clang/test/SemaCXX/constant-expression-cxx14.cpp

   1 // RUN: %clang_cc1 -std=c++23 -fsyntax-only -verify=expected,cxx20_23,cxx23          %s -fcxx-exceptions -triple=x86_64-linux-gnu
   2 // RUN: %clang_cc1 -std=c++20 -fsyntax-only -verify=expected,cxx14_20,cxx20_23,cxx20 %s -fcxx-exceptions -triple=x86_64-linux-gnu
   3 // RUN: %clang_cc1 -std=c++14 -fsyntax-only -verify=expected,cxx14_20,cxx14          %s -fcxx-exceptions -triple=x86_64-linux-gnu
   4
   5 struct S {
   6   // dummy ctor to make this a literal type
   7   constexpr S(int);
   8
   9   S();
  10
  11   int arr[10];
  12
  13   constexpr int &get(int n) { return arr[n]; }
  14   constexpr const int &get(int n) const { return arr[n]; }
  15 };
  16
  17 S s = S();
  18 const S &sr = s;
  19 static_assert(&s.get(4) - &sr.get(2) == 2, "");
  20
  21 // Compound-statements can be used in constexpr functions.
  22 constexpr int e() {{{{}} return 5; }}
  23 static_assert(e() == 5, "");
  24
  25 // Types can be defined in constexpr functions.
  26 constexpr int f() {
  27   enum E { e1, e2, e3 };
  28
  29   struct S {
  30     constexpr S(E e) : e(e) {}
  31     constexpr int get() { return e; }
  32     E e;
  33   };
  34
  35   return S(e2).get();
  36 }
  37 static_assert(f() == 1, "");
  38
  39 // Variables can be declared in constexpr functions.
  40 constexpr int g(int k) {
  41   const int n = 9;
  42   int k2 = k * k;
  43   int k3 = k2 * k;
  44   return 3 * k3 + 5 * k2 + n * k - 20;
  45 }
  46 static_assert(g(2) == 42, "");
  47 constexpr int h(int n) {  // expected-error {{constexpr function never produces a constant expression}}
  48   static const int m = n; // expected-note {{control flows through the definition of a static variable}} \
  49                           // cxx14_20-warning {{definition of a static variable in a constexpr function is a C++23 extension}}
  50   return m;
  51 }
  52 constexpr int i(int n) {        // expected-error {{constexpr function never produces a constant expression}}
  53   thread_local const int m = n; // expected-note {{control flows through the definition of a thread_local variable}} \
  54                                 // cxx14_20-warning {{definition of a thread_local variable in a constexpr function is a C++23 extension}}
  55   return m;
  56 }
  57
  58 // if-statements can be used in constexpr functions.
  59 constexpr int j(int k) {
  60   if (k == 5)
  61     return 1;
  62   if (k == 1)
  63     return 5;
  64   else {
  65     if (int n = 2 * k - 4) {
  66       return n + 1;
  67       return 2;
  68     }
  69   }
  70 } // expected-note 2{{control reached end of constexpr function}}
  71 static_assert(j(0) == -3, "");
  72 static_assert(j(1) == 5, "");
  73 static_assert(j(2), ""); // expected-error {{constant expression}} expected-note {{in call to 'j(2)'}}
  74 static_assert(j(3) == 3, "");
  75 static_assert(j(4) == 5, "");
  76 static_assert(j(5) == 1, "");
  77
  78 // There can be 0 return-statements.
  79 constexpr void k() {
  80 }
  81
  82 // If the return type is not 'void', no return statements => never a constant
  83 // expression, so still diagnose that case.
  84 [[noreturn]] constexpr int fn() { // expected-error {{no return statement in constexpr function}}
  85   fn();
  86 }
  87
  88 // We evaluate the body of a constexpr constructor, to check for side-effects.
  89 struct U {
  90   constexpr U(int n) {
  91     if (j(n)) {} // expected-note {{in call to 'j(2)'}}
  92   }
  93 };
  94 constexpr U u1{1};
  95 constexpr U u2{2}; // expected-error {{constant expression}} expected-note {{in call to 'U(2)'}}
  96
  97 // We allow expression-statements.
  98 constexpr int l(bool b) {
  99   if (b)
 100     throw "invalid value for b!"; // expected-note {{subexpression not valid}}
 101   return 5;
 102 }
 103 static_assert(l(false) == 5, "");
 104 static_assert(l(true), ""); // expected-error {{constant expression}} expected-note {{in call to 'l(true)'}}
 105
 106 // Potential constant expression checking is still applied where possible.
 107 constexpr int htonl(int x) { // expected-error {{never produces a constant expression}}
 108   typedef unsigned char uchar;
 109   uchar arr[4] = { uchar(x >> 24), uchar(x >> 16), uchar(x >> 8), uchar(x) };
 110   return *reinterpret_cast<int*>(arr); // expected-note {{reinterpret_cast is not allowed in a constant expression}}
 111 }
 112
 113 constexpr int maybe_htonl(bool isBigEndian, int x) {
 114   if (isBigEndian)
 115     return x;
 116
 117   typedef unsigned char uchar;
 118   uchar arr[4] = { uchar(x >> 24), uchar(x >> 16), uchar(x >> 8), uchar(x) };
 119   return *reinterpret_cast<int*>(arr); // expected-note {{reinterpret_cast is not allowed in a constant expression}}
 120 }
 121
 122 constexpr int swapped = maybe_htonl(false, 123); // expected-error {{constant expression}} expected-note {{in call}}
 123
 124 namespace NS {
 125   constexpr int n = 0;
 126 }
 127 constexpr int namespace_alias() {
 128   namespace N = NS;
 129   return N::n;
 130 }
 131
 132 namespace assign {
 133   constexpr int a = 0;
 134   const int b = 0;
 135   int c = 0; // expected-note {{here}}
 136
 137   constexpr void set(const int &a, int b) {
 138     const_cast<int&>(a) = b; // expected-note 3{{constant expression cannot modify an object that is visible outside that expression}}
 139   }
 140   constexpr int wrap(int a, int b) {
 141     set(a, b);
 142     return a;
 143   }
 144
 145   static_assert((set(a, 1), a) == 1, ""); // expected-error {{constant expression}} expected-note {{in call to 'set(a, 1)'}}
 146   static_assert((set(b, 1), b) == 1, ""); // expected-error {{constant expression}} expected-note {{in call to 'set(b, 1)'}}
 147   static_assert((set(c, 1), c) == 1, ""); // expected-error {{constant expression}} expected-note {{in call to 'set(c, 1)'}}
 148
 149   static_assert(wrap(a, 1) == 1, "");
 150   static_assert(wrap(b, 1) == 1, "");
 151   static_assert(wrap(c, 1) == 1, ""); // expected-error {{constant expression}} expected-note {{read of non-const variable 'c'}}
 152 }
 153
 154 namespace string_assign {
 155   template<typename T>
 156   constexpr void swap(T &a, T &b) {
 157     T tmp = a;
 158     a = b;
