[vectorIntrinsics] RFR: 8281562:[vectorapi] Add support for popcount operation

[Paul Sandoz]

On Wed, 9 Feb 2022 22:41:36 GMT, Smita Kamath <svkamath at openjdk.org> wrote:

> 8281562:[vectorapi] Add support for popcount operation

src/hotspot/share/prims/vectorSupport.cpp line 482:

> 480:       break;
> 481:     }
> 482:     case VECTOR_OP_POPCNT: {

Can the fall through ever occur? since the operation is only supported for `int` and `long`.

src/jdk.incubator.vector/share/classes/jdk/incubator/vector/IntVector.java line 449:

> 447:     /*package-private*/
> 448:     @ForceInline
> 449:     static int popcount(int a) {

This method is not needed.

src/jdk.incubator.vector/share/classes/jdk/incubator/vector/IntVector.java line 1806:

> 1804:     @ForceInline
> 1805:     public final
> 1806:     IntVector popcnt() {

I recommend not adding such a specific lanewise method for now, and let users use the operation directly.

src/jdk.incubator.vector/share/classes/jdk/incubator/vector/LongVector.java line 449:

> 447:     /*package-private*/
> 448:     @ForceInline
> 449:     static int popcount(long a) {

Method is unnecessary.

src/jdk.incubator.vector/share/classes/jdk/incubator/vector/VectorOperators.java line 454:

> 452:     public static final Unary NEG = unary("NEG", "-a", VectorSupport.VECTOR_OP_NEG, VO_ALL|VO_SPECIAL);
> 453:     /** Produce {@code bitCount(a)} */
> 454:     public static final Unary POPCNT = unary("POPCNT", "popcnt", VectorSupport.VECTOR_OP_POPCNT, VO_NOFP);

Suggest we rename to BIT_COUNT, so its the same as the method on `Integer` and `Long`. LIkewise for the internal opcode VECTOR_OP_POPCNT -> VECTOR_OP_BIT_COUNT.

test/jdk/jdk/incubator/vector/PopcountUnitTest.java line 39:

> 37: import java.util.stream.IntStream;
> 38: 
> 39: public class PopcountUnitTest {

You should replace this test by adding a bitcount test to test framework.

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PR: https://git.openjdk.java.net/panama-vector/pull/173