ChrisHegarty commented on PR #12311:
URL: https://github.com/apache/lucene/pull/12311#issuecomment-1557577587
@rmuir for the byte[] case, it seems to me that we want to size things so as
to optimise for the ShortVector preferred species, right? which is what you
seem to have done for a number of specific sizes - which I think it good. You
did ask if we could generalise this.
Based on the structure your latest commit, can we not just shape the stride
of the ByteVector based on the preferred ShortVector, e.g.
```
static final VectorSpecies<Byte> PREFERRED_BYTE_SPECIES =
ByteVector.SPECIES_MAX.withShape(VectorShape.forBitSize(ShortVector.SPECIES_PREFERRED.vectorBitSize()
>> 1));
@Benchmark
public int dotProductNewNew() {
int i = 0;
int res = 0;
// only vectorize if we'll at least enter the loop a single time
if (a.length >= ByteVector.SPECIES_64.length()) {
// optimized 256 bit implementation, processes 8 bytes at a time
int upperBound = PREFERRED_BYTE_SPECIES.loopBound(a.length);
IntVector acc1 = IntVector.zero(IntVector.SPECIES_PREFERRED);
IntVector acc2 = IntVector.zero(IntVector.SPECIES_PREFERRED);
for (; i < upperBound; i += PREFERRED_BYTE_SPECIES.length()) {
ByteVector va8 = ByteVector.fromArray(PREFERRED_BYTE_SPECIES, a,
i);
ByteVector vb8 = ByteVector.fromArray(PREFERRED_BYTE_SPECIES, b,
i);
Vector<Short> va16 = va8.convertShape(VectorOperators.B2S,
ShortVector.SPECIES_PREFERRED, 0);
Vector<Short> vb16 = vb8.convertShape(VectorOperators.B2S,
ShortVector.SPECIES_PREFERRED, 0);
Vector<Short> prod16 = va16.mul(vb16);
Vector<Integer> prod32_1 =
prod16.convertShape(VectorOperators.S2I, IntVector.SPECIES_PREFERRED, 0);
Vector<Integer> prod32_2 =
prod16.convertShape(VectorOperators.S2I, IntVector.SPECIES_PREFERRED, 1);
acc1 = acc1.add(prod32_1);
acc2 = acc2.add(prod32_2);
}
// reduce
res += acc1.add(acc2).reduceLanes(VectorOperators.ADD);
}
for (; i < a.length; i++) {
res += b[i] * a[i];
}
return res;
}
```
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