// RUN: %clang_cc1 -fsyntax-only -std=c++11 -pedantic -verify -fcxx-exceptions %s -fconstexpr-depth 128 -triple i686-pc-linux-gnu // A conditional-expression is a core constant expression unless it involves one // of the following as a potentially evaluated subexpression [...]: // - this (5.1.1 [expr.prim.general]) [Note: when evaluating a constant // expression, function invocation substitution (7.1.5 [dcl.constexpr]) // replaces each occurrence of this in a constexpr member function with a // pointer to the class object. -end note]; struct This { int this1 : this1; // expected-error {{undeclared}} int this2 : this->this1; // expected-error {{invalid}} void this3() { int n1[this->this1]; // expected-warning {{variable length array}} int n2[this1]; // expected-warning {{variable length array}} (void)n1, (void)n2; } }; // - an invocation of a function other than a constexpr constructor for a // literal class or a constexpr function [ Note: Overload resolution (13.3) // is applied as usual - end note ]; struct NonConstexpr1 { static int f() { return 1; } // expected-note {{here}} int n : f(); // expected-error {{constant expression}} expected-note {{non-constexpr function 'f' cannot be used in a constant expression}} }; struct NonConstexpr2 { constexpr NonConstexpr2(); // expected-note {{here}} int n; }; struct NonConstexpr3 { NonConstexpr3(); int m : NonConstexpr2().n; // expected-error {{constant expression}} expected-note {{undefined constructor 'NonConstexpr2'}} }; struct NonConstexpr4 { NonConstexpr4(); // expected-note {{declared here}} int n; }; struct NonConstexpr5 { int n : NonConstexpr4().n; // expected-error {{constant expression}} expected-note {{non-constexpr constructor 'NonConstexpr4' cannot be used in a constant expression}} }; // - an invocation of an undefined constexpr function or an undefined // constexpr constructor; struct UndefinedConstexpr { constexpr UndefinedConstexpr(); static constexpr int undefinedConstexpr1(); // expected-note {{here}} int undefinedConstexpr2 : undefinedConstexpr1(); // expected-error {{constant expression}} expected-note {{undefined function 'undefinedConstexpr1' cannot be used in a constant expression}} }; // - an invocation of a constexpr function with arguments that, when substituted // by function invocation substitution (7.1.5), do not produce a core constant // expression; namespace NonConstExprReturn { static constexpr const int &id_ref(const int &n) { return n; } struct NonConstExprFunction { int n : id_ref(16); // ok }; constexpr const int *address_of(const int &a) { return &a; } constexpr const int *return_param(int n) { // expected-note {{declared here}} return address_of(n); } struct S { int n : *return_param(0); // expected-error {{constant expression}} expected-note {{read of variable whose lifetime has ended}} }; } // - an invocation of a constexpr constructor with arguments that, when // substituted by function invocation substitution (7.1.5), do not produce all // constant expressions for the constructor calls and full-expressions in the // mem-initializers (including conversions); namespace NonConstExprCtor { struct T { constexpr T(const int &r) : r(r) { } const int &r; }; constexpr int n = 0; constexpr T t1(n); // ok 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}} struct S { int n : T(4).r; // ok }; } // - an invocation of a constexpr function or a constexpr constructor that would // exceed the implementation-defined recursion limits (see Annex B); namespace RecursionLimits { constexpr int RecurseForever(int n) { 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}} } struct AlsoRecurseForever { constexpr AlsoRecurseForever(int n) : 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}} {} int n; }; struct S { int k : RecurseForever(0); // expected-error {{constant expression}} expected-note {{in call to}} int l : AlsoRecurseForever(0).n; // expected-error {{constant expression}} expected-note {{in call to}} }; } // DR1458: taking the address of an object of incomplete class type namespace IncompleteClassTypeAddr { struct S; extern S s; constexpr S *p = &s; // ok static_assert(p, ""); extern S sArr[]; constexpr S (*p2)[] = &sArr; // ok struct S { constexpr S *operator&() const { return nullptr; } }; constexpr S *q = &s; // ok static_assert(!q, ""); } // - an operation that would have undefined behavior [Note: including, for // example, signed integer overflow (Clause 