Re: plugin help: Inserting a function call in gimple code?

[Rob Johnson <rob at cs dot sunysb dot edu>]

Martin Jambor wrote:
> Hi,
>
> On Wed, Jan 02, 2008 at 06:13:37PM -0500, Rob Johnson wrote:
> > I'm experimenting with the gimple plugin infrastructure and I'm having 
> > trouble instrumenting code in a way that is compatible with the optimizer.  
> > Here's a simple example that is intended to insert the function call 
> > "__memcheck_register_argv(argc, argv)" at the beginning of main.  The code 
> > runs during pass_plugin_gimple (which comes right after pass_apply_inline 
> > in passes.c) and works great with -O0, but causes the compiler to crash 
> > with -O1 or higher.
> >
> > -------------------------------------
> > tree argv_registrar_type;
> > tree argv_registrar;
> > tree argv_registrar_call;
> >
> > argv_registrar_type = build_function_type_list (void_type_node,
> >                                                 integer_type_node,
> >                                                 build_pointer_type
> >                                                 (build_pointer_type
> >                                                  (char_type_node)),
> >                                                 NULL_TREE);
> > argv_registrar = build_fn_decl ("__memcheck_register_argv",
> >                                 argv_registrar_type);
> > argv_registrar_call = build_call_expr (argv_registrar, 2,
> >                                        DECL_ARGUMENTS (cfun->decl),
> >                                        TREE_CHAIN (DECL_ARGUMENTS
> >                                                    (cfun->decl)));
>
> DECL_ARGUMENTS is a tree chain of PARM_DECLs and in SSA GIMPLE, scalar
> operands  (integers  and  pointer  are  both  scalar,  is_gimple_reg()
> predicate is there to identify  variables that need to be converted to
> SSA) need to be SSA_NAMEs of declarations (PARM_DECLs and VAR_DECLs in
> particular).
>
> Therefore I suspect you need to create a different chain of respective
> SSA_NAMES and pass that to build_call_expr().  You can get the default
> SSA_NAME by calling gimple_default_def().

Yes!  It seems it's slightly more complicated given that, with some 
optimization levels the code is sometimes turned into SSA and sometimes 
not, and that, depending on how the original program uses argv and argc, 
they may or may not already have default definitions.  If the original 
program doesn't touch argv/argc, then we also have to update the set of 
referenced vars.  Here's the code I wrote to construct the argc argument 
to the above call expression:

tree argc;

/* If we're doing SSA... */
if (cfun->gimple_df && cfun->gimple_df->default_defs)
  {
    argc = gimple_default_def (cfun, DECL_ARGUMENTS (cfun->decl));
    if (!argc)
      {
	argc = DECL_ARGUMENTS (cfun->decl);
	mark_sym_for_renaming (argc);
      }
    add_referenced_var (DECL_ARGUMENTS (cfun->decl));
  }
else
  argc = DECL_ARGUMENTS (cfun->decl);

The code for argv is similar.  Does that look right?

Once I get this plugin working, I will try to extract some useful 
building blocks for other plugin writers.  Thanks for your help!

Best,
Rob