RFR: 8262017: C2: assert(n != __null) failed: Bad immediate dominator info.

[Christian Hagedorn]

The wrong dominance information is caused by a `ConvL2I` node whose input gets a wrong type which is out of the range of the `ConvL2I`. As a consequence, the node becomes top and some data nodes are folded away which eventually results in the dominance assertion failure.

The wrong type information can be traced back to the overflow/underflow handling in range check elimination. Originally, the code in `PhaseIdealLoop::add_constraint()` covered the following special case for the adjustment of the pre loop limit:
https://github.com/openjdk/jdk/blob/cd33abb136d415455090cef4fe6211d9e6940948/src/hotspot/share/opto/loopTransform.cpp#L2370-L2394

This code, however, was removed later by accident:
https://github.com/openjdk/jdk/commit/afd852ccb8f8d36c721963ba68de695ce3e0e23d#diff-6a59f91cb710d682247df87c75faf602f0ff9f87e2855ead1b80719704fbedffL2370-L2394

This was only revealed after enabling more precise type information for phi nodes in [JDK-8257813](https://bugs.openjdk.java.net/browse/JDK-8257813) after which the testcase starts to fail.

The proposed fix is straight forward to reintroduce the wrongly removed code and adapt it to long instead of int.

Thanks,
Christian

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Commit messages:
 - 8262017: C2: assert(n != __null) failed: Bad immediate dominator info.

Changes: https://git.openjdk.java.net/jdk/pull/4362/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=4362&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8262017
  Stats: 92 lines in 2 files changed: 92 ins; 0 del; 0 mod
  Patch: https://git.openjdk.java.net/jdk/pull/4362.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/4362/head:pull/4362

PR: https://git.openjdk.java.net/jdk/pull/4362