Adding upstream version 1.64.0+dfsg1.upstream/1.64.0+dfsg1

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

3 files changed, 900 insertions, 0 deletions

diff --git a/compiler/rustc_arena/Cargo.toml b/compiler/rustc_arena/Cargo.toml
new file mode 100644
index 000000000..5c2aee6b4
--- /dev/null
+++ b/compiler/rustc_arena/Cargo.toml
@@ -0,0 +1,7 @@
+[package]
+name = "rustc_arena"
+version = "0.0.0"
+edition = "2021"
+
+[dependencies]
+smallvec = { version = "1.8.1", features = ["union", "may_dangle"] }
diff --git a/compiler/rustc_arena/src/lib.rs b/compiler/rustc_arena/src/lib.rs
new file mode 100644
index 000000000..a5f1cbc96
--- /dev/null
+++ b/compiler/rustc_arena/src/lib.rs
@@ -0,0 +1,645 @@
+//! The arena, a fast but limited type of allocator.
+//!
+//! Arenas are a type of allocator that destroy the objects within, all at
+//! once, once the arena itself is destroyed. They do not support deallocation
+//! of individual objects while the arena itself is still alive. The benefit
+//! of an arena is very fast allocation; just a pointer bump.
+//!
+//! This crate implements several kinds of arena.
+
+#![doc(
+    html_root_url = "https://doc.rust-lang.org/nightly/nightly-rustc/",
+    test(no_crate_inject, attr(deny(warnings)))
+)]
+#![feature(dropck_eyepatch)]
+#![feature(new_uninit)]
+#![feature(maybe_uninit_slice)]
+#![feature(min_specialization)]
+#![feature(decl_macro)]
+#![feature(rustc_attrs)]
+#![cfg_attr(test, feature(test))]
+#![feature(strict_provenance)]
+#![feature(ptr_const_cast)]
+
+use smallvec::SmallVec;
+
+use std::alloc::Layout;
+use std::cell::{Cell, RefCell};
+use std::cmp;
+use std::marker::{PhantomData, Send};
+use std::mem::{self, MaybeUninit};
+use std::ptr::{self, NonNull};
+use std::slice;
+
+#[inline(never)]
+#[cold]
+fn cold_path<F: FnOnce() -> R, R>(f: F) -> R {
+    f()
+}
+
+/// An arena that can hold objects of only one type.
+pub struct TypedArena<T> {
+    /// A pointer to the next object to be allocated.
+    ptr: Cell<*mut T>,
+
+    /// A pointer to the end of the allocated area. When this pointer is
+    /// reached, a new chunk is allocated.
+    end: Cell<*mut T>,
+
+    /// A vector of arena chunks.
+    chunks: RefCell<Vec<ArenaChunk<T>>>,
+
+    /// Marker indicating that dropping the arena causes its owned
+    /// instances of `T` to be dropped.
+    _own: PhantomData<T>,
+}
+
+struct ArenaChunk<T = u8> {
+    /// The raw storage for the arena chunk.
+    storage: NonNull<[MaybeUninit<T>]>,
+    /// The number of valid entries in the chunk.
+    entries: usize,
+}
+
+unsafe impl<#[may_dangle] T> Drop for ArenaChunk<T> {
+    fn drop(&mut self) {
+        unsafe { Box::from_raw(self.storage.as_mut()) };
+    }
+}
+
+impl<T> ArenaChunk<T> {
+    #[inline]
+    unsafe fn new(capacity: usize) -> ArenaChunk<T> {
+        ArenaChunk {
+            storage: NonNull::new(Box::into_raw(Box::new_uninit_slice(capacity))).unwrap(),
+            entries: 0,
+        }
+    }
+
+    /// Destroys this arena chunk.
+    #[inline]
+    unsafe fn destroy(&mut self, len: usize) {
+        // The branch on needs_drop() is an -O1 performance optimization.
+        // Without the branch, dropping TypedArena<u8> takes linear time.
+        if mem::needs_drop::<T>() {
+            let slice = &mut *(self.storage.as_mut());
+            ptr::drop_in_place(MaybeUninit::slice_assume_init_mut(&mut slice[..len]));
+        }
+    }
+
+    // Returns a pointer to the first allocated object.
