RFR: 8319408: RISC-V: MaxVectorSize is not consistently checked in several situations [v2]

[Hamlin Li]

> Hi,
> Can you review the change to fix the MaxVectorSize checking in vm_version_riscv.cpp?
> 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.

Hamlin Li has updated the pull request incrementally with one additional commit since the last revision:

  Refine log

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/16498/files
  - new: https://git.openjdk.org/jdk/pull/16498/files/06945065..19dc28fd

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=16498&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=16498&range=00-01

  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 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