RFR: 8250825: C2 crashes with assert(field != __null) failed: missing field

[jiefu(傅杰)]

Hi all,

JBS:    https://bugs.openjdk.java.net/browse/JDK-8250825
Webrev: http://cr.openjdk.java.net/~jiefu/8250825/webrev.00/

When C2 tries to inline an unsafe-access method, it may generate the following pattern in make_unsafe_address:
      ConP  ConL
         \  |
          \ |
          AddP
Current implementation of TypeOopPtr::TypeOopPtr(...) failed to recognize it as an unsafe operation, which leads to the crash.

Testing:
  - tier1-3 on Linux/x64

Could you please review it and give me some advice?

Thanks a lot.
Best regards,
Jie