672 lines · cpp
1// RUN: %clang_cc1 -fsyntax-only -std=c++11 -pedantic -verify=expected,cxx11 -fcxx-exceptions %s -fconstexpr-depth=128 -triple i686-pc-linux-gnu2// RUN: %clang_cc1 -fsyntax-only -std=c++2a -pedantic -verify=expected,cxx20 -fcxx-exceptions %s -fconstexpr-depth=128 -triple i686-pc-linux-gnu3 4// A conditional-expression is a core constant expression unless it involves one5// of the following as a potentially evaluated subexpression [...]:6 7// - this (5.1.1 [expr.prim.general]) [Note: when evaluating a constant8// expression, function invocation substitution (7.1.5 [dcl.constexpr])9// replaces each occurrence of this in a constexpr member function with a10// pointer to the class object. -end note];11struct This {12 int this1 : this1; // expected-error {{undeclared}}13 int this2 : this->this1; // expected-error {{invalid}}14 void this3() {15 int n1[this->this1]; // expected-warning {{variable length array}} expected-note {{'this'}}16 int n2[this1]; // expected-warning {{variable length array}} expected-note {{'this'}}17 (void)n1, (void)n2;18 }19};20 21// - an invocation of a function other than a constexpr constructor for a22// literal class or a constexpr function [ Note: Overload resolution (13.3)23// is applied as usual - end note ];24struct NonConstexpr1 {25 static int f() { return 1; } // expected-note {{here}}26 int n : f(); // expected-error {{constant expression}} expected-note {{non-constexpr function 'f' cannot be used in a constant expression}}27};28struct NonConstexpr2 {29 constexpr NonConstexpr2(); // expected-note {{here}}30 int n;31};32struct NonConstexpr3 {33 NonConstexpr3();34 int m : NonConstexpr2().n; // expected-error {{constant expression}} expected-note {{undefined constructor 'NonConstexpr2'}}35};36struct NonConstexpr4 {37 NonConstexpr4();38 int n;39};40struct NonConstexpr5 {41 int n : NonConstexpr4().n; // expected-error {{constant expression}} expected-note {{non-literal type 'NonConstexpr4' cannot be used in a constant expression}}42};43 44// - an invocation of an undefined constexpr function or an undefined45// constexpr constructor;46struct UndefinedConstexpr {47 constexpr UndefinedConstexpr();48 static constexpr int undefinedConstexpr1(); // expected-note {{here}}49 int undefinedConstexpr2 : undefinedConstexpr1(); // expected-error {{constant expression}} expected-note {{undefined function 'undefinedConstexpr1' cannot be used in a constant expression}}50};51 52// - an invocation of a constexpr function with arguments that, when substituted53// by function invocation substitution (7.1.5), do not produce a core constant54// expression;55namespace NonConstExprReturn {56 static constexpr const int &id_ref(const int &n) {57 return n;58 }59 struct NonConstExprFunction {60 int n : id_ref(16); // ok61 };62 constexpr const int *address_of(const int &a) {63 return &a;64 }65 constexpr const int *return_param(int n) {66 return address_of(n);67 }68 struct S {69 int n : *return_param(0); // expected-error {{constant expression}} expected-note {{read of object outside its lifetime}}70 };71}72 73// - an invocation of a constexpr constructor with arguments that, when74// substituted by function invocation substitution (7.1.5), do not produce all75// constant expressions for the constructor calls and full-expressions in the76// mem-initializers (including conversions);77namespace NonConstExprCtor {78 struct T {79 constexpr T(const int &r) :80 r(r) {81 }82 const int &r;83 };84 constexpr int n = 0;85 constexpr T t1(n); // ok86 constexpr T t2(0); // expected-error {{must be initialized by a constant expression}} expected-note {{temporary created here}} expected-note {{reference to temporary is not a constant expression}}87 88 struct S {89 int n : T(4).r; // ok90 };91}92 93// - an invocation of a constexpr function or a constexpr constructor that would94// exceed the implementation-defined recursion limits (see Annex B);95namespace RecursionLimits {96 constexpr int RecurseForever(int n) {97 return n + RecurseForever(n+1); // expected-note {{constexpr evaluation exceeded maximum depth of 128 calls}} expected-note 9{{in call to 'RecurseForever(}} expected-note {{skipping 118 calls}}98 }99 struct AlsoRecurseForever {100 constexpr AlsoRecurseForever(int n) :101 n(AlsoRecurseForever(n+1).n) // expected-note {{constexpr evaluation exceeded maximum depth of 128 calls}} expected-note 9{{in call to 'AlsoRecurseForever(}} expected-note {{skipping 118 calls}}102 {}103 int n;104 };105 struct S {106 int k : RecurseForever(0); // expected-error {{constant expression}} expected-note {{in call to}}107 int l : AlsoRecurseForever(0).n; // expected-error {{constant expression}} expected-note {{in call to}}108 };109}110 111// DR1458: taking the address of an object of incomplete class type112namespace IncompleteClassTypeAddr {113 struct S;114 extern S s;115 constexpr S *p = &s; // ok116 static_assert(p, "");117 118 extern S sArr[];119 constexpr S (*p2)[] = &sArr; // ok120 121 struct S {122 constexpr S *operator&() const { return nullptr; }123 };124 constexpr S *q = &s; // ok125 static_assert(!q, "");126}127 128// - an operation that would have undefined behavior [Note: including, for129// example, signed integer overflow (Clause 5 [expr]), certain pointer130// arithmetic (5.7 [expr.add]), division by zero (5.6 [expr.mul]), or certain131// shift operations (5.8 [expr.shift]) -end note];132namespace UndefinedBehavior {133 void f(int n) {134 switch (n) {135 case (int)4.4e9: // expected-error {{constant expression}} expected-note {{value 4.4E+9 is outside the range of representable values of type 'int'}}136 case (int)0x80000000u: // ok137 case (int)10000000000ll: // expected-note {{here}}138 case (unsigned int)10000000000ll: // expected-error {{duplicate case value}}139 case (int)(unsigned)(long long)4.4e9: // ok140 case (int)(float)1e300: // expected-error {{constant expression}} expected-note {{value +Inf is outside the range of representable values of type 'int'}}141 case (int)((float)1e37 / 1e30): // ok142 case (int)(__fp16)65536: // expected-error {{constant expression}} expected-note {{value +Inf is outside the range of representable values of type 'int'}}143 break;144 }145 }146 147 constexpr int int_min = ~0x7fffffff;148 constexpr int minus_int_min = -int_min; // expected-error {{constant expression}} expected-note {{value 2147483648 is outside the range}}149 constexpr int minus_int_min_from_shift = -(1<<31); // expected-error {{constant expression}} expected-note {{value 2147483648 is outside the range}}150 constexpr int div0 = 3 / 0; // expected-error {{constant expression}} expected-note {{division by zero}}151 constexpr int mod0 = 3 % 0; // expected-error {{constant expression}} expected-note {{division by zero}}152 constexpr int int_min_div_minus_1 = int_min / -1; // expected-error {{constant expression}} expected-note {{value 2147483648 is outside the range}}153 constexpr int int_min_mod_minus_1 = int_min % -1; // expected-error {{constant expression}} expected-note {{value 2147483648 is outside the range}}154 155 constexpr int shl_m1 = 0 << -1; // expected-error {{constant expression}} expected-note {{negative shift count -1}}156 constexpr int shl_0 = 0 << 0; // ok157 constexpr int shl_31 = 0 << 31; // ok158 constexpr int shl_32 = 0 << 32; // expected-error {{constant expression}} expected-note {{shift count 32 >= width of type 'int' (32}}159 constexpr int shl_unsigned_negative = unsigned(-3) << 1; // ok160 constexpr int shl_unsigned_into_sign = 1u << 31; // ok161 constexpr int shl_unsigned_overflow = 1024u << 31; // ok162 constexpr int shl_signed_negative = (-3) << 1; // cxx11-error {{constant expression}} cxx11-note {{left shift of negative value -3}}163 constexpr int shl_signed_ok = 1 << 30; // ok164 constexpr int shl_signed_into_sign = 1 << 31; // ok (DR1457)165 constexpr int shl_signed_into_sign_2 = 0x7fffffff << 1; // ok (DR1457)166 constexpr int shl_signed_off_end = 2 << 31; // cxx11-error {{constant expression}} cxx11-note {{signed left shift discards bits}} cxx11-warning {{signed shift result (0x100000000) requires 34 bits to represent, but 'int' only has 32 bits}}167 constexpr int shl_signed_off_end_2 = 0x7fffffff << 2; // cxx11-error {{constant expression}} cxx11-note {{signed left shift discards bits}} cxx11-warning {{signed shift result (0x1FFFFFFFC) requires 34 bits to represent, but 'int' only has 32 bits}}168 constexpr int shl_signed_overflow = 1024 << 31; // cxx11-error {{constant expression}} cxx11-note {{signed left shift discards bits}} cxx11-warning {{requires 43 bits to represent}}169 constexpr