diff --git a/clang/test/CodeGenCXX/cxx2a-three-way-comparison.cpp b/clang/test/CodeGenCXX/cxx2a-three-way-comparison.cpp
index 08ab41b..fd72d4a 100644
--- a/clang/test/CodeGenCXX/cxx2a-three-way-comparison.cpp
+++ b/clang/test/CodeGenCXX/cxx2a-three-way-comparison.cpp
@@ -1,5 +1,6 @@
 // RUN: %clang_cc1 -std=c++2a -emit-llvm %s -o - -triple %itanium_abi_triple | FileCheck %s --check-prefix=ITANIUM
 // RUN: not %clang_cc1 -std=c++2a -emit-llvm %s -o - -triple %ms_abi_triple 2>&1 | FileCheck %s --check-prefix=MSABI
+// RUN: not %clang_cc1 -std=c++2a -emit-llvm %s -o - -triple %itanium_abi_triple -DBUILTIN 2>&1 | FileCheck %s --check-prefix=BUILTIN
 // MSABI: cannot mangle this three-way comparison operator yet
 
 struct A {
@@ -11,3 +12,18 @@
 
 // ITANIUM: define {{.*}}@_Zssi1A(
 void operator<=>(int, A) {}
+
+int operator<=>(A, A);
+
+// ITANIUM: define {{.*}}_Z1f1A(
+int f(A a) {
+  // ITANIUM: %[[RET:.*]] = call {{.*}}_Zss1AS_(
+  // ITANIUM: ret i32 %[[RET]]
+  return a <=> a;
+}
+
+#ifdef BUILTIN
+void builtin(int a) {
+  a <=> a; // BUILTIN: cannot compile this scalar expression yet
+}
+#endif
diff --git a/clang/test/Parser/cxx2a-spaceship.cpp b/clang/test/Parser/cxx2a-spaceship.cpp
new file mode 100644
index 0000000..24cece3
--- /dev/null
+++ b/clang/test/Parser/cxx2a-spaceship.cpp
@@ -0,0 +1,18 @@
+// RUN: %clang_cc1 -std=c++2a -verify %s
+
+template<int> struct X {};
+
+X<1> operator<<(X<0>, X<0>);
+X<2> operator<=>(X<0>, X<1>);
+X<2> operator<=>(X<1>, X<0>);
+X<3> operator<(X<0>, X<2>);
+X<3> operator<(X<2>, X<0>);
+
+void f(X<0> x0, X<1> x1) {
+  X<2> a = x0 <=> x0 << x0;
+  X<2> b = x0 << x0 <=> x0; // expected-warning {{overloaded operator << has higher precedence than comparison operator}} expected-note 2{{}}
+  X<3> c = x0 < x0 <=> x1;
+  X<3> d = x1 <=> x0 < x0;
+  X<3> e = x0 < x0 <=> x0 << x0;
+  X<3> f = x0 << x0 <=> x0 < x0; // expected-warning {{overloaded operator << has higher precedence than comparison operator}} expected-note 2{{}}
+}
diff --git a/clang/test/SemaCXX/compare-cxx2a.cpp b/clang/test/SemaCXX/compare-cxx2a.cpp
new file mode 100644
index 0000000..61d3502
--- /dev/null
+++ b/clang/test/SemaCXX/compare-cxx2a.cpp
@@ -0,0 +1,166 @@
+// Force x86-64 because some of our heuristics are actually based
+// on integer sizes.
+
+// RUN: %clang_cc1 -triple x86_64-apple-darwin -fsyntax-only -pedantic -verify -Wsign-compare -std=c++2a %s
+
+void test0(long a, unsigned long b) {
+  enum EnumA {A};
+  enum EnumB {B};
+  enum EnumC {C = 0x10000};
+         // (a,b)
+
+  // FIXME: <=> should never produce -Wsign-compare warnings. All the possible error
+  // cases involve narrowing conversions and so are ill-formed.
