RFR: 8283094: Add Ideal transformation: x + (con - y) -> (x - y) + con [v6]

[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:

  do not transform for loop induction variable.

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Changes:
  - all: https://git.openjdk.java.net/jdk/pull/7795/files
  - new: https://git.openjdk.java.net/jdk/pull/7795/files/e9951dda..00b79922

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=7795&range=05
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=7795&range=04-05

  Stats: 4 lines in 1 file changed: 2 ins; 0 del; 2 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