Use VirtRegMap's Virt2SplitMap to keep track of the original live range before splitting.

All new virtual registers created for spilling or splitting point back to their original.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@125980 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/CodeGen/VirtRegMap.h b/lib/CodeGen/VirtRegMap.h
index a43ac5f..23101ce 100644
--- a/lib/CodeGen/VirtRegMap.h
+++ b/lib/CodeGen/VirtRegMap.h
@@ -214,7 +214,7 @@
     }
 
     /// @brief returns the live interval virtReg is split from.
-    unsigned getPreSplitReg(unsigned virtReg) {
+    unsigned getPreSplitReg(unsigned virtReg) const {
       return Virt2SplitMap[virtReg];
     }