Re: How to find out register information at the beginning of a basic block?

[Vladimir Makarov <vmakarov at redhat dot com>]

H.J. Lu wrote:
> On Mon, May 31, 2010 at 12:31 PM, Vladimir Makarov <vmakarov@redhat.com> wrote:
>   
> > H.J. Lu wrote:
> >     
> > > Hi,
> > >
> > > I am working on generating vzeroupper to avoid AVX->SSE transition
> > > penalty.
> > >
> > > I have generated vzeroupper on function return as well as function
> > > call.  I am working on a backend pass to eliminate those vzeroupper
> > > instructions when I can prove that the upper 128bits of AVX registers
> > > are dead at the point where vzeroupper is added. To do that, I need
> > > to find out if a register is live at the beginning of a basic block as
> > > well
> > > as its size. I thought dataflow might give me such info. But I couldn't
> > > find a way to access such information. Does anyone have any pointers?
> > >
> > >
> > >       
> > DF_LR_IN (bb) returns bitmap of livings prseudo regnos.
> > DF_LIVE_IN (bb) takes availability info into account.
> >
> > Size of hard registers is defined by hard_regno_nregs.
> >
> > It is more complicated if you need the size of pseudo.  The class of pseudo
> > is necessary for this but even if you know this there are complicated
> > situations, e.g.
> >     
>
> The new backend pass is run as the last pass and doesn't deal with pseudo
> registers. I have
>
>   df_chain_add_problem (DF_UD_CHAIN + DF_DU_CHAIN); <<< Is this correct?
>   
I don't think you need all these chains (of course if you really need 
it).  It is time consuming.

I guess df_live_add_problem () will be enough.