Constructing static variables in GIMPLE?

Constructing static variables in GIMPLE?

[Sean Callanan]

Dear mailing list:

I am writing GCC code that constructs GIMPLE (after pass_apply_inline  
and before pass_all_optimizations) for a function-level static  
variable that gets assigned to and passed to another function.  My  
problem is that I am getting undefined symbol errors for a renamed  
version of the symbol.
I define the variable as below:

--
static tree build_static(tree type, const char* name)
{
   tree ret = NULL;

   ret = build_decl(VAR_DECL, get_identifier(name), type);

   DECL_ARTIFICIAL(ret) = 1;     // declared by the compiler
   DECL_IGNORED_P(ret) = 1;      // no debug info
   TREE_READONLY(ret) = 0;       // writable
   DECL_EXTERNAL(ret) = 0;       // defined
   TREE_STATIC(ret) = 1;         // static
   TREE_USED(ret) = 1;           // used
   DECL_CONTEXT(ret) = cfun->decl;

   create_var_ann(ret);
   add_referenced_var(ret);

   return ret;
}
--

Here's an example where I use this function, and demonstrating how I  
use the variable.

--
   tree last_p = build_static(long_long_unsigned_type_node, "last_p");
   // ...
   tree subtraction = build2(MINUS_EXPR, long_long_unsigned_type_node,  
end_time, start_time);
   build_gimple_modify_stmt(last_p, subtraction);
   // ...
   tree last_p_temp = create_tmp_var(TREE_TYPE(last_p),  
get_name(last_p));
   tree last_p_name = make_ssa_name(last_p_temp, NULL);
   tree last_p_assignment = build_gimple_modify_stmt(last_p_name,  
last_p);
   SSA_NAME_DEF_STMT(last_p_name) = last_p_assignment;
--

As seen above, I (try to) respect SSA when reading from this variable,  
and when assigning to it (I create an SSA_NAME when using the value,  
and assign directly to the VAR_DECL).  I'm passing an SSA_NAME to the  
function.  However, when I compile, I'm getting linker errors of the  
form:

--
[...]/test.c:4: undefined reference to `last_p.2610'
--

Oddly, I don't get undefined references for `last_p'; I find it very  
odd that it's being renamed.  Does anyone know what's going on here?   
As always, I welcome corrections to my (admittedly novice-level)  
GIMPLE- and SSA-fu.
Thanks for looking at this.

Sincerely,
Sean Callanan

Re: Constructing static variables in GIMPLE?

[Sean Callanan]

Dear mailing list:

I solved my own problem.  This is how I construct a static variable:

--
static tree build_static(tree type, const char* name)
{
   tree ret = NULL;

   ret = build_decl(VAR_DECL, get_identifier(name), type);

   TREE_STATIC(ret) = 1;
   assemble_variable(ret, 0, 0, 0); // tree decl, int top_level, int  
at_end, int dont_output_data
   add_referenced_var(ret);

   return ret;
}
--

By the way, this only works for static variables; for automatic  
variables, this is how I do it:

--
static tree build_automatic(tree type, const char* name)
{
   tree ret = NULL;

   ret = build_decl(VAR_DECL, get_identifier(name), type);

   DECL_ARTIFICIAL(ret) = 1;     // declared by the compiler
   DECL_IGNORED_P(ret) = 1;      // no debug info
   TREE_READONLY(ret) = 0;       // writable
   DECL_EXTERNAL(ret) = 0;       // defined
   TREE_STATIC(ret) = 0;         // automatic
   TREE_USED(ret) = 1;           // used
   DECL_CONTEXT(ret) = cfun->decl;

   create_var_ann(ret);
   add_referenced_var(ret);

   HOST_WIDE_INT decl_size;

   if(TYPE_SIZE(type) && TREE_CODE(TYPE_SIZE(type)) == INTEGER_CST)
     {
       decl_size = tree_low_cst(TYPE_SIZE(type), 0);
     }
   else
     {
       decl_size = 0;
     }

   rtx decl_rtl = assign_stack_local(DECL_MODE(ret), decl_size, 0);

   SET_DECL_RTL(ret, decl_rtl);

   return ret;
}
--

Sincerely,
Sean Callanan


On Jun 13, 2008, at 1:57 AM, Sean Callanan wrote:

> Dear mailing list:
>
> I am writing GCC code that constructs GIMPLE (after  
> pass_apply_inline and before pass_all_optimizations) for a function- 
> level static variable that gets assigned to and passed to another  
> function.  My problem is that I am getting undefined symbol errors  
> for a renamed version of the symbol.
> I define the variable as below:
>
> --
> static tree build_static(tree type, const char* name)
> {
>  tree ret = NULL;
>
>  ret = build_decl(VAR_DECL, get_identifier(name), type);
>
>  DECL_ARTIFICIAL(ret) = 1;     // declared by the compiler
>  DECL_IGNORED_P(ret) = 1;      // no debug info
>  TREE_READONLY(ret) = 0;       // writable
>  DECL_EXTERNAL(ret) = 0;       // defined
>  TREE_STATIC(ret) = 1;         // static
>  TREE_USED(ret) = 1;           // used
>  DECL_CONTEXT(ret) = cfun->decl;
>
>  create_var_ann(ret);
>  add_referenced_var(ret);
>
>  return ret;
> }
> --
>
> Here's an example where I use this function, and demonstrating how I  
> use the variable.
>
> --
>  tree last_p = build_static(long_long_unsigned_type_node, "last_p");
>  // ...
>  tree subtraction = build2(MINUS_EXPR, long_long_unsigned_type_node,  
> end_time, start_time);
>  build_gimple_modify_stmt(last_p, subtraction);
>  // ...
>  tree last_p_temp = create_tmp_var(TREE_TYPE(last_p),  
> get_name(last_p));
>  tree last_p_name = make_ssa_name(last_p_temp, NULL);
>  tree last_p_assignment = build_gimple_modify_stmt(last_p_name,  
> last_p);
>  SSA_NAME_DEF_STMT(last_p_name) = last_p_assignment;
> --
>
> As seen above, I (try to) respect SSA when reading from this  
> variable, and when assigning to it (I create an SSA_NAME when using  
> the value, and assign directly to the VAR_DECL).  I'm passing an  
> SSA_NAME to the function.  However, when I compile, I'm getting  
> linker errors of the form:
>
> --
> [...]/test.c:4: undefined reference to `last_p.2610'
> --
>
> Oddly, I don't get undefined references for `last_p'; I find it very  
> odd that it's being renamed.  Does anyone know what's going on  
> here?  As always, I welcome corrections to my (admittedly novice- 
> level) GIMPLE- and SSA-fu.
> Thanks for looking at this.
>
> Sincerely,
> Sean Callanan