[intrinsics] performance improvements for the intrinsified version of Objects::hash

[Aleksey Shipilev]

On 3/15/19 3:13 AM, Vicente Romero wrote:
> Please see the performance of both implementations for the multi-threaded version [1].
> 
> [1]
> http://cr.openjdk.java.net/~vromero/intrinsics_benchmark_results/v9/benchmarkResults_intrinsics_all_data_v9.html

I'd drop "volatile" qualifier from the fields you are reading from. "volatile" (acquire) semantics
probably breaks some optimizations, and might not be the overwhelmingly common case for hashCode
computations. JMH breaks the folding across @Benchmark calls already. It might not matter that much
for the tests where you read all the fields and then call into Objects.hash, but better be safe than
sorry.

-Aleksey