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| 1 | +use arena::{TypedArena, DroplessArena}; |
| 2 | +use std::mem; |
| 3 | +use std::ptr; |
| 4 | +use std::slice; |
| 5 | +use std::cell::RefCell; |
| 6 | +use std::marker::PhantomData; |
| 7 | +use smallvec::SmallVec; |
| 8 | + |
| 9 | +#[macro_export] |
| 10 | +macro_rules! arena_types { |
| 11 | + ($macro:path, $args:tt, $tcx:lifetime) => ( |
| 12 | + $macro!($args, [ |
| 13 | + [] vtable_method: Option<( |
| 14 | + rustc::hir::def_id::DefId, |
| 15 | + rustc::ty::subst::SubstsRef<$tcx> |
| 16 | + )>, |
| 17 | + [few] mir_keys: rustc::util::nodemap::DefIdSet, |
| 18 | + [decode] specialization_graph: rustc::traits::specialization_graph::Graph, |
| 19 | + ], $tcx); |
| 20 | + ) |
| 21 | +} |
| 22 | + |
| 23 | +macro_rules! arena_for_type { |
| 24 | + ([][$ty:ty]) => { |
| 25 | + TypedArena<$ty> |
| 26 | + }; |
| 27 | + ([few $(, $attrs:ident)*][$ty:ty]) => { |
| 28 | + PhantomData<$ty> |
| 29 | + }; |
| 30 | + ([$ignore:ident $(, $attrs:ident)*]$args:tt) => { |
| 31 | + arena_for_type!([$($attrs),*]$args) |
| 32 | + }; |
| 33 | +} |
| 34 | + |
| 35 | +macro_rules! declare_arena { |
| 36 | + ([], [$($a:tt $name:ident: $ty:ty,)*], $tcx:lifetime) => { |
| 37 | + #[derive(Default)] |
| 38 | + pub struct Arena<$tcx> { |
| 39 | + dropless: DroplessArena, |
| 40 | + drop: DropArena, |
| 41 | + $($name: arena_for_type!($a[$ty]),)* |
| 42 | + } |
| 43 | + } |
| 44 | +} |
| 45 | + |
| 46 | +macro_rules! which_arena_for_type { |
| 47 | + ([][$arena:expr]) => { |
| 48 | + Some($arena) |
| 49 | + }; |
| 50 | + ([few$(, $attrs:ident)*][$arena:expr]) => { |
| 51 | + None |
| 52 | + }; |
| 53 | + ([$ignore:ident$(, $attrs:ident)*]$args:tt) => { |
| 54 | + which_arena_for_type!([$($attrs),*]$args) |
| 55 | + }; |
| 56 | +} |
| 57 | + |
| 58 | +macro_rules! impl_arena_allocatable { |
| 59 | + ([], [$($a:tt $name:ident: $ty:ty,)*], $tcx:lifetime) => { |
| 60 | + $( |
| 61 | + impl ArenaAllocatable for $ty {} |
| 62 | + unsafe impl<$tcx> ArenaField<$tcx> for $ty { |
| 63 | + #[inline] |
| 64 | + fn arena<'a>(_arena: &'a Arena<$tcx>) -> Option<&'a TypedArena<Self>> { |
| 65 | + which_arena_for_type!($a[&_arena.$name]) |
| 66 | + } |
| 67 | + } |
| 68 | + )* |
| 69 | + } |
| 70 | +} |
| 71 | + |
| 72 | +arena_types!(declare_arena, [], 'tcx); |
| 73 | + |
| 74 | +arena_types!(impl_arena_allocatable, [], 'tcx); |
| 75 | + |
| 76 | +pub trait ArenaAllocatable {} |
| 77 | + |
| 78 | +impl<T: Copy> ArenaAllocatable for T {} |
| 79 | + |
| 80 | +pub unsafe trait ArenaField<'tcx>: Sized { |
| 81 | + /// Returns a specific arena to allocate from. |
| 82 | + /// If None is returned, the DropArena will be used. |
| 83 | + fn arena<'a>(arena: &'a Arena<'tcx>) -> Option<&'a TypedArena<Self>>; |
| 84 | +} |
| 85 | + |
| 86 | +unsafe impl<'tcx, T> ArenaField<'tcx> for T { |
| 87 | + #[inline] |
| 88 | + default fn arena<'a>(_: &'a Arena<'tcx>) -> Option<&'a TypedArena<Self>> { |
| 89 | + panic!() |
| 90 | + } |
| 91 | +} |
| 92 | + |
| 93 | +impl<'tcx> Arena<'tcx> { |
| 94 | + #[inline] |
| 95 | + pub fn alloc<T: ArenaAllocatable>(&self, value: T) -> &mut T { |
| 96 | + if !mem::needs_drop::<T>() { |
| 97 | + return self.dropless.alloc(value); |
| 98 | + } |
| 99 | + match <T as ArenaField<'tcx>>::arena(self) { |
| 100 | + Some(arena) => arena.alloc(value), |
| 101 | + None => unsafe { self.drop.alloc(value) }, |
| 102 | + } |
| 103 | + } |
| 104 | + |
| 105 | + pub fn alloc_from_iter< |
| 106 | + T: ArenaAllocatable, |
| 107 | + I: IntoIterator<Item = T> |
| 108 | + >( |
| 109 | + &'a self, |
| 110 | + iter: I |
| 111 | + ) -> &'a mut [T] { |
| 112 | + if !mem::needs_drop::<T>() { |
