Question about undefined functions' parameters during LTO

[Erick Ochoa]

Hello,

I am trying to find out the arguments of functions which are undefined 
during LTO.

Basically:

gcc_assert(in_lto_p && !cnode->definition)
// Do we have arguments?
gcc_assert(DECL_ARGUMENTS(cnode->decl)) // fails
// No, we don't.

As I understand it, functions which are not defined are ones which have 
have been declared external.

I believe that, when building an application with -flto, the only 
functions which are not visible during LTO **and** are declared external 
are functions defined in libraries which have not been compiled with 
-flto. An example of this is glibc.

Indeed, I have implemented an analysis pass in gcc which prints out 
undefined functions, and it prints out the following:

undefined function __gcov_merge_add
undefined function fopen
undefined function printf
undefined function __builtin_putchar
undefined function calloc
undefined function __gcov_merge_topn
undefined function strtol
undefined function free
... and more

Now, I am not interested in the bodies of these. I am only interested in 
determining the type of the arguments passed to these functions. 
However, when I call the following function:

```
void
print_parameters_undefined_functions(const cgraph_node *cnode)
{
   gcc_assert(cnode);
   gcc_assert(in_lto_p);
   gcc_assert(!cnode->definition);

   tree function = cnode->decl;
   gcc_assert(function);
   enum tree_code code = TREE_CODE (function);
   bool is_function_decl = FUNCTION_DECL == code;
   gcc_assert (is_function_decl);

   log("about to print decl_arguments(%s)\n", cnode->name());
   for (tree parm = DECL_ARGUMENTS (function); parm; parm = 
DECL_CHAIN(parm))
   {
     log("hello world\n");
   }
```

I never see "hello world" but I do see "about to print...".
Does anyone have any idea on how to obtain the arguments to undefined 
functions?

The only way I see to do this, is to walk through the gimple 
instructions, find GIMPLE_CALL statements and look at the argument list 
at that moment. But I was wondering if there's a more efficient way to 
do it.

Thanks!