[Bug c++/114643] New: Call to a template function emitted but without the code for the template function itself

[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]

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.

[Bug ipa/114643] Call to a template function emitted but without the code for the template function itself

[pinskia at gcc dot gnu.org]

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

--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
This is a devirtualization issue ...

Let me find the dup.

[Bug ipa/114643] Call to a template function emitted but without the code for the template function itself

[pinskia at gcc dot gnu.org]

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

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
         Depends on|                            |62051

--- Comment #2 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
I think this is a dup of bug 62051.


Referenced Bugs:

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=62051
[Bug 62051] [11/12/13/14 Regression] Undefined reference to vtable with -O2 and
-fdevirtualize-speculatively

[Bug ipa/114643] Call to a template function emitted but without the code for the template function itself

[pinskia at gcc dot gnu.org]

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

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
         Depends on|                            |93115

--- Comment #3 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Maybe PR 93115 .


Referenced Bugs:

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=93115
[Bug 93115] gcc fails to emit inline function on llvm-roc project: -O1 -fPIC
-fdevirtualize -fdevirtualize-speculatively -fipa-cp -fipa-cp-clone
-fvisibility-inlines-hidden

[Bug ipa/114643] [11/12/13/14 Regression] Call to a template function emitted but without the code for the template function itself

[pinskia at gcc dot gnu.org]

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

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           See Also|                            |https://gcc.gnu.org/bugzill
                   |                            |a/show_bug.cgi?id=67650,
                   |                            |https://gcc.gnu.org/bugzill
                   |                            |a/show_bug.cgi?id=80916
      Known to fail|                            |8.1.0
            Summary|Call to a template function |[11/12/13/14 Regression]
                   |emitted but without the     |Call to a template function
                   |code for the template       |emitted but without the
                   |function itself             |code for the template
                   |                            |function itself
   Target Milestone|---                         |11.5
      Known to work|                            |7.5.0
         Depends on|62051, 93115                |

--- Comment #4 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Actually it more closely related to PR 67650 (and PR 80916) but both of those
were fixed. Looks like even though the function is not static, we are thinking
we can still refer to it.


Referenced Bugs:

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=62051
[Bug 62051] [11/12/13/14 Regression] Undefined reference to vtable with -O2 and
-fdevirtualize-speculatively
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=93115
[Bug 93115] gcc fails to emit inline function on llvm-roc project: -O1 -fPIC
-fdevirtualize -fdevirtualize-speculatively -fipa-cp -fipa-cp-clone
-fvisibility-inlines-hidden

[Bug ipa/114643] [11/12/13/14 Regression] Call to a template function emitted but without the code for the template function itself

[jakub at gcc dot gnu.org]

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

Jakub Jelinek <jakub at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |jakub at gcc dot gnu.org
   Last reconfirmed|                            |2024-04-22
             Status|UNCONFIRMED                 |NEW
     Ever confirmed|0                           |1
           Priority|P3                          |P2

--- Comment #5 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
Started with r8-6709-gb9aba9fde536dc3e0293653509f530322ee2753e

[Bug ipa/114643] [11/12/13/14 Regression] Call to a template function emitted but without the code for the template function itself

[pinskia at gcc dot gnu.org]

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

--- Comment #6 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
(In reply to Jakub Jelinek from comment #5)
> Started with r8-6709-gb9aba9fde536dc3e0293653509f530322ee2753e

That is almost definitely just exposed the bug I have not looked to see if
changing the params on the command line allows to expose it further back
though.