Question about creating global varaiable during IPA PASS.

Question about creating global varaiable during IPA PASS.

[Hanke Zhang]

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.)

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?

Thanks
Hanke Zhang

Re: Question about creating global varaiable during IPA PASS.

[Thomas Schwinge]

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

Re: Question about creating global varaiable during IPA PASS.

[Hanke Zhang]

Hi Thomas!

Thanks for your reply. That's exactly what I'm missing. When I add
varpool_node::finalize_decl() to my code, everything works fine!

Thomas Schwinge <thomas@schwinge.name> 于2023年12月16日周六 01:15写道：
>
> 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