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

[Jatin Bhateja]

On Mon, 16 Oct 2023 01:37:47 GMT, Xiaohong Gong <xgong at openjdk.org> wrote:

>> Jatin Bhateja has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   Review comments resolutions.
>
> 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>

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PR Review Comment: https://git.openjdk.org/valhalla/pull/931#discussion_r1360212953