RFR: 8277239: SIGSEGV in vrshift_reg_maskedNode::emit

[Jatin Bhateja]

Currently instruction selector differentiates between the two kinds of vector shift operations i.e. one with vector shift count and other with scalar shift count passed though LShiftCntV/RShiftCntV nodes by looking at the ideal opcode of shift count node.

A more robust scheme is to set a flag over vector shift node if it has variable vector shift count and replace the opcode based check with flag based check in various shift instruction selection patterns.

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Commit messages:
 - 8277239: SIGSEGV in vrshift_reg_maskedNode::emit

Changes: https://git.openjdk.java.net/jdk/pull/6431/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=6431&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8277239
  Stats: 134 lines in 5 files changed: 73 ins; 3 del; 58 mod
  Patch: https://git.openjdk.java.net/jdk/pull/6431.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/6431/head:pull/6431

PR: https://git.openjdk.java.net/jdk/pull/6431