[Bug c++/103490] New: Linkage type of typeinfo of polymorphic object with OOL functions

[lizekun.zek at bytedance dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103490

            Bug ID: 103490
           Summary: Linkage type of typeinfo of polymorphic object with
                    OOL functions
           Product: gcc
           Version: 11.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: lizekun.zek at bytedance dot com
  Target Milestone: ---

Hi guys,
  I found that the linkage of typeinfo of polymorphic object with OOL-functions
is weak, while that is strong for clang, and I want to attach a patch to make
the behavior of the two compilers consistent. However, I can't find the clear
definition of this in Itanium C++ ABI, so here are the questions:

1.It is easy to understand that we make the object with inlined-functions weak, 
  because it usually appears in a header file and may be defined several times, 
  so when functions are out-of-line, why do we make it weak?

2.In fact, I prefer the gcc way, are there any cases that show gcc is 
  better?

This is a case to show the issue.

---
test.h

class A{
public:
    virtual const int getA(){} ;
    virtual const int getB(){} ;
};

---
testA.cpp

#include<iostream>
#include "test.h"
using namespace std;

class Test : public A {
public:
    virtual const int getA() override;
};
const int Test ::getA() {
    return 1;
}


int main() {
    A * t=new Test();;
    cout << dynamic_cast<Test*>(t);
}
---

testB.cpp

#include "test.h"

class Test : A {
public:
    virtual const int getB() override;
};
const int Test :: getB() {
    return 2;
}