On 03/12/2020 11:47, Andrea Corallo via Gcc-help wrote:
> Hi all,
>
> I've a piece of code that reduced looks like this:
>
> #+begin_src C
> typedef struct {
> void (*fun_ptr)(void);
> } x_t;
>
> x_t *x;
>
> void
> f (void)
> {
> const x_t const *y = x;
> for (int i = 0; i < 1000; ++i)
> y->fun_ptr ();
> }
> #+end_src
>
> What is the correct way (if any) to express to the compiler that the
> value of y->fun_ptr does not get clobbered by the function call itself
> so the corresponding load to obtain its value can be moved out of the
> loop?
>
> My understanding is that the const qualifier is more for diagnostic
> reasons and is not sufficient for GCC to make this assumption. OTOH I
> cannot give 'fun_ptr' the attribute pure as it's not.
>
> Thanks
>
> Andrea
>
Why not just put the function pointer in a local variable? Then the
compiler will know that the value can't change.
R.
