[llvm-bugs] [Bug 35752] New: constexpr static variable template in class fails at link-time

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https://bugs.llvm.org/show_bug.cgi?id=35752

            Bug ID: 35752
           Summary: constexpr static variable template in class fails at
                    link-time
           Product: clang
           Version: 4.0
          Hardware: PC
                OS: Linux
            Status: NEW
          Severity: enhancement
          Priority: P
         Component: C++
          Assignee: unassignedclangbugs at nondot.org
          Reporter: emil.fresk at gmail.com
                CC: dgregor at apple.com, llvm-bugs at lists.llvm.org

Created attachment 19605
  --> https://bugs.llvm.org/attachment.cgi?id=19605&action=edit
Test file referred in the text

Hi all,

I have been testing variable templates under C++14 and C++17, however using a
constexpr static variable template in a class gives link-errors on optimization
level 0 and 1, while at a higher level it works fine (probably when the
variable template is inlined?).
It seems as if the variable template is never created, and the compiler gives
an undefined reference error at link-time.
This error has been tested on Clang 3.8, 4.0 and 5.0.



Test setup:
Linux 4.13.0-21-generic #24~16.04.1-Ubuntu Xenial



Compile commands:
-- Failing (-O0, -O1)
clang++-3.8 -std=c++14 test.cpp -O0
clang++-3.8 -std=c++14 test.cpp -O1
clang++-4.0 -std=c++14 test.cpp -O0
clang++-4.0 -std=c++14 test.cpp -O1
clang++-5.0 -std=c++14 test.cpp -O0
clang++-5.0 -std=c++14 test.cpp -O1

-- Working (-O2 or higher)
clang++-3.8 -std=c++14 test.cpp -O2
clang++-4.0 -std=c++14 test.cpp -O2
clang++-5.0 -std=c++14 test.cpp -O2



Compiler versions:
clang version 3.8.0-2ubuntu4 (tags/RELEASE_380/final)
clang version 4.0.0-1ubuntu1~16.04.2 (tags/RELEASE_400/rc1)
Sadly I am on the wrong computer to get the clang-5.0 version, but it is the
current one from the PPA (deb http://apt.llvm.org/xenial/
llvm-toolchain-xenial-5.0 main)



Error:
/tmp/test-cd1427.o: In function `test::test<run()::$_0>(run()::$_0&&)':
test.cpp:(.text+0x34): undefined reference to `test::make_vtable<run()::$_0>'
test.cpp:(.text+0x3f): undefined reference to `test::make_vtable<run()::$_0>'
clang: error: linker command failed with exit code 1 (use -v to see invocation)



Test code in attached test.cpp.

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