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             [] 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_hir::def_id::DefIdSet,
  45             [decode] specialization_graph: rustc::traits::specialization_graph::Graph,
  46             [] region_scope_tree: rustc::middle::region::ScopeTree,
  47             [] item_local_set: rustc_hir::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_hir::def_id::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                 rustc_span::symbol::Symbol,
  98                 rustc_hir::def_id::DefId,
  99             >,
 100             [few] resolve_lifetimes: rustc::middle::resolve_lifetime::ResolveLifetimes,
 101             [few] lint_levels: rustc::lint::LintLevelMap,
 102             [few] stability_index: rustc::middle::stability::Index<'tcx>,
 103             [few] features: rustc_feature::Features,
 104             [few] all_traits: Vec<rustc_hir::def_id::DefId>,
 105             [few] privacy_access_levels: rustc::middle::privacy::AccessLevels,
 106             [few] target_features_whitelist: rustc_data_structures::fx::FxHashMap<
 107                 String,
 108                 Option<rustc_span::symbol::Symbol>
 109             >,
 110             [few] wasm_import_module_map: rustc_data_structures::fx::FxHashMap<
 111                 rustc_hir::def_id::DefId,
 112                 String
 113             >,
 114             [few] get_lib_features: rustc::middle::lib_features::LibFeatures,
 115             [few] defined_lib_features: rustc::middle::lang_items::LanguageItems,
 116             [few] visible_parent_map: rustc_hir::def_id::DefIdMap<rustc_hir::def_id::DefId>,
 117             [few] foreign_module: rustc::middle::cstore::ForeignModule,
 118             [few] foreign_modules: Vec<rustc::middle::cstore::ForeignModule>,
 119             [few] reachable_non_generics: rustc_hir::def_id::DefIdMap<
 120                 rustc::middle::exported_symbols::SymbolExportLevel
 121             >,
 122             [few] crate_variances: rustc::ty::CrateVariancesMap<'tcx>,
 123             [few] inferred_outlives_crate: rustc::ty::CratePredicatesMap<'tcx>,
 124             [] upvars: rustc_data_structures::fx::FxIndexMap<rustc_hir::HirId, rustc_hir::Upvar>,
 125
 126             // HIR types
 127             [few] hir_forest: rustc::hir::map::Forest<$tcx>,
 128             [] arm: rustc_hir::Arm<$tcx>,
 129             [] attribute: syntax::ast::Attribute,
 130             [] block: rustc_hir::Block<$tcx>,
 131             [] bare_fn_ty: rustc_hir::BareFnTy<$tcx>,
 132             [few] global_asm: rustc_hir::GlobalAsm,
 133             [] generic_arg: rustc_hir::GenericArg<$tcx>,
 134             [] generic_args: rustc_hir::GenericArgs<$tcx>,
 135             [] generic_bound: rustc_hir::GenericBound<$tcx>,
 136             [] generic_param: rustc_hir::GenericParam<$tcx>,
 137             [] expr: rustc_hir::Expr<$tcx>,
 138             [] field: rustc_hir::Field<$tcx>,
 139             [] field_pat: rustc_hir::FieldPat<$tcx>,
 140             [] fn_decl: rustc_hir::FnDecl<$tcx>,
 141             [] foreign_item: rustc_hir::ForeignItem<$tcx>,
 142             [] impl_item_ref: rustc_hir::ImplItemRef<$tcx>,
 143             [] inline_asm: rustc_hir::InlineAsm<$tcx>,
 144             [] local: rustc_hir::Local<$tcx>,
 145             [few] macro_def: rustc_hir::MacroDef<$tcx>,
 146             [] param: rustc_hir::Param<$tcx>,
 147             [] pat: rustc_hir::Pat<$tcx>,
 148             [] path: rustc_hir::Path<$tcx>,
 149             [] path_segment: rustc_hir::PathSegment<$tcx>,
 150             [] poly_trait_ref: rustc_hir::PolyTraitRef<$tcx>,
 151             [] qpath: rustc_hir::QPath<$tcx>,
 152             [] stmt: rustc_hir::Stmt<$tcx>,
