RFR: 8319872: AArch64: [vectorapi] Implementation of unsigned (zero extended) casts [v3]

[Andrew Haley]

On Tue, 21 Nov 2023 13:24:34 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:
> 
>   add _sve_xunpk & remove dead code
>   
>   Change-Id: Ic19836feb8a73ea7e65443794f2a0eb1363f6e2f

src/hotspot/cpu/aarch64/c2_MacroAssembler_aarch64.cpp line 1412:

> 1410:       _sve_xunpk(is_unsigned, /* is_high */ false, dst, S, dst);
> 1411:       _sve_xunpk(is_unsigned, /* is_high */ false, dst, D, dst);
> 1412:       break;

Why is this change here? It doesn't do anything. Does it?

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PR Review Comment: https://git.openjdk.org/jdk/pull/16670#discussion_r1400743499