Remove `DropArena`.

Most arena-allocate types that impl `Drop` get their own `TypedArena`, but a
few infrequently used ones share a `DropArena`. This sharing adds complexity
but doesn't help performance or memory usage. Perhaps it was more effective in
the past prior to some other improvements to arenas.

This commit removes `DropArena` and the sharing of arenas via the `few`
attribute of the `arena_types` macro. This change removes over 100 lines of
code and nine uses of `unsafe` (one of which affects the parallel compiler) and
makes the remaining code easier to read.

1 files changed, 5 insertions, 10 deletions

diff --git a/compiler/rustc_hir/src/arena.rs b/compiler/rustc_hir/src/arena.rs
index 1a34dd04428..5091a7bccc5 100644
--- a/compiler/rustc_hir/src/arena.rs
+++ b/compiler/rustc_hir/src/arena.rs
@@ -1,10 +1,5 @@
 /// This declares a list of types which can be allocated by `Arena`.
 ///
-/// The `few` modifier will cause allocation to use the shared arena and recording the destructor.
-/// This is faster and more memory efficient if there's only a few allocations of the type.
-/// Leaving `few` out will cause the type to get its own dedicated `TypedArena` which is
-/// faster and more memory efficient if there is lots of allocations.
-///
 /// Specifying the `decode` modifier will add decode impls for `&T` and `&[T]`,
 /// where `T` is the type listed. These impls will appear in the implement_ty_decoder! macro.
 #[macro_export]
@@ -12,7 +7,7 @@ macro_rules! arena_types {
     ($macro:path, $tcx:lifetime) => (
         $macro!([
             // HIR types
-            [few] hir_krate: rustc_hir::Crate<$tcx>,
+            [] hir_krate: rustc_hir::Crate<$tcx>,
             [] arm: rustc_hir::Arm<$tcx>,
             [] asm_operand: (rustc_hir::InlineAsmOperand<$tcx>, Span),
             [] asm_template: rustc_ast::InlineAsmTemplatePiece,
@@ -29,14 +24,14 @@ macro_rules! arena_types {
             [] pat_field: rustc_hir::PatField<$tcx>,
             [] fn_decl: rustc_hir::FnDecl<$tcx>,
             [] foreign_item: rustc_hir::ForeignItem<$tcx>,
-            [few] foreign_item_ref: rustc_hir::ForeignItemRef,
+            [] foreign_item_ref: rustc_hir::ForeignItemRef,
             [] impl_item: rustc_hir::ImplItem<$tcx>,
             [] impl_item_ref: rustc_hir::ImplItemRef,
             [] item: rustc_hir::Item<$tcx>,
-            [few] inline_asm: rustc_hir::InlineAsm<$tcx>,
-            [few] llvm_inline_asm: rustc_hir::LlvmInlineAsm<$tcx>,
+            [] inline_asm: rustc_hir::InlineAsm<$tcx>,
+            [] llvm_inline_asm: rustc_hir::LlvmInlineAsm<$tcx>,
             [] local: rustc_hir::Local<$tcx>,
-            [few] mod_: rustc_hir::Mod<$tcx>,
+            [] mod_: rustc_hir::Mod<$tcx>,
             [] owner_info: rustc_hir::OwnerInfo<$tcx>,
             [] param: rustc_hir::Param<$tcx>,
             [] pat: rustc_hir::Pat<$tcx>,