RFR: 8287289: Gather/Scatter with Index Vector [v3]

[Xiaohong Gong]

On Sat, 8 Apr 2023 13:49:57 GMT, Quan Anh Mai <qamai at openjdk.org> wrote:

>> Hi,
>> 
>> This patch implements gather/scatter operations using an index vector in the form of an `IntVector` or a `LongVector` on arrays. According to the rationales in the [original PR](https://github.com/openjdk/panama-vector/pull/201), gathering/scattering using a vector is more flexible and can be used to implement the original interface of using an index array easily. Furthermore, 64-bit indexing is necessary for operating on `MemorySegment`s in the future, which can span a larger-than-4GiB space.
>> 
>> Please take a look and leave reviews.
>> Thanks a lot.
>
> Quan Anh Mai has updated the pull request incrementally with two additional commits since the last revision:
> 
>  - remove memory segment support
>  - load store from memory segment

test/hotspot/jtreg/compiler/vectorapi/VectorGatherScatterTest.java line 45:

> 43:  * @key randomness
> 44:  * @library /test/lib /
> 45:  * @requires vm.cpu.features ~= ".*sve.*" & (vm.opt.MaxVectorSize == "null" | vm.opt.MaxVectorSize >= 16)

We have to make sure this test is run with "MaxVectorSize >= 16", or following code will throw exception due to no vector shape maps (e.g. `32-bit/8-byte`):

 private static final VectorSpecies<Float> F_SPECIES =
            VectorSpecies.of(float.class, VectorShape.forBitSize(L_SPECIES.vectorBitSize() / 2));

We added the this requirement in case people run the tests with "-XX:MaxVectorSize=8".

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PR Review Comment: https://git.openjdk.org/panama-vector/pull/213#discussion_r1162244044