Re: [PATCH v2] combine: Improve change_zero_ext, call simplify_set afterwards.

[Dominik Vogt <vogt at linux dot vnet dot ibm dot com>]

On Sat, Dec 10, 2016 at 10:37:38AM -0600, Segher Boessenkool wrote:
> On Fri, Dec 09, 2016 at 04:23:44PM +0100, Dominik Vogt wrote:
> > 0001-*
> > 
> >   Deal with mode expanding zero_extracts in change_zero_ext.  The
> >   patch looks good to me, but not sure whether endianness is
> >   handled properly.  Is the second argument of gen_rtx_SUBREG
> >   correct?
> 
> > >From 600ed3dadd5bc2568ab53be8466686abaf27ff3f Mon Sep 17 00:00:00 2001
> > From: Dominik Vogt <vogt@linux.vnet.ibm.com>
> > Date: Fri, 9 Dec 2016 02:48:30 +0100
> > Subject: [PATCH 1/2] combine: Handle mode expanding zero_extracts in
> >  change_zero_ext.
> > 
> > Example:
> > 
> >   (zero_extract:DI (reg:SI)
> >                    (const_int 24)
> >                    (const_int 0))
> > 
> > -->
> > 
> >   (and:DI (subreg:DI (lshiftrt:SI (reg:SI) (const_int 8))
> >                      0)
> >           (const_int 16777215))
> > ---
> >  gcc/combine.c | 12 +++++++++---
> >  1 file changed, 9 insertions(+), 3 deletions(-)
> > 
> > diff --git a/gcc/combine.c b/gcc/combine.c
> > index b429453..e14a08f 100644
> > --- a/gcc/combine.c
> > +++ b/gcc/combine.c
> > @@ -11237,18 +11237,24 @@ change_zero_ext (rtx pat)
> >        if (GET_CODE (x) == ZERO_EXTRACT
> >  	  && CONST_INT_P (XEXP (x, 1))
> >  	  && CONST_INT_P (XEXP (x, 2))
> > -	  && GET_MODE (XEXP (x, 0)) == mode)
> > +	  && (GET_MODE (XEXP (x, 0)) == mode
> > +	      || GET_MODE_PRECISION (GET_MODE (XEXP (x, 0)))
> > +		 < GET_MODE_PRECISION (mode)))
> 
> If you make this <= you can collapse the two cases into one.
> 
> >  	{
> > +	  machine_mode inner_mode = GET_MODE (XEXP (x, 0));
> > +
> >  	  size = INTVAL (XEXP (x, 1));
> >  
> >  	  int start = INTVAL (XEXP (x, 2));
> >  	  if (BITS_BIG_ENDIAN)
> > -	    start = GET_MODE_PRECISION (mode) - size - start;
> > +	    start = GET_MODE_PRECISION (inner_mode) - size - start;
> >  
> >  	  if (start)
> > -	    x = gen_rtx_LSHIFTRT (mode, XEXP (x, 0), GEN_INT (start));
> > +	    x = gen_rtx_LSHIFTRT (inner_mode, XEXP (x, 0), GEN_INT (start));
> >  	  else
> >  	    x = XEXP (x, 0);
> > +	  if (mode != inner_mode)
> > +	    x = gen_rtx_SUBREG (mode, x, 0);
> 
> gen_lowpart_SUBREG instead?  It's easier to read, and code a little
> further down does the same thing.
> 
> Okay for trunk with those changes (did you bootstrap+regcheck this
> already?)  Thanks,

Patch with these changes and a fix because of not handling
VOIDmode attached.  Bootstrapped and regression tested on s390 and
s390x.

Ciao

Dominik ^_^  ^_^

-- 

Dominik Vogt
IBM Germany

Attachment: 0001-v2-ChangeLog
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Attachment: 0001-v2-combine-Handle-mode-expanding-zero_extracts-in-chang.patch
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