On Thu, Jan 24, 2013 at 7:06 AM, Sudakshina Das
<sudakshina1...@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.
> Sudakshina Das
