Update post order number for merged SCC.

Function loop_distribution::break_alias_scc_partitions needs to compute
SCC with runtime alias edges skipped.  As a result, partitions could be
re-assigned larger post order number than SCC's precedent partition and
distributed before the precedent one.  This fixes the issue by updating
the merged partition to the minimal post order in SCC.

gcc/
    PR tree-optimization/94125
    * tree-loop-distribution.c
    (loop_distribution::break_alias_scc_partitions): Update post order
    number for merged scc.

gcc/testsuite/
    PR tree-optimization/94125
    * gcc.dg/tree-ssa/pr94125.c: New test.

4 files changed, 58 insertions, 8 deletions

diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index 6718f71..53c9622 100644
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,3 +1,10 @@
+2020-03-16  Bin Cheng  <bin.cheng@linux.alibaba.com>
+
+	PR tree-optimization/94125
+	* tree-loop-distribution.c
+	(loop_distribution::break_alias_scc_partitions): Update post order
+	number for merged scc.
+
 2020-03-15  H.J. Lu  <hongjiu.lu@intel.com>
 
 	PR target/89229
diff --git a/gcc/testsuite/ChangeLog b/gcc/testsuite/ChangeLog
index f79f1c7..ab04066 100644
--- a/gcc/testsuite/ChangeLog
+++ b/gcc/testsuite/ChangeLog
@@ -1,3 +1,8 @@
+2020-03-16  Bin Cheng  <bin.cheng@linux.alibaba.com>
+
+	PR tree-optimization/94125
+	* gcc.dg/tree-ssa/pr94125.c: New test.
+
 2020-03-15  H.J. Lu  <hongjiu.lu@intel.com>
 
 	PR target/89229
diff --git a/gcc/testsuite/gcc.dg/tree-ssa/pr94125.c b/gcc/testsuite/gcc.dg/tree-ssa/pr94125.c
new file mode 100644
index 0000000..c339e51
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/tree-ssa/pr94125.c
@@ -0,0 +1,41 @@
+/* { dg-do run } */
+/* { dg-options "-O3" } */
+
+unsigned char b, f;
+short d[1][8][1], *g = &d[0][3][0];
+
+void __attribute__((noinline)) foo ()
+{
+  int k[256] = { 0, 0, 0, 4, 0, 0 };
+  for (int c = 252; c >= 0; c--)
+    {
+      b = f;
+      *g = k[c + 3];
+      k[c + 1] = 0;
+    }
+  for (int i = 0; i < 8; i++)
+    if (d[0][i][0] != 0)
+      __builtin_abort ();
+}
+
+void __attribute__((noinline)) bar ()
+{
+  int k[256] = { 0, 0, 0, 4, 0, 0 };
+  k[255] = 4;
+  for (int c = 0; c <=252; c++)
+    {
+      b = f;
+      *g = k[c + 3];
+      k[c + 1] = 0;
+    }
+  for (int i = 0; i < 8; i++)
+    if ((i == 3 && d[0][i][0] != 4) || (i != 3 && d[0][i][0] != 0))
+      __builtin_abort ();
+}
+
+int main ()
+{
+  foo ();
+  bar ();
+  return 0;
+}
diff --git a/gcc/tree-loop-distribution.c b/gcc/tree-loop-distribution.c
index 35d3821..4442321 100644
--- a/gcc/tree-loop-distribution.c
+++ b/gcc/tree-loop-distribution.c
@@ -2489,14 +2489,11 @@ loop_distribution::break_alias_scc_partitions (struct graph *rdg,
 	      if (cbdata.vertices_component[k] != i)
 		continue;
 
-	      /* Update postorder number so that merged reduction partition is
-		 sorted after other partitions.  */
-	      if (!partition_reduction_p (first)
-		  && partition_reduction_p (partition))
-		{
-		  gcc_assert (pg->vertices[k].post < pg->vertices[j].post);
-		  pg->vertices[j].post = pg->vertices[k].post;
-		}
+	      /* Update to the minimal postordeer number of vertices in scc so
+		 that merged partition is sorted correctly against others.  */
+	      if (pg->vertices[j].post > pg->vertices[k].post)
+		pg->vertices[j].post = pg->vertices[k].post;
+
 	      partition_merge_into (NULL, first, partition, FUSE_SAME_SCC);
 	      (*partitions)[k] = NULL;
 	      partition_free (partition);