Implement RAGreedy::splitAroundRegion and remove loop splitting.

Region splitting includes loop splitting as a subset, and it is more generic.
The splitting heuristics for variables that are live in more than one block are
now:

1. Try to create a region that covers multiple basic blocks.
2. Try to create a new live range for each block with multiple uses.
3. Spill.

Steps 2 and 3 are similar to what the standard spiller is doing.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@123853 91177308-0d34-0410-b5e6-96231b3b80d8

lib/CodeGen/LiveInterval.cpp

@@ -650,7 +650,9 @@ void LiveRange::dump() const {
 }
 
 void LiveInterval::print(raw_ostream &OS, const TargetRegisterInfo *TRI) const {
-  OS << PrintReg(reg, TRI) << ',' << weight;
+  OS << PrintReg(reg, TRI);
+  if (weight != 0)
+    OS << ',' << weight;
 
   if (empty())
     OS << " EMPTY";