Add an assertion about the integrity of the iterator.
Broken parent scope pointers in inlined DIVariables can cause
ensureAbstractVariableIsCreated to insert new abstract scopes, thus
invalidating the iterator in this loop and leading to hard-to-debug
crashes. Useful when manually reducing IR for testcases.

llvm-svn: 219628
diff --git a/llvm/lib/CodeGen/AsmPrinter/DwarfDebug.cpp b/llvm/lib/CodeGen/AsmPrinter/DwarfDebug.cpp
index 491681a..6e64188 100644
--- a/llvm/lib/CodeGen/AsmPrinter/DwarfDebug.cpp
+++ b/llvm/lib/CodeGen/AsmPrinter/DwarfDebug.cpp
@@ -1365,6 +1365,9 @@
     return;
   }
 
+#ifndef NDEBUG
+  size_t NumAbstractScopes = LScopes.getAbstractScopesList().size();
+#endif
   // Construct abstract scopes.
   for (LexicalScope *AScope : LScopes.getAbstractScopesList()) {
     DISubprogram SP(AScope->getScopeNode());
@@ -1377,6 +1380,8 @@
       if (!ProcessedVars.insert(DV))
         continue;
       ensureAbstractVariableIsCreated(DV, DV.getContext());
+      assert(LScopes.getAbstractScopesList().size() == NumAbstractScopes
+             && "ensureAbstractVariableIsCreated inserted abstract scopes");
     }
     constructAbstractSubprogramScopeDIE(AScope);
   }