RFR(M): 8057038: Speculative traps not robust when compilation and class unloading are concurrent

[Roland Westrelin]

Speculative traps recorded in a MethodData can be removed at a safepoint. During a compilation, as a MethodData is copied and translated by a compiler thread to build a ciMethodData, a safepoint can occur as speculative traps are being copied, and not yet copied speculative traps may be removed. That changes the layout of the traps.  The loop doing the copying doesn't handle it currently.

http://cr.openjdk.java.net/~roland/8057038/webrev.00/

Based on this previous RFR that I withdrew:

http://mail.openjdk.java.net/pipermail/hotspot-compiler-dev/2014-August/015150.html

Roland.