RFR: 8170785: Excessive allocation in ParseUtil.encodePath

[Claes Redestad]

Hi,

some users reports high allocation rates in ParseUtil.encodePath,
regardless of whether paths actually need to be encoded or not.
Since this is a commonly used utility it makes sense.

Webrev: http://cr.openjdk.java.net/~redestad/8170785/webrev.01
Bug: https://bugs.openjdk.java.net/browse/JDK-8170785

This patch provides a semantically neutral fast-path for cases when
the path does not need to be encoded (up to 5x speedup), reduces
allocation when the string has a prefix that does not need to be
encoded (1-2x speedup) and no regression when using a separator
that's not '/' or the first char needs encoding.

Interpreted performance is not affected much either: small positive
when no encoding is needed, neutral or negligible regression
otherwise.

Thanks!

/Claes