Re: An unreviewed ARM patch

[Kazu Hirata <kazu at codesourcery dot com>]

Hi Richard,

> > Could someone please review the following patch?
> >
> >    [patch] arm: Improve arm_rtx_costs_1 for Thumb2.
> >    http://gcc.gnu.org/ml/gcc-patches/2009-12/msg00958.html
>
> Hmm, I agree that there's probably some code in the rest of the MINUS
> case that should be shared.  I'm not convinced, however, that we should
> fall through into the PLUS case: most of the code from that point on
> will only apply if we have RSB (and we don't in Thumb-2).

Err, which form of RSB are you talking about?  IIRC, ARM has:

  RSB <Rd>, <Rn>, <shifter_operand>

Thumb-2 has:

  RSB <Rd>,<Rn>,#0
  RSB.W <Rd>,<Rn>,#<const>
  RSB <Rd>,<Rn>,<Rm>{,<shift>}

So, Thumb-2's RSB supports most of ARM's RSB, except somewhat exotic 
operands like variable shifts and rotations in <shifter_operand>.

Did you mean to say Thumb-1 above?

Thanks,

Kazu Hirata