 153             [] struct_field: rustc_hir::StructField<$tcx>,
 154             [] trait_item_ref: rustc_hir::TraitItemRef,
 155             [] ty: rustc_hir::Ty<$tcx>,
 156             [] type_binding: rustc_hir::TypeBinding<$tcx>,
 157             [] variant: rustc_hir::Variant<$tcx>,
 158             [] where_predicate: rustc_hir::WherePredicate<$tcx>,
 159         ], $tcx);
 160     )
 161 }
 162
 163 macro_rules! arena_for_type {
 164     ([][$ty:ty]) => {
 165         TypedArena<$ty>
 166     };
 167     ([few $(, $attrs:ident)*][$ty:ty]) => {
 168         PhantomData<$ty>
 169     };
 170     ([$ignore:ident $(, $attrs:ident)*]$args:tt) => {
 171         arena_for_type!([$($attrs),*]$args)
 172     };
 173 }
 174
 175 macro_rules! declare_arena {
 176     ([], [$($a:tt $name:ident: $ty:ty,)*], $tcx:lifetime) => {
 177         #[derive(Default)]
 178         pub struct Arena<$tcx> {
 179             dropless: DroplessArena,
 180             drop: DropArena,
 181             $($name: arena_for_type!($a[$ty]),)*
 182         }
 183     }
 184 }
 185
 186 macro_rules! which_arena_for_type {
 187     ([][$arena:expr]) => {
 188         Some($arena)
 189     };
 190     ([few$(, $attrs:ident)*][$arena:expr]) => {
 191         None
 192     };
 193     ([$ignore:ident$(, $attrs:ident)*]$args:tt) => {
 194         which_arena_for_type!([$($attrs),*]$args)
 195     };
 196 }
 197
 198 macro_rules! impl_arena_allocatable {
 199     ([], [$($a:tt $name:ident: $ty:ty,)*], $tcx:lifetime) => {
 200         $(
 201             impl ArenaAllocatable for $ty {}
 202             unsafe impl<$tcx> ArenaField<$tcx> for $ty {
 203                 #[inline]
 204                 fn arena<'a>(_arena: &'a Arena<$tcx>) -> Option<&'a TypedArena<Self>> {
 205                     which_arena_for_type!($a[&_arena.$name])
 206                 }
 207             }
 208         )*
 209     }
 210 }
 211
 212 arena_types!(declare_arena, [], 'tcx);
 213
 214 arena_types!(impl_arena_allocatable, [], 'tcx);
 215
 216 pub trait ArenaAllocatable {}
 217
 218 impl<T: Copy> ArenaAllocatable for T {}
 219
 220 unsafe trait ArenaField<'tcx>: Sized {
 221     /// Returns a specific arena to allocate from.
 222     /// If `None` is returned, the `DropArena` will be used.
 223     fn arena<'a>(arena: &'a Arena<'tcx>) -> Option<&'a TypedArena<Self>>;
 224 }
 225
 226 unsafe impl<'tcx, T> ArenaField<'tcx> for T {
 227     #[inline]
 228     default fn arena<'a>(_: &'a Arena<'tcx>) -> Option<&'a TypedArena<Self>> {
 229         panic!()
 230     }
 231 }
 232
 233 impl<'tcx> Arena<'tcx> {
 234     #[inline]
 235     pub fn alloc<T: ArenaAllocatable>(&self, value: T) -> &mut T {
 236         if !mem::needs_drop::<T>() {
 237             return self.dropless.alloc(value);
 238         }
 239         match <T as ArenaField<'tcx>>::arena(self) {
 240             Some(arena) => arena.alloc(value),
 241             None => unsafe { self.drop.alloc(value) },
 242         }
 243     }
 244
 245     #[inline]
 246     pub fn alloc_slice<T: Copy>(&self, value: &[T]) -> &mut [T] {
 247         if value.len() == 0 {
 248             return &mut [];
 249         }
 250         self.dropless.alloc_slice(value)
 251     }
 252
 253     pub fn alloc_from_iter<T: ArenaAllocatable, I: IntoIterator<Item = T>>(
 254         &'a self,
 255         iter: I,
 256     ) -> &'a mut [T] {
 257         if !mem::needs_drop::<T>() {
 258             return self.dropless.alloc_from_iter(iter);
 259         }
 260         match <T as ArenaField<'tcx>>::arena(self) {
 261             Some(arena) => arena.alloc_from_iter(iter),
 262             None => unsafe { self.drop.alloc_from_iter(iter) },
 263         }
 264     }
 265 }
 266
 267 /// Calls the destructor for an object when dropped.