+  (void)(a <=> (unsigned long) b); // expected-warning {{comparison of integers of different signs}}
+  (void)(a <=> (unsigned int) b);
+  (void)(a <=> (unsigned short) b);
+  (void)(a <=> (unsigned char) b);
+  (void)((long) a <=> b);  // expected-warning {{comparison of integers of different signs}}
+  (void)((int) a <=> b);  // expected-warning {{comparison of integers of different signs}}
+  (void)((short) a <=> b);  // expected-warning {{comparison of integers of different signs}}
+  (void)((signed char) a <=> b);  // expected-warning {{comparison of integers of different signs}}
+  (void)((long) a <=> (unsigned long) b);  // expected-warning {{comparison of integers of different signs}}
+  (void)((int) a <=> (unsigned int) b);  // expected-warning {{comparison of integers of different signs}}
+  (void)((short) a <=> (unsigned short) b);
+  (void)((signed char) a <=> (unsigned char) b);
+
+#if 0
+  // (A,b)
+  (void)(A <=> (unsigned long) b);
+  (void)(A <=> (unsigned int) b);
+  (void)(A <=> (unsigned short) b);
+  (void)(A <=> (unsigned char) b);
+  (void)((long) A <=> b);
+  (void)((int) A <=> b);
+  (void)((short) A <=> b);
+  (void)((signed char) A <=> b);
+  (void)((long) A <=> (unsigned long) b);
+  (void)((int) A <=> (unsigned int) b);
+  (void)((short) A <=> (unsigned short) b);
+  (void)((signed char) A <=> (unsigned char) b);
+
+  // (a,B)
+  (void)(a <=> (unsigned long) B);
+  (void)(a <=> (unsigned int) B);
+  (void)(a <=> (unsigned short) B);
+  (void)(a <=> (unsigned char) B);
+  (void)((long) a <=> B);
+  (void)((int) a <=> B);
+  (void)((short) a <=> B);
+  (void)((signed char) a <=> B);
+  (void)((long) a <=> (unsigned long) B);
+  (void)((int) a <=> (unsigned int) B);
+  (void)((short) a <=> (unsigned short) B);
+  (void)((signed char) a <=> (unsigned char) B);
+
+  // (C,b)
+  (void)(C <=> (unsigned long) b);
+  (void)(C <=> (unsigned int) b);
+  (void)(C <=> (unsigned short) b); // expected-warning {{comparison of constant 'C' (65536) with expression of type 'unsigned short' is always 'std::strong_ordering::greater'}}
+  (void)(C <=> (unsigned char) b);  // expected-warning {{comparison of constant 'C' (65536) with expression of type 'unsigned char' is always 'std::strong_ordering::greater'}}
+  (void)((long) C <=> b);
+  (void)((int) C <=> b);
+  (void)((short) C <=> b);
+  (void)((signed char) C <=> b);
+  (void)((long) C <=> (unsigned long) b);
+  (void)((int) C <=> (unsigned int) b);
+  (void)((short) C <=> (unsigned short) b);
+  (void)((signed char) C <=> (unsigned char) b);
+
+  // (a,C)
+  (void)(a <=> (unsigned long) C);
+  (void)(a <=> (unsigned int) C);
+  (void)(a <=> (unsigned short) C);
+  (void)(a <=> (unsigned char) C);
+  (void)((long) a <=> C);
+  (void)((int) a <=> C);
+  (void)((short) a <=> C); // expected-warning {{comparison of constant 'C' (65536) with expression of type 'short' is always 'std::strong_ordering::less'}}
+  (void)((signed char) a <=> C); // expected-warning {{comparison of constant 'C' (65536) with expression of type 'signed char' is always 'std::strong_ordering::less'}}
+  (void)((long) a <=> (unsigned long) C);
+  (void)((int) a <=> (unsigned int) C);
+  (void)((short) a <=> (unsigned short) C);
+  (void)((signed char) a <=> (unsigned char) C);
+#endif
+
+  // (0x80000,b)
+  (void)(0x80000 <=> (unsigned long) b);
+  (void)(0x80000 <=> (unsigned int) b);
+  (void)(0x80000 <=> (unsigned short) b); // expected-warning {{result of comparison of constant 524288 with expression of type 'unsigned short' is always 'std::strong_ordering::greater'}}
