RFR: 8339063: [aarch64] Skip verify_sve_vector_length after native calls if SVE supports 128 bits VL only

[Joshua Zhu]

On Tue, 27 Aug 2024 09:28:52 GMT, Joshua Zhu <jzhu at openjdk.org> wrote:

> Please review this minor enhancement that skips verify_sve_vector_length after native calls.
> It works on SVE micro-architecture that only supports 128-bit vector length.

Add some more background.

The maximum SVE vector length "VLmax" is determined by the hardware: 16 <= VLmax <= 256.
The value of VL can be configured at runtime: 16 <= VL <= VLmax, where VL must be a multiple of 16.

Once we find cpu's VLMax is 16 bytes only, the verification "verify_sve_vector_length()" after native calls is not required - in other words, VL cannot be configured to a value other than 16.

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PR Comment: https://git.openjdk.org/jdk/pull/20724#issuecomment-2312380459