- Make the machine cse dumb coalescer (as opposed to the more awesome simple

- Make the machine cse dumb coalescer (as opposed to the more awesome simple
  coalescer) handle sub-register classes.
- Add heuristics to avoid non-profitable cse. Given the current lack of live
  range splitting, avoid cse when an expression has PHI use and the would be
  new use is in a BB where the expression wasn't already being used.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@98043 91177308-0d34-0410-b5e6-96231b3b80d8