[Bug c++/85060] New: Object cannot call its inherited member function "without object"

[dingyuc at 126 dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=85060

            Bug ID: 85060
           Summary: Object cannot call its inherited member function
                    "without object"
           Product: gcc
           Version: 7.3.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: dingyuc at 126 dot com
  Target Milestone: ---

Created attachment 43746
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=43746&action=edit
The source code "hierarchy.cc" and a preprocessed file "hierarchy.ii"

The attached source code can be compiled and executed by older versions of g++
but not by g++ 7.0.0 - 7.3.1. I managed to simplify the case into three level
of classes where child and grandchild classes are templates. The code has been
tested on Archlinux, OS_X and some online compilers, all confirming it's a gcc7
problem.
Simply the command
    $ g++ hierarchy.cc
will yield
    hierarchy.cc: In member function ‘void CC<T>::bar()’:
    hierarchy.cc:20:32: error: cannot call member function ‘int CA::foo()’
without object
         const SPECIFIER m = CA::foo(); // Won't pass!!

Here is the complete source code for people bothered to untar:
$ cat hierarchy.cc 
#include <iostream>
#ifndef SPECIFIER
    #define SPECIFIER int    // fail with g++7
    // #define SPECIFIER auto   // fail with g++7, or invalid without c++11
    // #define SPECIFIER T      // pass with g++7 when int->T is possible
#endif

class CA {
public:
  int foo() { return 42; }
};

template <class T>
class CB : public CA { };

template <class T>
class CC : public CB<T> {
public:
  void bar() {
    const SPECIFIER m = CA::foo(); // Won't pass!!
    // const SPECIFIER m = this->CA::foo(); // This will work.
    std::cout << "THE ULTIMATE ANSWER: " << m << std::endl;
  }
};

int main(void) {
  CC<double> c;
  c.bar();
  return 0;
}