diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
index a75001963996229..7063fea41efda15 100644
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -99,6 +99,20 @@ C++ Specific Potentially Breaking Changes
     // Was error, now evaluates to false.
     constexpr bool b = f() == g();
 
+- The warning ``-Wdeprecated-literal-operator`` is now on by default, as this is
+  something that WG21 has shown interest in removing from the language. The
+  result is that anyone who is compiling with ``-Werror`` should see this
+  diagnostic.  To fix this diagnostic, simply removing the space character from
+  between the ``operator""`` and the user defined literal name will make the
+  source no longer deprecated. This is consistent with `CWG2521 <https://cplusplus.github.io/CWG/issues/2521.html>_`.
+
+  .. code-block:: c++
+
+    // Now diagnoses by default.
+    unsigned operator"" _udl_name(unsigned long long);
+    // Fixed version:
+    unsigned operator""_udl_name(unsigned long long);
+
 ABI Changes in This Version
 ---------------------------
 
@@ -215,6 +229,10 @@ Resolutions to C++ Defect Reports
 - Clang now allows trailing requires clause on explicit deduction guides.
   (`CWG2707: Deduction guides cannot have a trailing requires-clause <https://cplusplus.github.io/CWG/issues/2707.html>`_).
 
+- Clang now diagnoses a space in the first production of a ``literal-operator-id``
+  by default.
+  (`CWG2521: User-defined literals and reserved identifiers <https://cplusplus.github.io/CWG/issues/2521.html>`_).
+
 C Language Changes
 ------------------
 
@@ -378,6 +396,10 @@ Improvements to Clang's diagnostics
 - The warning for an unsupported type for a named register variable is now phrased ``unsupported type for named register variable``,
   instead of ``bad type for named register variable``. This makes it clear that the type is not supported at all, rather than being
   suboptimal in some way the error fails to mention (#GH111550).
+  
+- Clang now emits a ``-Wdepredcated-literal-operator`` diagnostic, even if the
+  name was a reserved name, which we improperly allowed to suppress the
+  diagnostic.
 
 Improvements to Clang's time-trace
 ----------------------------------
diff --git a/clang/include/clang/Basic/DiagnosticSemaKinds.td b/clang/include/clang/Basic/DiagnosticSemaKinds.td
index 9ae26e48fd322a4..e880771ef18f4c4 100644
--- a/clang/include/clang/Basic/DiagnosticSemaKinds.td
+++ b/clang/include/clang/Basic/DiagnosticSemaKinds.td
@@ -439,7 +439,7 @@ def warn_reserved_extern_symbol: Warning<
   InGroup<ReservedIdentifier>, DefaultIgnore;
 def warn_deprecated_literal_operator_id: Warning<
   "identifier %0 preceded by whitespace in a literal operator declaration "
-  "is deprecated">, InGroup<DeprecatedLiteralOperator>, DefaultIgnore;
+  "is deprecated">, InGroup<DeprecatedLiteralOperator>;
 def warn_reserved_module_name : Warning<
   "%0 is a reserved name for a module">, InGroup<ReservedModuleIdentifier>;
 def warn_import_implementation_partition_unit_in_interface_unit : Warning<
diff --git a/clang/lib/Basic/IdentifierTable.cpp b/clang/lib/Basic/IdentifierTable.cpp
index c9c9d927a5902ef..16151c94464f999 100644
--- a/clang/lib/Basic/IdentifierTable.cpp
+++ b/clang/lib/Basic/IdentifierTable.cpp
@@ -406,6 +406,9 @@ ReservedLiteralSuffixIdStatus
 IdentifierInfo::isReservedLiteralSuffixId() const {
   StringRef Name = getName();
 
+  // Note: the diag::warn_deprecated_literal_operator_id diagnostic depends on
+  // this being the first check we do, so if this order changes, we have to fix
+  // that as well.
   if (Name[0] != '_')
     return ReservedLiteralSuffixIdStatus::NotStartsWithUnderscore;
 
diff --git a/clang/lib/Sema/SemaExprCXX.cpp b/clang/lib/Sema/SemaExprCXX.cpp
index 8e9bcb10a80b46f..d39a545b66c151e 100644
--- a/clang/lib/Sema/SemaExprCXX.cpp
+++ b/clang/lib/Sema/SemaExprCXX.cpp
@@ -503,17 +503,23 @@ bool Sema::checkLiteralOperatorId(const CXXScopeSpec &SS,
     const IdentifierInfo *II = Name.Identifier;
     ReservedIdentifierStatus Status = II->isReserved(PP.getLangOpts());
     SourceLocation Loc = Name.getEndLoc();
-    if (!PP.getSourceManager().isInSystemHeader(Loc)) {
-      if (auto Hint = FixItHint::CreateReplacement(
-              Name.getSourceRange(),
-              (StringRef("operator\"\"") + II->getName()).str());
-          isReservedInAllContexts(Status)) {
-        Diag(Loc, diag::warn_reserved_extern_symbol)
-            << II << static_cast<int>(Status) << Hint;
-      } else {
-        Diag(Loc, diag::warn_deprecated_literal_operator_id) << II << Hint;
-      }
-    }
+
+    auto Hint = FixItHint::CreateReplacement(
+        Name.getSourceRange(),
+        (StringRef("operator\"\"") + II->getName()).str());
+
+    // Only emit this diagnostic if we start with an underscore, else the
+    // diagnostic for C++11 requiring a space between the quotes and the
+    // identifier conflicts with this and gets confusing. The diagnostic stating
+    // this is a reserved name should force the underscore, which gets this
+    // back.
+    if (II->isReservedLiteralSuffixId() !=
+        ReservedLiteralSuffixIdStatus::NotStartsWithUnderscore)
+      Diag(Loc, diag::warn_deprecated_literal_operator_id) << II << Hint;
+
+    if (isReservedInAllContexts(Status))
+      Diag(Loc, diag::warn_reserved_extern_symbol)
+          << II << static_cast<int>(Status) << Hint;
   }
 
   if (!SS.isValid())
diff --git a/clang/test/CXX/drs/cwg14xx.cpp b/clang/test/CXX/drs/cwg14xx.cpp
index 5301185d0469829..cb2f34bf5e427fc 100644
--- a/clang/test/CXX/drs/cwg14xx.cpp
+++ b/clang/test/CXX/drs/cwg14xx.cpp
@@ -627,7 +627,7 @@ int i = N::f();
 
