[gcc r14-5626] tree-optimization/112281 - loop distribution and zero dependence distances

[Richard Biener <rguenth@gcc.gnu.org>]

https://gcc.gnu.org/g:3b34902417259031823bff7f853f615a60464bbd

commit r14-5626-g3b34902417259031823bff7f853f615a60464bbd
Author: Richard Biener <rguenther@suse.de>
Date:   Mon Nov 20 13:39:52 2023 +0100

    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.

Diff:
---
 gcc/testsuite/gcc.dg/torture/pr112281-1.c | 18 ++++++++++++++++++
 gcc/testsuite/gcc.dg/torture/pr112281-2.c | 18 ++++++++++++++++++
 gcc/tree-loop-distribution.cc             | 18 ++++++++++++++----
 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 00000000000..711f5663195
--- /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 00000000000..d7671e3322b
--- /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 ffca535064b..95c1eea65be 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;