RFR: 8261553: Efficient mask generation using BMI2 BZHI instruction [v2]

[Jatin Bhateja]

On Thu, 11 Feb 2021 10:28:05 GMT, Claes Redestad <redestad at openjdk.org> wrote:

> * Rather than removing the old code, I believe the code calling bzhiq needs to be in a branch checking `VM_Version::supports_bmi2`. Otherwise you'll hit asserts on older hardware without this extension

Hi Claes, added missing safely check for BMI2,  its in general  rare that a target supporting AVX-512 does not support BMI2

> * Some demonstration of the performance benefit would be nice - either a new microbenchmark or a statistically significant result running some existing ones, e.g. `make test TEST=micro:ArrayCopy`

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PR: https://git.openjdk.java.net/jdk/pull/2522