Cache basic block bounds instead of asking SlotIndexes::getMBBRange all the time.

This speeds up the greedy register allocator by 15%.
DenseMap is not as fast as one might hope.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@126921 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/CodeGen/SplitKit.h b/lib/CodeGen/SplitKit.h
index 28c5c60..240f1fe 100644
--- a/lib/CodeGen/SplitKit.h
+++ b/lib/CodeGen/SplitKit.h
@@ -71,6 +71,8 @@
   ///
   struct BlockInfo {
     MachineBasicBlock *MBB;
+    SlotIndex Start;      ///< Beginining of block.
+    SlotIndex Stop;       ///< End of block.
     SlotIndex FirstUse;   ///< First instr using current reg.
     SlotIndex LastUse;    ///< Last instr using current reg.
     SlotIndex Kill;       ///< Interval end point inside block.