When I run tests with HS17 builds and -XX:+OptimizeStringConcat, the JVM will eventually core dump:
Error: guarantee(cont_offset != 0,"unhandled implicit exception in compiled code")
This happens only when -XX:+OptimizeStringConcat is enabled, so it seems different than 6914436, though of course they may have the same root cause. I have been using OptimizeStringConcat on HS17 in the latest JDK7 build but also in JDK6 builds my moving the libjvm.so
I have attached the fastdebug output and hs_err file; core file is at ftp://javaperf.sfbay/pub/cores/core.stringconcat.gz. And yes, it's one of those bugs I can only reproduce on our big spec tests, though it reproduces quite easily so I can get more info quickly.