+    #[inline]
+    fn start(&mut self) -> *mut T {
+        self.storage.as_ptr() as *mut T
+    }
+
+    // Returns a pointer to the end of the allocated space.
+    #[inline]
+    fn end(&mut self) -> *mut T {
+        unsafe {
+            if mem::size_of::<T>() == 0 {
+                // A pointer as large as possible for zero-sized elements.
+                ptr::invalid_mut(!0)
+            } else {
+                self.start().add((*self.storage.as_ptr()).len())
+            }
+        }
+    }
+}
+
+// The arenas start with PAGE-sized chunks, and then each new chunk is twice as
+// big as its predecessor, up until we reach HUGE_PAGE-sized chunks, whereupon
+// we stop growing. This scales well, from arenas that are barely used up to
+// arenas that are used for 100s of MiBs. Note also that the chosen sizes match
+// the usual sizes of pages and huge pages on Linux.
+const PAGE: usize = 4096;
+const HUGE_PAGE: usize = 2 * 1024 * 1024;
+
+impl<T> Default for TypedArena<T> {
+    /// Creates a new `TypedArena`.
+    fn default() -> TypedArena<T> {
+        TypedArena {
+            // We set both `ptr` and `end` to 0 so that the first call to
+            // alloc() will trigger a grow().
+            ptr: Cell::new(ptr::null_mut()),
+            end: Cell::new(ptr::null_mut()),
+            chunks: Default::default(),
+            _own: PhantomData,
+        }
+    }
+}
+
+trait IterExt<T> {
+    fn alloc_from_iter(self, arena: &TypedArena<T>) -> &mut [T];
+}
+
+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();
+        vec.alloc_from_iter(arena)
+    }
+}
+
+impl<T, const N: usize> IterExt<T> for std::array::IntoIter<T, N> {
+    #[inline]
+    fn alloc_from_iter(self, arena: &TypedArena<T>) -> &mut [T] {
+        let len = self.len();
+        if len == 0 {
+            return &mut [];
+        }
+        // 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);
+            mem::forget(self);
+            slice::from_raw_parts_mut(start_ptr, len)
+        }
+    }
+}
+
+impl<T> IterExt<T> for Vec<T> {
+    #[inline]
+    fn alloc_from_iter(mut self, arena: &TypedArena<T>) -> &mut [T] {
+        let len = self.len();
+        if len == 0 {
+            return &mut [];
+        }
+        // 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);
+            self.set_len(0);
+            slice::from_raw_parts_mut(start_ptr, len)
+        }
+    }
+}
+
+impl<A: smallvec::Array> IterExt<A::Item> for SmallVec<A> {
+    #[inline]
+    fn alloc_from_iter(mut self, arena: &TypedArena<A::Item>) -> &mut [A::Item] {
+        let len = self.len();
+        if len == 0 {
+            return &mut [];
+        }
+        // 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);
+            self.set_len(0);
+            slice::from_raw_parts_mut(start_ptr, len)
+        }
+    }
+}
+
+impl<T> TypedArena<T> {
+    /// Allocates an object in the `TypedArena`, returning a reference to it.
+    #[inline]
+    pub fn alloc(&self, object: T) -> &mut T {
+        if self.ptr == self.end {
+            self.grow(1)
+        }
+
+        unsafe {
+            if mem::size_of::<T>() == 0 {
+                self.ptr.set((self.ptr.get() as *mut u8).wrapping_offset(1) as *mut T);
+                let ptr = ptr::NonNull::<T>::dangling().as_ptr();
+                // Don't drop the object. This `write` is equivalent to `forget`.
+                ptr::write(ptr, object);
+                &mut *ptr
+            } else {
+                let ptr = self.ptr.get();
+                // Advance the pointer.
+                self.ptr.set(self.ptr.get().offset(1));
+                // Write into uninitialized memory.
+                ptr::write(ptr, object);
+                &mut *ptr
+            }
+        }
+    }
+
+    #[inline]
+    fn can_allocate(&self, additional: usize) -> bool {
+        // FIXME: this should *likely* use `offset_from`, but more
+        // investigation is needed (including running tests in miri).
+        let available_bytes = self.end.get().addr() - self.ptr.get().addr();
+        let additional_bytes = additional.checked_mul(mem::size_of::<T>()).unwrap();
+        available_bytes >= additional_bytes
+    }
+
+    /// Ensures there's enough space in the current chunk to fit `len` objects.
