RFR: 8359218: RISC-V: Only enable CRC32 intrinsic when AvoidUnalignedAccess == false

[Anjian Wen]

On Wed, 11 Jun 2025 10:58:44 GMT, Feilong Jiang <fjiang at openjdk.org> wrote:

>> When test **Specjvm** in p550, we can find the compress test result shown below.
>> 
>> 
>> before patch
>> -XX:-UseCompactObjectHeaders
>> Warmup (30s) begins: Wed Jun 11 16:10:18 CST 2025
>> Warmup (30s) ends:   Wed Jun 11 16:10:53 CST 2025
>> Warmup (30s) result: 68.98 ops/m
>> 
>> Iteration 1 (60s) begins: Wed Jun 11 16:10:53 CST 2025
>> Iteration 1 (60s) ends:   Wed Jun 11 16:11:57 CST 2025
>> Iteration 1 (60s) result: 71.25 ops/m
>> 
>> 
>> -XX:+UseCompactObjectHeaders
>> Warmup (30s) begins: Wed Jun 11 16:13:03 CST 2025
>> Warmup (30s) ends:   Wed Jun 11 16:13:42 CST 2025
>> Warmup (30s) result: 31.87 ops/m
>> 
>> Iteration 1 (60s) begins: Wed Jun 11 16:13:42 CST 2025
>> Iteration 1 (60s) ends:   Wed Jun 11 16:14:56 CST 2025
>> Iteration 1 (60s) result: 29.13 ops/m
>> 
>> 
>> Add flamegraph Before the patch
>> 1. With parmater -XX:-UseCompactObjectHeaders
>> 
>> java -XX:-UseCompactObjectHeaders -XX:+UseParallelGC -XX:+AlwaysPreTouch -Xms8g -Xmx8g -jar SPECjvm2008.jar -ikv -ict -coe -crf 0 -bt 4 -wt 30s -it 1m -i 4 compress
>> 
>> ![closeCompactObjectHeader](https://github.com/user-attachments/assets/cea7f230-799a-4e9c-a541-626dd485670f)
>> 
>> 
>> 2. With parmater -XX:+UseCompactObjectHeaders
>> 
>> java -XX:+UseCompactObjectHeaders -XX:+UseParallelGC -XX:+AlwaysPreTouch -Xms8g -Xmx8g -jar SPECjvm2008.jar -ikv -ict -coe -crf 0 -bt 4 -wt 30s -it 1m -i 4 compress
>> 
>> ![openparm](https://github.com/user-attachments/assets/24e07f17-4cb9-459d-b50d-8d1ad6355ebf)
>> 
>> 
>> The reason is that when enable compactObjectHeaders, the arraylist header turn to 4 Byte, but the copy instruction used in CRC intrinsic loop is 8 Byte one loop, which may reduce the performance when hardware is sensitive to unaligned access, we can close it when AvoidUnalignedAccesses is true
>> 
>> after patch 
>> 
>> -XX:-UseCompactObjectHeaders
>> Warmup (30s) begins: Wed Jun 11 16:23:22 CST 2025
>> Warmup (30s) ends:   Wed Jun 11 16:23:57 CST 2025
>> Warmup (30s) result: 68.61 ops/m
>> 
>> Iteration 1 (60s) begins: Wed Jun 11 16:23:57 CST 2025
>> Iteration 1 (60s) ends:   Wed Jun 11 16:25:00 CST 2025
>> Iteration 1 (60s) result: 71.57 ops/m
>> 
>> 
>> -XX:+UseCompactObjectHeaders
>> Warmup (30s) begins: Wed Jun 11 16:25:28 CST 2025
>> Warmup (30s) ends:   Wed Jun 11 16:26:03 CST 2025
>> Warmup (30s) result: 68.36 ops/m
>> 
>> Iteration 1 (60s) begins: Wed Jun 11 16:26:03 CST 2025
>> Iteration 1 (60s) ends:   Wed Jun 11 16:27:08 CST 2025
>> Iteration 1 (60s) result: 70.85 ops/m
>
> Looks fine.

@feilongjiang @RealFYang  Thanks for your reviews！

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PR Comment: https://git.openjdk.org/jdk/pull/25743#issuecomment-2966099409