RFR: 8262096: Vector API fails to work due to VectorShape initialization exception [v3]

[Jie Fu]

> Hi all,
> 
> Vector API fails to work when:
>  - case 1: MaxVectorSize is set to <=8, or
>  - case 2: C2 is disabled
> 
> The reason is that {max/preferred} VectorShape initialization fails in both cases.
> And the root cause is that VectorSupport_GetMaxLaneCount [1] returns unreasonable values (0 for case 1 and -1 for case 2).
> 
> Vector API should not depend on C2 to run.
> It should work even there is no JIT compiler since it's a Java-level api.
> So let's fix it.
> 
> Testing:
>   - jdk/incubator/vector with -XX:MaxVectorSize=default/8 on Linux/x64
> 
> Thanks.
> Best regards,
> Jie
> 
> [1] https://github.com/openjdk/jdk/blob/master/src/hotspot/share/prims/vectorSupport.cpp#L364

Jie Fu has updated the pull request incrementally with one additional commit since the last revision:

  Update the jtreg test

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

Changes:
  - all: https://git.openjdk.java.net/jdk/pull/2722/files
  - new: https://git.openjdk.java.net/jdk/pull/2722/files/724b36d4..aa475b0a

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=2722&range=02
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=2722&range=01-02

  Stats: 59 lines in 2 files changed: 10 ins; 48 del; 1 mod
  Patch: https://git.openjdk.java.net/jdk/pull/2722.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/2722/head:pull/2722

PR: https://git.openjdk.java.net/jdk/pull/2722