Re: User directed Function Multiversioning via Function Overloading (issue5752064)

[Sriraman Tallam <tmsriram at google dot com>]

On Tue, Nov 6, 2012 at 7:52 AM, Jason Merrill <jason@redhat.com> wrote:
> On 11/05/2012 09:38 PM, Sriraman Tallam wrote:
>>
>> +      /* For multi-versioned functions, more than one match is just fine.
>>
>> +        Call decls_match to make sure they are different because they are
>> +        versioned.  */
>> +      if (DECL_FUNCTION_VERSIONED (fn))
>> +       {
>> +          for (match = TREE_CHAIN (matches); match; match = TREE_CHAIN
>> (match))
>> +           if (!DECL_FUNCTION_VERSIONED (TREE_PURPOSE (match))
>> +               || decls_match (fn, TREE_PURPOSE (match)))
>> +             break;
>> +       }
>
>
> I still don't understand what this code is supposed to be doing.  Please
> remove it and instead modify the other loop to allow mismatches that are
> versions of the same function.

Ok, will do. I was trying to do for versioned functions what the other
loop was doing thought I could not come up with a test case to
exercise this code.


I will make all the other changes and get back asap.

Thanks,
-Sri.

>
>> +  /* If the olddecl is a version, so is the newdecl.  */
>> +  if (TREE_CODE (newdecl) == FUNCTION_DECL
>> +      && DECL_FUNCTION_VERSIONED (olddecl))
>> +    {
>> +      DECL_FUNCTION_VERSIONED (newdecl) = 1;
>> +      /* newdecl will be purged and is no longer a version.  */
>> +      delete_function_version (newdecl);
>> +    }
>
>
> Please make the comment clearer that the reason we're setting the flag on
> the newdecl is so that it'll be copied back into the olddecl; otherwise it
> seems odd to say it's a version and then it isn't a version.
>
>> +  /* If a pointer to a function that is multi-versioned is requested, the
>> +     pointer to the dispatcher function is returned instead.  This works
>> +     well because indirectly calling the function will dispatch the right
>> +     function version at run-time.  */
>>
>> +  if (DECL_FUNCTION_VERSIONED (fn))
>> +    {
>> +      tree dispatcher_decl = NULL;
>> +      gcc_assert (targetm.get_function_versions_dispatcher);
>> +      dispatcher_decl = targetm.get_function_versions_dispatcher (fn);
>> +      if (!dispatcher_decl)
>> +       {
>> +         error_at (input_location, "Pointer to a multiversioned function"
>> +                   " without a default is not allowed");
>> +         return error_mark_node;
>> +       }
>> +      retrofit_lang_decl (dispatcher_decl);
>> +      fn = dispatcher_decl;
>
>
> This code should use the get_function_version_dispatcher function in
> cp/call.c.
>
> Jason
>