 159     b = tmp;
 160   }
 161   template<typename Iterator>
 162   constexpr void reverse(Iterator begin, Iterator end) {
 163     while (begin != end && begin != --end)
 164       swap(*begin++, *end);
 165   }
 166   template<typename Iterator1, typename Iterator2>
 167   constexpr bool equal(Iterator1 a, Iterator1 ae, Iterator2 b, Iterator2 be) {
 168     while (a != ae && b != be)
 169       if (*a++ != *b++)
 170         return false;
 171     return a == ae && b == be;
 172   }
 173   constexpr bool test1(int n) {
 174     char stuff[100] = "foobarfoo";
 175     const char stuff2[100] = "oofraboof";
 176     reverse(stuff, stuff + n); // expected-note {{cannot refer to element 101 of array of 100 elements}}
 177     return equal(stuff, stuff + n, stuff2, stuff2 + n);
 178   }
 179   static_assert(!test1(1), "");
 180   static_assert(test1(3), "");
 181   static_assert(!test1(6), "");
 182   static_assert(test1(9), "");
 183   static_assert(!test1(100), "");
 184   static_assert(!test1(101), ""); // expected-error {{constant expression}} expected-note {{in call to 'test1(101)'}}
 185
 186   constexpr void f() { // expected-error{{constexpr function never produces a constant expression}} expected-note@+2{{assignment to dereferenced one-past-the-end pointer is not allowed in a constant expression}}
 187     char foo[10] = { "z" }; // expected-note {{here}}
 188     foo[10] = 'x'; // expected-warning {{past the end}}
 189   }
 190 }
 191
 192 namespace array_resize {
 193   constexpr int do_stuff(int k1, int k2) {
 194     int arr[1234] = { 1, 2, 3, 4 };
 195     arr[k1] = 5; // expected-note {{past-the-end}} expected-note {{cannot refer to element 1235}} expected-note {{cannot refer to element -1}}
 196     return arr[k2];
 197   }
 198   static_assert(do_stuff(1, 2) == 3, "");
 199   static_assert(do_stuff(0, 0) == 5, "");
 200   static_assert(do_stuff(1233, 1233) == 5, "");
 201   static_assert(do_stuff(1233, 0) == 1, "");
 202   static_assert(do_stuff(1234, 0) == 1, ""); // expected-error {{constant expression}} expected-note {{in call}}
 203   static_assert(do_stuff(1235, 0) == 1, ""); // expected-error {{constant expression}} expected-note {{in call}}
 204   static_assert(do_stuff(-1, 0) == 1, ""); // expected-error {{constant expression}} expected-note {{in call}}
 205 }
 206
 207 namespace potential_const_expr {
 208   constexpr void set(int &n) { n = 1; }
 209   constexpr int div_zero_1() { int z = 0; set(z); return 100 / z; } // no error
 210   constexpr int div_zero_2() { // expected-error {{never produces a constant expression}}
 211     int z = 0;
 212     return 100 / (set(z), 0); // expected-note {{division by zero}}
 213   }
 214   int n; // expected-note {{declared here}}
 215   constexpr int ref() { // expected-error {{never produces a constant expression}}
 216     int &r = n;
 217     return r; // expected-note {{read of non-const variable 'n'}}
 218   }
 219 }
 220
 221 namespace subobject {
 222   union A { constexpr A() : y(5) {} int x, y; };
 223   struct B { A a; };
 224   struct C : B {};
 225   union D { constexpr D() : c() {} constexpr D(int n) : n(n) {} C c; int n; };
 226   constexpr void f(D &d) {
 227     d.c.a.y = 3;
 228     // expected-note@-1 {{cannot modify an object that is visible outside}}
 229     // expected-note@-2 {{assignment to member 'c' of union with active member 'n'}}
 230   }
 231   constexpr bool check(D &d) { return d.c.a.y == 3; }
 232   // cxx20_23-note@-1 {{read of member 'y' of union with active member 'x'}}
 233
 234   constexpr bool g() { D d; f(d); return d.c.a.y == 3; }
 235   static_assert(g(), "");
 236
 237   D d;
 238   constexpr bool h() { f(d); return check(d); } // expected-note {{in call}}
 239   static_assert(h(), ""); // expected-error {{constant expression}} expected-note {{in call}}
 240
 241   constexpr bool i() { D d(0); f(d); return check(d); } // expected-note {{in call}}
 242   static_assert(i(), ""); // expected-error {{constant expression}} expected-note {{in call}}
 243
 244   constexpr bool j() { D d; d.c.a.x = 3; return check(d); } // cxx14-note {{assignment to member 'x' of union with active member 'y'}}
 245   // cxx20_23-note@-1 {{in call to 'check(d)'}}
 246   static_assert(j(), ""); // expected-error {{constant expression}} expected-note {{in call}}
 247 }
 248
 249 namespace lifetime {
 250   constexpr int &&id(int &&n) { return static_cast<int&&>(n); }
 251   constexpr int &&dead() { return id(0); } // expected-note {{temporary created here}}
 252   constexpr int bad() { int &&n = dead(); n = 1; return n; } // expected-note {{assignment to temporary whose lifetime has ended}}
 253   static_assert(bad(), ""); // expected-error {{constant expression}} expected-note {{in call}}
 254 }
 255
 256 namespace const_modify {
 257   constexpr int modify(int &n) { return n = 1; } // expected-note 2 {{modification of object of const-qualified type 'const int'}}
 258   constexpr int test1() { int k = 0; return modify(k); }
 259   constexpr int test2() { const int k = 0; return modify(const_cast<int&>(k)); } // expected-note 2 {{in call}}
 260   static_assert(test1() == 1, "");
 261   static_assert(test2() == 1, ""); // expected-error {{constant expression}} expected-note {{in call}}
 262   constexpr int i = test2(); // expected-error {{constant expression}} expected-note {{in call}}
 263 }
 264
 265 namespace null {
 266   constexpr int test(int *p) {
 267     return *p = 123; // expected-note {{assignment to dereferenced null pointer}}
 268   }
 269   static_assert(test(0), ""); // expected-error {{constant expression}} expected-note {{in call}}
 270 }
 271
 272 namespace incdec {
 273   template<typename T> constexpr T &ref(T &&r) { return r; }
 274   // cxx23-error@-1 {{non-const lvalue reference to type 'int' cannot bind to a temporary of type 'int'}}
 275   template<typename T> constexpr T postinc(T &&r) { return (r++, r); }
 276   template<typename T> constexpr T postdec(T &&r) { return (r--, r); }
 277
 278   template int &ref<int>(int &&);
 279   // cxx23-note@-1  {{in instantiation of function template specialization}}
 280
 281   static_assert(postinc(0) == 1, "");
 282   static_assert(postdec(0) == -1, "");
