RFR: 8278868: Add x86 vectorization support for Long.bitCount() [v7]

[Vamsi Parasa]

> Vectorization support of Integer.bitCount() already exists but currently the same support is lacking for Long.bitCount(). Similar to the C2 PopCountVI node, we created a C2 PopCountVL node and used vpopcntq x86 instruction to enable vectorized Long.bitCount(). This patch shows 2.57x improvement in performance on a JMH micro benchmark due to x86 vectorization.

Vamsi Parasa 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 seven additional commits since the last revision:

 - Merge branch 'master' of https://git.openjdk.java.net/jdk into vlong
 - Update IR framework test to check for non-zero count of PopCountVL
 - Update year in copyright notice. Add avx512dq check for vectorization test
 - Update popcount long test to use IR framework
 - Use generic vector node names
 - Add JMH micro benchmark to measure performance
 - 8278868:Add x86 vectorization support for Long.bitCount()

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Changes:
  - all: https://git.openjdk.java.net/jdk/pull/6857/files
  - new: https://git.openjdk.java.net/jdk/pull/6857/files/8cd298b6..d8b3cedd

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=6857&range=06
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=6857&range=05-06

  Stats: 12922 lines in 484 files changed: 9523 ins; 1562 del; 1837 mod
  Patch: https://git.openjdk.java.net/jdk/pull/6857.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/6857/head:pull/6857

PR: https://git.openjdk.java.net/jdk/pull/6857