constant-expression-cxx1y.cpp revision 692eafd2052fb6ca581530d6f3569eea9520a508 
1// RUN: %clang_cc1 -std=c++1y -verify %s -fcxx-exceptions -triple=x86_64-linux-gnu
2
3struct S {
4  // dummy ctor to make this a literal type
5  constexpr S(int);
6
7  S();
8
9  int arr[10];
10
11  constexpr int &get(int n) { return arr[n]; }
12  constexpr const int &get(int n) const { return arr[n]; }
13};
14
15S s = S();
16const S &sr = s;
17static_assert(&s.get(4) - &sr.get(2) == 2, "");
18
19// Compound-statements can be used in constexpr functions.
20constexpr int e() {{{{}} return 5; }}
21static_assert(e() == 5, "");
22
23// Types can be defined in constexpr functions.
24constexpr int f() {
25  enum E { e1, e2, e3 };
26
27  struct S {
28    constexpr S(E e) : e(e) {}
29    constexpr int get() { return e; }
30    E e;
31  };
32
33  return S(e2).get();
34}
35static_assert(f() == 1, "");
36
37// Variables can be declared in constexpr functions.
38constexpr int g(int k) {
39  const int n = 9;
40  int k2 = k * k;
41  int k3 = k2 * k;
42  return 3 * k3 + 5 * k2 + n * k - 20;
43}
44static_assert(g(2) == 42, "");
45constexpr int h(int n) {
46  static const int m = n; // expected-error {{static variable not permitted in a constexpr function}}
47  return m;
48}
49constexpr int i(int n) {
50  thread_local const int m = n; // expected-error {{thread_local variable not permitted in a constexpr function}}
51  return m;
52}
53
54// if-statements can be used in constexpr functions.
55constexpr int j(int k) {
56  if (k == 5)
57    return 1;
58  if (k == 1)
59    return 5;
60  else {
61    if (int n = 2 * k - 4) {
62      return n + 1;
63      return 2;
64    }
65  }
66} // expected-note 2{{control reached end of constexpr function}}
67static_assert(j(0) == -3, "");
68static_assert(j(1) == 5, "");
69static_assert(j(2), ""); // expected-error {{constant expression}} expected-note {{in call to 'j(2)'}}
70static_assert(j(3) == 3, "");
71static_assert(j(4) == 5, "");
72static_assert(j(5) == 1, "");
73
74// There can be 0 return-statements.
75constexpr void k() {
76}
77
78// If the return type is not 'void', no return statements => never a constant
79// expression, so still diagnose that case.
80[[noreturn]] constexpr int fn() { // expected-error {{no return statement in constexpr function}}
81  fn();
82}
83
84// We evaluate the body of a constexpr constructor, to check for side-effects.
85struct U {
86  constexpr U(int n) {
87    if (j(n)) {} // expected-note {{in call to 'j(2)'}}
88  }
89};
90constexpr U u1{1};
91constexpr U u2{2}; // expected-error {{constant expression}} expected-note {{in call to 'U(2)'}}
92
93// We allow expression-statements.
94constexpr int l(bool b) {
95  if (b)
96    throw "invalid value for b!"; // expected-note {{subexpression not valid}}
97  return 5;
98}
99static_assert(l(false) == 5, "");
100static_assert(l(true), ""); // expected-error {{constant expression}} expected-note {{in call to 'l(true)'}}
101
102// Potential constant expression checking is still applied where possible.
