[c++20] P0515R3: Parsing support and basic AST construction for operator <=>.

Adding the new enumerator forced a bunch more changes into this patch than I
would have liked. The -Wtautological-compare warning was extended to properly
check the new comparison operator, clang-format needed updating because it uses
precedence levels as weights for determining where to break lines (and several
operators increased their precedence levels with this change), thread-safety
analysis needed changes to build its own IL properly for the new operator.

All "real" semantic checking for this operator has been deferred to a future
patch. For now, we use the relational comparison rules and arbitrarily give
the builtin form of the operator a return type of 'void'.

llvm-svn: 320707

1 files changed, 27 insertions, 0 deletions

diff --git a/clang/test/SemaCXX/constant-expression-cxx2a.cpp b/clang/test/SemaCXX/constant-expression-cxx2a.cpp
new file mode 100644
index 00000000000..935cbefc7cb
--- /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 <=>
+}