Maintain LC SSA when doing SVE vectorization

The final loop IV use after the loop has that not in LC SSA
(and inserts not simplified _2 = _3 - 0 stmts).  In particular
since it splits the exit edge when there's a virtual PHI in the
destination it breaks virtual LC SSA form (but likely also
non-virtual).

The following properly inserts LC PHIs instead.

2022-07-04  Richard Biener  <rguenther@suse.de>

	* tree-vect-loop-manip.cc (vect_set_loop_condition_normal):
	Maintain LC SSA.

diff --git a/gcc/tree-vect-loop-manip.cc b/gcc/tree-vect-loop-manip.cc
index 5c31f0a809174b9c6fa5ea6fe487b47226be0ad9..d7410d7b4bde1351f7a0795a386dd8c0cf5cdddb 100644 (file)
--- a/gcc/tree-vect-loop-manip.cc
+++ b/gcc/tree-vect-loop-manip.cc
@@ -920,9 +920,22 @@ vect_set_loop_condition_normal (class loop *loop, tree niters, tree step,
 
   if (final_iv)
     {
-      gassign *assign = gimple_build_assign (final_iv, MINUS_EXPR,
-                                            indx_after_incr, init);
-      gsi_insert_on_edge_immediate (single_exit (loop), assign);
+      gassign *assign;
+      edge exit = single_exit (loop);
+      gcc_assert (single_pred_p (exit->dest));
+      tree phi_dest
+       = integer_zerop (init) ? final_iv : copy_ssa_name (indx_after_incr);
+      /* Make sure to maintain LC SSA form here and elide the subtraction
+        if the value is zero.  */
+      gphi *phi = create_phi_node (phi_dest, exit->dest);
+      add_phi_arg (phi, indx_after_incr, exit, UNKNOWN_LOCATION);
+      if (!integer_zerop (init))
+       {
+         assign = gimple_build_assign (final_iv, MINUS_EXPR,
+                                       phi_dest, init);
+         gimple_stmt_iterator gsi = gsi_after_labels (exit->dest);
+         gsi_insert_before (&gsi, assign, GSI_SAME_STMT);
+       }
     }
 
   return cond_stmt;