RFR: 8324573: HashMap::putAll should resize to sum of both map sizes [v3]

[Joshua Cao]

On Fri, 2 Feb 2024 04:51:33 GMT, jmehrens <duke at openjdk.org> wrote:

> Circling back to "the case where many keys exist in both maps". What are your thoughts on some optimized variant/refactoring of:
int s = Math.max(m.size() - this.size(), 1);

Calling `Math.max` is unnecessary here. Its ok if `s` ends up non-positive, presizing would become a no-op in that case.

I don't understand why there is a subtraction. If `m` is a larger map than `this`, and has all of `this`'s keys, the resulting map will have the same size as `m`. In this case, we should just presize to `m.size()`.

> Also, are we sure it is wise to actually call m.size() when we don't know the runtime of the size operation on the given map? 

Not sure, but the current code already calls `m.size()`. I can create a `int msize = m.size()` so we only call it once.

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PR Review Comment: https://git.openjdk.org/jdk/pull/17544#discussion_r1475575700