Index: llvm/trunk/lib/Support/YAMLTraits.cpp
===================================================================
--- llvm/trunk/lib/Support/YAMLTraits.cpp
+++ llvm/trunk/lib/Support/YAMLTraits.cpp
@@ -657,7 +657,12 @@
       }
       i = j + 1;
     } else if (MustQuote == QuotingType::Double &&
-               !sys::unicode::isPrintable(S[j])) {
+               !sys::unicode::isPrintable(S[j]) && (S[j] & 0x80) == 0) {
+      // If we're double quoting non-printable characters, we prefer printing
+      // them as "\x" + their hex representation. Note that special casing is
+      // needed for UTF-8, where a byte may be part of a UTF-8 sequence and
+      // appear as non-printable, in which case we want to print the correct
+      // unicode character and not its hex representation.
       output(StringRef(&Base[i], j - i)); // "flush"
       output(StringLiteral("\\x"));
 
Index: llvm/trunk/unittests/Support/YAMLIOTest.cpp
===================================================================
--- llvm/trunk/unittests/Support/YAMLIOTest.cpp
+++ llvm/trunk/unittests/Support/YAMLIOTest.cpp
@@ -2541,3 +2541,31 @@
   ostr.flush();
   EXPECT_EQ("'abc''fdf'", out);
 }
+
+TEST(YAMLIO, TestEscapedUTF8SingleQuoteInsideDoubleQuote) {
+  std::string Id = "parameter 'параметр' is unused";
+
+  std::string out;
+  llvm::raw_string_ostream ostr(out);
+  Output xout(ostr, nullptr, 0);
+
+  llvm::yaml::EmptyContext Ctx;
+  yamlize(xout, Id, true, Ctx);
+
+  ostr.flush();
+  EXPECT_EQ("\"parameter 'параметр' is unused\"", out);
+}
+
+TEST(YAMLIO, TestEscapedUTF8) {
+  std::string Id = "/*параметр*/";
+
+  std::string out;
+  llvm::raw_string_ostream ostr(out);
+  Output xout(ostr, nullptr, 0);
+
+  llvm::yaml::EmptyContext Ctx;
+  yamlize(xout, Id, true, Ctx);
+
+  ostr.flush();
+  EXPECT_EQ("\"/*параметр*/\"", out);
+}