 namespace cwg1479 { // cwg1479: 3.1
 #if __cplusplus >= 201103L
-  int operator"" _a(const char*, std::size_t = 0);
+  int operator""_a(const char*, std::size_t = 0);
   // since-cxx11-error@-1 {{literal operator cannot have a default argument}}
 #endif
 }
diff --git a/clang/test/CXX/drs/cwg25xx.cpp b/clang/test/CXX/drs/cwg25xx.cpp
index 1924008f15ba580..87a728088ee6e4f 100644
--- a/clang/test/CXX/drs/cwg25xx.cpp
+++ b/clang/test/CXX/drs/cwg25xx.cpp
@@ -88,6 +88,9 @@ operator""  _div();
 using ::cwg2521::operator"" _\u03C0___;
 using ::cwg2521::operator""_div;
 // since-cxx11-warning@-2 {{identifier '_π___' preceded by whitespace in a literal operator declaration is deprecated}}
+
+long double operator"" _RESERVED(long double);
+// since-cxx11-warning@-1 {{identifier '_RESERVED' preceded by whitespace in a literal operator declaration is deprecated}}
 #pragma clang diagnostic pop
 #endif
 } // namespace cwg2521
diff --git a/clang/test/CXX/lex/lex.literal/lex.ext/p1.cpp b/clang/test/CXX/lex/lex.literal/lex.ext/p1.cpp
index 1c227a1b10d385a..ec478fbba60a18e 100644
--- a/clang/test/CXX/lex/lex.literal/lex.ext/p1.cpp
+++ b/clang/test/CXX/lex/lex.literal/lex.ext/p1.cpp
@@ -1,4 +1,4 @@
-// RUN: %clang_cc1 -fsyntax-only -std=c++11 -verify %s
+// RUN: %clang_cc1 -fsyntax-only -std=c++11 -Wno-deprecated-literal-operator -verify %s
 
 void operator "" p31(long double); // expected-warning{{user-defined literal suffixes not starting with '_' are reserved}}
 void operator "" _p31(long double);
diff --git a/clang/test/CXX/lex/lex.literal/lex.ext/p10.cpp b/clang/test/CXX/lex/lex.literal/lex.ext/p10.cpp
index 1b5d3880cb61299..6a9d713ca72d2e3 100644
--- a/clang/test/CXX/lex/lex.literal/lex.ext/p10.cpp
+++ b/clang/test/CXX/lex/lex.literal/lex.ext/p10.cpp
@@ -1,4 +1,4 @@
-// RUN: %clang_cc1 -std=c++11 -verify %s
+// RUN: %clang_cc1 -std=c++11 -Wno-deprecated-literal-operator -verify %s
 
 using size_t = decltype(sizeof(int));
 void operator "" wibble(const char *); // expected-warning {{user-defined literal suffixes not starting with '_' are reserved; no literal will invoke this operator}}
diff --git a/clang/test/CXX/lex/lex.literal/lex.ext/p11.cpp b/clang/test/CXX/lex/lex.literal/lex.ext/p11.cpp
index 8b5fcf4b609b653..d69a58a7dfad206 100644
--- a/clang/test/CXX/lex/lex.literal/lex.ext/p11.cpp
+++ b/clang/test/CXX/lex/lex.literal/lex.ext/p11.cpp
@@ -6,16 +6,16 @@ template<typename T, typename U> struct same_type;
 template<typename T> struct same_type<T, T> {};
 template<typename T> using X = T;
 template<typename CharT, X<CharT>...>
-int operator "" _x(); // expected-warning {{string literal operator templates are a GNU extension}}
+int operator ""_x(); // expected-warning {{string literal operator templates are a GNU extension}}
 template<char...>
-double operator "" _x();
+double operator ""_x();
 
 auto a="string"_x;
 auto b=42_x;
 same_type<decltype(a), int> test_a;
 same_type<decltype(b), double> test_b;
 
-char operator "" _x(const char *begin, size_t size);
+char operator ""_x(const char *begin, size_t size);
 auto c="string"_x;
 auto d=L"string"_x;
 same_type<decltype(c), char> test_c;
diff --git a/clang/test/CXX/lex/lex.literal/lex.ext/p3.cpp b/clang/test/CXX/lex/lex.literal/lex.ext/p3.cpp
index d764989312c246a..e5ab09c628bcfab 100644
--- a/clang/test/CXX/lex/lex.literal/lex.ext/p3.cpp
+++ b/clang/test/CXX/lex/lex.literal/lex.ext/p3.cpp
@@ -1,18 +1,18 @@
 // RUN: %clang_cc1 -fsyntax-only -std=c++11 -verify %s
 
-int &operator "" _x1 (unsigned long long);
+int &operator ""_x1 (unsigned long long);
 int &i1 = 0x123_x1;
 
-double &operator "" _x1 (const char *);
+double &operator ""_x1 (const char *);
 int &i2 = 45_x1;
 
-template<char...> char &operator "" _x1 ();
+template<char...> char &operator ""_x1 ();
 int &i3 = 0377_x1;
 
 int &i4 = 90000000000000000000000000000000000000000000000_x1; // expected-error {{integer literal is too large to be represented in any integer type}}
 
-double &operator "" _x2 (const char *);
+double &operator ""_x2 (const char *);
 double &i5 = 123123123123123123123123123123123123123123123_x2;
 
-template<char...Cs> constexpr int operator "" _x3() { return sizeof...(Cs); }
+template<char...Cs> constexpr int operator ""_x3() { return sizeof...(Cs); }
 static_assert(123456789012345678901234567890123456789012345678901234567890_x3 == 60, "");
diff --git a/clang/test/CXX/lex/lex.literal/lex.ext/p4.cpp b/clang/test/CXX/lex/lex.literal/lex.ext/p4.cpp
index 011e832c69d7298..7dbe70ce084e761 100644
--- a/clang/test/CXX/lex/lex.literal/lex.ext/p4.cpp
+++ b/clang/test/CXX/lex/lex.literal/lex.ext/p4.cpp
@@ -1,18 +1,18 @@
 // RUN: %clang_cc1 -fsyntax-only -std=c++11 -verify %s
 
-int &operator "" _x1 (long double);
+int &operator ""_x1 (long double);
 int &i1 = 0.123_x1;
 
-double &operator "" _x1 (const char *);
+double &operator ""_x1 (const char *);
 int &i2 = 45._x1;
 
-template<char...> char &operator "" _x1 ();
+template<char...> char &operator ""_x1 ();
 int &i3 = 0377e-1_x1;
 
 int &i4 = 1e1000000_x1; // expected-warning {{too large for type 'long double'}}
 
-double &operator "" _x2 (const char *);
+double &operator ""_x2 (const char *);
 double &i5 = 1e1000000_x2;
 
-template<char...Cs> constexpr int operator "" _x3() { return sizeof...(Cs); }
+template<char...Cs> constexpr int operator ""_x3() { return sizeof...(Cs); }
 static_assert(1e1000000_x3 == 9, "");
diff --git a/clang/test/CXX/lex/lex.literal/lex.ext/p5.cpp b/clang/test/CXX/lex/lex.literal/lex.ext/p5.cpp
index aee20545ececfce..afadba282e626c9 100644
--- a/clang/test/CXX/lex/lex.literal/lex.ext/p5.cpp
+++ b/clang/test/CXX/lex/lex.literal/lex.ext/p5.cpp
@@ -3,19 +3,19 @@
 
 using size_t = decltype(sizeof(int));
 
