RFR: 8338023: Support two vector selectFrom API [v15]

[Sandhya Viswanathan]

On Thu, 3 Oct 2024 05:09:22 GMT, Jatin Bhateja <jbhateja at openjdk.org> wrote:

>> Hi All,
>> 
>> As per the discussion on panama-dev mailing list[1], patch adds the support for following new two vector permutation APIs.
>> 
>> 
>> Declaration:-
>>     Vector<E>.selectFrom(Vector<E> v1, Vector<E> v2)
>> 
>> 
>> Semantics:-
>>     Using index values stored in the lanes of "this" vector, assemble the values stored in first (v1) and second (v2) vector arguments. Thus, first and second vector serves as a table, whose elements are selected based on index value vector. API is applicable to all integral and floating-point types.  The result of this operation is semantically equivalent to expression v1.rearrange(this.toShuffle(), v2). Values held in index vector lanes must lie within valid two vector index range [0, 2*VLEN) else an IndexOutOfBoundException is thrown.  
>> 
>> Summary of changes:
>> -  Java side implementation of new selectFrom API.
>> -  C2 compiler IR and inline expander changes.
>> -  In absence of direct two vector permutation instruction in target ISA, a lowering transformation dismantles new IR into constituent IR supported by target platforms. 
>> -  Optimized x86 backend implementation for AVX512 and legacy target.
>> -  Function tests covering new API.
>> 
>> JMH micro included with this patch shows around 10-15x gain over existing rearrange API :-
>> Test System: Intel(R) Xeon(R) Platinum 8480+ [ Sapphire Rapids Server]
>> 
>> 
>>   Benchmark                                     (size)   Mode  Cnt      Score   Error   Units
>> SelectFromBenchmark.rearrangeFromByteVector     1024  thrpt    2   2041.762          ops/ms
>> SelectFromBenchmark.rearrangeFromByteVector     2048  thrpt    2   1028.550          ops/ms
>> SelectFromBenchmark.rearrangeFromIntVector      1024  thrpt    2    962.605          ops/ms
>> SelectFromBenchmark.rearrangeFromIntVector      2048  thrpt    2    479.004          ops/ms
>> SelectFromBenchmark.rearrangeFromLongVector     1024  thrpt    2    359.758          ops/ms
>> SelectFromBenchmark.rearrangeFromLongVector     2048  thrpt    2    178.192          ops/ms
>> SelectFromBenchmark.rearrangeFromShortVector    1024  thrpt    2   1463.459          ops/ms
>> SelectFromBenchmark.rearrangeFromShortVector    2048  thrpt    2    727.556          ops/ms
>> SelectFromBenchmark.selectFromByteVector        1024  thrpt    2  33254.830          ops/ms
>> SelectFromBenchmark.selectFromByteVector        2048  thrpt    2  17313.174          ops/ms
>> SelectFromBenchmark.selectFromIntVector         1024  thrpt    2  10756.804          ops/ms
>> S...
>
> Jatin Bhateja has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains 18 commits:
> 
>  - Review comments resolution.
>  - Merge branch 'master' of http://github.com/openjdk/jdk into JDK-8338023
>  - Review comments resolutions.
>  - Handling NPOT vector length for AArch64 SVE with vector sizes varying b/w 128 and 2048 bits at 128 bit increments.
>  - Incorporating review and documentation suggestions.
>  - Jcheck clearance
>  - Review comments resolution.
>  - Disabling VectorLoadShuffle bypassing optimization to comply with rearrange semantics at IR level.
>  - Documentation suggestions from Paul.
>  - Review resolutions.
>  - ... and 8 more: https://git.openjdk.org/jdk/compare/bdfb41f9...6215ab91

Thanks for making the changes. It looks to me that  the following checks at lines 2963-2071 in file vectorIntrinsics.cpp is now only needed when lowerSelectFromOp is false. Could you please verify and update accordingly?

 if (is_floating_point_type(elem_bt)) {
    if (!arch_supports_vector(Op_AndV, num_elem, index_elem_bt, VecMaskNotUsed)              ||
        !arch_supports_vector(cast_vopc, num_elem, index_elem_bt, VecMaskNotUsed)            ||
        !arch_supports_vector(Op_Replicate, num_elem, index_elem_bt, VecMaskNotUsed)) {
      log_if_needed("  ** index wrapping not supported: vlen=%d etype=%s" ,
                     num_elem, type2name(elem_bt));
      return false; // not supported
    }
  }

-------------

PR Comment: https://git.openjdk.org/jdk/pull/20508#issuecomment-2392036048