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* [Bug c++/114643] New: Call to a template function emitted but without the code for the template function itself
@ 2024-04-08 17:13 abbeyj+gcc at gmail dot com
  2024-04-08 17:17 ` [Bug ipa/114643] " pinskia at gcc dot gnu.org
                   ` (5 more replies)
  0 siblings, 6 replies; 7+ messages in thread
From: abbeyj+gcc at gmail dot com @ 2024-04-08 17:13 UTC (permalink / raw)
  To: gcc-bugs

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114643

            Bug ID: 114643
           Summary: Call to a template function emitted but without the
                    code for the template function itself
           Product: gcc
           Version: 14.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: abbeyj+gcc at gmail dot com
  Target Milestone: ---

When building the following example, a linker error is produced.

```
void foo();
template <class> class DynArray {
public:
  virtual void SetAlloc(unsigned);
  int *m_pElems;
  unsigned m_nNumElems;
  unsigned m_nNumAlloc;
  long m_nChunkSize;
};
void *DoRealloc(void *, long);
template <class T> void DynArray<T>::SetAlloc(unsigned new_size) {
  if (m_nChunkSize)
    new_size = m_nChunkSize * m_nChunkSize - 1 / m_nChunkSize;
  else if (m_nNumAlloc)
    if (new_size > m_nNumAlloc / 2)
      new_size = new_size > m_nNumAlloc + 1 ? new_size : m_nNumAlloc * 1.5 + 1;
  if (m_nNumElems && m_nNumAlloc && (new_size || m_pElems))
    m_pElems = (T *)DoRealloc(m_pElems, 0);
}
struct object {
  DynArray<int> d;
  void f(int size);
};
template <typename T> void deser(int size, T &x) {
  x.SetAlloc(0);
  if (size) {
    x.SetAlloc(size);
    foo();
  }
}
void object::f(int size) {
  deser(size, d);
}
```


Build with:
$ g++ -fPIC -O3 -Wall -Werror -fvisibility=hidden reloc.cxx -shared


Output:
> /usr/bin/ld: /tmp/ccLaKma6.o: relocation R_X86_64_PC32 against undefined symbol `_ZN8DynArrayIiE8SetAllocEj' can not be used when making a shared object; recompile with -fPIC
> /usr/bin/ld: final link failed: Bad value
> collect2: error: ld returned 1 exit status


The symbol in the above error message demangles to
`DynArray<int>::SetAlloc(unsigned int)`.

The error message suggests to compile with `-fPIC` but this is already being
compiled with `-fPIC`.  The issue seems to be that GCC emits a call to
`DynArray<int>::SetAlloc` but doesn't emit code for `DynArray<int>::SetAlloc`
itself.

The reproducer was minimized with the help of C-Reduce.  Very minor changes to
the code result in the problem not reproducing anymore.  This is the smallest
that I could manage to get it.

Godbolt link: https://godbolt.org/z/1Ynz1Khac

This appears to have started sometime around GCC 8.1 and still happens on the
trunk version that's currently available on Godbolt.

^ permalink raw reply	[flat|nested] 7+ messages in thread
end of thread, other threads:[~2024-04-22 23:00 UTC | newest]

Thread overview: 7+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2024-04-08 17:13 [Bug c++/114643] New: Call to a template function emitted but without the code for the template function itself abbeyj+gcc at gmail dot com
2024-04-08 17:17 ` [Bug ipa/114643] " pinskia at gcc dot gnu.org
2024-04-08 17:24 ` pinskia at gcc dot gnu.org
2024-04-08 21:13 ` pinskia at gcc dot gnu.org
2024-04-08 21:16 ` [Bug ipa/114643] [11/12/13/14 Regression] " pinskia at gcc dot gnu.org
2024-04-22 12:40 ` jakub at gcc dot gnu.org
2024-04-22 23:00 ` pinskia at gcc dot gnu.org

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