5 [expr]), certain pointer // arithmetic (5.7 [expr.add]), division by zero (5.6 [expr.mul]), or certain // shift operations (5.8 [expr.shift]) -end note]; namespace UndefinedBehavior { void f(int n) { switch (n) { case (int)4.4e9: // expected-error {{constant expression}} expected-note {{value 4.4E+9 is outside the range of representable values of type 'int'}} expected-note {{previous case defined here}} case (int)0x80000000u: // ok case (int)10000000000ll: // expected-note {{here}} case (unsigned int)10000000000ll: // expected-error {{duplicate case value}} case (int)(unsigned)(long long)4.4e9: // ok case (int)(float)1e300: // expected-error {{constant expression}} expected-note {{value 1.0E+300 is outside the range of representable values of type 'float'}} expected-error {{duplicate case value '2147483647'}} expected-note {{previous case defined here}} case (int)((float)1e37 / 1e30): // ok case (int)(__fp16)65536: // expected-error {{constant expression}} expected-note {{value 65536 is outside the range of representable values of type '__fp16'}} expected-error {{duplicate case value '2147483647'}} break; } } constexpr int int_min = ~0x7fffffff; constexpr int minus_int_min = -int_min; // expected-error {{constant expression}} expected-note {{value 2147483648 is outside the range}} constexpr int div0 = 3 / 0; // expected-error {{constant expression}} expected-note {{division by zero}} expected-warning {{undefined}} constexpr int mod0 = 3 % 0; // expected-error {{constant expression}} expected-note {{division by zero}} expected-warning {{undefined}} constexpr int int_min_div_minus_1 = int_min / -1; // expected-error {{constant expression}} expected-note {{value 2147483648 is outside the range}} constexpr int int_min_mod_minus_1 = int_min % -1; // expected-error {{constant expression}} expected-note {{value 2147483648 is outside the range}} constexpr int shl_m1 = 0 << -1; // expected-error {{constant expression}} expected-note {{negative shift count -1}} expected-warning {{negative}} constexpr int shl_0 = 0 << 0; // ok constexpr int shl_31 = 0 << 31; // ok constexpr int shl_32 = 0 << 32; // expected-error {{constant expression}} expected-note {{shift count 32 >= width of type 'int' (32}} expected-warning {{>= width of type}} constexpr int shl_unsigned_negative = unsigned(-3) << 1; // ok constexpr int shl_unsigned_into_sign = 1u << 31; // ok constexpr int shl_unsigned_overflow = 1024u << 31; // ok constexpr int shl_signed_negative = (-3) << 1; // expected-error {{constant expression}} expected-note {{left shift of negative value -3}} constexpr int shl_signed_ok = 1 << 30; // ok constexpr int shl_signed_into_sign = 1 << 31; // ok (DR1457) constexpr int shl_signed_into_sign_2 = 0x7fffffff << 1; // ok (DR1457) constexpr int shl_signed_off_end = 2 << 31; // expected-error {{constant expression}} expected-note {{signed left shift discards bits}} expected-warning {{signed shift result (0x100000000) requires 34 bits to represent, but 'int' only has 32 bits}} constexpr int shl_signed_off_end_2 = 0x7fffffff << 2; // expected-error {{constant expression}} expected-note {{signed left shift discards bits}} expected-warning {{signed shift result (0x1FFFFFFFC) requires 34 bits to represent, but 'int' only has 32 bits}} constexpr int shl_signed_overflow = 1024 << 31; // expected-error {{constant expression}} expected-note {{signed left shift discards bits}} expected-warning {{requires 43 bits to represent}} constexpr int shl_signed_ok2 = 1024 << 20; // ok constexpr int shr_m1 = 0 >> -1; // expected-error {{constant expression}} expected-note {{negative shift count -1}} expected-warning {{negative}} constexpr int shr_0 = 0 >> 0; // ok constexpr int shr_31 = 0 >> 31; // ok constexpr int shr_32 = 0 >> 32; // expected-error {{constant expression}} expected-note {{shift count 32 >= width of type}} expected-warning {{>= width of type}} struct S { int m; }; constexpr S s = { 5 }; constexpr const int *p = &s.m + 1; constexpr const int &f(const int *q) { return q[0]; } constexpr int n = (f(p), 0); // ok struct T { int n : f(p); // expected-error {{not an integral constant expression}} expected-note {{read of dereferenced one-past-the-end pointer}} }; namespace Ptr { struct A {}; struct B : A { int n; }; B a[3][3]; constexpr B *p = a[0] + 4; // expected-error {{constant expression}} expected-note {{element 4 of array of 3 elements}} B b = {}; constexpr A *pa = &b + 