RFR: 8309894: compiler/vectorapi/VectorLogicalOpIdentityTest.java fails on SVE system with UseSVE=0

[Emanuel Peter]

On Wed, 21 Jun 2023 09:45:40 GMT, Xiaohong Gong <xgong at openjdk.org> wrote:

> Besides, x86 just mask off the CPU features for JVM instead of really changing the hardware's features.

That is the question: what is the ground truth. On x86, the idea is to keep the flags and the cpu features in sync. So if the hardware does not support a flag value to be larger (eg trying to set `UseAVX=3` if only avx2 is available, we force it down to `UseAVX=2`). And if a flag restricts cpu features, we mask them off.

Of course, the hardware may support more features than the VM assumes. But still, that allows us to do some "cross cpu" testing - we can simulate avx1 features on a avx2 machine for example.

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PR Comment: https://git.openjdk.org/jdk/pull/14533#issuecomment-1600591097