 268 struct DropType {
 269     drop_fn: unsafe fn(*mut u8),
 270     obj: *mut u8,
 271 }
 272
 273 unsafe fn drop_for_type<T>(to_drop: *mut u8) {
 274     std::ptr::drop_in_place(to_drop as *mut T)
 275 }
 276
 277 impl Drop for DropType {
 278     fn drop(&mut self) {
 279         unsafe { (self.drop_fn)(self.obj) }
 280     }
 281 }
 282
 283 /// An arena which can be used to allocate any type.
 284 /// Allocating in this arena is unsafe since the type system
 285 /// doesn't know which types it contains. In order to
 286 /// allocate safely, you must store a PhantomData<T>
 287 /// alongside this arena for each type T you allocate.
 288 #[derive(Default)]
 289 struct DropArena {
 290     /// A list of destructors to run when the arena drops.
 291     /// Ordered so `destructors` gets dropped before the arena
 292     /// since its destructor can reference memory in the arena.
 293     destructors: RefCell<Vec<DropType>>,
 294     arena: DroplessArena,
 295 }
 296
 297 impl DropArena {
 298     #[inline]
 299     unsafe fn alloc<T>(&self, object: T) -> &mut T {
 300         let mem =
 301             self.arena.alloc_raw(mem::size_of::<T>(), mem::align_of::<T>()) as *mut _ as *mut T;
 302         // Write into uninitialized memory.
 303         ptr::write(mem, object);
 304         let result = &mut *mem;
 305         // Record the destructor after doing the allocation as that may panic
 306         // and would cause `object`'s destuctor to run twice if it was recorded before
 307         self.destructors
 308             .borrow_mut()
 309             .push(DropType { drop_fn: drop_for_type::<T>, obj: result as *mut T as *mut u8 });
 310         result
 311     }
 312
 313     #[inline]
 314     unsafe fn alloc_from_iter<T, I: IntoIterator<Item = T>>(&self, iter: I) -> &mut [T] {
 315         let mut vec: SmallVec<[_; 8]> = iter.into_iter().collect();
 316         if vec.is_empty() {
 317             return &mut [];
 318         }
 319         let len = vec.len();
 320
 321         let start_ptr = self
 322             .arena
 323             .alloc_raw(len.checked_mul(mem::size_of::<T>()).unwrap(), mem::align_of::<T>())
 324             as *mut _ as *mut T;
 325
 326         let mut destructors = self.destructors.borrow_mut();
 327         // Reserve space for the destructors so we can't panic while adding them
 328         destructors.reserve(len);
 329
 330         // Move the content to the arena by copying it and then forgetting
 331         // the content of the SmallVec
 332         vec.as_ptr().copy_to_nonoverlapping(start_ptr, len);
 333         mem::forget(vec.drain(..));
 334
 335         // Record the destructors after doing the allocation as that may panic
 336         // and would cause `object`'s destuctor to run twice if it was recorded before
 337         for i in 0..len {
 338             destructors.push(DropType {
 339                 drop_fn: drop_for_type::<T>,
 340                 obj: start_ptr.offset(i as isize) as *mut u8,
 341             });
 342         }
 343
 344         slice::from_raw_parts_mut(start_ptr, len)
 345     }
 346 }