+    #[inline]
+    fn ensure_capacity(&self, additional: usize) {
+        if !self.can_allocate(additional) {
+            self.grow(additional);
+            debug_assert!(self.can_allocate(additional));
+        }
+    }
+
+    #[inline]
+    unsafe fn alloc_raw_slice(&self, len: usize) -> *mut T {
+        assert!(mem::size_of::<T>() != 0);
+        assert!(len != 0);
+
+        self.ensure_capacity(len);
+
+        let start_ptr = self.ptr.get();
+        self.ptr.set(start_ptr.add(len));
+        start_ptr
+    }
+
+    #[inline]
+    pub fn alloc_from_iter<I: IntoIterator<Item = T>>(&self, iter: I) -> &mut [T] {
+        assert!(mem::size_of::<T>() != 0);
+        iter.alloc_from_iter(self)
+    }
+
+    /// Grows the arena.
+    #[inline(never)]
+    #[cold]
+    fn grow(&self, additional: usize) {
+        unsafe {
+            // We need the element size to convert chunk sizes (ranging from
+            // PAGE to HUGE_PAGE bytes) to element counts.
+            let elem_size = cmp::max(1, mem::size_of::<T>());
+            let mut chunks = self.chunks.borrow_mut();
+            let mut new_cap;
+            if let Some(last_chunk) = chunks.last_mut() {
+                // If a type is `!needs_drop`, we don't need to keep track of how many elements
+                // the chunk stores - the field will be ignored anyway.
+                if mem::needs_drop::<T>() {
+                    // FIXME: this should *likely* use `offset_from`, but more
+                    // investigation is needed (including running tests in miri).
+                    let used_bytes = self.ptr.get().addr() - last_chunk.start().addr();
+                    last_chunk.entries = used_bytes / mem::size_of::<T>();
+                }
+
+                // If the previous chunk's len is less than HUGE_PAGE
+                // bytes, then this chunk will be least double the previous
+                // chunk's size.
+                new_cap = (*last_chunk.storage.as_ptr()).len().min(HUGE_PAGE / elem_size / 2);
+                new_cap *= 2;
+            } else {
+                new_cap = PAGE / elem_size;
+            }
+            // Also ensure that this chunk can fit `additional`.
+            new_cap = cmp::max(additional, new_cap);
+
+            let mut chunk = ArenaChunk::<T>::new(new_cap);
+            self.ptr.set(chunk.start());
+            self.end.set(chunk.end());
+            chunks.push(chunk);
+        }
+    }
+
+    // Drops the contents of the last chunk. The last chunk is partially empty, unlike all other
+    // chunks.
+    fn clear_last_chunk(&self, last_chunk: &mut ArenaChunk<T>) {
+        // Determine how much was filled.
+        let start = last_chunk.start().addr();
+        // We obtain the value of the pointer to the first uninitialized element.
+        let end = self.ptr.get().addr();
+        // We then calculate the number of elements to be dropped in the last chunk,
+        // which is the filled area's length.
+        let diff = if mem::size_of::<T>() == 0 {
+            // `T` is ZST. It can't have a drop flag, so the value here doesn't matter. We get
+            // the number of zero-sized values in the last and only chunk, just out of caution.
+            // Recall that `end` was incremented for each allocated value.
+            end - start
+        } else {
+            // FIXME: this should *likely* use `offset_from`, but more
+            // investigation is needed (including running tests in miri).
+            (end - start) / mem::size_of::<T>()
+        };
+        // Pass that to the `destroy` method.
+        unsafe {
+            last_chunk.destroy(diff);
+        }
+        // Reset the chunk.
+        self.ptr.set(last_chunk.start());
+    }
+}
+
+unsafe impl<#[may_dangle] T> Drop for TypedArena<T> {
+    fn drop(&mut self) {
+        unsafe {
+            // Determine how much was filled.
+            let mut chunks_borrow = self.chunks.borrow_mut();
+            if let Some(mut last_chunk) = chunks_borrow.pop() {
+                // Drop the contents of the last chunk.
+                self.clear_last_chunk(&mut last_chunk);
+                // The last chunk will be dropped. Destroy all other chunks.
+                for chunk in chunks_borrow.iter_mut() {
+                    chunk.destroy(chunk.entries);
+                }
+            }
+            // Box handles deallocation of `last_chunk` and `self.chunks`.
