Re: [PATCH] rs6000: replace '(const_int 0)' to 'unspec:BLK [(const_int 0)]' for stack_tie

[David Edelsohn <dje.gcc@gmail.com>]

Hi, Jiufu

This definitely seems to be a better solution.

The TARGET_CONST_ANCHOR change should not be part of this patch.  Also
there is no ChangeLog for the patch.

This generally looks correct and consistent with other ports. I want
to give Segher a chance to double check it, if he wishes.

Thanks David

On Mon, Jun 12, 2023 at 9:19 AM Jiufu Guo <guojiufu@linux.ibm.com> wrote:
>
> Hi,
>
> For stack_tie, currently below insn is generated:
> (insn 15 14 16 3 (parallel [
>              (set (mem/c:BLK (reg/f:DI 1 1) [1  A8])
>                  (const_int 0 [0]))
>          ]) "/home/guojiufu/temp/gdb.c":13:3 922 {stack_tie}
>       (nil))
>
> It is "set (mem/c:BLK (reg/f:DI 1 1) (const_int 0 [0])".  This maybe
> looks like "a memory block is zerored", while actually stack_tie
> may be more like a placeholder, and does not generate any thing.
>
> To avoid potential misunderstand, "UNPSEC:BLK [(const_int 0)].." could
> be used here like other ports.
>
> This patch does this.  Bootstrap&regtest pass on ppc64{,le}.
> Is this ok for trunk?
>
> BR,
> Jeff (Jiufu Guo)
>
> ---
>  gcc/config/rs6000/predicates.md   | 11 +++++++----
>  gcc/config/rs6000/rs6000-logue.cc |  4 +++-
>  gcc/config/rs6000/rs6000.cc       |  4 ++++
>  gcc/config/rs6000/rs6000.md       | 14 ++++++++++----
>  4 files changed, 24 insertions(+), 9 deletions(-)
>
> diff --git a/gcc/config/rs6000/predicates.md b/gcc/config/rs6000/predicates.md
> index a16ee30f0c0..4748cb37ce8 100644
> --- a/gcc/config/rs6000/predicates.md
> +++ b/gcc/config/rs6000/predicates.md
> @@ -1854,10 +1854,13 @@ (define_predicate "stmw_operation"
>  (define_predicate "tie_operand"
>    (match_code "parallel")
>  {
> -  return (GET_CODE (XVECEXP (op, 0, 0)) == SET
> -         && MEM_P (XEXP (XVECEXP (op, 0, 0), 0))
> -         && GET_MODE (XEXP (XVECEXP (op, 0, 0), 0)) == BLKmode
> -         && XEXP (XVECEXP (op, 0, 0), 1) == const0_rtx);
> +  rtx set = XVECEXP (op, 0, 0);
> +  return (GET_CODE (set) == SET
> +         && MEM_P (SET_DEST (set))
> +         && GET_MODE (SET_DEST (set)) == BLKmode
> +         && GET_CODE (SET_SRC (set)) == UNSPEC
> +         && XINT (SET_SRC (set), 1) == UNSPEC_TIE
> +         && XVECEXP (SET_SRC (set), 0, 0) == const0_rtx);
>  })
>
>  ;; Match a small code model toc reference (or medium and large
> diff --git a/gcc/config/rs6000/rs6000-logue.cc b/gcc/config/rs6000/rs6000-logue.cc
> index bc6b153b59f..b99f43a8282 100644
> --- a/gcc/config/rs6000/rs6000-logue.cc
> +++ b/gcc/config/rs6000/rs6000-logue.cc
> @@ -1463,7 +1463,9 @@ rs6000_emit_stack_tie (rtx fp, bool hard_frame_needed)
>    while (--i >= 0)
>      {
>        rtx mem = gen_frame_mem (BLKmode, regs[i]);
> -      RTVEC_ELT (p, i) = gen_rtx_SET (mem, const0_rtx);
> +      RTVEC_ELT (p, i)