int shl_signed_ok2 = 1024 << 20; // ok170 171 constexpr int shr_m1 = 0 >> -1; // expected-error {{constant expression}} expected-note {{negative shift count -1}}172 constexpr int shr_0 = 0 >> 0; // ok173 constexpr int shr_31 = 0 >> 31; // ok174 constexpr int shr_32 = 0 >> 32; // expected-error {{constant expression}} expected-note {{shift count 32 >= width of type}}175 176 struct S {177 int m;178 };179 constexpr S s = { 5 };180 constexpr const int *p = &s.m + 1;181 constexpr const int &f(const int *q) {182 return q[0];183 }184 constexpr int n = (f(p), 0); // ok185 struct T {186 int n : f(p); // expected-error {{not an integral constant expression}} expected-note {{read of dereferenced one-past-the-end pointer}}187 };188 189 namespace Ptr {190 struct A {};191 struct B : A { int n; int m; };192 B a[3][3];193 constexpr B *p = a[0] + 4; // expected-error {{constant expression}} expected-note {{element 4 of array of 3 elements}}194 B b = {};195 constexpr A *pa = &b + 1; // expected-error {{constant expression}} expected-note {{base class of pointer past the end}}196 constexpr B *pb = (B*)((A*)&b + 1); // expected-error {{constant expression}} expected-note {{derived class of pointer past the end}}197 constexpr const int *pn = &(&b + 1)->n; // expected-error {{constant expression}} expected-note {{field of pointer past the end}}198 constexpr B *parr = &a[3][0]; // expected-error {{constant expression}} expected-note {{array element of pointer past the end}}199 200 constexpr A *na = nullptr;201 constexpr B *nb = nullptr;202 constexpr A &ra = *nb; // expected-error {{constant expression}} expected-note {{dereferencing a null pointer}}203 constexpr B &rb = (B&)*na; // expected-error {{constant expression}} expected-note {{dereferencing a null pointer}}204 static_assert((A*)nb == 0, "");205 static_assert((B*)na == 0, "");206 constexpr const int &nf = nb->n; // expected-error {{constant expression}} expected-note {{cannot access field of null pointer}}207 constexpr const int &mf = nb->m; // expected-error {{constant expression}} expected-note {{cannot access field of null pointer}}208 constexpr const int *np1 = (int*)nullptr + 0; // ok209 constexpr const int *np2 = &(*(int(*)[4])nullptr)[0]; // expected-error {{constant expression}} expected-note {{dereferencing a null pointer}}210 constexpr const int *np3 = &(*(int(*)[4])nullptr)[2]; // expected-error {{constant expression}} expected-note {{dereferencing a null pointer}}211 212 struct C {213 constexpr int f() const { return 0; }214 } constexpr c = C();215 constexpr int k1 = c.f(); // ok216 constexpr int k2 = ((C*)nullptr)->f(); // expected-error {{constant expression}} expected-note {{member call on dereferenced null pointer}}217 constexpr int k3 = (&c)[1].f(); // expected-error {{constant expression}} expected-note {{member call on dereferenced one-past-the-end pointer}}218 C c2;219 constexpr int k4 = c2.f(); // ok!220 221 constexpr int diff1 = &a[2] - &a[0];222 constexpr int diff2 = &a[1][3] - &a[1][0];223 constexpr int diff3 = &a[2][0] - &a[1][0]; // expected-error {{constant expression}} expected-note {{subtracted pointers are not elements of the same array}}224 static_assert(&a[2][0] == &a[1][3], "");225 constexpr int diff4 = (&b + 1) - &b;226 constexpr int diff5 = &a[1][2].n - &a[1][0].n; // expected-error {{constant expression}} expected-note {{subtracted pointers are not elements of the same array}}227 constexpr int diff6 = &a[1][2].n - &a[1][2].n;228 constexpr int diff7 = (A*)&a[0][1] - (A*)&a[0][0]; // expected-error {{constant expression}} expected-note {{subtracted pointers are not elements of the same array}}229 }230 231 namespace Overflow {232 // Signed int overflow.233 constexpr int n1 = 2 * 3 * 3 * 7 * 11 * 31 * 151 * 331; // ok234 constexpr int n2 = 65536 * 32768; // expected-error {{constant expression}} expected-note {{value 2147483648 is outside the range of }}235 constexpr int n3 = n1 + 1; // ok236 constexpr int n4 = n3 + 1; // expected-error {{constant expression}} expected-note {{value 2147483648 is outside the range of }}237 constexpr int n5 = -65536 * 32768; // ok238 constexpr int n6 = 3 * -715827883; // expected-error {{constant expression}} expected-note {{value -2147483649 is outside the range of }}239 constexpr int n7 = -n3 + -1; // ok240 