RFR: 8214761: Bug in parallel Kahan summation implementation [v3]

[Ian Graves]

> 8214761: Bug in parallel Kahan summation implementation

Ian Graves has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains six additional commits since the last revision:

 - Changing some comments.
 - Merge branch 'master' into kahan-summation-bug
 - Updates with more test coverage
 - stashing
 - Stashing
 - 8214761: Bug in parallel Kahan summation implementation

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Changes:
  - all: https://git.openjdk.java.net/jdk/pull/4674/files
  - new: https://git.openjdk.java.net/jdk/pull/4674/files/10b8dcda..905450d8

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=4674&range=02
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=4674&range=01-02

  Stats: 107423 lines in 2079 files changed: 73519 ins; 22961 del; 10943 mod
  Patch: https://git.openjdk.java.net/jdk/pull/4674.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/4674/head:pull/4674

PR: https://git.openjdk.java.net/jdk/pull/4674