src/librustc/arena.rs

   1 use arena::{DroplessArena, TypedArena};
   2 use smallvec::SmallVec;
   3 use std::cell::RefCell;
   4 use std::marker::PhantomData;
   5 use std::mem;
   6 use std::ptr;
   7 use std::slice;
   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::BodyAndCache<$tcx>>,
  27             [] mir: rustc::mir::BodyAndCache<$tcx>,
  28             [] steal_promoted: rustc::ty::steal::Steal<
  29                 rustc_index::vec::IndexVec<
  30                     rustc::mir::Promoted,
  31                     rustc::mir::BodyAndCache<$tcx>
  32                 >
  33             >,
  34             [] promoted: rustc_index::vec::IndexVec<
  35                 rustc::mir::Promoted,
  36                 rustc::mir::BodyAndCache<$tcx>
  37             >,
  38             [decode] tables: rustc::ty::TypeckTables<$tcx>,
  39             [decode] borrowck_result: rustc::mir::BorrowCheckResult<$tcx>,
  40             [] const_allocs: rustc::mir::interpret::Allocation,
  41             [] vtable_method: Option<(
  42                 rustc_hir::def_id::DefId,
  43                 rustc::ty::subst::SubstsRef<$tcx>
  44             )>,
  45             [few, decode] mir_keys: rustc_hir::def_id::DefIdSet,
  46             [decode] specialization_graph: rustc::traits::specialization_graph::Graph,
  47             [] region_scope_tree: rustc::middle::region::ScopeTree,
  48             [] item_local_set: rustc_hir::ItemLocalSet,
  49             [decode] mir_const_qualif: rustc_index::bit_set::BitSet<rustc::mir::Local>,
  50             [] trait_impls_of: rustc::ty::trait_def::TraitImpls,
  51             [] dropck_outlives:
  52                 rustc::infer::canonical::Canonical<'tcx,
  53                     rustc::infer::canonical::QueryResponse<'tcx,
  54                         rustc::traits::query::DropckOutlivesResult<'tcx>
  55                     >
  56                 >,
  57             [] normalize_projection_ty:
  58                 rustc::infer::canonical::Canonical<'tcx,
  59                     rustc::infer::canonical::QueryResponse<'tcx,
  60                         rustc::traits::query::NormalizationResult<'tcx>
  61                     >
  62                 >,
  63             [] implied_outlives_bounds:
  64                 rustc::infer::canonical::Canonical<'tcx,
  65                     rustc::infer::canonical::QueryResponse<'tcx,
  66                         Vec<rustc::traits::query::OutlivesBound<'tcx>>
  67                     >
  68                 >,
  69             [] type_op_subtype:
  70                 rustc::infer::canonical::Canonical<'tcx,
  71                     rustc::infer::canonical::QueryResponse<'tcx, ()>
  72                 >,
  73             [] type_op_normalize_poly_fn_sig:
  74                 rustc::infer::canonical::Canonical<'tcx,
  75                     rustc::infer::canonical::QueryResponse<'tcx, rustc::ty::PolyFnSig<'tcx>>
  76                 >,
  77             [] type_op_normalize_fn_sig:
  78                 rustc::infer::canonical::Canonical<'tcx,
  79                     rustc::infer::canonical::QueryResponse<'tcx, rustc::ty::FnSig<'tcx>>
  80                 >,
  81             [] type_op_normalize_predicate:
  82                 rustc::infer::canonical::Canonical<'tcx,
  83                     rustc::infer::canonical::QueryResponse<'tcx, rustc::ty::Predicate<'tcx>>
  84                 >,
  85             [] type_op_normalize_ty:
  86                 rustc::infer::canonical::Canonical<'tcx,
  87                     rustc::infer::canonical::QueryResponse<'tcx, rustc::ty::Ty<'tcx>>
  88                 >,
  89             [few] crate_inherent_impls: rustc::ty::CrateInherentImpls,
  90             [few] upstream_monomorphizations:
  91                 rustc_hir::def_id::DefIdMap<
  92                     rustc_data_structures::fx::FxHashMap<
  93                         rustc::ty::subst::SubstsRef<'tcx>,
  94                         rustc_hir::def_id::CrateNum
  95                     >
  96                 >,
  97             [few] diagnostic_items: rustc_data_structures::fx::FxHashMap<
  98                 rustc_span::symbol::Symbol,
  99                 rustc_hir::def_id::DefId,
 100             >,
 101             [few] resolve_lifetimes: rustc::middle::resolve_lifetime::ResolveLifetimes,
