RFR: 8305073: Fix VerifyLoopOptimizations - step 2 - verify idom [v4]

[Emanuel Peter]

> This is the second step in the `VerifyLoopOptimizations` revival.
> 
> Last step:
> [JDK-8173709](https://bugs.openjdk.org/browse/JDK-8173709) Fix VerifyLoopOptimizations - step 1 - minimal infrastructure 
> See PR for all the planned steps: https://github.com/openjdk/jdk/pull/13207
> 
> Bug fixing for this step:
> [JDK-8308084](https://bugs.openjdk.org/browse/JDK-8308084) C2 fix idom bug in PhaseIdealLoop::create_new_if_for_predicate
> (https://github.com/openjdk/jdk/pull/13980)
> 
> Next step:
> [JDK-8307982](https://bugs.openjdk.org/browse/JDK-8307982) Fix VerifyLoopOptimizations - step 3 - fix ctrl/loop
> 
> I added `TestVerifyLoopOptimizations.java` per @robcasloz 's request. It works just like `TestVerifyIterativeGVN.java`, with a simple `-Xcomp -XX:+VerifyLoopOptimizations` on a basically empty test. It fails until this patch is integrated: https://github.com/openjdk/jdk/pull/13980

Emanuel Peter has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains four commits:

 - Merge branch 'master' into JDK-8305073
 - add TestVerifyLoopOptimizations.java
 - remove bug fix, is fixed in JDK-8308084
 - 8305073: Fix VerifyLoopOptimizations - step 2 - verify idom

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Changes: https://git.openjdk.org/jdk/pull/13951/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=13951&range=03
  Stats: 52 lines in 2 files changed: 38 ins; 7 del; 7 mod
  Patch: https://git.openjdk.org/jdk/pull/13951.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/13951/head:pull/13951

PR: https://git.openjdk.org/jdk/pull/13951