Hi! Ping.
On Thu, 26 Nov 2015 14:31:56 +0100, I wrote:
> On Mon, 23 Nov 2015 12:13:07 +0100 (CET), Richard Biener <rguent...@suse.de>
> wrote:
> > On Fri, 20 Nov 2015, Jakub Jelinek wrote:
> > > If C/C++ array section reductions have non-zero (positive) bias, it is
> > > implemented by declaring a smaller private array and subtracting the bias
> > > from the start of the private array (because valid code may only
> > > dereference
> > > elements from bias onwards). But, this isn't something that is kosher in
> > > C/C++ pointer arithmetics and the alias oracle seems to get upset on that.
> > > So, the following patch fixes that by performing the subtraction on
> > > integral
> > > type instead of p+ -bias.
> >
> > So this still does use the biased pointer because you do not
> > re-write accesses (where you could have applied the biasing to
> > the indexes / offsets), right? Thus the patch is merely obfuscation
> > for GCC rather than making it kosher for C/C++ (you still have a
> > pointer pointing outside of the private array object)?
> >
> > I still hope to have a look where the alias oracle gets things
> > wrong (well, if so by accident at least).
>
> I understand this ("have a look where the alias oracle gets things
> wrong") to have happened in Richi's trunk r230793,
> <https://gcc.gnu.org/bugzilla/show_bug.cgi?id=68221#c5>?
>
> I've tested that with the original POINTER_PLUS_EXPR code restored and
> with Richi's r230793 applied, for x86_64 GNU/Linux there is no change for
> the libgomp.c/reduction-11.c, libgomp.c/reduction-12.c,
> libgomp.c++/reduction-11.C, libgomp.c++/reduction-12.C test cases
> (already PASSed), but for 32-bit x86, they now PASS instead of FAILing.
> That is, I tested with the following (part of r230672) reverted:
>
> > > --- gcc/omp-low.c.jj 2015-11-20 12:56:17.000000000 +0100
> > > +++ gcc/omp-low.c 2015-11-20 13:44:29.080374051 +0100
> > > @@ -4444,11 +4444,13 @@ lower_rec_input_clauses (tree clauses, g
> > >
> > > if (!integer_zerop (bias))
> > > {
> > > - bias = fold_convert_loc (clause_loc, sizetype, bias);
> > > - bias = fold_build1_loc (clause_loc, NEGATE_EXPR,
> > > - sizetype, bias);
> > > - x = fold_build2_loc (clause_loc, POINTER_PLUS_EXPR,
> > > - TREE_TYPE (x), x, bias);
> > > + bias = fold_convert_loc (clause_loc, pointer_sized_int_node,
> > > + bias);
> > > + yb = fold_convert_loc (clause_loc, pointer_sized_int_node,
> > > + x);
> > > + yb = fold_build2_loc (clause_loc, MINUS_EXPR,
> > > + pointer_sized_int_node, yb, bias);
> > > + x = fold_convert_loc (clause_loc, TREE_TYPE (x), yb);
> > > yb = create_tmp_var (ptype, name);
> > > gimplify_assign (yb, x, ilist);
> > > x = yb;
>
> OK to commit the following to trunk?
>
> commit 92b0eebfcbe914d3addeb97d4bb33f76a44dbe60
> Author: Thomas Schwinge <tho...@codesourcery.com>
> Date: Thu Nov 26 14:21:13 2015 +0100
>
> Restore original POINTER_PLUS_EXPR code
>
> PR middle-end/68221
> gcc/
> * omp-low.c (lower_rec_input_clauses): If C/C++ array reduction
> has non-zero bias, use pointer plus of negated bias instead of
> subtracting it in integer type.
> ---
> gcc/omp-low.c | 12 +++++-------
> 1 file changed, 5 insertions(+), 7 deletions(-)
>
> diff --git gcc/omp-low.c gcc/omp-low.c
> index 0b44588..927d9d9 100644
> --- gcc/omp-low.c
> +++ gcc/omp-low.c
> @@ -4451,13 +4451,11 @@ lower_rec_input_clauses (tree clauses, gimple_seq
> *ilist, gimple_seq *dlist,
>
> if (!integer_zerop (bias))
> {
> - bias = fold_convert_loc (clause_loc, pointer_sized_int_node,
> - bias);
> - yb = fold_convert_loc (clause_loc, pointer_sized_int_node,
> - x);
> - yb = fold_build2_loc (clause_loc, MINUS_EXPR,
> - pointer_sized_int_node, yb, bias);
> - x = fold_convert_loc (clause_loc, TREE_TYPE (x), yb);
> + bias = fold_convert_loc (clause_loc, sizetype, bias);
> + bias = fold_build1_loc (clause_loc, NEGATE_EXPR,
> + sizetype, bias);
> + x = fold_build2_loc (clause_loc, POINTER_PLUS_EXPR,
> + TREE_TYPE (x), x, bias);
> yb = create_tmp_var (ptype, name);
> gimplify_assign (yb, x, ilist);
> x = yb;
Grüße
Thomas
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