src/librustc/arena.rs

   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 /// This declares a list of types which can be allocated by `Arena`.
  10 ///
  11 /// The `few` modifier will cause allocation to use the shared arena and recording the destructor.
  12 /// This is faster and more memory efficient if there's only a few allocations of the type.
  13 /// Leaving `few` out will cause the type to get its own dedicated `TypedArena` which is
  14 /// faster and more memory efficient if there is lots of allocations.
  15 ///
  16 /// Specifying the `decode` modifier will add decode impls for &T and &[T] where T is the type
  17 /// listed. These impls will appear in the implement_ty_decoder! macro.
  18 #[macro_export]
  19 macro_rules! arena_types {
  20     ($macro:path, $args:tt, $tcx:lifetime) => (
  21         $macro!($args, [
  22             [] layouts: rustc::ty::layout::LayoutDetails,
  23             [] generics: rustc::ty::Generics,
  24             [] trait_def: rustc::ty::TraitDef,
  25             [] adt_def: rustc::ty::AdtDef,
  26             [] steal_mir: rustc::ty::steal::Steal<rustc::mir::Body<$tcx>>,
  27             [] mir: rustc::mir::Body<$tcx>,
  28             [] steal_promoted: rustc::ty::steal::Steal<
  29                 rustc_index::vec::IndexVec<
  30                     rustc::mir::Promoted,
  31                     rustc::mir::Body<$tcx>
  32                 >
  33             >,
  34             [] promoted: rustc_index::vec::IndexVec<
  35                 rustc::mir::Promoted,
  36                 rustc::mir::Body<$tcx>
  37             >,
  38             [] tables: rustc::ty::TypeckTables<$tcx>,
  39             [] const_allocs: rustc::mir::interpret::Allocation,
  40             [] vtable_method: Option<(
  41                 rustc::hir::def_id::DefId,
  42                 rustc::ty::subst::SubstsRef<$tcx>
  43             )>,
  44             [few, decode] mir_keys: rustc::util::nodemap::DefIdSet,
  45             [decode] specialization_graph: rustc::traits::specialization_graph::Graph,
  46             [] region_scope_tree: rustc::middle::region::ScopeTree,
  47             [] item_local_set: rustc::util::nodemap::ItemLocalSet,
  48             [decode] mir_const_qualif: rustc_index::bit_set::BitSet<rustc::mir::Local>,
  49             [] trait_impls_of: rustc::ty::trait_def::TraitImpls,
  50             [] dropck_outlives:
  51                 rustc::infer::canonical::Canonical<'tcx,
  52                     rustc::infer::canonical::QueryResponse<'tcx,
  53                         rustc::traits::query::dropck_outlives::DropckOutlivesResult<'tcx>
  54                     >
  55                 >,
  56             [] normalize_projection_ty:
  57                 rustc::infer::canonical::Canonical<'tcx,
  58                     rustc::infer::canonical::QueryResponse<'tcx,
  59                         rustc::traits::query::normalize::NormalizationResult<'tcx>
  60                     >
  61                 >,
  62             [] implied_outlives_bounds:
  63                 rustc::infer::canonical::Canonical<'tcx,
  64                     rustc::infer::canonical::QueryResponse<'tcx,
  65                         Vec<rustc::traits::query::outlives_bounds::OutlivesBound<'tcx>>
  66                     >
  67                 >,
  68             [] type_op_subtype:
  69                 rustc::infer::canonical::Canonical<'tcx,
  70                     rustc::infer::canonical::QueryResponse<'tcx, ()>
  71                 >,
  72             [] type_op_normalize_poly_fn_sig:
  73                 rustc::infer::canonical::Canonical<'tcx,
  74                     rustc::infer::canonical::QueryResponse<'tcx, rustc::ty::PolyFnSig<'tcx>>
  75                 >,
  76             [] type_op_normalize_fn_sig:
  77                 rustc::infer::canonical::Canonical<'tcx,
  78                     rustc::infer::canonical::QueryResponse<'tcx, rustc::ty::FnSig<'tcx>>
  79                 >,
  80             [] type_op_normalize_predicate:
  81                 rustc::infer::canonical::Canonical<'tcx,
  82                     rustc::infer::canonical::QueryResponse<'tcx, rustc::ty::Predicate<'tcx>>
  83                 >,
  84             [] type_op_normalize_ty:
  85                 rustc::infer::canonical::Canonical<'tcx,
