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Auto merge of #59536 - Zoxc:the-arena, r=eddyb
Introduce an arena type which may be used to allocate a list of types with destructors You can also specify that you want deserializers for `&'tcx [T]` and `&'tcx T` for a type in the list, which will allocate those using the arena. Based on #59517 and #59533. Look at the last commit for the interesting changes. An alternative to #56448. cc @michaelwoerister @eddyb r? @oli-obk
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,206 @@ | ||
| use arena::{TypedArena, DroplessArena}; | ||
| use std::mem; | ||
| use std::ptr; | ||
| use std::slice; | ||
| use std::cell::RefCell; | ||
| use std::marker::PhantomData; | ||
| use smallvec::SmallVec; | ||
|
|
||
| #[macro_export] | ||
| macro_rules! arena_types { | ||
| ($macro:path, $args:tt, $tcx:lifetime) => ( | ||
| $macro!($args, [ | ||
| [] vtable_method: Option<( | ||
| rustc::hir::def_id::DefId, | ||
| rustc::ty::subst::SubstsRef<$tcx> | ||
| )>, | ||
| [few] mir_keys: rustc::util::nodemap::DefIdSet, | ||
| [decode] specialization_graph: rustc::traits::specialization_graph::Graph, | ||
| ], $tcx); | ||
| ) | ||
| } | ||
|
|
||
| macro_rules! arena_for_type { | ||
| ([][$ty:ty]) => { | ||
| TypedArena<$ty> | ||
| }; | ||
| ([few $(, $attrs:ident)*][$ty:ty]) => { | ||
| PhantomData<$ty> | ||
| }; | ||
| ([$ignore:ident $(, $attrs:ident)*]$args:tt) => { | ||
| arena_for_type!([$($attrs),*]$args) | ||
| }; | ||
| } | ||
|
|
||
| macro_rules! declare_arena { | ||
| ([], [$($a:tt $name:ident: $ty:ty,)*], $tcx:lifetime) => { | ||
| #[derive(Default)] | ||
| pub struct Arena<$tcx> { | ||
| dropless: DroplessArena, | ||
| drop: DropArena, | ||
| $($name: arena_for_type!($a[$ty]),)* | ||
| } | ||
| } | ||
| } | ||
|
|
||
| macro_rules! which_arena_for_type { | ||
| ([][$arena:expr]) => { | ||
| Some($arena) | ||
| }; | ||
| ([few$(, $attrs:ident)*][$arena:expr]) => { | ||
| None | ||
| }; | ||
| ([$ignore:ident$(, $attrs:ident)*]$args:tt) => { | ||
| which_arena_for_type!([$($attrs),*]$args) | ||
| }; | ||
| } | ||
|
|
||
| macro_rules! impl_arena_allocatable { | ||
| ([], [$($a:tt $name:ident: $ty:ty,)*], $tcx:lifetime) => { | ||
| $( | ||
| impl ArenaAllocatable for $ty {} | ||
| unsafe impl<$tcx> ArenaField<$tcx> for $ty { | ||
| #[inline] | ||
| fn arena<'a>(_arena: &'a Arena<$tcx>) -> Option<&'a TypedArena<Self>> { | ||
| which_arena_for_type!($a[&_arena.$name]) | ||
| } | ||
| } | ||
| )* | ||
| } | ||
| } | ||
|
|
||
| arena_types!(declare_arena, [], 'tcx); | ||
|
|
||
| arena_types!(impl_arena_allocatable, [], 'tcx); | ||
|
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| pub trait ArenaAllocatable {} | ||
|
|
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| impl<T: Copy> ArenaAllocatable for T {} | ||
|
|
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| pub unsafe trait ArenaField<'tcx>: Sized { | ||
| /// Returns a specific arena to allocate from. | ||
| /// If None is returned, the DropArena will be used. | ||
| fn arena<'a>(arena: &'a Arena<'tcx>) -> Option<&'a TypedArena<Self>>; | ||
| } | ||
|
|
||
| unsafe impl<'tcx, T> ArenaField<'tcx> for T { | ||
| #[inline] | ||
| default fn arena<'a>(_: &'a Arena<'tcx>) -> Option<&'a TypedArena<Self>> { | ||
| panic!() | ||
| } | ||
| } | ||
|
|
||
| impl<'tcx> Arena<'tcx> { | ||
| #[inline] | ||
| pub fn alloc<T: ArenaAllocatable>(&self, value: T) -> &mut T { | ||
| if !mem::needs_drop::<T>() { | ||
| return self.dropless.alloc(value); | ||
| } | ||
| match <T as ArenaField<'tcx>>::arena(self) { | ||
| Some(arena) => arena.alloc(value), | ||
