// RUN: %clang_cc1 -std=c++23 -fsyntax-only -verify=expected,cxx20_23,cxx23 %s -fcxx-exceptions -triple=x86_64-linux-gnu
// RUN: %clang_cc1 -std=c++20 -fsyntax-only -verify=expected,cxx14_20,cxx20_23,cxx20 %s -fcxx-exceptions -triple=x86_64-linux-gnu
// RUN: %clang_cc1 -std=c++14 -fsyntax-only -verify=expected,cxx14_20,cxx14 %s -fcxx-exceptions -triple=x86_64-linux-gnu
struct S {
// dummy ctor to make this a literal type
constexpr S(int);
S();
int arr[10];
constexpr int &get(int n) { return arr[n]; }
constexpr const int &get(int n) const { return arr[n]; }
};
S s = S();
const S &sr = s;
static_assert(&s.get(4) - &sr.get(2) == 2, "");
// Compound-statements can be used in constexpr functions.
constexpr int e() {{{{}} return 5; }}
static_assert(e() == 5, "");
// Types can be defined in constexpr functions.
constexpr int f() {
enum E { e1, e2, e3 };
struct S {
constexpr S(E e) : e(e) {}
constexpr int get() { return e; }
E e;
};
return S(e2).get();
}
static_assert(f() == 1, "");
// Variables can be declared in constexpr functions.
constexpr int g(int k) {
const int n = 9;
int k2 = k * k;
int k3 = k2 * k;
return 3 * k3 + 5 * k2 + n * k - 20;
}
static_assert(g(2) == 42, "");
constexpr int h(int n) { // cxx14_20-error {{constexpr function never produces a constant expression}}
static const int m = n; // cxx14_20-note {{control flows through the definition of a static variable}} \
// cxx14_20-warning {{definition of a static variable in a constexpr function is a C++23 extension}}
return m;
}
constexpr int i(int n) { // cxx14_20-error {{constexpr function never produces a constant expression}}
thread_local const int m = n; // cxx14_20-note {{control flows through the definition of a thread_local variable}} \
// cxx14_20-warning {{definition of a thread_local variable in a constexpr function is a C++23 extension}}
return m;
}
// if-statements can be used in constexpr functions.
constexpr int j(int k) {
if (k == 5)
return 1;
if (k == 1)
return 5;
else {
if (int n = 2 * k - 4) {
return n + 1;
return 2;
}
}
} // expected-note 2{{control reached end of constexpr function}}
// cxx23-warning@-1 {{does not return a value in all control paths}}
static_assert(j(0) == -3, "");
static_assert(j(1) == 5, "");
static_assert(j(2), ""); // expected-error {{constant expression}} expected-note {{in call to 'j(2)'}}
static_assert(j(3) == 3, "");
static_assert(j(4) == 5, "");
static_assert(j(5) == 1, "");
// There can be 0 return-statements.
constexpr void k() {
}
// If the return type is not 'void', no return statements => never a constant
// expression, so still diagnose that case.
[[noreturn]] constexpr int fn() { // cxx14_20-error {{no return statement in constexpr function}}
fn();
}
// We evaluate the body of a constexpr constructor, to check for side-effects.
struct U {
constexpr U(int n) {
if (j(n)) {} // expected-note {{in call to 'j(2)'}}
}
};
constexpr U u1{1};
constexpr U u2{2}; // expected-error {{constant expression}} expected-note {{in call to 'U(2)'}}
// We allow expression-statements.
constexpr int l(bool b) {
if (b)
throw "invalid value for b!"; // expected-note {{subexpression not valid}}
return 5;
}
static_assert(l(false) == 5, "");
static_assert(l(true), ""); // expected-error {{constant expression}} expected-note {{in call to 'l(true)'}}
// Potential constant expression checking is still applied where possible.
constexpr int htonl(int x) { // cxx14_20-error {{never produces a constant expression}}
typedef unsigned char uchar;
uchar arr[4] = { uchar(x >> 24), uchar(x >> 16), uchar(x >> 8), uchar(x) };
return *reinterpret_cast<int*>(arr); // cxx14_20-note {{reinterpret_cast is not allowed in a constant expression}}
}
constexpr int maybe_htonl(bool isBigEndian, int x) {
if (isBigEndian)
return x;
typedef unsigned char uchar;
uchar arr[4] = { uchar(x >> 24), uchar(x >> 16), uchar(x >> 8), uchar(x) };
return *reinterpret_cast<int*>(arr); // expected-note {{reinterpret_cast is not allowed in a constant expression}}
}
constexpr int swapped = maybe_htonl(false, 123); // expected-error {{constant expression}} expected-note {{in call}}
namespace NS {
constexpr int n = 0;
}
constexpr int namespace_alias() {
namespace N = NS;
return N::n;
}
namespace assign {
constexpr int a = 0;
const int b = 0;
int c = 0; // expected-note {{here}}
constexpr void set(const int &a, int b) {
const_cast<int&>(a) = b; // expected-note 3{{constant expression cannot modify an object that is visible outside that expression}}
}
constexpr int wrap(int a, int b) {
set(a, b);
return a;
}
static_assert((set(a, 1), a) == 1, ""); // expected-error {{constant expression}} expected-note {{in call to 'set(a, 1)'}}
static_assert((set(b, 1), b) == 1, ""); // expected-error {{constant expression}} expected-note {{in call to 'set(b, 1)'}}
static_assert((set(c, 1), c) == 1, ""); // expected-error {{constant expression}} expected-note {{in call to 'set(c, 1)'}}
