RFR: 8267332: xor value should handle bounded values [v6]

[Nils Eliasson]

> In the discussion of https://github.com/openjdk/jdk/pull/3938 a limitation in C2 was found. C2 fails to eliminate obvious bound checks for indexes that are masked with xor.
> 
> The Xor for two values that have a lower bound of zero or more, the resulting lower bound is zero.
> The Xor for two values that have a upperbound above zero, the resulting upper bound is the max of the next_power_of_2-1.
> 
> Test supplied. 
> 
> Please review,
> Best regards,
> Nils Eliasson

Nils Eliasson 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 six additional commits since the last revision:

 - Merge branch 'master' into xor_bound
 - Removed unnecessary check
 - Updated test, fixed bound
 - fixed missing test case
 - Fix bounds check
 - fix xor value

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

Changes:
  - all: https://git.openjdk.java.net/jdk/pull/4136/files
  - new: https://git.openjdk.java.net/jdk/pull/4136/files/9be3b003..c3a3a612

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=4136&range=05
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=4136&range=04-05

  Stats: 4915 lines in 203 files changed: 2431 ins; 2058 del; 426 mod
  Patch: https://git.openjdk.java.net/jdk/pull/4136.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/4136/head:pull/4136

PR: https://git.openjdk.java.net/jdk/pull/4136