[lworld+vector] RFR: 8311675: [lworld+vector] Max Species support. [v3]

[Xiaohong Gong]

On Mon, 16 Oct 2023 07:15:14 GMT, Jatin Bhateja <jbhateja at openjdk.org> wrote:

>> src/hotspot/cpu/x86/vm_version_x86.cpp line 3257:
>> 
>>> 3255:   default:
>>> 3256:     assert(false, "Unexpected basic type");
>>> 3257:   }
>> 
>> If the return value is 0, what is the actual number of the multifields in payload? It seems not reasonable for `0`. WDYT?
>
> For x86 this leaf level routine is directly imported from Matcher.  _Matcher::max_vector_size_ will query it to get maximum vector size supported by a target. Agree that it needs to be tuned.
> 
> BTW I also see a discrepancy b/w lane count and max vector size for MaxSpecies in existing implementation.
> 
> 
> LPROMPT>cat test_max.java 
> 
> import jdk.incubator.vector.*;
> 
> public class test_max {
>    public static void main(String [] args) {
>       System.out.println(ByteVector.SPECIES_MAX);
>       System.out.println(ByteVector.broadcast(ByteVector.SPECIES_MAX, 1));
>    }
> } 
> LPROMPT>java -XX:MaxVectorSize=0 --add-modules=jdk.incubator.vector -XX:+PrintFlagsFinal -cp . test_max.java  | grep -e "MaxVectorSize"  -e "Species" -e "["
> OpenJDK 64-Bit Server VM warning: MaxVectorSize must be at least 4 on this platform
> [Global flags]
>      intx MaxVectorSize                            = 4                                      {C2 product} {command line}
> WARNING: Using incubator modules: jdk.incubator.vector
> warning: using incubating module(s): jdk.incubator.vector
> 1 warning
> Species[byte, 8, S_Max_BIT]
> [1, 1, 1, 1, 1, 1, 1, 1]
> LPROMPT>

Yes, it seems werid. I think it is because the min operation with 64-bit shape in java code. Please see my following comments.

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PR Review Comment: https://git.openjdk.org/valhalla/pull/931#discussion_r1360219456