From ac747a848124c1797140aa6c10b69d00e7ffc226 Mon Sep 17 00:00:00 2001 From: Nicholas Nethercote Date: Thu, 27 Jul 2023 14:56:28 +1000 Subject: [PATCH] Optimize `TokenKind::clone`. `TokenKind` would impl `Copy` if it weren't for `TokenKind::Interpolated`. This commit makes `clone` reflect that. --- compiler/rustc_ast/src/token.rs | 17 ++++++++++++++++- 1 file changed, 16 insertions(+), 1 deletion(-) diff --git a/compiler/rustc_ast/src/token.rs b/compiler/rustc_ast/src/token.rs index 303bdd3a30791..4c920e84f8679 100644 --- a/compiler/rustc_ast/src/token.rs +++ b/compiler/rustc_ast/src/token.rs @@ -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, @@ -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,