RFR(S): 8166836: Elimination of clone's ArrayCopyNode may make compilation fail silently

[Vladimir Ivanov]

> http://cr.openjdk.java.net/~roland/8166836/webrev.00/

Looks good.

> It's quite unfortunate that this wasn't found by testing because
> compilations where the graph is non schedulable simply fail. This could
> have gone unnoticed much longer. In debug builds shouldn't we abort the
> VM in C2Compiler::compile_method() if the compilation fails because of a
> non schedulable graph?

Sounds reasonable. I expect there are other cases when compilers bail 
out unexpectely. It would be good to have an assert checking it doesn't 
happen.

Best regards,
Vladimir Ivanov