+  (void)(0x80000 <=> (unsigned char) b); // expected-warning {{result of comparison of constant 524288 with expression of type 'unsigned char' is always 'std::strong_ordering::greater'}}
+  (void)((long) 0x80000 <=> b);
+  (void)((int) 0x80000 <=> b);
+  (void)((short) 0x80000 <=> b);
+  (void)((signed char) 0x80000 <=> b);
+  (void)((long) 0x80000 <=> (unsigned long) b);
+  (void)((int) 0x80000 <=> (unsigned int) b);
+  (void)((short) 0x80000 <=> (unsigned short) b);
+  (void)((signed char) 0x80000 <=> (unsigned char) b);
+
+  // (a,0x80000)
+  (void)(a <=> (unsigned long) 0x80000); // expected-warning {{comparison of integers of different signs}}
+  (void)(a <=> (unsigned int) 0x80000);
+  (void)(a <=> (unsigned short) 0x80000);
+  (void)(a <=> (unsigned char) 0x80000);
+  (void)((long) a <=> 0x80000);
+  (void)((int) a <=> 0x80000);
+  (void)((short) a <=> 0x80000); // expected-warning {{comparison of constant 524288 with expression of type 'short' is always 'std::strong_ordering::less'}}
+  (void)((signed char) a <=> 0x80000); // expected-warning {{comparison of constant 524288 with expression of type 'signed char' is always 'std::strong_ordering::less'}}
+  (void)((long) a <=> (unsigned long) 0x80000); // expected-warning {{comparison of integers of different signs}}
+  (void)((int) a <=> (unsigned int) 0x80000); // expected-warning {{comparison of integers of different signs}}
+  (void)((short) a <=> (unsigned short) 0x80000);
+  (void)((signed char) a <=> (unsigned char) 0x80000);
+}
+
+void test5(bool b) {
+  (void) (b <=> -10); // expected-warning{{comparison of constant -10 with expression of type 'bool' is always 'std::strong_ordering::greater'}}
+  (void) (b <=> -1); // expected-warning{{comparison of constant -1 with expression of type 'bool' is always 'std::strong_ordering::greater'}}
+  (void) (b <=> 0);
+  (void) (b <=> 1);
+  (void) (b <=> 2); // expected-warning{{comparison of constant 2 with expression of type 'bool' is always 'std::strong_ordering::less'}}
+  (void) (b <=> 10); // expected-warning{{comparison of constant 10 with expression of type 'bool' is always 'std::strong_ordering::less'}}
+}
+
+void test6(signed char sc) {
+  (void)(sc <=> 200); // expected-warning{{comparison of constant 200 with expression of type 'signed char' is always 'std::strong_ordering::less'}}
+  (void)(200 <=> sc); // expected-warning{{comparison of constant 200 with expression of type 'signed char' is always 'std::strong_ordering::greater'}}
+}
+
+// Test many signedness combinations.
+void test7(unsigned long other) {
+  // Common unsigned, other unsigned, constant unsigned
+  (void)((unsigned)other <=> (unsigned long)(0x1'ffff'ffff)); // expected-warning{{less}}
+  (void)((unsigned)other <=> (unsigned long)(0xffff'ffff));
+  (void)((unsigned long)other <=> (unsigned)(0x1'ffff'ffff));
+  (void)((unsigned long)other <=> (unsigned)(0xffff'ffff));
+
+  // Common unsigned, other signed, constant unsigned
+  (void)((int)other <=> (unsigned long)(0xffff'ffff'ffff'ffff)); // expected-warning{{different signs}}
+  (void)((int)other <=> (unsigned long)(0x0000'0000'ffff'ffff)); // expected-warning{{different signs}}
+  (void)((int)other <=> (unsigned long)(0x0000'0000'0fff'ffff)); // expected-warning{{different signs}}
+  (void)((int)other <=> (unsigned)(0x8000'0000));                // expected-warning{{different signs}}
+
+  // Common unsigned, other unsigned, constant signed
+  (void)((unsigned long)other <=> (int)(0xffff'ffff));  // expected-warning{{different signs}}
+
+  // Common unsigned, other signed, constant signed
+  // Should not be possible as the common type should also be signed.
