On Wed, Sep 8, 2021 at 2:55 AM Hongtao Liu via Gcc-patches
<gcc-patches@gcc.gnu.org> wrote:
>
> On Wed, Sep 8, 2021 at 5:33 PM Jakub Jelinek <ja...@redhat.com> wrote:
> >
> > On Wed, Sep 08, 2021 at 05:23:40PM +0800, Hongtao Liu wrote:
> > > > Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?
> > > >
> > > Patch LGTM.
> >
> > Thanks, committed.
> >
> > > PS:
> > > I'm curious why we need the post_reload splitter @xorsign<mode>3_1
> > > for scalar mode, can't we just expand them into and/xor operations in
> > > the expander, just like vector modes did.
> > > Let me do some experiments to see whether it is ok to remove the splitter.
> >
> > I bet it is the question how should the code look like before RA.
> > stv is somewhat related, but as that replaces whole chains, it can do:
> > (insn 14 5 6 2 (set (subreg:V2DI (reg:DI 92) 0)
> > (vec_concat:V2DI (mem/c:DI (symbol_ref:SI ("c") [flags 0x2]
> > <var_decl 0x7f65a131fd80 c>) [1 c+0 S8 A64])
> > (const_int 0 [0]))) "hohohou.c":6:9 -1
> > (nil))
> > on loads of memory.
> > But it stv still does use paradoxical subregs:
> > (insn 10 16 11 2 (set (subreg:V2DI (reg:DI 91) 0)
> > (minus:V2DI (subreg:V2DI (reg:DI 87) 0)
> > (subreg:V2DI (reg:DI 94) 0))) "hohohou.c":6:13 5003 {*subv2di3}
> > (expr_list:REG_DEAD (reg:DI 87)
> > (expr_list:REG_UNUSED (reg:CC 17 flags)
> > (nil))))
> > (insn 11 10 0 2 (set (mem/c:DI (symbol_ref:SI ("a") [flags 0x2] <var_decl
> > 0x7f65a131fc60 a>) [1 a+0 S8 A64])
> > (reg:DI 91)) "hohohou.c":6:5 76 {*movdi_internal}
> > (expr_list:REG_DEAD (reg:DI 91)
> > (nil)))
> > so perhaps just using paradoxical subregs everywhere would be ok?
> Yes, I think so.
> And I find paradoxical subreg like (subreg:V4SF (reg:SF)) are not
> allowed by validate_subreg until r11-621.
> That's why post_reload splitter is needed here.
That is not exactly true. It has been around since before 2005. See
https://gcc.gnu.org/PR24436 which is referencing the fixme comment in
validate_subreg.
Thanks,
Andrew Pinski
Thanks,
Andrew Pinski
> > Jakub
> >
>
>
>
> --
> BR,
> Hongtao
