Re: [PATCH] Fix up reduction-1{1,2} testcases (PR middle-end/68221)

[Thomas Schwinge <thomas at codesourcery dot com>]

Hi!

Ping.

On Wed, 23 Dec 2015 12:03:48 +0100, I wrote:
> Ping.
> 
> On Thu, 26 Nov 2015 14:31:56 +0100, I wrote:
> > On Mon, 23 Nov 2015 12:13:07 +0100 (CET), Richard Biener <rguenther@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 <thomas@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;


GrÃÃe
 Thomas

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