RFR: 8267332: xor value should handle bounded values

[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

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Commit messages:
 - fix xor value

Changes: https://git.openjdk.java.net/jdk/pull/4136/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=4136&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8267332
  Stats: 165 lines in 2 files changed: 165 ins; 0 del; 0 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