 283 #if __cplusplus <= 202002L
 284   static_assert(++ref(0) == 1, "");
 285   static_assert(ref(0)++ == 0, "");
 286   static_assert(--ref(0) == -1, "");
 287   static_assert(ref(0)-- == 0, "");
 288 #endif
 289
 290 #if __cplusplus <= 202002L
 291   constexpr int overflow_int_inc_1 = ref(0x7fffffff)++; // expected-error {{constant}} expected-note {{2147483648}}
 292   constexpr int overflow_int_inc_1_ok = ref(0x7ffffffe)++;
 293   constexpr int overflow_int_inc_2 = ++ref(0x7fffffff); // expected-error {{constant}} expected-note {{2147483648}}
 294   constexpr int overflow_int_inc_2_ok = ++ref(0x7ffffffe);
 295
 296   // inc/dec on short can't overflow because we promote to int first
 297   static_assert(++ref<short>(0x7fff) == (int)0xffff8000u, "");
 298   static_assert(--ref<short>(0x8000) == 0x7fff, "");
 299
 300   // inc on bool sets to true
 301   static_assert(++ref(false), "");
 302   // cxx14-warning@-1  {{incrementing expression of type bool}}
 303   // cxx20-error@-2 {{incrementing expression of type bool}}
 304   static_assert(++ref(true), "");
 305   // cxx14-warning@-1  {{incrementing expression of type bool}}
 306   // cxx20-error@-2 {{incrementing expression of type bool}}
 307 #endif
 308
 309   int arr[10];
 310   static_assert(postinc(&arr[0]) == &arr[1], "");
 311   static_assert(postdec(&arr[1]) == &arr[0], "");
 312 #if __cplusplus <= 202002L
 313   static_assert(++ref(&arr[0]) == &arr[1], "");
 314   static_assert(++ref(&arr[9]) == &arr[10], "");
 315   static_assert(++ref(&arr[10]) == &arr[11], ""); // expected-error {{constant}} expected-note {{cannot refer to element 11}}
 316   static_assert(ref(&arr[0])++ == &arr[0], "");
 317   static_assert(ref(&arr[10])++ == &arr[10], ""); // expected-error {{constant}} expected-note {{cannot refer to element 11}}
 318   static_assert(--ref(&arr[10]) == &arr[9], "");
 319   static_assert(--ref(&arr[1]) == &arr[0], "");
 320   static_assert(--ref(&arr[0]) != &arr[0], ""); // expected-error {{constant}} expected-note {{cannot refer to element -1}}
 321   static_assert(ref(&arr[1])-- == &arr[1], "");
 322   static_assert(ref(&arr[0])-- == &arr[0], ""); // expected-error {{constant}} expected-note {{cannot refer to element -1}}
 323 #endif
 324
 325   static_assert(postinc(0.0) == 1.0, "");
 326   static_assert(postdec(0.0) == -1.0, "");
 327 #if __cplusplus <= 202002L
 328   int x;
 329   static_assert(++ref(&x) == &x + 1, "");
 330
 331   static_assert(++ref(0.0) == 1.0, "");
 332   static_assert(ref(0.0)++ == 0.0, "");
 333   static_assert(--ref(0.0) == -1.0, "");
 334   static_assert(ref(0.0)-- == 0.0, "");
 335
 336   static_assert(++ref(1e100) == 1e100, "");
 337   static_assert(--ref(1e100) == 1e100, "");
 338 #endif
 339
 340   union U {
 341     int a, b;
 342   };
 343   constexpr int f(U u) {
 344     return ++u.b; // expected-note {{increment of member 'b' of union with active member 'a'}}
 345   }
 346   constexpr int wrong_member = f({0}); // expected-error {{constant}} expected-note {{in call to 'f({.a = 0})'}}
 347   constexpr int vol = --ref<volatile int>(0); // expected-error {{constant}} expected-note {{decrement of volatile-qualified}}
 348   // cxx20_23-warning@-1 {{decrement of object of volatile-qualified type 'volatile int' is deprecated}}
 349
 350   constexpr int incr(int k) {
 351     int x = k;
 352     if (x++ == 100)
 353       return x;
 354     return incr(x);
 355   }
 356   static_assert(incr(0) == 101, "");
 357 }
 358
 359 namespace compound_assign {
 360   constexpr bool test_int() {
 361     int a = 3;
 362     a += 6;
 363     if (a != 9) return false;
 364     a -= 2;
 365     if (a != 7) return false;
 366     a *= 3;
 367     if (a != 21) return false;
 368     if (&(a /= 10) != &a) return false;
 369     if (a != 2) return false;
 370     a <<= 3;
 371     if (a != 16) return false;
 372     a %= 6;
 373     if (a != 4) return false;
 374     a >>= 1;
 375     if (a != 2) return false;
 376     a ^= 10;
 377     if (a != 8) return false;
 378     a |= 5;
 379     if (a != 13) return false;
 380     a &= 14;
 381     if (a != 12) return false;
 382     a += -1.2;
 383     if (a != 10) return false;
 384     a -= 3.1;
 385     if (a != 6) return false;
 386     a *= 2.2;
 387     if (a != 13) return false;
 388     if (&(a /= 1.5) != &a) return false;
 389     if (a != 8) return false;
 390     return true;
 391   }
 392   static_assert(test_int(), "");
 393
 394   constexpr bool test_float() {
 395     float f = 123.;
 396     f *= 2;
 397     if (f != 246.) return false;
 398     if ((f -= 0.5) != 245.5) return false;
 399     if (f != 245.5) return false;
 400     f /= 0.5;
 401     if (f != 491.) return false;
 402     f += -40;
 403     if (f != 451.) return false;
 404     return true;
 405   }
 406   static_assert(test_float(), "");
 407
 408   constexpr bool test_bool() {
 409     bool b = false;
 410     b |= 2;
 411     if (b != true) return false;
 412     b <<= 1;
 413     if (b != true) return false;
 414     b *= 2;
 415     if (b != true) return false;
 416     b -= 1;
 417     if (b != false) return false;
 418     b -= 1;
 419     if (b != true) return false;
 420     b += -1;
 421     if (b != false) return false;
 422     b += 1;
 423     if (b != true) return false;
 424     b += 1;
 425     if (b != true) return false;
 426     b ^= b;
 427     if (b != false) return false;
 428     return true;
 429   }
 430   static_assert(test_bool(), "");
 431
 432   constexpr bool test_ptr() {
 433     int arr[123] = {};
 434     int *p = arr;
 435     if ((p += 4) != &arr[4]) return false;
 436     if (p != &arr[4]) return false;
 437     p += -1;
 438     if (p != &arr[3]) return false;
 439     if ((p -= -10) != &arr[13]) return false;
 440     if (p != &arr[13]) return false;
 441     p -= 11;
 442     if (p != &arr[2]) return false;
 443     return true;
 444   }
 445   static_assert(test_ptr(), "");
 446
 447   template<typename T>
 448   constexpr bool test_overflow() {
 449     T a = 1;
 450     while (a != a / 2)
 451       a *= 2; // expected-note {{value 2147483648 is outside the range}} expected-note {{ 9223372036854775808 }}
 452     return true;
 453   }
 454
