rustc/middle: improve allocations

src/librustc/middle/liveness.rs

@@ -474,13 +474,15 @@ fn visit_expr<'a, 'tcx>(ir: &mut IrMaps<'a, 'tcx>, expr: &'tcx Expr) {
         // construction site.
         let mut call_caps = Vec::new();
         ir.tcx.with_freevars(expr.id, |freevars| {
-            for fv in freevars {
+            call_caps.extend(freevars.iter().filter_map(|fv| {
                 if let Def::Local(rv) = fv.def {
                     let fv_ln = ir.add_live_node(FreeVarNode(fv.span));
                     let var_hid = ir.tcx.hir.node_to_hir_id(rv);
-                    call_caps.push(CaptureInfo { ln: fv_ln, var_hid });
+                    Some(CaptureInfo { ln: fv_ln, var_hid })
+                } else {
+                    None
                 }
-            }
+            }));
         });
         ir.set_captures(expr.id, call_caps);
 

src/librustc/middle/reachable.rs

@@ -371,7 +371,9 @@ impl<'a, 'tcx: 'a> ItemLikeVisitor<'tcx> for CollectPrivateImplItemsVisitor<'a,
                     return
                 }
 
-                for default_method in self.tcx.provided_trait_methods(trait_def_id) {
+                let provided_trait_methods = self.tcx.provided_trait_methods(trait_def_id);
+                self.worklist.reserve(provided_trait_methods.len());
+                for default_method in provided_trait_methods {
                     let node_id = self.tcx
                                       .hir
                                       .as_local_node_id(default_method.def_id)