[PATCH] tree-optimization/97838 - fix SLP leaf detection

[Richard Biener]

This properly handles reduction PHI nodes with unrepresented
initial value as leaf in the SLP graph.

Bootstrap & regtest running on x86_64-unknown-linux-gnu.

2020-11-16  Richard Biener  <rguent...@suse.de>

        PR tree-optimization/97838
        * tree-vect-slp.c (vect_slp_build_vertices): Properly handle
        a NULL child as leaf.

        * gcc.dg/vect/pr97838.c: New testcase.
---
 gcc/testsuite/gcc.dg/vect/pr97838.c | 11 +++++++++++
 gcc/tree-vect-slp.c                 |  7 ++++++-
 2 files changed, 17 insertions(+), 1 deletion(-)
 create mode 100644 gcc/testsuite/gcc.dg/vect/pr97838.c

diff --git a/gcc/testsuite/gcc.dg/vect/pr97838.c 
b/gcc/testsuite/gcc.dg/vect/pr97838.c
new file mode 100644
index 00000000000..06ec0358f6e
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/vect/pr97838.c
@@ -0,0 +1,11 @@
+/* { dg-do compile } */
+
+int a, b, c, d;
+
+void f() {
+  while (c++) {
+    int e = -1;
+    d = a ? e / a : e;
+    b ^= ~d;
+  }
+}
diff --git a/gcc/tree-vect-slp.c b/gcc/tree-vect-slp.c
index e4c2aa480e5..0fb463f4bd0 100644
--- a/gcc/tree-vect-slp.c
+++ b/gcc/tree-vect-slp.c
@@ -2609,13 +2609,18 @@ vect_slp_build_vertices (hash_set<slp_tree> &visited, 
slp_tree node,
   vertices.safe_push (node);
 
   bool leaf = true;
+  bool force_leaf = false;
   FOR_EACH_VEC_ELT (SLP_TREE_CHILDREN (node), i, child)
     if (child)
       {
        leaf = false;
        vect_slp_build_vertices (visited, child, vertices, leafs);
       }
-  if (leaf)
+    else
+      /* A NULL SLP_TREE_CHILDREN entry is a not represented initial
+        value of reductions which means the reduction itself is leaf.  */
+      force_leaf = true;
+  if (leaf || force_leaf)
     leafs.safe_push (node->vertex);
 }
 
-- 
2.26.2