code review 7722046: runtime: allocate first bucket table lazily

src/pkg/runtime/map_test.go

 // Copyright 2013 The Go Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
 package runtime_test
 
 import (
         "fmt"
         "math"
         "runtime"
@@ skipping 262 matching lines @@
         b[empty{}] = 1
         c[empty{}] = empty{}
 
         if len(a) != 1 {
                 t.Errorf("empty value insert problem")
         }
         if b[empty{}] != 1 {
                 t.Errorf("empty key returned wrong value")
         }
 }
+
+func BenchmarkNewEmptyMap(b *testing.B) {
+        b.ReportAllocs()
+        for i := 0; i < b.N; i++ {
+                _ = make(map[int]int)
+        }
+}