Auto merge of rust-lang#93343 - lqd:attrs, r=spastorino

Only traverse attrs once while checking for coherence override attributes In coherence, while checking for negative impls override attributes: only traverse the `DefId`s' attributes once. This PR is an easy way to get back some of the small perf loss in rust-lang#93175

Author: bors

compiler/rustc_trait_selection/src/traits/coherence.rs

@@ -13,6 +13,7 @@ use crate::traits::{
  self, FulfillmentContext, Normalized, Obligation, ObligationCause, PredicateObligation,
  PredicateObligations, SelectionContext,
 };
+use rustc_ast::Attribute;
 use rustc_hir::def_id::{DefId, LOCAL_CRATE};
 use rustc_middle::ty::fast_reject::{self, SimplifyParams, StripReferences};
 use rustc_middle::ty::fold::TypeFoldable;
@@ -160,24 +161,30 @@ impl OverlapMode {
 }
 
 fn overlap_mode<'tcx>(tcx: TyCtxt<'tcx>, impl1_def_id: DefId, impl2_def_id: DefId) -> OverlapMode {
- if tcx.has_attr(impl1_def_id, sym::rustc_strict_coherence)
- != tcx.has_attr(impl2_def_id, sym::rustc_strict_coherence)
- {
- bug!("Use strict coherence on both impls",);
- }
-
- if tcx.has_attr(impl1_def_id, sym::rustc_with_negative_coherence)
- != tcx.has_attr(impl2_def_id, sym::rustc_with_negative_coherence)
- {
- bug!("Use with negative coherence on both impls",);
- }
-
- if tcx.has_attr(impl1_def_id, sym::rustc_strict_coherence) {
- OverlapMode::Strict
- } else if tcx.has_attr(impl1_def_id, sym::rustc_with_negative_coherence) {
- OverlapMode::WithNegative
- } else {
- OverlapMode::Stable
+ // Find the possible coherence mode override opt-in attributes for each `DefId`
+ let find_coherence_attr = |attr: &Attribute| {
+ let name = attr.name_or_empty();
+ match name {
+ sym::rustc_with_negative_coherence | sym::rustc_strict_coherence => Some(name),
+ _ => None,
+ }
+ };
+ let impl1_coherence_mode = tcx.get_attrs(impl1_def_id).iter().find_map(find_coherence_attr);
+ let impl2_coherence_mode = tcx.get_attrs(impl2_def_id).iter().find_map(find_coherence_attr);
+
+ // If there are any (that currently happens in tests), they need to match. Otherwise, the
+ // default 1.0 rules are used.
+ match (impl1_coherence_mode, impl2_coherence_mode) {
+ (None, None) => OverlapMode::Stable,
+ (Some(sym::rustc_with_negative_coherence), Some(sym::rustc_with_negative_coherence)) => {
+ OverlapMode::WithNegative
+ }
+ (Some(sym::rustc_strict_coherence), Some(sym::rustc_strict_coherence)) => {
+ OverlapMode::Strict
+ }
+ (Some(mode), _) | (_, Some(mode)) => {
+ bug!("Use the same coherence mode on both impls: {}", mode)
+ }
  }
 }