 102             [few] lint_levels: rustc::lint::LintLevelMap,
 103             [few] stability_index: rustc::middle::stability::Index<'tcx>,
 104             [few] features: rustc_feature::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<rustc_span::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_hir::def_id::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_hir::def_id::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
 127             // Interned types
 128             [] tys: rustc::ty::TyS<$tcx>,
 129
 130             // HIR types
 131             [few] hir_krate: rustc_hir::Crate<$tcx>,
 132             [] arm: rustc_hir::Arm<$tcx>,
 133             [] attribute: syntax::ast::Attribute,
 134             [] block: rustc_hir::Block<$tcx>,
 135             [] bare_fn_ty: rustc_hir::BareFnTy<$tcx>,
 136             [few] global_asm: rustc_hir::GlobalAsm,
 137             [] generic_arg: rustc_hir::GenericArg<$tcx>,
 138             [] generic_args: rustc_hir::GenericArgs<$tcx>,
 139             [] generic_bound: rustc_hir::GenericBound<$tcx>,
 140             [] generic_param: rustc_hir::GenericParam<$tcx>,
 141             [] expr: rustc_hir::Expr<$tcx>,
 142             [] field: rustc_hir::Field<$tcx>,
 143             [] field_pat: rustc_hir::FieldPat<$tcx>,
 144             [] fn_decl: rustc_hir::FnDecl<$tcx>,
 145             [] foreign_item: rustc_hir::ForeignItem<$tcx>,
 146             [] impl_item_ref: rustc_hir::ImplItemRef<$tcx>,
 147             [] inline_asm: rustc_hir::InlineAsm<$tcx>,
 148             [] local: rustc_hir::Local<$tcx>,
 149             [few] macro_def: rustc_hir::MacroDef<$tcx>,
 150             [] param: rustc_hir::Param<$tcx>,
 151             [] pat: rustc_hir::Pat<$tcx>,
 152             [] path: rustc_hir::Path<$tcx>,
 153             [] path_segment: rustc_hir::PathSegment<$tcx>,
 154             [] poly_trait_ref: rustc_hir::PolyTraitRef<$tcx>,
 155             [] qpath: rustc_hir::QPath<$tcx>,
 156             [] stmt: rustc_hir::Stmt<$tcx>,
 157             [] struct_field: rustc_hir::StructField<$tcx>,
 158             [] trait_item_ref: rustc_hir::TraitItemRef,
 159             [] ty: rustc_hir::Ty<$tcx>,
 160             [] type_binding: rustc_hir::TypeBinding<$tcx>,
 161             [] variant: rustc_hir::Variant<$tcx>,
 162             [] where_predicate: rustc_hir::WherePredicate<$tcx>,
 163         ], $tcx);
 164     )
 165 }
 166
 167 macro_rules! arena_for_type {
 168     ([][$ty:ty]) => {
 169         TypedArena<$ty>
 170     };
 171     ([few $(, $attrs:ident)*][$ty:ty]) => {
 172         PhantomData<$ty>
 173     };
 174     ([$ignore:ident $(, $attrs:ident)*]$args:tt) => {
 175         arena_for_type!([$($attrs),*]$args)
 176     };
 177 }
 178
 179 macro_rules! declare_arena {
 180     ([], [$($a:tt $name:ident: $ty:ty,)*], $tcx:lifetime) => {
 181         #[derive(Default)]
 182         pub struct Arena<$tcx> {
 183             pub dropless: DroplessArena,
 184             drop: DropArena,
 185             $($name: arena_for_type!($a[$ty]),)*
 186         }
 187     }
 188 }
 189
 190 macro_rules! which_arena_for_type {
 191     ([][$arena:expr]) => {
 192         Some($arena)
 193     };
 194     ([few$(, $attrs:ident)*][$arena:expr]) => {
 195         None
 196     };
 197     ([$ignore:ident$(, $attrs:ident)*]$args:tt) => {
 198         which_arena_for_type!([$($attrs),*]$args)
 199     };
 200 }
 201
 202 macro_rules! impl_arena_allocatable {
 203     ([], [$($a:tt $name:ident: $ty:ty,)*], $tcx:lifetime) => {
 204         $(
 205             impl ArenaAllocatable for $ty {}
 206             unsafe impl<$tcx> ArenaField<$tcx> for $ty {
 207                 #[inline]
 208                 fn arena<'a>(_arena: &'a Arena<$tcx>) -> Option<&'a TypedArena<Self>> {
 209                     which_arena_for_type!($a[&_arena.$name])
 210                 }
 211             }
 212         )*
 213     }
 214 }
 215
 216 arena_types!(declare_arena, [], 'tcx);
 217
 218 arena_types!(impl_arena_allocatable, [], 'tcx);
 219
 220 #[marker]
 221 pub trait ArenaAllocatable {}
 222
 223 impl<T: Copy> ArenaAllocatable for T {}
 224
 225 unsafe trait ArenaField<'tcx>: Sized {
 226     /// Returns a specific arena to allocate from.
 227     /// If `None` is returned, the `DropArena` will be used.
