Internal compiler error in ropeimpl.h, 2.96

[Jean-Francois Panisset]

 < 200006060719.JAA01306@loewis.home.cs.tu-berlin.de >"Martin v. Loewis" writes
>> time reducing the test case to a more manageable size. Unfortunately,
>> I have not been able to add it to the GNATS entry, so for what it's worth,
>> here is this reduced test case:
>
>Thanks, I've added it to the PR. Sending small examples is not
>mandatory, but highly appreciated. Since you already spend quite some
>time on this: Would you be interested in working on a fix yourself?
>
>Just run cc1plus in a debugger, and run the (simplified) file, passing
>-quiet as an option (i.e. r -quiet newfile.cc). That will quickly get
>you to the point where it crashes. 
>
>Regards,
>Martin

I spent a couple of hours gdb-ing pt.c, but I have to admit that
I'm in over my head. I did manage to get what I believe to be the
minimal test case:

template<class T>
struct base
{
  void mf();
};

template<class T>
struct derived : public base<T>
{
  ~derived()
  {
    mf();
  }
};

template <class T>
void base<T>::mf()
{
  ((derived<T>*)this)->derived<T>::~derived();
}

derived<char> bar;


For what it's worth, here is a stack trace at the point at which
the compiler segfaults:

Program received signal SIGSEGV, Segmentation fault.
0x8201f0f in tsubst_decl (t=0x4012a880, args=0x40129d00, type=0x4012a900, 
    in_decl=0x4011eb00) at ../../../gcc/cp/pt.c:5943
5943                tmpl = DECL_TI_TEMPLATE (t);
(gdb) where
#0  0x8201f0f in tsubst_decl (t=0x4012a880, args=0x40129d00, type=0x4012a900, 
    in_decl=0x4011eb00) at ../../../gcc/cp/pt.c:5943
#1  0x82034d1 in tsubst_copy (t=0x401298e0, args=0x40129d00, complain=1, 
    in_decl=0x4011eb00) at ../../../gcc/cp/pt.c:6981
#2  0x8204017 in tsubst_expr (t=0x401298e0, args=0x40129d00, complain=1, 
    in_decl=0x4011eb00) at ../../../gcc/cp/pt.c:7427
#3  0x8203a4e in tsubst_expr (t=0x40129900, args=0x40129d00, complain=1, 
    in_decl=0x4011eb00) at ../../../gcc/cp/pt.c:7185
#4  0x8203cdb in tsubst_expr (t=0x40129300, args=0x40129d00, complain=1, 
    in_decl=0x4011eb00) at ../../../gcc/cp/pt.c:7297
#5  0x82063b0 in instantiate_decl (d=0x4012ad80, defer_ok=0)
    at ../../../gcc/cp/pt.c:9715
#6  0x82064d2 in instantiate_pending_templates () at ../../../gcc/cp/pt.c:9794
#7  0x82139bc in finish_file () at ../../../gcc/cp/decl2.c:3583
#8  0x82261f1 in yyparse () at parse.y:434
#9  0x804b6ae in compile_file (name=0x40123400 "ropecrash4.C")
    at ../../gcc/toplev.c:2288
#10 0x804e81e in main (argc=4, argv=0xbffff9d4) at ../../gcc/toplev.c:4702

The lines in question are:

5940            /* Check to see if we already have this specialization.  */
5941            if (!local_p)
5942              {
5943                tmpl = DECL_TI_TEMPLATE (t);
5944                gen_tmpl = most_general_template (tmpl);
5945                argvec = tsubst (DECL_TI_ARGS (t), args, /*complain=*/1, in_decl);
5946                spec = retrieve_specialization (gen_tmpl, argvec);
5947              }
5948            else
5949              spec = retrieve_local_specialization (t);


And the problem is that:

#define DECL_TI_TEMPLATE(NODE)      TI_TEMPLATE (DECL_TEMPLATE_INFO (NODE))

#define DECL_TEMPLATE_INFO(NODE) \
  (DECL_LANG_SPECIFIC(VAR_TEMPL_TYPE_OR_FUNCTION_DECL_CHECK (NODE))->decl_flags.u.template_info)

#define DECL_LANG_SPECIFIC(NODE) (DECL_CHECK (NODE)->decl.lang_specific)

(gdb) p t->decl.lang_specific
$30 = (struct lang_decl *) 0x0

i.e. a nil pointer is being dereferenced. Unfortunately, it looks like
gcc internals is not something you can just "pick up" in a couple
of hours of running the debugger :-(

Thanks!
JF

Jean-Francois Panisset                                panisset@discreet.com
Software Engineer
Discreet Logic