RFR: 8253525: Implement getInstanceSize/sizeOf intrinsics [v7]

[Aleksey Shipilev]

> This is fork off the SizeOf JEP, JDK-8249196. There is already the entry point in JDK that can use the intrinsic like this: `Instrumentation.getInstanceSize`. Therefore, we can implement the C1/C2 intrinsic now, hook it up to `Instrumentation`, and let the tools use that fast path today.
> 
> With this patch, JOL is able to be close to `deepSizeOf` implementation from SizeOf JEP. 
> 
> Example performance improvements for sizing up a custom linked list:
> 
> Benchmark                     (size)  Mode  Cnt       Score      Error  Units
> 
> # Default
> LinkedChainBench.linkedChain       1  avgt    5     705.835 ±    8.051  ns/op
> LinkedChainBench.linkedChain      10  avgt    5    3148.874 ±   37.856  ns/op
> LinkedChainBench.linkedChain     100  avgt    5   28693.256 ±  142.254  ns/op
> LinkedChainBench.linkedChain    1000  avgt    5  290161.590 ± 4594.631  ns/op
> 
> # Instrumentation attached, no intrinsics
> LinkedChainBench.linkedChain       1  avgt    5    159.659 ±   19.238  ns/op
> LinkedChainBench.linkedChain      10  avgt    5    717.659 ±   22.540  ns/op
> LinkedChainBench.linkedChain     100  avgt    5   7739.394 ±  111.683  ns/op
> LinkedChainBench.linkedChain    1000  avgt    5  80724.238 ± 2887.794  ns/op
> 
> # Instrumentation attached, new intrinsics
> LinkedChainBench.linkedChain       1  avgt    5     95.254 ±   0.808  ns/op
> LinkedChainBench.linkedChain      10  avgt    5    261.564 ±   8.524  ns/op
> LinkedChainBench.linkedChain     100  avgt    5   3367.192 ±  21.128  ns/op
> LinkedChainBench.linkedChain    1000  avgt    5  34148.851 ± 373.080  ns/op

Aleksey Shipilev has updated the pull request incrementally with one additional commit since the last revision:

  Drop parentheses around comparisons

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

Changes:
  - all: https://git.openjdk.java.net/jdk/pull/650/files
  - new: https://git.openjdk.java.net/jdk/pull/650/files/1b7290a3..89881e9f

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=650&range=06
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=650&range=05-06

  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.java.net/jdk/pull/650.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/650/head:pull/650

PR: https://git.openjdk.java.net/jdk/pull/650