+        }
+    }
+}
+
+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 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>,
+
+    /// A vector of arena chunks.
+    chunks: RefCell<Vec<ArenaChunk>>,
+}
+
+unsafe impl Send for DroplessArena {}
+
+impl Default for DroplessArena {
+    #[inline]
+    fn default() -> DroplessArena {
+        DroplessArena {
+            start: Cell::new(ptr::null_mut()),
+            end: Cell::new(ptr::null_mut()),
+            chunks: Default::default(),
+        }
+    }
+}
+
+impl DroplessArena {
+    #[inline(never)]
+    #[cold]
+    fn grow(&self, additional: usize) {
+        unsafe {
+            let mut chunks = self.chunks.borrow_mut();
+            let mut new_cap;
+            if let Some(last_chunk) = chunks.last_mut() {
+                // There is no need to update `last_chunk.entries` because that
+                // field isn't used by `DroplessArena`.
+
+                // If the previous chunk's len is less than HUGE_PAGE
+                // bytes, then this chunk will be least double the previous
+                // chunk's size.
+                new_cap = (*last_chunk.storage.as_ptr()).len().min(HUGE_PAGE / 2);
+                new_cap *= 2;
+            } else {
+                new_cap = PAGE;
+            }
+            // Also ensure that this chunk can fit `additional`.
+            new_cap = cmp::max(additional, new_cap);
+
+            let mut chunk = ArenaChunk::new(new_cap);
+            self.start.set(chunk.start());
+            self.end.set(chunk.end());
+            chunks.push(chunk);
+        }
+    }
+
+    /// Allocates a byte slice with specified layout from the current memory
+    /// chunk. Returns `None` if there is no free space left to satisfy the
+    /// request.
+    #[inline]
+    fn alloc_raw_without_grow(&self, layout: Layout) -> Option<*mut u8> {
+        let start = self.start.get().addr();
+        let old_end = self.end.get();
+        let end = old_end.addr();
+
+        let align = layout.align();
+        let bytes = layout.size();
+
+        let new_end = end.checked_sub(bytes)? & !(align - 1);
+        if start <= new_end {
+            let new_end = old_end.with_addr(new_end);
+            self.end.set(new_end);
+            Some(new_end)
+        } else {
+            None
+        }
+    }
+
+    #[inline]
+    pub fn alloc_raw(&self, layout: Layout) -> *mut u8 {
+        assert!(layout.size() != 0);
+        loop {
+            if let Some(a) = self.alloc_raw_without_grow(layout) {
+                break a;
+            }
+            // No free space left. Allocate a new chunk to satisfy the request.
+            // On failure the grow will panic or abort.
+            self.grow(layout.size());
+        }
+    }
+
+    #[inline]
+    pub fn alloc<T>(&self, object: T) -> &mut T {
+        assert!(!mem::needs_drop::<T>());
+
+        let mem = self.alloc_raw(Layout::for_value::<T>(&object)) as *mut T;
+
+        unsafe {
+            // Write into uninitialized memory.
+            ptr::write(mem, object);
+            &mut *mem
+        }
+    }
+
+    /// Allocates a slice of objects that are copied into the `DroplessArena`, returning a mutable
+    /// reference to it. Will panic if passed a zero-sized type.
