Fix PR46194: fix the computation of distance vectors.

2011-02-04  Sebastian Pop  <sebastian.pop@amd.com>

	PR tree-optimization/46194
	* tree-data-ref.c (analyze_miv_subscript): Remove comment.
	(build_classic_dist_vector_1): Do not represent classic distance
	vectors when the access functions are variating in different loops.

	* gcc.dg/autopar/pr46194.c: New.

From-SVN: r169847

gcc/ChangeLog

+2011-02-04  Sebastian Pop  <sebastian.pop@amd.com>
+
+	PR tree-optimization/46194
+	* tree-data-ref.c (analyze_miv_subscript): Remove comment.
+	(build_classic_dist_vector_1): Do not represent classic distance
+	vectors when the access functions are variating in different loops.
+
 2011-02-04  Joseph Myers  <joseph@codesourcery.com>
 
 	* config/mips/iris6.opt: New.

gcc/testsuite/ChangeLog

+2011-02-04  Sebastian Pop  <sebastian.pop@amd.com>
+
+	PR tree-optimization/46194
+	* gcc.dg/autopar/pr46194.c: New.
+
 2011-02-04  H.J. Lu  <hongjiu.lu@intel.com>
 
 	PR tree-optimization/43695

gcc/testsuite/gcc.dg/autopar/pr46194.c

+/* PR tree-optimization/46194 */
+/* { dg-do compile } */
+/* { dg-options "-O -ftree-parallelize-loops=2 -fdump-tree-parloops-details" } */
+
+#define N 1000
+int a[N];
+
+int foo (void)
+{
+  int j;
+  int i;
+
+  /* This is not blocked as it is not profitable.  */
+  for (i = 0; i < N; i++)
+    for (j = 0; j < N; j++)
+      a[j] = a[i] + 1;
+
+  return a[0];
+}
+
+/* This loop cannot be parallelized due to a dependence.  */
+
+/* { dg-final { scan-tree-dump-times "SUCCESS: may be parallelized" 0 "parloops" } } */
+/* { dg-final { cleanup-tree-dump "parloops" } } */

gcc/tree-data-ref.c

@@ -2681,14 +2681,6 @@ analyze_miv_subscript (tree chrec_a,
 		       tree *last_conflicts,
 		       struct loop *loop_nest)
 {
-  /* FIXME:  This is a MIV subscript, not yet handled.
-     Example: (A[{1, +, 1}_1] vs. A[{1, +, 1}_2]) that comes from
-     (A[i] vs. A[j]).
-
-     In the SIV test we had to solve a Diophantine equation with two
-     variables.  In the MIV case we have to solve a Diophantine
-     equation with 2*n variables (if the subscript uses n IVs).
-  */
   tree type, difference;
 
   dependence_stats.num_miv++;
@@ -2960,29 +2952,19 @@ build_classic_dist_vector_1 (struct data_dependence_relation *ddr,
 	  && TREE_CODE (access_fn_b) == POLYNOMIAL_CHREC)
 	{
 	  int dist, index;
-	  int index_a = index_in_loop_nest (CHREC_VARIABLE (access_fn_a),
-					    DDR_LOOP_NEST (ddr));
-	  int index_b = index_in_loop_nest (CHREC_VARIABLE (access_fn_b),
-					    DDR_LOOP_NEST (ddr));
-
-	  /* The dependence is carried by the outermost loop.  Example:
-	     | loop_1
-	     |   A[{4, +, 1}_1]
-	     |   loop_2
-	     |     A[{5, +, 1}_2]
-	     |   endloop_2
-	     | endloop_1
-	     In this case, the dependence is carried by loop_1.  */
-	  index = index_a < index_b ? index_a : index_b;
-	  *index_carry = MIN (index, *index_carry);
+	  int var_a = CHREC_VARIABLE (access_fn_a);
+	  int var_b = CHREC_VARIABLE (access_fn_b);
 
-	  if (chrec_contains_undetermined (SUB_DISTANCE (subscript)))
+	  if (var_a != var_b
+	      || chrec_contains_undetermined (SUB_DISTANCE (subscript)))
 	    {
 	      non_affine_dependence_relation (ddr);
 	      return false;
 	    }
 
 	  dist = int_cst_value (SUB_DISTANCE (subscript));
+	  index = index_in_loop_nest (var_a, DDR_LOOP_NEST (ddr));
+	  *index_carry = MIN (index, *index_carry);
 
 	  /* This is the subscript coupling test.  If we have already
 	     recorded a distance for this loop (a distance coming from