use crate::deriving::generic::ty::*;
use crate::deriving::generic::*;
use crate::deriving::{path_std, pathvec_std};
-use rustc_ast::MetaItem;
+use rustc_ast::{ExprKind, ItemKind, MetaItem, PatKind};
use rustc_expand::base::{Annotatable, ExtCtxt};
use rustc_span::symbol::{sym, Ident};
use rustc_span::Span;
let attrs = thin_vec![cx.attr_word(sym::inline, span)];
+ // Order in which to perform matching
+ let tag_then_data = if let Annotatable::Item(item) = item
+ && let ItemKind::Enum(def, _) = &item.kind {
+ let dataful: Vec<bool> = def.variants.iter().map(|v| !v.data.fields().is_empty()).collect();
+ match dataful.iter().filter(|&&b| b).count() {
+ // No data, placing the tag check first makes codegen simpler
+ 0 => true,
+ 1..=2 => false,
+ _ => {
+ (0..dataful.len()-1).any(|i| {
+ if dataful[i] && let Some(idx) = dataful[i+1..].iter().position(|v| *v) {
+ idx >= 2
+ } else {
+ false
+ }
+ })
+ }
+ }
+ } else {
+ true
+ };
let partial_cmp_def = MethodDef {
name: sym::partial_cmp,
generics: Bounds::empty(),
attributes: attrs,
unify_fieldless_variants: true,
combine_substructure: combine_substructure(Box::new(|cx, span, substr| {
- cs_partial_cmp(cx, span, substr)
+ cs_partial_cmp(cx, span, substr, tag_then_data)
})),
};
trait_def.expand(cx, mitem, item, push)
}
-pub fn cs_partial_cmp(cx: &mut ExtCtxt<'_>, span: Span, substr: &Substructure<'_>) -> BlockOrExpr {
+fn cs_partial_cmp(
+ cx: &mut ExtCtxt<'_>,
+ span: Span,
+ substr: &Substructure<'_>,
+ tag_then_data: bool,
+) -> BlockOrExpr {
let test_id = Ident::new(sym::cmp, span);
let equal_path = cx.path_global(span, cx.std_path(&[sym::cmp, sym::Ordering, sym::Equal]));
let partial_cmp_path = cx.std_path(&[sym::cmp, sym::PartialOrd, sym::partial_cmp]);
let args = vec![field.self_expr.clone(), other_expr.clone()];
cx.expr_call_global(field.span, partial_cmp_path.clone(), args)
}
- CsFold::Combine(span, expr1, expr2) => {
- let eq_arm =
- cx.arm(span, cx.pat_some(span, cx.pat_path(span, equal_path.clone())), expr1);
- let neq_arm =
- cx.arm(span, cx.pat_ident(span, test_id), cx.expr_ident(span, test_id));
- cx.expr_match(span, expr2, vec![eq_arm, neq_arm])
+ CsFold::Combine(span, mut expr1, expr2) => {
+ // When the item is an enum, this expands to
+ // ```
+ // match (expr2) {
+ // Some(Ordering::Equal) => expr1,
+ // cmp => cmp
+ // }
+ // ```
+ // where `expr2` is `partial_cmp(self_tag, other_tag)`, and `expr1` is a `match`
+ // against the enum variants. This means that we begin by comparing the enum tags,
+ // before either inspecting their contents (if they match), or returning
+ // the `cmp::Ordering` of comparing the enum tags.
