Fix DbgStopPointInst->getFileName/getDirectory, broken by the MDNodification in
r80406, and readd a -print-dbginfo test.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@80778 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Analysis/ValueTracking.cpp b/lib/Analysis/ValueTracking.cpp
index cb2d624..aa71f1d 100644
--- a/lib/Analysis/ValueTracking.cpp
+++ b/lib/Analysis/ValueTracking.cpp
@@ -1058,6 +1058,11 @@
                                  StopAtNul);
   }
   
+  if (MDString *MDStr = dyn_cast<MDString>(V)) {
+    Str = MDStr->getString();
+    return true;
+  }
+
   // The GEP instruction, constant or instruction, must reference a global
   // variable that is a constant and is initialized. The referenced constant
   // initializer is the array that we'll use for optimization.