Re: Question about creating global varaiable during IPA PASS.

[Thomas Schwinge <thomas@schwinge.name>]

Hi Hanke!

On 2023-12-13T17:04:57+0800, Hanke Zhang via Gcc <gcc@gcc.gnu.org> wrote:
> Hi, I'm trying to create a global variable in my own PASS which
> located at the LATE_IPA_PASSES. (I'm using GCC 10.3.0.)

I can't comment on IPA aspects, or whether something was different on
oldish GCC 10 (why using that one, by the way?), and I've not actually
verified what you're doing here:

> And after creating it, I added the attributes like the following.
>
> // 1. create the var
> tree new_name = get_identifier (xx);
> tree new_type = build_pointer_type (xx);
> tree new_var = build_decl (UNKNOWN_LOCATION, VAR_DECL, new_name, new_type);
> add_attributes (new_var);
>
> static void
> add_attributes (tree var)
> {
> DECL_ARTIFICIAL (var) = 1;
> DECL_EXTERNAL (var) = 0;
> TREE_STATIC (var) = 1;
> TREE_PUBLIC (var) = 1;
> TREE_USED (var) = 1;
> DECL_CONTEXT (var) = NULL_TREE;
> TREE_THIS_VOLATILE (var) = 0;
> TREE_ADDRESSABLE (var) = 0;
> TREE_READONLY (var) = 0;
> if (is_global_var (var))
>   set_decl_tls_model (var, TLS_MODEL_NONE);
> }
>
> But when I try to compile some example files with -flto, error occurs.
>
> /usr/bin/ld: xxx.ltrans0.ltrans.o: in function `xxx':
> xxx.c: undefined reference to `glob_var'
> xxx.c: undefined reference to `glob_var'
> xxx.c: undefined reference to `glob_var'
>
> Here `glob_var' is the global varaiable created in my PASS.
>
> I would like to ask, am I using some attributes incorrectly?

..., but are you maybe simply missing to
'varpool_node::add (var);' or 'varpool_node::finalize_decl (var);' or
something like that?  See other uses of those, and description in
'gcc/cgraph.h', 'struct [...] varpool_node':

      /* Add the variable DECL to the varpool.
         Unlike finalize_decl function is intended to be used
         by middle end and allows insertion of new variable at arbitrary point
         of compilation.  */
      static void add (tree decl);

      /* Mark DECL as finalized.  By finalizing the declaration, frontend instruct
         the middle end to output the variable to asm file, if needed or externally
         visible.  */
      static void finalize_decl (tree decl);

If that's not it, we'll have to look in more detail.


Grüße
 Thomas