[8u] backport of 8078866: compiler/eliminateAutobox/6934604/TestIntBoxing.java assert(p_f->Opcode() == Op_IfFalse) failed

[Roland Westrelin]

8u backport request. 8078866 was pushed to jdk9 friday last week and it hasn’t caused any new failures during nightly testing. The change applies cleanly to 8u.

https://bugs.openjdk.java.net/browse/JDK-8078866
http://hg.openjdk.java.net/jdk9/hs-comp/hotspot/rev/ac1a9d805f11

Roland.