[riscv-port] RFR: 8279292: riscv: Intrinsify multiplyToLen and squareToLen [v4]

[Fei Yang]

On Mon, 27 Dec 2021 12:49:13 GMT, Feilong Jiang <fjiang at openjdk.org> wrote:

>> BigInteger intrinsic: MultiplyToLen and SquareToLen intrinsic are missed in current vm. They should be implemented.
>> The JMH tests show that the MultiplyToLen intrinsic improve the performance by up to 2x ~ 3x and the SquareToLen intrinsic improve the performance by up to 1.8x ~ 2x when the length of BigInteger changed from 1 to 5000, compared with that of C2.
>> 
>> Full jtreg tests on qemu and hotspot/jdk tier1 test on Unmathced are passed without new failures.
>> 
>> JMH tests and results on D1 and Unmatched list as follows:
>> [MyBenchmark.txt](https://github.com/openjdk/riscv-port/files/7779255/MyBenchmark.txt)
>> 
>> [squareToLen_unmatched.txt](https://github.com/openjdk/riscv-port/files/7779247/squareToLen_unmatched.txt)
>> [squareToLen_d1.txt](https://github.com/openjdk/riscv-port/files/7779248/squareToLen_d1.txt)
>> [multiplyToLen_unmatched.txt](https://github.com/openjdk/riscv-port/files/7779249/multiplyToLen_unmatched.txt)
>> [multiplyToLen_d1.txt](https://github.com/openjdk/riscv-port/files/7779250/multiplyToLen_d1.txt)
>
> Feilong Jiang has updated the pull request incrementally with one additional commit since the last revision:
> 
>   recover deleted comment

Changes requested by fyang (Lead).

src/hotspot/cpu/riscv/macroAssembler_riscv.cpp line 3424:

> 3422:   const Register jdx = tmp1;
> 3423: 
> 3424:   // Check if x and y are both 8-byte aligned.

I think the code logic for avoiding unaligned access should be under control of option AvoidUnalignedAccesses.

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PR: https://git.openjdk.java.net/riscv-port/pull/38