RFR(M): 8073480: C2 should optimize explicit range checks

[Roland Westrelin]

Here is a new webrev for this:

http://cr.openjdk.java.net/~roland/8073480/webrev.01/

I took Vladimir’s comments into account (added test for null inputs in several places, strengthen the test to make sure a middle guard is a null check, renamed functions) and added code that look for a ConvI2L between the range check and a memory access that follows and annotate that ConvI2L with a tighter type so the movslq that Paul spotted are removed from the final code. 

Roland.