RFR: 8284880: Re-examine sun.invoke.util.Wrapper hash tables

[Claes Redestad]

This patch examines and optimizes `Wrapper` lookups.

First wrote a few simple microbenchmarks to verify there are actual speedups from using perfect hash tables in `sun.invoke.util.Wrapper` compared to simpler lookup mechanisms (such as if-else or switch). Turns out there _is_ a speed-up for the case of `char` -> `Wrapper`, but not when mapping from `Class<?>` -> `Wrapper`, so let's drop those. The `forPrimitiveType` case didn't use the `FROM_CHAR` table for some reason, which is remedied.  

Micros show benefits across the board for warmed up case:


Baseline, OOTB
Benchmark                  Mode  Cnt   Score   Error  Units
Wrappers.forBasicType      avgt    5  14.387 ? 0.127  ns/op
Wrappers.forPrimitive      avgt    5  38.818 ? 0.592  ns/op
Wrappers.forPrimitiveType  avgt    5  26.085 ? 2.291  ns/op
Wrappers.forWrapper        avgt    5  44.459 ? 1.635  ns/op

Patch, OOTB
Benchmark                  Mode  Cnt   Score   Error  Units
Wrappers.forBasicType      avgt    5  14.357 ? 0.133  ns/op
Wrappers.forPrimitive      avgt    5  23.930 ? 0.071  ns/op
Wrappers.forPrimitiveType  avgt    5  14.343 ? 0.017  ns/op
Wrappers.forWrapper        avgt    5  27.622 ? 0.022  ns/op


For `-Xint` case (`Wrapper` use is prominent during warmup, e.g., when spinning up of MHs) there are decent or even great wins in all cases but `forPrimitiveType` - which was changed from a simple switch to use the hash lookup. Since the interpreter penalty is small in absolute terms and the win on JITed code is significant this seems like a reasonable trade-off:


Baseline, -Xint
Benchmark                  Mode  Cnt     Score     Error  Units
Wrappers.forBasicType      avgt    5  1246.144 ? 149.933  ns/op
Wrappers.forPrimitive      avgt    5  4955.297 ? 329.869  ns/op
Wrappers.forPrimitiveType  avgt    5   716.840 ?  62.568  ns/op
Wrappers.forWrapper        avgt    5  5774.700 ? 367.627  ns/op

Patch, -Xint
Benchmark                  Mode  Cnt     Score     Error  Units
Wrappers.forBasicType      avgt    5  1068.096 ? 101.728  ns/op
Wrappers.forPrimitive      avgt    5  1146.670 ?  59.142  ns/op
Wrappers.forPrimitiveType  avgt    5   998.037 ? 118.144  ns/op
Wrappers.forWrapper        avgt    5  3581.226 ?  20.167  ns/op

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

Commit messages:
 - Revert accidental changes to MethodType
 - Fix typo
 - Missed some changes refactoring, import DontInline
 - Merge branch 'master' into wrappers
 - Cleanup, use mask instead of modulo
 - Cleanup, add forPrimitiveType micro, reinstantiate char hashing
 - Add required add-exports to BuildMicrobenchmark.gmk
 - Fix imports
 - Tune sun.invoke.util.Wrapper accessors

Changes: https://git.openjdk.java.net/jdk/pull/8242/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=8242&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8284880
  Stats: 256 lines in 3 files changed: 157 ins; 59 del; 40 mod
  Patch: https://git.openjdk.java.net/jdk/pull/8242.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/8242/head:pull/8242

PR: https://git.openjdk.java.net/jdk/pull/8242