On Tue, Dec 20, 2016 at 04:29:07PM +0100, Andre Vehreschild wrote:
> > The first one is GCC internal type for representing sizes, the latter is
> > the C size_t (usually they have the same precision, they always have the
> > same signedness (unsigned)).
> > In the past sizetype actually has been a signed type with very special
> > behavior.
>
> I am still wondering if it does not make sense to have something like
> gfc_size_t_zero_node to prevent us from repeating build_zero_cst
> (size_type_node) all the time. I had to use it 16 times, i.e., 16 times the
> code for building a zero size type node is generated instead of a reference to
> a "constant". And I don't want to know how often size_zero_node is used in the
> wrong location.
built_int_cst (size_type_node, 0) is actually faster than build_zero_cst,
one fewer level of indirection.
The 0 constant is cached in the type itself, so it actually in the end
is basically just:
return TREE_VEC_ELT (TYPE_CACHED_VALUES (type), 1);
Adding a variable to hold gfc_size_t_zero_node would mean you'd need to add
a GC root to hold it.
Note, sizetype should be still what is usually used, only if you in the ABI
have something declared as C size_t, then size_type_node should be used.
Jakub