constexpr int n8 = -1 + n7; // expected-error {{constant expression}} expected-note {{value -2147483649 is outside the range of }}241 constexpr int n9 = n3 - 0; // ok242 constexpr int n10 = n3 - -1; // expected-error {{constant expression}} expected-note {{value 2147483648 is outside the range of }}243 constexpr int n11 = -1 - n3; // ok244 constexpr int n12 = -2 - n3; // expected-error {{constant expression}} expected-note {{value -2147483649 is outside the range of }}245 constexpr int n13 = n5 + n5; // expected-error {{constant expression}} expected-note {{value -4294967296 is outside the range of }}246 constexpr int n14 = n3 - n5; // expected-error {{constant expression}} expected-note {{value 4294967295 is outside the range of }}247 constexpr int n15 = n5 * n5; // expected-error {{constant expression}} expected-note {{value 4611686018427387904 is outside the range of }}248 constexpr signed char c1 = 100 * 2; // ok expected-warning{{changes value}}249 constexpr signed char c2 = '\x64' * '\2'; // also ok expected-warning{{changes value}}250 constexpr long long ll1 = 0x7fffffffffffffff; // ok251 constexpr long long ll2 = ll1 + 1; // expected-error {{constant}} expected-note {{ 9223372036854775808 }}252 constexpr long long ll3 = -ll1 - 1; // ok253 constexpr long long ll4 = ll3 - 1; // expected-error {{constant}} expected-note {{ -9223372036854775809 }}254 constexpr long long ll5 = ll3 * ll3; // expected-error {{constant}} expected-note {{ 85070591730234615865843651857942052864 }}255 256 // Yikes.257 char melchizedek[2200000000];258 typedef decltype(melchizedek[1] - melchizedek[0]) ptrdiff_t;259 constexpr ptrdiff_t d1 = &melchizedek[0x7fffffff] - &melchizedek[0]; // ok260 constexpr ptrdiff_t d2 = &melchizedek[0x80000000u] - &melchizedek[0]; // expected-error {{constant expression}} expected-note {{ 2147483648 }}261 constexpr ptrdiff_t d3 = &melchizedek[0] - &melchizedek[0x80000000u]; // ok262 constexpr ptrdiff_t d4 = &melchizedek[0] - &melchizedek[0x80000001u]; // expected-error {{constant expression}} expected-note {{ -2147483649 }}263 264 // Unsigned int overflow.265 static_assert(65536u * 65536u == 0u, ""); // ok266 static_assert(4294967295u + 1u == 0u, ""); // ok267 static_assert(0u - 1u == 4294967295u, ""); // ok268 static_assert(~0u * ~0u == 1u, ""); // ok269 270 template<typename T> constexpr bool isinf(T v) { return v && v / 2 == v; }271 272 // Floating-point overflow and NaN.273 constexpr float f1 = 1e38f * 3.4028f; // ok274 constexpr float f2 = 1e38f * 3.4029f; // ok, +inf is in range of representable values275 constexpr float f3 = 1e38f / -.2939f; // ok276 constexpr float f4 = 1e38f / -.2938f; // ok, -inf is in range of representable values277 constexpr float f5 = 2e38f + 2e38f; // ok, +inf is in range of representable values278 constexpr float f6 = -2e38f - 2e38f; // ok, -inf is in range of representable values279 constexpr float f7 = 0.f / 0.f; // expected-error {{constant expression}} expected-note {{division by zero}}280 constexpr float f8 = 1.f / 0.f; // expected-error {{constant expression}} expected-note {{division by zero}}281 constexpr float f9 = 1e308 / 1e-308; // ok, +inf282 constexpr float f10 = f2 - f2; // expected-error {{constant expression}} expected-note {{produces a NaN}}283 constexpr float f11 = f2 + f4; // expected-error {{constant expression}} expected-note {{produces a NaN}}284 constexpr float f12 = f2 / f2; // expected-error {{constant expression}} expected-note {{produces a NaN}}285#pragma float_control(push)286#pragma float_control(except, on)287constexpr float pi = 3.14f;288constexpr unsigned ubig = 0xFFFFFFFF;289constexpr float ce = 1.0 / 3.0; // not-expected-error {{constant expression}} not-expected-note {{floating point arithmetic suppressed in strict evaluation modes}}290constexpr int ci = (int) pi;291constexpr float fbig = (float) ubig; // not-expected-error {{constant expression}} not-expected-note {{floating point arithmetic suppressed in strict evaluation modes}}292constexpr float fabspi = __builtin_fabs(pi); // no error expected293constexpr float negpi = -pi; // expect no error on unary operator294#pragma float_control(pop)295 static_assert(!isinf(f1), "");296 static_assert(isinf(f2), "");297 static_assert(!isinf(f3), "");298 static_assert(isinf(f4), "");299 