tcg: make CPUClass.cpu_exec_* optional

This will let us simplify the code that initializes CPU class
methods, when we move cpu_exec_*() to a separate struct.

Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>
Signed-off-by: Claudio Fontana <cfontana@suse.de>
Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Message-Id: <20201212155530.23098-11-cfontana@suse.de>
Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>
diff --git a/accel/tcg/cpu-exec.c b/accel/tcg/cpu-exec.c
index 58117f1..36dde32 100644
--- a/accel/tcg/cpu-exec.c
+++ b/accel/tcg/cpu-exec.c
@@ -240,14 +240,18 @@
 {
     CPUClass *cc = CPU_GET_CLASS(cpu);
 
-    cc->cpu_exec_enter(cpu);
+    if (cc->cpu_exec_enter) {
+        cc->cpu_exec_enter(cpu);
+    }
 }
 
 static void cpu_exec_exit(CPUState *cpu)
 {
     CPUClass *cc = CPU_GET_CLASS(cpu);
 
-    cc->cpu_exec_exit(cpu);
+    if (cc->cpu_exec_exit) {
+        cc->cpu_exec_exit(cpu);
+    }
 }
 
 void cpu_exec_step_atomic(CPUState *cpu)
@@ -619,7 +623,8 @@
            True when it is, and we should restart on a new TB,
            and via longjmp via cpu_loop_exit.  */
         else {
-            if (cc->cpu_exec_interrupt(cpu, interrupt_request)) {
+            if (cc->cpu_exec_interrupt &&
+                cc->cpu_exec_interrupt(cpu, interrupt_request)) {
                 if (need_replay_interrupt(interrupt_request)) {
                     replay_interrupt();
                 }