static_assert(wrap(a, 1) == 1, "");
static_assert(wrap(b, 1) == 1, "");
static_assert(wrap(c, 1) == 1, ""); // expected-error {{constant expression}} expected-note {{read of non-const variable 'c'}}
}
namespace string_assign {
template<typename T>
constexpr void swap(T &a, T &b) {
T tmp = a;
a = b;
b = tmp;
}
template<typename Iterator>
constexpr void reverse(Iterator begin, Iterator end) {
while (begin != end && begin != --end)
swap(*begin++, *end);
}
template<typename Iterator1, typename Iterator2>
constexpr bool equal(Iterator1 a, Iterator1 ae, Iterator2 b, Iterator2 be) {
while (a != ae && b != be)
if (*a++ != *b++)
return false;
return a == ae && b == be;
}
constexpr bool test1(int n) {
char stuff[100] = "foobarfoo";
const char stuff2[100] = "oofraboof";
reverse(stuff, stuff + n); // expected-note {{cannot refer to element 101 of array of 100 elements}}
return equal(stuff, stuff + n, stuff2, stuff2 + n);
}
static_assert(!test1(1), "");
static_assert(test1(3), "");
static_assert(!test1(6), "");
static_assert(test1(9), "");
static_assert(!test1(100), "");
static_assert(!test1(101), ""); // expected-error {{constant expression}} expected-note {{in call to 'test1(101)'}}
constexpr void f() { // cxx14_20-error{{constexpr function never produces a constant expression}} cxx14_20-note@+2{{assignment to dereferenced one-past-the-end pointer is not allowed in a constant expression}}
char foo[10] = { "z" }; // expected-note {{here}}
foo[10] = 'x'; // expected-warning {{past the end}}
}
}
namespace array_resize {
constexpr int do_stuff(int k1, int k2) {
int arr[1234] = { 1, 2, 3, 4 };
arr[k1] = 5; // expected-note {{past-the-end}} expected-note {{cannot refer to element 1235}} expected-note {{cannot refer to element -1}}
return arr[k2];
}
static_assert(do_stuff(1, 2) == 3, "");
static_assert(do_stuff(0, 0) == 5, "");
static_assert(do_stuff(1233, 1233) == 5, "");
static_assert(do_stuff(1233, 0) == 1, "");
static_assert(do_stuff(1234, 0) == 1, ""); // expected-error {{constant expression}} expected-note {{in call}}
static_assert(do_stuff(1235, 0) == 1, ""); // expected-error {{constant expression}} expected-note {{in call}}
static_assert(do_stuff(-1, 0) == 1, ""); // expected-error {{constant expression}} expected-note {{in call}}
}
namespace potential_const_expr {
constexpr void set(int &n) { n = 1; }
constexpr int div_zero_1() { int z = 0; set(z); return 100 / z; } // no error
constexpr int div_zero_2() { // cxx14_20-error {{never produces a constant expression}}
int z = 0;
return 100 / (set(z), 0); // cxx14_20-note {{division by zero}}
}
int n; // cxx14_20-note {{declared here}}
constexpr int ref() { // cxx14_20-error {{never produces a constant expression}}
int &r = n;
return r; // cxx14_20-note {{read of non-const variable 'n'}}
}
}
namespace subobject {
union A { constexpr A() : y(5) {} int x, y; };
struct B { A a; };
struct C : B {};
union D { constexpr D() : c() {} constexpr D(int n) : n(n) {} C c; int n; };
constexpr void f(D &d) {
d.c.a.y = 3;
// expected-note@-1 {{cannot modify an object that is visible outside}}
// expected-note@-2 {{assignment to member 'c' of union with active member 'n'}}
}
constexpr bool check(D &d) { return d.c.a.y == 3; }
// cxx20_23-note@-1 {{read of member 'y' of union with active member 'x'}}
constexpr bool g() { D d; f(d); return d.c.a.y == 3; }
static_assert(g(), "");
D d;
constexpr bool h() { f(d); return check(d); } // expected-note {{in call}}
static_assert(h(), ""); // expected-error {{constant expression}} expected-note {{in call}}
constexpr bool i() { D d(0); f(d); return check(d); } // expected-note {{in call}}
static_assert(i(), ""); // expected-error {{constant expression}} expected-note {{in call}}
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'}}
// cxx20_23-note@-1 {{in call to 'check(d)'}}
static_assert(j(), ""); // expected-error {{constant expression}} expected-note {{in call}}
}
namespace lifetime {
constexpr int &&id(int &&n) { return static_cast<int&&>(n); }
constexpr int &&dead() { return id(0); } // expected-note {{temporary created here}}
constexpr int bad() { int &&n = dead(); n = 1; return n; } // expected-note {{assignment to temporary whose lifetime has ended}}
static_assert(bad(), ""); // expected-error {{constant expression}} expected-note {{in call}}
}
namespace const_modify {
constexpr int modify(int &n) { return n = 1; } // expected-note 2 {{modification of object of const-qualified type 'const int'}}
constexpr int test1() { int k = 0; return modify(k); }
constexpr int test2() { const int k = 0; return modify(const_cast<int&>(k)); } // expected-note 2 {{in call}}
static_assert(test1() == 1, "");
static_assert(test2() == 1, ""); // expected-error {{constant expression}} expected-note {{in call}}
constexpr int i = test2(); // expected-error {{constant expression}} expected-note {{in call}}
}
namespace null {
