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Optimize async drop glue for some old types

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This commit is contained in:
Daria Sukhonina 2024-05-03 15:47:23 +03:00
parent a47173c4f7
commit 7cdd95e1a6
11 changed files with 161 additions and 89 deletions
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1
compiler/rustc_hir/src/lang_items.rs
View file

@ -176,6 +176,7 @@ pub fn extract(attrs: &[ast::Attribute]) -> Option<(Symbol, Span)> {
AsyncDropSlice, sym::async_drop_slice, async_drop_slice_fn, Target::Fn, GenericRequirement::Exact(1);
AsyncDropChain, sym::async_drop_chain, async_drop_chain_fn, Target::Fn, GenericRequirement::Exact(2);
AsyncDropNoop, sym::async_drop_noop, async_drop_noop_fn, Target::Fn, GenericRequirement::Exact(0);
AsyncDropDeferredDropInPlace, sym::async_drop_deferred_drop_in_place, async_drop_deferred_drop_in_place_fn, Target::Fn, GenericRequirement::Exact(1);
AsyncDropFuse, sym::async_drop_fuse, async_drop_fuse_fn, Target::Fn, GenericRequirement::Exact(1);
AsyncDropDefer, sym::async_drop_defer, async_drop_defer_fn, Target::Fn, GenericRequirement::Exact(1);
AsyncDropEither, sym::async_drop_either, async_drop_either_fn, Target::Fn, GenericRequirement::Exact(3);

4
compiler/rustc_middle/src/ty/adt.rs
View file

@ -579,8 +579,8 @@ pub fn destructor(self, tcx: TyCtxt<'tcx>) -> Option<Destructor> {
tcx.adt_destructor(self.did())
}
// FIXME(zetanumbers): consider supporting this method in same places where
// `destructor` is referenced
// FIXME: consider combining this method with `AdtDef::destructor` and removing
// this version
pub fn async_destructor(self, tcx: TyCtxt<'tcx>) -> Option<AsyncDestructor> {
tcx.adt_async_destructor(self.did())
}

48
compiler/rustc_middle/src/ty/sty.rs
View file

@ -25,7 +25,7 @@
use std::borrow::Cow;
use std::iter;
use std::ops::{ControlFlow, Range};
use ty::util::IntTypeExt;
use ty::util::{AsyncDropGlueMorphology, IntTypeExt};
use rustc_type_ir::TyKind::*;
use rustc_type_ir::{self as ir, BoundVar, CollectAndApply, DynKind};
@ -1951,11 +1951,22 @@ pub fn discriminant_ty(self, tcx: TyCtxt<'tcx>) -> Ty<'tcx> {
}
/// Returns the type of the async destructor of this type.
pub fn async_destructor_ty(self, tcx: TyCtxt<'tcx>, param_env: ParamEnv<'tcx>) -> Ty<'tcx> {
if self.is_async_destructor_noop(tcx, param_env) || matches!(self.kind(), ty::Error(_)) {
return Ty::async_destructor_combinator(tcx, LangItem::AsyncDropNoop)
.instantiate_identity();
pub fn async_destructor_ty(self, tcx: TyCtxt<'tcx>) -> Ty<'tcx> {
match self.async_drop_glue_morphology(tcx) {
AsyncDropGlueMorphology::Noop => {
return Ty::async_destructor_combinator(tcx, LangItem::AsyncDropNoop)
.instantiate_identity();
}
AsyncDropGlueMorphology::DeferredDropInPlace => {
let drop_in_place =
Ty::async_destructor_combinator(tcx, LangItem::AsyncDropDeferredDropInPlace)
.instantiate(tcx, &[self.into()]);
return Ty::async_destructor_combinator(tcx, LangItem::AsyncDropFuse)
.instantiate(tcx, &[drop_in_place.into()]);
}
AsyncDropGlueMorphology::Custom => (),
}
match *self.kind() {
ty::Param(_) | ty::Alias(..) | ty::Infer(ty::TyVar(_)) => {
let assoc_items = tcx
@ -1974,19 +1985,13 @@ pub fn async_destructor_ty(self, tcx: TyCtxt<'tcx>, param_env: ParamEnv<'tcx>) -
.adt_async_destructor_ty(
tcx,
adt_def.variants().iter().map(|v| v.fields.iter().map(|f| f.ty(tcx, args))),
param_env,
),
ty::Tuple(tys) => self.adt_async_destructor_ty(tcx, iter::once(tys), param_env),
ty::Closure(_, args) => self.adt_async_destructor_ty(
tcx,
iter::once(args.as_closure().upvar_tys()),
param_env,
),
ty::CoroutineClosure(_, args) => self.adt_async_destructor_ty(
tcx,
iter::once(args.as_coroutine_closure().upvar_tys()),
param_env,
),
ty::Tuple(tys) => self.adt_async_destructor_ty(tcx, iter::once(tys)),
ty::Closure(_, args) => {
self.adt_async_destructor_ty(tcx, iter::once(args.as_closure().upvar_tys()))
}
ty::CoroutineClosure(_, args) => self
.adt_async_destructor_ty(tcx, iter::once(args.as_coroutine_closure().upvar_tys())),
ty::Adt(adt_def, _) => {
assert!(adt_def.is_union());
@ -2008,17 +2013,12 @@ pub fn async_destructor_ty(self, tcx: TyCtxt<'tcx>, param_env: ParamEnv<'tcx>) -
}
}
fn adt_async_destructor_ty<I>(
self,
tcx: TyCtxt<'tcx>,
variants: I,
param_env: ParamEnv<'tcx>,
) -> Ty<'tcx>
fn adt_async_destructor_ty<I>(self, tcx: TyCtxt<'tcx>, variants: I) -> Ty<'tcx>
where
I: Iterator + ExactSizeIterator,
I::Item: IntoIterator<Item = Ty<'tcx>>,
{
debug_assert!(!self.is_async_destructor_noop(tcx, param_env));
debug_assert_eq!(self.async_drop_glue_morphology(tcx), AsyncDropGlueMorphology::Custom);
let defer = Ty::async_destructor_combinator(tcx, LangItem::AsyncDropDefer);
let chain = Ty::async_destructor_combinator(tcx, LangItem::AsyncDropChain);

