Consider polarity in sizedness fast path

1 files changed, 4 insertions, 3 deletions

diff --git a/compiler/rustc_trait_selection/src/traits/util.rs b/compiler/rustc_trait_selection/src/traits/util.rs
index a05bae53566..141454bfe37 100644
--- a/compiler/rustc_trait_selection/src/traits/util.rs
+++ b/compiler/rustc_trait_selection/src/traits/util.rs
@@ -368,16 +368,17 @@ pub fn sizedness_fast_path<'tcx>(tcx: TyCtxt<'tcx>, predicate: ty::Predicate<'tc
     // Proving `Sized`/`MetaSized`, very often on "obviously sized" types like
     // `&T`, accounts for about 60% percentage of the predicates we have to prove. No need to
     // canonicalize and all that for such cases.
-    if let ty::PredicateKind::Clause(ty::ClauseKind::Trait(trait_ref)) =
+    if let ty::PredicateKind::Clause(ty::ClauseKind::Trait(trait_pred)) =
         predicate.kind().skip_binder()
+        && trait_pred.polarity == ty::PredicatePolarity::Positive
     {
-        let sizedness = match tcx.as_lang_item(trait_ref.def_id()) {
+        let sizedness = match tcx.as_lang_item(trait_pred.def_id()) {
             Some(LangItem::Sized) => SizedTraitKind::Sized,
             Some(LangItem::MetaSized) => SizedTraitKind::MetaSized,
             _ => return false,
         };
 
-        if trait_ref.self_ty().has_trivial_sizedness(tcx, sizedness) {
+        if trait_pred.self_ty().has_trivial_sizedness(tcx, sizedness) {
             debug!("fast path -- trivial sizedness");
             return true;
         }