[PATCH] Fix PR91293

[Richard Biener]

The following fixes wrong-code when SLP ends up swapping operands
of a reduction stmt, confusing code-generation later.  Fixed by
not doing such swapping.

Bootstrapped on x86_64-unknown-linux-gnu, testing in progress.

Richard.

2019-07-31  Richard Biener  <rguent...@suse.de>

        PR tree-optimization/91293
        * tree-vect-slp.c (vect_build_slp_tree_2): Do not swap operands
        of reduction stmts.

        * gcc.dg/vect/pr91293-1.c: New testcase.
        * gcc.dg/vect/pr91293-2.c: Likewise.
        * gcc.dg/vect/pr91293-3.c: Likewise.

Index: gcc/tree-vect-slp.c
===================================================================
--- gcc/tree-vect-slp.c (revision 273930)
+++ gcc/tree-vect-slp.c (working copy)
@@ -1296,6 +1296,9 @@ vect_build_slp_tree_2 (vec_info *vinfo,
          && nops == 2
          && oprnds_info[1]->first_dt == vect_internal_def
          && is_gimple_assign (stmt_info->stmt)
+         /* Swapping operands for reductions breaks assumptions later on.  */
+         && STMT_VINFO_DEF_TYPE (stmt_info) != vect_reduction_def
+         && STMT_VINFO_DEF_TYPE (stmt_info) != vect_double_reduction_def
          /* Do so only if the number of not successful permutes was nor more
             than a cut-ff as re-trying the recursive match on
             possibly each level of the tree would expose exponential
Index: gcc/testsuite/gcc.dg/vect/pr91293-1.c
===================================================================
--- gcc/testsuite/gcc.dg/vect/pr91293-1.c       (nonexistent)
+++ gcc/testsuite/gcc.dg/vect/pr91293-1.c       (working copy)
@@ -0,0 +1,19 @@
+/* { dg-do run } */
+/* { dg-additional-options "-msse4.1" { target { sse4_runtime } } } */
+
+long long a;
+unsigned b, c;
+int d = 62;
+void e(long long *f, int p2) { *f = p2; }
+int main()
+{
+  for (int g = 2; g <= d; g++)
+    {
+      b += g + 4;
+      c += 5 - g;
+    }
+  e(&a, b);
+  if (a != 2196)
+    __builtin_abort ();
+  return 0;
+}
Index: gcc/testsuite/gcc.dg/vect/pr91293-2.c
===================================================================
--- gcc/testsuite/gcc.dg/vect/pr91293-2.c       (nonexistent)
+++ gcc/testsuite/gcc.dg/vect/pr91293-2.c       (working copy)
@@ -0,0 +1,19 @@
+/* { dg-do run } */
+/* { dg-additional-options "-msse4.1" { target { sse4_runtime } } } */
+
+long long a;
+unsigned b, c;
+int d = 62;
+void e(long long *f, int p2) { *f = p2; }
+int main()
+{
+  for (int g = 2; g <= d; g++)
+    {
+      c += 5 - g;
+      b += g + 4;
+    }
+  e(&a, b);
+  if (a != 2196)
+    __builtin_abort ();
+  return 0;
+}
Index: gcc/testsuite/gcc.dg/vect/pr91293-3.c
===================================================================
--- gcc/testsuite/gcc.dg/vect/pr91293-3.c       (nonexistent)
+++ gcc/testsuite/gcc.dg/vect/pr91293-3.c       (working copy)
@@ -0,0 +1,20 @@
+/* { dg-do run } */
+/* { dg-additional-options "-msse4.1" { target { sse4_runtime } } } */
+
+long long a;
+unsigned b, c;
+int d = 62;
+void e(long long *f, int p2) { *f = p2; }
+int xx = 5, yy = 4;
+int main()
+{
+  for (int g = 2; g <= d; g++)
+    {
+      c += xx - g;
+      b += yy + g;
+    }
+  e(&a, b);
+  if (a != 2196)
+    __builtin_abort ();
+  return 0;
+}