[PATCH vs] Take known zero bits into account when checking extraction.

[Dominik Vogt]

On Wed, May 11, 2016 at 10:40:11AM +0200, Bernd Schmidt wrote:
> On 05/11/2016 09:42 AM, Dominik Vogt wrote:
> >On Tue, May 10, 2016 at 05:05:06PM +0200, Bernd Schmidt wrote:
> >>Earlier in the discussion you mentioned the intention to remove
> >>these costs. Nothing else in the function does cost calculations -
> >>maybe you can try placing a gcc_unreachable into the case where the
> >>costs would prevent the transformation to see if it ever triggers.
> >
> >You mean to try it out locally or as part of the patch?
> 
> I meant try it out locally. I'm almost certain the patch shouldn't
> be trying to use costs here.

That's what I mentioned somewhere during the discussion.  The s390
backend just uses COSTS_N_INSNS(1) for AND as well as ZERO_EXTEND,
so this won't ever trigger.  I just left the rtx_cost call in the
patch for further discussion as Jeff said he liked the approach.
We don't need it to achieve the behaviour we want for s390.

Ciao

Dominik ^_^  ^_^

-- 

Dominik Vogt
IBM Germany