RFR: 8338023: Support two vector selectFrom API [v13]

[Sandhya Viswanathan]

On Tue, 24 Sep 2024 07:10:24 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 incrementally with one additional commit since the last revision:
> 
>   Handling NPOT vector length for AArch64 SVE with vector sizes varying b/w 128 and 2048 bits at 128 bit increments.

src/hotspot/share/opto/vectorIntrinsics.cpp line 2689:

> 2687:         !arch_supports_vector(cast_vopc, num_elem, T_BYTE, VecMaskNotUsed)                   ||
> 2688:         !arch_supports_vector(Op_VectorLoadShuffle, num_elem, index_elem_bt, VecMaskNotUsed) ||
> 2689:         !arch_supports_vector(Op_Replicate, num_elem, T_BYTE, VecMaskNotUsed)) {

Where SelectFromTwoVector is not supported, the alternate implementation is as part of SelectFromTwoVectorNode::Ideal() instead of right here.  A comment both here as well as in the Ideal() implementation is needed to keep these checks in sync.

src/hotspot/share/opto/vectornode.cpp line 2120:

> 2118:   // are held in a byte vector which are later transformed to target specific permutation
> 2119:   // index format by subsequent VectorLoadShuffle.
> 2120:   int cast_vopc = VectorCastNode::opcode(0, index_elem_bt, true);

Good to use -1 when we are not sending an actual opcode:
int cast_vopc = VectorCastNode::opcode(-1, index_elem_bt, true);

src/hotspot/share/opto/vectornode.cpp line 2126:

> 2124:   Node* bcast_lane_cnt_m1_vec = phase->transform(VectorNode::scalar2vector(lane_cnt_m1, num_elem, Type::get_const_basic_type(T_BYTE), false));
> 2125: 
> 2126:   // Compute the blend mask for merging two indipendently permututed vectors

Typo indipendently -> independently

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

PR Review Comment: https://git.openjdk.org/jdk/pull/20508#discussion_r1781867326
PR Review Comment: https://git.openjdk.org/jdk/pull/20508#discussion_r1781873682
PR Review Comment: https://git.openjdk.org/jdk/pull/20508#discussion_r1781888912