On Tue, Mar 11, 2014 at 11:58:01AM +0100, Richard Biener wrote:
> On Mon, Mar 10, 2014 at 11:14 AM, Jakub Jelinek <ja...@redhat.com> wrote:
> > On Mon, Mar 10, 2014 at 11:10:05AM +0100, Uros Bizjak wrote:
> >> > Well, better is non-obvious, while it is smaller (which is good for
> >> > initialization and thus rarely executed code), the common case is that
> >> > *jcr_list is 0 (gcj is used rarely these days) and for the common case
> >> > it is
> >> > one instruction longer.
> >> > Perhaps at least use if (__builtin_expect (*jcr_list != NULL, 0))?
> >> > Otherwise looks good to me.
> >>
> >> Following source:
> >>
> >> void frame_dummy (void)
> >> {
> >> void **jcr_list = __JCR_LIST__;
> >> if (__builtin_expect (*jcr_list != 0, 0))
> >> register_classes (jcr_list);
> >> }
> >>
> >> generates exactly the same code while avoiding the warning. So,
> >> following your concern, I am testing following patch:
> >
> > But then the asm is gone and it can start to break any time soon.
> > For GCC __JCR_LIST__ is simply a zero sized local array and thus
> > dereferencing it's first element is invalid. It doesn't know that we use
> > linker magic to populate the array.
>
> You can also declare it extern and define the symbol in a global asm ...
But then you need to know how (which is quite target dependent).
Or define it in some other CU and ld -r it together, but supposedly not all
linkers can do ld -r.
Jakub