-int &operator "" _x1 (const char *);
-double &operator "" _x1 (const char *, size_t);
+int &operator ""_x1 (const char *);
+double &operator ""_x1 (const char *, size_t);
 double &i1 = "foo"_x1;
 #if __cplusplus >= 202002L
 using char8 = float;
-float &operator "" _x1 (const char8_t *, size_t);
+float &operator ""_x1 (const char8_t *, size_t);
 #else
 using char8 = double;
 #endif
 char8 &i2 = u8"foo"_x1;
 double &i3 = L"foo"_x1; // expected-error {{no matching literal operator for call to 'operator""_x1' with arguments of types 'const wchar_t *' and 'unsigned long'}}
 
-char &operator "" _x1(const wchar_t *, size_t);
+char &operator ""_x1(const wchar_t *, size_t);
 char &i4 = L"foo"_x1; // ok
 double &i5 = R"(foo)"_x1; // ok
 char8 &i6 = u\
diff --git a/clang/test/CXX/lex/lex.literal/lex.ext/p6.cpp b/clang/test/CXX/lex/lex.literal/lex.ext/p6.cpp
index 23cd7081d5e3ee9..b1df641f2dc43c8 100644
--- a/clang/test/CXX/lex/lex.literal/lex.ext/p6.cpp
+++ b/clang/test/CXX/lex/lex.literal/lex.ext/p6.cpp
@@ -2,13 +2,13 @@
 
 using size_t = decltype(sizeof(int));
 
-int &operator "" _x1 (const char *);
+int &operator ""_x1 (const char *);
 double &i1 = 'a'_x1; // expected-error {{no matching literal operator}}
-double &operator "" _x1 (wchar_t);
+double &operator ""_x1 (wchar_t);
 double &i2 = L'a'_x1;
 double &i3 = 'a'_x1; // expected-error {{no matching literal operator}}
-double &i4 = operator"" _x1('a'); // ok
+double &i4 = operator""_x1('a'); // ok
 
-char &operator "" _x1(char16_t);
+char &operator ""_x1(char16_t);
 char &i5 = u'a'_x1; // ok
 double &i6 = L'a'_x1; // ok
diff --git a/clang/test/CXX/lex/lex.literal/lex.ext/p7.cpp b/clang/test/CXX/lex/lex.literal/lex.ext/p7.cpp
index 0b40ecdc143fcb0..d571fcb8697eb01 100644
--- a/clang/test/CXX/lex/lex.literal/lex.ext/p7.cpp
+++ b/clang/test/CXX/lex/lex.literal/lex.ext/p7.cpp
@@ -10,9 +10,9 @@ template<typename T> struct same_type<T, T> {};
 
 namespace std_example {
 
-long double operator "" _w(long double);
-std::string operator "" _w(const char16_t*, size_t);
-unsigned operator "" _w(const char*);
+long double operator ""_w(long double);
+std::string operator ""_w(const char16_t*, size_t);
+unsigned operator ""_w(const char*);
 int main() {
   auto v1 = 1.2_w;    // calls operator""_w(1.2L)
   auto v2 = u"one"_w; // calls operator""_w(u"one", 3)
diff --git a/clang/test/CXX/lex/lex.literal/lex.ext/p8.cpp b/clang/test/CXX/lex/lex.literal/lex.ext/p8.cpp
index d9078221ff5e3a8..67d976263e01674 100644
--- a/clang/test/CXX/lex/lex.literal/lex.ext/p8.cpp
+++ b/clang/test/CXX/lex/lex.literal/lex.ext/p8.cpp
@@ -1,7 +1,7 @@
 // RUN: %clang_cc1 -std=c++11 -verify %s
 
 using size_t = decltype(sizeof(int));
-constexpr const char *operator "" _id(const char *p, size_t) { return p; }
+constexpr const char *operator ""_id(const char *p, size_t) { return p; }
 constexpr const char *s = "foo"_id "bar" "baz"_id "quux";
 
 constexpr bool streq(const char *p, const char *q) {
@@ -9,8 +9,8 @@ constexpr bool streq(const char *p, const char *q) {
 }
 static_assert(streq(s, "foobarbazquux"), "");
 
-constexpr const char *operator "" _trim(const char *p, size_t n) {
-  return *p == ' ' ? operator "" _trim(p + 1, n - 1) : p;
+constexpr const char *operator ""_trim(const char *p, size_t n) {
+  return *p == ' ' ? operator ""_trim(p + 1, n - 1) : p;
 }
 constexpr const char *t = "   " " "_trim "  foo";
 static_assert(streq(t, "foo"), "");
diff --git a/clang/test/CXX/lex/lex.literal/lex.ext/p9.cpp b/clang/test/CXX/lex/lex.literal/lex.ext/p9.cpp
index 65e27b41b066804..fbdedd119d3d68e 100644
--- a/clang/test/CXX/lex/lex.literal/lex.ext/p9.cpp
+++ b/clang/test/CXX/lex/lex.literal/lex.ext/p9.cpp
@@ -1,7 +1,7 @@
 // RUN: %clang_cc1 -std=c++11 -fsyntax-only -verify %s
 
 using size_t = decltype(sizeof(int));
-void operator "" _x(const wchar_t *, size_t);
+void operator ""_x(const wchar_t *, size_t);
 
 namespace std_example {
 
diff --git a/clang/test/CXX/over/over.oper/over.literal/p2.cpp b/clang/test/CXX/over/over.oper/over.literal/p2.cpp
index f3ebadd2b8b9bc1..cf26806e9e7d757 100644
--- a/clang/test/CXX/over/over.oper/over.literal/p2.cpp
+++ b/clang/test/CXX/over/over.oper/over.literal/p2.cpp
@@ -1,43 +1,43 @@
 // RUN: %clang_cc1 -std=c++11 %s -verify
 
-void operator "" _a(const char *);
+void operator ""_a(const char *);
 
 namespace N {
-  using ::operator "" _a;
+  using ::operator ""_a;
 
-  void operator "" _b(const char *);
+  void operator ""_b(const char *);
 }
 
-using N::operator "" _b;
+using N::operator ""_b;
 
 class C {
-  void operator "" _c(const char *); // expected-error {{must be in a namespace or global scope}}
+  void operator ""_c(const char *); // expected-error {{must be in a namespace or global scope}}
 
-  static void operator "" _c(unsigned long long); // expected-error {{must be in a namespace or global scope}}
+  static void operator ""_c(unsigned long long); // expected-error {{must be in a namespace or global scope}}
 
-  friend void operator "" _d(const char *);
+  friend void operator ""_d(const char *);
 };
 
-int operator "" _e; // expected-error {{cannot be the name of a variable}}
+int operator ""_e; // expected-error {{cannot be the name of a variable}}
 
 void f() {
-  int operator "" _f; // expected-error {{cannot be the name of a variable}}
+  int operator ""_f; // expected-error {{cannot be the name of a variable}}
 }
 
 extern "C++" {
-  void operator "" _g(const char *);
+  void operator ""_g(const char *);
 }
 
