[gcc r12-1377] Use stablesort for sorting association chain

[Richard Biener]

https://gcc.gnu.org/g:e9d322ced1433da8e7c69243cfa941ea462d6290

commit r12-1377-ge9d322ced1433da8e7c69243cfa941ea462d6290
Author: Richard Biener <rguenther@suse.de>
Date:   Fri Jun 11 08:04:41 2021 +0200

    Use stablesort for sorting association chain
    
    This should preserve the original association order as much as possible
    for the initial SLP discovery attempt and also improve consistency.
    
    2021-06-11  Richard Biener  <rguenther@suse.de>
    
            * tree-vect-slp.c (vect_build_slp_tree_2): Use stablesort
            to sort operands of the associative chain.

Diff:
---
 gcc/tree-vect-slp.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/gcc/tree-vect-slp.c b/gcc/tree-vect-slp.c
index c4f8f38012f..6237a61ffd4 100644
--- a/gcc/tree-vect-slp.c
+++ b/gcc/tree-vect-slp.c
@@ -1865,7 +1865,7 @@ vect_build_slp_tree_2 (vec_info *vinfo, slp_tree node,
 	  /* Now we have a set of chains with the same length.  */
 	  /* 1. pre-sort according to def_type and operation.  */
 	  for (unsigned lane = 0; lane < group_size; ++lane)
-	    chains[lane].sort (dt_sort_cmp, vinfo);
+	    chains[lane].stablesort (dt_sort_cmp, vinfo);
 	  if (dump_enabled_p ())
 	    {
 	      dump_printf_loc (MSG_NOTE, vect_location,