DebugInfo: Support imported modules (using directives) within lexical blocks.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@181272 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/CodeGen/CGDebugInfo.cpp b/lib/CodeGen/CGDebugInfo.cpp
index 6beba66..ddcb931 100644
--- a/lib/CodeGen/CGDebugInfo.cpp
+++ b/lib/CodeGen/CGDebugInfo.cpp
@@ -2930,9 +2930,12 @@
 }
 
 void CGDebugInfo::EmitUsingDirective(const UsingDirectiveDecl &UD) {
+  llvm::DIScope Scope =
+      LexicalBlockStack.empty()
+          ? getContextDescriptor(cast<Decl>(UD.getDeclContext()))
+          : llvm::DIScope(LexicalBlockStack.back());
   DBuilder.createImportedModule(
-      getContextDescriptor(cast<Decl>(UD.getDeclContext())),
-      getOrCreateNameSpace(UD.getNominatedNamespace()),
+      Scope, getOrCreateNameSpace(UD.getNominatedNamespace()),
       getLineNumber(UD.getLocation()));
 }