Auto merge of rust-lang#139288 - compiler-errors:folder-experiment-2, r=<try>

Folder experiment: Account for TypeFlags in OpportunisticRegionResolver

**NOTE:** This is one of a series of perf experiments that I've come up with while sick in bed. I'm assigning them to lqd b/c you're a good reviewer and you'll hopefully be awake when these experiments finish, lol.

r? lqd

The `OpportunisticRegionResolver` is hot, so let's avoid unnecessarily folding predicates. This will likey end up being a noop, so close this if it's perf neutral.

Author: bors

compiler/rustc_infer/src/infer/resolve.rs

@@ -107,6 +107,10 @@ impl<'a, 'tcx> TypeFolder<TyCtxt<'tcx>> for OpportunisticRegionResolver<'a, 'tcx
             ct.super_fold_with(self)
         }
     }
+
+    fn fold_predicate(&mut self, p: ty::Predicate<'tcx>) -> ty::Predicate<'tcx> {
+        if !p.has_infer_regions() { p } else { p.super_fold_with(self) }
+    }
 }
 
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