bjoernager/rust
bjoernager/rust
1
Fork 0
Code Activity

Improve the comments in Symbol::interner.

Browse source
This commit is contained in:
Nicholas Nethercote 2021-12-03 07:12:31 +11:00
parent 207c80f105
commit 66153d76e2
1 changed files with 13 additions and 6 deletions
Download patch file Download diff file Expand all files Collapse all files

19
compiler/rustc_span/src/symbol.rs
View file

@ -1716,8 +1716,9 @@ pub(crate) struct Interner(Lock<InternerInner>);
// found that to regress performance up to 2% in some cases. This might be // found that to regress performance up to 2% in some cases. This might be
// revisited after further improvements to `indexmap`. // revisited after further improvements to `indexmap`.
// //
// This type is private to prevent accidentally constructing more than one `Interner` on the same // This type is private to prevent accidentally constructing more than one
// thread, which makes it easy to mixup `Symbol`s between `Interner`s. // `Interner` on the same thread, which makes it easy to mixup `Symbol`s
// between `Interner`s.
#[derive(Default)] #[derive(Default)]
struct InternerInner { struct InternerInner {
arena: DroplessArena, arena: DroplessArena,
@ -1743,14 +1744,20 @@ impl Interner {
let name = Symbol::new(inner.strings.len() as u32); let name = Symbol::new(inner.strings.len() as u32);
// `from_utf8_unchecked` is safe since we just allocated a `&str` which is known to be // SAFETY: we convert from `&str` to `&[u8]`, clone it into the arena,
// UTF-8. // and immediately convert the clone back to `&[u8], all because there
// is no `inner.arena.alloc_str()` method. This is clearly safe.
let string: &str = let string: &str =
unsafe { str::from_utf8_unchecked(inner.arena.alloc_slice(string.as_bytes())) }; unsafe { str::from_utf8_unchecked(inner.arena.alloc_slice(string.as_bytes())) };
// It is safe to extend the arena allocation to `'static` because we only access
// these while the arena is still alive. // SAFETY: we can extend the arena allocation to `'static` because we
// only access these while the arena is still alive.
let string: &'static str = unsafe { &*(string as *const str) }; let string: &'static str = unsafe { &*(string as *const str) };
inner.strings.push(string); inner.strings.push(string);
// This second hash table lookup can be avoided by using `RawEntryMut`,
// but this code path isn't hot enough for it to be worth it. See
// #91445 for details.
inner.names.insert(string, name); inner.names.insert(string, name);
name name
} }