Re: [IFUNC] PATCH: Add an ifunc attribute

["H.J. Lu" <hjl dot tools at gmail dot com>]

On Sun, Jun 28, 2009 at 10:20 AM, Richard
Guenther<richard.guenther@gmail.com> wrote:
> On Sun, Jun 28, 2009 at 7:01 PM, H.J. Lu<hjl.tools@gmail.com> wrote:
>> On Sun, Jun 28, 2009 at 9:57 AM, Richard
>> Guenther<richard.guenther@gmail.com> wrote:
>>> On Sun, Jun 28, 2009 at 6:37 PM, H.J. Lu<hjl.tools@gmail.com> wrote:
>>>> On Sun, Jun 28, 2009 at 9:17 AM, Richard
>>>> Guenther<richard.guenther@gmail.com> wrote:
>>>>> On Sun, Jun 28, 2009 at 5:10 PM, H.J. Lu<hongjiu.lu@intel.com> wrote:
>>>>>> Hi,
>>>>>>
>>>>>> Here is a patch to add ifunc attribute, including many testscases
>>>>>> in C and C++. ?Any comments?
>>>>>
>>>>> +/* Get the function return type inside function body. ?Return a pointer
>>>>> + ? to the function for IFUNC function. ?*/
>>>>> +
>>>>> +static inline tree
>>>>> +function_return_type (const_tree decl)
>>>>> +{
>>>>> + ?if (DECL_IS_IFUNC (decl))
>>>>> + ? ?return build_pointer_type (TREE_TYPE (decl));
>>>>> + ?else
>>>>> + ? ?return TREE_TYPE (TREE_TYPE (decl));
>>>>> +}
>>>>>
>>>>> that's just ... gross. ?Instead adjust the function signature properly.
>>>>> Which of course makes your proposal not viable at all.
>>>>>
>>>>> I think your solution is overdesigned. ?Do you really expect so much
>>>>> usage that you need to make it easy to use from C++ (easy as in
>>>>> not mangle manually)?
>>>>>
>>>>
>>>> I was told that people do want to use ifunc attribute in C++ class.
>>>
>>> They will be able to. ?Just not in a way that is 100% pretty and feels
>>> integrated.
>>>
>>> So what.
>>
>> There are a dozen C++ ifunc tests on ifunc branch. Can you show
>> me what the different C++ syntax looks like with a different ifunc
>> attribute approach?
>
> It's a straight-forward substitution.
>
> struct Foo {
> ?int foo1(void);
> ?int foo(void);
> };
>
> __typeof(&Foo::foo) __attribute__((ifunc))
> blah(void) asm("_ZN3Foo3fooEv");

User has to mangled the name him/herself. Any change
to prototype of foo needs update it by hand.

>
> __typeof(&Foo::foo) blah(void)
> {
> ?return &Foo::foo1;
> }

How do you handle

class ifunc
{
private:
  int foo1 (int);
  int foo2 (float);

public:
  int foo (int);
  int foo (float);
  int bar (int);
  int bar (float);
};

int
__attribute__ ((ifunc))
ifunc::foo (int)
{
  return &ifunc::foo1;
}

int
__attribute__ ((ifunc))
ifunc::foo (float)
{
  return &ifunc::foo2;
}

where you have 2 Foo::foo with different parameters?


H.J.