RFR: 8304759: Add BitMap iterators [v2]

[Kim Barrett]

On Wed, 29 Mar 2023 09:31:40 GMT, Axel Boldt-Christmas <aboldtch at openjdk.org> wrote:

>> src/hotspot/share/utilities/bitMap.hpp line 420:
>> 
>>> 418:   // Returns the index of the last set bit in the remaining iteration range.
>>> 419:   // precondition: !is_empty()
>>> 420:   idx_t last() const;
>> 
>> The comments for `first()` and `last()` are a little misleading. The invariant that the `first()`/`last()` is a set bit is only true for `first()` in the forward iterator and for `last()` in the reverse iterator. 
>> 
>> It seems more like a contract that if you use `first()` then you must have created `IteratorImpl(const BitMap* map, idx_t beg, idx_t end)` with `beg` being a set bit. And if you use `last()` then you must have created it with `end-1` being a set bit.
>
> Or `beg == end`, that is an `is_empty()` Iterator

Yes, you are correct.  Some of the comments for IteratorImpl didn't get properly updated.  I'll clean that up.

-------------

PR Review Comment: https://git.openjdk.org/jdk/pull/13184#discussion_r1152186946