RFR: 8251322: Improve BitMap::iterate

[David Holmes]

Hi Kim,

On 9/08/2020 5:44 pm, Kim Barrett wrote:
> Please review this improvement to BitMap::iterate.  The code is both
> simplified and made more performant by using get_next_one_bit to scan
> the bitmap.  Making it inline may allow the compiler to devirtualize
> and possibly inline the closure invocation.  These changes result in
> some configurations executing ~1M fewer instructions during startup.
> 
> CR:
> https://bugs.openjdk.java.net/browse/JDK-8251322
> 
> Webrev:
> https://cr.openjdk.java.net/~kbarrett/8251322/open.00/

The new code looks much clearer and simpler! Only one minor comment.
The old code clearly documents the range as being right-open, whereas this:

// Iteration support.  Applies the closure to the index for each set bit,
// starting from the least index in the range to the greatest, in order.

does not clearly state so.

Thanks,
David
-----

> Testing:
> mach5 tier1-3.
> Used Linux-x64 perf on java -version to examine startup impact.
> 
>