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This commit is contained in:
Nicholas Nethercote 2022-01-26 10:33:41 +11:00
parent 0c17893d49
commit 9065c7ced6
1 changed files with 21 additions and 7 deletions
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28
compiler/rustc_arena/src/lib.rs
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@ -125,6 +125,11 @@ impl<I, T> IterExt<T> for I
where
I: IntoIterator<Item = T>,
{
// This default collects into a `SmallVec` and then allocates by copying
// from it. The specializations below for types like `Vec` are more
// efficient, copying directly without the intermediate collecting step.
// This default could be made more efficient, like
// `DroplessArena::alloc_from_iter`, but it's not hot enough to bother.
#[inline]
default fn alloc_from_iter(self, arena: &TypedArena<T>) -> &mut [T] {
let vec: SmallVec<[_; 8]> = self.into_iter().collect();
@ -139,7 +144,7 @@ impl<T, const N: usize> IterExt<T> for std::array::IntoIter<T, N> {
if len == 0 {
return &mut [];
}
// Move the content to the arena by copying and then forgetting it
// Move the content to the arena by copying and then forgetting it.
unsafe {
let start_ptr = arena.alloc_raw_slice(len);
self.as_slice().as_ptr().copy_to_nonoverlapping(start_ptr, len);
@ -156,7 +161,7 @@ impl<T> IterExt<T> for Vec<T> {
if len == 0 {
return &mut [];
}
// Move the content to the arena by copying and then forgetting it
// Move the content to the arena by copying and then forgetting it.
unsafe {
let start_ptr = arena.alloc_raw_slice(len);
self.as_ptr().copy_to_nonoverlapping(start_ptr, len);
@ -173,7 +178,7 @@ impl<A: smallvec::Array> IterExt<A::Item> for SmallVec<A> {
if len == 0 {
return &mut [];
}
// Move the content to the arena by copying and then forgetting it
// Move the content to the arena by copying and then forgetting it.
unsafe {
let start_ptr = arena.alloc_raw_slice(len);
self.as_ptr().copy_to_nonoverlapping(start_ptr, len);
@ -520,10 +525,19 @@ 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`.
/// Declare an `Arena` containing one dropless arena and many typed arenas (the
/// types of the typed arenas are specified by the arguments).
///
/// There are three cases of interest.
/// - Types that are `Copy`: these need not be specified in the arguments. They
/// will use the `DroplessArena`.
/// - Types that are `!Copy` and `!Drop`: these must be specified in the
/// arguments. An empty `TypedArena` will be created for each one, but the
/// `DroplessArena` will always be used and the `TypedArena` will stay empty.
/// This is odd but harmless, because an empty arena allocates no memory.
/// - Types that are `!Copy` and `Drop`: these must be specified in the
/// arguments. The `TypedArena` will be used for them.
///
#[rustc_macro_transparency = "semitransparent"]
pub macro declare_arena([$($a:tt $name:ident: $ty:ty,)*]) {
#[derive(Default)]