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<head>
<base href="http://llvm.org/bugs/" />
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<body><table border="1" cellspacing="0" cellpadding="8">
<tr>
<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW --- - clang fails to compile code with member constexpr functions"
href="http://llvm.org/bugs/show_bug.cgi?id=20219">20219</a>
</td>
</tr>
<tr>
<th>Summary</th>
<td>clang fails to compile code with member constexpr functions
</td>
</tr>
<tr>
<th>Product</th>
<td>clang
</td>
</tr>
<tr>
<th>Version</th>
<td>3.4
</td>
</tr>
<tr>
<th>Hardware</th>
<td>Macintosh
</td>
</tr>
<tr>
<th>OS</th>
<td>MacOS X
</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++1y
</td>
</tr>
<tr>
<th>Assignee</th>
<td>unassignedclangbugs@nondot.org
</td>
</tr>
<tr>
<th>Reporter</th>
<td>sarang.baheti@gmail.com
</td>
</tr>
<tr>
<th>CC</th>
<td>llvmbugs@cs.uiuc.edu
</td>
</tr>
<tr>
<th>Classification</th>
<td>Unclassified
</td>
</tr></table>
<p>
<div>
<pre>Clang details:
Apple LLVM version 5.1 (clang-503.0.40) (based on LLVM 3.4svn)
Target: x86_64-apple-darwin13.3.0
Thread model: posix
Hi,
While trying out relaxed constraints on constexpr in C++1y/C++14, I am running
into this odd behavior where member constexpr functions (const qualified) with
constexpr local variables will lead to compilation failure:
Code that fails:
Code.cpp (compile: clang -std=c++1y -Wall code.cpp -o code1y)
---------------------------------------------------
/*
constexpr int gcd_impl(int a, int b)
{
return b == 0 ? a : gcd_impl(b, a%b);
}
constexpr int max(int a, int b)
{
return a > b ? a : b;
}
constexpr int min(int a, int b)
{
return a < b ? a : b;
}
constexpr int gcd(int a, int b)
{
return a == b ? a : gcd_impl(max(a,b), min(a,b));
}
*/
template<int N, int D>
class Rational
{
private:
constexpr auto gcd_impl(int a, int b) const
{
return b == 0 ? a : gcd_impl(b, a%b);
}
constexpr auto max(int a, int b)const
{
return a > b ? a : b;
}
constexpr auto min(int a, int b)const
{
return a < b ? a : b;
}
constexpr auto gcd(int a, int b) const
{
return a == b ? a : gcd_impl(max(a,b), min(a,b));
}
public:
constexpr Rational()
{}
template<int N1, int D1>
constexpr bool operator==(const Rational<N1, D1>&) const
{
return N * D1 == D * N1;
}
template<int N1, int D1>
constexpr auto add(const Rational<N1,D1>&) const
{
constexpr auto num = N *D1 + D * N1;
constexpr auto factor = gcd(num, D*D1);
return Rational<num/factor, D*D1/factor>();
}
constexpr int numerator() const
{
return N;
}
constexpr int denominator() const
{
return D;
}
};
int main()
{
constexpr auto onehalf = Rational<1,2>();
constexpr auto onefourth = Rational<1,4>();
constexpr auto threefourth = onehalf.add(onefourth);
auto num = threefourth.numerator();
auto den = threefourth.denominator();
return 0;
}
fails with error:
------------------------------------------------------------
code.cpp:32:29: fatal error: recursive template instantiation exceeded maximum
depth of 256
return b == 0 ? a : gcd_impl(b, a%b);
^
code.cpp:32:29: note: in instantiation of member function 'Rational<1,
2>::gcd_impl' requested here
return b == 0 ? a : gcd_impl(b, a%b);
^
code.cpp:32:29: note: in instantiation of member function 'Rational<1,
2>::gcd_impl' requested here
return b == 0 ? a : gcd_impl(b, a%b);
^
code.cpp:32:29: note: in instantiation of member function 'Rational<1,
2>::gcd_impl' requested here
return b == 0 ? a : gcd_impl(b, a%b);
^
code.cpp:32:29: note: in instantiation of member function 'Rational<1,
2>::gcd_impl' requested here
return b == 0 ? a : gcd_impl(b, a%b);
^
code.cpp:32:29: note: in instantiation of member function 'Rational<1,
2>::gcd_impl' requested here
return b == 0 ? a : gcd_impl(b, a%b);
^
code.cpp:32:29: note: (skipping 247 contexts in backtrace; use
-ftemplate-backtrace-limit=0 to see all)
code.cpp:32:29: note: in instantiation of member function 'Rational<1,
2>::gcd_impl' requested here
return b == 0 ? a : gcd_impl(b, a%b);
^
code.cpp:32:29: note: in instantiation of member function 'Rational<1,
2>::gcd_impl' requested here
return b == 0 ? a : gcd_impl(b, a%b);
^
code.cpp:47:29: note: in instantiation of member function 'Rational<1,
2>::gcd_impl' requested here
return a == b ? a : gcd_impl(max(a,b), min(a,b));
^
code.cpp:66:33: note: in instantiation of member function 'Rational<1, 2>::gcd'
requested here
constexpr auto factor = gcd(num, D*D1);
^
code.cpp:87:42: note: in instantiation of function template specialization
'Rational<1, 2>::add<1, 4>' requested here
constexpr auto threefourth = onehalf.add(onefourth);
^
code.cpp:32:29: note: use -ftemplate-depth=N to increase recursive template
instantiation depth
return b == 0 ? a : gcd_impl(b, a%b);
^
1 error generated.
If I move comment the constexpr functions defined in Rational class and
uncomment the ones defined outside everything works as expected.
The generated assembly is correct as well
Sarang</pre>
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