[Bug c++/42340] New: templated member func vanish from assembler code when -O2 is used

[Bug c++/42340] New: templated member func vanish from assembler code when -O2 is used

[jaeschke at de dot ibm dot com]

Using the below code snipped (bug.C), and compiling it using:

  gcc -Wall -O2 -save-temps -c -o bug.o bug.C

causes _ZN1B1fIiEEvPT_ to disappear from the .s-file, and later on breaking the
link. Using -O1 works fine.

---- bug.C ----

struct B {
    template <class T> void f(T * t);
    void dummyInst();
};

template <class T> void
B::f(T * t)
{
}

void
B::dummyInst() {
    f((int*)0);
}


-- 
           Summary: templated member func vanish from assembler code when -
                    O2 is used
           Product: gcc
           Version: 4.4.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: jaeschke at de dot ibm dot com
 GCC build triplet: i486-linux-gnu
  GCC host triplet: i486-linux-gnu
GCC target triplet: i486-linux-gnu


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=42340

[Bug c++/42340] templated member func vanish from assembler code when -O2 is used

[paolo dot carlini at oracle dot com]

------- Comment #1 from paolo dot carlini at oracle dot com  2009-12-09 11:08 -------
I'm seeing this happening in 4.3.x too, isn't new in 4.4.x.

Now, I'm not sure to understand which is the problem: indeed, it disappears,
but it's also true that nothing calls it. I would ask you to provide a short
testcase which doesn't link anymore and was fine before (4.2.x?). Thanks.


-- 

paolo dot carlini at oracle dot com changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |WAITING


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=42340

[Bug c++/42340] templated member func vanish from assembler code when -O2 is used

[redi at gcc dot gnu dot org]

------- Comment #2 from redi at gcc dot gnu dot org  2009-12-09 11:29 -------
If another translation unit is relying on finding an instantiation in bug.o
then you should use an explicit instantiation to ensure it is present, or the
other translation unit should include the definition of B::f


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=42340

[Bug c++/42340] templated member func vanish from assembler code when -O2 is used

[paolo dot carlini at oracle dot com]

------- Comment #3 from paolo dot carlini at oracle dot com  2009-12-09 11:34 -------
This is expected, any optimizing compiler (e.g., ICC behaves the same as GCC)
will get rid of that implicit instantiation, while inlining. Really, this is
not going to change.


-- 

paolo dot carlini at oracle dot com changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|WAITING                     |RESOLVED
         Resolution|                            |INVALID


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=42340