Re: Re: [PATCH 1/2] [RISC-V] disable shrink-wrap-separate if zcmp enabled.

[Kito Cheng <kito.cheng@gmail.com>]

-msave-restore is a different story; it's only enabled when the user
requests, but `-march` describes the capability of the target
architecture, not specify the preference of performance or size, which
should be determined by -O1~-O3/-Ofast or -Os/-Oz.

On Mon, May 8, 2023 at 4:54 PM Fei Gao <gaofei@eswincomputing.com> wrote:
>
> On 2023-05-08 16:05  Kito Cheng <kito.cheng@gmail.com> wrote:
> >
> >> > diff --git a/gcc/config/riscv/riscv.cc b/gcc/config/riscv/riscv.cc
> >> > index 45a63cab9c9..629e5e45cac 100644
> >> > --- a/gcc/config/riscv/riscv.cc
> >> > +++ b/gcc/config/riscv/riscv.cc
> >> > @@ -5729,7 +5729,8 @@ riscv_get_separate_components (void)
> >> >
> >> >    if (riscv_use_save_libcall (&cfun->machine->frame)
> >> >        || cfun->machine->interrupt_handler_p
> >> > -      || !cfun->machine->frame.gp_sp_offset.is_constant ())
> >> > +      || !cfun->machine->frame.gp_sp_offset.is_constant ()
> >> > +      || TARGET_ZCMP)
> >> >      return components;
> >>
> >> I think this is a bad idea. I have a use case where we use the C
> >> extensions but still compile for -O2 because we want the code to be
> >> fast as possible but still having the savings of the C extensions.
> >
> >Yeah, agree, so I would prefer to drop this from the patch series.
>
> Zcmp is a little different here than C.
> C extension is done fully in AS.  So  we have the code to be
> fast as possible but still having the savings of the C extensions.
>
> Zcmp and shrink-wrap-separate are both done in prologue/epilogue pass
> and you can only have one switch active to direct sregs save and restore.
> In my understanding, zcmp push and pop insns seem to
> be mutually exclusive in functionality to shrink-wrap-separate.
> It's not expected to see zcmp insns at the begining/end of prologue/epilogue,
> and also repeated store/load sregs in separate blocks.
>
> Same for save and restore, and i guess that's why we have
> riscv_use_save_libcall (&cfun->machine->frame) check here.
>
> BR,
> Fei
>
> >
> >> Thanks,
> >> Andrew Pinski