On Thu, 2 Jun 2022 03:27:59 GMT, Xiaohong Gong <xg...@openjdk.org> wrote:

>> Currently the vector load with mask when the given index happens out of the 
>> array boundary is implemented with pure java scalar code to avoid the IOOBE 
>> (IndexOutOfBoundaryException). This is necessary for architectures that do 
>> not support the predicate feature. Because the masked load is implemented 
>> with a full vector load and a vector blend applied on it. And a full vector 
>> load will definitely cause the IOOBE which is not valid. However, for 
>> architectures that support the predicate feature like SVE/AVX-512/RVV, it 
>> can be vectorized with the predicated load instruction as long as the 
>> indexes of the masked lanes are within the bounds of the array. For these 
>> architectures, loading with unmasked lanes does not raise exception.
>> This patch adds the vectorization support for the masked load with IOOBE 
>> part. Please see the original java implementation (FIXME: optimize):
>>   @ForceInline
>>   public static
>>   ByteVector fromArray(VectorSpecies<Byte> species,
>>                        byte[] a, int offset,
>>                        VectorMask<Byte> m) {
>>   ByteSpecies vsp = (ByteSpecies) species;
>>       if (offset >= 0 && offset <= (a.length - species.length())) {
>>           return vsp.dummyVector().fromArray0(a, offset, m);
>>       }
>>       // FIXME: optimize
>>       checkMaskFromIndexSize(offset, vsp, m, 1, a.length);
>>       return vsp.vOp(m, i -> a[offset + i]);
>>   }
>> Since it can only be vectorized with the predicate load, the hotspot must 
>> check whether the current backend supports it and falls back to the java 
>> scalar version if not. This is different from the normal masked vector load 
>> that the compiler will generate a full vector load and a vector blend if the 
>> predicate load is not supported. So to let the compiler make the expected 
>> action, an additional flag (i.e. `usePred`) is added to the existing 
>> "loadMasked" intrinsic, with the value "true" for the IOOBE part while 
>> "false" for the normal load. And the compiler will fail to intrinsify if the 
>> flag is "true" and the predicate load is not supported by the backend, which 
>> means that normal java path will be executed.
>> Also adds the same vectorization support for masked:
>>  - fromByteArray/fromByteBuffer
>>  - fromBooleanArray
>>  - fromCharArray
>> The performance for the new added benchmarks improve about `1.88x ~ 30.26x` 
>> on the x86 AVX-512 system:
>> Benchmark                                          before   After  Units
>> LoadMaskedIOOBEBenchmark.byteLoadArrayMaskIOOBE   737.542 1387.069 ops/ms
>> LoadMaskedIOOBEBenchmark.doubleLoadArrayMaskIOOBE 118.366  330.776 ops/ms
>> LoadMaskedIOOBEBenchmark.floatLoadArrayMaskIOOBE  233.832 6125.026 ops/ms
>> LoadMaskedIOOBEBenchmark.intLoadArrayMaskIOOBE    233.816 7075.923 ops/ms
>> LoadMaskedIOOBEBenchmark.longLoadArrayMaskIOOBE   119.771  330.587 ops/ms
>> LoadMaskedIOOBEBenchmark.shortLoadArrayMaskIOOBE  431.961  939.301 ops/ms
>> Similar performance gain can also be observed on 512-bit SVE system.
> Xiaohong Gong has updated the pull request with a new target base due to a 
> merge or a rebase. The pull request now contains five commits:
>  - Merge branch 'jdk:master' into JDK-8283667
>  - Use integer constant for offsetInRange all the way through
>  - Rename "use_predicate" to "needs_predicate"
>  - Rename the "usePred" to "offsetInRange"
>  - 8283667: [vectorapi] Vectorization for masked load with IOOBE with 
> predicate feature

Marked as reviewed by sviswanathan (Reviewer).


PR: https://git.openjdk.java.net/jdk/pull/8035

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