Fix 'unrecognizable instruction' error for convert_vector (IFN_VEC_CONVERT)

Author: antoyo

gcc/jit/jit-playback.cc

@@ -1556,6 +1556,9 @@ convert_vector (location *loc,
 
   tree t_vector = vector->as_tree ();
 
+  /* It seems IFN_VEC_CONVERT only work on registers, not on memory.  */
+  if (TREE_CODE (t_vector) == VAR_DECL)
+    DECL_REGISTER (t_vector) = 1;
   tree t_result = build_call_expr_internal_loc (UNKNOWN_LOCATION, IFN_VEC_CONVERT, type->as_tree (), 1, t_vector);
 
   if (loc)