Hi! 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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