103constexpr int htonl(int x) { // expected-error {{never produces a constant expression}}
104  typedef unsigned char uchar;
105  uchar arr[4] = { uchar(x >> 24), uchar(x >> 16), uchar(x >> 8), uchar(x) };
106  return *reinterpret_cast<int*>(arr); // expected-note {{reinterpret_cast is not allowed in a constant expression}}
107}
108
109constexpr int maybe_htonl(bool isBigEndian, int x) {
110  if (isBigEndian)
111    return x;
112
113  typedef unsigned char uchar;
114  uchar arr[4] = { uchar(x >> 24), uchar(x >> 16), uchar(x >> 8), uchar(x) };
115  return *reinterpret_cast<int*>(arr); // expected-note {{reinterpret_cast is not allowed in a constant expression}}
116}
117
118constexpr int swapped = maybe_htonl(false, 123); // expected-error {{constant expression}} expected-note {{in call}}
119
120namespace NS {
121  constexpr int n = 0;
122}
123constexpr int namespace_alias() {
124  namespace N = NS;
125  return N::n;
126}
127
128namespace assign {
129  constexpr int a = 0;
130  const int b = 0;
131  int c = 0; // expected-note 2{{here}}
132
133  constexpr void set(const int &a, int b) {
134    const_cast<int&>(a) = b; // expected-note 2{{constant expression cannot modify an object that is visible outside that expression}}
135  }
136  constexpr int wrap(int a, int b) {
137    set(a, b);
138    return a;
139  }
140
141  static_assert((set(a, 1), a) == 1, ""); // expected-error {{constant expression}} expected-note {{in call to 'set(a, 1)'}}
142  static_assert((set(b, 1), b) == 1, ""); // expected-error {{constant expression}} expected-note {{in call to 'set(b, 1)'}}
143  static_assert((set(c, 1), c) == 1, ""); // expected-error {{constant expression}} expected-note {{read of non-const variable 'c'}}
144
145  static_assert(wrap(a, 1) == 1, "");
146  static_assert(wrap(b, 1) == 1, "");
147  static_assert(wrap(c, 1) == 1, ""); // expected-error {{constant expression}} expected-note {{read of non-const variable 'c'}}
148}
149
150namespace string_assign {
151  template<typename T>
152  constexpr void swap(T &a, T &b) {
153    T tmp = a;
154    a = b;
155    b = tmp;
156  }
157  template<typename Iterator>
158  constexpr void reverse(Iterator begin, Iterator end) {
159    while (begin != end && begin != --end)
160      swap(*begin++, *end);
161  }
162  template<typename Iterator1, typename Iterator2>
163  constexpr bool equal(Iterator1 a, Iterator1 ae, Iterator2 b, Iterator2 be) {
164    while (a != ae && b != be)
165      if (*a++ != *b++)
166        return false;
167    return a == ae && b == be;
168  }
169  constexpr bool test1(int n) {
170    char stuff[100] = "foobarfoo";
171    const char stuff2[100] = "oofraboof";
172    reverse(stuff, stuff + n); // expected-note {{cannot refer to element 101 of array of 100 elements}}
173    return equal(stuff, stuff + n, stuff2, stuff2 + n);
174  }
175  static_assert(!test1(1), "");
176  static_assert(test1(3), "");
177  static_assert(!test1(6), "");
178  static_assert(test1(9), "");
179  static_assert(!test1(100), "");
180  static_assert(!test1(101), ""); // expected-error {{constant expression}} expected-note {{in call to 'test1(101)'}}
181
182  // FIXME: We should be able to reject this before it's called
183  constexpr void f() {
184    char foo[10] = { "z" }; // expected-note {{here}}
185    foo[10] = 'x'; // expected-warning {{past the end}} expected-note {{assignment to dereferenced one-past-the-end pointer}}
186  }
187  constexpr int k = (f(), 0); // expected-error {{constant expression}} expected-note {{in call}}
188}
189
190namespace array_resize {
191  constexpr int do_stuff(int k1, int k2) {
192    int arr[1234] = { 1, 2, 3, 4 };
193    arr[k1] = 5; // expected-note {{past-the-end}} expected-note {{cannot refer to element 1235}} expected-note {{cannot refer to element -1}}
194    return arr[k2];
195  }
196  static_assert(do_stuff(1, 2) == 3, "");
197  static_assert(do_stuff(0, 0) == 5, "");
198  static_assert(do_stuff(1233, 1233) == 5, "");
199  static_assert(do_stuff(1233, 0) == 1, "");
200  static_assert(do_stuff(1234, 0) == 1, ""); // expected-error {{constant expression}} expected-note {{in call}}
201  static_assert(do_stuff(1235, 0) == 1, ""); // expected-error {{constant expression}} expected-note {{in call}}
202  static_assert(do_stuff(-1, 0) == 1, ""); // expected-error {{constant expression}} expected-note {{in call}}
203}
204
205namespace potential_const_expr {
206  constexpr void set(int &n) { n = 1; }
207  constexpr int div_zero_1() { int z = 0; set(z); return 100 / z; } // no error
208  constexpr int div_zero_2() { // expected-error {{never produces a constant expression}}
209    int z = 0;