139
compiler/rustc_middle/src/ty/util.rs
View file

@ -421,6 +421,25 @@ pub fn calculate_async_dtor(
Some(ty::AsyncDestructor { future, ctor })
}
/// Returns async drop glue morphology for a definition. To get async drop
/// glue morphology for a type see [`Ty::async_drop_glue_morphology`].
//
// FIXME: consider making this a query
pub fn async_drop_glue_morphology(self, did: DefId) -> AsyncDropGlueMorphology {
let ty: Ty<'tcx> = self.type_of(did).instantiate_identity();
// Async drop glue morphology is an internal detail, so reveal_all probably
// should be fine
let param_env = ty::ParamEnv::reveal_all();
if ty.needs_async_drop(self, param_env) {
AsyncDropGlueMorphology::Custom
} else if ty.needs_drop(self, param_env) {
AsyncDropGlueMorphology::DeferredDropInPlace
} else {
AsyncDropGlueMorphology::Noop
}
}
/// Returns the set of types that are required to be alive in
/// order to run the destructor of `def` (see RFCs 769 and
/// 1238).
@ -1177,6 +1196,18 @@ fn fold_const(&mut self, ct: ty::Const<'tcx>) -> ty::Const<'tcx> {
}
}
/// Indicates the form of `AsyncDestruct::Destructor`. Used to simplify async
/// drop glue for types not using async drop.
#[derive(Clone, Copy, PartialEq, Eq, Debug)]
pub enum AsyncDropGlueMorphology {
/// Async destructor simply does nothing
Noop,
/// Async destructor simply runs `drop_in_place`
DeferredDropInPlace,
/// Async destructor has custom logic
Custom,
}
impl<'tcx> Ty<'tcx> {
/// Returns the `Size` for primitive types (bool, uint, int, char, float).
pub fn primitive_size(self, tcx: TyCtxt<'tcx>) -> Size {
@ -1342,27 +1373,16 @@ fn is_trivially_unpin(self) -> bool {
}
}
/// Checks whether values of this type `T` implement has noop async destructor.
/// Get morphology of the async drop glue, needed for types which do not
/// use async drop. To get async drop glue morphology for a definition see
/// [`TyCtxt::async_drop_glue_morphology`]. Used for `AsyncDestruct::Destructor`
/// type construction.
//
// FIXME: implement optimization to make ADTs, which do not need drop,
// to skip fields or to have noop async destructor, use `needs_(async_)drop`
pub fn is_async_destructor_noop(
self,
tcx: TyCtxt<'tcx>,
param_env: ty::ParamEnv<'tcx>,
) -> bool {
// TODO: check on the most generic version of your type
self.is_async_destructor_trivially_noop()
|| self.needs_async_drop(tcx, param_env)
|| self.needs_drop(tcx, param_env)
}
/// Fast path helper for testing if a type has noop async destructor.
///
/// Returning `true` means the type is known to have noop async destructor
/// implementation. Returning `true` means nothing -- could be
/// `Drop`, might not be.
fn is_async_destructor_trivially_noop(self) -> bool {
// FIXME: implement optimization to not instantiate a certain morphology of
// async drop glue too soon to allow per type optimizations, see array case
// for more info. Perhaps then remove this method and use `needs_(async_)drop`
// instead.
pub fn async_drop_glue_morphology(self, tcx: TyCtxt<'tcx>) -> AsyncDropGlueMorphology {
match self.kind() {
ty::Int(_)
| ty::Uint(_)
@ -1374,37 +1394,43 @@ fn is_async_destructor_trivially_noop(self) -> bool {
| ty::Ref(..)
| ty::RawPtr(..)
| ty::FnDef(..)
| ty::FnPtr(_) => true,
ty::Tuple(tys) => tys.is_empty(),
ty::Adt(adt_def, _) => adt_def.is_manually_drop(),
