bors 9f82651a5f Auto merge of #103659 - clubby789:improve-partialord-derive, r=nagisa ... Special-case deriving `PartialOrd` for enums with dataless variants I was able to get slightly better codegen by flipping the derived `PartialOrd` logic for two-variant enums. I also tried to document the implementation of the derive macro to make the special-case logic a little clearer. ```rs #[derive(PartialEq, PartialOrd)] pub enum A<T> { A, B(T) } ``` ```diff impl<T: ::core::cmp::PartialOrd> ::core::cmp::PartialOrd for A<T> { #[inline] fn partial_cmp( &self, other: &A<T>, ) -> ::core::option::Option<::core::cmp::Ordering> { let __self_tag = ::core::intrinsics::discriminant_value(self); let __arg1_tag = ::core::intrinsics::discriminant_value(other); - match ::core::cmp::PartialOrd::partial_cmp(&__self_tag, &__arg1_tag) { - ::core::option::Option::Some(::core::cmp::Ordering::Equal) => { - match (self, other) { - (A::B(__self_0), A::B(__arg1_0)) => { - ::core::cmp::PartialOrd::partial_cmp(__self_0, __arg1_0) - } - _ => ::core::option::Option::Some(::core::cmp::Ordering::Equal), - } + match (self, other) { + (A::B(__self_0), A::B(__arg1_0)) => { + ::core::cmp::PartialOrd::partial_cmp(__self_0, __arg1_0) } - cmp => cmp, + _ => ::core::cmp::PartialOrd::partial_cmp(&__self_tag, &__arg1_tag), } } } ``` Godbolt: [Current](https://godbolt.org/z/GYjEzG1T8), [New](https://godbolt.org/z/GoK78qx15) I'm not sure how common a case comparing two enums like this (such as `Option`) is, and if it's worth the slowdown of adding a special case to the derive. If it causes overall regressions it might be worth just manually implementing this for `Option`.		2023-01-28 22:11:11 +00:00
..
src	Auto merge of #103659 - clubby789:improve-partialord-derive, r=nagisa	2023-01-28 22:11:11 +00:00
Cargo.toml	rustdoc: use ThinVec for cleaned generics	2022-11-02 16:17:22 -07:00