[PATCH] tree-optimization/115959 - ICE with SLP condition reduction

[Richard Biener]

The following fixes how during reduction epilogue generation we
gather conditional compares for condition reductions, thereby
following the reduction chain via STMT_VINFO_REDUC_IDX.  The issue
is that SLP nodes for COND_EXPRs can have either three or four
children dependent on whether we have legacy GENERIC expressions
in the transitional pattern GIMPLE for the COND_EXPR condition.

Bootstrapped and tested on x86_64-unknown-linux-gnu, pushed.

        PR tree-optimization/115959
        * tree-vect-loop.cc (vect_create_epilog_for_reduction):
        Get at the REDUC_IDX child in a safer way for COND_EXPR
        nodes.

        * gcc.dg/vect/pr115959.c: New testcase.
---
 gcc/testsuite/gcc.dg/vect/pr115959.c | 14 ++++++++++++++
 gcc/tree-vect-loop.cc                | 10 +++++++---
 2 files changed, 21 insertions(+), 3 deletions(-)
 create mode 100644 gcc/testsuite/gcc.dg/vect/pr115959.c

diff --git a/gcc/testsuite/gcc.dg/vect/pr115959.c 
b/gcc/testsuite/gcc.dg/vect/pr115959.c
new file mode 100644
index 00000000000..181d5522018
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/vect/pr115959.c
@@ -0,0 +1,14 @@
+/* { dg-do compile } */
+
+int a;
+_Bool *b;
+void f()
+{
+  int t = a;
+  for (int e = 0; e < 2048; e++)
+    {
+      if (!b[e])
+       t = 0;
+    }
+  a = t;
+}
diff --git a/gcc/tree-vect-loop.cc b/gcc/tree-vect-loop.cc
index 2d68db613f8..191a37a1e1a 100644
--- a/gcc/tree-vect-loop.cc
+++ b/gcc/tree-vect-loop.cc
@@ -6107,9 +6107,13 @@ vect_create_epilog_for_reduction (loop_vec_info 
loop_vinfo,
                    (std::make_pair (gimple_assign_rhs1 (vec_stmt),
                                     STMT_VINFO_REDUC_IDX (cond_info) == 2));
                }
-             /* ???  We probably want to have REDUC_IDX on the SLP node?  */
-             cond_node = SLP_TREE_CHILDREN
-                           (cond_node)[STMT_VINFO_REDUC_IDX (cond_info)];
+             /* ???  We probably want to have REDUC_IDX on the SLP node?
+                We have both three and four children COND_EXPR nodes
+                dependent on whether the comparison is still embedded
+                as GENERIC.  So work backwards.  */
+             int slp_reduc_idx = (SLP_TREE_CHILDREN (cond_node).length () - 3
+                                  + STMT_VINFO_REDUC_IDX (cond_info));
+             cond_node = SLP_TREE_CHILDREN (cond_node)[slp_reduc_idx];
            }
        }
       else
-- 
2.35.3