[dwarfdump] Verify that CUs have a unit DIE.

This patch adds a check to the DWARF verifier to detect CUs without a
unit DIE.

Differential revision: https://reviews.llvm.org/D38363

llvm-svn: 314426
diff --git a/llvm/lib/DebugInfo/DWARF/DWARFVerifier.cpp b/llvm/lib/DebugInfo/DWARF/DWARFVerifier.cpp
index 096d5ff..eadb982 100644
--- a/llvm/lib/DebugInfo/DWARF/DWARFVerifier.cpp
+++ b/llvm/lib/DebugInfo/DWARF/DWARFVerifier.cpp
@@ -179,9 +179,14 @@
     }
   }
 
-  DieRangeInfo RI;
-  DWARFDie Die = Unit.getUnitDIE(/* ExtractUnitDIEOnly = */ false);
-  NumUnitErrors += verifyDieRanges(Die, RI);
+  if (DWARFDie Die = Unit.getUnitDIE(/* ExtractUnitDIEOnly = */ false)) {
+    DieRangeInfo RI;
+    NumUnitErrors += verifyDieRanges(Die, RI);
+  } else {
+    OS << "error: Compilation unit without unit DIE.\n";
+    NumUnitErrors++;
+  }
+
   return NumUnitErrors == 0;
 }