RFR: 8278949: Cleanups for 8277850 [v2]

[Roland Westrelin]

> When 8277850 (C2: optimize mask checks in counted loops) was reviewed,
> John made a number of comments and suggestions after the change was
> integrated. This change includes all of his comments, extra tests to
> cover all cases. I also moved the AndIL_add_shift_and_mask() call in
> AndXNode::Ideal() up so the expression with a non constant mask can be
> optimized as well.

Roland Westrelin 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 four additional commits since the last revision:

 - renaming AndIL_shift_and_mask -> AndIL_shift_and_mask_is_always_zero
 - Merge branch 'master' into JDK-8278949
 - whitespaces
 - John's comments

-------------

Changes:
  - all: https://git.openjdk.java.net/jdk/pull/6876/files
  - new: https://git.openjdk.java.net/jdk/pull/6876/files/45dab951..e2933fac

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=6876&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=6876&range=00-01

  Stats: 6073 lines in 233 files changed: 2747 ins; 2337 del; 989 mod
  Patch: https://git.openjdk.java.net/jdk/pull/6876.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/6876/head:pull/6876

PR: https://git.openjdk.java.net/jdk/pull/6876