Swap should be better done native?

[Martin Buchholz]

Alan, please file a bug and review this change.

Synopsis: Optimize java/nio/Bits.java
Description:
Use intrinsified reverseBytes operation; elide no-op constructs


So I have a proposed patch:
http://cr.openjdk.java.net/~martin/webrevs/openjdk7/nioBits.java/

I was surprised that I had written a benchmark for this years ago,
and also surprised how much faster the swapping got by using
the intrinsified methods

Below are before/after benchmark results:

==> javac -Xlint:all SwapMicroBenchmark.java
==> java -server -esa -ea SwapMicroBenchmark
Method                   Millis Ratio
swap char BIG_ENDIAN         84 1.000
swap char LITTLE_ENDIAN      49 0.585
swap short BIG_ENDIAN        97 1.153
swap short LITTLE_ENDIAN     49 0.589
swap int BIG_ENDIAN          70 0.834
swap int LITTLE_ENDIAN       25 0.308
swap long BIG_ENDIAN         77 0.913
swap long LITTLE_ENDIAN      10 0.125
applying nioBits.java
now at: nioBits.java
Recompiled:
/usr/local/google/home/martin/ws/upstream/src/share/classes/java/nio/Bits.java
==> javac -Xlint:all SwapMicroBenchmark.java
==> java -server -esa -ea SwapMicroBenchmark
Method                   Millis Ratio
swap char BIG_ENDIAN         67 1.000
swap char LITTLE_ENDIAN      50 0.741
swap short BIG_ENDIAN        68 1.010
swap short LITTLE_ENDIAN     50 0.739
swap int BIG_ENDIAN          20 0.306
swap int LITTLE_ENDIAN       26 0.393
swap long BIG_ENDIAN         13 0.202
swap long LITTLE_ENDIAN      10 0.157

Martin