[llvm-bugs] [Bug 29033] New: non-constexpr recursive variable templates are instanciated wrongly

[via llvm-bugs]

https://llvm.org/bugs/show_bug.cgi?id=29033

            Bug ID: 29033
           Summary: non-constexpr recursive variable templates are
                    instanciated wrongly
           Product: clang
           Version: 3.8
          Hardware: PC
                OS: Linux
            Status: NEW
          Severity: normal
          Priority: P
         Component: C++14
          Assignee: unassignedclangbugs at nondot.org
          Reporter: felix.morgner at gmail.com
                CC: llvm-bugs at lists.llvm.org
    Classification: Unclassified

Created attachment 16980
  --> https://llvm.org/bugs/attachment.cgi?id=16980&action=edit
Code generated by clang++ -std=c++14 -Wall -Wextra -pedantic -S

The following code:

#include <iostream>

template<std::size_t N>
auto fibo_v{fibo_v<N-1> + fibo_v<N-2>};

template<>
auto fibo_v<0>{0};

template<>
auto fibo_v<1>{1};

int main()
  {
  std::cout << fibo_v<4> << '\n';
  }

produces 0 as its output. Adding constexpr to the variable declarations
resolves this and produces the correct result 3.

As far as i can tell, N3651 lifted the restriction on variable templates to be
constexpr, thus i would expect the same result with and without constexpr in
the declarations.

GCC 6.1.1 produces the correct output, regardless of constexpr being in place
or not.

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