diff options
Diffstat (limited to 'compiler/rustc_builtin_macros/src/deriving/cmp/partial_ord.rs')
| -rw-r--r-- | compiler/rustc_builtin_macros/src/deriving/cmp/partial_ord.rs | 85 |
1 files changed, 75 insertions, 10 deletions
diff --git a/compiler/rustc_builtin_macros/src/deriving/cmp/partial_ord.rs b/compiler/rustc_builtin_macros/src/deriving/cmp/partial_ord.rs index c9dc89212..9f4624790 100644 --- a/compiler/rustc_builtin_macros/src/deriving/cmp/partial_ord.rs +++ b/compiler/rustc_builtin_macros/src/deriving/cmp/partial_ord.rs @@ -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; @@ -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(), @@ -30,7 +51,7 @@ pub fn expand_deriving_partial_ord( attributes: attrs, fieldless_variants_strategy: FieldlessVariantsStrategy::Unify, combine_substructure: combine_substructure(Box::new(|cx, span, substr| { - cs_partial_cmp(cx, span, substr) + cs_partial_cmp(cx, span, substr, tag_then_data) })), }; @@ -38,6 +59,7 @@ pub fn expand_deriving_partial_ord( span, path: path_std!(cmp::PartialOrd), skip_path_as_bound: false, + needs_copy_as_bound_if_packed: true, additional_bounds: vec![], supports_unions: false, methods: vec![partial_cmp_def], @@ -47,7 +69,12 @@ 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]); @@ -71,15 +98,53 @@ pub fn cs_partial_cmp(cx: &mut ExtCtxt<'_>, span: Span, substr: &Substructure<'_ let [other_expr] = &field.other_selflike_exprs[..] else { cx.span_bug(field.span, "not exactly 2 arguments in `derive(Ord)`"); }; - let args = vec![field.self_expr.clone(), other_expr.clone()]; + let args = thin_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, thin_vec![eq_arm, neq_arm]) + } } CsFold::Fieldless => cx.expr_some(span, cx.expr_path(equal_path.clone())), }, |