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)