RFC - VRP1 default mode

[Andrew MacLeod via Gcc-patches]

Figured I would ask what you guys think of making ranger the default for 
the VRP1 pass now.

With partial equivalences and the other bits I checked in the past few 
weeks I'm not aware of much that the legacy VRP pass gets that ranger 
doesn't.  The only exception to that which I am aware of is the trick 
played with the unreachable edges to set global ranges, but that is done 
in the DOM passes now anyway... so it just happens slightly later in the 
optimization cycle. There is one test case that needs adjustment for 
that which was just checking for a mask in DOM2 
(gcc.dg/tree-ssa/pr107009.c).   At this point I have not aware of 
anything that Id be concerned about, and the testsuite seems to run 
cleanly.

We could change the default now and see if any issues show up, giving us 
a chance to address them. The code base has been well exercised for a 
while so risk should be low.  We could also reduce code size by 
stripping out unneeded code if we so desired.

Or we could leave things as they are for one more cycle.  My preference 
would be to make the switch now and let it play out. Thoughts?

Andrew