace!("collecting {:?} with {:#?}", alloc_id, fn_instance);
output.push(create_fn_mono_item(fn_instance));
}
}
None => bug!("alloc id without corresponding allocation: {}", alloc_id),
}
}
/// Scan 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<MonoItem<'tcx>>,
) {
let body = tcx.instance_mir(instance.def);
MirNeighborCollector {
tcx,
body: &body,
output,
param_substs: instance.substs,
}.visit_body(&body);
let param_env = ty::ParamEnv::reveal_all();
for i in 0..body.promoted.len() {
use rustc_data_structures::indexed_vec::Idx;
let i = Promoted::new(i);
let cid = GlobalId {
instance,
promoted: Some(i),
};
match tcx.const_eval(param_env.and(cid)) {
Ok(val) => collect_const(tcx, val, instance.substs, output),
Err(ErrorHandled::Reported) => {},
Err(ErrorHandled::TooGeneric) => span_bug!(
body.promoted[i].span, "collection encountered polymorphic constant",
),
}
}
}
fn def_id_to_string(tcx: TyCtxt<'_>, def_id: DefId) -> String {
let mut output = String::new();
let printer = DefPathBasedNames::new(tcx, false, false);
printer.push_def_path(def_id, &mut output);
output
}
fn collect_const<'tcx>(
tcx: TyCtxt<'tcx>,
constant: &'tcx ty::Const<'tcx>,
param_substs: SubstsRef<'tcx>,
output: &mut Vec<MonoItem<'tcx>>,
) {
debug!("visiting const {:?}", constant);
match constant.val {
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);
}
}
ConstValue::Unevaluated(def_id, substs) => {
let param_env = ty::ParamEnv::reveal_all();
let substs = tcx.subst_and_normalize_erasing_regions(
param_substs,
param_env,
&substs,
);
let instance = ty::Instance::resolve(tcx,
param_env,
def_id,
substs).unwrap();
let cid = GlobalId {
instance,
promoted: None,
};
match tcx.const_eval(param_env.and(cid)) {
Ok(val) => collect_const(tcx, val, param_substs, output),
Err(ErrorHandled::Reported) => {},
Err(ErrorHandled::TooGeneric) => span_bug!(
tcx.def_span(def_id), "collection encountered polymorphic constant",
),
}
}
_ => {},
}
}
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