ty::Bool => todo!(),
ty::Char => todo!(),
ty::Int(_) => todo!(),
ty::Uint(_) => todo!(),
ty::Float(_) => todo!(),
ty::Adt(_, _) => todo!(),
ty::Foreign(_) => todo!(),
ty::Str => todo!(),
ty::Array(_, _) => todo!(),
ty::Pat(_, _) => todo!(),
ty::Slice(_) => todo!(),
ty::RawPtr(_, _) => todo!(),
ty::Ref(_, _, _) => todo!(),
ty::FnDef(_, _) => todo!(),
ty::FnPtr(_) => todo!(),
ty::Dynamic(_, _, _) => todo!(),
ty::Closure(_, _) => todo!(),
ty::CoroutineClosure(_, _) => todo!(),
ty::Coroutine(_, _) => todo!(),
ty::CoroutineWitness(_, _) => todo!(),
ty::Never => todo!(),
ty::Tuple(_) => todo!(),
ty::Alias(_, _) => todo!(),
ty::Param(_) => todo!(),
ty::Bound(_, _) => todo!(),
ty::Placeholder(_) => todo!(),
ty::Infer(_) => todo!(),
ty::Error(_) => todo!(),
| ty::FnPtr(_)
| ty::Infer(ty::FreshIntTy(_))
| ty::Infer(ty::FreshFloatTy(_)) => AsyncDropGlueMorphology::Noop,
ty::Tuple(tys) if tys.is_empty() => AsyncDropGlueMorphology::Noop,
ty::Adt(adt_def, _) if adt_def.is_manually_drop() => AsyncDropGlueMorphology::Noop,
// Foreign types can never have destructors.
ty::Foreign(_) => AsyncDropGlueMorphology::Noop,
// FIXME: implement dynamic types async drops
ty::Error(_) | ty::Dynamic(..) => AsyncDropGlueMorphology::DeferredDropInPlace,
ty::Tuple(_) | ty::Array(_, _) | ty::Slice(_) => {
// Assume worst-case scenario, because we can instantiate async
// destructors in different orders:
//
// 1. Instantiate [T; N] with T = String and N = 0
// 2. Instantiate <[String; 0] as AsyncDestruct>::Destructor
//
// And viceversa, thus we cannot rely on String not using async
// drop or array having zero (0) elements
AsyncDropGlueMorphology::Custom
}
ty::Pat(ty, _) => ty.async_drop_glue_morphology(tcx),
ty::Adt(adt_def, _) => tcx.async_drop_glue_morphology(adt_def.did()),
ty::Closure(did, _)
| ty::CoroutineClosure(did, _)
| ty::Coroutine(did, _)
| ty::CoroutineWitness(did, _) => tcx.async_drop_glue_morphology(*did),
ty::Alias(..) | ty::Param(_) | ty::Bound(..) | ty::Placeholder(..) | ty::Infer(_) => {
// No specifics, but would usually mean forwarding async drop glue
AsyncDropGlueMorphology::Custom
}
}
}
@ -1451,7 +1477,11 @@ pub fn needs_drop(self, tcx: TyCtxt<'tcx>, param_env: ty::ParamEnv<'tcx>) -> boo
/// (Note that this implies that if `ty` has an async destructor attached,
/// then `needs_async_drop` will definitely return `true` for `ty`.)
///
/// Note that this method is used to check eligible types in unions.
/// When constructing `AsyncDestruct::Destructor` type, use
/// [`Ty::async_drop_glue_morphology`] instead.
//
// FIXME(zetanumbers): Note that this method is used to check eligible types
// in unions.
#[inline]
pub fn needs_async_drop(self, tcx: TyCtxt<'tcx>, param_env: ty::ParamEnv<'tcx>) -> bool {
// Avoid querying in simple cases.
@ -1647,10 +1677,13 @@ pub fn determine<P>(self_arg_ty: Ty<'tcx>, is_self_ty: P) -> ExplicitSelf<'tcx>
}
}
// FIXME(zetanumbers): make specifying asyncness explicit
/// Returns a list of types such that the given type needs drop if and only if
/// *any* of the returned types need drop. Returns `Err(AlwaysRequiresDrop)` if
/// this type always needs drop.
//
// FIXME(zetanumbers): consider replacing this with only
// `needs_drop_components_with_async`
#[inline]
pub fn needs_drop_components<'tcx>(
tcx: TyCtxt<'tcx>,
ty: Ty<'tcx>,

