Add an assertion, update DefInst even though no one uses it (dangling pointers
don't help anyone)

llvm-svn: 25081
diff --git a/llvm/lib/CodeGen/VirtRegMap.cpp b/llvm/lib/CodeGen/VirtRegMap.cpp
index 26498b7..f27ae2a 100644
--- a/llvm/lib/CodeGen/VirtRegMap.cpp
+++ b/llvm/lib/CodeGen/VirtRegMap.cpp
@@ -393,6 +393,7 @@
       
       // Otherwise, reload it and remember that we have it.
       PhysReg = VRM.getPhys(VirtReg);
+      assert(PhysReg && "Must map virtreg to physreg!");
       const TargetRegisterClass* RC =
         MBB.getParent()->getSSARegMap()->getRegClass(VirtReg);