[gcc r12-2570] tree-optimization/101615 - SLP permute opt of existing vectors

[gcc r12-2570] tree-optimization/101615 - SLP permute opt of existing vectors

[Richard Biener]

https://gcc.gnu.org/g:6bb6e2044ced33d08175361b8e39a9c5d4a868a6

commit r12-2570-g6bb6e2044ced33d08175361b8e39a9c5d4a868a6
Author: Richard Biener <rguenther@suse.de>
Date:   Wed Jul 28 14:16:35 2021 +0200

    tree-optimization/101615 - SLP permute opt of existing vectors
    
    This fixes one issue discovered when analyzing PR101615, namely
    we happily push permutes to pre-existing vectors but end up
    not actually permuting them.  In fact we don't want to, so force
    materialization on the external.
    
    It doesn't fix the original testcase though.
    
    2021-07-28  Richard Biener  <rguenther@suse.de>
    
            PR tree-optimization/101615
            * tree-vect-slp.c (vect_optimize_slp): Pre-existing vector
            external nodes cannot be permuted so make them perm_out 0.
    
            * gcc.dg/vect/bb-slp-pr101615-1.c: New testcase.

Diff:
---
 gcc/testsuite/gcc.dg/vect/bb-slp-pr101615-1.c | 30 +++++++++++++++++++++++++++
 gcc/tree-vect-slp.c                           |  6 ++++--
 2 files changed, 34 insertions(+), 2 deletions(-)

diff --git a/gcc/testsuite/gcc.dg/vect/bb-slp-pr101615-1.c b/gcc/testsuite/gcc.dg/vect/bb-slp-pr101615-1.c
new file mode 100644
index 00000000000..d1c9c02d517
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/vect/bb-slp-pr101615-1.c
@@ -0,0 +1,30 @@
+/* { dg-do run } */
+/* { dg-additional-options "-w -Wno-psabi" } */
+
+#include "tree-vect.h"
+
+typedef int v4si __attribute__((vector_size(16)));
+
+int a[4];
+int b[4];
+
+void __attribute__((noipa))
+foo (v4si x)
+{
+  b[0] = a[3] + x[0];
+  b[1] = a[2] + x[1];
+  b[2] = a[1] + x[2];
+  b[3] = a[0] + x[3];
+}
+
+int main()
+{
+  check_vect ();
+  for (int i = 0; i < 4; ++i)
+    a[i] = i;
+  v4si x = (v4si) { 8, 6, 4, 2 };
+  foo (x);
+  if (b[0] != 11 || b[1] != 8 || b[2] != 5 || b[3] != 2)
+    __builtin_abort ();
+  return 0;
+}
diff --git a/gcc/tree-vect-slp.c b/gcc/tree-vect-slp.c
index b9d88c2d943..07cc24a60e1 100644
--- a/gcc/tree-vect-slp.c
+++ b/gcc/tree-vect-slp.c
@@ -3648,8 +3648,10 @@ vect_optimize_slp (vec_info *vinfo)
       slp_tree node = vertices[idx].node;
 
       /* Handle externals and constants optimistically throughout the
-	 iteration.  */
-      if (SLP_TREE_DEF_TYPE (node) == vect_external_def
+	 iteration.  But treat existing vectors as fixed since we
+	 do not handle permuting them below.  */
+      if ((SLP_TREE_DEF_TYPE (node) == vect_external_def
+	   && !SLP_TREE_VEC_DEFS (node).exists ())
 	  || SLP_TREE_DEF_TYPE (node) == vect_constant_def)
 	continue;