There was a (commented out) assert that the entry node to each SCC we
find would be a SILArgument. This is not always the case, so I removed
the assert and added a test case that demonstrates this.
I tightened up the IV recognition code a little bit as well.
Swift SVN r19885
The induction variable analysis derives from the SCC visitor CRTP-style
and uses it to drive analysis to find the IVs of a function.
The current definition of induction variable is very weak, but enough to
use for very basic bounds-check elimination.
This is not quite ready for real use. There is an assert that I've
commented out that is firing but should not be, and that will require
some more investigation.
Swift SVN r19845