 455   static_assert(test_overflow<int>(), ""); // expected-error {{constant}} expected-note {{call}}
 456   static_assert(test_overflow<unsigned>(), ""); // ok, unsigned overflow is defined
 457   static_assert(test_overflow<short>(), ""); // ok, short is promoted to int before multiplication
 458   static_assert(test_overflow<unsigned short>(), ""); // ok
 459   static_assert(test_overflow<unsigned long long>(), ""); // ok
 460   static_assert(test_overflow<long long>(), ""); // expected-error {{constant}} expected-note {{call}}
 461   static_assert(test_overflow<float>(), ""); // ok
 462   static_assert(test_overflow<double>(), ""); // ok
 463
 464   constexpr short test_promotion(short k) {
 465     short s = k;
 466     s *= s;
 467     return s;
 468   }
 469   static_assert(test_promotion(100) == 10000, "");
 470   static_assert(test_promotion(200) == -25536, "");
 471   static_assert(test_promotion(256) == 0, "");
 472
 473   constexpr const char *test_bounds(const char *p, int o) {
 474     return p += o; // expected-note {{element 5 of}} expected-note {{element -1 of}} expected-note {{element 1000 of}}
 475   }
 476   static_assert(test_bounds("foo", 0)[0] == 'f', "");
 477   static_assert(test_bounds("foo", 3)[0] == 0, "");
 478   static_assert(test_bounds("foo", 4)[-3] == 'o', "");
 479   static_assert(test_bounds(&"foo"[4], -4)[0] == 'f', "");
 480   static_assert(test_bounds("foo", 5) != 0, ""); // expected-error {{constant}} expected-note {{call}}
 481   static_assert(test_bounds("foo", -1) != 0, ""); // expected-error {{constant}} expected-note {{call}}
 482   static_assert(test_bounds("foo", 1000) != 0, ""); // expected-error {{constant}} expected-note {{call}}
 483 }
 484
 485 namespace loops {
 486   constexpr int fib_loop(int a) {
 487     int f_k = 0, f_k_plus_one = 1;
 488     for (int k = 1; k != a; ++k) {
 489       int f_k_plus_two = f_k + f_k_plus_one;
 490       f_k = f_k_plus_one;
 491       f_k_plus_one = f_k_plus_two;
 492     }
 493     return f_k_plus_one;
 494   }
 495   static_assert(fib_loop(46) == 1836311903, "");
 496
 497   constexpr bool breaks_work() {
 498     int a = 0;
 499     for (int n = 0; n != 100; ++n) {
 500       ++a;
 501       if (a == 5) continue;
 502       if ((a % 5) == 0) break;
 503     }
 504
 505     int b = 0;
 506     while (b != 17) {
 507       ++b;
 508       if (b == 6) continue;
 509       if ((b % 6) == 0) break;
 510     }
 511
 512     int c = 0;
 513     do {
 514       ++c;
 515       if (c == 7) continue;
 516       if ((c % 7) == 0) break;
 517     } while (c != 21);
 518
 519     return a == 10 && b == 12 && c == 14;
 520   }
 521   static_assert(breaks_work(), "");
 522
 523   void not_constexpr();
 524   constexpr bool no_cont_after_break() {
 525     for (;;) {
 526       break;
 527       not_constexpr();
 528     }
 529     while (true) {
 530       break;
 531       not_constexpr();
 532     }
 533     do {
 534       break;
 535       not_constexpr();
 536     } while (true);
 537     return true;
 538   }
 539   static_assert(no_cont_after_break(), "");
 540
 541   constexpr bool cond() {
 542     for (int a = 1; bool b = a != 3; ++a) {
 543       if (!b)
 544         return false;
 545     }
 546     while (bool b = true) {
 547       b = false;
 548       break;
 549     }
 550     return true;
 551   }
 552   static_assert(cond(), "");
 553
 554   constexpr int range_for() {
 555     int arr[] = { 1, 2, 3, 4, 5 };
 556     int sum = 0;
 557     for (int x : arr)
 558       sum += x;
 559     return sum;
 560   }
 561   static_assert(range_for() == 15, "");
 562
 563   template<int...N> struct ints {};
 564   template<typename A, typename B> struct join_ints;
 565   template<int...As, int...Bs> struct join_ints<ints<As...>, ints<Bs...>> {
 566     using type = ints<As..., sizeof...(As) + Bs...>;
 567   };
 568   template<unsigned N> struct make_ints {
 569     using type = typename join_ints<typename make_ints<N/2>::type, typename make_ints<(N+1)/2>::type>::type;
 570   };
 571   template<> struct make_ints<0> { using type = ints<>; };
 572   template<> struct make_ints<1> { using type = ints<0>; };
 573
 574   struct ignore { template<typename ...Ts> constexpr ignore(Ts &&...) {} };
 575
 576   template<typename T, unsigned N> struct array {
 577     constexpr array() : arr{} {}
 578     template<typename ...X>
 579     constexpr array(X ...x) : arr{} {
 580       init(typename make_ints<sizeof...(X)>::type{}, x...);
 581     }
 582     template<int ...I, typename ...X> constexpr void init(ints<I...>, X ...x) {
 583       ignore{arr[I] = x ...};
 584     }
 585     T arr[N];
 586     struct iterator {
 587       T *p;
 588       constexpr explicit iterator(T *p) : p(p) {}
 589       constexpr bool operator!=(iterator o) { return p != o.p; }
 590       constexpr iterator &operator++() { ++p; return *this; }
 591       constexpr T &operator*() { return *p; }
 592     };
 593     constexpr iterator begin() { return iterator(arr); }
 594     constexpr iterator end() { return iterator(arr + N); }
 595   };
 596
 597   constexpr int range_for_2() {
 598     array<int, 5> arr { 1, 2, 3, 4, 5 };
 599     int sum = 0;
 600     for (int k : arr) {
 601       sum += k;
 602       if (sum > 8) break;
 603     }
 604     return sum;
 605   }
 606   static_assert(range_for_2() == 10, "");
 607 }
 608
 609 namespace assignment_op {
 610   struct A {
 611     constexpr A() : n(5) {}
 612     int n;
 613     struct B {
 614       int k = 1;
 615       union U {
 616         constexpr U() : y(4) {}
 617         int x;
 618         int y;
 619       } u;
 620     } b;
 621   };
 622   constexpr bool testA() {
 623     A a, b;
 624     a.n = 7;
 625     a.b.u.y = 5;
 626     b = a;
 627     return b.n == 7 && b.b.u.y == 5 && b.b.k == 1;
 628   }
 629   static_assert(testA(), "");
 630
 631   struct B {
 632     bool assigned = false;
 633     constexpr B &operator=(const B&) {
 634       assigned = true;
 635       return *this;
 636     }
 637   };
 638   struct C : B {
 639     B b;
 640     int n = 5;
 641   };
 642   constexpr bool testC() {
 643     C c, d;
 644     c.n = 7;
 645     d = c;
 646     c.n = 3;
 647     return d.n == 7 && d.assigned && d.b.assigned;
