On Fri, 27 Oct 2023 05:09:15 GMT, Jatin Bhateja <jbhat...@openjdk.org> wrote:
>> src/jdk.incubator.vector/share/classes/jdk/incubator/vector/ByteVector.java
>> line 3062:
>>
>>> 3060: // Constant folding should sweep out following conditonal
>>> logic.
>>> 3061: if (isp.length() > IntVector.SPECIES_PREFERRED.length()) {
>>> 3062: lsp = IntVector.SPECIES_PREFERRED;
>>
>> What happens if the needed index vector length is larger that the max vector
>> length of int type?
>> For example, byte vectors with `SPECIES_128`, may needs an index vector with
>> `IntVector.SPECIES_512` species? And on some architectures like NEON, or SVE
>> with 128-bit max vector size, the preferred species is only `SPECIES_128`.
>
> For x86 backend implementation we emit a gather loop hence index species is
> not used for sub-word, I am performing the index out of bound in a loop which
> operate a max integer vector granularity supported by target.
> https://github.com/openjdk/jdk/pull/16354/files#diff-13cc2d6ec18e487ddae05cda671bdb6bb7ffd42ff7bc51a2e00c8c5e622bd55dR3641
>
> Because there is cap on max integral vector size, thus for targets supporting
> direct sub-word gather instruction will have to emit an instruction sequence
> comprising of partial indexMap loads into integral vectors and issue multiple
> gather operations.
I see, thanks for the explanation! It's different from SVE, which the index
should be an int vector with the same length of the target vector. We have to
generate the index vectors. So the array length check to the given index map is
necessary in java side.
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PR Review Comment: https://git.openjdk.org/jdk/pull/16354#discussion_r1374215257