constexpr int test(int *p) {
return *p = 123; // expected-note {{assignment to dereferenced null pointer}}
}
static_assert(test(0), ""); // expected-error {{constant expression}} expected-note {{in call}}
}
namespace incdec {
template<typename T> constexpr T &ref(T &&r) { return r; }
// cxx23-error@-1 {{non-const lvalue reference to type 'int' cannot bind to a temporary of type 'int'}}
template<typename T> constexpr T postinc(T &&r) { return (r++, r); }
template<typename T> constexpr T postdec(T &&r) { return (r--, r); }
template int &ref<int>(int &&);
// cxx23-note@-1 {{in instantiation of function template specialization}}
static_assert(postinc(0) == 1, "");
static_assert(postdec(0) == -1, "");
#if __cplusplus <= 202002L
static_assert(++ref(0) == 1, "");
static_assert(ref(0)++ == 0, "");
static_assert(--ref(0) == -1, "");
static_assert(ref(0)-- == 0, "");
#endif
#if __cplusplus <= 202002L
constexpr int overflow_int_inc_1 = ref(0x7fffffff)++; // expected-error {{constant}} expected-note {{2147483648}}
constexpr int overflow_int_inc_1_ok = ref(0x7ffffffe)++;
constexpr int overflow_int_inc_2 = ++ref(0x7fffffff); // expected-error {{constant}} expected-note {{2147483648}}
constexpr int overflow_int_inc_2_ok = ++ref(0x7ffffffe);
// inc/dec on short can't overflow because we promote to int first
static_assert(++ref<short>(0x7fff) == (int)0xffff8000u, "");
static_assert(--ref<short>(0x8000) == 0x7fff, "");
// inc on bool sets to true
static_assert(++ref(false), "");
// cxx14-warning@-1 {{incrementing expression of type bool}}
// cxx20-error@-2 {{incrementing expression of type bool}}
static_assert(++ref(true), "");
// cxx14-warning@-1 {{incrementing expression of type bool}}
// cxx20-error@-2 {{incrementing expression of type bool}}
#endif
int arr[10];
static_assert(postinc(&arr[0]) == &arr[1], "");
static_assert(postdec(&arr[1]) == &arr[0], "");
#if __cplusplus <= 202002L
static_assert(++ref(&arr[0]) == &arr[1], "");
static_assert(++ref(&arr[9]) == &arr[10], "");
static_assert(++ref(&arr[10]) == &arr[11], ""); // expected-error {{constant}} expected-note {{cannot refer to element 11}}
static_assert(ref(&arr[0])++ == &arr[0], "");
static_assert(ref(&arr[10])++ == &arr[10], ""); // expected-error {{constant}} expected-note {{cannot refer to element 11}}
static_assert(--ref(&arr[10]) == &arr[9], "");
static_assert(--ref(&arr[1]) == &arr[0], "");
static_assert(--ref(&arr[0]) != &arr[0], ""); // expected-error {{constant}} expected-note {{cannot refer to element -1}}
static_assert(ref(&arr[1])-- == &arr[1], "");
static_assert(ref(&arr[0])-- == &arr[0], ""); // expected-error {{constant}} expected-note {{cannot refer to element -1}}
#endif
static_assert(postinc(0.0) == 1.0, "");
static_assert(postdec(0.0) == -1.0, "");
#if __cplusplus <= 202002L
int x;
static_assert(++ref(&x) == &x + 1, "");
static_assert(++ref(0.0) == 1.0, "");
static_assert(ref(0.0)++ == 0.0, "");
static_assert(--ref(0.0) == -1.0, "");
static_assert(ref(0.0)-- == 0.0, "");
static_assert(++ref(1e100) == 1e100, "");
static_assert(--ref(1e100) == 1e100, "");
#endif
union U {
int a, b;
};
constexpr int f(U u) {
return ++u.b; // expected-note {{increment of member 'b' of union with active member 'a'}}
}
constexpr int wrong_member = f({0}); // expected-error {{constant}} expected-note {{in call to 'f({.a = 0})'}}
constexpr int vol = --ref<volatile int>(0); // expected-error {{constant}} expected-note {{decrement of volatile-qualified}}
// cxx20_23-warning@-1 {{decrement of object of volatile-qualified type 'volatile int' is deprecated}}
constexpr int incr(int k) {
int x = k;
if (x++ == 100)
return x;
return incr(x);
}
static_assert(incr(0) == 101, "");
}
namespace compound_assign {
constexpr bool test_int() {
int a = 3;
a += 6;
if (a != 9) return false;
a -= 2;
if (a != 7) return false;
a *= 3;
if (a != 21) return false;
if (&(a /= 10) != &a) return false;
if (a != 2) return false;
a <<= 3;
if (a != 16) return false;
a %= 6;
if (a != 4) return false;
a >>= 1;
if (a != 2) return false;
a ^= 10;
if (a != 8) return false;
a |= 5;
if (a != 13) return false;
a &= 14;
if (a != 12) return false;
a += -1.2;
if (a != 10) return false;
a -= 3.1;
if (a != 6) return false;
a *= 2.2;
if (a != 13) return false;
if (&(a /= 1.5) != &a) return false;
if (a != 8) return false;
return true;
}
static_assert(test_int(), "");
constexpr bool test_float() {
float f = 123.;
f *= 2;
if (f != 246.) return false;
if ((f -= 0.5) != 245.5) return false;
if (f != 245.5) return false;
f /= 0.5;
if (f != 491.) return false;
f += -40;
if (f != 451.) return false;
return true;
}
static_assert(test_float(), "");
constexpr bool test_bool() {
bool b = false;
b |= 2;
if (b != true) return false;
b <<= 1;
if (b != true) return false;
b *= 2;
if (b != true) return false;
b -= 1;
if (b != false) return false;
b -= 1;
if (b != true) return false;
b += -1;
