[cfe-dev] "You don't pay for what you don't use" principle violation?

[Jacob Carlborg]

On 05/05/14 00:08, Fernando Pelliccioni wrote:
> Hi all,
>
> Is there any reason why the following code produces the attached
> assembly code?
>
>      struct X { int v; };
>
>      int func( X** x, int n )
>      {
>          int sum = 0;
>
>          while ( n > 0 )
>          {
>              sum += (*x)->v;
>              ++x;
>              --n;
>          }
>          return sum;
>      }
>
>      int main() {}
>
> The "func" function is not used, I think it should be omitted by the
> compiler.

I guess that's to support separate compilation. The compiler might also 
need global static analyzing to determine that a function is not used.

> If I change the function to a template function
>
>      template <typename T>
>      int func( T** x, int n )
>      {
>          int sum = 0;
>
>          while ( n > 0 )
>          {
>              sum += (*x)->v;
>              ++x;
>              --n;
>          }
>          return sum;
>      }
>
> Then, no code is generated.

Templates need to be instantiate for their code to be generated. The 
compiler won't event completely analyze the function unless it's 
instantiated.

-- 
/Jacob Carlborg