Rollup merge of #101690 - kadiwa4:avoid_iterator_last, r=oli-obk

Avoid `Iterator::last`

Adapters like `Filter` and `Map` use the default implementation of `Iterator::last` which is not short-circuiting (and so does `core::str::Split`). The predicate function will be run for every single item of the underlying iterator. I hope that removing those calls to `last` results in slight performance improvements.

compiler/rustc_hir/src/hir.rs

@@ -576,8 +576,7 @@ impl<'hir> Generics<'hir> {
         if self.has_where_clause_predicates {
             self.predicates
                 .iter()
-                .filter(|p| p.in_where_clause())
-                .last()
+                .rfind(|&p| p.in_where_clause())
                 .map_or(end, |p| p.span())
                 .shrink_to_hi()
                 .to(end)