if (b != false) return false;
b += 1;
if (b != true) return false;
b += 1;
if (b != true) return false;
b ^= b;
if (b != false) return false;
return true;
}
static_assert(test_bool(), "");
constexpr bool test_ptr() {
int arr[123] = {};
int *p = arr;
if ((p += 4) != &arr[4]) return false;
if (p != &arr[4]) return false;
p += -1;
if (p != &arr[3]) return false;
if ((p -= -10) != &arr[13]) return false;
if (p != &arr[13]) return false;
p -= 11;
if (p != &arr[2]) return false;
return true;
}
static_assert(test_ptr(), "");
template<typename T>
constexpr bool test_overflow() {
T a = 1;
while (a != a / 2)
a *= 2; // expected-note {{value 2147483648 is outside the range}} expected-note {{ 9223372036854775808 }}
return true;
}
static_assert(test_overflow<int>(), ""); // expected-error {{constant}} expected-note {{call}}
static_assert(test_overflow<unsigned>(), ""); // ok, unsigned overflow is defined
static_assert(test_overflow<short>(), ""); // ok, short is promoted to int before multiplication
static_assert(test_overflow<unsigned short>(), ""); // ok
static_assert(test_overflow<unsigned long long>(), ""); // ok
static_assert(test_overflow<long long>(), ""); // expected-error {{constant}} expected-note {{call}}
static_assert(test_overflow<float>(), ""); // ok
static_assert(test_overflow<double>(), ""); // ok
constexpr short test_promotion(short k) {
short s = k;
s *= s;
return s;
}
static_assert(test_promotion(100) == 10000, "");
static_assert(test_promotion(200) == -25536, "");
static_assert(test_promotion(256) == 0, "");
constexpr const char *test_bounds(const char *p, int o) {
return p += o; // expected-note {{element 5 of}} expected-note {{element -1 of}} expected-note {{element 1000 of}}
}
static_assert(test_bounds("foo", 0)[0] == 'f', "");
static_assert(test_bounds("foo", 3)[0] == 0, "");
static_assert(test_bounds("foo", 4)[-3] == 'o', "");
static_assert(test_bounds(&"foo"[4], -4)[0] == 'f', "");
static_assert(test_bounds("foo", 5) != 0, ""); // expected-error {{constant}} expected-note {{call}}
static_assert(test_bounds("foo", -1) != 0, ""); // expected-error {{constant}} expected-note {{call}}
static_assert(test_bounds("foo", 1000) != 0, ""); // expected-error {{constant}} expected-note {{call}}
}
namespace loops {
constexpr int fib_loop(int a) {
int f_k = 0, f_k_plus_one = 1;
for (int k = 1; k != a; ++k) {
int f_k_plus_two = f_k + f_k_plus_one;
f_k = f_k_plus_one;
f_k_plus_one = f_k_plus_two;
}
return f_k_plus_one;
}
static_assert(fib_loop(46) == 1836311903, "");
constexpr bool breaks_work() {
int a = 0;
for (int n = 0; n != 100; ++n) {
++a;
if (a == 5) continue;
if ((a % 5) == 0) break;
}
int b = 0;
while (b != 17) {
++b;
if (b == 6) continue;
if ((b % 6) == 0) break;
}
int c = 0;
do {
++c;
if (c == 7) continue;
if ((c % 7) == 0) break;
} while (c != 21);
return a == 10 && b == 12 && c == 14;
}
static_assert(breaks_work(), "");
void not_constexpr();
constexpr bool no_cont_after_break() {
for (;;) {
break;
not_constexpr();
}
while (true) {
break;
not_constexpr();
}
do {
break;
not_constexpr();
} while (true);
return true;
}
static_assert(no_cont_after_break(), "");
constexpr bool cond() {
for (int a = 1; bool b = a != 3; ++a) {
if (!b)
return false;
}
while (bool b = true) {
b = false;
break;
}
return true;
}
static_assert(cond(), "");
constexpr int range_for() {
int arr[] = { 1, 2, 3, 4, 5 };
int sum = 0;
for (int x : arr)
sum += x;
return sum;
}
static_assert(range_for() == 15, "");
template<int...N> struct ints {};
template<typename A, typename B> struct join_ints;
template<int...As, int...Bs> struct join_ints<ints<As...>, ints<Bs...>> {
using type = ints<As..., sizeof...(As) + Bs...>;
};
template<unsigned N> struct make_ints {
using type = typename join_ints<typename make_ints<N/2>::type, typename make_ints<(N+1)/2>::type>::type;
};
template<> struct make_ints<0> { using type = ints<>; };
template<> struct make_ints<1> { using type = ints<0>; };
struct ignore { template<typename ...Ts> constexpr ignore(Ts &&...) {} };
template<typename T, unsigned N> struct array {
constexpr array() : arr{} {}
template<typename ...X>
constexpr array(X ...x) : arr{} {
init(typename make_ints<sizeof...(X)>::type{}, x...);
}
template<int ...I, typename ...X> constexpr void init(ints<I...>, X ...x) {
ignore{arr[I] = x ...};
}
T arr[N];
struct iterator {
T *p;
constexpr explicit iterator(T *p) : p(p) {}
constexpr bool operator!=(iterator o) { return p != o.p; }
constexpr iterator &operator++() { ++p; return *this; }
constexpr T &operator*() { return *p; }
};
constexpr iterator begin() { return iterator(arr); }
constexpr iterator end() { return iterator(arr + N); }
};
constexpr int range_for_2() {
array<int, 5> arr { 1, 2, 3, 4, 5 };
int sum = 0;
for (int k : arr) {
sum += k;
if (sum > 8) break;
}
return sum;
}
static_assert(range_for_2() == 10, "");
}
namespace assignment_op {
struct A {
constexpr A() : n(5) {}