static_assert(isinf(f5), "");300 static_assert(isinf(f6), "");301 static_assert(isinf(f9), "");302 }303 304#if __cplusplus >= 201703L305namespace CompoundAssignment {306constexpr int rem() { // expected-error {{constexpr function never produces a constant expression}}307 int x = ~__INT_MAX__;308 return x%=-1; // cxx20-note {{value 2147483648 is outside the range of representable values of type 'int'}}309}310}311#endif312}313 314// - a lambda-expression (5.1.2);315struct Lambda {316 int n : []{ return 1; }(); // cxx11-error {{constant expression}} cxx11-error {{integral constant expression}} cxx11-note {{non-literal type}}317};318 319// - an lvalue-to-rvalue conversion (4.1) unless it is applied to320namespace LValueToRValue {321 // - a non-volatile glvalue of integral or enumeration type that refers to a322 // non-volatile const object with a preceding initialization, initialized323 // with a constant expression [Note: a string literal (2.14.5 [lex.string])324 // corresponds to an array of such objects. -end note], or325 volatile const int vi = 1; // expected-note 2{{here}}326 const int ci = 1;327 volatile const int &vrci = ci;328 static_assert(vi, ""); // expected-error {{constant expression}} expected-note {{read of volatile-qualified type}}329 static_assert(const_cast<int&>(vi), ""); // expected-error {{constant expression}} expected-note {{read of volatile object 'vi'}}330 static_assert(vrci, ""); // expected-error {{constant expression}} expected-note {{read of volatile-qualified type}}331 332 // - a non-volatile glvalue of literal type that refers to a non-volatile333 // object defined with constexpr, or that refers to a sub-object of such an334 // object, or335 struct V {336 constexpr V() : v(1) {}337 volatile int v; // expected-note {{not literal because}}338 };339 constexpr V v; // expected-error {{non-literal type}}340 struct S {341 constexpr S(int=0) : i(1), v(const_cast<volatile int&>(vi)) {}342 constexpr S(const S &s) : i(2), v(const_cast<volatile int&>(vi)) {}343 int i;344 volatile int &v;345 };346 constexpr S s; // ok347 constexpr volatile S vs; // expected-note {{here}}348 constexpr const volatile S &vrs = s; // ok349 static_assert(s.i, "");350 static_assert(s.v, ""); // expected-error {{constant expression}} expected-note {{read of volatile-qualified type}}351 static_assert(const_cast<int&>(s.v), ""); // expected-error {{constant expression}} expected-note {{read of volatile object 'vi'}}352 static_assert(vs.i, ""); // expected-error {{constant expression}} expected-note {{read of volatile-qualified type}}353 static_assert(const_cast<int&>(vs.i), ""); // expected-error {{constant expression}} expected-note {{read of volatile object 'vs'}}354 static_assert(vrs.i, ""); // expected-error {{constant expression}} expected-note {{read of volatile-qualified type}}355 356 // - a non-volatile glvalue of literal type that refers to a non-volatile357 // temporary object whose lifetime has not ended, initialized with a358 // constant expression;359 constexpr volatile S f() { return S(); } // cxx20-warning {{volatile-qualified return type 'volatile S' is deprecated}}360 static_assert(f().i, ""); // expected-error {{constant expression}} expected-note {{read of volatile-qualified type}}361 static_assert(((volatile const S&&)(S)0).i, ""); // expected-error {{constant expression}} expected-note {{read of volatile-qualified type}}362}363 364// DR1312: The proposed wording for this defect has issues, so we ignore this365// bullet and instead prohibit casts from pointers to cv void (see core-20842366// and core-20845).367//368// - an lvalue-to-rvalue conversion (4.1 [conv.lval]) that is applied to a369// glvalue of type cv1 T that refers to an object of type cv2 U, where T and U370// are neither the same type nor similar types (4.4 [conv.qual]);371 372// - an lvalue-to-rvalue conversion (4.1) that is applied to a glvalue that373// refers to a non-active member of a union or a subobject thereof;374namespace LValueToRValueUnion {375 // test/SemaCXX/constant-expression-cxx11.cpp contains more thorough testing376 // of this.377 union U { int a, b; } constexpr u = U();378 static_assert(u.a == 0, "");379 constexpr const int *bp = &u.b;380 constexpr int b = *bp; // expected-error {{constant expression}} expected-note {{read of member 'b' of