210    return 100 / (set(z), 0); // expected-note {{division by zero}}
211  }
212  int n; // expected-note {{declared here}}
213  constexpr int ref() { // expected-error {{never produces a constant expression}}
214    int &r = n;
215    return r; // expected-note {{read of non-const variable 'n'}}
216  }
217}
218
219namespace subobject {
220  union A { constexpr A() : y(5) {} int x, y; };
221  struct B { A a; };
222  struct C : B {};
223  union D { constexpr D() : c() {} constexpr D(int n) : n(n) {} C c; int n; };
224  constexpr void f(D &d) {
225    d.c.a.y = 3;
226    // expected-note@-1 {{cannot modify an object that is visible outside}}
227    // expected-note@-2 {{assignment to member 'c' of union with active member 'n'}}
228  }
229  constexpr bool check(D &d) { return d.c.a.y == 3; }
230
231  constexpr bool g() { D d; f(d); return d.c.a.y == 3; }
232  static_assert(g(), "");
233
234  D d;
235  constexpr bool h() { f(d); return check(d); } // expected-note {{in call}}
236  static_assert(h(), ""); // expected-error {{constant expression}} expected-note {{in call}}
237
238  constexpr bool i() { D d(0); f(d); return check(d); } // expected-note {{in call}}
239  static_assert(i(), ""); // expected-error {{constant expression}} expected-note {{in call}}
240
241  constexpr bool j() { D d; d.c.a.x = 3; return check(d); } // expected-note {{assignment to member 'x' of union with active member 'y'}}
242  static_assert(j(), ""); // expected-error {{constant expression}} expected-note {{in call}}
243}
244
245namespace lifetime {
246  constexpr int &&id(int &&n) { return static_cast<int&&>(n); }
247  constexpr int &&dead() { return id(0); } // expected-note {{temporary created here}}
248  constexpr int bad() { int &&n = dead(); n = 1; return n; } // expected-note {{assignment to temporary whose lifetime has ended}}
249  static_assert(bad(), ""); // expected-error {{constant expression}} expected-note {{in call}}
250}
251
252namespace const_modify {
253  constexpr int modify(int &n) { return n = 1; } // expected-note {{modification of object of const-qualified type 'const int'}}
254  constexpr int test1() { int k = 0; return modify(k); }
255  constexpr int test2() { const int k = 0; return modify(const_cast<int&>(k)); } // expected-note {{in call}}
256  static_assert(test1() == 1, "");
257  static_assert(test2() == 1, ""); // expected-error {{constant expression}} expected-note {{in call}}
258}
259
260namespace null {
261  constexpr int test(int *p) {
262    return *p = 123; // expected-note {{assignment to dereferenced null pointer}}
263  }
264  static_assert(test(0), ""); // expected-error {{constant expression}} expected-note {{in call}}
265}
266
267namespace incdec {
268  template<typename T> constexpr T &ref(T &&r) { return r; }
269  template<typename T> constexpr T postinc(T &&r) { return (r++, r); }
270  template<typename T> constexpr T postdec(T &&r) { return (r--, r); }
271
272  static_assert(++ref(0) == 1, "");
273  static_assert(ref(0)++ == 0, "");
274  static_assert(postinc(0) == 1, "");
275  static_assert(--ref(0) == -1, "");
276  static_assert(ref(0)-- == 0, "");
277  static_assert(postdec(0) == -1, "");
278
279  constexpr int overflow_int_inc_1 = ref(0x7fffffff)++; // expected-error {{constant}} expected-note {{2147483648}}
280  constexpr int overflow_int_inc_1_ok = ref(0x7ffffffe)++;
281  constexpr int overflow_int_inc_2 = ++ref(0x7fffffff); // expected-error {{constant}} expected-note {{2147483648}}
282  constexpr int overflow_int_inc_2_ok = ++ref(0x7ffffffe);
283
284  // inc/dec on short can't overflow because we promote to int first
285  static_assert(++ref<short>(0x7fff) == (int)0xffff8000u, "");
286  static_assert(--ref<short>(0x8000) == 0x7fff, "");
287
288  // inc on bool sets to true
289  static_assert(++ref(false), ""); // expected-warning {{deprecated}}
290  static_assert(++ref(true), ""); // expected-warning {{deprecated}}
291
292  int arr[10];
293  static_assert(++ref(&arr[0]) == &arr[1], "");
294  static_assert(++ref(&arr[9]) == &arr[10], "");
295  static_assert(++ref(&arr[10]) == &arr[11], ""); // expected-error {{constant}} expected-note {{cannot refer to element 11}}
296  static_assert(ref(&arr[0])++ == &arr[0], "");
297  static_assert(ref(&arr[10])++ == &arr[10], ""); // expected-error {{constant}} expected-note {{cannot refer to element 11}}
298  static_assert(postinc(&arr[0]) == &arr[1], "");
299  static_assert(--ref(&arr[10]) == &arr[9], "");
300  static_assert(--ref(&arr[1]) == &arr[0], "");
301  static_assert(--ref(&arr[0]) != &arr[0], ""); // expected-error {{constant}} expected-note {{cannot refer to element -1}}
302  static_assert(ref(&arr[1])-- == &arr[1], "");
