RFR: 8281631: HashMap copy constructor and putAll can over-allocate table [v21]

[XenoAmess]

On Sun, 20 Feb 2022 18:04:50 GMT, XenoAmess <duke at openjdk.java.net> wrote:

>> 8281631: HashMap copy constructor and putAll can over-allocate table
>
> XenoAmess has updated the pull request incrementally with three additional commits since the last revision:
> 
>  - refine test
>  - 1. optimize IdentityHashMap that when calling ::new(Map), do not call map.size() twice but once.
>    2. delete the this((int) ((1 + m.size()) * 1.1)); as it makes the table over-allocate when size = 19.
>  - refine test

src/java.base/share/classes/java/util/IdentityHashMap.java line 270:

> 268:      */
> 269:     public IdentityHashMap(Map<? extends K, ? extends V> m) {
> 270:         this(m, m.size());

I actually do not know if this change shall be in this pr, or in a new issue.
But the original codes can cause IdentityHashMap to over-allocate at size == 19.
@stuart-marks what do you think about this?

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PR: https://git.openjdk.java.net/jdk/pull/7431