int n;
struct B {
int k = 1;
union U {
constexpr U() : y(4) {}
int x;
int y;
} u;
} b;
};
constexpr bool testA() {
A a, b;
a.n = 7;
a.b.u.y = 5;
b = a;
return b.n == 7 && b.b.u.y == 5 && b.b.k == 1;
}
static_assert(testA(), "");
struct B {
bool assigned = false;
constexpr B &operator=(const B&) {
assigned = true;
return *this;
}
};
struct C : B {
B b;
int n = 5;
};
constexpr bool testC() {
C c, d;
c.n = 7;
d = c;
c.n = 3;
return d.n == 7 && d.assigned && d.b.assigned;
}
static_assert(testC(), "");
}
namespace switch_stmt {
constexpr bool no_such_case(int n) {
switch (n) { case 1: return false; }
return true;
}
static_assert(no_such_case(0), "");
constexpr int f(char k) {
bool b = false;
int z = 6;
switch (k) {
return -1;
case 0:
if (false) {
case 1:
z = 1;
for (; b;) {
return 5;
while (0)
case 2: return 2;
case 7: z = 7;
do case 6: {
return z;
if (false)
case 3: return 3;
case 4: z = 4;
} while (1);
case 5: b = true;
case 9: z = 9;
}
return z;
} else if (false) case 8: z = 8;
else if (false) {
case 10:
z = -10;
break;
}
else z = 0;
return z;
default:
return -1;
}
return -z;
}
static_assert(f(0) == 0, "");
static_assert(f(1) == 1, "");
static_assert(f(2) == 2, "");
static_assert(f(3) == 3, "");
static_assert(f(4) == 4, "");
static_assert(f(5) == 5, "");
static_assert(f(6) == 6, "");
static_assert(f(7) == 7, "");
static_assert(f(8) == 8, "");
static_assert(f(9) == 9, "");
static_assert(f(10) == 10, "");
// Check that we can continue an outer loop from within a switch.
constexpr bool contin() {
for (int n = 0; n != 10; ++n) {
switch (n) {
case 0:
++n;
continue;
case 1:
return false;
case 2:
return true;
}
}
return false;
}
static_assert(contin(), "");
constexpr bool switch_into_for() {
int n = 0;
switch (n) {
for (; n == 1; ++n) {
return n == 1;
case 0: ;
}
}
return false;
}
static_assert(switch_into_for(), "");
constexpr void duff_copy(char *a, const char *b, int n) {
switch ((n - 1) % 8 + 1) {
for ( ; n; n = (n - 1) & ~7) {
case 8: a[n-8] = b[n-8];
case 7: a[n-7] = b[n-7];
case 6: a[n-6] = b[n-6];
case 5: a[n-5] = b[n-5];
case 4: a[n-4] = b[n-4];
case 3: a[n-3] = b[n-3];
case 2: a[n-2] = b[n-2];
case 1: a[n-1] = b[n-1];
}
case 0: ;
}
}
constexpr bool test_copy(const char *str, int n) {
char buffer[16] = {};
duff_copy(buffer, str, n);
for (int i = 0; i != sizeof(buffer); ++i)
if (buffer[i] != (i < n ? str[i] : 0))
return false;
return true;
}
static_assert(test_copy("foo", 0), "");
static_assert(test_copy("foo", 1), "");
static_assert(test_copy("foo", 2), "");
static_assert(test_copy("hello world", 0), "");
static_assert(test_copy("hello world", 7), "");
static_assert(test_copy("hello world", 8), "");
static_assert(test_copy("hello world", 9), "");
static_assert(test_copy("hello world", 10), "");
static_assert(test_copy("hello world", 10), "");
}
namespace deduced_return_type {
constexpr auto f() { return 0; }
template<typename T> constexpr auto g(T t) { return t; }
static_assert(f() == 0, "");
static_assert(g(true), "");
}
namespace modify_temporary_during_construction {
struct A { int &&temporary; int x; int y; };
constexpr int f(int &r) { r *= 9; return r - 12; }
constexpr A a = { 6, f(a.temporary), a.temporary }; // expected-note {{temporary created here}}
static_assert(a.x == 42, "");
static_assert(a.y == 54, "");
constexpr int k = a.temporary++; // expected-error {{constant expression}} expected-note {{outside the expression that created the temporary}}
}
namespace std {
typedef decltype(sizeof(int)) size_t;
template <class _E>
class initializer_list
{
const _E* __begin_;
size_t __size_;
constexpr initializer_list(const _E* __b, size_t __s)
: __begin_(__b),
__size_(__s)
{}
public:
typedef _E value_type;
typedef const _E& reference;
typedef const _E& const_reference;
typedef size_t size_type;
typedef const _E* iterator;
typedef const _E* const_iterator;
constexpr initializer_list() : __begin_(nullptr), __size_(0) {}
constexpr size_t size() const {return __size_;}
constexpr const _E* begin() const {return __begin_;}
constexpr const _E* end() const {return __begin_ + __size_;}
};
}
namespace InitializerList {
constexpr int sum(std::initializer_list<int> ints) {
int total = 0;
for (int n : ints) total += n;
return total;
}
static_assert(sum({1, 2, 3, 4, 5}) == 15, "");
}
namespace StmtExpr {
constexpr int f(int k) {
switch (k) {
case 0:
return 0;
({ // expected-note {{jump enters a statement expression}}
case 1:// expected-error {{cannot jump from switch statement to this case label}} \
// expected-note {{not supported}}
return 1;
});
}
}
static_assert(f(1) == 1, ""); // expected-error {{constant expression}} expected-note {{in call}}
constexpr int g() {
return ({ int n; n; }); // expected-note {{read of uninitialized object}}
}
static_assert(g() == 0, ""); // expected-error {{constant expression}} expected-note {{in call}}
// FIXME: We should handle the void statement expression case.