 648   }
 649   static_assert(testC(), "");
 650 }
 651
 652 namespace switch_stmt {
 653   constexpr bool no_such_case(int n) {
 654     switch (n) { case 1: return false; }
 655     return true;
 656   }
 657   static_assert(no_such_case(0), "");
 658
 659   constexpr int f(char k) {
 660     bool b = false;
 661     int z = 6;
 662     switch (k) {
 663       return -1;
 664     case 0:
 665       if (false) {
 666       case 1:
 667         z = 1;
 668         for (; b;) {
 669           return 5;
 670           while (0)
 671             case 2: return 2;
 672           case 7: z = 7;
 673           do case 6: {
 674             return z;
 675             if (false)
 676               case 3: return 3;
 677             case 4: z = 4;
 678           } while (1);
 679           case 5: b = true;
 680           case 9: z = 9;
 681         }
 682         return z;
 683       } else if (false) case 8: z = 8;
 684       else if (false) {
 685       case 10:
 686         z = -10;
 687         break;
 688       }
 689       else z = 0;
 690       return z;
 691     default:
 692       return -1;
 693     }
 694     return -z;
 695   }
 696   static_assert(f(0) == 0, "");
 697   static_assert(f(1) == 1, "");
 698   static_assert(f(2) == 2, "");
 699   static_assert(f(3) == 3, "");
 700   static_assert(f(4) == 4, "");
 701   static_assert(f(5) == 5, "");
 702   static_assert(f(6) == 6, "");
 703   static_assert(f(7) == 7, "");
 704   static_assert(f(8) == 8, "");
 705   static_assert(f(9) == 9, "");
 706   static_assert(f(10) == 10, "");
 707
 708   // Check that we can continue an outer loop from within a switch.
 709   constexpr bool contin() {
 710     for (int n = 0; n != 10; ++n) {
 711       switch (n) {
 712       case 0:
 713         ++n;
 714         continue;
 715       case 1:
 716         return false;
 717       case 2:
 718         return true;
 719       }
 720     }
 721     return false;
 722   }
 723   static_assert(contin(), "");
 724
 725   constexpr bool switch_into_for() {
 726     int n = 0;
 727     switch (n) {
 728       for (; n == 1; ++n) {
 729         return n == 1;
 730       case 0: ;
 731       }
 732     }
 733     return false;
 734   }
 735   static_assert(switch_into_for(), "");
 736
 737   constexpr void duff_copy(char *a, const char *b, int n) {
 738     switch ((n - 1) % 8 + 1) {
 739       for ( ; n; n = (n - 1) & ~7) {
 740       case 8: a[n-8] = b[n-8];
 741       case 7: a[n-7] = b[n-7];
 742       case 6: a[n-6] = b[n-6];
 743       case 5: a[n-5] = b[n-5];
 744       case 4: a[n-4] = b[n-4];
 745       case 3: a[n-3] = b[n-3];
 746       case 2: a[n-2] = b[n-2];
 747       case 1: a[n-1] = b[n-1];
 748       }
 749       case 0: ;
 750     }
 751   }
 752
 753   constexpr bool test_copy(const char *str, int n) {
 754     char buffer[16] = {};
 755     duff_copy(buffer, str, n);
 756     for (int i = 0; i != sizeof(buffer); ++i)
 757       if (buffer[i] != (i < n ? str[i] : 0))
 758         return false;
 759     return true;
 760   }
 761   static_assert(test_copy("foo", 0), "");
 762   static_assert(test_copy("foo", 1), "");
 763   static_assert(test_copy("foo", 2), "");
 764   static_assert(test_copy("hello world", 0), "");
 765   static_assert(test_copy("hello world", 7), "");
 766   static_assert(test_copy("hello world", 8), "");
 767   static_assert(test_copy("hello world", 9), "");
 768   static_assert(test_copy("hello world", 10), "");
 769   static_assert(test_copy("hello world", 10), "");
 770 }
 771
 772 namespace deduced_return_type {
 773   constexpr auto f() { return 0; }
 774   template<typename T> constexpr auto g(T t) { return t; }
 775   static_assert(f() == 0, "");
 776   static_assert(g(true), "");
 777 }
 778
 779 namespace modify_temporary_during_construction {
 780   struct A { int &&temporary; int x; int y; };
 781   constexpr int f(int &r) { r *= 9; return r - 12; }
 782   constexpr A a = { 6, f(a.temporary), a.temporary }; // expected-note {{temporary created here}}
 783   static_assert(a.x == 42, "");
 784   static_assert(a.y == 54, "");
 785   constexpr int k = a.temporary++; // expected-error {{constant expression}} expected-note {{outside the expression that created the temporary}}
 786 }
 787
 788 namespace std {
 789   typedef decltype(sizeof(int)) size_t;
 790
 791   template <class _E>
 792   class initializer_list
 793   {
 794     const _E* __begin_;
 795     size_t    __size_;
 796
 797     constexpr initializer_list(const _E* __b, size_t __s)
 798       : __begin_(__b),
 799         __size_(__s)
 800     {}
 801
 802   public:
 803     typedef _E        value_type;
 804     typedef const _E& reference;
 805     typedef const _E& const_reference;
 806     typedef size_t    size_type;
 807
 808     typedef const _E* iterator;
 809     typedef const _E* const_iterator;
 810
 811     constexpr initializer_list() : __begin_(nullptr), __size_(0) {}
 812
 813     constexpr size_t    size()  const {return __size_;}
 814     constexpr const _E* begin() const {return __begin_;}
 815     constexpr const _E* end()   const {return __begin_ + __size_;}
 816   };
 817 }
 818
 819 namespace InitializerList {
 820   constexpr int sum(std::initializer_list<int> ints) {
 821     int total = 0;
 822     for (int n : ints) total += n;
 823     return total;
 824   }
 825   static_assert(sum({1, 2, 3, 4, 5}) == 15, "");
 826 }
 827
 828 namespace StmtExpr {
 829   constexpr int f(int k) {
 830     switch (k) {
 831     case 0:
 832       return 0;
 833
 834       ({  // expected-note {{jump enters a statement expression}}
 835         case 1:// expected-error {{cannot jump from switch statement to this case label}} \
 836                // expected-note  {{not supported}}
 837           return 1;
 838       });
 839     }
 840   }
 841   static_assert(f(1) == 1, ""); // expected-error {{constant expression}} expected-note {{in call}}
 842
 843   constexpr int g() {
 844     return ({ int n; n; }); // expected-note {{read of uninitialized object}}
 845   }
 846   static_assert(g() == 0, ""); // expected-error {{constant expression}} expected-note {{in call}}
 847
 848   // FIXME: We should handle the void statement expression case.
