RFR: 8262508: Vector API's ergonomics is incorrect

[Jie Fu]

Hi all,

The ergonomics (e.g., EnableVectorReboxing/EnableVectorAggressiveReboxing) for Vector API doesn't work as expected.

There are two sets of rules for Vector API.
One is in Arguments::apply_ergo() [1], which sets the flags to be false.
And the other is in Modules::define_module() [2], which sets the flags to be true.

The value of EnableVectorReboxing and EnableVectorAggressiveReboxing may be changed (from specified true to false) in [1] if EnableVectorSupport=false (which is the default value).
It would be wrong when EnableVectorSupport isn't specified in the command line since it will be set true later in [2]
So rules in [1] should not be executed if EnableVectorSupport isn't specified.

Thanks.
Best regards,
Jie

[1] https://github.com/openjdk/jdk/blob/master/src/hotspot/share/runtime/arguments.cpp#L4081
[2] https://github.com/openjdk/jdk/blob/master/src/hotspot/share/classfile/modules.cpp#L462

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Commit messages:
 - 8262508: Vector API's ergonomics is incorrect

Changes: https://git.openjdk.java.net/jdk/pull/2771/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=2771&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8262508
  Stats: 82 lines in 2 files changed: 81 ins; 0 del; 1 mod
  Patch: https://git.openjdk.java.net/jdk/pull/2771.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/2771/head:pull/2771

PR: https://git.openjdk.java.net/jdk/pull/2771