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<base href="https://llvm.org/bugs/" />
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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW --- - constexpr allows uninitialized variables"
href="https://llvm.org/bugs/show_bug.cgi?id=25736">25736</a>
</td>
</tr>
<tr>
<th>Summary</th>
<td>constexpr allows uninitialized variables
</td>
</tr>
<tr>
<th>Product</th>
<td>clang
</td>
</tr>
<tr>
<th>Version</th>
<td>3.7
</td>
</tr>
<tr>
<th>Hardware</th>
<td>PC
</td>
</tr>
<tr>
<th>OS</th>
<td>Linux
</td>
</tr>
<tr>
<th>Status</th>
<td>NEW
</td>
</tr>
<tr>
<th>Severity</th>
<td>normal
</td>
</tr>
<tr>
<th>Priority</th>
<td>P
</td>
</tr>
<tr>
<th>Component</th>
<td>C++14
</td>
</tr>
<tr>
<th>Assignee</th>
<td>unassignedclangbugs@nondot.org
</td>
</tr>
<tr>
<th>Reporter</th>
<td>tomilovanatoliy@gmail.com
</td>
</tr>
<tr>
<th>CC</th>
<td>llvm-bugs@lists.llvm.org
</td>
</tr>
<tr>
<th>Classification</th>
<td>Unclassified
</td>
</tr></table>
<p>
<div>
<pre>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.</pre>
</div>
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