Request for Reviews(M): 7092905: C2: Keep track of the number of dead nodes

[Bharadwaj Yadavalli]

Addressed comments on my previous RFR. Changes athttp://cr.openjdk.java.net/~bharadwaj/7092905/webrev_02/

These changes are made to keep an (almost) accurate running count of the reachable (live) flow graph nodes. This will result in a more realistic node count for various phases of C2 to decide on whether to proceed with optimizations or not. Prior to these changes, C2 bails out of compilation based on the number of nodes created which typically larger than the number of reachable (live) nodes.