| None => unsafe { self.drop.alloc(value) }, | ||
| } | ||
| } | ||
|
|
||
| pub fn alloc_from_iter< | ||
| T: ArenaAllocatable, | ||
| I: IntoIterator<Item = T> | ||
| >( | ||
| &'a self, | ||
| iter: I | ||
| ) -> &'a mut [T] { | ||
| if !mem::needs_drop::<T>() { | ||
| return self.dropless.alloc_from_iter(iter); | ||
| } | ||
| match <T as ArenaField<'tcx>>::arena(self) { | ||
| Some(arena) => arena.alloc_from_iter(iter), | ||
| None => unsafe { self.drop.alloc_from_iter(iter) }, | ||
| } | ||
| } | ||
| } | ||
|
|
||
| /// Calls the destructor for an object when dropped. | ||
| struct DropType { | ||
| drop_fn: unsafe fn(*mut u8), | ||
| obj: *mut u8, | ||
| } | ||
|
|
||
| unsafe fn drop_for_type<T>(to_drop: *mut u8) { | ||
| std::ptr::drop_in_place(to_drop as *mut T) | ||
| } | ||
|
|
||
| impl Drop for DropType { | ||
| fn drop(&mut self) { | ||
| unsafe { | ||
| (self.drop_fn)(self.obj) | ||
| } | ||
| } | ||
| } | ||
|
|
||
| /// An arena which can be used to allocate any type. | ||
| /// Allocating in this arena is unsafe since the type system | ||
| /// doesn't know which types it contains. In order to | ||
| /// allocate safely, you must store a PhantomData<T> | ||
| /// alongside this arena for each type T you allocate. | ||
| #[derive(Default)] | ||
| struct DropArena { | ||
| /// A list of destructors to run when the arena drops. | ||
| /// Ordered so `destructors` gets dropped before the arena | ||
| /// since its destructor can reference memory in the arena. | ||
| destructors: RefCell<Vec<DropType>>, | ||
| arena: DroplessArena, | ||
| } | ||
|
|
||
| impl DropArena { | ||
| #[inline] | ||
| unsafe fn alloc<T>(&self, object: T) -> &mut T { | ||
| let mem = self.arena.alloc_raw( | ||
| mem::size_of::<T>(), | ||
| mem::align_of::<T>() | ||
| ) as *mut _ as *mut T; | ||
| // Write into uninitialized memory. | ||
| ptr::write(mem, object); | ||
| let result = &mut *mem; | ||
| // Record the destructor after doing the allocation as that may panic | ||
| // and would cause `object`'s destuctor to run twice if it was recorded before | ||
| self.destructors.borrow_mut().push(DropType { | ||
| drop_fn: drop_for_type::<T>, | ||
| obj: result as *mut T as *mut u8, | ||
| }); | ||
| result | ||
| } | ||
|
|
||
| #[inline] | ||
| unsafe fn alloc_from_iter<T, I: IntoIterator<Item = T>>(&self, iter: I) -> &mut [T] { | ||
| let mut vec: SmallVec<[_; 8]> = iter.into_iter().collect(); | ||
| if vec.is_empty() { | ||
| return &mut []; | ||
| } | ||
| let len = vec.len(); | ||
|
|
||
| let start_ptr = self.arena.alloc_raw( | ||
| len.checked_mul(mem::size_of::<T>()).unwrap(), | ||
| mem::align_of::<T>() | ||
| ) as *mut _ as *mut T; | ||
|
|
||
| let mut destructors = self.destructors.borrow_mut(); | ||
| // Reserve space for the destructors so we can't panic while adding them | ||
| destructors.reserve(len); | ||
|
|
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| // Move the content to the arena by copying it and then forgetting | ||
| // the content of the SmallVec | ||
| vec.as_ptr().copy_to_nonoverlapping(start_ptr, len); | ||
| mem::forget(vec.drain()); | ||
|
|
||
| // Record the destructors after doing the allocation as that may panic | ||
| // and would cause `object`'s destuctor to run twice if it was recorded before | ||
| for i in 0..len { | ||
| destructors.push(DropType { | ||
| drop_fn: drop_for_type::<T>, | ||
| obj: start_ptr.offset(i as isize) as *mut u8, | ||
| }); | ||
| } | ||
|
|
||
| slice::from_raw_parts_mut(start_ptr, len) | ||
| } | ||
| } |
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