[PATCH v3 1/2] target/riscv: add Zicond as an experimental extension

[Philipp Tomsich]

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 v3:
- don't add this to MAINTAINERS, as it is an official extension

Changes in v2:
- gates availability of the instructions through a REQUIRE_ZICOND
  macro (these were previously always enabled)

 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 +
 5 files changed, 64 insertions(+)
 create mode 100644 target/riscv/insn_trans/trans_rvzicond.c.inc

diff --git a/target/riscv/cpu.c b/target/riscv/cpu.c
index 14a7027095..98177d8328 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),
@@ -1097,6 +1098,9 @@ 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 bcf0826753..aaf3acb753 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 01cc30a365..93850938ae 100644
--- a/target/riscv/translate.c
+++ b/target/riscv/translate.c
@@ -1076,6 +1076,7 @@ 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