add test for review discussion

Author: sethp

clang/test/SemaCXX/static-assert-diagnostics.cpp

@@ -0,0 +1,117 @@
+// RUN: %clang_cc1 -std=c++2a -verify %s
+
+struct A {
+  int a, b[3], c;
+  bool operator==(const A&) const = default;
+};
+
+constexpr auto a0 = A{0, 0, 3, 4, 5};
+
+// expected-note@+1 {{evaluates to '{0, {0, 3, 4}, 5} == {1, {2, 3, 4}, 5}'}}
+static_assert(a0 == A{1, {2, 3, 4}, 5}); // expected-error {{failed}}
+
+struct _arr {
+  const int b[3];
+  constexpr bool operator==(const int rhs[3]) const {
+    for (unsigned i = 0; i < sizeof(b) / sizeof(int); i++)
+      if (b[i] != rhs[i])
+        return false;
+    return true;
+  }
+};
+
+// TODO[seth] syntactically sort of valid but almost entirely unusuable
+// (it's an int *, not an int [3] )
+// constexpr int _[3] = {...}; would work, but that's not piecewise substitutable
+// maybe it's ok? I mean, not like we can do better really...
+constexpr auto _ = (int[3]){2, 3, 4};
+
+// output: '{{2, 3, 4}} == {0, 3, 4}'  (the `{{` breaks VerifyDiagnosticConsumer::ParseDirective)
+// expected-note@+1 {{evaluates to}}
+static_assert(_arr{2, 3, 4} == a0.b); // expected-error {{failed}}
+
+struct B {
+  int a, c; // named the same just to keep things fresh
+  bool operator==(const B&) const = default;
+};
+
+// expected-note@+1 {{evaluates to '{7, 6} == {8, 6}'}}
+static_assert(B{7, 6} == B{8, 6}); // expected-error {{failed}}
+
+typedef int v4si __attribute__((__vector_size__(16)));
+
+struct C: A, B {
+  enum { E1, E2 } e;
+  bool operator==(const C&) const = default;
+};
+
+constexpr auto cc = C{A{1, {2, 3, 4}, 5}, B{7, 6}, C::E1};
+
+// actually '{{1, {2, 3, 4}, 5}, {7, 6}, 0} == {{0, {0, 3, 4}, 5}, {5, 0}, 1}'  (the `{{` breaks VerifyDiagnosticConsumer::ParseDirective)
+// expected-note@+1 {{evaluates to}}
+static_assert(cc == C{a0, {5}, C::E2}); // expected-error {{failed}}
+
+// this little guy? oh, I wouldn't worry about this little guy
+namespace std {
+template <class To, class From>
+constexpr To bit_cast(const From &from) {
+  static_assert(sizeof(To) == sizeof(From));
+  return __builtin_bit_cast(To, from);
+}
+} // namespace std
+
+typedef int v4si __attribute__((__vector_size__(16)));
+
+struct V {
+  v4si v;
+
+  // doesn't work
+  // vectors are not contextually convertable to `bool`, and
+  // `==` on vectors produces a vector of element-wise results
+  // bool operator==(const V&) const = default;
+
+  constexpr bool operator==(const V& rhs) const {
+    // doesn't work
+    // __builtin_reduce_and is not valid in a constant expression
+    // return __builtin_reduce_and(b == rhs.b) && __builtin_reduce_and(v == rhs.v);
+
+    // also doesn't work
+    // surprisingly, b[0] is also not valid in a constant expression (nor v[0])
+    // return b[0] == rhs.b[0] && ...
+
+    struct cmp {
+      unsigned char v [sizeof(v4si)];
+      bool operator==(const cmp&) const = default;
+    };
+    return std::bit_cast<cmp>(v) == std::bit_cast<cmp>(rhs.v);
+  };
+
+};
+// todo[seth] do I cause infinite evaluator recursion if I move this up into the function above?
+static_assert(V{1, 2, 3, 4} == V{1, 2, 3, 4});
+
+// '{{1, 2, 3, 4}} == {{1, 2, 0, 4}}'
+// expected-note@+1 {{evaluates to}}
+static_assert(V{1, 2, 3, 4} == V{1, 2, 0, 4}); // expected-error {{failed}}
+
+constexpr auto v = (v4si){1, 2, 3, 4};
+constexpr auto vv = V{{1, 2, 3, 4}};
+
+
+// there appears to be no constexpr-compatible way to write an == for
+// two `bool4`s at this time, since std::bit_cast doesn't support it
+// typedef bool bool4 __attribute__((ext_vector_type(4)));
+
+// so we use a bool8
+typedef bool bool8 __attribute__((ext_vector_type(8)));
+
+struct BV {
+  bool8 b;
+  constexpr bool operator==(const BV& rhs) const {
+    return std::bit_cast<unsigned char>(b) == std::bit_cast<unsigned char>(rhs.b);
+  }
+};
+
+// '{{false, true, false, false, false, false, false, false}} == {{true, false, false, false, false, false, false, false}}'
+// expected-note@+1 {{evaluates to}}
+static_assert(BV{{0, 1}} == BV{{1, 0}}); // expected-error {{failed}}