Enable loop splitting in RegAllocGreedy.

The heuristics split around the largest loop where the current register may be
allocated without interference.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@122106 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/CodeGen/MachineLoopRanges.h

@@ -49,6 +49,9 @@ private:
   MachineLoopRange(const MachineLoop*, Allocator&, SlotIndexes&);
 
 public:
+  /// getLoop - Return the mapped machine loop.
+  const MachineLoop *getLoop() const { return Loop; }
+
   /// overlaps - Return true if this loop overlaps the given range of machine
   /// inteructions.
   bool overlaps(SlotIndex Start, SlotIndex Stop);