[Bug rtl-optimization/70961] Regrename ignores preferred_rename_class

["stefan at franke dot ms" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=70961

Stefan "Bebbo" Franke <stefan at franke dot ms> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |stefan at franke dot ms

--- Comment #6 from Stefan "Bebbo" Franke <stefan at franke dot ms> ---
Simply remove the outer loop and iterate only once:

  has_preferred_class = (preferred_class != NO_REGS);
  for (new_reg = 0; new_reg < FIRST_PSEUDO_REGISTER; new_reg++)
    {
      if (has_preferred_class
          && !TEST_HARD_REG_BIT(reg_class_contents[preferred_class],
                                   new_reg))
        continue;

      if (!check_new_reg_p (old_reg, new_reg, this_head, *unavailable))
        continue;

      if (!best_rename)
        return new_reg;

      /* In the first pass, we force the renaming of registers that
       don't belong to PREFERRED_CLASS to registers that do, even
       though the latters were used not very long ago.
       Also use a register if no best_new_reg was found till now  */
      if ((tick[best_new_reg] > tick[new_reg]
          || (old_reg == best_new_reg && new_reg < old_reg)))
        best_new_reg = new_reg;
    }

The last "if" is my experimental version. I am also testing (with m68k) an
extended preferred_rename_class2 method, which uses the register to return a
maybe better class:

  preferred_class = (enum reg_class) targetm.preferred_rename_class2 (
      super_class, old_reg);

And yes, the code is smaller and faster.