 849   constexpr int h() { // expected-error {{never produces a constant}}
 850     ({ if (true) {} }); // expected-note {{not supported}}
 851     return 0;
 852   }
 853 }
 854
 855 namespace VirtualFromBase {
 856   struct S1 {
 857     virtual int f() const;
 858   };
 859   struct S2 {
 860     virtual int f();
 861   };
 862   template <typename T> struct X : T {
 863     constexpr X() {}
 864     double d = 0.0;
 865     constexpr int f() { return sizeof(T); }
 866   };
 867
 868   // Non-virtual f(), OK.
 869   constexpr X<X<S1>> xxs1;
 870   constexpr X<S1> *p = const_cast<X<X<S1>>*>(&xxs1);
 871   static_assert(p->f() == sizeof(S1), "");
 872
 873   // Virtual f(), not OK.
 874   constexpr X<X<S2>> xxs2;
 875   constexpr X<S2> *q = const_cast<X<X<S2>>*>(&xxs2);
 876   static_assert(q->f() == sizeof(X<S2>), ""); // cxx14-error {{constant expression}} cxx14-note {{virtual function}}
 877 }
 878
 879 namespace Lifetime {
 880   constexpr int &get(int &&r) { return r; }
 881   // cxx23-error@-1 {{non-const lvalue reference to type 'int' cannot bind to a temporary of type 'int'}}
 882   constexpr int f() {
 883     int &r = get(123);
 884     return r;
 885     // cxx14_20-note@-1 {{read of object outside its lifetime}}
 886   }
 887   static_assert(f() == 123, ""); // expected-error {{constant expression}} cxx14_20-note {{in call}}
 888
 889   constexpr int g() {
 890     int *p = 0;
 891     {
 892       int n = 0;
 893       p = &n;
 894       n = 42;
 895     }
 896     *p = 123; // expected-note {{assignment to object outside its lifetime}}
 897     return *p;
 898   }
 899   static_assert(g() == 42, ""); // expected-error {{constant expression}} expected-note {{in call}}
 900
 901   constexpr int h(int n) {
 902     int *p[4] = {};
 903     int &&r = 1;
 904     p[0] = &r;
 905     while (int a = 1) {
 906       p[1] = &a;
 907       for (int b = 1; int c = 1; ) {
 908         p[2] = &b, p[3] = &c;
 909         break;
 910       }
 911       break;
 912     }
 913     *p[n] = 0; // expected-note 3{{assignment to object outside its lifetime}}
 914     return *p[n];
 915   }
 916   static_assert(h(0) == 0, ""); // ok, lifetime-extended
 917   static_assert(h(1) == 0, ""); // expected-error {{constant expression}} expected-note {{in call}}
 918   static_assert(h(2) == 0, ""); // expected-error {{constant expression}} expected-note {{in call}}
 919   static_assert(h(3) == 0, ""); // expected-error {{constant expression}} expected-note {{in call}}
 920
 921   constexpr void lifetime_versus_loops() {
 922     int *p = 0;
 923     for (int i = 0; i != 2; ++i) {
 924       int *q = p;
 925       int n = 0;
 926       p = &n;
 927       if (i)
 928         // This modifies the 'n' from the previous iteration of the loop outside
 929         // its lifetime.