union with active member 'a'}}381 382 extern const U pu;383 constexpr const int *pua = &pu.a;384 constexpr const int *pub = &pu.b;385 constexpr U pu = { .b = 1 }; // cxx11-warning {{C++20 extension}}386 constexpr const int a2 = *pua; // expected-error {{constant expression}} expected-note {{read of member 'a' of union with active member 'b'}}387 constexpr const int b2 = *pub; // ok388}389 390// - an id-expression that refers to a variable or data member of reference type391// unless the reference has a preceding initialization, initialized with a392// constant expression;393namespace References {394 const int a = 2;395 int &b = *const_cast<int*>(&a);396 int c = 10; // expected-note 2 {{here}}397 int &d = c;398 constexpr int e = 42;399 int &f = const_cast<int&>(e);400 extern int &g; // expected-note {{here}}401 constexpr int &h(); // expected-note {{here}}402 int &i = h(); // expected-note {{here}}403 constexpr int &j() { return b; }404 int &k = j();405 406 struct S {407 int A : a;408 int B : b;409 int C : c; // expected-error {{constant expression}} expected-note {{read of non-const variable 'c'}}410 int D : d; // expected-error {{constant expression}} expected-note {{read of non-const variable 'c'}}411 int D2 : &d - &c + 1;412 int E : e / 2;413 int F : f - 11;414 int G : g; // expected-error {{constant expression}} expected-note {{initializer of 'g' is unknown}}415 int H : h(); // expected-error {{constant expression}} expected-note {{undefined function 'h'}}416 int I : i; // expected-error {{constant expression}} expected-note {{initializer of 'i' is not a constant expression}}417 int J : j();418 int K : k;419 };420}421 422// - a dynamic_cast (5.2.7);423namespace DynamicCast {424 struct S { int n; };425 constexpr S s { 16 };426 struct T {427 int n : dynamic_cast<const S*>(&s)->n; // cxx11-warning {{constant expression}} cxx11-note {{dynamic_cast}}428 };429}430 431// - a reinterpret_cast (5.2.10);432namespace ReinterpretCast {433 struct S { int n; };434 constexpr S s { 16 };435 struct T {436 int n : reinterpret_cast<const S*>(&s)->n; // expected-warning {{constant expression}} expected-note {{reinterpret_cast}}437 };438 struct U {439 int m : (long)(S*)6; // expected-warning {{constant expression}} expected-note {{reinterpret_cast}}440 };441 void f();442 constexpr void* fp1 = (void*)f; // expected-error {{constant expression}} expected-note {{reinterpret_cast}}443 constexpr int* fp2 = (int*)f; // expected-error {{constant expression}} expected-note {{reinterpret_cast}}444 constexpr int (*fp3)() = (int(*)())f; // expected-error {{constant expression}} expected-note {{reinterpret_cast}}445 constexpr int (&fp4)() = (int(&)())f; // expected-error {{constant expression}} expected-note {{reinterpret_cast}}446}447 448// - a pseudo-destructor call (5.2.4);449namespace PseudoDtor {450 int k;451 typedef int I;452 struct T {453 int n : (k.~I(), 1); // expected-error {{constant expression}} expected-note {{visible outside that expression}}454 };455 456 constexpr int f(int a = 1) { // cxx11-error {{constant expression}} expected-note {{destroying object 'a' whose lifetime has already ended}}457 return (458 a.~I(), // cxx11-note {{pseudo-destructor}}459 0);460 }461 static_assert(f() == 0, ""); // expected-error {{constant expression}}462 463 // This is OK in C++20: the union has no active member after the464 // pseudo-destructor call, so the union destructor has no effect.465 union U { int x; };466 constexpr int g(U u = {1}) { // cxx11-error {{constant expression}}467 return (468 u.x.~I(), // cxx11-note 2{{pseudo-destructor}}469 0);470 }471 static_assert(g() == 0, ""); // cxx11-error {{constant expression}} cxx11-note {{in call}}472}473 474// - increment or decrement operations (5.2.6, 5.3.2);475namespace IncDec {476 int k = 2;477 struct T {478 int n : ++k; // expected-error {{constant expression}} cxx20-note {{visible outside}}479 int m : --k; // expected-error {{constant expression}} cxx20-note {{visible outside}}480 };481}482 483// - a typeid expression (5.2.8) whose operand is of a polymorphic class type;484namespace std {485 struct type_info {486 virtual ~type_info();487 const char *name;488 };489}490namespace TypeId {491 struct S { virtual void f(); };492 constexpr S *p = 0;493 constexpr const std::type_info &ti1 = typeid(*p); // expected-error {{must be initialized by a constant expression}} cxx11-note {{typeid applied to expression of polymorphic type 'S'}} cxx20-note {{dereferencing a null pointer}}494 495 struct T {} t;496 constexpr const std::type_info &ti2 = typeid(t);497}498 499// - a new-expression (5.3.4);500// - a delete-expression (5.3.5);501namespace NewDelete {502 constexpr int *p = 0;503 struct T {504 int n : *new int(4); // expected-warning {{constant expression}} cxx11-note {{until C++20}} cxx20-note {{was not deallocated}}505 int m : (delete p, 2); // cxx11-warning {{constant expression}} cxx11-note {{until C++20}}506 };507}508 509// - a relational (5.9) or equality (5.10) operator where the result is510// unspecified;511namespace UnspecifiedRelations {512 int a, b;513 constexpr int *p = &a, *q = &b;514 // C++11 [expr.rel]p2: If two pointers p and q of the same type point to515 // different objects that are not members of the same array or to different516 // functions, or if only one of them is null, the results of p<q, p>q, p<=q,517 // and p>=q are unspecified.518 constexpr bool u1 = p < q; // expected-error {{constant expression}} expected-note {{comparison between pointers to unrelated objects '&a' and '&b' has unspecified value}}519 constexpr bool u2 = p > q; // expected-error {{constant expression}} expected-note {{comparison between pointers to unrelated objects '&a' and '&b' has unspecified value}}520 constexpr bool u3 = p <= q; // expected-error {{constant expression}} expected-note {{comparison between pointers to unrelated objects '&a' and '&b' has unspecified value}}521 constexpr bool u4 = p >= q; // expected-error {{constant expression}} expected-note {{comparison between pointers to unrelated objects '&a' and '&b' has unspecified value}}522 constexpr bool u5 = p < (int*)0; // expected-error {{constant expression}} expected-note {{comparison between pointers to unrelated objects '&a' and 'nullptr' has unspecified value}}523 constexpr bool u6 = p <= (int*)0; // expected-error {{constant expression}} expected-note {{comparison between pointers to unrelated objects '&a' and 'nullptr' has unspecified value}}524 constexpr bool u7 = p > (int*)0; // expected-error {{constant expression}} expected-note {{comparison between pointers to unrelated objects '&a' and 'nullptr' has unspecified value}}525 constexpr bool u8 = p >= (int*)0; // expected-error {{constant expression}} expected-note {{comparison between pointers to unrelated objects '&a' and 'nullptr' has unspecified value}}526 constexpr bool u9 = (int*)0 < q; // expected-error {{constant expression}} expected-note {{comparison between pointers to unrelated objects 'nullptr' and '&b' has unspecified value}}527 constexpr bool u10 = (int*)0 <= q; // expected-error {{constant expression}} expected-note {{comparison between pointers to unrelated objects 'nullptr' and '&b' has unspecified value}}528 constexpr bool u11 = (int*)0 > q; // expected-error {{constant expression}} expected-note {{comparison between pointers to unrelated objects 'nullptr' and '&b' has unspecified value}}529 constexpr bool u12 = (int*)0 >= q; // expected-error {{constant expression}} expected-note {{comparison between pointers to unrelated objects 'nullptr' and '&b' has unspecified value}}530 void f(), g();531 532 constexpr void (*pf)() = &f, (*pg)() = &g;533 constexpr bool u13 = pf < pg; // expected-error {{constant expression}} expected-note {{comparison between pointers to unrelated objects '&f' and '&g' has unspecified value}}534 // expected-warning@-1 {{ordered comparison of function pointers}}535 constexpr bool u14 = pf == pg;536 537 // If two pointers point to non-static data members of the same object with538 // different access control, the result is unspecified.539 struct A {540 public:541 constexpr A() : a(0), b(0) {}542 int a;543 constexpr bool cmp() const { return &a < &b; } // expected-note {{comparison of address of fields 'a' and 'b' of 'A' with differing access specifiers (public vs private) has unspecified value}}544 private:545 int b;546 };547 static_assert(A().cmp(), ""); // expected-error {{constant expression}} expected-note {{in call}}548 class B {549 public:550 A a;551 constexpr bool cmp() const { return &a.a < &b.a; } // expected-note {{comparison of address of