Re: [PATCH v2 1/2] target/riscv: add Zicond as an experimental extension

[Alistair Francis]

On Sat, Jan 21, 2023 at 12:36 PM Philipp Tomsich
<philipp.tomsich@vrull.eu> wrote:
>
> This implements the Zicond (conditional integer operations) extension,
> as of version 1.0-draft-20230120 as an experimental extension in QEMU
> ("x-zicond").
>
> The Zicond extension acts as a building block for branchless sequences
> including conditional-{arithmetic,logic,select,move}.  Refer to the
> specification for usage scenarios and application guidance.
>
> The following instructions constitute Zicond:
>   - czero.eqz rd, rs1, rs2  =>  rd = (rs2 == 0) ? 0 : rs1
>   - czero.nez rd, rs1, rs2  =>  rd = (rs2 != 0) ? 0 : rs1
>
> See
>   
> https://github.com/riscv/riscv-zicond/releases/download/v1.0-draft-20230120/riscv-zicond_1.0-draft-20230120.pdf
> for the (current version of the) Zicond specification and usage details.
>
> Signed-off-by: Philipp Tomsich <philipp.tomsich@vrull.eu>
> ---
>
> Changes in v2:
> - gates availability of the instructions through a REQUIRE_ZICOND
>   macro (these were previously always enabled)
>
>  MAINTAINERS                                  |  7 +++
>  target/riscv/cpu.c                           |  4 ++
>  target/riscv/cpu.h                           |  1 +
>  target/riscv/insn32.decode                   |  4 ++
>  target/riscv/insn_trans/trans_rvzicond.c.inc | 54 ++++++++++++++++++++
>  target/riscv/translate.c                     |  1 +
>  6 files changed, 71 insertions(+)
>  create mode 100644 target/riscv/insn_trans/trans_rvzicond.c.inc
>
> diff --git a/MAINTAINERS b/MAINTAINERS
> index 08ad1e5341..ca914c42fa 100644
> --- a/MAINTAINERS
> +++ b/MAINTAINERS
> @@ -295,6 +295,13 @@ F: include/hw/riscv/
>  F: linux-user/host/riscv32/
>  F: linux-user/host/riscv64/
>
> +RISC-V Zicond extension
> +M: Philipp Tomsich <philipp.tomsich@vrull.eu>
> +M: Christoph Muellner <christoph.muellner@vrull.eu>
> +L: qemu-riscv@nongnu.org
> +S: Supported
> +F: target/riscv/insn_trans/trans_zicond.c.inc

I don't think we need a maintainers entry for official extensions,
that seems like it's going to get out of hand very quickly.

