RFR: 8257190: simplify PhaseIdealLoop constructors [v2]

[Xin Liu]

> 8257190: simplify PhaseIdealLoop constructors

Xin Liu has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains three additional commits since the last revision:

 - Merge branch 'master' into JDK-8257190
 - 8257190: simplify PhaseIdealLoop constructors
   
   update the comments of the verify constructors.
 - 8257190: simplify PhaseIdealLoop constructors

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Changes:
  - all: https://git.openjdk.java.net/jdk/pull/1473/files
  - new: https://git.openjdk.java.net/jdk/pull/1473/files/738546fb..3731d0b9

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=1473&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=1473&range=00-01

  Stats: 9458 lines in 216 files changed: 6272 ins; 2298 del; 888 mod
  Patch: https://git.openjdk.java.net/jdk/pull/1473.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/1473/head:pull/1473

PR: https://git.openjdk.java.net/jdk/pull/1473