[PATCH] tree-optimization/115395 - wrong-code with SLP reduction in epilog

[Richard Biener]

When we continue a non-SLP reduction from the main loop in the
epilog with a SLP reduction we currently fail to handle an
adjustment by the initial value because that's not a thing with SLP.
As long as we have the possibility to mix SLP and non-SLP we have
to handle it though.

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

        PR tree-optimization/115395
        * tree-vect-loop.cc (vect_create_epilog_for_reduction):
        Handle STMT_VINFO_REDUC_EPILOGUE_ADJUSTMENT also for SLP
        reductions of group_size one.

        * gcc.dg/vect/pr115395.c: New testcase.
---
 gcc/testsuite/gcc.dg/vect/pr115395.c | 27 +++++++++++++++++++++++++++
 gcc/tree-vect-loop.cc                | 27 ++++++++-------------------
 2 files changed, 35 insertions(+), 19 deletions(-)
 create mode 100644 gcc/testsuite/gcc.dg/vect/pr115395.c

diff --git a/gcc/testsuite/gcc.dg/vect/pr115395.c 
b/gcc/testsuite/gcc.dg/vect/pr115395.c
new file mode 100644
index 00000000000..cd1cee9f3df
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/vect/pr115395.c
@@ -0,0 +1,27 @@
+/* { dg-additional-options "-mavx2" { target avx2_runtime } } */
+
+#include "tree-vect.h"
+
+struct {
+  long header_size;
+  long start_offset;
+  long end_offset;
+} myrar_dbo[5] = {{0, 87, 6980}, {0, 7087, 13980}, {0, 14087, 0}};
+
+int i;
+long offset;
+
+int main()
+{
+  check_vect ();
+
+  offset += myrar_dbo[0].start_offset;
+  while (i < 2) {
+    i++;
+    offset += myrar_dbo[i].start_offset - myrar_dbo[i - 1].end_offset;
+  }
+  if (offset != 301)
+    abort();
+
+  return 0;
+}
diff --git a/gcc/tree-vect-loop.cc b/gcc/tree-vect-loop.cc
index f598403df46..d894ac1c067 100644
--- a/gcc/tree-vect-loop.cc
+++ b/gcc/tree-vect-loop.cc
@@ -6047,25 +6047,14 @@ vect_create_epilog_for_reduction (loop_vec_info 
loop_vinfo,
 
   tree induc_val = NULL_TREE;
   tree adjustment_def = NULL;
-  if (slp_node)
-    {
-      /* Optimize: for induction condition reduction, if we can't use zero
-        for induc_val, use initial_def.  */
-      if (STMT_VINFO_REDUC_TYPE (reduc_info) == INTEGER_INDUC_COND_REDUCTION)
-       induc_val = STMT_VINFO_VEC_INDUC_COND_INITIAL_VAL (reduc_info);
-      /* ???  Coverage for 'else' isn't clear.  */
-    }
+  /* Optimize: for induction condition reduction, if we can't use zero
+     for induc_val, use initial_def.  */
+  if (STMT_VINFO_REDUC_TYPE (reduc_info) == INTEGER_INDUC_COND_REDUCTION)
+    induc_val = STMT_VINFO_VEC_INDUC_COND_INITIAL_VAL (reduc_info);
+  else if (double_reduc)
+    ;
   else
-    {
-      /* Optimize: for induction condition reduction, if we can't use zero
-         for induc_val, use initial_def.  */
-      if (STMT_VINFO_REDUC_TYPE (reduc_info) == INTEGER_INDUC_COND_REDUCTION)
-       induc_val = STMT_VINFO_VEC_INDUC_COND_INITIAL_VAL (reduc_info);
-      else if (double_reduc)
-       ;
-      else
-       adjustment_def = STMT_VINFO_REDUC_EPILOGUE_ADJUSTMENT (reduc_info);
-    }
+    adjustment_def = STMT_VINFO_REDUC_EPILOGUE_ADJUSTMENT (reduc_info);
 
   stmt_vec_info single_live_out_stmt[] = { stmt_info };
   array_slice<const stmt_vec_info> live_out_stmts = single_live_out_stmt;
@@ -6890,7 +6879,7 @@ vect_create_epilog_for_reduction (loop_vec_info 
loop_vinfo,
 
   if (adjustment_def)
     {
-      gcc_assert (!slp_reduc);
+      gcc_assert (!slp_reduc || group_size == 1);
       gimple_seq stmts = NULL;
       if (double_reduc)
        {
-- 
2.35.3