RFR: 8271202: C1: assert(false) failed: live_in set of first block must be empty

[Martin Doerr]

I have written a checker which detects usage of the illegal phi function. In case of the reproducer provided in the JBS bug ("Reduced.java"), it finds the following and bails out:

invalidating local 8 because of type mismatch (new_value is NULL)
Bailing out because StoreIndexed (id 98) uses illegal phi (id 68)

I haven't checked why that node uses the illegal phi. That still seems to be a bug. Maybe there's a better solution to the underlying problem, but I hope my checker is useful to analyze bugs and to make C1 more resilient.

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Commit messages:
 - 8271202: C1: assert(false) failed: live_in set of first block must be empty

Changes: https://git.openjdk.java.net/jdk/pull/6683/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=6683&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8271202
  Stats: 51 lines in 1 file changed: 46 ins; 0 del; 5 mod
  Patch: https://git.openjdk.java.net/jdk/pull/6683.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/6683/head:pull/6683

PR: https://git.openjdk.java.net/jdk/pull/6683