RFR(S): 8016277: Crash in nmethod::is_compiled_by_c1() on x86

[Roland Westrelin]

http://cr.openjdk.java.net/~roland/8016277/webrev.00/

Once an nmethod becomes zombie, its Method can be reclaimed so the reference to the Method in the nmethod becomes invalid.

My change sets the nmethod's _method to NULL once the nmethod is in the zombie state so that we risk using an invalid reference. The crash itself was cause by nmethod::is_native_method() (which uses the Method pointer of the nmethod) called from nmethod::is_compiled_by_c1() by some verification code. I changed the implementation of the nmethod::is_compiled_by_* so that they don't need to call is_native_method() (a call that was anyway useless because for a native method the compiler() is NULL).

Roland.