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Auto merge of #103556 - clubby789:specialize-option-partial-eq, r=scottmcm

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Manually implement PartialEq for Option<T> and specialize non-nullable types

This PR manually implements `PartialEq` and `StructuralPartialEq` for `Option`, which seems to produce slightly better codegen than the automatically derived implementation.

It also allows specializing on the `core::num::NonZero*` and `core::ptr::NonNull` types, taking advantage of the niche optimization by transmuting the `Option<T>` to `T` to be compared directly, which can be done in just two instructions.

A comparison of the original, new and specialized code generation is available [here](https://godbolt.org/z/dE4jxdYsa).
This commit is contained in:
bors 2022-11-26 08:56:20 +00:00
commit 8841bee954
4 changed files with 128 additions and 2 deletions
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compiler/rustc_macros/src/lib.rs
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@ -48,7 +48,7 @@ pub fn symbols(input: TokenStream) -> TokenStream {
/// `u32::MAX`. You can also customize things like the `Debug` impl,
/// what traits are derived, and so forth via the macro.
#[proc_macro]
#[allow_internal_unstable(step_trait, rustc_attrs, trusted_step)]
#[allow_internal_unstable(step_trait, rustc_attrs, trusted_step, spec_option_partial_eq)]
pub fn newtype_index(input: TokenStream) -> TokenStream {
newtype::newtype(input)
}