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Optimize TokenKind::clone. #114119

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merged 1 commit into from
Jul 28, 2023
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Optimize TokenKind::clone. #114119

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17 changes: 16 additions & 1 deletion compiler/rustc_ast/src/token.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -226,7 +226,9 @@ fn ident_can_begin_type(name: Symbol, span: Span, is_raw: bool) -> bool {
.contains(&name)
}

#[derive(Clone, PartialEq, Encodable, Decodable, Debug, HashStable_Generic)]
// SAFETY: due to the `Clone` impl below, all fields of all variants other than
// `Interpolated` must impl `Copy`.
#[derive(PartialEq, Encodable, Decodable, Debug, HashStable_Generic)]
pub enum TokenKind {
/* Expression-operator symbols. */
Eq,
Expand Down Expand Up @@ -299,6 +301,19 @@ pub enum TokenKind {
Eof,
}

impl Clone for TokenKind {
fn clone(&self) -> Self {
// `TokenKind` would impl `Copy` if it weren't for `Interpolated`. So
// for all other variants, this implementation of `clone` is just like
// a copy. This is faster than the `derive(Clone)` version which has a
// separate path for every variant.
match self {
Interpolated(nt) => Interpolated(nt.clone()),
_ => unsafe { std::ptr::read(self) },
}
}
}

#[derive(Clone, PartialEq, Encodable, Decodable, Debug, HashStable_Generic)]
pub struct Token {
pub kind: TokenKind,
Expand Down