Add tests for CWG issues 6, 212, 232, 2823.

Unfortunately this adds two more "no"s to cxx_dr_status.

Author: zygoloid

clang/test/CXX/drs/cwg0xx.cpp

@@ -90,6 +90,24 @@ namespace cwg5 { // cwg5: 3.1
   const C c = e;
 } // namespace cwg5
 
+namespace cwg6 { // cwg6 codegen is tested in cwg6.cpp
+#if __cplusplus >= 201103L
+  struct Counter {
+    int copies;
+    constexpr Counter(int copies) : copies(copies) {}
+    constexpr Counter(const Counter& other) : copies(other.copies + 1) {}
+  };
+
+  // Passing an lvalue by value makes a non-elidable copy.
+  constexpr int PassByValue(Counter c) { return c.copies; }
+  constexpr int PassByValue2(Counter c) { return PassByValue(c); }
+  constexpr int PassByValue3(Counter c) { return PassByValue2(c); }
+  static_assert(PassByValue(Counter(0)) == 0, "expect no copies");
+  static_assert(PassByValue2(Counter(0)) == 1, "expect 1 copy");
+  static_assert(PassByValue3(Counter(0)) == 2, "expect 2 copies");
+#endif
+} // namespace cwg6
+
 namespace cwg7 { // cwg7: 3.4
   class A { public: ~A(); };
   class B : virtual private A {}; // #cwg7-B

clang/test/CXX/drs/cwg28xx.cpp

@@ -61,6 +61,22 @@ namespace cwg2819 { // cwg2819: 19 c++26
 #endif
 } // namespace cwg2819
 
+namespace cwg2823 { // cwg2823: no
+#if __cplusplus >= 201103L
+  constexpr int *p = 0;
+  constexpr int *q1 = &*p; // expected-error {{constant expression}} expected-note {{dereferencing a null pointer}}
+  // FIXME: invalid: dereferencing a null pointer.
+  constexpr int *q2 = &p[0];
+
+  int arr[32];
+  constexpr int *r = arr;
+  // FIXME: invalid: dereferencing a past-the-end pointer.
+  constexpr int *s1 = &*(r + 32);
+  // FIXME: invalid: dereferencing a past-the-end pointer.
+  constexpr int *s2 = &r[32];
+#endif
+}
+
 namespace cwg2847 { // cwg2847: 19 review 2024-03-01
 
 #if __cplusplus >= 202002L

clang/test/CXX/drs/cwg2xx.cpp

@@ -230,6 +230,37 @@ namespace cwg211 { // cwg211: 2.7
   };
 } // namespace cwg211
 
+namespace cwg212 { // cwg212: yes
+  template<typename T> struct Base;
+  template<typename T> struct Derived;
+
+  int *overload(void*);
+  float *overload(Base<int>*);
+  double *overload(Base<long>*);
+
+  void f(Derived<int> *p) {
+    // OK, calls void* overload.
+    int *a = overload(p);
+
+    Base<int> *q = p; // expected-error {{cannot initialize}}
+  }
+
+  template<typename T> struct Base {};
+  template<typename T> struct Derived : Base<T> {};
+
+  void g(Derived<long> *p) {
+    // OK, instantiates and calls Base<long>* overlod.
+    double *b = overload(p);
+    (void)b;
+  }
+
+  void h(Derived<float> *p) {
+    // OK, instantiates and converts.
+    Base<float> *q = p;
+    (void)q;
+  }
+}
+
 namespace cwg213 { // cwg213: 2.7
   template <class T> struct A : T {
     void h(T t) {
@@ -593,6 +624,9 @@ namespace cwg231 { // cwg231: 2.7
   }
 } // namespace cwg231
 
+// 232 is NAD; the desired behavior is described in 2823.
+// cwg232: dup 2823
+
 // cwg234: na
 // cwg235: na
 

clang/test/CXX/drs/cwg6.cpp

@@ -0,0 +1,31 @@
+// RUN: %clang_cc1 -std=c++98 %s -triple x86_64-linux-gnu -emit-llvm -o - -fexceptions -fcxx-exceptions -pedantic-errors | FileCheck %s --check-prefixes CHECK
+// RUN: %clang_cc1 -std=c++11 %s -triple x86_64-linux-gnu -emit-llvm -o - -fexceptions -fcxx-exceptions -pedantic-errors | FileCheck %s --check-prefixes CHECK
+// RUN: %clang_cc1 -std=c++14 %s -triple x86_64-linux-gnu -emit-llvm -o - -fexceptions -fcxx-exceptions -pedantic-errors | FileCheck %s --check-prefixes CHECK
+// RUN: %clang_cc1 -std=c++17 %s -triple x86_64-linux-gnu -emit-llvm -o - -fexceptions -fcxx-exceptions -pedantic-errors | FileCheck %s --check-prefixes CHECK
+// RUN: %clang_cc1 -std=c++20 %s -triple x86_64-linux-gnu -emit-llvm -o - -fexceptions -fcxx-exceptions -pedantic-errors | FileCheck %s --check-prefixes CHECK
+// RUN: %clang_cc1 -std=c++23 %s -triple x86_64-linux-gnu -emit-llvm -o - -fexceptions -fcxx-exceptions -pedantic-errors | FileCheck %s --check-prefixes CHECK
+// RUN: %clang_cc1 -std=c++2c %s -triple x86_64-linux-gnu -emit-llvm -o - -fexceptions -fcxx-exceptions -pedantic-errors | FileCheck %s --check-prefixes CHECK
+
+namespace cwg6 { // cwg6: yes
+
+struct A {
+  A();
+  A(const A&);
+  ~A();
+};
+
+inline void f(A a) {}
+
+// CHECK-LABEL: define {{.*}} @_ZN4cwg64callEv
+void call() {
+  A a;
+  // We copy the parameter here, even though object is not mutated by f and
+  // otherwise satisfies the criteria for the proposed CWG6 optimization.
+  // CHECK: {{call|invoke}} {{.*}} @_ZN4cwg61AC1ERKS0_
+  // CHECK: {{call|invoke}} {{.*}} @_ZN4cwg61fE
+  f(a);
+  // CHECK: {{call|invoke}} {{.*}} @_ZN4cwg61AD1Ev
+  // CHECK: {{call|invoke}} {{.*}} @_ZN4cwg61AD1Ev
+}
+
+} // namespace cwg6