target/mips/translate: Extract decode_opc_legacy() from decode_opc()

As we will slowly move to decodetree generated decoders,
extract the legacy decoding from decode_opc(), so new
decoders are added in decode_opc() while old code is
removed from decode_opc_legacy().

Signed-off-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-Id: <20201215225757.764263-2-f4bug@amsat.org>

target/mips/translate.c

@@ -30517,30 +30517,13 @@ static void gen_msa(CPUMIPSState *env, DisasContext *ctx)
 }
-static void decode_opc(CPUMIPSState *env, DisasContext *ctx)
+static bool decode_opc_legacy(CPUMIPSState *env, DisasContext *ctx)
 {
     int32_t offset;
     int rs, rt, rd, sa;
     uint32_t op, op1;
     int16_t imm;
-    /* make sure instructions are on a word boundary */
-    if (ctx->base.pc_next & 0x3) {
-        env->CP0_BadVAddr = ctx->base.pc_next;
-        generate_exception_err(ctx, EXCP_AdEL, EXCP_INST_NOTAVAIL);
-        return;
-    }
-
-    /* Handle blikely not taken case */
-    if ((ctx->hflags & MIPS_HFLAG_BMASK_BASE) == MIPS_HFLAG_BL) {
-        TCGLabel *l1 = gen_new_label();
-
-        tcg_gen_brcondi_tl(TCG_COND_NE, bcond, 0, l1);
-        tcg_gen_movi_i32(hflags, ctx->hflags & ~MIPS_HFLAG_BMASK);
-        gen_goto_tb(ctx, 1, ctx->base.pc_next + 4);
-        gen_set_label(l1);
-    }
-
     op = MASK_OP_MAJOR(ctx->opcode);
     rs = (ctx->opcode >> 21) & 0x1f;
     rt = (ctx->opcode >> 16) & 0x1f;
@@ -31268,9 +31251,35 @@ static void decode_opc(CPUMIPSState *env, DisasContext *ctx)
         break;
     default:            /* Invalid */
         MIPS_INVAL("major opcode");
-        gen_reserved_instruction(ctx);
-        break;
+        return false;
     }
+    return true;
+}
+
+static void decode_opc(CPUMIPSState *env, DisasContext *ctx)
+{
+    /* make sure instructions are on a word boundary */
+    if (ctx->base.pc_next & 0x3) {
+        env->CP0_BadVAddr = ctx->base.pc_next;
+        generate_exception_err(ctx, EXCP_AdEL, EXCP_INST_NOTAVAIL);
+        return;
+    }
+
+    /* Handle blikely not taken case */
+    if ((ctx->hflags & MIPS_HFLAG_BMASK_BASE) == MIPS_HFLAG_BL) {
+        TCGLabel *l1 = gen_new_label();
+
+        tcg_gen_brcondi_tl(TCG_COND_NE, bcond, 0, l1);
+        tcg_gen_movi_i32(hflags, ctx->hflags & ~MIPS_HFLAG_BMASK);
+        gen_goto_tb(ctx, 1, ctx->base.pc_next + 4);
+        gen_set_label(l1);
+    }
+
+    if (decode_opc_legacy(env, ctx)) {
+        return;
+    }
+
+    gen_reserved_instruction(ctx);
 }
 static void mips_tr_init_disas_context(DisasContextBase *dcbase, CPUState *cs)