-template<char...> void operator "" _h() {}
+template<char...> void operator ""_h() {}
 
-template<> void operator "" _h<'a', 'b', 'c'>() {}
+template<> void operator ""_h<'a', 'b', 'c'>() {}
 
-template void operator "" _h<'a', 'b', 'c', 'd'>();
+template void operator ""_h<'a', 'b', 'c', 'd'>();
 
 namespace rdar13605348 {
 
 class C {
-  double operator"" _x(long double value) { return double(value); } // expected-error{{literal operator 'operator""_x' must be in a namespace or global scope}}
+  double operator""_x(long double value) { return double(value); } // expected-error{{literal operator 'operator""_x' must be in a namespace or global scope}}
   double value() { return 3.2_x; } // expected-error{{no matching literal operator for call to}}
 };
 
diff --git a/clang/test/CXX/over/over.oper/over.literal/p3.cpp b/clang/test/CXX/over/over.oper/over.literal/p3.cpp
index 674ace9aee19291..53ebe102630843b 100644
--- a/clang/test/CXX/over/over.oper/over.literal/p3.cpp
+++ b/clang/test/CXX/over/over.oper/over.literal/p3.cpp
@@ -3,38 +3,38 @@
 using size_t = decltype(sizeof(int));
 
 // Acceptable parameter declarations
-char operator "" _a(const char *);
-char operator "" _a(const char []);
-char operator "" _a(unsigned long long);
-char operator "" _a(long double);
-char operator "" _a(char);
-char operator "" _a(const volatile char);
-char operator "" _a(wchar_t);
-char operator "" _a(char16_t);
-char operator "" _a(char32_t);
-char operator "" _a(const char *, size_t);
-char operator "" _a(const wchar_t *, size_t);
-char operator "" _a(const char16_t *, size_t);
-char operator "" _a(const char32_t *, size_t);
-char operator "" _a(const char [32], size_t);
+char operator ""_a(const char *);
+char operator ""_a(const char []);
+char operator ""_a(unsigned long long);
+char operator ""_a(long double);
+char operator ""_a(char);
+char operator ""_a(const volatile char);
+char operator ""_a(wchar_t);
+char operator ""_a(char16_t);
+char operator ""_a(char32_t);
+char operator ""_a(const char *, size_t);
+char operator ""_a(const wchar_t *, size_t);
+char operator ""_a(const char16_t *, size_t);
+char operator ""_a(const char32_t *, size_t);
+char operator ""_a(const char [32], size_t);
 
 // Unacceptable parameter declarations
-char operator "" _b(); // expected-error {{parameter}}
-char operator "" _b(const wchar_t *); // expected-error {{parameter}}
-char operator "" _b(long long); // expected-error {{parameter}}
-char operator "" _b(double); // expected-error {{parameter}}
-char operator "" _b(short); // expected-error {{parameter}}
-char operator "" _a(char, int = 0); // expected-error {{parameter}}
-char operator "" _b(unsigned short); // expected-error {{parameter}}
-char operator "" _b(signed char); // expected-error {{parameter}}
-char operator "" _b(unsigned char); // expected-error {{parameter}}
-char operator "" _b(const short *, size_t); // expected-error {{parameter}}
-char operator "" _b(const unsigned short *, size_t); // expected-error {{parameter}}
-char operator "" _b(const signed char *, size_t); // expected-error {{parameter}}
-char operator "" _b(const unsigned char *, size_t); // expected-error {{parameter}}
-char operator "" _a(const volatile char *, size_t); // expected-error {{parameter}}
-char operator "" _a(volatile wchar_t *, size_t); // expected-error {{parameter}}
-char operator "" _a(char16_t *, size_t); // expected-error {{parameter}}
-char operator "" _a(const char32_t *, size_t, bool = false); // expected-error {{parameter}}
-char operator "" _a(const char *, signed long); // expected-error {{parameter}}
-char operator "" _a(const char *, size_t = 0); // expected-error {{default argument}}
+char operator ""_b(); // expected-error {{parameter}}
+char operator ""_b(const wchar_t *); // expected-error {{parameter}}
+char operator ""_b(long long); // expected-error {{parameter}}
+char operator ""_b(double); // expected-error {{parameter}}
+char operator ""_b(short); // expected-error {{parameter}}
+char operator ""_a(char, int = 0); // expected-error {{parameter}}
+char operator ""_b(unsigned short); // expected-error {{parameter}}
+char operator ""_b(signed char); // expected-error {{parameter}}
+char operator ""_b(unsigned char); // expected-error {{parameter}}
+char operator ""_b(const short *, size_t); // expected-error {{parameter}}
+char operator ""_b(const unsigned short *, size_t); // expected-error {{parameter}}
+char operator ""_b(const signed char *, size_t); // expected-error {{parameter}}
+char operator ""_b(const unsigned char *, size_t); // expected-error {{parameter}}
+char operator ""_a(const volatile char *, size_t); // expected-error {{parameter}}
+char operator ""_a(volatile wchar_t *, size_t); // expected-error {{parameter}}
+char operator ""_a(char16_t *, size_t); // expected-error {{parameter}}
+char operator ""_a(const char32_t *, size_t, bool = false); // expected-error {{parameter}}
+char operator ""_a(const char *, signed long); // expected-error {{parameter}}
+char operator ""_a(const char *, size_t = 0); // expected-error {{default argument}}
diff --git a/clang/test/CXX/over/over.oper/over.literal/p5.cpp b/clang/test/CXX/over/over.oper/over.literal/p5.cpp
index bfad5f00cf6c75c..593aa57b76a81cd 100644
--- a/clang/test/CXX/over/over.oper/over.literal/p5.cpp
+++ b/clang/test/CXX/over/over.oper/over.literal/p5.cpp
@@ -3,20 +3,20 @@
 using size_t = decltype(sizeof(int));
 template<char...> struct S {};
 
-template<char...> void operator "" _a();
-template<char... C> S<C...> operator "" _a();
+template<char...> void operator ""_a();
+template<char... C> S<C...> operator ""_a();
 
 template<typename T> struct U {
-  friend int operator "" _a(const char *, size_t);
+  friend int operator ""_a(const char *, size_t);
   // FIXME: It's not entirely clear whether this is intended to be legal.
-  friend U operator "" _a(const T *, size_t); // expected-error {{parameter}}
+  friend U operator ""_a(const T *, size_t); // expected-error {{parameter}}
 };
 template<char...> struct V {
-  friend void operator "" _b(); // expected-error {{parameters}}
+  friend void operator ""_b(); // expected-error {{parameters}}
 };
 
