http://gcc.gnu.org/bugzilla/show_bug.cgi?id=53419
--- Comment #8 from Richard Guenther <rguenth at gcc dot gnu.org> 2012-05-21
09:30:52 UTC ---
(In reply to comment #6)
> (In reply to comment #5)
> > > extern func_ptr_t init_array_begin[1];
> > > extern func_ptr_t init_array_end[1];
> >
> > The array sizes say they are size of one. If you want to be correct and not
> > allow GCC to optimize away the check because array overflow, use [] instead
> > of
> > [1].
>
> Good point. Do you happen to know if
> extern func_ptr_t init_array_begin[];
> extern func_ptr_t init_array_end[];
> is say, C89 compatible? I ask, because I thought I ran into problems with
> some
> older compilers given the above syntax.
Yes, it's C89 compatible.
> typedef unsigned int size_t;
>
> typedef void (*func_ptr_t) (void);
> extern func_ptr_t init_array_begin[1];
> extern func_ptr_t init_array_end[1];
>
> void
> per_thread_init (void)
> {
> size_t n_init = (init_array_end - init_array_begin);
> int i;
> for (i = 0; i < n_init; ++i)
> {
> func_ptr_t init_func = init_array_begin[i];
> if (init_func)
> (*init_func) ();
> }
> }
>
> Questions regarding the optimization of the above.
>
> If the compiler concludes that n_init must be 1, then code that creates an
> endless loop is not a valid optimization?
>
> Simplifying so that the loop executes only once might be, but I'm still having
> a little trouble adjusting to that idea.
size_t n_init = (init_array_end - init_array_begin);
is by itself also undefined - you are taking the difference between two
pointers to two distinct objects. I suppose you should instead declare
extern func_ptr_t init_array_begin[];
extern func_ptr_t *init_array_end;
> Is there an -f option that disables this sort of optimization?
-fno-tree-vrp will, for your case.
>
>
> 1
