diff options
| -rw-r--r-- | compiler/rustc_arena/src/lib.rs | 15 | ||||
| -rw-r--r-- | compiler/rustc_hir/src/arena.rs | 2 | ||||
| -rw-r--r-- | compiler/rustc_middle/src/arena.rs | 2 |
3 files changed, 14 insertions, 5 deletions
diff --git a/compiler/rustc_arena/src/lib.rs b/compiler/rustc_arena/src/lib.rs index 39def2a6f1f..6f9ecb9cd21 100644 --- a/compiler/rustc_arena/src/lib.rs +++ b/compiler/rustc_arena/src/lib.rs @@ -111,7 +111,7 @@ impl<T> Default for TypedArena<T> { // alloc() will trigger a grow(). ptr: Cell::new(ptr::null_mut()), end: Cell::new(ptr::null_mut()), - chunks: RefCell::new(vec![]), + chunks: Default::default(), _own: PhantomData, } } @@ -325,13 +325,17 @@ unsafe impl<#[may_dangle] T> Drop for TypedArena<T> { unsafe impl<T: Send> Send for TypedArena<T> {} +/// An arena that can hold objects of multiple different types that impl `Copy` +/// and/or satisfy `!mem::needs_drop`. pub struct DroplessArena { /// A pointer to the start of the free space. start: Cell<*mut u8>, /// A pointer to the end of free space. /// - /// The allocation proceeds from the end of the chunk towards the start. + /// The allocation proceeds downwards from the end of the chunk towards the + /// start. (This is slightly simpler and faster than allocating upwards, + /// see <https://fitzgeraldnick.com/2019/11/01/always-bump-downwards.html>.) /// When this pointer crosses the start pointer, a new chunk is allocated. end: Cell<*mut u8>, @@ -516,6 +520,10 @@ impl DroplessArena { } } +// Declare an `Arena` containing one dropless arena and many typed arenas (the +// types of the typed arenas are specified by the arguments). The dropless +// arena will be used for any types that impl `Copy`, and also for any of the +// specified types that satisfy `!mem::needs_drop`. #[rustc_macro_transparency = "semitransparent"] pub macro declare_arena([$($a:tt $name:ident: $ty:ty,)*]) { #[derive(Default)] @@ -532,6 +540,7 @@ pub macro declare_arena([$($a:tt $name:ident: $ty:ty,)*]) { ) -> &'a mut [Self]; } + // Any type that impls `Copy` can be arena-allocated in the `DroplessArena`. impl<'tcx, T: Copy> ArenaAllocatable<'tcx, ()> for T { #[inline] fn allocate_on<'a>(self, arena: &'a Arena<'tcx>) -> &'a mut Self { @@ -544,7 +553,6 @@ pub macro declare_arena([$($a:tt $name:ident: $ty:ty,)*]) { ) -> &'a mut [Self] { arena.dropless.alloc_from_iter(iter) } - } $( impl<'tcx> ArenaAllocatable<'tcx, $ty> for $ty { @@ -577,6 +585,7 @@ pub macro declare_arena([$($a:tt $name:ident: $ty:ty,)*]) { value.allocate_on(self) } + // Any type that impls `Copy` can have slices be arena-allocated in the `DroplessArena`. #[inline] pub fn alloc_slice<T: ::std::marker::Copy>(&self, value: &[T]) -> &mut [T] { if value.is_empty() { diff --git a/compiler/rustc_hir/src/arena.rs b/compiler/rustc_hir/src/arena.rs index 175845fb9e5..f19ca497d8b 100644 --- a/compiler/rustc_hir/src/arena.rs +++ b/compiler/rustc_hir/src/arena.rs @@ -1,4 +1,4 @@ -/// This declares a list of types which can be allocated by `Arena`. +/// This higher-order macro declares a list of types which can be allocated by `Arena`. /// /// Specifying the `decode` modifier will add decode impls for `&T` and `&[T]`, /// where `T` is the type listed. These impls will appear in the implement_ty_decoder! macro. diff --git a/compiler/rustc_middle/src/arena.rs b/compiler/rustc_middle/src/arena.rs index 530437f50eb..ee2e190e7cd 100644 --- a/compiler/rustc_middle/src/arena.rs +++ b/compiler/rustc_middle/src/arena.rs @@ -1,4 +1,4 @@ -/// This declares a list of types which can be allocated by `Arena`. +/// This higher-order macro declares a list of types which can be allocated by `Arena`. /// /// Specifying the `decode` modifier will add decode impls for `&T` and `&[T]` where `T` is the type /// listed. These impls will appear in the implement_ty_decoder! macro. |