Re: [PATCH 1/3] RISC-V: Allocate "various" operand type

[Nelson Chu <nelson@rivosinc.com>]

On Mon, Nov 28, 2022 at 2:39 PM Tsukasa OI <research_trasio@irq.a4lg.com> wrote:
>
> From: Tsukasa OI <research_trasio@irq.a4lg.com>
>
> This commit intends to move operands that require very special handling or
> operand types that are so minor (e.g. only useful on a few instructions)
> under "W".  I also intend this "W" to be "temporary" operand storage until
> we can find good two character (or less) operand type.
>
> In this commit, prefetch offset operand "f" for 'Zicbop' extension is moved
> to "Wif" because of its special handling (and allocating single character
> "f" for this operand type seemed too much).
>
> Current expected allocation guideline is as follows:
>
> 1.  'W'
> 2.  The most closely related single-letter extension in lowercase
>     (strongly recommended but not mandatory)
> 3.  Identify operand type
>
> The author currently plans to allocate following three-character operand
> types (for operands including instructions from unratified extensions).
>
> 1.  "Wif" ('Zicbop': fetch offset)

Maybe just "if" without the W?  W seems redundant.  If the offset is
immediate then using "i + <xxx>" seems more clear to understand.

> 2.  "Wfv" (unratified 'Zfa': value operand from FLI.[HSDQ] instructions)

We probably also need to modify other old operand names to comply with
the new naming rules.  But for now the current operand names seem
enough, maybe we can find better naming rules in the future, it's not
urgent.

> 3.  "Wfm" / "WfM"
>     'Zfh', 'F', 'D', 'Q': rounding modes "m" with special handling
>                           solely for widening conversion instructions.

I still think these similar checks, including the rounding mode
checks, should be checked in different match_opcode functions, that
should be enough.  There is no way to make assembly wrong until you
are using the .insn directives, and we don't need to check if the
operands are valid or not for them, since .insn is used to allow users
to write an unsupported instruction.  Please don't continue trying to
add various operand names to support these, it is really hard to
maintain.  I should have already said that, so this is the last time I
mention it.