+    ///
+    /// Panics:
+    ///
+    ///  - Zero-sized types
+    ///  - Zero-length slices
+    #[inline]
+    pub fn alloc_slice<T>(&self, slice: &[T]) -> &mut [T]
+    where
+        T: Copy,
+    {
+        assert!(!mem::needs_drop::<T>());
+        assert!(mem::size_of::<T>() != 0);
+        assert!(!slice.is_empty());
+
+        let mem = self.alloc_raw(Layout::for_value::<[T]>(slice)) as *mut T;
+
+        unsafe {
+            mem.copy_from_nonoverlapping(slice.as_ptr(), slice.len());
+            slice::from_raw_parts_mut(mem, slice.len())
+        }
+    }
+
+    #[inline]
+    unsafe fn write_from_iter<T, I: Iterator<Item = T>>(
+        &self,
+        mut iter: I,
+        len: usize,
+        mem: *mut T,
+    ) -> &mut [T] {
+        let mut i = 0;
+        // Use a manual loop since LLVM manages to optimize it better for
+        // slice iterators
+        loop {
+            let value = iter.next();
+            if i >= len || value.is_none() {
+                // We only return as many items as the iterator gave us, even
+                // though it was supposed to give us `len`
+                return slice::from_raw_parts_mut(mem, i);
+            }
+            ptr::write(mem.add(i), value.unwrap());
+            i += 1;
+        }
+    }
+
+    #[inline]
+    pub fn alloc_from_iter<T, I: IntoIterator<Item = T>>(&self, iter: I) -> &mut [T] {
+        let iter = iter.into_iter();
+        assert!(mem::size_of::<T>() != 0);
+        assert!(!mem::needs_drop::<T>());
+
+        let size_hint = iter.size_hint();
+
+        match size_hint {
+            (min, Some(max)) if min == max => {
+                // We know the exact number of elements the iterator will produce here
+                let len = min;
+
+                if len == 0 {
+                    return &mut [];
+                }
+
+                let mem = self.alloc_raw(Layout::array::<T>(len).unwrap()) as *mut T;
+                unsafe { self.write_from_iter(iter, len, mem) }
+            }
+            (_, _) => {
+                cold_path(move || -> &mut [T] {
+                    let mut vec: SmallVec<[_; 8]> = iter.collect();
+                    if vec.is_empty() {
+                        return &mut [];
+                    }
+                    // Move the content to the arena by copying it and then forgetting
+                    // the content of the SmallVec
+                    unsafe {
+                        let len = vec.len();
+                        let start_ptr =
+                            self.alloc_raw(Layout::for_value::<[T]>(vec.as_slice())) as *mut T;
+                        vec.as_ptr().copy_to_nonoverlapping(start_ptr, len);
+                        vec.set_len(0);
+                        slice::from_raw_parts_mut(start_ptr, len)
+                    }
+                })
+            }
+        }
+    }
+}
+
+/// 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)]
+    pub struct Arena<'tcx> {
+        pub dropless: $crate::DroplessArena,
+        $($name: $crate::TypedArena<$ty>,)*
+    }
+
+    pub trait ArenaAllocatable<'tcx, C = rustc_arena::IsNotCopy>: Sized {
+        fn allocate_on<'a>(self, arena: &'a Arena<'tcx>) -> &'a mut Self;
+        fn allocate_from_iter<'a>(
+            arena: &'a Arena<'tcx>,
+            iter: impl ::std::iter::IntoIterator<Item = Self>,
+        ) -> &'a mut [Self];
+    }
+
+    // Any type that impls `Copy` can be arena-allocated in the `DroplessArena`.
+    impl<'tcx, T: Copy> ArenaAllocatable<'tcx, rustc_arena::IsCopy> for T {
+        #[inline]
+        fn allocate_on<'a>(self, arena: &'a Arena<'tcx>) -> &'a mut Self {
+            arena.dropless.alloc(self)
+        }
+        #[inline]
+        fn allocate_from_iter<'a>(
+            arena: &'a Arena<'tcx>,
+            iter: impl ::std::iter::IntoIterator<Item = Self>,
+        ) -> &'a mut [Self] {
+            arena.dropless.alloc_from_iter(iter)
+        }
+    }
+    $(
+        impl<'tcx> ArenaAllocatable<'tcx, rustc_arena::IsNotCopy> for $ty {
+            #[inline]
+            fn allocate_on<'a>(self, arena: &'a Arena<'tcx>) -> &'a mut Self {
+                if !::std::mem::needs_drop::<Self>() {
+                    arena.dropless.alloc(self)
+                } else {
+                    arena.$name.alloc(self)
+                }
+            }
+
+            #[inline]
+            fn allocate_from_iter<'a>(
+                arena: &'a Arena<'tcx>,
+                iter: impl ::std::iter::IntoIterator<Item = Self>,
+            ) -> &'a mut [Self] {
+                if !::std::mem::needs_drop::<Self>() {
+                    arena.dropless.alloc_from_iter(iter)
+                } else {
+                    arena.$name.alloc_from_iter(iter)
+                }
+            }
+        }
+    )*
+
+    impl<'tcx> Arena<'tcx> {
+        #[inline]
+        pub fn alloc<T: ArenaAllocatable<'tcx, C>, C>(&self, value: T) -> &mut T {
+            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() {
+                return &mut [];
+            }
+            self.dropless.alloc_slice(value)
+        }
+
+        pub fn alloc_from_iter<'a, T: ArenaAllocatable<'tcx, C>, C>(
+            &'a self,
+            iter: impl ::std::iter::IntoIterator<Item = T>,
+        ) -> &'a mut [T] {
+            T::allocate_from_iter(self, iter)
+        }
+    }
+}
+
+// Marker types that let us give different behaviour for arenas allocating
+// `Copy` types vs `!Copy` types.