  86                     rustc::infer::canonical::QueryResponse<'tcx, rustc::ty::Ty<'tcx>>
  87                 >,
  88             [few] crate_inherent_impls: rustc::ty::CrateInherentImpls,
  89             [few] upstream_monomorphizations:
  90                 rustc::util::nodemap::DefIdMap<
  91                     rustc_data_structures::fx::FxHashMap<
  92                         rustc::ty::subst::SubstsRef<'tcx>,
  93                         rustc::hir::def_id::CrateNum
  94                     >
  95                 >,
  96             [few] diagnostic_items: rustc_data_structures::fx::FxHashMap<
  97                 syntax::symbol::Symbol,
  98                 rustc::hir::def_id::DefId,
  99             >,
 100             [few] resolve_lifetimes: rustc::middle::resolve_lifetime::ResolveLifetimes,
 101             [decode] generic_predicates: rustc::ty::GenericPredicates<'tcx>,
 102             [few] lint_levels: rustc::lint::LintLevelMap,
 103             [few] stability_index: rustc::middle::stability::Index<'tcx>,
 104             [few] features: syntax::feature_gate::Features,
 105             [few] all_traits: Vec<rustc::hir::def_id::DefId>,
 106             [few] privacy_access_levels: rustc::middle::privacy::AccessLevels,
 107             [few] target_features_whitelist: rustc_data_structures::fx::FxHashMap<
 108                 String,
 109                 Option<syntax::symbol::Symbol>
 110             >,
 111             [few] wasm_import_module_map: rustc_data_structures::fx::FxHashMap<
 112                 rustc::hir::def_id::DefId,
 113                 String
 114             >,
 115             [few] get_lib_features: rustc::middle::lib_features::LibFeatures,
 116             [few] defined_lib_features: rustc::middle::lang_items::LanguageItems,
 117             [few] visible_parent_map: rustc::util::nodemap::DefIdMap<rustc::hir::def_id::DefId>,
 118             [few] foreign_module: rustc::middle::cstore::ForeignModule,
 119             [few] foreign_modules: Vec<rustc::middle::cstore::ForeignModule>,
 120             [few] reachable_non_generics: rustc::util::nodemap::DefIdMap<
 121                 rustc::middle::exported_symbols::SymbolExportLevel
 122             >,
 123             [few] crate_variances: rustc::ty::CrateVariancesMap<'tcx>,
 124             [few] inferred_outlives_crate: rustc::ty::CratePredicatesMap<'tcx>,
 125             [] upvars: rustc_data_structures::fx::FxIndexMap<rustc::hir::HirId, rustc::hir::Upvar>,
 126         ], $tcx);
 127     )
 128 }
 129
 130 macro_rules! arena_for_type {
 131     ([][$ty:ty]) => {
 132         TypedArena<$ty>
 133     };
 134     ([few $(, $attrs:ident)*][$ty:ty]) => {
 135         PhantomData<$ty>
 136     };
 137     ([$ignore:ident $(, $attrs:ident)*]$args:tt) => {
 138         arena_for_type!([$($attrs),*]$args)
 139     };
 140 }
 141
 142 macro_rules! declare_arena {
 143     ([], [$($a:tt $name:ident: $ty:ty,)*], $tcx:lifetime) => {
 144         #[derive(Default)]
 145         pub struct Arena<$tcx> {
 146             dropless: DroplessArena,
 147             drop: DropArena,
 148             $($name: arena_for_type!($a[$ty]),)*
 149         }
 150     }
 151 }
 152
 153 macro_rules! which_arena_for_type {
 154     ([][$arena:expr]) => {
 155         Some($arena)
 156     };
 157     ([few$(, $attrs:ident)*][$arena:expr]) => {
 158         None
 159     };
 160     ([$ignore:ident$(, $attrs:ident)*]$args:tt) => {
 161         which_arena_for_type!([$($attrs),*]$args)
 162     };
 163 }
 164
 165 macro_rules! impl_arena_allocatable {
 166     ([], [$($a:tt $name:ident: $ty:ty,)*], $tcx:lifetime) => {
 167         $(
 168             impl ArenaAllocatable for $ty {}
 169             unsafe impl<$tcx> ArenaField<$tcx> for $ty {
 170                 #[inline]
 171                 fn arena<'a>(_arena: &'a Arena<$tcx>) -> Option<&'a TypedArena<Self>> {
 172                     which_arena_for_type!($a[&_arena.$name])
 173                 }
 174             }
 175         )*
 176     }
 177 }
 178
 179 arena_types!(declare_arena, [], 'tcx);
 180
 181 arena_types!(impl_arena_allocatable, [], 'tcx);
 182
 183 pub trait ArenaAllocatable {}
 184
 185 impl<T: Copy> ArenaAllocatable for T {}
 186
 187 unsafe trait ArenaField<'tcx>: Sized {
 188     /// Returns a specific arena to allocate from.
 189     /// If `None` is returned, the `DropArena` will be used.
