RFR: 8257221: C2: RegMask::is_bound_set split set handling broken since JDK-8221404 [v3]

[Claes Redestad]

> This patch adds more tests for RegMask::is_bound* operations, and fixes a bug I introduced in JDK-8221404 where I mixed up the formula for how much we need to shift the "bit" when checking a split set.

Claes Redestad 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 eight additional commits since the last revision:

 - Merge branch 'master' into regmask_bound
 - Clean-up is_bound_set test
 - Split out the optimization
 - Add is_bound_set test, fix bug caused by 8221404
 - Add is_bound_pair test, remove redundant test in else branch, fix accidentally 32-bit uint bit
 - Merge branch 'master' into regmask_bound
 - Merge branch 'master' into regmask_bound
 - C2: Optimize is_bound

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Changes:
  - all: https://git.openjdk.java.net/jdk/pull/1486/files
  - new: https://git.openjdk.java.net/jdk/pull/1486/files/2937939d..6980ee00

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=1486&range=02
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=1486&range=01-02

  Stats: 4859 lines in 111 files changed: 2274 ins; 1906 del; 679 mod
  Patch: https://git.openjdk.java.net/jdk/pull/1486.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/1486/head:pull/1486

PR: https://git.openjdk.java.net/jdk/pull/1486