+
+  // Common signed, other signed, constant signed
+  (void)((int)other <=> (long)(0xffff'ffff));           // expected-warning{{less}}
+  (void)((int)other <=> (long)(0xffff'ffff'0000'0000)); // expected-warning{{greater}}
+  (void)((int)other <=> (long)(0x0fff'ffff));
+  (void)((int)other <=> (long)(0xffff'ffff'f000'0000));
+
+  // Common signed, other signed, constant unsigned
+  (void)((int)other <=> (unsigned char)(0xffff));
+  (void)((int)other <=> (unsigned char)(0xff));
+
+  // Common signed, other unsigned, constant signed
+  (void)((unsigned char)other <=> (int)(0xff));
+  (void)((unsigned char)other <=> (int)(0xffff));  // expected-warning{{less}}
+
+  // Common signed, other unsigned, constant unsigned
+  (void)((unsigned char)other <=> (unsigned short)(0xff));
+  (void)((unsigned char)other <=> (unsigned short)(0x100)); // expected-warning{{less}}
+  (void)((unsigned short)other <=> (unsigned char)(0xff));
+}
diff --git a/clang/test/SemaCXX/constant-expression-cxx2a.cpp b/clang/test/SemaCXX/constant-expression-cxx2a.cpp
new file mode 100644
index 0000000..935cbefc
--- /dev/null
+++ b/clang/test/SemaCXX/constant-expression-cxx2a.cpp
@@ -0,0 +1,27 @@
+// RUN: %clang_cc1 -std=c++2a -verify %s -fcxx-exceptions -triple=x86_64-linux-gnu
+
+namespace ThreeWayComparison {
+  struct A {
+    int n;
+    constexpr friend int operator<=>(const A &a, const A &b) {
+      return a.n < b.n ? -1 : a.n > b.n ? 1 : 0;
+    }
+  };
+  static_assert(A{1} <=> A{2} < 0);
+  static_assert(A{2} <=> A{1} > 0);
+  static_assert(A{2} <=> A{2} == 0);
+
+  // Note: not yet supported.
+  static_assert(1 <=> 2 < 0); // expected-error {{invalid operands}}
+  static_assert(2 <=> 1 > 0); // expected-error {{invalid operands}}
+  static_assert(1 <=> 1 == 0); // expected-error {{invalid operands}}
+  constexpr int k = (1 <=> 1, 0);
+  // expected-error@-1 {{constexpr variable 'k' must be initialized by a constant expression}}
+  // expected-warning@-2 {{three-way comparison result unused}}
+
+  constexpr void f() { // expected-error {{constant expression}}
+    void(1 <=> 1); // expected-note {{constant expression}}
+  }
+
+  // TODO: defaulted operator <=>
+}
diff --git a/clang/test/SemaTemplate/cxx1z-fold-expressions.cpp b/clang/test/SemaTemplate/cxx1z-fold-expressions.cpp
index aefee92..383f51d 100644
--- a/clang/test/SemaTemplate/cxx1z-fold-expressions.cpp
+++ b/clang/test/SemaTemplate/cxx1z-fold-expressions.cpp
@@ -1,4 +1,5 @@
 // RUN: %clang_cc1 -std=c++1z -verify %s
+// RUN: %clang_cc1 -std=c++2a -verify %s
 
 template<typename ...T> constexpr auto sum(T ...t) { return (... + t); }
 template<typename ...T> constexpr auto product(T ...t) { return (t * ...); }
@@ -76,3 +77,18 @@
   return (t.*....*ts);
 }
 static_assert(&apply(a, &A::b, &A::B::c, &A::B::C::d, &A::B::C::D::e) == &a.b.c.d.e);
+
+#if __cplusplus > 201703L
+// The <=> operator is unique among binary operators in not being a
+// fold-operator.
+// FIXME: This diagnostic is not great.
+template<typename ...T> constexpr auto spaceship1(T ...t) { return (t <=> ...); } // expected-error {{expected expression}}
+template<typename ...T> constexpr auto spaceship2(T ...t) { return (... <=> t); } // expected-error {{expected expression}}
+template<typename ...T> constexpr auto spaceship3(T ...t) { return (t <=> ... <=> 0); } // expected-error {{expected expression}}
+#endif
+
+// The GNU binary conditional operator ?: is not recognized as a fold-operator.
+// FIXME: Why not? This seems like it would be useful.
+template<typename ...T> constexpr auto binary_conditional1(T ...t) { return (t ?: ...); } // expected-error {{expected expression}}
+template<typename ...T> constexpr auto binary_conditional2(T ...t) { return (... ?: t); } // expected-error {{expected expression}}
+template<typename ...T> constexpr auto binary_conditional3(T ...t) { return (t ?: ... ?: 0); } // expected-error {{expected expression}}