Rollup merge of #143307 - compiler-errors:fast-path-nitpicks, r=lcnr

Fast path nitpicks

Miscellaneous commits that I didn't really want to fold into anything else.

Fixes one theoretical bug with the fast path not considering polarity for `T: !Sized` bounds.

2 files changed, 6 insertions, 15 deletions

diff --git a/compiler/rustc_trait_selection/src/traits/query/type_op/prove_predicate.rs b/compiler/rustc_trait_selection/src/traits/query/type_op/prove_predicate.rs
index 18971c47831..22eeb285b37 100644
--- a/compiler/rustc_trait_selection/src/traits/query/type_op/prove_predicate.rs
+++ b/compiler/rustc_trait_selection/src/traits/query/type_op/prove_predicate.rs
@@ -21,19 +21,9 @@ impl<'tcx> super::QueryTypeOp<'tcx> for ProvePredicate<'tcx> {
 
         if let ty::PredicateKind::Clause(ty::ClauseKind::WellFormed(term)) =
             key.value.predicate.kind().skip_binder()
+            && term.is_trivially_wf(tcx)
         {
-            match term.as_type()?.kind() {
-                ty::Param(_)
-                | ty::Bool
-                | ty::Char
-                | ty::Int(_)
-                | ty::Float(_)
-                | ty::Str
-                | ty::Uint(_) => {
-                    return Some(());
-                }
-                _ => {}
-            }
+            return Some(());
         }
 
         None
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;
         }