[PATCH, rs6000] Avoid optimization problem for VEC_PERM_EXPR

Bill Schmidt wschmidt@linux.vnet.ibm.com
Fri Jan 24 01:48:00 GMT 2014



On Thu, 2014-01-23 at 19:42 -0500, David Edelsohn wrote:
> On Thu, Jan 23, 2014 at 6:43 PM, Bill Schmidt
> <wschmidt@linux.vnet.ibm.com> wrote:
> > Hi,
> >
> > While testing another patch, I hit a regression at -O2 for two of the
> > vector shuffle tests.  This patch fixes the problem.
> >
> > The problem was introduced with the little endian fixes for
> > VEC_PERM_EXPR.  The original change performed the necessary
> > transformation at expand time, but this is incorrect.  This creates a
> > technically incorrect representation in the RTL, and RTL simplification
> > can subsequently fold the expression in an unexpected way.  The correct
> > fix is to delay the transformation until final code generation.
> >
> > Bootstrapped and tested on powerpc64{,le}-unknown-linux-gnu with no
> > regressions.  Is this ok for trunk?  I will also plan to backport this
> > to ibm/gcc-4_8-branch after burn-in.
> >
> > Thanks,
> > Bill
> >
> >
> > 2014-01-23  Bill Schmidt  <wschmidt@linux.vnet.ibm.com>
> >
> >         * config/rs6000/rs6000.c (rs6000_expand_vec_perm_const_1): Remove
> >         correction for little endian...
> >         * config/rs6000/vsx.md (vsx_xxpermdi2_<mode>_1): ...and move it to
> >         here.
> 
> Okay. Would you please move the comment also?

Oh, sure.  Will do.

Bill
> 
> Thanks, David
> 



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