RFR: 8262096: Vector API fails to work due to VectorShape initialization exception [v5]

[Vladimir Ivanov]

On Sat, 27 Feb 2021 03:23:12 GMT, Jie Fu <jiefu at openjdk.org> wrote:

>> 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 with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains seven additional commits since the last revision:
> 
>  - Fix in jdk/incubator/vector/VectorShape.java
>  - Merge branch 'master' into JDK-8262096
>  - Revert changes
>  - Remove -XX:TieredStopAtLevel=3
>  - Update the jtreg test
>  - The numerator should be 8 (byte)
>  - 8262096: Vector API fails to work due to VectorShape initialization exception

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

Sounds reasonable.

test/jdk/jdk/incubator/vector/PreferredSpeciesTest.java line 42:

> 40:  * @modules jdk.incubator.vector java.base/jdk.internal.vm.vector
> 41:  * @run testng/othervm -XX:MaxVectorSize=8 PreferredSpeciesTest
> 42:  * @run testng/othervm -XX:MaxVectorSize=4 PreferredSpeciesTest

`-XX:MaxVectorSize` is C2-specific. It's better to specify either `-XX:-IgnoreUnrecognizedVMOptions` or `@requires vm.compiler2.enabled`.

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Marked as reviewed by vlivanov (Reviewer).

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