1; // expected-error {{constant expression}} expected-note {{base class of pointer past the end}} constexpr B *pb = (B*)((A*)&b + 1); // expected-error {{constant expression}} expected-note {{derived class of pointer past the end}} constexpr const int *pn = &(&b + 1)->n; // expected-error {{constant expression}} expected-note {{field of pointer past the end}} constexpr B *parr = &a[3][0]; // expected-error {{constant expression}} expected-note {{array element of pointer past the end}} constexpr A *na = nullptr; constexpr B *nb = nullptr; constexpr A &ra = *nb; // expected-error {{constant expression}} expected-note {{cannot access base class of null pointer}} constexpr B &rb = (B&)*na; // expected-error {{constant expression}} expected-note {{cannot access derived class of null pointer}} static_assert((A*)nb == 0, ""); static_assert((B*)na == 0, ""); constexpr const int &nf = nb->n; // expected-error {{constant expression}} expected-note {{cannot access field of null pointer}} constexpr const int *np1 = (int*)nullptr + 0; // ok constexpr const int *np2 = &(*(int(*)[4])nullptr)[0]; // ok constexpr const int *np3 = &(*(int(*)[4])nullptr)[2]; // expected-error {{constant expression}} expected-note {{cannot perform pointer arithmetic on null pointer}} struct C { constexpr int f() const { return 0; } } constexpr c = C(); constexpr int k1 = c.f(); // ok constexpr int k2 = ((C*)nullptr)->f(); // expected-error {{constant expression}} expected-note {{cannot call member function on null pointer}} constexpr int k3 = (&c)[1].f(); // expected-error {{constant expression}} expected-note {{cannot call member function on pointer past the end of object}} C c2; constexpr int k4 = c2.f(); // ok! constexpr int diff1 = &a[2] - &a[0]; constexpr int diff2 = &a[1][3] - &a[1][0]; constexpr int diff3 = &a[2][0] - &a[1][0]; // expected-error {{constant expression}} expected-note {{subtracted pointers are not elements of the same array}} static_assert(&a[2][0] == &a[1][3], ""); constexpr int diff4 = (&b + 1) - &b; 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}} constexpr int diff6 = &a[1][2].n - &a[1][2].n; 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}} } namespace Overflow { // Signed int overflow. constexpr int n1 = 2 * 3 * 3 * 7 * 11 * 31 * 151 * 331; // ok constexpr int n2 = 65536 * 32768; // expected-error {{constant expression}} expected-note {{value 2147483648 is outside the range of }} constexpr int n3 = n1 + 1; // ok constexpr int n4 = n3 + 1; // expected-error {{constant expression}} expected-note {{value 2147483648 is outside the range of }} constexpr int n5 = -65536 * 32768; // ok constexpr int n6 = 3 * -715827883; // expected-error {{constant expression}} expected-note {{value -2147483649 is outside the range of }} constexpr int n7 = -n3 + -1; // ok constexpr int n8 = -1 + n7; // expected-error {{constant expression}} expected-note {{value -2147483649 is outside the range of }} constexpr int n9 = n3 - 0; // ok constexpr int n10 = n3 - -1; // expected-error {{constant expression}} expected-note {{value 2147483648 is outside the range of }} constexpr int n11 = -1 - n3; // ok constexpr int n12 = -2 - n3; // expected-error {{constant expression}} expected-note {{value -2147483649 is outside the range of }} constexpr int n13 = n5 + n5; // expected-error {{constant expression}} expected-note {{value -4294967296 is outside the range of }} constexpr int n14 = n3 - n5; // expected-error {{constant expression}} expected-note {{value 4294967295 is outside the range of }} constexpr int n15 = n5 * n5; // expected-error {{constant expression}} expected-note {{value 4611686018427387904 is outside the range of }} constexpr signed char c1 = 100 * 2; // ok constexpr signed char c2 = '\x64' * '\2'; // also ok constexpr long long ll1 = 0x7fffffffffffffff; // ok constexpr long long ll2 = ll1 + 1; // expected-error {{constant}} expected-note {{ 9223372036854775808 }} constexpr long long ll3 = -ll1 - 1; // ok constexpr long long ll4 = ll3 - 1; // expected-error {{constant}} expected-note {{ -9223372036854775809 }} constexpr long long ll5 = ll3 * ll3; // expected-error {{constant}} expected-note {{ 85070591730234615865843651857942052864 }} // Yikes. char melchizedek[2200000000]; typedef decltype(melchizedek[1] - melchizedek[0]) ptrdiff_t; constexpr ptrdiff_t d1 = &melchizedek[0x7fffffff] - &melchizedek[0]; // ok constexpr ptrdiff_t d2 = &melchizedek[0x80000000u] - &melchizedek[0]; // expected-error {{constant expression}} expected-note {{ 2147483648 }} constexpr ptrdiff_t d3 = &melchizedek[0] - &melchizedek[0x80000000u]; // ok constexpr ptrdiff_t d4 = &melchizedek[0] - &melchizedek[0x80000001u]; // expected-error {{constant expression}} expected-note {{ -2147483649 }} // Unsigned int overflow. static_assert(65536u * 65536u == 0u, ""); // ok static_assert(4294967295u + 1u == 0u, ""); // ok static_assert(0u - 1u == 4294967295u, ""); // ok static_assert(~0u * ~0u == 1u, ""); // ok // Floating-point overflow and NaN. constexpr float f1 = 1e38f * 3.4028f; // ok constexpr float f2 = 1e38f * 3.4029f; // expected-error {{constant expression}} expected-note {{floating point arithmetic produces an infinity}} constexpr float f3 = 1e38f / -.2939f; // ok constexpr float f4 = 1e38f / -.2938f; // expected-error {{constant expression}} expected-note {{floating point arithmetic produces an infinity}} constexpr float f5 = 2e38f + 2e38f; // expected-error {{constant expression}} expected-note {{floating point arithmetic produces an infinity}} constexpr float f6 = -2e38f - 2e38f; // expected-error {{constant expression}} expected-note {{floating point arithmetic produces an infinity}} constexpr float f7 = 0.f / 0.f; // expected-error {{constant expression}} expected-note {{floating point arithmetic produces a NaN}} } } // - a lambda-expression (5.1.2); struct Lambda { int n : []{ return 1; }(); // expected-error {{constant expression}} expected-error {{integral constant expression}} }; // - an lvalue-to-rvalue conversion (4.1) unless it is applied to namespace LValueToRValue { // - a non-volatile glvalue of integral or enumeration type that refers to a // non-volatile const object with a preceding initialization, initialized // with a constant expression [Note: a string literal (2.14.5 [lex.string]) // corresponds to an array of such objects. -end note], or volatile const int vi = 1; // expected-note 2{{here}} const int ci = 1; volatile const int &vrci = ci; static_assert(vi, ""); // expected-error {{constant expression}} expected-note {{read of volatile-qualified type}} static_assert(const_cast<int&>(vi), ""); // expected-error {{constant expression}} expected-note {{read of volatile object 'vi'}} static_assert(vrci, ""); // expected-error {{constant expression}} expected-note {{read of volatile-qualified type}} // - a non-volatile glvalue of literal type that refers to a non-volatile // object defined with constexpr, or that refers to a sub-object of such an // object, or struct V { constexpr V() : v(1) {} volatile int v; // expected-note {{not literal because}} }; constexpr V v; // expected-error {{non-literal type}} struct S { constexpr S(int=0) : i(1), v(const_cast<volatile int&>(vi)) {} constexpr S(const S &s) : i(2), v(const_cast<volatile int&>(vi)) {} int i; volatile int &v; }; constexpr S s; // ok constexpr volatile S vs; // expected-note {{here}} constexpr const volatile S &vrs = s; // ok static_assert(s.i, ""); static_assert(s.v, ""); // expected-error {{constant expression}} expected-note {{read of volatile-qualified type}} static_assert(const_cast<int&>(s.v), ""); // expected-error {{constant expression}} expected-note {{read of volatile object 'vi'}} static_assert(vs.i, ""); // expected-error {{constant expression}} expected-note {{read of volatile-qualified type}} static_assert(const_cast<int&>(vs.i), ""); // expected-error {{constant expression}} expected-note {{read of volatile object 'vs'}} static_assert(vrs.i, ""); // expected-error {{constant expression}} expected-note {{read of volatile-qualified type}} // - a non-volatile glvalue of literal type that refers to a non-volatile // temporary object whose lifetime has not ended, initialized with a // constant expression; constexpr volatile S f() { return S(); } static_assert(f().i, ""); // ok! there's no lvalue-to-rvalue conversion here! static_assert(((volatile const S&&)(S)0).i, ""); // expected-error {{constant expression}} expected-note {{read of volatile-qualified type}} } // DR1312: The proposed wording for this defect has issues, so we ignore this // bullet and instead prohibit casts from pointers to cv void (see core-20842 // and core-20845). // // - an lvalue-to-rvalue conversion (4.1 [conv.lval]) that is applied to a // glvalue of type cv1 T that refers to an object of type cv2 U, where T and U // are neither the same type nor similar types (4.4 [conv.qual]); // - an lvalue-to-rvalue conversion (4.1) that is applied to a glvalue that // refers to a non-active member of a union or a subobject thereof; namespace LValueToRValueUnion { // test/SemaCXX/constant-expression-cxx11.cpp contains more thorough testing // of this. union U { int a, b; } constexpr u = U(); static_assert(u.a == 0, ""); constexpr const int *bp = &u.b; constexpr int b = *bp; // expected-error {{constant expression}} expected-note {{read of member 'b' of union with active member 'a'}} extern const U pu; constexpr const int *pua = &pu.a; constexpr const int *pub = &pu.b; constexpr U pu = { .b = 1 }; // expected-warning {{C99 feature}} constexpr const int a2 = *pua; // expected-error {{constant expression}} expected-note {{read of member 'a' of union with active member 'b'}} constexpr const int b2 = *pub; // ok } // - an id-expression that refers to a variable or data member of reference type // unless the reference has a preceding initialization, initialized with a // constant expression; namespace References { const int a = 2; int &b = *const_cast<int*>(&a); int c = 10; // expected-note 2 {{here}} int &d = c; constexpr int e = 42; int &f = const_cast<int&>(e); extern int &g; constexpr int &h(); // expected-note {{here}} int &i = h(); // expected-note {{here}} constexpr int &j() { return b; } int &k = j(); struct S { int A : a; int B : b; int C : c; // expected-error {{constant expression}} expected-note {{read of non-const variable 'c'}} int D : d; // expected-error {{constant expression}} expected-note {{read of non-const variable 'c'}} int D2 : &d - &c + 1; int E : e / 2; int F : f - 11; int G : g; // expected-error {{constant expression}} int H : h(); // expected-error {{constant expression}} expected-note {{undefined function 'h'}} int I : i; // expected-error {{constant expression}} expected-note {{initializer of 'i' is not a constant expression}} int J : j(); int K : k; }; } // - a dynamic_cast (5.2.7); namespace DynamicCast { struct S { int n; }; constexpr S s { 16 }; struct T { int n : dynamic_cast<const S*>(&s)->n; // expected-warning {{constant expression}} expected-note {{dynamic_cast}} }; } // - a reinterpret_cast (5.2.10); namespace ReinterpretCast { struct S { int n; }; constexpr S s { 16 }; struct T { int n : reinterpret_cast<const S*>(&s)->n; // expected-warning {{constant expression}} expected-note {{reinterpret_cast}} }; struct U { int m : (long)(S*)6; // expected-warning {{constant expression}} expected-note {{reinterpret_cast}} }; } // - a pseudo-destructor call (5.2.4); namespace PseudoDtor { int k; typedef int I; struct T { int n : (k.~I(), 0); // expected-error {{constant expression}} }; } // - increment or decrement operations (5.2.6, 5.3.2); namespace IncDec { int k = 2; struct T { int n : ++k; // expected-error {{constant expression}} int m : --k; // expected-error {{constant expression}} }; } // - a typeid expression (5.2.8) whose operand is of a polymorphic class type; namespace std { struct type_info { virtual ~type_info(); const char *name; }; } namespace TypeId { struct S { virtual void f(); }; constexpr S *p = 0; constexpr const std::type_info &ti1 = typeid(*p); // expected-error {{must be initialized by a constant expression}} expected-note {{typeid applied to expression of polymorphic type 'TypeId::S'}} struct T {} t; constexpr const std::type_info &ti2 = typeid(t); } // - a new-expression (5.3.4); // - a delete-expression (5.3.5); namespace NewDelete { int *p = 0; struct T { int n : *new int(4); // expected-error {{constant expression}} int m : (delete p, 2); // expected-error {{constant expression}} }; } // - a relational (5.9) or equality (5.10) operator where the result is // unspecified; namespace UnspecifiedRelations { int a, b; constexpr int *p = &a, *q = &b; // C++11 [expr.rel]p2: If two pointers p and q of the same type point to // different objects that are not members of the same array or to different // functions, or if only one of them is null, the results of p<q, p>q, p<=q, // and p>=q are unspecified. constexpr bool u1 = p < q; // expected-error {{constant expression}} constexpr bool u2 = p > q; // expected-error {{constant expression}} constexpr bool u3 = p <= q; // expected-error {{constant expression}} constexpr bool u4 = p >= q; // expected-error {{constant expression}} constexpr bool u5 = p < 0; // expected-error {{constant expression}} constexpr bool u6 = p <= 