constexpr int h() { // cxx14_20-error {{never produces a constant}}
({ if (true) {} }); // cxx14_20-note {{not supported}}
return 0;
}
}
namespace VirtualFromBase {
struct S1 {
virtual int f() const;
};
struct S2 {
virtual int f();
};
template <typename T> struct X : T {
constexpr X() {}
double d = 0.0;
constexpr int f() { return sizeof(T); }
};
// Non-virtual f(), OK.
constexpr X<X<S1>> xxs1;
constexpr X<S1> *p = const_cast<X<X<S1>>*>(&xxs1);
static_assert(p->f() == sizeof(S1), "");
// Virtual f(), not OK.
constexpr X<X<S2>> xxs2;
constexpr X<S2> *q = const_cast<X<X<S2>>*>(&xxs2);
static_assert(q->f() == sizeof(X<S2>), ""); // cxx14-error {{constant expression}} cxx14-note {{virtual function}}
}
namespace Lifetime {
constexpr int &get(int &&r) { return r; }
// cxx23-error@-1 {{non-const lvalue reference to type 'int' cannot bind to a temporary of type 'int'}}
constexpr int f() {
int &r = get(123);
return r;
// cxx14_20-note@-1 {{read of object outside its lifetime}}
}
static_assert(f() == 123, ""); // expected-error {{constant expression}} cxx14_20-note {{in call}}
constexpr int g() {
int *p = 0;
{
int n = 0;
p = &n;
n = 42;
}
*p = 123; // expected-note {{assignment to object outside its lifetime}}
return *p;
}
static_assert(g() == 42, ""); // expected-error {{constant expression}} expected-note {{in call}}
constexpr int h(int n) {
int *p[4] = {};
int &&r = 1;
p[0] = &r;
while (int a = 1) {
p[1] = &a;
for (int b = 1; int c = 1; ) {
p[2] = &b, p[3] = &c;
break;
}
break;
}
*p[n] = 0; // expected-note 3{{assignment to object outside its lifetime}}
return *p[n];
}
static_assert(h(0) == 0, ""); // ok, lifetime-extended
static_assert(h(1) == 0, ""); // expected-error {{constant expression}} expected-note {{in call}}
static_assert(h(2) == 0, ""); // expected-error {{constant expression}} expected-note {{in call}}
static_assert(h(3) == 0, ""); // expected-error {{constant expression}} expected-note {{in call}}
constexpr void lifetime_versus_loops() {
int *p = 0;
for (int i = 0; i != 2; ++i) {
int *q = p;
int n = 0;
p = &n;
if (i)
// This modifies the 'n' from the previous iteration of the loop outside
// its lifetime.
++*q; // expected-note {{increment of object outside its lifetime}}
}
}
static_assert((lifetime_versus_loops(), true), ""); // expected-error {{constant expression}} expected-note {{in call}}
}
namespace Bitfields {
struct A {
bool b : 1;
int n : 4;
unsigned u : 5;
};
constexpr bool test() {
A a {};
a.b += 2;
--a.n;
--a.u;
a.n = -a.n * 3;
return a.b == true && a.n == 3 && a.u == 31;
}
static_assert(test(), "");
}
namespace PR17615 {
struct A {
int &&r;
constexpr A(int &&r) : r(static_cast<int &&>(r)) {}
constexpr A() : A(0) {
(void)+r; // expected-note {{outside its lifetime}}
}
};
constexpr int k = A().r; // expected-error {{constant expression}} expected-note {{in call to}}
}
namespace PR17331 {
template<typename T, unsigned int N>
constexpr T sum(const T (&arr)[N]) {
T result = 0;
for (T i : arr)
result += i;
return result;
}
constexpr int ARR[] = { 1, 2, 3, 4, 5 };
static_assert(sum(ARR) == 15, "");
}
namespace EmptyClass {
struct E1 {} e1;
union E2 {} e2; // expected-note 4{{here}}
struct E3 : E1 {} e3;
template<typename E>
constexpr int f(E &a, int kind) {
switch (kind) {
case 0: { E e(a); return 0; } // expected-note {{read}} expected-note {{in call}}
case 1: { E e(static_cast<E&&>(a)); return 0; } // expected-note {{read}} expected-note {{in call}}
case 2: { E e; e = a; return 0; } // expected-note {{read}} expected-note {{in call}}
case 3: { E e; e = static_cast<E&&>(a); return 0; } // expected-note {{read}} expected-note {{in call}}
}
}
constexpr int test1 = f(e1, 0);
constexpr int test2 = f(e2, 0); // expected-error {{constant expression}} expected-note {{in call}}
constexpr int test3 = f(e3, 0);
constexpr int test4 = f(e1, 1);
constexpr int test5 = f(e2, 1); // expected-error {{constant expression}} expected-note {{in call}}
constexpr int test6 = f(e3, 1);
constexpr int test7 = f(e1, 2);
constexpr int test8 = f(e2, 2); // expected-error {{constant expression}} expected-note {{in call}}
constexpr int test9 = f(e3, 2);
constexpr int testa = f(e1, 3);
constexpr int testb = f(e2, 3); // expected-error {{constant expression}} expected-note {{in call}}
constexpr int testc = f(e3, 3);
}
namespace SpeculativeEvalWrites {
// Ensure that we don't try to speculatively evaluate writes.
