Hexagon (target/hexagon) Use QEMU decodetree (32-bit instructions)

The Decodetree Specification can be found here
https://www.qemu.org/docs/master/devel/decodetree.html

Covers all 32-bit instructions, including HVX

We generate separate decoders for each instruction class.  The reason
will be more apparent in the next patch in this series.

We add 2 new scripts
    gen_decodetree.py        Generate the input to decodetree.py
    gen_trans_funcs.py       Generate the trans_* functions used by the
                             output of decodetree.py

Since the functions generated by decodetree.py take DisasContext * as an
argument, we add the argument to a couple of functions that didn't need
it previously.  We also set the insn field in DisasContext during decode
because it is used by the trans_* functions.

There is a g_assert_not_reached() in decode_insns() in decode.c to
verify we never try to use the old decoder on 32-bit instructions

Signed-off-by: Taylor Simpson <ltaylorsimpson@gmail.com>
Reviewed-by: Brian Cain <bcain@quicinc.com>
Message-Id: <20240115221443.365287-2-ltaylorsimpson@gmail.com>
Signed-off-by: Brian Cain <bcain@quicinc.com>

1 files changed, 132 insertions, 0 deletions

diff --git a/target/hexagon/gen_trans_funcs.py b/target/hexagon/gen_trans_funcs.py
new file mode 100755
index 0000000000..c907131009
--- /dev/null
+++ b/target/hexagon/gen_trans_funcs.py
@@ -0,0 +1,132 @@
+#!/usr/bin/env python3
+
+##
+##  Copyright (c) 2024 Taylor Simpson <ltaylorsimpson@gmail.com>
+##
+##  This program is free software; you can redistribute it and/or modify
+##  it under the terms of the GNU General Public License as published by
+##  the Free Software Foundation; either version 2 of the License, or
+##  (at your option) any later version.
+##
+##  This program is distributed in the hope that 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/>.
+##
+
+import io
+import re
+
+import sys
+import textwrap
+import iset
+import hex_common
+
+encs = {
+    tag: "".join(reversed(iset.iset[tag]["enc"].replace(" ", "")))
+    for tag in iset.tags
+    if iset.iset[tag]["enc"] != "MISSING ENCODING"
+}
+
+
+regre = re.compile(r"((?<!DUP)[MNORCPQXSGVZA])([stuvwxyzdefg]+)([.]?[LlHh]?)(\d+S?)")
+immre = re.compile(r"[#]([rRsSuUm])(\d+)(?:[:](\d+))?")
+
+
+def ordered_unique(l):
+    return sorted(set(l), key=l.index)
+
+
+def skip_tag(tag, classes):
+    enc_class = iset.iset[tag]["enc_class"]
+    return enc_class not in classes
+
+
+def code_fmt(txt):
+    return textwrap.indent(textwrap.dedent(txt), "    ")
+
+open_curly = "{"
+close_curly = "}"
+
+def mark_which_imm_extended(f, tag):
+    immre = re.compile(r"IMMEXT\([rRsSuUm]")
+    imm = immre.findall(hex_common.semdict[tag])
+    if len(imm) == 0:
+        # No extended operand found
+        return
+    letter = re.split("\\(", imm[0])[1]
+    f.write(code_fmt(f"""\
+        insn->which_extended = {0 if letter.islower() else 1};
+    """))
+
+##
+## Generate the QEMU decodetree trans_<tag> function for each instruction
+##     For A2_add: Rd32=add(Rs32,Rt32)
+##     We produce:
+##     static bool trans_A2_add(DisasContext *ctx, arg_A2_add *args)
+##     {
+##         Insn *insn = ctx->insn;
+##         insn->opcode = A2_add;
+##         insn->regno[0] = args->Rd;
+##         insn->regno[1] = args->Rs;
+##         insn->regno[2] = args->Rt;
+##         return true;
+##     }
+##
+def gen_trans_funcs(f, classes):
+    f.write(f"/* DO NOT MODIFY - This file is generated by {sys.argv[0]} */\n\n")
+    for tag in sorted(encs.keys(), key=iset.tags.index):
+        if skip_tag(tag, classes):
+            continue
+
+        regs = ordered_unique(regre.findall(iset.iset[tag]["syntax"]))
+        imms = ordered_unique(immre.findall(iset.iset[tag]["syntax"]))
+
+        f.write(textwrap.dedent(f"""\
+            static bool trans_{tag}(DisasContext *ctx, arg_{tag} *args)
+            {open_curly}
+                Insn *insn = ctx->insn;
+                insn->opcode = {tag};
+        """))
+
+        regno = 0
+        for reg in regs:
+            reg_type = reg[0]
+            reg_id = reg[1]
+            f.write(code_fmt(f"""\
+                insn->regno[{regno}] = args->{reg_type}{reg_id};
+            """))
+            regno += 1
+
+        if len(imms) != 0:
+            mark_which_imm_extended(f, tag)
+
+        for imm in imms:
+            imm_type = imm[0]
+            imm_letter = "i" if imm_type.islower() else "I"
+            immno = 0 if imm_type.islower() else 1
+            imm_shift = int(imm[2]) if imm[2] else 0
+            if imm_shift:
+                f.write(code_fmt(f"""\
+                    insn->immed[{immno}] =
+                        shift_left(ctx, args->{imm_type}{imm_letter},
+                                   {imm_shift}, {immno});
+                """))
+            else:
+                f.write(code_fmt(f"""\
+                    insn->immed[{immno}] = args->{imm_type}{imm_letter};
+                """))
+
+        f.write(textwrap.dedent(f"""\
+                return true;
+            {close_curly}
+        """))
+
+
+if __name__ == "__main__":
+    hex_common.read_semantics_file(sys.argv[1])
+    with open(sys.argv[2], "w") as f:
+        gen_trans_funcs(f, { "NORMAL", "EXT_mmvec" })