A pass that worked in gcc-4.6.2 fails in gcc-4.7.2

[Sudakshina Das]

Dear all,

I am currently updating a pass that was made for gcc-4.6.*, so that it
works for gcc.4.7.2.

In the pass for gcc-4.6.*, a code fragment from tree-ssa-structalias.c
was picked up and used.
Given below is the fragment taken form create_function_info_for () .
This fragment was used to create variable information for the function
and it was picked up to perform a similar operation in the added pass
as well.

But in gcc-4.7.2 some changes are introduced in the fragment. The code
given below shows the changes that have been introduced in
create_function_info_for () of tree-ssa-structalias.c in gcc-4.7.2
along with the original code in the comments.

  /* Add one representative for all further args.  */
  if (is_varargs)
    {
      varinfo_t argvi;
      const char *newname;
      char *tempname;
      tree decl;

      asprintf (&tempname, "%s.varargs", name);
      newname = ggc_strdup (tempname);
      free (tempname);

      /* We need sth that can be pointed to for va_start.  */

/**************** CHANGED CODE in GCC-4.7.2 ***************/
      decl = build_fake_var_decl (ptr_type_node);

/************ ORIGINAL CODE in GCC-4.6.2 *******************
/*      decl = create_tmp_var_raw (ptr_type_node, name);
        get_var_ann (decl);
*/

      argvi = new_var_info (decl, newname);
      argvi->offset = fi_parm_base + num_args;
      argvi->size = ~0;
      argvi->is_full_var = true;
      argvi->is_heap_var = true;
      argvi->fullsize = vi->fullsize;
      gcc_assert (prev_vi->offset < argvi->offset);
      prev_vi->next = argvi;
      prev_vi = argvi;
    }

  return vi;


So I made the same changes in the pass where this fragment was used.
But after making the changes the pass is now giving an "internal
compiler error" and a "segmentation fault" at runtime.

After debugging I could narrow it down to the function
build_fake_var_decl() and to be specific at the memory allocation
statement highlighted below.


tree
build_fake_var_decl (tree type)
{
/************************ My debugging showed that the control came
here *********************/
  tree decl = (tree) XOBNEW (&fake_var_decl_obstack, struct tree_var_decl);
/************************ But did not come here
**********************************************************/
  memset (decl, 0, sizeof (struct tree_var_decl));
  TREE_SET_CODE (decl, VAR_DECL);
  TREE_TYPE (decl) = type;
  DECL_UID (decl) = allocate_decl_uid ();
  SET_DECL_PT_UID (decl, -1);
  layout_decl (decl, 0);
  return decl;
}

The builf_fake_var_decl() function is a gcc function defined in
tree-ssa-structalias.c. To be able to use it in my pass, I removed the
keyword static in its definition.

I cannot figure out what can possibly cause this error in the XOBNEW function.

Please help!!!

Sudakshina Das