RFR: 8278868: Add x86 vectorization support for Long.bitCount() [v9]

[Vladimir Kozlov]

On Mon, 10 Jan 2022 06:05:54 GMT, Vamsi Parasa <duke at openjdk.java.net> wrote:

>> Vectorization support of Integer.bitCount() already exists but currently the same support is lacking for Long.bitCount(). Similar to the C2 PopCountVI node, we created a C2 PopCountVL node and used vpopcntq x86 instruction to enable vectorized Long.bitCount(). This patch shows 2.57x improvement in performance on a JMH micro benchmark due to x86 vectorization.
>
> Vamsi Parasa has updated the pull request incrementally with one additional commit since the last revision:
> 
>   aditional checks for the test

`TestPopCountVectorLong.java ` was not ran on these systems because it has `@requires vm.cpu.features ~= ".*avx512dq.*"`
And I did not test other tiers because tier1 had failures.

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PR: https://git.openjdk.java.net/jdk/pull/6857