RFR: 8294194: Create intrinsics compress and expand

[Stuart Monteith]

The java.lang.Long and java.lang.Integer classes have the methods "compress(i, mask)" and "expand(i, mask)". They compile down to 236 assembler instructions. There are no scalar instructions that perform the equivalent functions on aarch64, instead the intrinsics can be implemented with vector instructions included in SVE2; expand with BDEP, compress with BEXT.

Only the first lane of each vector will be used, two MOV instructions will move the inputs from GPRs into temporary vector registers, and another to do the reverse for the result. Autovectorization for this functionality is/will be implemented separately.

Running on an SVE2 enabled system, I ran the following benchmarks:

        org.openjdk.bench.java.lang.Integers
        org.openjdk.bench.java.lang.Longs

The time for each operation reduced to 56% to 72% of the original run time:

Benchmark               Result  error   Unit    % against non-SVE2
Integers.expand         2.106   0.011   us/op
Integers.expand-SVE     1.431   0.009   us/op   67.95%
Longs.expand            2.606   0.006   us/op
Longs.expand-SVE        1.46    0.003   us/op   56.02%
Integers.compress       1.982   0.004   us/op
Integers.compress-SVE   1.427   0.003   us/op   72.00%
Longs.compress          2.501   0.002   us/op
Longs.compress-SVE      1.441   0.003   us/op   57.62%

-------------

Commit messages:
 - 8294194: Create intrinsics compress and expand

Changes: https://git.openjdk.org/jdk/pull/10537/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=10537&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8294194
  Stats: 85 lines in 2 files changed: 81 ins; 1 del; 3 mod
  Patch: https://git.openjdk.org/jdk/pull/10537.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/10537/head:pull/10537

PR: https://git.openjdk.org/jdk/pull/10537