Re: PATCH: PR rtl-optimization/55093: [4.8 Regression] [x32] -maddress-mode=long failed

[Vladimir Makarov <vmakarov at redhat dot com>]

On 10/30/2012 06:34 AM, Richard Sandiford wrote:
> "H.J. Lu" <hjl.tools@gmail.com> writes:
> > > > LRA has
> > > >
> > > >        if (REG_P (reg) && (ep = get_elimination (reg)) != NULL)
> > > >          {
> > > >            rtx to_rtx = replace_p ? ep->to_rtx : ep->from_rtx;
> > > >
> > > >            if (! replace_p)
> > > >              {
> > > >                offset += (ep->offset - ep->previous_offset);
> > > >                offset = trunc_int_for_mode (offset, GET_MODE (plus_cst_src));
> > > >              }
> > > >
> > > >            if (GET_CODE (XEXP (plus_cst_src, 0)) == SUBREG)
> > > >              to_rtx = gen_lowpart (GET_MODE (XEXP (plus_cst_src, 0)), to_rtx);
> > > >
> > > > Reload has
> > > >
> > > >              rtx to_rtx = ep->to_rtx;
> > > >              offset += ep->offset;
> > > >              offset = trunc_int_for_mode (offset, GET_MODE (plus_cst_src));
> > > >
> > > >              if (GET_CODE (XEXP (plus_cst_src, 0)) == SUBREG)
> > > >                to_rtx = gen_lowpart (GET_MODE (XEXP (plus_cst_src, 0)),
> > > >                                      to_rtx);
> > > >
> > > > (gdb) call debug_rtx (ep->to_rtx)
> > > > (reg/f:DI 7 sp)
> > > > (gdb) call debug_rtx (ep->from_rtx)
> > > > (reg/f:DI 16 argp)
> > > > (gdb)
> > > >
> > > > gen_lowpart returns (reg/f:DI 7 sp) for reload and (reg:SI 16 argp)
> > > > for LRA.   They are caused by
> > > >
> > > >    if (FRAME_POINTER_REGNUM != ARG_POINTER_REGNUM
> > > >        /* We should convert arg register in LRA after the elimination
> > > >           if it is possible.  */
> > > >        && xregno == ARG_POINTER_REGNUM
> > > >        && ! lra_in_progress)
> > > >      return -1;
> > > >
> > > > It doesn't work in this case.
> > > This testcase shows that LRA can't convert arg register after
> > > the elimination.
> > Here is a patch to remove ra_in_progress check for
> > ARG_POINTER_REGNUM.  Tested on Linux.x86-64.
> > OK to install?
> Thanks HJ.  This looks good to me.  As well as your testcase, I think
> it would be dangerous to reduce this kind of subreg during non-final
> elimination in cases where the argument pointer occupies more than one
> hard register (like avr IIRC).  We could end up with something like
> ARG_POINTER_REGNUM+1, which wouldn't show up as an elimination register
> during the rest of LRA.
>
> It's important that we do get rid of the subreg during the final
> elimination stage, but I think alter_subreg already handles that case.
>
> Since this code is outside the LRA files: patch is OK if Vlad agrees.
I added this code for a reason probably to solve some target problems.

So I am not sure but let us try.

It is ok for me to commit the patch if there are no regressions on 
x86/x86-64.