fields 'a' and 'b' of 'B' with differing access specifiers (public vs protected) has unspecified value}}552 protected:553 A b;554 };555 static_assert(B().cmp(), ""); // expected-error {{constant expression}} expected-note {{in call}}556 557 // If two pointers point to different base sub-objects of the same object, or558 // one points to a base subobject and the other points to a member, the result559 // of the comparison is unspecified. This is not explicitly called out by560 // [expr.rel]p2, but is covered by 'Other pointer comparisons are561 // unspecified'.562 struct C {563 int c[2];564 };565 struct D {566 int d;567 };568 struct E : C, D {569 struct Inner {570 int f;571 } e;572 } e;573 constexpr bool base1 = &e.c[0] < &e.d; // expected-error {{constant expression}} expected-note {{comparison of addresses of subobjects of different base classes has unspecified value}}574 constexpr bool base2 = &e.c[1] < &e.e.f; // expected-error {{constant expression}} expected-note {{comparison of address of base class subobject 'C' of class 'E' to field 'e' has unspecified value}}575 constexpr bool base3 = &e.e.f < &e.d; // expected-error {{constant expression}} expected-note {{comparison of address of base class subobject 'D' of class 'E' to field 'e' has unspecified value}}576 577 // [expr.rel]p3: Pointers to void can be compared [...] if both pointers578 // represent the same address or are both the null pointer [...]; otherwise579 // the result is unspecified.580 // Same address restriction removed by CWG2749581 struct S { int a, b; } s;582 constexpr void *null = 0;583 constexpr void *pv = (void*)&s.a;584 constexpr void *qv = (void*)&s.b;585 constexpr bool v1 = null < (int*)0;586 constexpr bool v2 = null < pv; // expected-error {{constant expression}} expected-note {{comparison between pointers to unrelated objects 'nullptr' and '&s.a' has unspecified value}}587 constexpr bool v3 = null == pv;588 constexpr bool v4 = qv == pv;589 constexpr bool v5 = qv >= pv;590 constexpr bool v6 = qv > null; // expected-error {{constant expression}} expected-note {{comparison between pointers to unrelated objects '&s.b' and 'nullptr' has unspecified value}}591 constexpr bool v7 = qv <= (void*)&s.b;592 constexpr bool v8 = qv > (void*)&s.a;593}594 595// - an assignment or a compound assignment (5.17); or596namespace Assignment {597 int k;598 struct T {599 int n : (k = 9); // expected-error {{constant expression}} cxx20-note {{visible outside}}600 int m : (k *= 2); // expected-error {{constant expression}} cxx20-note {{visible outside}}601 };602 603 struct Literal {604 constexpr Literal(const char *name) : name(name) {}605 const char *name;606 };607 struct Expr {608 constexpr Expr(Literal l) : IsLiteral(true), l(l) {}609 bool IsLiteral;610 union {611 Literal l;612 // ...613 };614 };615 struct MulEq {616 constexpr MulEq(Expr a, Expr b) : LHS(a), RHS(b) {}617 Expr LHS;618 Expr RHS;619 };620 constexpr MulEq operator*=(Expr a, Expr b) { return MulEq(a, b); }621 Literal a("a");622 Literal b("b");623 MulEq c = a *= b; // ok624}625 626// - a throw-expression (15.1)627namespace Throw {628 struct S {629 int n : (throw "hello", 10); // expected-error {{constant expression}}630 };631}632 633// PR9999634template<unsigned int v>635class bitWidthHolding {636public:637 static const638 unsigned int width = (v == 0 ? 0 : bitWidthHolding<(v >> 1)>::width + 1);639};640 641static const int width=bitWidthHolding<255>::width;642 643template<bool b>644struct always_false {645 static const bool value = false;646};647 648template<bool b>649struct and_or {650 static const bool and_value = b && and_or<always_false<b>::value>::and_value;651 static const bool or_value = !b || and_or<always_false<b>::value>::or_value;652};653 654static const bool and_value = and_or<true>::and_value;655static const bool or_value = and_or<true>::or_value;656 657static_assert(and_value == false, "");658static_assert(or_value == true, "");659 660namespace rdar13090123 {661 typedef __INTPTR_TYPE__ intptr_t;662 663 constexpr intptr_t f(intptr_t x) {664 return (((x) >> 21) * 8);665 }666 667 extern "C" int foo;668 669 constexpr intptr_t i = f((intptr_t)&foo - 10); // expected-error{{constexpr variable 'i' must be initialized by a constant expression}} \670 // expected-note{{reinterpret_cast}}671}672