RFR: 8353786: Migrate Vector API math library support to FFM API [v14]

[Fei Yang]

On Thu, 24 Apr 2025 23:29:28 GMT, Vladimir Ivanov <vlivanov at openjdk.org> wrote:

>> Migrate Vector API math library (SVML and SLEEF) linkage from native code (in JVM) to Java FFM API.
>> 
>> Since FFM API doesn't support vector calling conventions yet, migration affects only symbol lookup for now. But it still enables significant simplifications on JVM side.
>> 
>> The patch consists of the following parts:
>>   * on-demand symbol lookup in Java code replaces eager lookup from native code during JVM startup;
>>   * 2 new VM intrinsics for vector calls (support unary and binary shapes) (code separated from unary/binary vector operations);
>>   * new internal interface to query supported CPU ISA extensions (`jdk.incubator.vector.CPUFeatures`) used for CPU dispatching.
>> 
>> `java.lang.foreign` API is used to perform symbol lookup in vector math library, then the address is cached and fed into corresponding JVM intrinsic, so C2 can turn it into a direct vector call in generated code.
>> 
>> Once `java.lang.foreign` supports vectors & vector calling conventions, VM intrinsics can go away. 
>> 
>> Performance is on par with original implementation (tested with microbenchmarks on linux-x64 and macosx-aarch64).
>> 
>> Testing: hs-tier1 - hs-tier6, microbenchmarks (on linux-x64 and macosx-aarch64)
>> 
>> Thanks!
>
> Vladimir Ivanov has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Improve comments

src/hotspot/cpu/riscv/riscv.ad line 1947:

> 1945: // Vector calling convention not yet implemented.
> 1946: bool Matcher::supports_vector_calling_convention(void) {
> 1947:   return EnableVectorSupport;

You might want to remove the use of `UseVectorStubs` in `Matcher::vector_return_value` at L1951.

assert(EnableVectorSupport && UseVectorStubs, "sanity");

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PR Review Comment: https://git.openjdk.org/jdk/pull/24462#discussion_r2059390324