-template<char... C, int N = 0> void operator "" _b(); // expected-error {{template}}
-template<char... C> void operator "" _b(int N = 0); // expected-error {{template}}
-template<char, char...> void operator "" _b(); // expected-error {{template}}
-template<typename T> T operator "" _b(const char *); // expected-error {{template}}
-template<typename T> int operator "" _b(const T *, size_t); // expected-error {{template}}
+template<char... C, int N = 0> void operator ""_b(); // expected-error {{template}}
+template<char... C> void operator ""_b(int N = 0); // expected-error {{template}}
+template<char, char...> void operator ""_b(); // expected-error {{template}}
+template<typename T> T operator ""_b(const char *); // expected-error {{template}}
+template<typename T> int operator ""_b(const T *, size_t); // expected-error {{template}}
diff --git a/clang/test/CXX/over/over.oper/over.literal/p6.cpp b/clang/test/CXX/over/over.oper/over.literal/p6.cpp
index 9ecf9ccccb14c6b..265050e0a009675 100644
--- a/clang/test/CXX/over/over.oper/over.literal/p6.cpp
+++ b/clang/test/CXX/over/over.oper/over.literal/p6.cpp
@@ -1,15 +1,15 @@
 // RUN: %clang_cc1 -std=c++11 %s -verify
 
 // expected-note@+1 {{extern "C" language linkage specification begins here}}
-extern "C" void operator "" _a(const char *); // expected-error {{must have C++ linkage}}
-extern "C" template<char...> void operator "" _b(); // expected-error {{must have C++ linkage}}
+extern "C" void operator ""_a(const char *); // expected-error {{must have C++ linkage}}
+extern "C" template<char...> void operator ""_b(); // expected-error {{must have C++ linkage}}
 // expected-note@-1 {{extern "C" language linkage specification begins here}}
 
 extern "C" { // expected-note 4 {{extern "C" language linkage specification begins here}}
-  void operator "" _c(const char *); // expected-error {{must have C++ linkage}}
-  template<char...> void operator "" _d(); // expected-error {{must have C++ linkage}}
+  void operator ""_c(const char *); // expected-error {{must have C++ linkage}}
+  template<char...> void operator ""_d(); // expected-error {{must have C++ linkage}}
   namespace N {
-    void operator "" _e(const char *); // expected-error {{must have C++ linkage}}
-    template<char...> void operator "" _f(); // expected-error {{must have C++ linkage}}
+    void operator ""_e(const char *); // expected-error {{must have C++ linkage}}
+    template<char...> void operator ""_f(); // expected-error {{must have C++ linkage}}
   }
 }
diff --git a/clang/test/CXX/over/over.oper/over.literal/p7.cpp b/clang/test/CXX/over/over.oper/over.literal/p7.cpp
index 74e9457bb55c38c..244f043d4412e73 100644
--- a/clang/test/CXX/over/over.oper/over.literal/p7.cpp
+++ b/clang/test/CXX/over/over.oper/over.literal/p7.cpp
@@ -1,17 +1,17 @@
 // RUN: %clang_cc1 -std=c++11 %s -verify
 // expected-no-diagnostics
 
-constexpr int operator "" _a(const char *c) {
+constexpr int operator ""_a(const char *c) {
   return c[0];
 }
 
-static_assert(operator "" _a("foo") == 'f', "");
+static_assert(operator ""_a("foo") == 'f', "");
 
 void puts(const char *);
-static inline void operator "" _puts(const char *c) {
+static inline void operator ""_puts(const char *c) {
   puts(c);
 }
 void f() {
-  operator "" _puts("foo");
-  operator "" _puts("bar");
+  operator ""_puts("foo");
+  operator ""_puts("bar");
 }
diff --git a/clang/test/CXX/over/over.oper/over.literal/p8.cpp b/clang/test/CXX/over/over.oper/over.literal/p8.cpp
index 6644bae7e610d1f..8aa31e1acd6e157 100644
--- a/clang/test/CXX/over/over.oper/over.literal/p8.cpp
+++ b/clang/test/CXX/over/over.oper/over.literal/p8.cpp
@@ -5,13 +5,13 @@ namespace std {
   using size_t = decltype(sizeof(int));
 }
 
-void operator "" _km(long double); // ok
-string operator "" _i18n(const char*, std::size_t); // ok
-template<char...> int operator "" \u03C0(); // ok, UCN for lowercase pi // expected-warning {{reserved}}
+void operator ""_km(long double); // ok
+string operator ""_i18n(const char*, std::size_t); // ok
+template<char...> int operator ""\u03C0(); // ok, UCN for lowercase pi // expected-warning {{reserved}}
 float operator ""E(const char *); // expected-error {{invalid suffix on literal}} expected-warning {{reserved}}
 float operator " " B(const char *); // expected-error {{must be '""'}} expected-warning {{reserved}}
-string operator "" 5X(const char *, std::size_t); // expected-error {{expected identifier}}
-double operator "" _miles(double); // expected-error {{parameter}}
+string operator ""5X(const char *, std::size_t); // expected-error {{expected identifier}}
+double operator ""_miles(double); // expected-error {{parameter}}
 template<char...> int operator "" j(const char*); // expected-error {{template}}
 
 float operator ""_E(const char *);
diff --git a/clang/test/FixIt/fixit-c++11.cpp b/clang/test/FixIt/fixit-c++11.cpp
index 10f4a9d0554ccc2..e635c14e0c21557 100644
--- a/clang/test/FixIt/fixit-c++11.cpp
+++ b/clang/test/FixIt/fixit-c++11.cpp
@@ -74,8 +74,8 @@ const char *p = "foo"bar; // expected-error {{requires a space between}}
 #define ord - '0'
 int k = '4'ord; // expected-error {{requires a space between}}
 
-void operator"x" _y(char); // expected-error {{must be '""'}}
-void operator L"" _z(char); // expected-error {{encoding prefix}}
+void operator"x"_y(char); // expected-error {{must be '""'}}
+void operator L""_z(char); // expected-error {{encoding prefix}}
 void operator "x" "y" U"z" ""_whoops "z" "y"(char); // expected-error {{must be '""'}}
 
 void f() {
diff --git a/clang/test/Parser/cxx11-user-defined-literals.cpp b/clang/test/Parser/cxx11-user-defined-literals.cpp
index cdd06729efc39a7..27a7181bc9f9170 100644
--- a/clang/test/Parser/cxx11-user-defined-literals.cpp
+++ b/clang/test/Parser/cxx11-user-defined-literals.cpp
@@ -39,19 +39,19 @@ int cake() __attribute__((availability(macosx, unavailable, message = "is a lie"
 #endif
 
