RFR: 8353786: Migrate Vector API math library support to FFM API

[Chen Liang]

On Fri, 4 Apr 2025 22:52:24 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!

src/jdk.incubator.vector/share/classes/jdk/incubator/vector/CPUFeatures.java line 44:

> 42:         String featuresString = VectorSupport.getCPUFeatures();
> 43:         debug(featuresString);
> 44:         String[] features = featuresString.toLowerCase().split(", "); // ", " is used as a delimiter

Please use `toLowerCase(Locale.ROOT)`: if the system locale is turkish, `I` and dotless i are two letters, and the dotless i will fail in the subsequent `validateFeatures` assertion. Same for `hasFeature`.

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PR Review Comment: https://git.openjdk.org/jdk/pull/24462#discussion_r2031714743