Rollup merge of #93365 - nnethercote:more-arena-cleanups, r=oli-obk
More arena cleanups A sequel to #90990. r? `@oli-obk`
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commit
0eb6753fc5
1 changed files with 40 additions and 21 deletions
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@ -45,24 +45,24 @@ pub struct TypedArena<T> {
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end: Cell<*mut T>,
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/// A vector of arena chunks.
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chunks: RefCell<Vec<TypedArenaChunk<T>>>,
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chunks: RefCell<Vec<ArenaChunk<T>>>,
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/// Marker indicating that dropping the arena causes its owned
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/// instances of `T` to be dropped.
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_own: PhantomData<T>,
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}
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struct TypedArenaChunk<T> {
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struct ArenaChunk<T = u8> {
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/// The raw storage for the arena chunk.
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storage: Box<[MaybeUninit<T>]>,
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/// The number of valid entries in the chunk.
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entries: usize,
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}
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impl<T> TypedArenaChunk<T> {
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impl<T> ArenaChunk<T> {
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#[inline]
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unsafe fn new(capacity: usize) -> TypedArenaChunk<T> {
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TypedArenaChunk { storage: Box::new_uninit_slice(capacity), entries: 0 }
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unsafe fn new(capacity: usize) -> ArenaChunk<T> {
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ArenaChunk { storage: Box::new_uninit_slice(capacity), entries: 0 }
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}
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/// Destroys this arena chunk.
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@ -125,6 +125,11 @@ impl<I, T> IterExt<T> for I
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where
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I: IntoIterator<Item = T>,
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{
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// This default collects into a `SmallVec` and then allocates by copying
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// from it. The specializations below for types like `Vec` are more
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// efficient, copying directly without the intermediate collecting step.
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// This default could be made more efficient, like
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// `DroplessArena::alloc_from_iter`, but it's not hot enough to bother.
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#[inline]
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default fn alloc_from_iter(self, arena: &TypedArena<T>) -> &mut [T] {
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let vec: SmallVec<[_; 8]> = self.into_iter().collect();
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@ -139,7 +144,7 @@ impl<T, const N: usize> IterExt<T> for std::array::IntoIter<T, N> {
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if len == 0 {
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return &mut [];
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}
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// Move the content to the arena by copying and then forgetting it
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// Move the content to the arena by copying and then forgetting it.
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unsafe {
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let start_ptr = arena.alloc_raw_slice(len);
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self.as_slice().as_ptr().copy_to_nonoverlapping(start_ptr, len);
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@ -156,7 +161,7 @@ impl<T> IterExt<T> for Vec<T> {
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if len == 0 {
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return &mut [];
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}
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// Move the content to the arena by copying and then forgetting it
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// Move the content to the arena by copying and then forgetting it.
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unsafe {
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let start_ptr = arena.alloc_raw_slice(len);
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self.as_ptr().copy_to_nonoverlapping(start_ptr, len);
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@ -173,7 +178,7 @@ impl<A: smallvec::Array> IterExt<A::Item> for SmallVec<A> {
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if len == 0 {
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return &mut [];
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}
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// Move the content to the arena by copying and then forgetting it
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// Move the content to the arena by copying and then forgetting it.
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unsafe {
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let start_ptr = arena.alloc_raw_slice(len);
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self.as_ptr().copy_to_nonoverlapping(start_ptr, len);
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@ -272,7 +277,7 @@ impl<T> TypedArena<T> {
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// Also ensure that this chunk can fit `additional`.
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new_cap = cmp::max(additional, new_cap);
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let mut chunk = TypedArenaChunk::<T>::new(new_cap);
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let mut chunk = ArenaChunk::<T>::new(new_cap);
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self.ptr.set(chunk.start());
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self.end.set(chunk.end());
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chunks.push(chunk);
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@ -281,7 +286,7 @@ impl<T> TypedArena<T> {
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// Drops the contents of the last chunk. The last chunk is partially empty, unlike all other
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// chunks.
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fn clear_last_chunk(&self, last_chunk: &mut TypedArenaChunk<T>) {
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fn clear_last_chunk(&self, last_chunk: &mut ArenaChunk<T>) {
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// Determine how much was filled.
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let start = last_chunk.start() as usize;
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// We obtain the value of the pointer to the first uninitialized element.
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@ -340,7 +345,7 @@ pub struct DroplessArena {
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end: Cell<*mut u8>,
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/// A vector of arena chunks.
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chunks: RefCell<Vec<TypedArenaChunk<u8>>>,
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chunks: RefCell<Vec<ArenaChunk>>,
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}
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unsafe impl Send for DroplessArena {}
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@ -378,7 +383,7 @@ impl DroplessArena {
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// Also ensure that this chunk can fit `additional`.
