target/arm: Split out disas_a64_legacy

Split out all of the decode stuff from aarch64_tr_translate_insn.
Call it disas_a64_legacy to indicate it will be replaced.

Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Message-id: 20230512144106.3608981-2-peter.maydell@linaro.org
[PMM: Rebased]
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>

target/arm/tcg/translate-a64.c

@@ -14200,6 +14200,49 @@ static bool btype_destination_ok(uint32_t insn, bool bt, int btype)
     return false;
 }
 
+/* C3.1 A64 instruction index by encoding */
+static void disas_a64_legacy(DisasContext *s, uint32_t insn)
+{
+    switch (extract32(insn, 25, 4)) {
+    case 0x0:
+        if (!extract32(insn, 31, 1) || !disas_sme(s, insn)) {
+            unallocated_encoding(s);
+        }
+        break;
+    case 0x1: case 0x3: /* UNALLOCATED */
+        unallocated_encoding(s);
+        break;
+    case 0x2:
+        if (!disas_sve(s, insn)) {
+            unallocated_encoding(s);
+        }
+        break;
+    case 0x8: case 0x9: /* Data processing - immediate */
+        disas_data_proc_imm(s, insn);
+        break;
+    case 0xa: case 0xb: /* Branch, exception generation and system insns */
+        disas_b_exc_sys(s, insn);
+        break;
+    case 0x4:
+    case 0x6:
+    case 0xc:
+    case 0xe:      /* Loads and stores */
+        disas_ldst(s, insn);
+        break;
+    case 0x5:
+    case 0xd:      /* Data processing - register */
+        disas_data_proc_reg(s, insn);
+        break;
+    case 0x7:
+    case 0xf:      /* Data processing - SIMD and floating point */
+        disas_data_proc_simd_fp(s, insn);
+        break;
+    default:
+        assert(FALSE); /* all 15 cases should be handled above */
+        break;
+    }
+}
+
 static void aarch64_tr_init_disas_context(DisasContextBase *dcbase,
                                           CPUState *cpu)
 {
@@ -14401,44 +14444,7 @@ static void aarch64_tr_translate_insn(DisasContextBase *dcbase, CPUState *cpu)
         disas_sme_fa64(s, insn);
     }
 
-    switch (extract32(insn, 25, 4)) {
-    case 0x0:
-        if (!extract32(insn, 31, 1) || !disas_sme(s, insn)) {
-            unallocated_encoding(s);
-        }
-        break;
-    case 0x1: case 0x3: /* UNALLOCATED */
-        unallocated_encoding(s);
-        break;
-    case 0x2:
-        if (!disas_sve(s, insn)) {
-            unallocated_encoding(s);
-        }
-        break;
-    case 0x8: case 0x9: /* Data processing - immediate */
-        disas_data_proc_imm(s, insn);
-        break;
-    case 0xa: case 0xb: /* Branch, exception generation and system insns */
-        disas_b_exc_sys(s, insn);
-        break;
-    case 0x4:
-    case 0x6:
-    case 0xc:
-    case 0xe:      /* Loads and stores */
-        disas_ldst(s, insn);
-        break;
-    case 0x5:
-    case 0xd:      /* Data processing - register */
-        disas_data_proc_reg(s, insn);
-        break;
-    case 0x7:
-    case 0xf:      /* Data processing - SIMD and floating point */
-        disas_data_proc_simd_fp(s, insn);
-        break;
-    default:
-        assert(FALSE); /* all 15 cases should be handled above */
-        break;
-    }
+    disas_a64_legacy(s, insn);
 
     /*
      * After execution of most insns, btype is reset to 0.