constant-expression-cxx1y.cpp revision bebf5b1bcfbf591dd3cd80c4aebd6486bb34f41c 
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#if 0 // FIXME: once implementation is complete...
160    while (begin != end && begin != --end)
161      swap(*begin++, *end);
162#else
163    if (begin != end) {
164      end = end - 1;
165      if (begin == end)
166        return;
167      swap(*begin, *end);
168      begin = begin + 1;
169      reverse(begin, end);
170    }
171#endif
172  }
173  template<typename Iterator1, typename Iterator2>
174  constexpr bool equal(Iterator1 a, Iterator1 ae, Iterator2 b, Iterator2 be) {
175#if 0 // FIXME: once implementation is complete...
176    while (a != ae && b != be) {
177      if (*a != *b)
178        return false;
179      ++a, ++b;
180    }
181#else
182    if (a != ae && b != be) {
183      if (*a != *b)
184        return false;
185      a = a + 1;
186      b = b + 1;
187      return equal(a, ae, b, be);
188    }
189#endif
190    return a == ae && b == be;
191  }
192  constexpr bool test1(int n) {
193    char stuff[100] = "foobarfoo";
194    const char stuff2[100] = "oofraboof";
195    reverse(stuff, stuff + n); // expected-note {{cannot refer to element 101 of array of 100 elements}}
196    return equal(stuff, stuff + n, stuff2, stuff2 + n);
197  }
198  static_assert(!test1(1), "");
199  static_assert(test1(3), "");
200  static_assert(!test1(6), "");
201  static_assert(test1(9), "");
202  static_assert(!test1(100), "");
203  static_assert(!test1(101), ""); // expected-error {{constant expression}} expected-note {{in call to 'test1(101)'}}
204
205  // FIXME: We should be able to reject this before it's called
206  constexpr void f() {
207    char foo[10] = { "z" }; // expected-note {{here}}
208    foo[10] = 'x'; // expected-warning {{past the end}} expected-note {{assignment to dereferenced one-past-the-end pointer}}
209  }
210  constexpr int k = (f(), 0); // expected-error {{constant expression}} expected-note {{in call}}
211}
212
213namespace array_resize {
214  constexpr int do_stuff(int k1, int k2) {
215    int arr[1234] = { 1, 2, 3, 4 };
216    arr[k1] = 5; // expected-note {{past-the-end}} expected-note {{cannot refer to element 1235}} expected-note {{cannot refer to element -1}}
217    return arr[k2];
218  }
219  static_assert(do_stuff(1, 2) == 3, "");
220  static_assert(do_stuff(0, 0) == 5, "");
221  static_assert(do_stuff(1233, 1233) == 5, "");
222  static_assert(do_stuff(1233, 0) == 1, "");
223  static_assert(do_stuff(1234, 0) == 1, ""); // expected-error {{constant expression}} expected-note {{in call}}
224  static_assert(do_stuff(1235, 0) == 1, ""); // expected-error {{constant expression}} expected-note {{in call}}
225  static_assert(do_stuff(-1, 0) == 1, ""); // expected-error {{constant expression}} expected-note {{in call}}
226}
227
228namespace potential_const_expr {
229  constexpr void set(int &n) { n = 1; }
230  constexpr int div_zero_1() { int z = 0; set(z); return 100 / z; } // no error
231  constexpr int div_zero_2() { // expected-error {{never produces a constant expression}}
232    int z = 0;
233    return 100 / (set(z), 0); // expected-note {{division by zero}}
234  }
235}
236
237namespace subobject {
238  union A { constexpr A() : y(5) {} int x, y; };
239  struct B { A a; };
240  struct C : B {};
241  union D { constexpr D() : c() {} constexpr D(int n) : n(n) {} C c; int n; };
242  constexpr void f(D &d) {
243    d.c.a.y = 3;
244    // expected-note@-1 {{cannot modify an object that is visible outside}}
245    // expected-note@-2 {{assignment to member 'c' of union with active member 'n'}}
246  }
247  constexpr bool check(D &d) { return d.c.a.y == 3; }
248
249  constexpr bool g() { D d; f(d); return d.c.a.y == 3; }
250  static_assert(g(), "");
251
252  D d;
253  constexpr bool h() { f(d); return check(d); } // expected-note {{in call}}
254  static_assert(h(), ""); // expected-error {{constant expression}} expected-note {{in call}}
255
256  constexpr bool i() { D d(0); f(d); return check(d); } // expected-note {{in call}}
257  static_assert(i(), ""); // expected-error {{constant expression}} expected-note {{in call}}
258
259  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'}}
260  static_assert(j(), ""); // expected-error {{constant expression}} expected-note {{in call}}
261}
262
263namespace lifetime {
264  constexpr int &&id(int &&n) { return static_cast<int&&>(n); }
265  constexpr int &&dead() { return id(0); } // expected-note {{temporary created here}}
266  constexpr int bad() { int &&n = dead(); n = 1; return n; } // expected-note {{assignment to temporary whose lifetime has ended}}
267  static_assert(bad(), ""); // expected-error {{constant expression}} expected-note {{in call}}
268}
269
270namespace const_modify {
271  constexpr int modify(int &n) { return n = 1; } // expected-note {{modification of object of const-qualified type 'const int'}}
272  constexpr int test1() { int k = 0; return modify(k); }
273  constexpr int test2() { const int k = 0; return modify(const_cast<int&>(k)); } // expected-note {{in call}}
274  static_assert(test1() == 1, "");
275  static_assert(test2() == 1, ""); // expected-error {{constant expression}} expected-note {{in call}}
276}
277
278namespace null {
279  constexpr int test(int *p) {
280    return *p = 123; // expected-note {{assignment to dereferenced null pointer}}
281  }
282  static_assert(test(0), ""); // expected-error {{constant expression}} expected-note {{in call}}
283}
284