Re: [PATCH] RISC-V: Optimal RVV epilogue logic.

[Philipp Tomsich <philipp.tomsich@vrull.eu>]

On Mon, 14 Nov 2022 at 17:29, jiawei <jiawei@iscas.ac.cn> wrote:
>
> Skip add insn generate if the adjust size equal to zero.
>
> gcc/ChangeLog:
>
>         * config/riscv/riscv.cc (riscv_expand_epilogue):
>                                 New if control segement.
>
> ---
>  gcc/config/riscv/riscv.cc | 18 ++++++++++--------
>  1 file changed, 10 insertions(+), 8 deletions(-)
>
> diff --git a/gcc/config/riscv/riscv.cc b/gcc/config/riscv/riscv.cc
> index 02a01ca0b7c..af138db7545 100644
> --- a/gcc/config/riscv/riscv.cc
> +++ b/gcc/config/riscv/riscv.cc
> @@ -5186,24 +5186,26 @@ riscv_expand_epilogue (int style)
>         }
>
>        /* Get an rtx for STEP1 that we can add to BASE.  */
> -      rtx adjust = GEN_INT (step1.to_constant ());
> -      if (!SMALL_OPERAND (step1.to_constant ()))
> +      if (step1.to_constant () != 0){
> +        rtx adjust = GEN_INT (step1.to_constant ());
> +        if (!SMALL_OPERAND (step1.to_constant ()))

Please take a look at the recent improvements for the add<mode>3
expander (recently submitted as
https://patchwork.ozlabs.org/project/gcc/patch/20221109230718.3240479-1-philipp.tomsich@vrull.eu/).
Maybe you also want to use the test for the addi_operand(...) instead
of SMALL_OPERAND?

>         {
>           riscv_emit_move (RISCV_PROLOGUE_TEMP (Pmode), adjust);
>           adjust = RISCV_PROLOGUE_TEMP (Pmode);
>         }
>
> -      insn = emit_insn (
> +        insn = emit_insn (
>                gen_add3_insn (stack_pointer_rtx, stack_pointer_rtx, adjust));
>
> -      rtx dwarf = NULL_RTX;
> -      rtx cfa_adjust_rtx = gen_rtx_PLUS (Pmode, stack_pointer_rtx,
> +        rtx dwarf = NULL_RTX;
> +        rtx cfa_adjust_rtx = gen_rtx_PLUS (Pmode, stack_pointer_rtx,
>                                          GEN_INT (step2));
>
> -      dwarf = alloc_reg_note (REG_CFA_DEF_CFA, cfa_adjust_rtx, dwarf);
> -      RTX_FRAME_RELATED_P (insn) = 1;
> +        dwarf = alloc_reg_note (REG_CFA_DEF_CFA, cfa_adjust_rtx, dwarf);
> +        RTX_FRAME_RELATED_P (insn) = 1;
>
> -      REG_NOTES (insn) = dwarf;
> +        REG_NOTES (insn) = dwarf;
> +      }
>      }
>    else if (frame_pointer_needed)
>      {
> --
> 2.25.1
>