constexpr int f() {
int i = 0;
int a = 0;
// __builtin_object_size speculatively evaluates its first argument.
__builtin_object_size((i = 1, &a), 0);
return i;
}
static_assert(!f(), "");
}
namespace PR27989 {
constexpr int f(int n) {
int a = (n = 1, 0);
return n;
}
static_assert(f(0) == 1, "");
}
namespace const_char {
template <int N>
constexpr int sum(const char (&Arr)[N]) {
int S = 0;
for (unsigned I = 0; I != N; ++I)
S += Arr[I]; // expected-note 2{{read of non-constexpr variable 'Cs' is not allowed}}
return S;
}
// As an extension, we support evaluating some things that are `const` as though
// they were `constexpr` when folding, but it should not be allowed in normal
// constexpr evaluation.
const char Cs[] = {'a', 'b'}; // expected-note 2{{declared here}}
void foo() __attribute__((enable_if(sum(Cs) == 'a' + 'b', "")));
void run() { foo(); }
static_assert(sum(Cs) == 'a' + 'b', ""); // expected-error{{not an integral constant expression}} expected-note{{in call to 'sum<2>(Cs)'}}
constexpr int S = sum(Cs); // expected-error{{must be initialized by a constant expression}} expected-note{{in call}}
}
constexpr void PR28739(int n) { // cxx14_20-error {{never produces a constant}}
int *p = &n; // expected-note {{array 'p' declared here}}
p += (__int128)(unsigned long)-1; // cxx14_20-note {{cannot refer to element 18446744073709551615 of non-array object in a constant expression}}
// 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)}}
}
constexpr void Void(int n) {
void(n + 1);
void();
}
constexpr int void_test = (Void(0), 1);
namespace PR19741 {
constexpr void addone(int &m) { m++; }
struct S {
int m = 0;
constexpr S() { addone(m); }
};
constexpr bool evalS() {
constexpr S s;
return s.m == 1;
}
static_assert(evalS(), "");
struct Nested {
struct First { int x = 42; };
union {
First first;
int second;
};
int x;
constexpr Nested(int x) : first(), x(x) { x = 4; }
constexpr Nested() : Nested(42) {
addone(first.x);
x = 3;
}
};
constexpr bool evalNested() {
constexpr Nested N;
return N.first.x == 43;
}
static_assert(evalNested(), "");
} // namespace PR19741
namespace Mutable {
struct A { mutable int n; }; // expected-note 2{{here}}
constexpr int k = A{123}.n; // ok
static_assert(k == 123, "");
struct Q { A &&a; int b = a.n; };
constexpr Q q = { A{456} }; // expected-note {{temporary}}
static_assert(q.b == 456, "");
static_assert(q.a.n == 456, ""); // expected-error {{constant expression}} expected-note {{outside the expression that created the temporary}}
constexpr A a = {123};
constexpr int m = a.n; // expected-error {{constant expression}} expected-note {{mutable}}
constexpr Q r = { static_cast<A&&>(const_cast<A&>(a)) }; // expected-error {{constant expression}} expected-note@-8 {{mutable}}
struct B {
mutable int n; // expected-note {{here}}
int m;
constexpr B() : n(1), m(n) {} // ok
};
constexpr B b;
constexpr int p = b.n; // expected-error {{constant expression}} expected-note {{mutable}}
}
namespace IndirectFields {
// Reference indirect field.
struct A {
struct {
union {
int x = x = 3; // cxx14-note {{outside its lifetime}}
};
};
constexpr A() {}
};
static_assert(A().x == 3, ""); // cxx14-error{{not an integral constant expression}} cxx14-note{{in call to 'A()'}}
// Reference another indirect field, with different 'this'.
struct B {
struct {
union {
int x = 3;
};
int y = x;
};
constexpr B() {}
};
static_assert(B().y == 3, "");
// Nested evaluation of indirect field initializers.
struct C {
union {
int x = 1;
};
};
struct D {
struct {
C c;
int y = c.x + 1;
};
};
static_assert(D().y == 2, "");
// Explicit 'this'.
