RFR(XS): 8240794: [BACKOUT] 8238384 CTW: C2 compilation fails with "assert(store != load->find_exact_control(load->in(0))) failed: dependence cycle found"

[Roland Westrelin]

8238384 is suspected to cause a couple hard to reproduce new bugs so
let's back it out for now. The backout change applies cleanly:

http://cr.openjdk.java.net/~roland/8240794/webrev.00/

Roland.