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

["Vladimir N. Makarov" <vmakarov at redhat dot com>]

On 05/31/2010 08:17 PM, 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.
> >
> >      
> My impression is hard_regno_nregs tells me that number of
> hard registers given machine mode occupy. It doesn't tell me
> the live size of a hard register at the beginning of a basic
> block. How do I get this information?
>    
If you mean what part of hard register lives, then as I know there is no 
such infrastructure code.  As I remember Ken Zadeck tried to implement 
something analogous in the old RA.  You could try to find this code in 
archives.