RFR: 8319408: RISC-V: MaxVectorSize is not consistently checked in several situations

[Hamlin Li]

Hi,
Can you review the change to add intrinsic for CmpU3 and CmpUL3?
Thanks!

Current logic will not check whether (MaxVectorSize < 16), after the assignment `MaxVectorSize = _initial_vector_length;`, in following situation.
a) if FLAG_IS_DEFAULT(MaxVectorSize) == true
b) if FLAG_IS_DEFAULT(MaxVectorSize) == false and (MaxVectorSize >= 16) and is_power_of_2(MaxVectorSize) and (MaxVectorSize > _initial_vector_length)

And in original code, the logic is not consistent for the situations between MaxVectorSize < 16 and MaxVectorSize >= 16, when is_power_of_2(MaxVectorSize) == false; for the former (<16) it's to disable RVV, for the latter (>=16) it's vm_exit.

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Commit messages:
 - Initial commit

Changes: https://git.openjdk.org/jdk/pull/16498/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=16498&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8319408
  Stats: 16 lines in 1 file changed: 7 ins; 7 del; 2 mod
  Patch: https://git.openjdk.org/jdk/pull/16498.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/16498/head:pull/16498

PR: https://git.openjdk.org/jdk/pull/16498