Extended Description

The following program does not compile with clang r193986:

template
constexpr T PI = T(3.14);

template
constexpr T TAU = 2 * PI;

// A: Without this line using TAU below results in a compile error
//constexpr double HALF_PI = PI / 2;

int main(int argc, char**)
{
return TAU * argc;
}

This results in:

/LLVM/build/Release+Asserts/bin/clang -c -std=c++1y clang.cpp
clang.cpp:5:23: error: constexpr variable 'TAU' must be initialized by a constant expression
constexpr T TAU = 2 * PI;
~~~~^
clang.cpp:13:12: note: in instantiation of variable template specialization 'TAU' requested here
return TAU * argc;
^
1 error generated.

After uncommenting the line below "A", the code compiles successfully.

It seems that a constexpr variable template cannot be used in the definition of another constexpr variable template when it is not used in the definition of a non-template constexpr variable as well.