 228     fn arena<'a>(arena: &'a Arena<'tcx>) -> Option<&'a TypedArena<Self>>;
 229 }
 230
 231 unsafe impl<'tcx, T> ArenaField<'tcx> for T {
 232     #[inline]
 233     default fn arena<'a>(_: &'a Arena<'tcx>) -> Option<&'a TypedArena<Self>> {
 234         panic!()
 235     }
 236 }
 237
 238 impl<'tcx> Arena<'tcx> {
 239     #[inline]
 240     pub fn alloc<T: ArenaAllocatable>(&self, value: T) -> &mut T {
 241         if !mem::needs_drop::<T>() {
 242             return self.dropless.alloc(value);
 243         }
 244         match <T as ArenaField<'tcx>>::arena(self) {
 245             Some(arena) => arena.alloc(value),
 246             None => unsafe { self.drop.alloc(value) },
 247         }
 248     }
 249
 250     #[inline]
 251     pub fn alloc_slice<T: Copy>(&self, value: &[T]) -> &mut [T] {
 252         if value.len() == 0 {
 253             return &mut [];
 254         }
 255         self.dropless.alloc_slice(value)
 256     }
 257
 258     pub fn alloc_from_iter<T: ArenaAllocatable, I: IntoIterator<Item = T>>(
 259         &'a self,
 260         iter: I,
 261     ) -> &'a mut [T] {
 262         if !mem::needs_drop::<T>() {
 263             return self.dropless.alloc_from_iter(iter);
 264         }
 265         match <T as ArenaField<'tcx>>::arena(self) {
 266             Some(arena) => arena.alloc_from_iter(iter),
 267             None => unsafe { self.drop.alloc_from_iter(iter) },
 268         }
 269     }
 270 }
 271
 272 /// Calls the destructor for an object when dropped.
 273 struct DropType {
 274     drop_fn: unsafe fn(*mut u8),
 275     obj: *mut u8,
 276 }
 277
 278 unsafe fn drop_for_type<T>(to_drop: *mut u8) {
 279     std::ptr::drop_in_place(to_drop as *mut T)
 280 }
 281
 282 impl Drop for DropType {
 283     fn drop(&mut self) {
 284         unsafe { (self.drop_fn)(self.obj) }
 285     }
 286 }
 287
 288 /// An arena which can be used to allocate any type.
 289 /// Allocating in this arena is unsafe since the type system
 290 /// doesn't know which types it contains. In order to
 291 /// allocate safely, you must store a PhantomData<T>
 292 /// alongside this arena for each type T you allocate.
 293 #[derive(Default)]
 294 struct DropArena {
 295     /// A list of destructors to run when the arena drops.
 296     /// Ordered so `destructors` gets dropped before the arena
 297     /// since its destructor can reference memory in the arena.
 298     destructors: RefCell<Vec<DropType>>,
 299     arena: DroplessArena,
 300 }
 301
 302 impl DropArena {
 303     #[inline]
 304     unsafe fn alloc<T>(&self, object: T) -> &mut T {
 305         let mem =
 306             self.arena.alloc_raw(mem::size_of::<T>(), mem::align_of::<T>()) as *mut _ as *mut T;
 307         // Write into uninitialized memory.
 308         ptr::write(mem, object);
 309         let result = &mut *mem;
 310         // Record the destructor after doing the allocation as that may panic
 311         // and would cause `object`'s destuctor to run twice if it was recorded before
 312         self.destructors
 313             .borrow_mut()
 314             .push(DropType { drop_fn: drop_for_type::<T>, obj: result as *mut T as *mut u8 });
 315         result
 316     }
 317
 318     #[inline]
 319     unsafe fn alloc_from_iter<T, I: IntoIterator<Item = T>>(&self, iter: I) -> &mut [T] {
 320         let mut vec: SmallVec<[_; 8]> = iter.into_iter().collect();
 321         if vec.is_empty() {
 322             return &mut [];
 323         }
 324         let len = vec.len();
 325
 326         let start_ptr = self
 327             .arena
 328             .alloc_raw(len.checked_mul(mem::size_of::<T>()).unwrap(), mem::align_of::<T>())
 329             as *mut _ as *mut T;
 330
 331         let mut destructors = self.destructors.borrow_mut();
 332         // Reserve space for the destructors so we can't panic while adding them
 333         destructors.reserve(len);
 334
 335         // Move the content to the arena by copying it and then forgetting
 336         // the content of the SmallVec
 337         vec.as_ptr().copy_to_nonoverlapping(start_ptr, len);
 338         mem::forget(vec.drain(..));
 339
 340         // Record the destructors after doing the allocation as that may panic
 341         // and would cause `object`'s destuctor to run twice if it was recorded before
 342         for i in 0..len {
 343             destructors.push(DropType {
 344                 drop_fn: drop_for_type::<T>,
 345                 obj: start_ptr.offset(i as isize) as *mut u8,
 346             });
 347         }
 348
 349         slice::from_raw_parts_mut(start_ptr, len)
 350     }
 351 }