Re: [PATCH rdma-core 4/8] mlx5: Avoid sparse complaints about !!

[Bart Van Assche <Bart.VanAssche-Sjgp3cTcYWE@public.gmane.org>]

On Thu, 2017-07-13 at 11:20 -0600, Jason Gunthorpe wrote:
> On Thu, Jul 13, 2017 at 12:51:16AM -0700, Christoph Hellwig wrote:
> > >  			if (qp->qp_cap_cache & MLX5_RX_CSUM_VALID)
> > > -				wc->wc_flags |= (!!(cqe->hds_ip_ext & MLX5_CQE_L4_OK) &
> > > -						 !!(cqe->hds_ip_ext & MLX5_CQE_L3_OK) &
> > > -						(get_cqe_l3_hdr_type(cqe) ==
> > > -						MLX5_CQE_L3_HDR_TYPE_IPV4)) <<
> > > -						IBV_WC_IP_CSUM_OK_SHIFT;
> > > +				wc->wc_flags |=
> > > +				    ((bool)(cqe->hds_ip_ext & MLX5_CQE_L4_OK) &
> > > +				     (bool)(cqe->hds_ip_ext & MLX5_CQE_L3_OK) &
> > > +				     (get_cqe_l3_hdr_type(cqe) ==
> > > +				      MLX5_CQE_L3_HDR_TYPE_IPV4))
> > > +				    << IBV_WC_IP_CSUM_OK_SHIFT;
> > 
> > Meh.  This code is complete crap.  Please factor it out into a little
> > helper that mere humans can read first.  And then replace the odd ^ used
> > as && with proper if constructs and all should make much more sense.
> 
> As far as I could make out, this ugly thing is designed like this for
> performance.

Hello Jason,

How about using an expression like the below to avoid that branches get inserted
for testing the MLX5_CQE_L4_OK and MLX5_CQE_L3_OK flags?

(cqe->hds_ip_ext & (MLX5_CQE_L4_OK | MLX5_CQE_L3_OK)) == MLX5_CQE_L4_OK | MLX5_CQE_L3_OK

Bart.--
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