Push to result vector instead of allocating

Co-authored-by: lcnr <bastian_kauschke@hotmail.de>

compiler/rustc_metadata/src/rmeta/decoder/cstore_impl.rs

@@ -415,7 +415,7 @@ pub fn load_macro_untracked(&self, id: DefId, sess: &Session) -> LoadedMacro {
 
         let span = data.get_span(id.index, sess);
 
-        let attrs: Vec<_> = data.get_item_attrs(id.index, sess).collect();
+        let attrs = data.get_item_attrs(id.index, sess).collect();
 
         let ident = data.item_ident(id.index, sess);
 

compiler/rustc_trait_selection/src/traits/select/candidate_assembly.rs

@@ -353,16 +353,13 @@ fn assemble_candidates_from_caller_bounds<'o>(
             all_bounds.filter(|p| p.def_id() == stack.obligation.predicate.def_id());
 
         // Keep only those bounds which may apply, and propagate overflow if it occurs.
-        let mut param_candidates = vec![];
         for bound in matching_bounds {
             let wc = self.evaluate_where_clause(stack, bound)?;
             if wc.may_apply() {
-                param_candidates.push(ParamCandidate(bound));
+                candidates.vec.push(ParamCandidate(bound));
             }
         }
 
-        candidates.vec.extend(param_candidates);
-
         Ok(())
     }