FULL PRODUCT VERSION :
java version "9"
Java(TM) SE Runtime Environment (build 9+180)
Java HotSpot(TM) 64-Bit Server VM (build 9+180, mixed mode)
And all version before

ADDITIONAL OS VERSION INFORMATION :
mac os sierra 10.12.6 (16G29)

A DESCRIPTION OF THE PROBLEM :
java.util.HashMap , method
this "if statement" (code line: near 770 in jdk 9+180)
 if ((tab[index] = hd) != null)
                hd.treeify(tab);

 not need here:

final void treeifyBin(Node<K,V>[] tab, int hash) {
        int n, index; Node<K,V> e;
        if (tab == null || (n = tab.length) < MIN_TREEIFY_CAPACITY)
            resize();
        else if ((e = tab[index = (n - 1) & hash]) != null) {
            TreeNode<K,V> hd = null, tl = null;
            do {
                TreeNode<K,V> p = replacementTreeNode(e, null);
                if (tl == null)
                    hd = p;
                else {
                    p.prev = tl;
                    tl.next = p;
                }
                tl = p;
            } while ((e = e.next) != null);
            if ((tab[index] = hd) != null)
                hd.treeify(tab);
        }
    }

STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
read the code

EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
read the code
ACTUAL -
read the code

REPRODUCIBILITY :
This bug can be reproduced always.