Vector API Questions

[John Rose]

I think those are hardware specialized shuffles, right? So try a shuffle. We should try to recognize fixed shuffles that can be handled by special instructions. That’s the basic approach. It doesn’t need a new primitive but maybe some convenience functions and better instruction selection. 

> On Sep 5, 2021, at 1:09 PM, Scott Palmer <swpalmer at gmail.com> wrote:
> 
> Is this list appropriate for questions involving the Vector API?  (I scanned the list at https://mail.openjdk.java.net/mailman/listinfo but didn’t see anything)
> 
> E.g. questions such as, 
> 
> Are there plans to support operation XXX?  
> 
> I’m looking for something like: https://www.felixcloutier.com/x86/punpcklbw:punpcklwd:punpckldq:punpcklqdq
> 
> Or performance related queries?
> 
> I tried to convert this simple operation to use the Vector API (on 2MB source buffers) and the result iI got was 15x slower than this byte-wise loop:
> 
>     void widen(ByteBuffer srcBuff , ByteBuffer dstBuff ) {
>            while (srcBuff.hasRemaining()) {
>                dstBuff.putShort((short) (srcBuff.get() << 8));
>            }
>    }
> 
> 
> My attempt using JDK 16 on macOS (Intel) looked like:
> 
>    final int BYTE_PREFERRED_SPECIES_LENGTH = ByteVector.SPECIES_PREFERRED.length();
>    final int loopBound = ByteVector.SPECIES_PREFERRED.loopBound(srcBuff.remaining());
>    int si = 0;
>    int di = 0;
>    for (; si < loopBound; si += BYTE_PREFERRED_SPECIES_LENGTH) {
>                ByteVector srcVec = ByteVector.fromByteBuffer(ByteVector.SPECIES_PREFERRED, srcBuff, si, NATIVE_ORDER);
>                srcVec.convert(VectorOperators.B2S, 0)
>                        .lanewise(VectorOperators.LSHL, 8)
>                        .intoByteBuffer(dstBuff, di, NATIVE_ORDER);
>                di += BYTE_PREFERRED_SPECIES_LENGTH;
> 
>                srcVec.convert(VectorOperators.B2S, 1)
>                        .lanewise(VectorOperators.LSHL, 8)
>                        .intoByteBuffer(dstBuff, PD_di, NATIVE_ORDER);
>                di += BYTE_PREFERRED_SPECIES_LENGTH;
>    }
> 
> If this is the wrong place for these kinds of questions, please point me in the right direction.
> 
> Thanks,
> 
> Scott