| 113 | + return self.dropless.alloc_from_iter(iter); |
| 114 | + } |
| 115 | + match <T as ArenaField<'tcx>>::arena(self) { |
| 116 | + Some(arena) => arena.alloc_from_iter(iter), |
| 117 | + None => unsafe { self.drop.alloc_from_iter(iter) }, |
| 118 | + } |
| 119 | + } |
| 120 | +} |
| 121 | + |
| 122 | +/// Calls the destructor for an object when dropped. |
| 123 | +struct DropType { |
| 124 | + drop_fn: unsafe fn(*mut u8), |
| 125 | + obj: *mut u8, |
| 126 | +} |
| 127 | + |
| 128 | +unsafe fn drop_for_type<T>(to_drop: *mut u8) { |
| 129 | + std::ptr::drop_in_place(to_drop as *mut T) |
| 130 | +} |
| 131 | + |
| 132 | +impl Drop for DropType { |
| 133 | + fn drop(&mut self) { |
| 134 | + unsafe { |
| 135 | + (self.drop_fn)(self.obj) |
| 136 | + } |
| 137 | + } |
| 138 | +} |
| 139 | + |
| 140 | +/// An arena which can be used to allocate any type. |
| 141 | +/// Allocating in this arena is unsafe since the type system |
| 142 | +/// doesn't know which types it contains. In order to |
| 143 | +/// allocate safely, you must store a PhantomData<T> |
| 144 | +/// alongside this arena for each type T you allocate. |
| 145 | +#[derive(Default)] |
| 146 | +struct DropArena { |
| 147 | + /// A list of destructors to run when the arena drops. |
| 148 | + /// Ordered so `destructors` gets dropped before the arena |
| 149 | + /// since its destructor can reference memory in the arena. |
| 150 | + destructors: RefCell<Vec<DropType>>, |
| 151 | + arena: DroplessArena, |
| 152 | +} |
| 153 | + |
| 154 | +impl DropArena { |
| 155 | + #[inline] |
| 156 | + unsafe fn alloc<T>(&self, object: T) -> &mut T { |
| 157 | + let mem = self.arena.alloc_raw( |
| 158 | + mem::size_of::<T>(), |
| 159 | + mem::align_of::<T>() |
| 160 | + ) as *mut _ as *mut T; |
| 161 | + // Write into uninitialized memory. |
| 162 | + ptr::write(mem, object); |
| 163 | + let result = &mut *mem; |
| 164 | + // Record the destructor after doing the allocation as that may panic |
| 165 | + // and would cause `object`'s destuctor to run twice if it was recorded before |
| 166 | + self.destructors.borrow_mut().push(DropType { |
| 167 | + drop_fn: drop_for_type::<T>, |
| 168 | + obj: result as *mut T as *mut u8, |
| 169 | + }); |
| 170 | + result |
| 171 | + } |
| 172 | + |
| 173 | + #[inline] |
| 174 | + unsafe fn alloc_from_iter<T, I: IntoIterator<Item = T>>(&self, iter: I) -> &mut [T] { |
| 175 | + let mut vec: SmallVec<[_; 8]> = iter.into_iter().collect(); |
| 176 | + if vec.is_empty() { |
| 177 | + return &mut []; |
| 178 | + } |
| 179 | + let len = vec.len(); |
| 180 | + |
| 181 | + let start_ptr = self.arena.alloc_raw( |
| 182 | + len.checked_mul(mem::size_of::<T>()).unwrap(), |
| 183 | + mem::align_of::<T>() |
| 184 | + ) as *mut _ as *mut T; |
| 185 | + |
| 186 | + let mut destructors = self.destructors.borrow_mut(); |
| 187 | + // Reserve space for the destructors so we can't panic while adding them |
| 188 | + destructors.reserve(len); |
| 189 | + |
| 190 | + // Move the content to the arena by copying it and then forgetting |
| 191 | + // the content of the SmallVec |
| 192 | + vec.as_ptr().copy_to_nonoverlapping(start_ptr, len); |
| 193 | + mem::forget(vec.drain()); |
| 194 | + |
| 195 | + // Record the destructors after doing the allocation as that may panic |
| 196 | + // and would cause `object`'s destuctor to run twice if it was recorded before |
| 197 | + for i in 0..len { |
| 198 | + destructors.push(DropType { |
| 199 | + drop_fn: drop_for_type::<T>, |
| 200 | + obj: start_ptr.offset(i as isize) as *mut u8, |
| 201 | + }); |
| 202 | + } |
| 203 | + |
| 204 | + slice::from_raw_parts_mut(start_ptr, len) |
| 205 | + } |
| 206 | +} |
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