caa902613a
[[expr.const]/5.14](https://eel.is/c++draft/expr.const#5.14) says that constexpr cast from <code>*cv* void\*</code> to `T*` is OK if the pointee type is similar to `T`, but Clang currently only permits the conversion if the types are the same except top-level cv-qualifiers. This patch also allows casting `(void*)nullptr`, implementing the resolution of [CWG2819](https://cplusplus.github.io/CWG/issues/2819). --------- Co-authored-by: Vlad Serebrennikov <serebrennikov.vladislav@gmail.com>
47 lines
2.2 KiB
C++
47 lines
2.2 KiB
C++
// RUN: %clang_cc1 -fsyntax-only -std=c++2c -verify=expected,cxx26 %s
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// RUN: %clang_cc1 -fsyntax-only -std=c++2b -verify=expected,cxx23 %s
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struct S {};
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struct T : S {} t;
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consteval void test() {
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void* a = &t;
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const void* b = &t;
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volatile void* c = &t;
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(void)static_cast<T*>(a);
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(void)static_cast<const T*>(a);
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(void)static_cast<volatile T*>(a);
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(void)(T*)(a);
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(void)(const T*)(a);
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(void)(volatile T*)(a);
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(void)static_cast<T*>(b); // expected-error {{static_cast from 'const void *' to 'T *' casts away qualifiers}}
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(void)static_cast<volatile T*>(b); // expected-error {{static_cast from 'const void *' to 'volatile T *' casts away qualifiers}}
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(void)static_cast<const T*>(b);
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(void)static_cast<volatile const T*>(b);
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(void)static_cast<T*>(c); // expected-error{{static_cast from 'volatile void *' to 'T *' casts away qualifiers}}
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(void)static_cast<volatile T*>(c);
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(void)static_cast<const T*>(b);
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(void)static_cast<volatile const T*>(b);
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}
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void err() {
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constexpr void* a = &t;
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constexpr auto err1 = static_cast<int*>(a); // expected-error{{constexpr variable 'err1' must be initialized by a constant expression}} \
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// cxx23-note {{cast from 'void *' is not allowed in a constant expression in C++ standards before C++2c}} \
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// cxx26-note {{cast from 'void *' is not allowed in a constant expression because the pointed object type 'T' is not similar to the target type 'int'}}
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constexpr auto err2 = static_cast<S*>(a); // expected-error{{constexpr variable 'err2' must be initialized by a constant expression}} \
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// cxx23-note {{cast from 'void *' is not allowed in a constant expression in C++ standards before C++2c}} \
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// cxx26-note {{cast from 'void *' is not allowed in a constant expression because the pointed object type 'T' is not similar to the target type 'S'}}
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}
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int* p;
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constexpr int** pp = &p;
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constexpr void* vp = pp;
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constexpr auto cvp = static_cast<const int* volatile*>(vp);
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// cxx23-error@-1 {{constant expression}}
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// cxx23-note@-2 {{cast from 'void *' is not allowed in a constant expression}}
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