+pub struct IsCopy;
+pub struct IsNotCopy;
+
+#[cfg(test)]
+mod tests;
diff --git a/compiler/rustc_arena/src/tests.rs b/compiler/rustc_arena/src/tests.rs
new file mode 100644
index 000000000..ad6146434
--- /dev/null
+++ b/compiler/rustc_arena/src/tests.rs
@@ -0,0 +1,248 @@
+extern crate test;
+use super::TypedArena;
+use std::cell::Cell;
+use test::Bencher;
+
+#[allow(dead_code)]
+#[derive(Debug, Eq, PartialEq)]
+struct Point {
+    x: i32,
+    y: i32,
+    z: i32,
+}
+
+impl<T> TypedArena<T> {
+    /// Clears the arena. Deallocates all but the longest chunk which may be reused.
+    fn clear(&mut self) {
+        unsafe {
+            // Clear the last chunk, which is partially filled.
+            let mut chunks_borrow = self.chunks.borrow_mut();
+            if let Some(mut last_chunk) = chunks_borrow.last_mut() {
+                self.clear_last_chunk(&mut last_chunk);
+                let len = chunks_borrow.len();
+                // If `T` is ZST, code below has no effect.
+                for mut chunk in chunks_borrow.drain(..len - 1) {
+                    chunk.destroy(chunk.entries);
+                }
+            }
+        }
+    }
+}
+
+#[test]
+pub fn test_unused() {
+    let arena: TypedArena<Point> = TypedArena::default();
+    assert!(arena.chunks.borrow().is_empty());
+}
+
+#[test]
+fn test_arena_alloc_nested() {
+    struct Inner {
+        value: u8,
+    }
+    struct Outer<'a> {
+        inner: &'a Inner,
+    }
+    enum EI<'e> {
+        I(Inner),
+        O(Outer<'e>),
+    }
+
+    struct Wrap<'a>(TypedArena<EI<'a>>);
+
+    impl<'a> Wrap<'a> {
+        fn alloc_inner<F: Fn() -> Inner>(&self, f: F) -> &Inner {
+            let r: &EI<'_> = self.0.alloc(EI::I(f()));
+            if let &EI::I(ref i) = r {
+                i
+            } else {
+                panic!("mismatch");
+            }
+        }
+        fn alloc_outer<F: Fn() -> Outer<'a>>(&self, f: F) -> &Outer<'_> {
+            let r: &EI<'_> = self.0.alloc(EI::O(f()));
+            if let &EI::O(ref o) = r {
+                o
+            } else {
+                panic!("mismatch");
+            }
+        }
+    }
+
+    let arena = Wrap(TypedArena::default());
+
+    let result = arena.alloc_outer(|| Outer { inner: arena.alloc_inner(|| Inner { value: 10 }) });
+
+    assert_eq!(result.inner.value, 10);
+}
+
+#[test]
+pub fn test_copy() {
+    let arena = TypedArena::default();
+    #[cfg(not(miri))]
+    const N: usize = 100000;
+    #[cfg(miri)]
+    const N: usize = 1000;
+    for _ in 0..N {
+        arena.alloc(Point { x: 1, y: 2, z: 3 });
+    }
+}
+
+#[bench]
+pub fn bench_copy(b: &mut Bencher) {
+    let arena = TypedArena::default();
+    b.iter(|| arena.alloc(Point { x: 1, y: 2, z: 3 }))
+}
+
+#[bench]
+pub fn bench_copy_nonarena(b: &mut Bencher) {
+    b.iter(|| {
+        let _: Box<_> = Box::new(Point { x: 1, y: 2, z: 3 });
+    })
+}
+
+#[allow(dead_code)]
+struct Noncopy {
+    string: String,
+    array: Vec<i32>,
+}
+
+#[test]
+pub fn test_noncopy() {
+    let arena = TypedArena::default();
+    #[cfg(not(miri))]
+    const N: usize = 100000;
+    #[cfg(miri)]
+    const N: usize = 1000;
+    for _ in 0..N {
