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Special-case deriving PartialOrd for enums with dataless variants #103659

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merged 1 commit into from
Jan 29, 2023
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Special-case deriving PartialOrd for enums with dataless variants #103659

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82 changes: 73 additions & 9 deletions compiler/rustc_builtin_macros/src/deriving/cmp/partial_ord.rs
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Original file line number Diff line number Diff line change
@@ -1,7 +1,7 @@
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;
Expand All @@ -21,6 +21,27 @@ pub fn expand_deriving_partial_ord(

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(),
Expand All @@ -30,7 +51,7 @@ pub fn expand_deriving_partial_ord(
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)
})),
};

Expand All @@ -47,7 +68,12 @@ pub fn expand_deriving_partial_ord(
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]);
Expand All @@ -74,12 +100,50 @@ pub fn cs_partial_cmp(cx: &mut ExtCtxt<'_>, span: Span, substr: &Substructure<'_
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())),
},
Expand Down
51 changes: 23 additions & 28 deletions tests/ui/deriving/deriving-all-codegen.stdout
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Original file line number Diff line number Diff line change
Expand Up @@ -888,23 +888,20 @@ impl ::core::cmp::PartialOrd for Mixed {
-> ::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),
}
}
}
Expand Down Expand Up @@ -1018,18 +1015,16 @@ impl ::core::cmp::PartialOrd for Fielded {
-> ::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),
}
}
}
Expand Down