 930         ++*q; // expected-note {{increment of object outside its lifetime}}
 931     }
 932   }
 933   static_assert((lifetime_versus_loops(), true), ""); // expected-error {{constant expression}} expected-note {{in call}}
 934 }
 935
 936 namespace Bitfields {
 937   struct A {
 938     bool b : 1;
 939     int n : 4;
 940     unsigned u : 5;
 941   };
 942   constexpr bool test() {
 943     A a {};
 944     a.b += 2;
 945     --a.n;
 946     --a.u;
 947     a.n = -a.n * 3;
 948     return a.b == true && a.n == 3 && a.u == 31;
 949   }
 950   static_assert(test(), "");
 951 }
 952
 953 namespace PR17615 {
 954   struct A {
 955     int &&r;
 956     constexpr A(int &&r) : r(static_cast<int &&>(r)) {}
 957     constexpr A() : A(0) {
 958       (void)+r; // expected-note {{outside its lifetime}}
 959     }
 960   };
 961   constexpr int k = A().r; // expected-error {{constant expression}} expected-note {{in call to}}
 962 }
 963
 964 namespace PR17331 {
 965   template<typename T, unsigned int N>
 966   constexpr T sum(const T (&arr)[N]) {
 967     T result = 0;
 968     for (T i : arr)
 969       result += i;
 970     return result;
 971   }
 972
 973   constexpr int ARR[] = { 1, 2, 3, 4, 5 };
 974   static_assert(sum(ARR) == 15, "");
 975 }
 976
 977 namespace EmptyClass {
 978   struct E1 {} e1;
 979   union E2 {} e2; // expected-note 4{{here}}
 980   struct E3 : E1 {} e3;
 981
 982   template<typename E>
 983   constexpr int f(E &a, int kind) {
 984     switch (kind) {
 985     case 0: { E e(a); return 0; } // expected-note {{read}} expected-note {{in call}}
 986     case 1: { E e(static_cast<E&&>(a)); return 0; } // expected-note {{read}} expected-note {{in call}}
 987     case 2: { E e; e = a; return 0; } // expected-note {{read}} expected-note {{in call}}
 988     case 3: { E e; e = static_cast<E&&>(a); return 0; } // expected-note {{read}} expected-note {{in call}}
 989     }
 990   }
 991   constexpr int test1 = f(e1, 0);
 992   constexpr int test2 = f(e2, 0); // expected-error {{constant expression}} expected-note {{in call}}
 993   constexpr int test3 = f(e3, 0);
 994   constexpr int test4 = f(e1, 1);
 995   constexpr int test5 = f(e2, 1); // expected-error {{constant expression}} expected-note {{in call}}
 996   constexpr int test6 = f(e3, 1);
 997   constexpr int test7 = f(e1, 2);
 998   constexpr int test8 = f(e2, 2); // expected-error {{constant expression}} expected-note {{in call}}
 999   constexpr int test9 = f(e3, 2);
1000   constexpr int testa = f(e1, 3);
1001   constexpr int testb = f(e2, 3); // expected-error {{constant expression}} expected-note {{in call}}
1002   constexpr int testc = f(e3, 3);
1003 }
1004
1005 namespace SpeculativeEvalWrites {
1006   // Ensure that we don't try to speculatively evaluate writes.
1007   constexpr int f() {
1008     int i = 0;
1009     int a = 0;
1010     // __builtin_object_size speculatively evaluates its first argument.
1011     __builtin_object_size((i = 1, &a), 0);
1012     return i;
1013   }
1014
1015   static_assert(!f(), "");
1016 }
1017
1018 namespace PR27989 {
1019   constexpr int f(int n) {
1020     int a = (n = 1, 0);
1021     return n;
1022   }
1023   static_assert(f(0) == 1, "");
1024 }
1025
1026 namespace const_char {
1027 template <int N>
1028 constexpr int sum(const char (&Arr)[N]) {
1029   int S = 0;
1030   for (unsigned I = 0; I != N; ++I)
1031     S += Arr[I]; // expected-note 2{{read of non-constexpr variable 'Cs' is not allowed}}
1032   return S;
1033 }
1034
1035 // As an extension, we support evaluating some things that are `const` as though
1036 // they were `constexpr` when folding, but it should not be allowed in normal
1037 // constexpr evaluation.
1038 const char Cs[] = {'a', 'b'}; // expected-note 2{{declared here}}
1039 void foo() __attribute__((enable_if(sum(Cs) == 'a' + 'b', "")));
1040 void run() { foo(); }
1041
1042 static_assert(sum(Cs) == 'a' + 'b', ""); // expected-error{{not an integral constant expression}} expected-note{{in call to 'sum<2>(Cs)'}}
1043 constexpr int S = sum(Cs); // expected-error{{must be initialized by a constant expression}} expected-note{{in call}}
1044 }
1045
1046 constexpr void PR28739(int n) { // expected-error {{never produces a constant}}
1047   int *p = &n;                  // expected-note {{array 'p' declared here}}
1048   p += (__int128)(unsigned long)-1; // expected-note {{cannot refer to element 18446744073709551615 of non-array object in a constant expression}}
1049   // expected-warning@-1 {{the pointer incremented by 18446744073709551615 refers past the last possible element for an array in 64-bit address space containing 32-bit (4-byte) elements (max possible 4611686018427387904 elements)}}
1050 }
1051
1052 constexpr void Void(int n) {
1053   void(n + 1);
1054   void();
1055 }
1056 constexpr int void_test = (Void(0), 1);
1057
1058 namespace PR19741 {
1059 constexpr void addone(int &m) { m++; }
1060
1061 struct S {
1062   int m = 0;
1063   constexpr S() { addone(m); }
1064 };
1065 constexpr bool evalS() {
1066   constexpr S s;
1067   return s.m == 1;
1068 }
1069 static_assert(evalS(), "");
1070
1071 struct Nested {
1072   struct First { int x = 42; };
1073   union {
1074     First first;
1075     int second;
1076   };
1077   int x;
1078   constexpr Nested(int x) : first(), x(x) { x = 4; }
1079   constexpr Nested() : Nested(42) {
1080     addone(first.x);
1081     x = 3;
1082   }
1083 };
1084 constexpr bool evalNested() {
1085   constexpr Nested N;
1086   return N.first.x == 43;
1087 }
1088 static_assert(evalNested(), "");
1089 } // namespace PR19741
1090
1091 namespace Mutable {
1092   struct A { mutable int n; }; // expected-note 2{{here}}
1093   constexpr int k = A{123}.n; // ok
1094   static_assert(k == 123, "");
1095
1096   struct Q { A &&a; int b = a.n; };
1097   constexpr Q q = { A{456} }; // expected-note {{temporary}}
1098   static_assert(q.b == 456, "");
1099   static_assert(q.a.n == 456, ""); // expected-error {{constant expression}} expected-note {{outside the expression that created the temporary}}
1100
1101   constexpr A a = {123};
1102   constexpr int m = a.n; // expected-error {{constant expression}} expected-note {{mutable}}
1103
1104   constexpr Q r = { static_cast<A&&>(const_cast<A&>(a)) }; // expected-error {{constant expression}} expected-note@-8 {{mutable}}
1105
1106   struct B {
1107     mutable int n; // expected-note {{here}}
1108     int m;
1109     constexpr B() : n(1), m(n) {} // ok
1110   };
1111   constexpr B b;
1112   constexpr int p = b.n; // expected-error {{constant expression}} expected-note {{mutable}}
1113 }
1114
1115 namespace IndirectFields {
1116
1117 // Reference indirect field.
1118 struct A {
1119   struct {
1120     union {
1121       int x = x = 3; // cxx14-note {{outside its lifetime}}
1122     };
1123   };
1124   constexpr A() {}
1125 };
1126 static_assert(A().x == 3, ""); // cxx14-error{{not an integral constant expression}} cxx14-note{{in call to 'A()'}}
1127
1128 // Reference another indirect field, with different 'this'.
1129 struct B {
1130   struct {
1131     union {
1132       int x = 3;
1133     };
1134     int y = x;
1135   };
1136   constexpr B() {}
1137 };
1138 static_assert(B().y == 3, "");
1139
1140 // Nested evaluation of indirect field initializers.
