RFR: 8251322: Improve BitMap::iterate

[Kim Barrett]

> On Aug 9, 2020, at 5:26 AM, Thomas Stüfe <thomas.stuefe at gmail.com> wrote:
> 
> Hi Kim,
> 
> LGTM

Thanks.

> 
> ..Thomas
> 
> On Sun, Aug 9, 2020 at 9:46 AM Kim Barrett <kim.barrett at oracle.com> 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/
> 
> Testing:
> mach5 tier1-3.
> Used Linux-x64 perf on java -version to examine startup impact.