[PATCH, take 2] Fix PR tree-optimization/49960 ,Fix self data dependence

[Razya Ladelsky]

Jakub Jelinek <jakub@redhat.com> wrote on 21/11/2011 05:07:54 PM:

> From: Jakub Jelinek <jakub@redhat.com>
> To: Razya Ladelsky/Haifa/IBM@IBMIL
> Cc: GCC Patches <gcc-patches@gcc.gnu.org>, Richard Guenther 
> <richard.guenther@gmail.com>
> Date: 21/11/2011 05:08 PM
> Subject: Re: [PATCH, take 2] Fix PR tree-optimization/49960 ,Fix 
> self data dependence
> 
> On Mon, Nov 21, 2011 at 04:54:09PM +0200, Razya Ladelsky wrote:
> > Although compute_affine_dependence() can't do anything meaningful for 
the 
> > gather data refs,
> > it may still be assigning values to the dependence relation structure, 
if 
> > you need to use them. 
> > Therefore I did not skip the call to compute_self_dependence(), which 
> > indeed calls
> > compute_affine_depepndence().
> > 
> > 
> > If you think it's redundant, we can remove it.
> 
> It is not just redundant, but harmful.  compute_affine_dependence 
assumes
> that base and offset are simple IVs, that is not true for gather deps.
> So please do remove it.
> 
>    Jakub
> 

Jakub,

I have some non-affine cases for which compute_affine_dependence is called 
(as it is called for 
ALL dependences from compte_all_depepndences()), and no harm is done.
I looked a little bit closer into the code, and this is what happens for 
non affine accesses:

initialize_data_dependence_relation() assigns 
DDR_ARE_DEPENDENT (res) = chrec_dont_know for the dr.

Then, compute_affine_depepndence()
tests if (DDR_ARE_DEPENDENT (ddr) == NULL_TREE), and does nothing 
otherwise.
Since the dr was initialized with chrec_dont_know, no harm is done.

Anyway, since it is useless for your gather case, I'll just remove it, 
along with compute_self_dependence().

OK?

Thanks,
Razya