303  static_assert(ref(&arr[0])-- == &arr[0], ""); // expected-error {{constant}} expected-note {{cannot refer to element -1}}
304  static_assert(postdec(&arr[1]) == &arr[0], "");
305
306  int x;
307  static_assert(++ref(&x) == &x + 1, "");
308
309  static_assert(++ref(0.0) == 1.0, "");
310  static_assert(ref(0.0)++ == 0.0, "");
311  static_assert(postinc(0.0) == 1.0, "");
312  static_assert(--ref(0.0) == -1.0, "");
313  static_assert(ref(0.0)-- == 0.0, "");
314  static_assert(postdec(0.0) == -1.0, "");
315
316  static_assert(++ref(1e100) == 1e100, "");
317  static_assert(--ref(1e100) == 1e100, "");
318
319  union U {
320    int a, b;
321  };
322  constexpr int f(U u) {
323    return ++u.b; // expected-note {{increment of member 'b' of union with active member 'a'}}
324  }
325  constexpr int wrong_member = f({0}); // expected-error {{constant}} expected-note {{in call to 'f({.a = 0})'}}
326  constexpr int vol = --ref<volatile int>(0); // expected-error {{constant}} expected-note {{decrement of volatile-qualified}}
327
328  constexpr int incr(int k) {
329    int x = k;
330    if (x++ == 100)
331      return x;
332    return incr(x);
333  }
334  static_assert(incr(0) == 101, "");
335}
336
337namespace loops {
338  constexpr int fib_loop(int a) {
339    int f_k = 0, f_k_plus_one = 1;
340    for (int k = 1; k != a; ++k) {
341      int f_k_plus_two = f_k + f_k_plus_one;
342      f_k = f_k_plus_one;
343      f_k_plus_one = f_k_plus_two;
344    }
345    return f_k_plus_one;
346  }
347  static_assert(fib_loop(46) == 1836311903, "");
348
349  constexpr bool breaks_work() {
350    int a = 0;
351    for (int n = 0; n != 100; ++n) {
352      ++a;
353      if (a == 5) continue;
354      if ((a % 5) == 0) break;
355    }
356
357    int b = 0;
358    while (b != 17) {
359      ++b;
360      if (b == 6) continue;
361      if ((b % 6) == 0) break;
362    }
363
364    int c = 0;
365    do {
366      ++c;
367      if (c == 7) continue;
368      if ((c % 7) == 0) break;
369    } while (c != 21);
370
371    return a == 10 && b == 12 & c == 14;
372  }
373  static_assert(breaks_work(), "");
374
375  void not_constexpr();
376  constexpr bool no_cont_after_break() {
377    for (;;) {
378      break;
379      not_constexpr();
380    }
381    while (true) {
382      break;
383      not_constexpr();
384    }
385    do {
386      break;
387      not_constexpr();
388    } while (true);
389    return true;
390  }
391  static_assert(no_cont_after_break(), "");
392
393  constexpr bool cond() {
394    for (int a = 1; bool b = a != 3; ++a) {
395      if (!b)
396        return false;
397    }
398    while (bool b = true) {
399      b = false;
400      break;
401    }
402    return true;
403  }
404  static_assert(cond(), "");
405
406  constexpr int range_for() {
407    int arr[] = { 1, 2, 3, 4, 5 };
408    int sum = 0;
409    for (int x : arr)
410      sum = sum + x;
411    return sum;
412  }
413  static_assert(range_for() == 15, "");
414
415  template<int...N> struct ints {};
416  template<typename A, typename B> struct join_ints;
417  template<int...As, int...Bs> struct join_ints<ints<As...>, ints<Bs...>> {
418    using type = ints<As..., sizeof...(As) + Bs...>;
419  };
420  template<unsigned N> struct make_ints {
421    using type = typename join_ints<typename make_ints<N/2>::type, typename make_ints<(N+1)/2>::type>::type;
422  };
423  template<> struct make_ints<0> { using type = ints<>; };
424  template<> struct make_ints<1> { using type = ints<0>; };
425
426  struct ignore { template<typename ...Ts> constexpr ignore(Ts &&...) {} };
427
428  template<typename T, unsigned N> struct array {
429    constexpr array() : arr{} {}
430    template<typename ...X>
431    constexpr array(X ...x) : arr{} {
432      init(typename make_ints<sizeof...(X)>::type{}, x...);
433    }
434    template<int ...I, typename ...X> constexpr void init(ints<I...>, X ...x) {
435      ignore{arr[I] = x ...};
436    }
437    T arr[N];
438    struct iterator {
439      T *p;
440      constexpr explicit iterator(T *p) : p(p) {}
441      constexpr bool operator!=(iterator o) { return p != o.p; }
442      constexpr iterator &operator++() { ++p; return *this; }
443      constexpr T &operator*() { return *p; }
444    };
445    constexpr iterator begin() { return iterator(arr); }
446    constexpr iterator end() { return iterator(arr + N); }
447  };
448
449  constexpr int range_for_2() {
450    array<int, 5> arr { 1, 2, 3, 4, 5 };
451    int sum = 0;
452    for (int k : arr) {
453      sum = sum + k;
454      if (sum > 8) break;
455    }
456    return sum;
457  }
458  static_assert(range_for_2() == 10, "");
459}
460