Re: [PATCH] PR 78534 Change character length from int to size_t

[Andre Vehreschild <vehre at gmx dot de>]

On Tue, 20 Dec 2016 16:40:13 +0100
Jakub Jelinek <jakub@redhat.com> wrote:

> 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.

Well, then how about:

#define gfc_size_t_zero_node build_int_cst (size_type_node, 0)

We can't get any faster and for new and old gfortran-hackers one identifier's
meaning is faster to grasp than two's.

- Andre
-- 
Andre Vehreschild * Email: vehre ad gmx dot de