https://llvm.org/bugs/show_bug.cgi?id=25736
Bug ID: 25736
Summary: constexpr allows uninitialized variables
Product: clang
Version: 3.7
Hardware: PC
OS: Linux
Status: NEW
Severity: normal
Priority: P
Component: C++14
Assignee: unassignedclangb...@nondot.org
Reporter: tomilovanato...@gmail.com
CC: llvm-bugs@lists.llvm.org
Classification: Unclassified
Given a code:
#include <type_traits>
struct A { int i; };
template< typename type >
struct C { constexpr C() = default; type a; };
struct V { V() = default; C< A > d; };
constexpr bool test()
{
V v;
static_assert(std::is_trivially_default_constructible< V >::value,
"!");
return (v.d.a.i == 0);
}
static_assert(test(), "!");
It compiles without errors by `clang`. Compilation by `g++` failed with error:
main.cpp: In function 'constexpr bool test()':
main.cpp:12:11: error: uninitialized variable 'v' in 'constexpr' function
V v;
^
main.cpp:8:12: note: 'struct V' has no user-provided default constructor
struct V { V() = default; C< A > d; };
^
main.cpp:8:16: note: constructor is not user-provided because it is explicitly
defaulted in the class body
struct V { V() = default; C< A > d; };
^
main.cpp:3:20: note: and the implicitly-defined constructor does not initialize
'int A::i'
struct A { int i; };
^
main.cpp: At global scope:
main.cpp:17:5: error: non-constant condition for static assertion
static_assert(test(), "!");
^
main.cpp:17:23: error: 'constexpr bool test()' called in a constant expression
static_assert(test(), "!");
^
If I remove `template`s and substitute `A` directly, then `clang` sees
uninitialized during default construction variables.
If I remove `constexpr` specifier of `C::C()` default constructor, then `clang`
also sees wrong things.
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