target/arm: Create decodetree skeleton for A64

The A64 translator uses a hand-written decoder for everything except
SVE or SME.  It's fairly well structured, but it's becoming obvious
that it's still more painful to add instructions to than the A32
translator, because putting a new instruction into the right place in
a hand-written decoder is much harder than adding new instruction
patterns to a decodetree file.

As the first step in conversion to decodetree, create the skeleton of
the decodetree decoder; where it does not handle instructions we will
fall back to the legacy decoder (which will be for everything at the
moment, since there are no patterns in a64.decode).

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 20230512144106.3608981-3-peter.maydell@linaro.org

target/arm/tcg/a64.decode

@@ -0,0 +1,20 @@
+# AArch64 A64 allowed instruction decoding
+#
+#  Copyright (c) 2023 Linaro, Ltd
+#
+# This library is free software; you can redistribute it and/or
+# modify it under the terms of the GNU Lesser General Public
+# License as published by the Free Software Foundation; either
+# version 2.1 of the License, or (at your option) any later version.
+#
+# This library 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
+# Lesser General Public License for more details.
+#
+# You should have received a copy of the GNU Lesser General Public
+# License along with this library; if not, see <http://www.gnu.org/licenses/>.
+
+#
+# This file is processed by scripts/decodetree.py
+#

target/arm/tcg/meson.build

@@ -13,6 +13,7 @@ gen = [
   decodetree.process('a32-uncond.decode', extra_args: '--static-decode=disas_a32_uncond'),
   decodetree.process('t32.decode', extra_args: '--static-decode=disas_t32'),
   decodetree.process('t16.decode', extra_args: ['-w', '16', '--static-decode=disas_t16']),
+  decodetree.process('a64.decode', extra_args: ['--static-decode=disas_a64']),
 ]
 
 arm_ss.add(gen)

target/arm/tcg/translate-a64.c

@@ -56,6 +56,13 @@ enum a64_shift_type {
     A64_SHIFT_TYPE_ROR = 3
 };
 
+/*
+ * Include the generated decoders.
+ */
+
+#include "decode-sme-fa64.c.inc"
+#include "decode-a64.c.inc"
+
 /* Table based decoder typedefs - used when the relevant bits for decode
  * are too awkwardly scattered across the instruction (eg SIMD).
  */
@@ -14100,12 +14107,6 @@ static void disas_data_proc_simd_fp(DisasContext *s, uint32_t insn)
     }
 }
 
-/*
- * Include the generated SME FA64 decoder.
- */
-
-#include "decode-sme-fa64.c.inc"
-
 static bool trans_OK(DisasContext *s, arg_OK *a)
 {
     return true;
@@ -14444,7 +14445,10 @@ static void aarch64_tr_translate_insn(DisasContextBase *dcbase, CPUState *cpu)
         disas_sme_fa64(s, insn);
     }
 
-    disas_a64_legacy(s, insn);
+
+    if (!disas_a64(s, insn)) {
+        disas_a64_legacy(s, insn);
+    }
 
     /*
      * After execution of most insns, btype is reset to 0.