RFR: 8293409: [vectorapi] Intrinsify VectorSupport.indexVector

[Xiaohong Gong]

On Thu, 13 Oct 2022 07:18:24 GMT, Jatin Bhateja <jbhateja at openjdk.org> wrote:

>> "`VectorSupport.indexVector()`" is used to compute a vector that contains the index values based on a given vector and a scale value (`i.e. index = vec + iota * scale`). This function is widely used in other APIs like "`VectorMask.indexInRange`" which is useful to the tail loop vectorization. And it can be easily implemented with the vector instructions.
>> 
>> This patch adds the vector intrinsic implementation of it. The steps are:
>> 
>>   1) Load the const "iota" vector.
>> 
>>   We extend the "`vector_iota_indices`" stubs from byte to other integral types. For floating point vectors, it needs an additional vector cast to get the right iota values.
>> 
>>   2) Compute indexes with "`vec + iota * scale`"
>> 
>> Here is the performance result to the new added micro benchmark on ARM NEON:
>> 
>> Benchmark                              Gain
>> IndexVectorBenchmark.byteIndexVector   1.477
>> IndexVectorBenchmark.doubleIndexVector 5.031
>> IndexVectorBenchmark.floatIndexVector  5.342
>> IndexVectorBenchmark.intIndexVector    5.529
>> IndexVectorBenchmark.longIndexVector   3.177
>> IndexVectorBenchmark.shortIndexVector  5.841
>> 
>> 
>> Please help to review and share the feedback! Thanks in advance!
>
> src/hotspot/share/opto/vectorIntrinsics.cpp line 2978:
> 
>> 2976:       case T_DOUBLE: {
>> 2977:         scale = gvn().transform(new ConvI2LNode(scale));
>> 2978:         scale = gvn().transform(new ConvL2DNode(scale));
> 
> Any specific reason for not directly using ConvI2D for double case.

Good catch, I think it's ok to use ConvI2D here. I will change this. Thanks!

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PR: https://git.openjdk.org/jdk/pull/10332