RFR: 8358032: Use crypto pmull for CRC32/CRC32C intrinsics on Ampere CPU

[Andrew Haley]

On Tue, 3 Jun 2025 07:14:03 GMT, Liming Liu <lliu at openjdk.org> wrote:

> This PR is to enable the use of crypto pmull for CRC32/CRC32C intrinsics on Ampere CPU. There is an option UseCryptoPmullForCRC32 that can enable crypto pmull, but directly enabling it on Ampere CPU will cause the following problems.
> 
> 1. There will be regressions (-14% ~ -8%) on Ampere1 when the length is 64. When <= 128, both kernel_crc32_using_crc32 and kernel_crc32_using_crypto_pmull use the loop labeled as CRC_by32_loop, but their implements are a little different, and the loop in kernel_crc32_using_crc32 is better at hiding latency on Ampere1. So this PR takes the loop in kernel_crc32_using_crc32 to kernel_crc32_using_crypto_pmull, and does the same for CRC32C intrinsic.
> 
> 2. The intrinsics only use crypto pmull when the length is higher than 383, while the loop in kernel_crc32_common_fold_using_crypto_pmull looks able to handle 256, and if it handles 256 on Ampere1, the improvements can be as high as 110% compared with kernel_crc32_using_crc32/kernel_crc32c_using_crc32c. However, there are regressions (~-6%) on Neoverse V1 when the length is 256. So this PR introduces a new option named CryptoPmullForCRC32LowLimit. It defaults to 256 since the code could handle 256, while it is set to 384 for V1/V2 to keep the old behavior on these platforms.
> 
> The performance regressions and improvements were measured with the following microbenchmarks:
> org.openjdk.bench.java.util.TestCRC32.testCRC32Update
> org.openjdk.bench.java.util.TestCRC32C.testCRC32CUpdate
> 
> Ran the following JTReg tests on Ampere1 and did not find problems:
> test/hotspot/jtreg/compiler/intrinsics/zip/TestCRC32.java
> test/hotspot/jtreg/compiler/intrinsics/zip/TestCRC32C.java

src/hotspot/cpu/aarch64/globals_aarch64.hpp line 95:

> 93:           "Minimum size in bytes when Crypto PMULL will be used."       \
> 94:           "Value must be a multiple of 128.")                           \
> 95:           range(256, max_jint)                                          \

This shouldn't be a general product flag.
Suggestion:

  product(intx, CryptoPmullForCRC32LowLimit, 256, DIAGNOSTIC,           \
          "Minimum size in bytes when Crypto PMULL will be used."       \
          "Value must be a multiple of 128.")                           \
          range(256, max_jint)                                          \

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PR Review Comment: https://git.openjdk.org/jdk/pull/25609#discussion_r2123135028