 // But they can appear in expressions.
-constexpr char operator"" _id(char c) { return c; }
-constexpr wchar_t operator"" _id(wchar_t c) { return c; }
-constexpr char16_t operator"" _id(char16_t c) { return c; }
-constexpr char32_t operator"" _id(char32_t c) { return c; }
+constexpr char operator""_id(char c) { return c; }
+constexpr wchar_t operator""_id(wchar_t c) { return c; }
+constexpr char16_t operator""_id(char16_t c) { return c; }
+constexpr char32_t operator""_id(char32_t c) { return c; }
 
 using size_t = decltype(sizeof(int));
-constexpr const char operator"" _id(const char *p, size_t n) { return *p; }
-constexpr const wchar_t operator"" _id(const wchar_t *p, size_t n) { return *p; }
-constexpr const char16_t operator"" _id(const char16_t *p, size_t n) { return *p; }
-constexpr const char32_t operator"" _id(const char32_t *p, size_t n) { return *p; }
+constexpr const char operator""_id(const char *p, size_t n) { return *p; }
+constexpr const wchar_t operator""_id(const wchar_t *p, size_t n) { return *p; }
+constexpr const char16_t operator""_id(const char16_t *p, size_t n) { return *p; }
+constexpr const char32_t operator""_id(const char32_t *p, size_t n) { return *p; }
 
-constexpr unsigned long long operator"" _id(unsigned long long n) { return n; }
-constexpr long double operator"" _id(long double d) { return d; }
+constexpr unsigned long long operator""_id(unsigned long long n) { return n; }
+constexpr long double operator""_id(long double d) { return d; }
 
 template<int n> struct S {};
 S<"a"_id> sa;
@@ -98,19 +98,22 @@ _no_such_suffix; // expected-error {{'operator""_no_such_suffix'}}
 // is "" in translation phase 7.
 void operator "\
 " _foo(unsigned long long); // ok
+// expected-warning@-1{{identifier '_foo' preceded by whitespace in a literal operator declaration is deprecated}}
 
 void operator R"xyzzy()xyzzy" _foo(long double); // ok
+// expected-warning@-1{{identifier '_foo' preceded by whitespace in a literal operator declaration is deprecated}}
 
 void operator"" "" R"()" "" _foo(const char *); // ok
+// expected-warning@-1{{identifier '_foo' preceded by whitespace}}
 
 void operator ""_no_space(const char *); // ok
 
 // Ensure we diagnose the bad cases.
-void operator "\0" _non_empty(const char *); // expected-error {{must be '""'}}
-void operator L"" _not_char(const char *); // expected-error {{cannot have an encoding prefix}}
+void operator "\0"_non_empty(const char *); // expected-error {{must be '""'}}
+void operator L""_not_char(const char *); // expected-error {{cannot have an encoding prefix}}
 void operator "" ""
 U"" // expected-error {{cannot have an encoding prefix}}
-"" _also_not_char(const char *);
+""_also_not_char(const char *);
 void operator "" u8"" "\u0123" "hello"_all_of_the_things ""(const char*); // expected-error {{must be '""'}}
 
 // Make sure we treat UCNs and UTF-8 as equivalent.
diff --git a/clang/test/SemaCXX/cxx11-user-defined-literals-unused.cpp b/clang/test/SemaCXX/cxx11-user-defined-literals-unused.cpp
index cd93ffbf21edf4a..cf95ae7de98e948 100644
--- a/clang/test/SemaCXX/cxx11-user-defined-literals-unused.cpp
+++ b/clang/test/SemaCXX/cxx11-user-defined-literals-unused.cpp
@@ -1,8 +1,8 @@
 // RUN: %clang_cc1 -std=c++11 -verify %s -Wunused
 
 namespace {
-double operator"" _x(long double value) { return double(value); }
-int operator"" _ii(long double value) { return int(value); } // expected-warning {{not needed and will not be emitted}}
+double operator""_x(long double value) { return double(value); }
+int operator""_ii(long double value) { return int(value); } // expected-warning {{not needed and will not be emitted}}
 }
 
 namespace rdar13589856 {
diff --git a/clang/test/SemaCXX/cxx11-user-defined-literals.cpp b/clang/test/SemaCXX/cxx11-user-defined-literals.cpp
index b5d4d9976c1372f..bdf88ee01c3a121 100644
--- a/clang/test/SemaCXX/cxx11-user-defined-literals.cpp
+++ b/clang/test/SemaCXX/cxx11-user-defined-literals.cpp
@@ -6,18 +6,18 @@ enum class LitKind {
   CharStr, WideStr, Char16Str, Char32Str,
   Integer, Floating, Raw, Template
 };
-constexpr LitKind operator"" _kind(char p) { return LitKind::Char; }
-constexpr LitKind operator"" _kind(wchar_t p) { return LitKind::WideChar; }
-constexpr LitKind operator"" _kind(char16_t p) { return LitKind::Char16; }
-constexpr LitKind operator"" _kind(char32_t p) { return LitKind::Char32; }
-constexpr LitKind operator"" _kind(const char *p, size_t n) { return LitKind::CharStr; }
-constexpr LitKind operator"" _kind(const wchar_t *p, size_t n) { return LitKind::WideStr; }
-constexpr LitKind operator"" _kind(const char16_t *p, size_t n) { return LitKind::Char16Str; }
-constexpr LitKind operator"" _kind(const char32_t *p, size_t n) { return LitKind::Char32Str; }
-constexpr LitKind operator"" _kind(unsigned long long n) { return LitKind::Integer; }
-constexpr LitKind operator"" _kind(long double n) { return LitKind::Floating; }
-constexpr LitKind operator"" _kind2(const char *p) { return LitKind::Raw; }
-template<char ...Cs> constexpr LitKind operator"" _kind3() { return LitKind::Template; }
+constexpr LitKind operator""_kind(char p) { return LitKind::Char; }
+constexpr LitKind operator""_kind(wchar_t p) { return LitKind::WideChar; }
+constexpr LitKind operator""_kind(char16_t p) { return LitKind::Char16; }
+constexpr LitKind operator""_kind(char32_t p) { return LitKind::Char32; }
+constexpr LitKind operator""_kind(const char *p, size_t n) { return LitKind::CharStr; }
+constexpr LitKind operator""_kind(const wchar_t *p, size_t n) { return LitKind::WideStr; }
+constexpr LitKind operator""_kind(const char16_t *p, size_t n) { return LitKind::Char16Str; }
+constexpr LitKind operator""_kind(const char32_t *p, size_t n) { return LitKind::Char32Str; }
+constexpr LitKind operator""_kind(unsigned long long n) { return LitKind::Integer; }
+constexpr LitKind operator""_kind(long double n) { return LitKind::Floating; }
+constexpr LitKind operator""_kind2(const char *p) { return LitKind::Raw; }
+template<char ...Cs> constexpr LitKind operator""_kind3() { return LitKind::Template; }
 
 static_assert('x'_kind == LitKind::Char, "");
 static_assert(L'x'_kind == LitKind::WideChar, "");
@@ -41,7 +41,7 @@ static_assert(4e6_kind3 == LitKind::Template, "");
 constexpr const char *fractional_digits_impl(const char *p) {
   return *p == '.' ? p + 1 : *p ? fractional_digits_impl(p + 1) : 0;
 }
-constexpr const char *operator"" _fractional_digits(const char *p) {
+constexpr const char *operator""_fractional_digits(const char *p) {
   return fractional_digits_impl(p) ?: p;
 }
 constexpr bool streq(const char *p, const char *q) {
@@ -56,57 +56,57 @@ static_assert(streq(1e+97_fractional_digits, "1e+97"), "");
 static_assert(streq(0377_fractional_digits, "0377"), "");
 static_assert(streq(0377.5_fractional_digits, "5"), "");
 