Nelson

> gas/ChangeLog:
>
>         * config/tc-riscv.c (validate_riscv_insn, riscv_ip): Move from
>         "f" to "Wif".
>
> opcodes/ChangeLog:
>
>         * riscv-dis.c (print_insn_args): Move from "f" to "Wif".
>         * riscv-opc.c (riscv_opcodes): Reflect new operand type.
> ---
>  gas/config/tc-riscv.c | 64 +++++++++++++++++++++++++++++++------------
>  opcodes/riscv-dis.c   | 26 ++++++++++++++----
>  opcodes/riscv-opc.c   |  6 ++--
>  3 files changed, 71 insertions(+), 25 deletions(-)
>
> diff --git a/gas/config/tc-riscv.c b/gas/config/tc-riscv.c
> index 0682eb355241..bb0e18ac8d52 100644
> --- a/gas/config/tc-riscv.c
> +++ b/gas/config/tc-riscv.c
> @@ -1359,7 +1359,6 @@ validate_riscv_insn (const struct riscv_opcode *opc, int length)
>         case 'j': used_bits |= ENCODE_ITYPE_IMM (-1U); break;
>         case 'a': used_bits |= ENCODE_JTYPE_IMM (-1U); break;
>         case 'p': used_bits |= ENCODE_BTYPE_IMM (-1U); break;
> -       case 'f': /* Fall through.  */
>         case 'q': used_bits |= ENCODE_STYPE_IMM (-1U); break;
>         case 'u': used_bits |= ENCODE_UTYPE_IMM (-1U); break;
>         case 'z': break; /* Zero immediate.  */
> @@ -1386,6 +1385,21 @@ validate_riscv_insn (const struct riscv_opcode *opc, int length)
>                 goto unknown_validate_operand;
>             }
>           break;
> +       case 'W': /* Various operands.  */
> +         switch (*++oparg)
> +           {
> +           case 'i':
> +             switch (*++oparg)
> +               {
> +               case 'f': used_bits |= ENCODE_STYPE_IMM (-1U); break;
> +               default:
> +                 goto unknown_validate_operand;
> +               }
> +             break;
> +           default:
> +             goto unknown_validate_operand;
> +           }
> +         break;
>         case 'X': /* Integer immediate.  */
>           {
>             size_t n;
> @@ -3401,22 +3415,37 @@ riscv_ip (char *str, struct riscv_cl_insn *ip, expressionS *imm_expr,
>               imm_expr->X_op = O_absent;
>               continue;
>
> -           case 'f': /* Prefetch offset, pseudo S-type but lower 5-bits zero.  */
> -             if (riscv_handle_implicit_zero_offset (imm_expr, asarg))
> -               continue;
> -             my_getExpression (imm_expr, asarg);
> -             check_absolute_expr (ip, imm_expr, false);
> -             if (((unsigned) (imm_expr->X_add_number) & 0x1fU)
> -                 || imm_expr->X_add_number >= (signed) RISCV_IMM_REACH / 2
> -                 || imm_expr->X_add_number < -(signed) RISCV_IMM_REACH / 2)
> -               as_bad (_("improper prefetch offset (%ld)"),
> -                       (long) imm_expr->X_add_number);
> -             ip->insn_opcode |=
> -               ENCODE_STYPE_IMM ((unsigned) (imm_expr->X_add_number) &
> -                                 ~ 0x1fU);
> -             imm_expr->X_op = O_absent;
> -             asarg = expr_end;
> -             continue;
> +           case 'W': /* Various operands.  */
> +             switch (*++oparg)
> +               {
> +               case 'i':
> +                 switch (*++oparg)
> +                   {
> +                   case 'f':
> +                     /* Prefetch offset for 'Zicbop' extension.
> +                        pseudo S-type but lower 5-bits zero.  */
> +                     if (riscv_handle_implicit_zero_offset (imm_expr, asarg))
> +                       continue;
> +                     my_getExpression (imm_expr, asarg);
> +                     check_absolute_expr (ip, imm_expr, false);
> +                     if (((unsigned) (imm_expr->X_add_number) & 0x1fU)
> +                         || imm_expr->X_add_number >= RISCV_IMM_REACH / 2
> +                         || imm_expr->X_add_number < -RISCV_IMM_REACH / 2)
> +                       as_bad (_ ("improper prefetch offset (%ld)"),
> +                               (long) imm_expr->X_add_number);
> +                     ip->insn_opcode |= ENCODE_STYPE_IMM (
> +                         (unsigned) (imm_expr->X_add_number) & ~0x1fU);
> +                     imm_expr->X_op = O_absent;
> +                     asarg = expr_end;
> +                     continue;
> +                   default:
> +                     goto unknown_riscv_ip_operand;
> +                   }
> +                 break;
> +               default:
> +                 goto unknown_riscv_ip_operand;
> +               }
> +             break;
>
>             case 'X': /* Integer immediate.  */
>               {
> @@ -3469,6 +3498,7 @@ riscv_ip (char *str, struct riscv_cl_insn *ip, expressionS *imm_expr,
>                   }
>               }
>               break;
> +
>             default:
>             unknown_riscv_ip_operand:
>               as_fatal (_("internal: unknown argument type `%s'"),
> diff --git a/opcodes/riscv-dis.c b/opcodes/riscv-dis.c
> index 0e1f3b4610aa..1e6716e8e58c 100644
> --- a/opcodes/riscv-dis.c
> +++ b/opcodes/riscv-dis.c
> @@ -473,11 +473,6 @@ print_insn_args (const char *oparg, insn_t l, bfd_vma pc, disassemble_info *info
>                  (int)EXTRACT_STYPE_IMM (l));
>           break;
>
> -       case 'f':
> -         print (info->stream, dis_style_address_offset, "%d",
> -                (int)EXTRACT_STYPE_IMM (l));
> -         break;
> -
>         case 'a':
>           info->target = EXTRACT_JTYPE_IMM (l) + pc;
>           (*info->print_address_func) (info->target, info);
> @@ -582,6 +577,27 @@ print_insn_args (const char *oparg, insn_t l, bfd_vma pc, disassemble_info *info
>           print (info->stream, dis_style_immediate, "%d", rs1);
>           break;
>
> +       case 'W': /* Various operands.  */
> +         {
> +           switch (*++oparg)
> +             {
> +             case 'i':
> +               switch (*++oparg)
> +                 {
> +                 case 'f':
> +                   print (info->stream, dis_style_address_offset, "%d",
> +                          (int) EXTRACT_STYPE_IMM (l));
> +                   break;
> +                 default:
> +                   goto undefined_modifier;
> +                 }
> +                 break;
> +             default:
> +               goto undefined_modifier;
> +             }
> +         }
> +         break;
> +
>         case 'X': /* Integer immediate.  */
>           {
>             size_t n;
> diff --git a/opcodes/riscv-opc.c b/opcodes/riscv-opc.c
> index 0e691544f9bc..653eb60f2a58 100644
> --- a/opcodes/riscv-opc.c
> +++ b/opcodes/riscv-opc.c
> @@ -313,9 +313,9 @@ const struct riscv_opcode riscv_opcodes[] =
>  /* name, xlen, isa, operands, match, mask, match_func, pinfo.  */
>
>  /* Standard hints.  */
> -{"prefetch.i",  0, INSN_CLASS_ZICBOP, "f(s)", MATCH_PREFETCH_I, MASK_PREFETCH_I, match_opcode, 0 },
> -{"prefetch.r",  0, INSN_CLASS_ZICBOP, "f(s)", MATCH_PREFETCH_R, MASK_PREFETCH_R, match_opcode, 0 },
> -{"prefetch.w",  0, INSN_CLASS_ZICBOP, "f(s)", MATCH_PREFETCH_W, MASK_PREFETCH_W, match_opcode, 0 },
> +{"prefetch.i",  0, INSN_CLASS_ZICBOP, "Wif(s)", MATCH_PREFETCH_I, MASK_PREFETCH_I, match_opcode, 0 },
> +{"prefetch.r",  0, INSN_CLASS_ZICBOP, "Wif(s)", MATCH_PREFETCH_R, MASK_PREFETCH_R, match_opcode, 0 },
> +{"prefetch.w",  0, INSN_CLASS_ZICBOP, "Wif(s)", MATCH_PREFETCH_W, MASK_PREFETCH_W, match_opcode, 0 },
>  {"pause",       0, INSN_CLASS_ZIHINTPAUSE, "", MATCH_PAUSE, MASK_PAUSE, match_opcode, 0 },
>
>  /* Basic RVI instructions and aliases.  */
> --
> 2.38.1
>