RFR: 8319872: AArch64: [vectorapi] Implementation of unsigned (zero extended) casts [v2]

[Andrew Haley]

On Thu, 16 Nov 2023 08:44:26 GMT, Eric Liu <eliu at openjdk.org> wrote:

>> Vector API defines zero-extend operations [1], which are going to be intrinsified and generated to `VectorUCastNode` by C2. This patch adds backend implementation for `VectorUCastNode` on AArch64.
>> 
>> The micro benchmark shows significant performance improvement. In my test machine (SVE, 256-bit), the result is shown as below:
>> 
>> 
>> 
>>   Benchmark                     Before     After       Units   Gain
>>   VectorZeroExtend.byte2Int     3168.251   243012.399  ops/ms  75.70
>>   VectorZeroExtend.byte2Long    3212.201   216291.588  ops/ms  66.33
>>   VectorZeroExtend.byte2Short   3391.968   182655.365  ops/ms  52.85
>>   VectorZeroExtend.int2Long     1012.197    80448.553  ops/ms  78.48
>>   VectorZeroExtend.short2Int    1812.471   153416.828  ops/ms  83.65
>>   VectorZeroExtend.short2Long   1788.382   129794.814  ops/ms  71.58
>> 
>> 
>> On other Neon systems, we can get similar performance boost as a result of intrinsification success.
>> 
>> Since `VectorUCastNode` only used in Vector API's zero extension currently, this patch also adds assertion on nodes' definitions to clarify their usages.
>> 
>> [TEST]
>> compiler/vectorapi and jdk/incubator/vector passed on NEON and SVE machines.
>> 
>> [1] https://github.com/openjdk/jdk/blob/master/src/jdk.incubator.vector/share/classes/jdk/incubator/vector/VectorOperators.java#L726
>
> Eric Liu has updated the pull request incrementally with one additional commit since the last revision:
> 
>   update m4
>   
>   Change-Id: I82bf5f9384f79e09965a0498ad2de45cec6f0a29

src/hotspot/cpu/aarch64/c2_MacroAssembler_aarch64.cpp line 1352:

> 1350:       // 4B/8B to 4S/8S
> 1351:       assert(dst_vlen_in_bytes == 8 || dst_vlen_in_bytes == 16, "unsupported");
> 1352:       (this->*ext)(dst, T8H, src, T8B);

One thing might make this cleaner: I suggest you make `_xshll` protected rather than private, then here

`_xshll(is_unsigned, dst, T8H, src, T8B, 0);`

src/hotspot/cpu/aarch64/c2_MacroAssembler_aarch64.cpp line 1415:

> 1413:       break;
> 1414:     case S:
> 1415:       (this->*unpklo)(dst, H, src);

AS above: try making` is_unsigned` a parameter.

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PR Review Comment: https://git.openjdk.org/jdk/pull/16670#discussion_r1395359612
PR Review Comment: https://git.openjdk.org/jdk/pull/16670#discussion_r1395362740