SMS improvements branch

[Mostafa Hagog]

There are several improvements of SMS that were introduced to 4.0 but
rejected and are waiting for 4.1 to open.  There is also additional
work that we are planning to do for improving SMS, here is a list
of the items and their status:
I. Infrastructure work:
    1. Change SMS to work in cfglayout mode. (DONE, for 4.1)
    2. Build and use loop information in SMS. (DONE, for 4.1)
    3. Add loop versioning to RTL (in cfglayout mode). (DONE, for 4.1)
    4. Loop peeling in SMS to make SMS applicable for more loops.
       (Started, for 4.1)
    5. Use doloop analysis instead of BCT to check for counted loops.
      (Started, for 4.1)
    6. Port tree data dependency analysis routines to the RTL level
       so we can have better dependancy. (Future, Beyond 4.1)
    7. Improve alias analysis in the RTL level. (Future, Beyond 4.1)

II. SMS related work :
   1. Use of alias sets to remove memory dependencies. (DONE, for 4.1)
   2. Remove register anti-dependencies. (DONE, for 4.1)
   3. Add backtracking to the SMS. (DONE, for 4.1)
   4. Consider register pressure in SMS. (Beyond 4.1)

I am thinking of opening a development branch for the sake of SMS
improvements, unless someone knows of an existing branch that
this work could be put in.

Mostafa.