struct E {
int n = 0;
struct {
void *x = this;
};
void *y = this;
};
constexpr E e1 = E();
static_assert(e1.x != e1.y, "");
constexpr E e2 = E{0};
static_assert(e2.x != e2.y, "");
} // namespace IndirectFields
constexpr bool indirect_builtin_constant_p(const char *__s) {
return __builtin_constant_p(*__s);
}
constexpr bool n = indirect_builtin_constant_p("a");
__attribute__((enable_if(indirect_builtin_constant_p("a") == n, "OK")))
int test_in_enable_if() { return 0; }
int n2 = test_in_enable_if();
template <bool n = indirect_builtin_constant_p("a")>
int test_in_template_param() { return 0; }
int n3 = test_in_template_param();
void test_in_case(int n) {
switch (n) {
case indirect_builtin_constant_p("abc"):
break;
}
}
enum InEnum1 {
ONE = indirect_builtin_constant_p("abc")
};
enum InEnum2 : int {
TWO = indirect_builtin_constant_p("abc")
};
enum class InEnum3 {
THREE = indirect_builtin_constant_p("abc")
};
// [class.ctor]p4:
// A constructor can be invoked for a const, volatile or const volatile
// object. const and volatile semantics are not applied on an object under
// construction. They come into effect when the constructor for the most
// derived object ends.
namespace ObjectsUnderConstruction {
struct A {
int n;
constexpr A() : n(1) { n = 2; }
};
struct B {
const A a;
constexpr B(bool mutate) {
if (mutate)
const_cast<A &>(a).n = 3; // expected-note {{modification of object of const-qualified type 'const int'}}
}
};
constexpr B b(false);
static_assert(b.a.n == 2, "");
constexpr B bad(true); // expected-error {{must be initialized by a constant expression}} expected-note {{in call to 'B(true)'}}
struct C {
int n;
constexpr C() : n(1) { n = 2; }
};
constexpr int f(bool get) {
volatile C c; // expected-note {{here}}
return get ? const_cast<int&>(c.n) : 0; // expected-note {{read of volatile object 'c'}}
}
static_assert(f(false) == 0, ""); // ok, can modify volatile c.n during c's initialization: it's not volatile then
static_assert(f(true) == 2, ""); // expected-error {{constant}} expected-note {{in call}}
struct Aggregate {
int x = 0;
int y = ++x;
};
constexpr Aggregate aggr1;
static_assert(aggr1.x == 1 && aggr1.y == 1, "");
// FIXME: This is not specified by the standard, but sanity requires it.
constexpr Aggregate aggr2 = {};
static_assert(aggr2.x == 1 && aggr2.y == 1, "");
// The lifetime of 'n' begins at the initialization, not before.
constexpr int n = ++const_cast<int&>(n); // expected-error {{constant expression}} expected-note {{increment of object outside its lifetime}}
}
namespace PR39728 {
struct Comment0 {
Comment0 &operator=(const Comment0 &) = default;
~Comment0() = default;
};
constexpr void f() {
Comment0 a;
a = a;
}
static_assert((f(), true), "");
struct Comment1 {
constexpr Comment1 &operator=(const Comment1 &) = default; // OK
~Comment1() = default;
};
}
namespace TemporaryWithBadPointer {
constexpr int *get_bad_pointer() {
int n = 0; // expected-note 2{{here}}
return &n; // expected-warning {{stack}}
}
constexpr int *bad_pointer = get_bad_pointer(); // expected-error {{constant expression}} expected-note {{pointer to 'n' is not a constant expression}}
struct DoBadThings { int *&℘ int n; };
constexpr DoBadThings dbt = { // expected-error {{constant expression}}
nullptr, // expected-note {{pointer to 'n' is not a constant expression}}
(dbt.wp = get_bad_pointer(), 0)
};
constexpr DoBadThings dbt2 = { // ok
get_bad_pointer(),
(dbt2.wp = nullptr, 0)
};
}
namespace UninitCompoundAssign {
constexpr int scalar(int a) {
int sum; // cxx14-warning {{uninitialized variable in a constexpr function is a C++20 extension}}
sum += a; // expected-note {{read of uninitialized object}};
return 0;
}
static_assert(scalar(3), ""); // expected-error {{constant expression}} \
// expected-note {{in call to 'scalar(3)'}}
constexpr int array(int a) {
int arr[3]; // cxx14-warning {{uninitialized variable in a constexpr function is a C++20 extension}}
arr[1] += a; // expected-note {{read of uninitialized object}};
return 0;
}
static_assert(array(3), ""); // expected-error {{constant expression}} \
// expected-note {{in call to 'array(3)'}}
struct Foo {
int val; // cxx14-note{{member not initialized by constructor}}
constexpr Foo() {} // cxx14-warning {{constexpr constructor that does not initialize all members is a C++20 extension}}
};
constexpr int field(int a) {
Foo f;
f.val += a; // expected-note {{read of uninitialized object}};
return 0;
}
static_assert(field(3), ""); // expected-error {{constant expression}} \
// expected-note {{in call to 'field(3)'}}
}
namespace literal_comparison {
constexpr bool different_in_loop(bool b = false) {
if (b) return false;
const char *p[2] = {};
for (const char *&r : p)
r = "hello";
return p[0] == p[1]; // expected-note {{addresses of literals}}
}
constexpr bool check = different_in_loop();
// expected-error@-1 {{}} expected-note@-1 {{in call}}
}
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