[Bug tree-optimization/113896] [12 Regression] Assigning array elements in the wrong order after floating point optimization since r12-8841

[rguenth at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113896

--- Comment #4 from Richard Biener <rguenth at gcc dot gnu.org> ---
I have a bit of a deja-vu here.  The SLP permute optimization phase was
rewritten for GCC 13, the following fixes the latent issue for GCC 12:

diff --git a/gcc/tree-vect-slp.cc b/gcc/tree-vect-slp.cc
index af477c31aa3..b3e3d9e7009 100644
--- a/gcc/tree-vect-slp.cc
+++ b/gcc/tree-vect-slp.cc
@@ -4058,6 +4058,15 @@ vect_optimize_slp (vec_info *vinfo)
                {
                  /* Preserve the special VEC_PERM we use to shield existing
                     vector defs from the rest.  But make it a no-op.  */
+                 auto_vec<stmt_vec_info, 64> saved;
+                 saved.create (SLP_TREE_SCALAR_STMTS (old).length ());
+                 for (unsigned i = 0;
+                      i < SLP_TREE_SCALAR_STMTS (old).length (); ++i)
+                   saved.quick_push (SLP_TREE_SCALAR_STMTS (old)[i]);
+                 for (unsigned i = 0;
+                      i < SLP_TREE_SCALAR_STMTS (old).length (); ++i)
+                   SLP_TREE_SCALAR_STMTS (old)[i]
+                     = saved[SLP_TREE_LANE_PERMUTATION (old)[i].second];
                  unsigned i = 0;
                  for (std::pair<unsigned, unsigned> &p
                       : SLP_TREE_LANE_PERMUTATION (old))