RFR: 8262096: Vector API fails to work due to VectorShape initialization exception [v4]

[Jie Fu]

On Fri, 26 Feb 2021 15:48:18 GMT, Vladimir Ivanov <vlivanov at openjdk.org> wrote:

> > I'd like to keep DoubleVector.SPECIES_PREFERRED.length() <= VectorSupport.getMaxLaneCount(double.class) for Java programmers since the VectorSupport_GetMaxLaneCount is used to implement a Java API.
> 
> It doesn't make much sense to me. `VectorSupport` is an internal API for `jdk.incubator.vector` to consume.
> It's `jdk.incubator.vector` job to interpret the result and adapt accordingly.

Okay, I'm fine to fix it in jdk/incubator/vector/VectorShape.java if we don't keep something like that.

For the updated fix, the {max/preferred} shape will be initialized as shape-64-bit if hotspot doesn't support vectorization.

Testing:
  - jdk/incubator/vector with MaxVectorSize=default/8/4 on Linux/x64 
  - jdk/incubator/vector without C2 on Linux/x64

Any comments?
Thanks.

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