On Fri, 20 Nov 2015, Jakub Jelinek wrote:
> Hi!
>
> 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).
Richard.
> Bootstrapped/regtested on x86_64-linux and i686-linux, committed to trunk.
>
> 2015-11-20 Jakub Jelinek <ja...@redhat.com>
>
> PR middle-end/68221
> * omp-low.c (lower_rec_input_clauses): If C/C++ array reduction
> has non-zero bias, subtract it in integer type instead of
> pointer plus of negated bias.
>
> * testsuite/libgomp.c/reduction-11.c: Remove xfail.
> * testsuite/libgomp.c/reduction-12.c: Likewise.
> * testsuite/libgomp.c++/reduction-11.C: Likewise.
> * testsuite/libgomp.c++/reduction-12.C: Likewise.
>
> --- 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;
> --- libgomp/testsuite/libgomp.c/reduction-11.c.jj 2015-11-05
> 16:03:53.000000000 +0100
> +++ libgomp/testsuite/libgomp.c/reduction-11.c 2015-11-20
> 13:38:24.448520879 +0100
> @@ -1,4 +1,4 @@
> -/* { dg-do run { xfail *-*-* } } */
> +/* { dg-do run } */
>
> char z[10] = { 0 };
>
> --- libgomp/testsuite/libgomp.c/reduction-12.c.jj 2015-11-05
> 16:03:53.000000000 +0100
> +++ libgomp/testsuite/libgomp.c/reduction-12.c 2015-11-20
> 13:38:34.565378078 +0100
> @@ -1,4 +1,4 @@
> -/* { dg-do run { xfail *-*-* } } */
> +/* { dg-do run } */
>
> struct A { int t; };
> struct B { char t; };
> --- libgomp/testsuite/libgomp.c++/reduction-11.C.jj 2015-11-05
> 16:03:53.000000000 +0100
> +++ libgomp/testsuite/libgomp.c++/reduction-11.C 2015-11-20
> 13:37:53.921951766 +0100
> @@ -1,4 +1,4 @@
> -// { dg-do run { xfail *-*-* } }
> +// { dg-do run }
>
> char z[10] = { 0 };
>
> --- libgomp/testsuite/libgomp.c++/reduction-12.C.jj 2015-11-05
> 16:03:53.000000000 +0100
> +++ libgomp/testsuite/libgomp.c++/reduction-12.C 2015-11-20
> 13:38:03.983809741 +0100
> @@ -1,4 +1,4 @@
> -// { dg-do run { xfail *-*-* } }
> +// { dg-do run }
>
> template <typename T>
> struct A
>
> Jakub
>
>
--
Richard Biener <rguent...@suse.de>
SUSE LINUX GmbH, GF: Felix Imendoerffer, Jane Smithard, Graham Norton, HRB
21284 (AG Nuernberg)
