RFR: 8267399: C2: java/text/Normalizer/ConformanceTest.java test failed with assertion

[Roland Westrelin]

This was found with Shenandoah but has nothing specific to Shenandoah.

For the inner loop of the test case:

- the loop limit, len, is known to be either 1 or 2. As a consequence
  the type of the iv phi is set to [0..2].

- range check elimination is applied which causes the pre/main/post
  loops to be added and the limit of the main loop to be adjusted. C2
  computes the limit of the main loop as TypeINT:INT.

- the main loop is peeled. So now the type of the iv phi is 2 and it
  constant folds. Because the main loop limit has type TypeInt::INT,
  the exit condition of the loop doesn't constant fold. But the loop
  no longer has the shape of a counted loop because the iv phi doesn't
  exist anymore.

The crash then occurs when some other loop opts is attempted and loop
strip mining verification code checks that the shape of the main loop
is that of a counted loop.

The fix I propose is to add a CastII at range elimination time that
captures the bounds of the limit before RC is applied. This way the
type of the limit is not lost and the main loop backbranch can be
properly eliminated in the chain of events above.

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Commit messages:
 - fix

Changes: https://git.openjdk.java.net/jdk/pull/4388/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=4388&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8267399
  Stats: 72 lines in 2 files changed: 72 ins; 0 del; 0 mod
  Patch: https://git.openjdk.java.net/jdk/pull/4388.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/4388/head:pull/4388

PR: https://git.openjdk.java.net/jdk/pull/4388