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From: Sebastian Pop <sebpop@gmail.com>
Date: Thu, 03 Feb 2011 18:11:00 -0000
Message-ID: <AANLkTikuR3Ba2-DVwtrtxEVfLNnMCv_T+oo+wCt_9q8F@mail.gmail.com>
Subject: Re: [Bug tree-optimization/46194] [4.5/4.6 Regression] gcc.dg/graphite/block-0.c FAILs with -ftree-parallelize-loops
To: "jakub at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
Cc: gcc-bugs@gcc.gnu.org
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Here is the loop kernel from block-0.c

  for (i =3D 0; i < N; i++)
    for (j =3D 0; j < N; j++)
      a[j] =3D a[i] + 1;

On Fri, Dec 31, 2010 at 06:01, jakub at gcc dot gnu.org
<gcc-bugzilla@gcc.gnu.org> wrote:
> =A0access_fn_A: {0, +, 1}_1
> =A0access_fn_B: {0, +, 1}_2
>
> =A0(subscript
> =A0iterations_that_access_an_element_twice_in_A: [0 + 1 * x_1]
> =A0last_conflict: 1000
> =A0iterations_that_access_an_element_twice_in_B: [0 + 1 * x_1]

I think that this representation of affine functions is wrong:
the access in B should read [0 + 0 * x_1 + 1 * x_2] and that
would not lead to a wrong conclusion like the following...

> =A0last_conflict: 1000
> =A0(Subscript distance: 0
> =A0)
> =A0)
> =A0inner loop index: 0
> =A0loop nest: (1 2 )
> =A0distance_vector: =A0 0 =A0 0
> =A0direction_vector: =A0 =A0 =3D =A0 =A0=3D
> )