RFR: 8280579: Shenandoah: Skip regions in the back of sorted array when choosing cset [v3]

[Yude Lin]

> Can I have review on this small change that skips some unnecessary work in cset choosing?
> 
> When choosing regions to add to cset, we sort the regions from most garbage to least garbage. We then iterate the sorted array. We can break early from the loop if we find a region with (garbage <= garbage_threshold). Because we know the regions left won't have enough garbage and won't be added anyway.

Yude Lin has refreshed the contents of this pull request, and previous commits have been removed. The incremental views will show differences compared to the previous content of the PR. The pull request contains one new commit since the last revision:

  8280579: Shenandoah: Skip regions in the back of sorted array when choosing cset

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Changes:
  - all: https://git.openjdk.java.net/jdk/pull/7211/files
  - new: https://git.openjdk.java.net/jdk/pull/7211/files/cfa75958..6aebfea6

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=7211&range=02
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=7211&range=01-02

  Stats: 9 lines in 1 file changed: 5 ins; 0 del; 4 mod
  Patch: https://git.openjdk.java.net/jdk/pull/7211.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/7211/head:pull/7211

PR: https://git.openjdk.java.net/jdk/pull/7211