+        arena.alloc(Noncopy { string: "hello world".to_string(), array: vec![1, 2, 3, 4, 5] });
+    }
+}
+
+#[test]
+pub fn test_typed_arena_zero_sized() {
+    let arena = TypedArena::default();
+    #[cfg(not(miri))]
+    const N: usize = 100000;
+    #[cfg(miri)]
+    const N: usize = 1000;
+    for _ in 0..N {
+        arena.alloc(());
+    }
+}
+
+#[test]
+pub fn test_typed_arena_clear() {
+    let mut arena = TypedArena::default();
+    for _ in 0..10 {
+        arena.clear();
+        #[cfg(not(miri))]
+        const N: usize = 10000;
+        #[cfg(miri)]
+        const N: usize = 100;
+        for _ in 0..N {
+            arena.alloc(Point { x: 1, y: 2, z: 3 });
+        }
+    }
+}
+
+#[bench]
+pub fn bench_typed_arena_clear(b: &mut Bencher) {
+    let mut arena = TypedArena::default();
+    b.iter(|| {
+        arena.alloc(Point { x: 1, y: 2, z: 3 });
+        arena.clear();
+    })
+}
+
+#[bench]
+pub fn bench_typed_arena_clear_100(b: &mut Bencher) {
+    let mut arena = TypedArena::default();
+    b.iter(|| {
+        for _ in 0..100 {
+            arena.alloc(Point { x: 1, y: 2, z: 3 });
+        }
+        arena.clear();
+    })
+}
+
+// Drop tests
+
+struct DropCounter<'a> {
+    count: &'a Cell<u32>,
+}
+
+impl Drop for DropCounter<'_> {
+    fn drop(&mut self) {
+        self.count.set(self.count.get() + 1);
+    }
+}
+
+#[test]
+fn test_typed_arena_drop_count() {
+    let counter = Cell::new(0);
+    {
+        let arena: TypedArena<DropCounter<'_>> = TypedArena::default();
+        for _ in 0..100 {
+            // Allocate something with drop glue to make sure it doesn't leak.
+            arena.alloc(DropCounter { count: &counter });
+        }
+    };
+    assert_eq!(counter.get(), 100);
+}
+
+#[test]
+fn test_typed_arena_drop_on_clear() {
+    let counter = Cell::new(0);
+    let mut arena: TypedArena<DropCounter<'_>> = TypedArena::default();
+    for i in 0..10 {
+        for _ in 0..100 {
+            // Allocate something with drop glue to make sure it doesn't leak.
+            arena.alloc(DropCounter { count: &counter });
+        }
+        arena.clear();
+        assert_eq!(counter.get(), i * 100 + 100);
+    }
+}
+
+thread_local! {
+    static DROP_COUNTER: Cell<u32> = Cell::new(0)
+}
+
+struct SmallDroppable;
+
+impl Drop for SmallDroppable {
+    fn drop(&mut self) {
+        DROP_COUNTER.with(|c| c.set(c.get() + 1));
+    }
+}
+
+#[test]
+fn test_typed_arena_drop_small_count() {
+    DROP_COUNTER.with(|c| c.set(0));
+    {
+        let arena: TypedArena<SmallDroppable> = TypedArena::default();
+        for _ in 0..100 {
+            // Allocate something with drop glue to make sure it doesn't leak.
+            arena.alloc(SmallDroppable);
+        }
+        // dropping
+    };
+    assert_eq!(DROP_COUNTER.with(|c| c.get()), 100);
+}
+
+#[bench]
+pub fn bench_noncopy(b: &mut Bencher) {
+    let arena = TypedArena::default();
+    b.iter(|| {
+        arena.alloc(Noncopy { string: "hello world".to_string(), array: vec![1, 2, 3, 4, 5] })
+    })
+}
+
+#[bench]
+pub fn bench_noncopy_nonarena(b: &mut Bencher) {
+    b.iter(|| {
+        let _: Box<_> =
+            Box::new(Noncopy { string: "hello world".to_string(), array: vec![1, 2, 3, 4, 5] });
+    })
+}