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

[Sudakshina Das <sudakshina1990 at gmail dot com>]

On Thu, Jan 24, 2013 at 5:15 PM, Richard Biener
<richard.guenther@gmail.com> wrote:
>
> On Thu, Jan 24, 2013 at 7:06 AM, Sudakshina Das
> <sudakshina1990@gmail.com> wrote:
> > 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!!!
>
> Don't use build_fake_var_decl, use what 4.6 did, create_tmp_var_raw.
>
> Richard.
>
>

But 4.6 used get_var_ann() also along with create_tmp_var_raw()  which
has been removed from 4.7.

> > Sudakshina Das