RFR: 8365218: [JVMCI] AArch64 CPU features are not computed correctly after 8364128

[Doug Simon]

On Mon, 11 Aug 2025 13:59:55 GMT, Yudi Zheng <yzheng at openjdk.org> wrote:

> https://github.com/openjdk/jdk/pull/26515 changes the `VM_Version::CPU_` constant values on AArch64 and Graal now sees unsupported CPU features. This may result in SIGILL due to Graal emitting unsupported instructions, such as `CPU_SHA3`-based eor3 instructions in AArch64 SHA3 stubs.

src/jdk.internal.vm.ci/share/classes/jdk/vm/ci/hotspot/HotSpotJVMCIBackendFactory.java line 45:

> 43: 
> 44:     /**
> 45:      * Converts a bit mask of CPU features to enum constants.

What's the difference between this new method and the existing `convertFeatures` methods? Is there some way we can consolidate all these versions as they look quite similar at a glance. If not, then please add javadoc to each explaining what's unique about it.

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PR Review Comment: https://git.openjdk.org/jdk/pull/26727#discussion_r2267009657