> +       = gen_rtx_SET (mem, gen_rtx_UNSPEC (BLKmode, gen_rtvec (1, const0_rtx),
> +                                           UNSPEC_TIE));
>      }
>
>    emit_insn (gen_stack_tie (gen_rtx_PARALLEL (VOIDmode, p)));
> diff --git a/gcc/config/rs6000/rs6000.cc b/gcc/config/rs6000/rs6000.cc
> index d197c3f3289..0c81ebea711 100644
> --- a/gcc/config/rs6000/rs6000.cc
> +++ b/gcc/config/rs6000/rs6000.cc
> @@ -1760,6 +1760,10 @@ static const struct attribute_spec rs6000_attribute_table[] =
>
>  #undef TARGET_UPDATE_IPA_FN_TARGET_INFO
>  #define TARGET_UPDATE_IPA_FN_TARGET_INFO rs6000_update_ipa_fn_target_info
> +
> +#undef TARGET_CONST_ANCHOR
> +#define TARGET_CONST_ANCHOR 0x8000
> +
>
>
>  /* Processor table.  */
> diff --git a/gcc/config/rs6000/rs6000.md b/gcc/config/rs6000/rs6000.md
> index b0db8ae508d..fdcf8347812 100644
> --- a/gcc/config/rs6000/rs6000.md
> +++ b/gcc/config/rs6000/rs6000.md
> @@ -158,6 +158,7 @@ (define_c_enum "unspec"
>     UNSPEC_HASHCHK
>     UNSPEC_XXSPLTIDP_CONST
>     UNSPEC_XXSPLTIW_CONST
> +   UNSPEC_TIE
>    ])
>
>  ;;
> @@ -10828,7 +10829,9 @@ (define_expand "restore_stack_block"
>    operands[4] = gen_frame_mem (Pmode, operands[1]);
>    p = rtvec_alloc (1);
>    RTVEC_ELT (p, 0) = gen_rtx_SET (gen_frame_mem (BLKmode, operands[0]),
> -                                 const0_rtx);
> +                                 gen_rtx_UNSPEC (BLKmode,
> +                                                 gen_rtvec (1, const0_rtx),
> +                                                 UNSPEC_TIE));
>    operands[5] = gen_rtx_PARALLEL (VOIDmode, p);
>  })
>
> @@ -10866,7 +10869,9 @@ (define_expand "restore_stack_nonlocal"
>    operands[5] = gen_frame_mem (Pmode, operands[3]);
>    p = rtvec_alloc (1);
>    RTVEC_ELT (p, 0) = gen_rtx_SET (gen_frame_mem (BLKmode, operands[0]),
> -                                 const0_rtx);
> +                                 gen_rtx_UNSPEC (BLKmode,
> +                                                 gen_rtvec (1, const0_rtx),
> +                                                 UNSPEC_TIE));
>    operands[6] = gen_rtx_PARALLEL (VOIDmode, p);
>  })
>
> @@ -13898,7 +13903,8 @@ (define_insn "*save_fpregs_<mode>_r1"
>  ; not be moved over loads from or stores to stack memory.
>  (define_insn "stack_tie"
>    [(match_parallel 0 "tie_operand"
> -                  [(set (mem:BLK (reg 1)) (const_int 0))])]
> +                  [(set (mem:BLK (reg 1))
> +                   (unspec:BLK [(const_int 0)] UNSPEC_TIE))])]
>    ""
>    ""
>    [(set_attr "length" "0")])
> @@ -13910,7 +13916,7 @@ (define_insn "stack_restore_tie"
>    [(set (match_operand:SI 0 "gpc_reg_operand" "=r,r")
>         (plus:SI (match_operand:SI 1 "gpc_reg_operand" "r,r")
>                  (match_operand:SI 2 "reg_or_cint_operand" "O,rI")))
> -   (set (mem:BLK (scratch)) (const_int 0))]
> +   (set (mem:BLK (scratch)) (unspec:BLK [(const_int 0)] UNSPEC_TIE))]
>    "TARGET_32BIT"
>    "@
>     mr %0,%1
> --
> 2.39.3
>