1141 struct C {
1142   union {
1143     int x = 1;
1144   };
1145 };
1146 struct D {
1147   struct {
1148     C c;
1149     int y = c.x + 1;
1150   };
1151 };
1152 static_assert(D().y == 2, "");
1153
1154 // Explicit 'this'.
1155 struct E {
1156   int n = 0;
1157   struct {
1158     void *x = this;
1159   };
1160   void *y = this;
1161 };
1162 constexpr E e1 = E();
1163 static_assert(e1.x != e1.y, "");
1164 constexpr E e2 = E{0};
1165 static_assert(e2.x != e2.y, "");
1166
1167 } // namespace IndirectFields
1168
1169 constexpr bool indirect_builtin_constant_p(const char *__s) {
1170   return __builtin_constant_p(*__s);
1171 }
1172 constexpr bool n = indirect_builtin_constant_p("a");
1173
1174 __attribute__((enable_if(indirect_builtin_constant_p("a") == n, "OK")))
1175 int test_in_enable_if() { return 0; }
1176 int n2 = test_in_enable_if();
1177
1178 template <bool n = indirect_builtin_constant_p("a")>
1179 int test_in_template_param() { return 0; }
1180 int n3 = test_in_template_param();
1181
1182 void test_in_case(int n) {
1183   switch (n) {
1184     case indirect_builtin_constant_p("abc"):
1185     break;
1186   }
1187 }
1188 enum InEnum1 {
1189   ONE = indirect_builtin_constant_p("abc")
1190 };
1191 enum InEnum2 : int {
1192   TWO = indirect_builtin_constant_p("abc")
1193 };
1194 enum class InEnum3 {
1195   THREE = indirect_builtin_constant_p("abc")
1196 };
1197
1198 // [class.ctor]p4:
1199 //   A constructor can be invoked for a const, volatile or const volatile
1200 //   object. const and volatile semantics are not applied on an object under
1201 //   construction. They come into effect when the constructor for the most
1202 //   derived object ends.
1203 namespace ObjectsUnderConstruction {
1204   struct A {
1205     int n;
1206     constexpr A() : n(1) { n = 2; }
1207   };
1208   struct B {
1209     const A a;
1210     constexpr B(bool mutate) {
1211       if (mutate)
1212         const_cast<A &>(a).n = 3; // expected-note {{modification of object of const-qualified type 'const int'}}
1213     }
1214   };
1215   constexpr B b(false);
1216   static_assert(b.a.n == 2, "");
1217   constexpr B bad(true); // expected-error {{must be initialized by a constant expression}} expected-note {{in call to 'B(true)'}}
1218
1219   struct C {
1220     int n;
1221     constexpr C() : n(1) { n = 2; }
1222   };
1223   constexpr int f(bool get) {
1224     volatile C c; // expected-note {{here}}
1225     return get ? const_cast<int&>(c.n) : 0; // expected-note {{read of volatile object 'c'}}
1226   }
1227   static_assert(f(false) == 0, ""); // ok, can modify volatile c.n during c's initialization: it's not volatile then
1228   static_assert(f(true) == 2, ""); // expected-error {{constant}} expected-note {{in call}}
1229
1230   struct Aggregate {
1231     int x = 0;
1232     int y = ++x;
1233   };
1234   constexpr Aggregate aggr1;
1235   static_assert(aggr1.x == 1 && aggr1.y == 1, "");
1236   // FIXME: This is not specified by the standard, but sanity requires it.
1237   constexpr Aggregate aggr2 = {};
1238   static_assert(aggr2.x == 1 && aggr2.y == 1, "");
1239
1240   // The lifetime of 'n' begins at the initialization, not before.
1241   constexpr int n = ++const_cast<int&>(n); // expected-error {{constant expression}} expected-note {{increment of object outside its lifetime}}
1242 }
1243
1244 namespace PR39728 {
1245   struct Comment0 {
1246     Comment0 &operator=(const Comment0 &) = default;
1247     ~Comment0() = default;
1248   };
1249   constexpr void f() {
1250     Comment0 a;
1251     a = a;
1252   }
1253   static_assert((f(), true), "");
1254   struct Comment1 {
1255     constexpr Comment1 &operator=(const Comment1 &) = default; // OK
1256     ~Comment1() = default;
1257   };
1258 }
1259
1260 namespace TemporaryWithBadPointer {
1261   constexpr int *get_bad_pointer() {
1262     int n = 0; // expected-note 2{{here}}
1263     return &n; // expected-warning {{stack}}
1264   }
1265   constexpr int *bad_pointer = get_bad_pointer(); // expected-error {{constant expression}} expected-note {{pointer to 'n' is not a constant expression}}
1266
1267   struct DoBadThings { int *&&wp; int n; };
1268   constexpr DoBadThings dbt = { // expected-error {{constant expression}}
1269     nullptr, // expected-note {{pointer to 'n' is not a constant expression}}
1270     (dbt.wp = get_bad_pointer(), 0)
1271   };
1272
1273   constexpr DoBadThings dbt2 = { // ok
1274     get_bad_pointer(),
1275     (dbt2.wp = nullptr, 0)
1276   };
1277 }
1278
1279 namespace UninitCompoundAssign {
1280 constexpr int scalar(int a) {
1281   int sum; // cxx14-warning {{uninitialized variable in a constexpr function is a C++20 extension}}
1282   sum += a; // expected-note {{read of uninitialized object}};
1283   return 0;
1284 }
1285 static_assert(scalar(3), ""); // expected-error {{constant expression}} \
1286                               // expected-note {{in call to 'scalar(3)'}}
1287
1288 constexpr int array(int a) {
1289   int arr[3]; // cxx14-warning {{uninitialized variable in a constexpr function is a C++20 extension}}
1290   arr[1] += a; // expected-note {{read of uninitialized object}};
1291   return 0;
1292 }
1293 static_assert(array(3), ""); // expected-error {{constant expression}} \
1294                              // expected-note {{in call to 'array(3)'}}
1295
1296 struct Foo {
1297   int val; // cxx14-note{{member not initialized by constructor}}
1298   constexpr Foo() {} // cxx14-warning {{constexpr constructor that does not initialize all members is a C++20 extension}}
1299 };
1300 constexpr int field(int a) {
1301   Foo f;
1302   f.val += a; // expected-note {{read of uninitialized object}};
1303   return 0;
1304 }
1305 static_assert(field(3), ""); // expected-error {{constant expression}} \
1306                              // expected-note {{in call to 'field(3)'}}
1307 }