RFR: 8214761: Bug in parallel Kahan summation implementation [v4]

[Ian Graves]

> 8214761: Bug in parallel Kahan summation implementation

Ian Graves has updated the pull request incrementally with one additional commit since the last revision:

  Fixing compensation test

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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/905450d8..722826fc

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=4674&range=03
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=4674&range=02-03

  Stats: 13 lines in 1 file changed: 5 ins; 4 del; 4 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