RFR: 8292698: Improve performance of DataInputStream [v2]

[Сергей Цыпанов]

> I found out that reading from `DataInputStream` wrapping `ByteArrayInputStream` (as well as `BufferedInputStream` or any `InputStream` relying on `byte[]`) can be significantly improved by accessing volatile `in` field only once per operation.
> 
> Current implementation does it for each call of `in.read()`, i.e. in `readInt()` method we do it 4 times:
> 
> public final int readInt() throws IOException {
>     int ch1 = in.read();
>     int ch2 = in.read();
>     int ch3 = in.read();
>     int ch4 = in.read();
>     if ((ch1 | ch2 | ch3 | ch4) < 0)
>         throw new EOFException();
>     return ((ch1 << 24) + (ch2 << 16) + (ch3 << 8) + (ch4 << 0));
> }
> 
> Apparently accessing volatile reference with underlying `byte[]` prevents runtime from doing some optimizations, so dereferencing local variable should be more efficient.
> 
> Benchmarking:
> 
> baseline:
> 
> Benchmark                     Mode  Cnt   Score   Error  Units
> DataInputStreamTest.readChar  avgt   20  22,889 ± 0,648  us/op
> DataInputStreamTest.readInt   avgt   20  21,804 ± 0,197  us/op
> 
> patch:
> 
> Benchmark                     Mode  Cnt   Score   Error  Units
> DataInputStreamTest.readChar  avgt   20  11,018 ± 0,089  us/op
> DataInputStreamTest.readInt   avgt   20   5,608 ± 0,087  us/op

Сергей Цыпанов has updated the pull request incrementally with one additional commit since the last revision:

  8292698: Revert dubious changes

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/9956/files
  - new: https://git.openjdk.org/jdk/pull/9956/files/31a9c451..a2378ded

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=9956&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=9956&range=00-01

  Stats: 3 lines in 1 file changed: 0 ins; 3 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/9956.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/9956/head:pull/9956

PR: https://git.openjdk.org/jdk/pull/9956