RFR: 8283094: Add Ideal transformation: x + (con - y) -> (x - y) + con [v2]

[Zhiqiang Zang]

> Hello,
> 
> `x + (con - y)  -> (x - y) + con` is a widely seen pattern; however it is missing in current implementation, which prevents some obvious constant folding from happening, such as `x + (1 - y) + 2` will be not optimized at all, rather than into `x - y + 3`.
> 
> This pull request adds this transformation.

Zhiqiang Zang has updated the pull request incrementally with one additional commit since the last revision:

  comment out "x+(0-y)" -> "(x-y)" and "(0-y)+x" -> "(x-y)" because they
  are covered already.

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

Changes:
  - all: https://git.openjdk.java.net/jdk/pull/7795/files
  - new: https://git.openjdk.java.net/jdk/pull/7795/files/d24b6754..7c899d8a

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=7795&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=7795&range=00-01

  Stats: 62 lines in 2 files changed: 52 ins; 10 del; 0 mod
  Patch: https://git.openjdk.java.net/jdk/pull/7795.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/7795/head:pull/7795

PR: https://git.openjdk.java.net/jdk/pull/7795