[Bug tree-optimization/32461] [4.3 Regression] Segmentation fault in build_classic_dist_vector_1() at tree-data-ref.c:2700

["richard dot guenther at gmail dot com" <gcc-bugzilla at gcc dot gnu dot org>]

------- Comment #10 from richard dot guenther at gmail dot com  2007-06-23 19:24 -------
Subject: Re:  [4.3 Regression] Segmentation fault in
build_classic_dist_vector_1() at tree-data-ref.c:2700

On 6/23/07, Richard Guenther <richard.guenther@gmail.com> wrote:
> On 6/23/07, Sebastian Pop <spop@gcc.gnu.org> wrote:
> > Hi,
> >
> > In data dependence analysis, when the dependence distance is
> > lexicographically negative, we recompute the dependence by inverting
> > the source and the sink memory accesses, and thus we compute the
> > dependence again but in the opposite direction.  In one way we
> > compute:
> >
> > MINUS_EXPR
> > (unsigned int) i_434 + 1
> > (unsigned int) i_434
> > =
> > 1
> >
> > but when going the other way, backwards, we have to compute:
> >
> > MINUS_EXPR
> > (unsigned int) i_434
> > (unsigned int) i_434 + 1
> > =
> > ~(unsigned int) i_434 + (unsigned int) i_434
> >
> > and instead of getting an integer_cst, we get that ugly expression
> > from fold, the dependence test fails, and everything goes wrong from
> > that point.
> >
> > With this patch we get the expected 0xffffffffffffffff for the above
> > case.  The patch teaches fold how to compute the minus expression for
> > unsigned int and pointer expressions.
> >
> > Bootstrapped and tested on i686-linux.  Okay for trunk?
>
> First - can you check why the asociate: case in fold_binary does not do
> the transformation and maybe fix that instead if possible?
>
> Then there is a ChangeLog missing.  Further...
>
> +         && integer_zerop (fold_build2 (MINUS_EXPR, type, arg0,
> +                                        TREE_OPERAND (arg1, 0))))
>
> to avoid creating trees and just throwing them away you should use
> operand_equal_p (arg0, TREE_OPERAND (arg1, 0)) instead.  You
> similarly may want to check operand 1 for A - (B + A)?
>
> +         && TYPE_UNSIGNED (type)
>
> you should check TYPE_OVERFLOW_WRAPS (type)  instead.

Oh - and there is omit_two_operands which you should use to
omit the two As.  This takes care of side-effects.

Richard.


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=32461