[cfe-dev] Using IFUNC with template functions

[Amrita H S via cfe-dev]

Hi All,

I want to have a template function as an ifunc. Find below my test program.

// Test Program
#include <iostream>

int glob_t = 2;
typedef void (*VOID_FUNC_P)(void);

template <typename T>
T add_isa1(T x, T y) {
   std::cout << "ISA1 implementation" << std::endl;
   return x + y;
}

template <typename T>
T add_isa2(T x, T y) {
   std::cout << "ISA2 implementation" << std::endl;
   return x + y;
}

template <typename T>
static VOID_FUNC_P add_resolver(void) {
   T (*T_p)(T,T) = NULL;
   switch (glob_t) {
      case 1:
              T_p = add_isa1;
              break;
      case 2:
              T_p = add_isa2;
              break;
   }
   return reinterpret_cast<VOID_FUNC_P>(T_p);
}

template VOID_FUNC_P add_resolver<int>(void);
template VOID_FUNC_P add_resolver<double>(void);

// explicit/manual instantiation of possibilities
int add(int, int) __attribute((ifunc("_Z12add_resolverIiEPFvvEv")));
double add(double, double)
__attribute((ifunc("_Z12add_resolverIdEPFvvEv")));

int main()
{
   //int res = add(1,68);
   double res = add(1.68,68.01);
   std::cout << "Res = " << res << std::endl;
   return 0;
}


I have to explicitly declare the ifunc resolver function for all possible
combinations of template arguments. In reality, I think it would be
impractical for programmers to do this kind of manual/explicit
instantiation.
I am interested to know if there any other better way to use ifuncs with
template functions. If there is none, is it worth suggesting to the C++
standards?


Thanks and Regards,
Amrita H S
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