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new_cap = cmp::max(additional, new_cap);
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let mut chunk = TypedArenaChunk::<u8>::new(new_cap);
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let mut chunk = ArenaChunk::new(new_cap);
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self.start.set(chunk.start());
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self.end.set(chunk.end());
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chunks.push(chunk);
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@ -520,10 +525,19 @@ impl DroplessArena {
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}
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}
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// Declare an `Arena` containing one dropless arena and many typed arenas (the
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// types of the typed arenas are specified by the arguments). The dropless
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// arena will be used for any types that impl `Copy`, and also for any of the
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// specified types that satisfy `!mem::needs_drop`.
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/// Declare an `Arena` containing one dropless arena and many typed arenas (the
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/// types of the typed arenas are specified by the arguments).
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///
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/// There are three cases of interest.
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/// - Types that are `Copy`: these need not be specified in the arguments. They
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/// will use the `DroplessArena`.
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/// - Types that are `!Copy` and `!Drop`: these must be specified in the
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/// arguments. An empty `TypedArena` will be created for each one, but the
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/// `DroplessArena` will always be used and the `TypedArena` will stay empty.
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/// This is odd but harmless, because an empty arena allocates no memory.
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/// - Types that are `!Copy` and `Drop`: these must be specified in the
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/// arguments. The `TypedArena` will be used for them.
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///
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#[rustc_macro_transparency = "semitransparent"]
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pub macro declare_arena([$($a:tt $name:ident: $ty:ty,)*]) {
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#[derive(Default)]
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@ -532,7 +546,7 @@ pub macro declare_arena([$($a:tt $name:ident: $ty:ty,)*]) {
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$($name: $crate::TypedArena<$ty>,)*
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}
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pub trait ArenaAllocatable<'tcx, T = Self>: Sized {
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pub trait ArenaAllocatable<'tcx, C = rustc_arena::IsNotCopy>: Sized {
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fn allocate_on<'a>(self, arena: &'a Arena<'tcx>) -> &'a mut Self;
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fn allocate_from_iter<'a>(
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arena: &'a Arena<'tcx>,
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@ -541,7 +555,7 @@ pub macro declare_arena([$($a:tt $name:ident: $ty:ty,)*]) {
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}
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// Any type that impls `Copy` can be arena-allocated in the `DroplessArena`.
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impl<'tcx, T: Copy> ArenaAllocatable<'tcx, ()> for T {
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impl<'tcx, T: Copy> ArenaAllocatable<'tcx, rustc_arena::IsCopy> for T {
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#[inline]
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fn allocate_on<'a>(self, arena: &'a Arena<'tcx>) -> &'a mut Self {
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arena.dropless.alloc(self)
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@ -555,7 +569,7 @@ pub macro declare_arena([$($a:tt $name:ident: $ty:ty,)*]) {
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}
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}
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$(
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impl<'tcx> ArenaAllocatable<'tcx, $ty> for $ty {
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impl<'tcx> ArenaAllocatable<'tcx, rustc_arena::IsNotCopy> for $ty {
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#[inline]
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fn allocate_on<'a>(self, arena: &'a Arena<'tcx>) -> &'a mut Self {
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if !::std::mem::needs_drop::<Self>() {
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@ -581,7 +595,7 @@ pub macro declare_arena([$($a:tt $name:ident: $ty:ty,)*]) {
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impl<'tcx> Arena<'tcx> {
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#[inline]
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pub fn alloc<T: ArenaAllocatable<'tcx, U>, U>(&self, value: T) -> &mut T {
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pub fn alloc<T: ArenaAllocatable<'tcx, C>, C>(&self, value: T) -> &mut T {
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value.allocate_on(self)
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}
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@ -594,7 +608,7 @@ pub macro declare_arena([$($a:tt $name:ident: $ty:ty,)*]) {
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self.dropless.alloc_slice(value)
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}
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pub fn alloc_from_iter<'a, T: ArenaAllocatable<'tcx, U>, U>(
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pub fn alloc_from_iter<'a, T: ArenaAllocatable<'tcx, C>, C>(
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&'a self,
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iter: impl ::std::iter::IntoIterator<Item = T>,
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) -> &'a mut [T] {
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@ -603,5 +617,10 @@ pub macro declare_arena([$($a:tt $name:ident: $ty:ty,)*]) {
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}
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}
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// Marker types that let us give different behaviour for arenas allocating
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// `Copy` types vs `!Copy` types.
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pub struct IsCopy;
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pub struct IsNotCopy;
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#[cfg(test)]
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mod tests;
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