RFR: 8188046: java.lang.Math.mutliplyHigh does not run in constant time

[Brian Burkhalter]

Please consider this proposal to remove the fast path in `java.lang.Math.multiplyHigh()` the small performance improvement of which is eclipsed by the branch penalty.

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Commit messages:
 - 8188046: java.lang.Math.mutliplyHigh does not run in constant time

Changes: https://git.openjdk.java.net/jdk/pull/4660/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=4660&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8188046
  Stats: 25 lines in 1 file changed: 0 ins; 11 del; 14 mod
  Patch: https://git.openjdk.java.net/jdk/pull/4660.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/4660/head:pull/4660

PR: https://git.openjdk.java.net/jdk/pull/4660