Fix up reduction-1{1,2} testcases (PR middle-end/68221)

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.

Bootstrapped/regtested on x86_64-linux and i686-linux, committed to trunk.

2015-11-20  Jakub Jelinek  <jakub@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.


	Jakub

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  <jakub@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
> 
>