 190     fn arena<'a>(arena: &'a Arena<'tcx>) -> Option<&'a TypedArena<Self>>;
 191 }
 192
 193 unsafe impl<'tcx, T> ArenaField<'tcx> for T {
 194     #[inline]
 195     default fn arena<'a>(_: &'a Arena<'tcx>) -> Option<&'a TypedArena<Self>> {
 196         panic!()
 197     }
 198 }
 199
 200 impl<'tcx> Arena<'tcx> {
 201     #[inline]
 202     pub fn alloc<T: ArenaAllocatable>(&self, value: T) -> &mut T {
 203         if !mem::needs_drop::<T>() {
 204             return self.dropless.alloc(value);
 205         }
 206         match <T as ArenaField<'tcx>>::arena(self) {
 207             Some(arena) => arena.alloc(value),
 208             None => unsafe { self.drop.alloc(value) },
 209         }
 210     }
 211
 212     #[inline]
 213     pub fn alloc_slice<T: Copy>(&self, value: &[T]) -> &mut [T] {
 214         if value.len() == 0 {
 215             return &mut []
 216         }
 217         self.dropless.alloc_slice(value)
 218     }
 219
 220     pub fn alloc_from_iter<
 221         T: ArenaAllocatable,
 222         I: IntoIterator<Item = T>
 223     >(
 224         &'a self,
 225         iter: I
 226     ) -> &'a mut [T] {
 227         if !mem::needs_drop::<T>() {
 228             return self.dropless.alloc_from_iter(iter);
 229         }
 230         match <T as ArenaField<'tcx>>::arena(self) {
 231             Some(arena) => arena.alloc_from_iter(iter),
 232             None => unsafe { self.drop.alloc_from_iter(iter) },
 233         }
 234     }
 235 }
 236
 237 /// Calls the destructor for an object when dropped.
 238 struct DropType {
 239     drop_fn: unsafe fn(*mut u8),
 240     obj: *mut u8,
 241 }
 242
 243 unsafe fn drop_for_type<T>(to_drop: *mut u8) {
 244     std::ptr::drop_in_place(to_drop as *mut T)
 245 }
 246
 247 impl Drop for DropType {
 248     fn drop(&mut self) {
 249         unsafe {
 250             (self.drop_fn)(self.obj)
 251         }
 252     }
 253 }
 254
 255 /// An arena which can be used to allocate any type.
 256 /// Allocating in this arena is unsafe since the type system
 257 /// doesn't know which types it contains. In order to
 258 /// allocate safely, you must store a PhantomData<T>
 259 /// alongside this arena for each type T you allocate.
 260 #[derive(Default)]
 261 struct DropArena {
 262     /// A list of destructors to run when the arena drops.
 263     /// Ordered so `destructors` gets dropped before the arena
 264     /// since its destructor can reference memory in the arena.
 265     destructors: RefCell<Vec<DropType>>,
 266     arena: DroplessArena,
 267 }
 268
 269 impl DropArena {
 270     #[inline]
 271     unsafe fn alloc<T>(&self, object: T) -> &mut T {
 272         let mem = self.arena.alloc_raw(
 273             mem::size_of::<T>(),
 274             mem::align_of::<T>()
 275         ) as *mut _ as *mut T;
 276         // Write into uninitialized memory.
 277         ptr::write(mem, object);
 278         let result = &mut *mem;
 279         // Record the destructor after doing the allocation as that may panic
 280         // and would cause `object`'s destuctor to run twice if it was recorded before
 281         self.destructors.borrow_mut().push(DropType {
 282             drop_fn: drop_for_type::<T>,
 283             obj: result as *mut T as *mut u8,
 284         });
 285         result
 286     }
 287
 288     #[inline]
 289     unsafe fn alloc_from_iter<T, I: IntoIterator<Item = T>>(&self, iter: I) -> &mut [T] {
 290         let mut vec: SmallVec<[_; 8]> = iter.into_iter().collect();
 291         if vec.is_empty() {
 292             return &mut [];
 293         }
 294         let len = vec.len();
 295
 296         let start_ptr = self.arena.alloc_raw(
 297             len.checked_mul(mem::size_of::<T>()).unwrap(),
 298             mem::align_of::<T>()
 299         ) as *mut _ as *mut T;
 300
 301         let mut destructors = self.destructors.borrow_mut();
 302         // Reserve space for the destructors so we can't panic while adding them
 303         destructors.reserve(len);
 304
 305         // Move the content to the arena by copying it and then forgetting
 306         // the content of the SmallVec
 307         vec.as_ptr().copy_to_nonoverlapping(start_ptr, len);
 308         mem::forget(vec.drain());
 309
 310         // Record the destructors after doing the allocation as that may panic
 311         // and would cause `object`'s destuctor to run twice if it was recorded before
 312         for i in 0..len {
 313             destructors.push(DropType {
 314                 drop_fn: drop_for_type::<T>,
 315                 obj: start_ptr.offset(i as isize) as *mut u8,
 316             });
 317         }
 318
 319         slice::from_raw_parts_mut(start_ptr, len)
 320     }
 321 }