[15] RFR(XS): 8238756: C2: assert(((n) == __null || !VerifyIterativeGVN || !((n)->is_dead()))) failed: can not use dead node

[Christian Hagedorn]

Hi

Please review the following patch:
https://bugs.openjdk.java.net/browse/JDK-8238756
http://cr.openjdk.java.net/~chagedorn/8238756/webrev.00/

The dead hook node is set as an input to the phi node in replace_edge(), 
letting the assertion of set_req() fail with VerifyIterativeGVN. I 
suggest to just set a dummy input to prevent the hook from being dead.

Thank you!

Best regards,
Christian