RFR: 8286847: Rotate vectors don't support byte or short [v2]

[Xiaohong Gong]

On Wed, 18 May 2022 01:13:00 GMT, Haomin <duke at openjdk.java.net> wrote:

>> static void test_fun(byte[] a0, int[] b0, byte[] c0) {
>>     for (int i=0; i<ARRLEN; i++) {
>>       c0[i] = (byte)(a0[i] << (7) | a0[i] >>> (-7));
>>     }   
>>   }
>> 
>> 
>> when I implement RotateLeftV in loongarch.ad, I found this executed by c2 vector and executed by interpreter are not equal.
>> 
>> It's executed on x86 would create an assert error.
>> 
>> 
>>  # Internal Error (/home/wanghaomin/jdk/src/hotspot/share/opto/vectornode.cpp:347), pid=26469, tid=26485
>>  # assert(false) failed: not supported: byte
>> 
>> 
>> RotateLeftV for byte, short values produces incorrect Java result. Because java code should convert a byte, short value into int value, and then do RotateI.
>
> Haomin has updated the pull request incrementally with one additional commit since the last revision:
> 
>   modify testcase

src/hotspot/share/opto/vectornode.cpp line 158:

> 156:     default:     return 0; // RotateLeftV for byte, short values produces incorrect Java result.
> 157:                            // Because java code should convert a byte, short value into int value,
> 158:                            // and then do RotateI.

I‘m afraid this will influence the VectorAPI intrinsification for `ByteVector `and `ShortVector`. Did you test the benchmarks for these two APIs with the subword type?

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PR: https://git.openjdk.java.net/jdk/pull/8740