Re: Rewrite some jump.c routines to use flags

[Eric Botcazou <ebotcazou at adacore dot com>]

> No, no trivial paths unfortunately.  I'd hoped that inlining and
> jump threading would give us very similar code, but no such luck.
> condition_to_flags is a table lookup, but then flags_to_condition
> is a branch tree.

Too bad.  Perhaps this would be an interesting optimization exercise.

> If that's a concern, I can drop the changes to the existing
> functions and just use the new flags for the follow-on patch.

IMO the net pessimization is a little hard to swallow, although it probably 
doesn't matter much in practice.  I'd suggest adding the new logic in every 
case, but keeping the fast path when it's a nop:

 enum rtx_code
 swap_condition (enum rtx_code code)
 {
  /* Deal with the trivial cases first.  */
  switch (code)
    {
    case EQ:
    case NE:
    case UNORDERED:
    case ORDERED:
    case UNEQ:
    case LTGT:
      return code;
    default:
      break;
    }

  unsigned int flags = condition_to_flags (code);
  flags = ((flags & ~(FLAGS_GT | FLAGS_LT))
          | (flags & FLAGS_GT ? FLAGS_LT : 0)
          | (flags & FLAGS_LT ? FLAGS_GT : 0));
  return flags_to_condition (flags, true);
 }

OK with this additional change.

-- 
Eric Botcazou