RFR: 8271055: Crash during deoptimization with "assert(bb->is_reachable()) failed: getting result from unreachable basicblock" with -XX:+VerifyStack

[Dean Long]

Reproduced the problem with a new JASM test rather than relying on idiosyncrasies of javac.
The fix is to not look at the next instruction (which might be the beginning of an unreachable block) if the current instruction doesn't fall through (like "goto"!).

-------------

Commit messages:
 - Don't look at next bytecode if the current bytecode doesn't fall through

Changes: https://git.openjdk.java.net/jdk/pull/7331/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=7331&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8271055
  Stats: 121 lines in 3 files changed: 120 ins; 0 del; 1 mod
  Patch: https://git.openjdk.java.net/jdk/pull/7331.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/7331/head:pull/7331

PR: https://git.openjdk.java.net/jdk/pull/7331