37
compiler/rustc_mir_transform/src/shim/async_destructor_ctor.rs
View file

@ -12,7 +12,7 @@
Terminator, TerminatorKind, UnwindAction, UnwindTerminateReason, RETURN_PLACE,
};
use rustc_middle::ty::adjustment::PointerCoercion;
use rustc_middle::ty::util::Discr;
use rustc_middle::ty::util::{AsyncDropGlueMorphology, Discr};
use rustc_middle::ty::{self, Ty, TyCtxt};
use rustc_middle::{bug, span_bug};
use rustc_span::source_map::respan;
@ -116,15 +116,25 @@ fn new(tcx: TyCtxt<'tcx>, def_id: DefId, self_ty: Option<Ty<'tcx>>) -> Self {
}
fn build(self) -> Body<'tcx> {
let (tcx, def_id, Some(self_ty)) = (self.tcx, self.def_id, self.self_ty) else {
let (tcx, Some(self_ty)) = (self.tcx, self.self_ty) else {
return self.build_zst_output();
};
match self_ty.async_drop_glue_morphology(tcx) {
AsyncDropGlueMorphology::Noop => span_bug!(
self.span,
"async drop glue shim generator encountered type with noop async drop glue morphology"
),
AsyncDropGlueMorphology::DeferredDropInPlace => {
return self.build_deferred_drop_in_place();
}
AsyncDropGlueMorphology::Custom => (),
}
let surface_drop_kind = || {
let param_env = tcx.param_env_reveal_all_normalized(def_id);
if self_ty.has_surface_async_drop(tcx, param_env) {
let adt_def = self_ty.ty_adt_def()?;
if adt_def.async_destructor(tcx).is_some() {
Some(SurfaceDropKind::Async)
} else if self_ty.has_surface_drop(tcx, param_env) {
} else if adt_def.destructor(tcx).is_some() {
Some(SurfaceDropKind::Sync)
} else {
None
@ -267,6 +277,13 @@ fn build_zst_output(mut self) -> Body<'tcx> {
self.return_()
}
fn build_deferred_drop_in_place(mut self) -> Body<'tcx> {
self.put_self();
let deferred = self.combine_deferred_drop_in_place();
self.combine_fuse(deferred);
self.return_()
}
fn build_fused_async_surface(mut self) -> Body<'tcx> {
self.put_self();
let surface = self.combine_async_surface();
@ -441,6 +458,14 @@ fn combine_sync_surface(&mut self) -> Ty<'tcx> {
)
}
fn combine_deferred_drop_in_place(&mut self) -> Ty<'tcx> {
self.apply_combinator(
1,
LangItem::AsyncDropDeferredDropInPlace,
&[self.self_ty.unwrap().into()],
)
}
fn combine_fuse(&mut self, inner_future_ty: Ty<'tcx>) -> Ty<'tcx> {
self.apply_combinator(1, LangItem::AsyncDropFuse, &[inner_future_ty.into()])
}
@ -481,7 +506,7 @@ fn return_(mut self) -> Body<'tcx> {
if let Some(ty) = self.self_ty {
debug_assert_eq!(
output.ty(&self.locals, self.tcx),
ty.async_destructor_ty(self.tcx, self.param_env),
ty.async_destructor_ty(self.tcx),
"output async destructor types did not match for type: {ty:?}",
);
}

