RFR: 8317721: RISC-V: Implement CRC32 intrinsic [v3]

[ArsenyBochkarev]

On Thu, 21 Dec 2023 22:20:15 GMT, ArsenyBochkarev <duke at openjdk.org> wrote:

>> Hi everyone! Please review this port of [AArch64](https://github.com/openjdk/jdk/blob/master/src/hotspot/cpu/aarch64/stubGenerator_aarch64.cpp#L4224) `_updateBytesCRC32`, `_updateByteBufferCRC32` and `_updateCRC32` intrinsics. This patch introduces only the plain (non-vectorized, no Zbc) version.
>> 
>> ### Correctness checks
>> 
>> Tier 1/2 tests are ok.
>> 
>> ### Performance results on T-Head board
>> 
>> #### Results for enabled intrinsic:
>> 
>> Used test is `test/micro/org/openjdk/bench/java/util/TestCRC32.java`
>> 
>> | Benchmark                                             |  (count) |  Mode | Cnt    | Score |   Error |  Units |
>> | --- | ---- | ----- | --- | ---- | --- | ---- |
>> | CRC32.TestCRC32.testCRC32Update  |     64  | thrpt     | 24 | 3730.929 | 37.773 | ops/ms |
>> | CRC32.TestCRC32.testCRC32Update  |    128 |  thrpt    | 24 | 2126.673 |  2.032 | ops/ms |
>> | CRC32.TestCRC32.testCRC32Update  |    256 | thrpt    |  24 | 1134.330 |  6.714 | ops/ms |
>> | CRC32.TestCRC32.testCRC32Update  |    512 | thrpt    |  24 |  584.017 |  2.267 | ops/ms |
>> | CRC32.TestCRC32.testCRC32Update  |   2048 |  thrpt   |   24 |  151.173 |  0.346 | ops/ms |
>> | CRC32.TestCRC32.testCRC32Update  |   16384 | thrpt |  24 |   19.113 |  0.008 | ops/ms |
>> | CRC32.TestCRC32.testCRC32Update  |  65536 | thrpt  | 24  |   4.647 | 0.022 | ops/ms |
>> 
>> #### Results for disabled intrinsic:
>> 
>> | Benchmark                                            | (count)  |  Mode | Cnt |   Score  |  Error   | Units     |
>> | --------------------------------------------------- | ---------- | --------- | ---- | ----------- | --------- | ---------- | 
>> | CRC32.TestCRC32.testCRC32Update |      64    |  thrpt   | 15  | 798.365 | 35.486 | ops/ms |
>> | CRC32.TestCRC32.testCRC32Update |     128   |  thrpt   | 15  | 677.756 | 46.619 | ops/ms |
>> | CRC32.TestCRC32.testCRC32Update |     256   |  thrpt   | 15  | 552.781 | 27.143 | ops/ms |
>> | CRC32.TestCRC32.testCRC32Update |     512   |  thrpt   | 15  | 429.304 | 12.518 | ops/ms |
>> | CRC32.TestCRC32.testCRC32Update |    2048  |  thrpt   | 15  | 166.738 |  0.935  | ops/ms |
>> | CRC32.TestCRC32.testCRC32Update |   16384 |  thrpt   | 15  |  25.060  | 0.034   | ops/ms |
>> | CRC32.TestCRC32.testCRC32Update |   65536 |  thrpt   | 15  |   6.196   | 0.030   | ops/ms |
>
> ArsenyBochkarev has updated the pull request incrementally with five additional commits since the last revision:
> 
>  - Use MacroAssembler::lwu instead of Assembler::lwu
>  - Save instruction when getting table3 address
>  - Left note on how table elements are accessed
>  - Fix comment for result register
>  - Remove unused L_by16 label

Hello again everyone! I was able to optimize regressions for most cases on big amount of data by partially unrolling the big loop and disposing from loop counter (previously in `len` register). Results for `-XX:+UseZba` of StarFive VisionFive2 board:

| Benchmark                     |   (count) |  Mode | Cnt  |   Score  |  Error  | Units |
| ------------------------------ | ------------ | --------- | ----- | ---------- | ----------- | ----- |
| CRC32.TestCRC32.testCRC32Update |      64 | thrpt |  12 | 4215.728 | 3.972 | ops/ms |
| CRC32.TestCRC32.testCRC32Update |     128 | thrpt |  12 | 2607.882 |  1.627 |  ops/ms |
| CRC32.TestCRC32.testCRC32Update |     256 | thrpt |  12 | 1364.899 |  8.857 | ops/ms |
| CRC32.TestCRC32.testCRC32Update |     512 | thrpt |  12 |  704.316 |  3.222 | ops/ms |
| CRC32.TestCRC32.testCRC32Update |    2048 | thrpt  | 12 |  180.738 |  0.474 | ops/ms |
| CRC32.TestCRC32.testCRC32Update |   16384 | thrpt  | 12 |   22.722 |  0.059 | ops/ms |
| CRC32.TestCRC32.testCRC32Update |   65536 | thrpt  | 12 |    5.327 |  0.019 | ops/ms |

while the results for `-XX:-UseCRC32Intrinsics` are [here](https://github.com/openjdk/jdk/pull/17046#issuecomment-1850364667)

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

PR Comment: https://git.openjdk.org/jdk/pull/17046#issuecomment-1883404214