-int operator"" _ambiguous(char); // expected-note {{candidate}}
+int operator""_ambiguous(char); // expected-note {{candidate}}
 namespace N {
-  void *operator"" _ambiguous(char); // expected-note {{candidate}}
+  void *operator""_ambiguous(char); // expected-note {{candidate}}
 }
 using namespace N;
 int k = 'x'_ambiguous; // expected-error {{ambiguous}}
 
-int operator"" _deleted(unsigned long long) = delete; // expected-note {{here}}
+int operator""_deleted(unsigned long long) = delete; // expected-note {{here}}
 int m = 42_deleted; // expected-error {{attempt to use a deleted}}
 
 namespace Using {
   namespace M {
-    int operator"" _using(char);
+    int operator""_using(char);
   }
   int k1 = 'x'_using; // expected-error {{no matching literal operator for call to 'operator""_using'}}
 
-  using M::operator "" _using;
+  using M::operator ""_using;
   int k2 = 'x'_using;
 }
 
 namespace AmbiguousRawTemplate {
-  int operator"" _ambig1(const char *); // expected-note {{candidate}}
-  template<char...> int operator"" _ambig1(); // expected-note {{candidate}}
+  int operator""_ambig1(const char *); // expected-note {{candidate}}
+  template<char...> int operator""_ambig1(); // expected-note {{candidate}}
 
   int k1 = 123_ambig1; // expected-error {{call to 'operator""_ambig1' is ambiguous}}
 
   namespace Inner {
-    template<char...> int operator"" _ambig2(); // expected-note 3{{candidate}}
+    template<char...> int operator""_ambig2(); // expected-note 3{{candidate}}
   }
-  int operator"" _ambig2(const char *); // expected-note 3{{candidate}}
-  using Inner::operator"" _ambig2;
+  int operator""_ambig2(const char *); // expected-note 3{{candidate}}
+  using Inner::operator""_ambig2;
 
   int k2 = 123_ambig2; // expected-error {{call to 'operator""_ambig2' is ambiguous}}
 
   namespace N {
-    using Inner::operator"" _ambig2;
+    using Inner::operator""_ambig2;
 
     int k3 = 123_ambig2; // ok
 
-    using AmbiguousRawTemplate::operator"" _ambig2;
+    using AmbiguousRawTemplate::operator""_ambig2;
 
     int k4 = 123_ambig2; // expected-error {{ambiguous}}
 
     namespace M {
 
-      template<char...> int operator"" _ambig2();
+      template<char...> int operator""_ambig2();
 
       int k5 = 123_ambig2; // ok
     }
 
-    int operator"" _ambig2(unsigned long long);
+    int operator""_ambig2(unsigned long long);
 
     int k6 = 123_ambig2; // ok
     int k7 = 123._ambig2; // expected-error {{ambiguous}}
@@ -121,7 +121,7 @@ template<char C, char...Cs> constexpr unsigned hash(unsigned a) {
  return hash<Cs...>(mash(a ^ mash(C)));
 }
 template<typename T, T v> struct constant { constexpr static T value = v; };
-template<char...Cs> constexpr unsigned operator"" _hash() {
+template<char...Cs> constexpr unsigned operator""_hash() {
   return constant<unsigned, hash<Cs...>(0)>::value;
 }
 static_assert(0x1234_hash == 0x103eff5e, "");
@@ -129,7 +129,7 @@ static_assert(hash<'0', 'x', '1', '2', '3', '4'>(0) == 0x103eff5e, "");
 
 // Functions and literal suffixes go in separate namespaces.
 namespace Namespace {
-  template<char...> int operator"" _x();
+  template<char...> int operator""_x();
   int k = _x(); // expected-error {{undeclared identifier '_x'}}
 
   int _y(unsigned long long);
@@ -138,7 +138,7 @@ namespace Namespace {
 
 namespace PR14950 {
   template<...> // expected-error {{expected template parameter}}
-  int operator"" _b(); // expected-error {{no function template matches function template specialization}}
+  int operator""_b(); // expected-error {{no function template matches function template specialization}}
   int main() { return 0_b; } // expected-error {{no matching literal operator for call to 'operator""_b'}}
 }
 
diff --git a/clang/test/SemaCXX/cxx2a-consteval.cpp b/clang/test/SemaCXX/cxx2a-consteval.cpp
index ae331055c52b2e8..fef4674d178412e 100644
--- a/clang/test/SemaCXX/cxx2a-consteval.cpp
+++ b/clang/test/SemaCXX/cxx2a-consteval.cpp
@@ -158,17 +158,17 @@ int i3 = f1(f1(f1(&f1, &f1), f1(&f1, &f1), f1(f1(&f1, &f1), &f1)));
 
 namespace user_defined_literal {
 
-consteval int operator"" _test(unsigned long long i) {
+consteval int operator""_test(unsigned long long i) {
 // expected-note@-1+ {{declared here}}
   return 0;
 }
 
 int i = 0_test;
 
-auto ptr = &operator"" _test;
+auto ptr = &operator""_test;
 // expected-error@-1 {{take address}}
 
-consteval auto operator"" _test1(unsigned long long i) {
+consteval auto operator""_test1(unsigned long long i) {
   return &f_eval;
 }
 
diff --git a/clang/test/SemaCXX/cxx98-compat.cpp b/clang/test/SemaCXX/cxx98-compat.cpp
index 3ce69d6908c5b22..28547d42c64902d 100644
--- a/clang/test/SemaCXX/cxx98-compat.cpp
+++ b/clang/test/SemaCXX/cxx98-compat.cpp
@@ -84,7 +84,7 @@ struct DelayedDefaultArgumentParseInitList {
   }
 };
 
-int operator"" _hello(const char *); // expected-warning {{literal operators are incompatible with C++98}}
+int operator""_hello(const char *); // expected-warning {{literal operators are incompatible with C++98}}
 
 enum EnumFixed : int { // expected-warning {{enumeration types with a fixed underlying type are incompatible with C++98}}
 };
diff --git a/clang/test/SemaCXX/literal-operators.cpp b/clang/test/SemaCXX/literal-operators.cpp
index 067e151606202ee..2a41e048914b786 100644
--- a/clang/test/SemaCXX/literal-operators.cpp
+++ b/clang/test/SemaCXX/literal-operators.cpp
@@ -3,46 +3,46 @@
 #include <stddef.h>
 
 struct tag {
-  void operator "" _tag_bad (const char *); // expected-error {{literal operator 'operator""_tag_bad' must be in a namespace or global scope}}
-  friend void operator "" _tag_good (const char *);
+  void operator ""_tag_bad (const char *); // expected-error {{literal operator 'operator""_tag_bad' must be in a namespace or global scope}}
+  friend void operator ""_tag_good (const char *);
 };
 
