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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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2
compiler/rustc_macros/src/lib.rs
View file

@ -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)
}

26
compiler/rustc_macros/src/newtype.rs
View file

@ -192,6 +192,30 @@ impl Parse for Newtype {
}
}
};
let spec_partial_eq_impl = if let Lit::Int(max) = &max {
if let Ok(max_val) = max.base10_parse::<u32>() {
quote! {
impl core::option::SpecOptionPartialEq for #name {
#[inline]
fn eq(l: &Option<Self>, r: &Option<Self>) -> bool {
if #max_val < u32::MAX {
l.map(|i| i.private).unwrap_or(#max_val+1) == r.map(|i| i.private).unwrap_or(#max_val+1)
} else {
match (l, r) {
(Some(l), Some(r)) => r == l,
(None, None) => true,
_ => false
}
}
}
}
}
} else {
quote! {}
}
} else {
quote! {}
};
Ok(Self(quote! {
#(#attrs)*
@ -293,6 +317,8 @@ impl Parse for Newtype {
#step
#spec_partial_eq_impl
impl From<#name> for u32 {
#[inline]
fn from(v: #name) -> u32 {