Fix FP returnStdMoveLocal (#4244)

Author: chrchr-github

lib/checkfunctions.cpp

@@ -658,7 +658,7 @@ void CheckFunctions::returnLocalStdMove()
             if (retval->variable() && retval->variable()->isLocal() && !retval->variable()->isVolatile())
                 copyElisionError(retval);
             // RVO
-            if (Token::Match(retval, "(|{") && !retval->isCast())
+            if (Token::Match(retval, "(|{") && !retval->isCast() && !(retval->valueType() && retval->valueType()->reference != Reference::None))
                 copyElisionError(retval);
         }
     }

test/testfunctions.cpp

@@ -1731,6 +1731,18 @@ class TestFunctions : public TestFixture {
         check("struct A{} a; A f1() { return std::move(a); }\n"
               "A f2() { volatile A var; return std::move(var); }");
         ASSERT_EQUALS("", errout.str());
+
+        check("struct S { std::string msg{ \"abc\" }; };\n"
+              "std::unique_ptr<S> get(std::vector<std::unique_ptr<S>>& v) {\n"
+              "    return std::move(v.front());\n"
+              "}\n"
+              "int main() {\n"
+              "    std::vector<std::unique_ptr<S>> v;\n"
+              "    v.emplace_back(std::make_unique<S>());\n"
+              "    auto p = get(v);\n"
+              "    std::cout << p->msg;\n"
+              "}\n");
+        ASSERT_EQUALS("", errout.str());
     }
 
     void negativeMemoryAllocationSizeError() { // #389