RFR: 8353786: Migrate Vector API math library support to FFM API [v10]

[Hamlin Li]

On Thu, 17 Apr 2025 18:03:47 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 with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains 24 additional commits since the last revision:
> 
>  - Merge remote-tracking branch 'origin/master' into vector.math.01.java
>  - RVV and SVE adjustments
>  - fix broken merge
>  - Merge branch 'master' into vector.math.01.java
>  - Fix debugName handling
>  - Merge branch 'master' into vector.math.01.java
>  - RVV and SVE adjustments
>  - Merge branch 'master' into vector.math.01.java
>  - Fix windows-aarch64 build failure
>  - features_string -> cpu_info_string
>  - ... and 14 more: https://git.openjdk.org/jdk/compare/88f7b422...88eacc48

I just ran some basic tests on riscv, seems there are some issues, also have some comments.

src/hotspot/share/runtime/abstract_vm_version.cpp line 349:

> 347:   assert(features_offset <= cpu_info_string_len, "");
> 348:   if (features_offset < cpu_info_string_len) {
> 349:     assert(cpu_info_string[features_offset + 0] == ',', "");

This assert fails on riscv.

src/hotspot/share/runtime/abstract_vm_version.hpp line 61:

> 59:   static const char* _features_string;
> 60: 
> 61:   static const char* _cpu_info_string;

Not quite sure the reason to introduce `_cpu_info_string`.
Seems to me you could just use _features_string, and remove _cpu_info_string and its related code, e.g. `extract_features_string`. Please check the code in `test/lib/jdk/test/whitebox/cpuinfo/CPUInfo.java`

src/jdk.incubator.vector/share/classes/jdk/incubator/vector/CPUFeatures.java line 45:

> 43:         String featuresString = VectorSupport.getCPUFeatures();
> 44:         debug(featuresString);
> 45:         String[] features = featuresString.toLowerCase(Locale.ROOT).split(", "); // ", " is used as a delimiter

On riscv, it's splitted by " ",  for the fix please refer to CPUInfo.java in test.

src/jdk.incubator.vector/share/classes/jdk/incubator/vector/CPUFeatures.java line 82:

> 80:         return features;
> 81:     }
> 82: }

Maybe an extra line needed at the end of this file?

-------------

PR Review: https://git.openjdk.org/jdk/pull/24462#pullrequestreview-2784177749
PR Review Comment: https://git.openjdk.org/jdk/pull/24462#discussion_r2054468091
PR Review Comment: https://git.openjdk.org/jdk/pull/24462#discussion_r2054692791
PR Review Comment: https://git.openjdk.org/jdk/pull/24462#discussion_r2054472788
PR Review Comment: https://git.openjdk.org/jdk/pull/24462#discussion_r2054157269