[gcc r12-10456] tree-optimization/112281 - loop distribution and zero dependence distances

[Richard Biener via Gcc-cvs]

https://gcc.gnu.org/g:5db4b5449df8f59a61438f8db1836dbc9b53f02e

commit r12-10456-g5db4b5449df8f59a61438f8db1836dbc9b53f02e
Author: Richard Biener <rguent...@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.
    
    (cherry picked from commit 3b34902417259031823bff7f853f615a60464bbd)

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 000000000000..711f5663195c
--- /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 000000000000..d7671e3322b4
--- /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 606eb05e64a5..1b7d2a1ea7d2 100644
--- a/gcc/tree-loop-distribution.cc
+++ b/gcc/tree-loop-distribution.cc
@@ -2117,9 +2117,6 @@ 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.  */
@@ -2132,7 +2129,20 @@ 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;