tree-optimization/112281 - loop distribution and zero dependence distances

The following fixes an omission in dependence testing for loop
distribution.  When the overall dependence distance is not zero but
the dependence direction in the innermost common loop is = there is
a conflict between the partitions and we have to merge them.

	PR tree-optimization/112281
	* tree-loop-distribution.cc
	(loop_distribution::pg_add_dependence_edges): For = in the
	innermost common loop record a partition conflict.

	* gcc.dg/torture/pr112281-1.c: New testcase.
	* gcc.dg/torture/pr112281-2.c: Likewise.

3 files changed, 50 insertions, 4 deletions

diff --git a/gcc/testsuite/gcc.dg/torture/pr112281-1.c b/gcc/testsuite/gcc.dg/torture/pr112281-1.c
new file mode 100644
index 0000000..711f566
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/torture/pr112281-1.c
@@ -0,0 +1,18 @@
+/* { dg-do run } */
+/* { dg-additional-options "-ftree-loop-distribution" } */
+
+struct {
+  int : 8;
+  int a;
+} b, d[4] = {{0}, {0}, {0}, {5}};
+int c, e;
+int main() {
+  for (c = 2; c; c--)
+    for (e = 0; e < 2; e++) {
+      d[c] = b = d[c + 1];
+      d[c + 1].a = 0;
+    }
+  if (b.a != 0)
+    __builtin_abort();
+  return 0;
+}
diff --git a/gcc/testsuite/gcc.dg/torture/pr112281-2.c b/gcc/testsuite/gcc.dg/torture/pr112281-2.c
new file mode 100644
index 0000000..d7671e3
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/torture/pr112281-2.c
@@ -0,0 +1,18 @@
+/* { dg-do run } */
+/* { dg-additional-options "-ftree-loop-distribution" } */
+
+struct {
+  int : 8;
+  int a;
+} b, d[4] = {{5}, {0}, {0}, {0}};
+int c, e;
+int main() {
+  for (c = 0; c < 2; c++)
+    for (e = 0; e < 2; e++) {
+      d[c + 1] = b = d[c];
+      d[c].a = 0;
+    }
+  if (b.a != 0)
+    __builtin_abort();
+  return 0;
+}
diff --git a/gcc/tree-loop-distribution.cc b/gcc/tree-loop-distribution.cc
index ffca535..95c1eea 100644
--- a/gcc/tree-loop-distribution.cc
+++ b/gcc/tree-loop-distribution.cc
@@ -2155,9 +2155,6 @@ loop_distribution::pg_add_dependence_edges (struct graph *rdg, int dir,
 	    }
 	  else if (DDR_ARE_DEPENDENT (ddr) == NULL_TREE)
 	    {
-	      if (DDR_REVERSED_P (ddr))
-		this_dir = -this_dir;
-
 	      /* Known dependences can still be unordered througout the
 		 iteration space, see gcc.dg/tree-ssa/ldist-16.c and
 		 gcc.dg/tree-ssa/pr94969.c.  */
@@ -2170,7 +2167,20 @@ loop_distribution::pg_add_dependence_edges (struct graph *rdg, int dir,
 	      /* Else as the distance vector is lexicographic positive swap
 		 the dependence direction.  */
 	      else
-		this_dir = -this_dir;
+		{
+		  if (DDR_REVERSED_P (ddr))
+		    this_dir = -this_dir;
+		  this_dir = -this_dir;
+
+		  /* When then dependence distance of the innermost common
+		     loop of the DRs is zero we have a conflict.  */
+		  auto l1 = gimple_bb (DR_STMT (dr1))->loop_father;
+		  auto l2 = gimple_bb (DR_STMT (dr2))->loop_father;
+		  int idx = index_in_loop_nest (find_common_loop (l1, l2)->num,
+						DDR_LOOP_NEST (ddr));
+		  if (DDR_DIST_VECT (ddr, 0)[idx] == 0)
+		    this_dir = 2;
+		}
 	    }
 	  else
 	    this_dir = 0;