+ // ```
+ // match partial_cmp(self_tag, other_tag) {
+ // Some(Ordering::Equal) => match (self, other) {
+ // (Self::A(self_0), Self::A(other_0)) => partial_cmp(self_0, other_0),
+ // (Self::B(self_0), Self::B(other_0)) => partial_cmp(self_0, other_0),
+ // _ => Some(Ordering::Equal)
+ // }
+ // cmp => cmp
+ // }
+ // ```
+ // If we have any certain enum layouts, flipping this results in better codegen
+ // ```
+ // match (self, other) {
+ // (Self::A(self_0), Self::A(other_0)) => partial_cmp(self_0, other_0),
+ // _ => partial_cmp(self_tag, other_tag)
+ // }
+ // ```
+ // Reference: https://github.com/rust-lang/rust/pull/103659#issuecomment-1328126354
+
+ if !tag_then_data
+ && let ExprKind::Match(_, arms) = &mut expr1.kind
+ && let Some(last) = arms.last_mut()
+ && let PatKind::Wild = last.pat.kind {
+ last.body = expr2;
+ expr1
+ } else {
+ let eq_arm =
+ cx.arm(span, cx.pat_some(span, cx.pat_path(span, equal_path.clone())), expr1);
+ let neq_arm =
+ cx.arm(span, cx.pat_ident(span, test_id), cx.expr_ident(span, test_id));
+ cx.expr_match(span, expr2, vec![eq_arm, neq_arm])
+ }
}
CsFold::Fieldless => cx.expr_some(span, cx.expr_path(equal_path.clone())),
},
-> ::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) {
- (Mixed::R(__self_0), Mixed::R(__arg1_0)) =>
- ::core::cmp::PartialOrd::partial_cmp(__self_0, __arg1_0),
- (Mixed::S { d1: __self_0, d2: __self_1 }, Mixed::S {
- d1: __arg1_0, d2: __arg1_1 }) =>
- match ::core::cmp::PartialOrd::partial_cmp(__self_0,
- __arg1_0) {
- ::core::option::Option::Some(::core::cmp::Ordering::Equal)
- => ::core::cmp::PartialOrd::partial_cmp(__self_1, __arg1_1),
- cmp => cmp,
- },
- _ =>
- ::core::option::Option::Some(::core::cmp::Ordering::Equal),
+ match (self, other) {
+ (Mixed::R(__self_0), Mixed::R(__arg1_0)) =>
+ ::core::cmp::PartialOrd::partial_cmp(__self_0, __arg1_0),
+ (Mixed::S { d1: __self_0, d2: __self_1 }, Mixed::S {
+ d1: __arg1_0, d2: __arg1_1 }) =>
+ match ::core::cmp::PartialOrd::partial_cmp(__self_0, __arg1_0)
+ {
+ ::core::option::Option::Some(::core::cmp::Ordering::Equal)
+ => ::core::cmp::PartialOrd::partial_cmp(__self_1, __arg1_1),
+ cmp => cmp,
},
- cmp => cmp,
+ _ =>
+ ::core::cmp::PartialOrd::partial_cmp(&__self_tag,
+ &__arg1_tag),
}
}
}
-> ::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) {
- (Fielded::X(__self_0), Fielded::X(__arg1_0)) =>
- ::core::cmp::PartialOrd::partial_cmp(__self_0, __arg1_0),
- (Fielded::Y(__self_0), Fielded::Y(__arg1_0)) =>
- ::core::cmp::PartialOrd::partial_cmp(__self_0, __arg1_0),
- (Fielded::Z(__self_0), Fielded::Z(__arg1_0)) =>
- ::core::cmp::PartialOrd::partial_cmp(__self_0, __arg1_0),
- _ => unsafe { ::core::intrinsics::unreachable() }
- },
- cmp => cmp,
+ match (self, other) {
+ (Fielded::X(__self_0), Fielded::X(__arg1_0)) =>
+ ::core::cmp::PartialOrd::partial_cmp(__self_0, __arg1_0),
+ (Fielded::Y(__self_0), Fielded::Y(__arg1_0)) =>
+ ::core::cmp::PartialOrd::partial_cmp(__self_0, __arg1_0),
+ (Fielded::Z(__self_0), Fielded::Z(__arg1_0)) =>
+ ::core::cmp::PartialOrd::partial_cmp(__self_0, __arg1_0),
+ _ =>
+ ::core::cmp::PartialOrd::partial_cmp(&__self_tag,
+ &__arg1_tag),
}
}
}