0; // expected-error {{constant expression}} constexpr bool u7 = p > 0; // expected-error {{constant expression}} constexpr bool u8 = p >= 0; // expected-error {{constant expression}} constexpr bool u9 = 0 < q; // expected-error {{constant expression}} constexpr bool u10 = 0 <= q; // expected-error {{constant expression}} constexpr bool u11 = 0 > q; // expected-error {{constant expression}} constexpr bool u12 = 0 >= q; // expected-error {{constant expression}} void f(), g(); constexpr void (*pf)() = &f, (*pg)() = &g; constexpr bool u13 = pf < pg; // expected-error {{constant expression}} constexpr bool u14 = pf == pg; // If two pointers point to non-static data members of the same object with // different access control, the result is unspecified. struct A { public: constexpr A() : a(0), b(0) {} int a; 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}} private: int b; }; static_assert(A().cmp(), ""); // expected-error {{constant expression}} expected-note {{in call}} class B { public: A a; 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}} protected: A b; }; static_assert(B().cmp(), ""); // expected-error {{constant expression}} expected-note {{in call}} // If two pointers point to different base sub-objects of the same object, or // one points to a base subobject and the other points to a member, the result // of the comparison is unspecified. This is not explicitly called out by // [expr.rel]p2, but is covered by 'Other pointer comparisons are // unspecified'. struct C { int c[2]; }; struct D { int d; }; struct E : C, D { struct Inner { int f; } e; } e; 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}} 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}} 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}} // [expr.rel]p3: Pointers to void can be compared [...] if both pointers // represent the same address or are both the null pointer [...]; otherwise // the result is unspecified. struct S { int a, b; } s; constexpr void *null = 0; constexpr void *pv = (void*)&s.a; constexpr void *qv = (void*)&s.b; constexpr bool v1 = null < 0; constexpr bool v2 = null < pv; // expected-error {{constant expression}} constexpr bool v3 = null == pv; // ok constexpr bool v4 = qv == pv; // ok constexpr bool v5 = qv >= pv; // expected-error {{constant expression}} expected-note {{unequal pointers to void}} constexpr bool v6 = qv > null; // expected-error {{constant expression}} constexpr bool v7 = qv <= (void*)&s.b; // ok constexpr bool v8 = qv > (void*)&s.a; // expected-error {{constant expression}} expected-note {{unequal pointers to void}} } // - an assignment or a compound assignment (5.17); or namespace Assignment { int k; struct T { int n : (k = 9); // expected-error {{constant expression}} int m : (k *= 2); // expected-error {{constant expression}} }; struct Literal { constexpr Literal(const char *name) : name(name) {} const char *name; }; struct Expr { constexpr Expr(Literal l) : IsLiteral(true), l(l) {} bool IsLiteral; union { Literal l; // ... }; }; struct MulEq { constexpr MulEq(Expr a, Expr b) : LHS(a), RHS(b) {} Expr LHS; Expr RHS; }; constexpr MulEq operator*=(Expr a, Expr b) { return MulEq(a, b); } Literal a("a"); Literal b("b"); MulEq c = a *= b; // ok } // - a throw-expression (15.1) namespace Throw { struct S { int n : (throw "hello", 10); // expected-error {{constant expression}} }; } // PR9999 template<unsigned int v> class bitWidthHolding { public: static const unsigned int width = (v == 0 ? 0 : bitWidthHolding<(v >> 1)>::width + 1); }; static const int width=bitWidthHolding<255>::width; template<bool b> struct always_false { static const bool value = false; }; template<bool b> struct and_or { static const bool and_value = b && and_or<always_false<b>::value>::and_value; static const bool or_value = !b || and_or<always_false<b>::value>::or_value; }; static const bool and_value = and_or<true>::and_value; static const bool or_value = and_or<true>::or_value; static_assert(and_value == false, ""); static_assert(or_value == true, ""); namespace rdar13090123 { typedef __INTPTR_TYPE__ intptr_t; constexpr intptr_t f(intptr_t x) { return (((x) >> 21) * 8); // expected-note{{subexpression not valid in a constant expression}} } extern "C" int foo; constexpr intptr_t i = f((intptr_t)&foo - 10); // expected-error{{constexpr variable 'i' must be initialized by a constant expression}} \ // expected-note{{in call to 'f((char*)&foo + -10)'}} }