JDK-8147527: Wrong code generated for postfix unary operators

[Jan Lahoda]

Hello,

As noted here:
http://mail.openjdk.java.net/pipermail/compiler-dev/2016-October/010452.html

javac sometimes generates code incorrectly, as discussed further in the 
thread.

The proposed fix is to not reuse the AST nodes on multiple places.

Bug: https://bugs.openjdk.java.net/browse/JDK-8147527
Webrev: http://cr.openjdk.java.net/~jlahoda/8147527/webrev.00/

Any feedback is welcome.

Thanks to Bernard for his work on this.

Jan