RFR: 8278471: Reorder optimizations in addnode Ideal [v2]

[Zhiqiang Zang]

> Reorder optimizations in addnode so special cases appear before general cases; otherwise the special cases would be never covered.
> 
> `(a - b) + (c - d)` subsumes both `(a - b) + (b - c)` and `(a - b) + (c - a)`. Therefore `(a - b) + (b - c)` and `(a - b) + (c - a)` have to be placed before `(a - b) + (c - d)` so that they can work.

Zhiqiang Zang has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains three commits:

 - Merge master.
 - Merge master.
 - reorder optimizations in addnode so special cases appear before general cases.

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Changes: https://git.openjdk.java.net/jdk/pull/6752/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=6752&range=01
  Stats: 20 lines in 1 file changed: 10 ins; 10 del; 0 mod
  Patch: https://git.openjdk.java.net/jdk/pull/6752.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/6752/head:pull/6752

PR: https://git.openjdk.java.net/jdk/pull/6752