re PR tree-optimization/81740 (wrong code at -O3 in both 32-bit and 64-bit modes…

re PR tree-optimization/81740 (wrong code at -O3 in both 32-bit and 64-bit modes on x86_64-linux-gnu)

2019-03-26  Bin Cheng  <bin.cheng@linux.alibaba.com>

	PR tree-optimization/81740
	* tree-vect-data-refs.c (vect_analyze_data_ref_dependence):
	In case of outer loop vectorization, check for backward dependence
	at the inner loop if outer loop dependence is reversed.

	* gcc.dg/vect/pr81740-1.c: New testcase.
	* gcc.dg/vect/pr81740-2.c: Likewise.

From-SVN: r269938

gcc/ChangeLog

+2019-03-26  Bin Cheng  <bin.cheng@linux.alibaba.com>
+
+	PR tree-optimization/81740
+	* tree-vect-data-refs.c (vect_analyze_data_ref_dependence):
+	In case of outer loop vectorization, check for backward dependence
+	at the inner loop if outer loop dependence is reversed.
+
 2019-03-26  Alan Modra  <amodra@gmail.com>
 
 	* config/rs6000/rs6000.c (rs6000_init_hard_regno_mode_ok): Correct

gcc/testsuite/ChangeLog

+2019-03-26  Bin Cheng  <bin.cheng@linux.alibaba.com>
+
+	PR tree-optimization/81740
+	* gcc.dg/vect/pr81740-1.c: New testcase.
+	* gcc.dg/vect/pr81740-2.c: Likewise.
+
 2019-03-26  Iain Buclaw  <ibuclaw@gdcproject.org>
 
 	* gdc.test/gdc-test.exp (gdc-do-test): Sort and remove duplicate

gcc/testsuite/gcc.dg/vect/pr81740-1.c

+/* { dg-do run } */
+/* { dg-require-effective-target vect_int } */
+
+#include "tree-vect.h"
+
+int a[8][10] = { [2][5] = 4 }, c;
+
+int
+main ()
+{
+  short b;
+  int i, d;
+  check_vect ();
+  for (b = 4; b >= 0; b--)
+    for (c = 0; c <= 6; c++)
+      a[c + 1][b + 2] = a[c][b + 1];
+  for (i = 0; i < 8; i++)
+    for (d = 0; d < 10; d++)
+      if (a[i][d] != (i == 3 && d == 6) * 4)
+	__builtin_abort ();
+  return 0;
+}

gcc/testsuite/gcc.dg/vect/pr81740-2.c

+/* { dg-do run } */
+/* { dg-require-effective-target vect_int } */
+
+#include "tree-vect.h"
+
+int a[8][10] = { [2][5] = 4 }, c;
+
+int
+main ()
+{
+  short b;
+  int i, d;
+  check_vect ();
+  for (b = 4; b >= 0; b--)
+    for (c = 6; c >= 0; c--)
+      a[c + 1][b + 2] = a[c][b + 1];
+  for (i = 0; i < 8; i++)
+    for (d = 0; d < 10; d++)
+      if (a[i][d] != (i == 3 && d == 6) * 4)
+	__builtin_abort ();
+  return 0;
+}
+
+/* { dg-final { scan-tree-dump "OUTER LOOP VECTORIZED" "vect" } } */

gcc/tree-vect-data-refs.c

@@ -473,8 +473,22 @@ vect_analyze_data_ref_dependence (struct data_dependence_relation *ddr,
 	     reversed (to make distance vector positive), and the actual
 	     distance is negative.  */
 	  if (dump_enabled_p ())
-	    dump_printf_loc (MSG_MISSED_OPTIMIZATION, vect_location,
+	    dump_printf_loc (MSG_NOTE, vect_location,
 	                     "dependence distance negative.\n");
+	  /* When doing outer loop vectorization, we need to check if there is
+	     a backward dependence at the inner loop level if the dependence
+	     at the outer loop is reversed.  See PR81740.  */
+	  if (nested_in_vect_loop_p (loop, stmtinfo_a)
+	      || nested_in_vect_loop_p (loop, stmtinfo_b))
+	    {
+	      unsigned inner_depth = index_in_loop_nest (loop->inner->num,
+							 DDR_LOOP_NEST (ddr));
+	      if (dist_v[inner_depth] < 0)
+		return opt_result::failure_at (stmtinfo_a->stmt,
+					       "not vectorized, dependence "
+					       "between data-refs %T and %T\n",
+					       DR_REF (dra), DR_REF (drb));
+	    }
 	  /* Record a negative dependence distance to later limit the
 	     amount of stmt copying / unrolling we can perform.
 	     Only need to handle read-after-write dependence.  */
@@ -490,7 +504,7 @@ vect_analyze_data_ref_dependence (struct data_dependence_relation *ddr,
 	{
 	  /* The dependence distance requires reduction of the maximal
 	     vectorization factor.  */
-	  *max_vf = abs (dist);
+	  *max_vf = abs_dist;
 	  if (dump_enabled_p ())
 	    dump_printf_loc (MSG_NOTE, vect_location,
 	                     "adjusting maximal vectorization factor to %i\n",