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<base href="https://bugs.llvm.org/">
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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - Incorrect initialization of static data members in recursive class templates"
href="https://bugs.llvm.org/show_bug.cgi?id=49458">49458</a>
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<th>Summary</th>
<td>Incorrect initialization of static data members in recursive class templates
</td>
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<th>Product</th>
<td>clang
</td>
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<th>Version</th>
<td>trunk
</td>
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<th>Hardware</th>
<td>PC
</td>
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<th>OS</th>
<td>Linux
</td>
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<th>Status</th>
<td>NEW
</td>
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<th>Severity</th>
<td>normal
</td>
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<th>Priority</th>
<td>P
</td>
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<th>Component</th>
<td>C++
</td>
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<th>Assignee</th>
<td>unassignedclangbugs@nondot.org
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<th>Reporter</th>
<td>maltsevm@gmail.com
</td>
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<th>CC</th>
<td>blitzrakete@gmail.com, dgregor@apple.com, erik.pilkington@gmail.com, llvm-bugs@lists.llvm.org, richard-llvm@metafoo.co.uk
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<div>
<pre>When the following code is compiled with Clang and run, it produces an
assertion failure:
$ cat test.cpp
#include <assert.h>
template <int x, int y>
struct GCD {
static int value;
};
template <int x, int y>
int GCD<x, y>::value = GCD<y, x % y>::value;
template<int x>
struct GCD<x, 0> {
static int value;
};
template<int x>
int GCD<x, 0>::value = x;
int main() {
assert((GCD<9, 6>::value) == 3);
}
$ clang test.cpp
$ ./a.out
a.out: test.cpp:20: int main(): Assertion `(GCD<9, 6>::value) == 3' failed.
Aborted (core dumped)
>From the generated LLVM IR it is clear that GCD<3, 0>::value is initialized in
the data section, whereas GCD<9, 6>::value and GCD<6, 3>::value initially have
value zero and are initialized at run time. The order of initialization however
is incorrect (according to my understanding of
<a href="http://eel.is/c++draft/temp.point#4">http://eel.is/c++draft/temp.point#4</a>), as if was performed using the following
code:
GCD<9, 6>::value = GCD<6, 3>::value;
GCD<6, 3>::value = GCD<3, 0>::value;
The program works as expected when compiled with GCC.</pre>
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