-namespace ns { void operator "" _ns_good (const char *); }
+namespace ns { void operator ""_ns_good (const char *); }
 
 // Check extern "C++" declarations
-extern "C++" void operator "" _extern_good (const char *);
-extern "C++" { void operator "" _extern_good (const char *); }
+extern "C++" void operator ""_extern_good (const char *);
+extern "C++" { void operator ""_extern_good (const char *); }
 
-void fn () { void operator "" _fn_good (const char *); }
+void fn () { void operator ""_fn_good (const char *); }
 
 // One-param declarations (const char * was already checked)
-void operator "" _good (char);
-void operator "" _good (wchar_t);
-void operator "" _good (char16_t);
-void operator "" _good (char32_t);
-void operator "" _good (unsigned long long);
-void operator "" _good (long double);
+void operator ""_good (char);
+void operator ""_good (wchar_t);
+void operator ""_good (char16_t);
+void operator ""_good (char32_t);
+void operator ""_good (unsigned long long);
+void operator ""_good (long double);
 
 // Two-param declarations
-void operator "" _good (const char *, size_t);
-void operator "" _good (const wchar_t *, size_t);
-void operator "" _good (const char16_t *, size_t);
-void operator "" _good (const char32_t *, size_t);
+void operator ""_good (const char *, size_t);
+void operator ""_good (const wchar_t *, size_t);
+void operator ""_good (const char16_t *, size_t);
+void operator ""_good (const char32_t *, size_t);
 
 // Check typedef and array equivalences
-void operator "" _good (const char[]);
+void operator ""_good (const char[]);
 typedef const char c;
-void operator "" _good (c*);
+void operator ""_good (c*);
 
 // Check extra cv-qualifiers
-void operator "" _cv_good (volatile const char *, const size_t); // expected-error {{invalid literal operator parameter type 'const volatile char *', did you mean 'const char *'?}}
+void operator ""_cv_good (volatile const char *, const size_t); // expected-error {{invalid literal operator parameter type 'const volatile char *', did you mean 'const char *'?}}
 
 // Template declaration
-template <char...> void operator "" _good ();
+template <char...> void operator ""_good ();
 
-template <typename...> void operator "" _invalid(); // expected-error {{template parameter list for literal operator must be either 'char...' or 'typename T, T...'}}
-template <wchar_t...> void operator "" _invalid();  // expected-error {{template parameter list for literal operator must be either 'char...' or 'typename T, T...'}}
-template <unsigned long long...> void operator "" _invalid();  // expected-error {{template parameter list for literal operator must be either 'char...' or 'typename T, T...'}}
+template <typename...> void operator ""_invalid(); // expected-error {{template parameter list for literal operator must be either 'char...' or 'typename T, T...'}}
+template <wchar_t...> void operator ""_invalid();  // expected-error {{template parameter list for literal operator must be either 'char...' or 'typename T, T...'}}
+template <unsigned long long...> void operator ""_invalid();  // expected-error {{template parameter list for literal operator must be either 'char...' or 'typename T, T...'}}
 
 _Complex float operator""if(long double); // expected-warning {{reserved}}
 _Complex float test_if_1() { return 2.0f + 1.5if; };
diff --git a/clang/test/SemaCXX/no-warn-user-defined-literals-in-system-headers.cpp b/clang/test/SemaCXX/no-warn-user-defined-literals-in-system-headers.cpp
index ee5b0c47b9ffcd2..61b08954c40b586 100644
--- a/clang/test/SemaCXX/no-warn-user-defined-literals-in-system-headers.cpp
+++ b/clang/test/SemaCXX/no-warn-user-defined-literals-in-system-headers.cpp
@@ -1,4 +1,4 @@
-// RUN: %clang_cc1 -fsyntax-only -verify -std=c++11 -Wsystem-headers -isystem %S %s
+// RUN: %clang_cc1 -fsyntax-only -verify -std=c++11 -isystem %S %s
 
 #include <no-warn-user-defined-literals-in-system-headers.h>
 
diff --git a/clang/test/SemaCXX/reserved-identifier.cpp b/clang/test/SemaCXX/reserved-identifier.cpp
index eaa5fe8330337e7..a3e6d8ead61fd8a 100644
--- a/clang/test/SemaCXX/reserved-identifier.cpp
+++ b/clang/test/SemaCXX/reserved-identifier.cpp
@@ -76,7 +76,8 @@ namespace {
 int _barbatruc; // no-warning
 }
 
-long double operator"" _BarbeBleue(long double) // expected-warning {{identifier '_BarbeBleue' is reserved because it starts with '_' followed by a capital letter}}
+long double operator"" _BarbeBleue(long double) // expected-warning {{identifier '_BarbeBleue' is reserved because it starts with '_' followed by a capital letter}}\
+                                                // expected-warning {{identifier '_BarbeBleue' preceded by whitespace in a literal operator declaration is deprecated}}
 {
   return 0.;
 }
@@ -86,10 +87,11 @@ long double operator""_SacreBleu(long double) // no-warning
   return 0.;
 }
 
-long double sacrebleu = operator"" _SacreBleu(1.2); // expected-warning {{identifier '_SacreBleu' is reserved because it starts with '_' followed by a capital letter}}
+long double sacrebleu = operator"" _SacreBleu(1.2); // expected-warning {{identifier '_SacreBleu' is reserved because it starts with '_' followed by a capital letter}} \
+                                                    // expected-warning {{identifier '_SacreBleu' preceded by whitespace in a literal operator declaration is deprecated}}
 long double sangbleu = operator""_SacreBleu(1.2);   // no-warning
 
-void operator"" _lowercase(unsigned long long); // no-warning
+void operator"" _lowercase(unsigned long long); // expected-warning {{identifier '_lowercase' preceded by whitespace in a literal operator declaration is deprecated}}
 void operator""_lowercase(unsigned long long); // no-warning
 
 struct _BarbeRouge { // expected-warning {{identifier '_BarbeRouge' is reserved because it starts with '_' followed by a capital letter}}
diff --git a/clang/test/SemaCXX/warn-xor-as-pow.cpp b/clang/test/SemaCXX/warn-xor-as-pow.cpp
index 88719bd1a9d7757..ade977f97e43665 100644
--- a/clang/test/SemaCXX/warn-xor-as-pow.cpp
+++ b/clang/test/SemaCXX/warn-xor-as-pow.cpp
@@ -19,10 +19,10 @@
 #define flexor 7
 
 #ifdef __cplusplus
-constexpr long long operator"" _xor(unsigned long long v) { return v; }
+constexpr long long operator""_xor(unsigned long long v) { return v; }
 
-constexpr long long operator"" _0b(unsigned long long v) { return v; }
-constexpr long long operator"" _0X(unsigned long long v) { return v; }
+constexpr long long operator""_0b(unsigned long long v) { return v; }
+constexpr long long operator""_0X(unsigned long long v) { return v; }
 #else
 #define xor ^ // iso646.h
 #endif