[Bug c++/64547] New: A non-const constexpr function is rejected incorrectly

[ville.voutilainen at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64547

            Bug ID: 64547
           Summary: A non-const constexpr function is rejected incorrectly
           Product: gcc
           Version: 5.0
            Status: UNCONFIRMED
          Keywords: rejects-valid
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: ville.voutilainen at gmail dot com
                CC: jason at redhat dot com

struct X 
{
    int x; 
    constexpr int get() const {return x;} 
    constexpr void set(int foo) {x = foo;}
}; 

constexpr int bar() 
{
    X x{42}; 
    x.set(666); 
    return x.get();
} 

int main() 
{
    constexpr int foo = bar();
}

Clang accepts the code, gcc rejects with 

constexpr-member.cpp: In function ‘int main()’:
constexpr-member.cpp:17:28:   in constexpr expansion of ‘bar()’
constexpr-member.cpp:11:10:   in constexpr expansion of ‘x.X::set(666)’
constexpr-member.cpp:17:29: error: constexpr call flows off the end of the
function
     constexpr int foo = bar();