Alistair

> +
>  RISC-V XVentanaCondOps extension
>  M: Philipp Tomsich <philipp.tomsich@vrull.eu>
>  L: qemu-riscv@nongnu.org
> diff --git a/target/riscv/cpu.c b/target/riscv/cpu.c
> index cc75ca7667..f214b03e95 100644
> --- a/target/riscv/cpu.c
> +++ b/target/riscv/cpu.c
> @@ -73,6 +73,7 @@ struct isa_ext_data {
>  static const struct isa_ext_data isa_edata_arr[] = {
>      ISA_EXT_DATA_ENTRY(h, false, PRIV_VERSION_1_12_0, ext_h),
>      ISA_EXT_DATA_ENTRY(v, false, PRIV_VERSION_1_12_0, ext_v),
> +    ISA_EXT_DATA_ENTRY(zicond, true, PRIV_VERSION_1_12_0, ext_zicond),
>      ISA_EXT_DATA_ENTRY(zicsr, true, PRIV_VERSION_1_10_0, ext_icsr),
>      ISA_EXT_DATA_ENTRY(zifencei, true, PRIV_VERSION_1_10_0, ext_ifencei),
>      ISA_EXT_DATA_ENTRY(zihintpause, true, PRIV_VERSION_1_10_0, 
> ext_zihintpause),
> @@ -1080,6 +1081,9 @@ static Property riscv_cpu_extensions[] = {
>      DEFINE_PROP_BOOL("x-smaia", RISCVCPU, cfg.ext_smaia, false),
>      DEFINE_PROP_BOOL("x-ssaia", RISCVCPU, cfg.ext_ssaia, false),
>
> +    /* Zicond 1.0-draft-20230120 */
> +    DEFINE_PROP_BOOL("x-zicond", RISCVCPU, cfg.ext_zicond, false),
> +
>      DEFINE_PROP_END_OF_LIST(),
>  };
>
> diff --git a/target/riscv/cpu.h b/target/riscv/cpu.h
> index f5609b62a2..4b6ff800d3 100644
> --- a/target/riscv/cpu.h
> +++ b/target/riscv/cpu.h
> @@ -446,6 +446,7 @@ struct RISCVCPUConfig {
>      bool ext_zkt;
>      bool ext_ifencei;
>      bool ext_icsr;
> +    bool ext_zicond;
>      bool ext_zihintpause;
>      bool ext_smstateen;
>      bool ext_sstc;
> diff --git a/target/riscv/insn32.decode b/target/riscv/insn32.decode
> index b7e7613ea2..ca812c2f7a 100644
> --- a/target/riscv/insn32.decode
> +++ b/target/riscv/insn32.decode
> @@ -890,3 +890,7 @@ sm3p1       00 01000 01001 ..... 001 ..... 0010011 @r2
>  # *** RV32 Zksed Standard Extension ***
>  sm4ed       .. 11000 ..... ..... 000 ..... 0110011 @k_aes
>  sm4ks       .. 11010 ..... ..... 000 ..... 0110011 @k_aes
> +
> +# *** Zicond Standard Extension ***
> +czero_eqz   0000111 ..... ..... 101 ..... 0110011 @r
> +czero_nez   0000111 ..... ..... 111 ..... 0110011 @r
> diff --git a/target/riscv/insn_trans/trans_rvzicond.c.inc 
> b/target/riscv/insn_trans/trans_rvzicond.c.inc
> new file mode 100644
> index 0000000000..20e9694a2c
> --- /dev/null
> +++ b/target/riscv/insn_trans/trans_rvzicond.c.inc
> @@ -0,0 +1,54 @@
> +/*
> + * RISC-V translation routines for the XVentanaCondOps extension.
> + *
> + * Copyright (c) 2022 VRULL GmbH.
> + *
> + * This program is free software; you can redistribute it and/or modify it
> + * under the terms and conditions of the GNU General Public License,
> + * version 2 or later, as published by the Free Software Foundation.
> + *
> + * This program is distributed in the hope it will be useful, but WITHOUT
> + * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
> + * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License for
> + * more details.
> + *
> + * You should have received a copy of the GNU General Public License along 
> with
> + * this program.  If not, see <http://www.gnu.org/licenses/>.
> + */
> +
> +#define REQUIRE_ZICOND(ctx) do {                 \
> +    if (!ctx->cfg_ptr->ext_zicond) {             \
> +        return false;                            \
> +    }                                            \
> +} while (0)
> +
> +/* Emits "$rd = ($rs2 <cond> $zero) ? $zero : $rs1" */
> +static inline void gen_czero(TCGv dest, TCGv src1, TCGv src2, TCGCond cond)
> +{
> +    TCGv zero = tcg_constant_tl(0);
> +    tcg_gen_movcond_tl(cond, dest, src2, zero, zero, src1);
> +}
> +
> +static inline void gen_czero_eqz(TCGv dest, TCGv src1, TCGv src2)
> +{
> +    gen_czero(dest, src1, src2, TCG_COND_EQ);
> +}
> +
> +static inline void gen_czero_nez(TCGv dest, TCGv src1, TCGv src2)
> +{
> +    gen_czero(dest, src1, src2, TCG_COND_NE);
> +}
> +
> +static bool trans_czero_eqz(DisasContext *ctx, arg_r *a)
> +{
> +    REQUIRE_ZICOND(ctx);
> +
> +    return gen_logic(ctx, a, gen_czero_eqz);
> +}
> +
> +static bool trans_czero_nez(DisasContext *ctx, arg_r *a)
> +{
> +    REQUIRE_ZICOND(ctx);
> +
> +    return gen_logic(ctx, a, gen_czero_nez);
> +}
> diff --git a/target/riscv/translate.c b/target/riscv/translate.c
> index df38db7553..1468748835 100644
> --- a/target/riscv/translate.c
> +++ b/target/riscv/translate.c
> @@ -1061,6 +1061,7 @@ static uint32_t opcode_at(DisasContextBase *dcbase, 
> target_ulong pc)
>  #include "insn_trans/trans_rvv.c.inc"
>  #include "insn_trans/trans_rvb.c.inc"
>  #include "insn_trans/trans_rvzawrs.c.inc"
> +#include "insn_trans/trans_rvzicond.c.inc"
>  #include "insn_trans/trans_rvzfh.c.inc"
>  #include "insn_trans/trans_rvk.c.inc"
>  #include "insn_trans/trans_privileged.c.inc"
> --
> 2.34.1
>
>