This patch adds initial version of code dealing with function
invariant constants (constant or {frame|arg}_pointer + constant). It
is simple but a very important case of rematerialization (important
because such constants might become a part of existing insns).
Dealing with such constants needs a lot of changes in cost
calculation, coloring, local allocator, coalescing (before and after
the allocation) and in synchronization optimization.
Not all of this implemented yet. So there is still a lot of work to
do. But mostly the code already works for x86 (at least all of
spec2000 tests work well).