autovectorizer doesn't support multistep widen mult

[Paulo Matos]

Hello,

Is there any technical reason (besides nobody bothers to implement it) why GCC 
doesn't support multistep conversions for widen mult?

In tree-vect-stmts.c:
  /* Check if it's a multi-step conversion that can be done using intermediate
     types.  */

  prev_type = vectype;
  prev_mode = vec_mode;

  if (!CONVERT_EXPR_CODE_P (code))
    return false;

Is there any reason we only proceed for convert expr codes?

Thanks,

Paulo Matos