RFR: 8172751: OSR compilation at unreachable bci causes C1 crash

[Andreas Woess]

Hi all,

please review the following patch:
http://cr.openjdk.java.net/~aw/8172751/webrev/
https://bugs.openjdk.java.net/browse/JDK-8172751

This is a small fix for a extremely unlikely but consistently
reproducible crash (see included test) in the C1 GraphBuilder with OSR.
AFAICT, the problem is that we may never visit the osr entry block if
it's found to be unreachable during parsing due to constant folding.

The patch simply changes the existing assertion to a bailout. We'd crash
immediately after it trying to get the osr block's state (in a product
build; in a debug build the assertion fails).Observed on JDK 8u* and 9.

Thanks,
Andreas