Index: lib/AST/ASTImporter.cpp
===================================================================
--- lib/AST/ASTImporter.cpp
+++ lib/AST/ASTImporter.cpp
@@ -90,6 +90,13 @@
     return getCanonicalForwardRedeclChain<FunctionDecl>(FD);
   }
 
+  void updateAttrAndFlags(const Decl *From, Decl *To) {
+    // Check if some flags or attrs are new in 'From' and copy into 'To'.
+    // FIXME: Other flags or attrs?
+    if (From->isUsed(false) && !To->isUsed(false))
+      To->setIsUsed();
+  }
+
   class ASTNodeImporter : public TypeVisitor<ASTNodeImporter, QualType>,
                           public DeclVisitor<ASTNodeImporter, Decl *>,
                           public StmtVisitor<ASTNodeImporter, Stmt *> {
@@ -3018,6 +3025,7 @@
       // An equivalent variable with external linkage has been found. Link 
       // the two declarations, then merge them.
       Importer.Imported(D, MergeWithVar);
+      updateAttrAndFlags(D, MergeWithVar);
       
       if (VarDecl *DDef = D->getDefinition()) {
         if (VarDecl *ExistingDef = MergeWithVar->getDefinition()) {
@@ -6837,6 +6845,8 @@
   if (Pos != ImportedDecls.end()) {
     Decl *ToD = Pos->second;
     Importer.ImportDefinitionIfNeeded(FromD, ToD);
+    // If FromD has some updated flags after last import, apply it.
+    updateAttrAndFlags(FromD, ToD);
     return ToD;
   }
   
Index: unittests/AST/ASTImporterTest.cpp
===================================================================
--- unittests/AST/ASTImporterTest.cpp
+++ unittests/AST/ASTImporterTest.cpp
@@ -290,6 +290,7 @@
     std::string FileName;
     std::unique_ptr<ASTUnit> Unit;
     TranslationUnitDecl *TUDecl = nullptr;
+    std::unique_ptr<ASTImporter> Importer;
     TU(StringRef Code, StringRef FileName, ArgVector Args)
         : Code(Code), FileName(FileName),
           Unit(tooling::buildASTFromCodeWithArgs(this->Code, Args,
@@ -297,6 +298,16 @@
           TUDecl(Unit->getASTContext().getTranslationUnitDecl()) {
       Unit->enableSourceFileDiagnostics();
     }
+
+    Decl *import(ASTUnit *ToAST, Decl *FromDecl) {
+      assert(ToAST);
+      if (!Importer) {
+        Importer.reset(new ASTImporter(
+            ToAST->getASTContext(), ToAST->getFileManager(),
+            Unit->getASTContext(), Unit->getFileManager(), false));
+      }
+      return Importer->Import(FromDecl);
+    }
   };
 
   // We may have several From contexts and related translation units. In each
@@ -329,14 +340,10 @@
     ToAST = tooling::buildASTFromCodeWithArgs(ToCode, ToArgs, OutputFileName);
     ToAST->enableSourceFileDiagnostics();
 
-    ASTContext &FromCtx = FromTU.Unit->getASTContext(),
-               &ToCtx = ToAST->getASTContext();
+    ASTContext &FromCtx = FromTU.Unit->getASTContext();
 
     createVirtualFileIfNeeded(ToAST.get(), InputFileName, FromTU.Code);
 
-    ASTImporter Importer(ToCtx, ToAST->getFileManager(), FromCtx,
-                         FromTU.Unit->getFileManager(), false);
-
     IdentifierInfo *ImportedII = &FromCtx.Idents.get(Identifier);
     assert(ImportedII && "Declaration with the given identifier "
                          "should be specified in test!");
@@ -347,7 +354,8 @@
 
     assert(FoundDecls.size() == 1);
 
-    Decl *Imported = Importer.Import(FoundDecls.front());
+    Decl *Imported = FromTU.import(ToAST.get(), FoundDecls.front());
+
     assert(Imported);
     return std::make_tuple(*FoundDecls.begin(), Imported);
   }
@@ -401,11 +409,7 @@
     assert(It != FromTUs.end());
     createVirtualFileIfNeeded(ToAST.get(), It->FileName, It->Code);
 
-    ASTContext &FromCtx = From->getASTContext(),
-               &ToCtx = ToAST->getASTContext();
-    ASTImporter Importer(ToCtx, ToAST->getFileManager(), FromCtx,
-                         FromCtx.getSourceManager().getFileManager(), false);
-    return Importer.Import(From);
+    return It->import(ToAST.get(), From);
   }
 
   ~ASTImporterTestBase() {
@@ -469,6 +473,48 @@
   EXPECT_THAT(RedeclsD1, ::testing::ContainerEq(RedeclsD2));
 }
 
+TEST_P(ASTImporterTestBase, ImportDoesUpdateUsedFlag) {
+  auto Pattern = varDecl(hasName("x"));
+  VarDecl *Imported1;
+  {
+    Decl *FromTU = getTuDecl("extern int x;", Lang_CXX, "input0.cc");
+    auto *FromD = FirstDeclMatcher<VarDecl>().match(FromTU, Pattern);
+    Imported1 = cast<VarDecl>(Import(FromD, Lang_CXX));
+  }
+  VarDecl *Imported2;
+  {
+    Decl *FromTU = getTuDecl("int x;", Lang_CXX, "input1.cc");
+    auto *FromD = FirstDeclMatcher<VarDecl>().match(FromTU, Pattern);
+    Imported2 = cast<VarDecl>(Import(FromD, Lang_CXX));
+  }
+  EXPECT_EQ(Imported1->getCanonicalDecl(), Imported2->getCanonicalDecl());
+  EXPECT_FALSE(Imported2->isUsed(false));
+  {
+    Decl *FromTU = getTuDecl(
+        "extern int x; int f() { return x; }", Lang_CXX, "input2.cc");
+    auto *FromD =
+        FirstDeclMatcher<FunctionDecl>().match(FromTU, functionDecl());
+    Import(FromD, Lang_CXX);
+  }
+  EXPECT_TRUE(Imported2->isUsed(false));
+}
+
+TEST_P(ASTImporterTestBase, ReimportWithUsedFlag) {
+  auto Pattern = varDecl(hasName("x"));
+  
+  Decl *FromTU = getTuDecl("int x;", Lang_CXX, "input0.cc");
+  auto *FromD = FirstDeclMatcher<VarDecl>().match(FromTU, Pattern);
+  
+  auto *Imported1 = cast<VarDecl>(Import(FromD, Lang_CXX));
+  
+  ASSERT_FALSE(Imported1->isUsed(false));
+
+  FromD->setIsUsed();
+  auto *Imported2 = cast<VarDecl>(Import(FromD, Lang_CXX));
+  
+  EXPECT_EQ(Imported1, Imported2);
+  EXPECT_TRUE(Imported2->isUsed(false));
+}
 
 TEST_P(ImportExpr, ImportStringLiteral) {
   MatchVerifier<Decl> Verifier;