* Fixed a reduction bug which occasionally led to infinite-cost (invalid)
register allocation solutions despite the existence finite-cost solutions.
* Significantly reduced memory usage (>50% reduction).
* Simplified a lot of the solver code.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@94514 91177308-0d34-0410-b5e6-96231b3b80d8
