* Update file header comment

*** Revamp the code which handled unreachable code in the function.  Now the
    code is much more efficient for high-degree basic blocks, such as those
    that occur in the 252.eon SPEC benchmark.

For the interested, the time to promote a SINGLE alloca in _ZN7mrScene4ReadERSi
function used to be > 3.5s.  Now it is < .075s.  The function has a LOT of
allocas in it, so it appeared to be infinite looping, this should make it much
nicer.  :)

llvm-svn: 8863