[Bug c++/87567] New: constexpr evaluation rejects call to non-constexpr function

[raphael.kubo.da.costa at intel dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=87567

            Bug ID: 87567
           Summary: constexpr evaluation rejects call to non-constexpr
                    function
           Product: gcc
           Version: 9.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: raphael.kubo.da.costa at intel dot com
  Target Milestone: ---

This is similar to bug 86678, and can be reproduced with trunk:

constexpr bool always_false() { return false; }
int f() { return 1; }
constexpr int g() {
  while (always_false())
    return f();
  return 0;
}

<source>: In function 'constexpr int g()':
<source>:5:13: error: call to non-'constexpr' function 'int f()'
5 |     return f();
  |            ~^~

It works with MSVC, ICC and clang (GCC also works if `while' is replaced with
`if').