1
compiler/rustc_span/src/symbol.rs
View file

@ -430,6 +430,7 @@
async_drop,
async_drop_chain,
async_drop_defer,
async_drop_deferred_drop_in_place,
async_drop_either,
async_drop_fuse,
async_drop_in_place,

2
compiler/rustc_trait_selection/src/solve/normalizes_to/mod.rs
View file

@ -839,7 +839,7 @@ fn consider_builtin_async_destruct_candidate(
| ty::Str
| ty::Slice(_)
| ty::Tuple(_)
| ty::Error(_) => self_ty.async_destructor_ty(ecx.interner(), goal.param_env),
| ty::Error(_) => self_ty.async_destructor_ty(ecx.interner()),
// We do not call `Ty::async_destructor_ty` on alias, param, or placeholder
// types, which return `<self_ty as AsyncDestruct>::AsyncDestructor`

2
compiler/rustc_trait_selection/src/traits/project.rs
View file

@ -1560,7 +1560,7 @@ fn confirm_builtin_candidate<'cx, 'tcx>(
let destructor_def_id = tcx.associated_item_def_ids(trait_def_id)[0];
assert_eq!(destructor_def_id, item_def_id);
(self_ty.async_destructor_ty(tcx, obligation.param_env).into(), Vec::new())
(self_ty.async_destructor_ty(tcx).into(), Vec::new())
} else if lang_items.pointee_trait() == Some(trait_def_id) {
let metadata_def_id = tcx.require_lang_item(LangItem::Metadata, None);
assert_eq!(metadata_def_id, item_def_id);

3
compiler/rustc_ty_utils/src/instance.rs
View file

@ -4,6 +4,7 @@
use rustc_middle::bug;
use rustc_middle::query::Providers;
use rustc_middle::traits::{BuiltinImplSource, CodegenObligationError};
use rustc_middle::ty::util::AsyncDropGlueMorphology;
use rustc_middle::ty::GenericArgsRef;
use rustc_middle::ty::{self, Instance, TyCtxt, TypeVisitableExt};
use rustc_span::sym;
@ -59,7 +60,7 @@ fn resolve_instance<'tcx>(
} else if Some(def_id) == tcx.lang_items().async_drop_in_place_fn() {
let ty = args.type_at(0);
if !ty.is_async_destructor_noop(tcx, param_env) {
if ty.async_drop_glue_morphology(tcx) != AsyncDropGlueMorphology::Noop {
match *ty.kind() {
ty::Closure(..)
| ty::CoroutineClosure(..)

2
compiler/rustc_ty_utils/src/needs_drop.rs
View file

@ -36,7 +36,7 @@ fn needs_async_drop_raw<'tcx>(tcx: TyCtxt<'tcx>, query: ty::ParamEnvAnd<'tcx, Ty
// it needs async drop.
let adt_has_async_dtor =
|adt_def: ty::AdtDef<'tcx>| adt_def.async_destructor(tcx).map(|_| DtorType::Significant);
let res = drop_tys_helper(tcx, query.value, query.param_env, adt_has_dtor, false)
let res = drop_tys_helper(tcx, query.value, query.param_env, adt_has_async_dtor, false)
.filter(filter_array_elements(tcx, query.param_env))
.next()
.is_some();

11
library/core/src/future/async_drop.rs
View file

@ -161,6 +161,11 @@ trait AsyncDestruct {
/// wrapped future completes by returning `Poll::Ready(())` on poll. This
/// is useful for constructing async destructors to guarantee this
/// "fuse" property
//
// FIXME: Consider optimizing combinators to not have to use fuse in majority
// of cases, perhaps by adding `#[(rustc_)idempotent(_future)]` attribute for
// async functions and blocks with the unit return type. However current layout
// optimizations currently encode `None` case into the async block's discriminant.
struct Fuse<T> {
inner: Option<T>,
}
@ -251,6 +256,12 @@ async fn chain<F, G>(first: F, last: G)
}
}
#[cfg(not(bootstrap))]
#[lang = "async_drop_deferred_drop_in_place"]
async unsafe fn deferred_drop_in_place<T>(to_drop: *mut T) {
unsafe { crate::ptr::drop_in_place(to_drop) }
}
/// Used for noop async destructors. We don't use [`core::future::Ready`]
/// because it panics after its second poll, which could be potentially
/// bad if that would happen during the cleanup.