cc->cme should not be marked.

cc is callcache.

cc->klass (klass) should not be marked because if the klass is
free'ed, the cc->klass will be cleared by `vm_cc_invalidate()`.

cc->cme (cme) should not be marked because if cc is invalidated
when cme is free'ed.
- klass marks cme if klass uses cme.
- caller classe's ccs->cme marks cc->cme.
- if cc is invalidated (klass doesn't refer the cc),
  cc is invalidated by `vm_cc_invalidate()` and cc->cme is
  not be accessed.
- On the multi-Ractors, cme will be collected with global GC
  so that it is safe if GC is not interleaving while accessing
  cc and cme.

fix [Bug #19436]

```ruby
10_000.times{|i|
  # p i if (i%1_000) == 0

  str = "x" * 1_000_000
  def str.foo = nil
  eval "def call#{i}(s) = s.foo"
  send "call#{i}", str
}
```

Without this patch:

```
real    1m5.639s
user    0m6.637s
sys     0m58.292s
```

and with this patch:

```
real    0m2.045s
user    0m1.627s
sys     0m0.164s
```

gc.c

@@ -7015,11 +7015,22 @@ gc_mark_imemo(rb_objspace_t *objspace, VALUE obj)
       case imemo_callinfo:
         return;
       case imemo_callcache:
-        {
-            const struct rb_callcache *cc = (const struct rb_callcache *)obj;
-            // should not mark klass here
-            gc_mark(objspace, (VALUE)vm_cc_cme(cc));
-        }
+        /* cc is callcache.
+         *
+         * cc->klass (klass) should not be marked because if the klass is
+         * free'ed, the cc->klass will be cleared by `vm_cc_invalidate()`.
+         *
+         * cc->cme (cme) should not be marked because if cc is invalidated
+         * when cme is free'ed.
+         * - klass marks cme if klass uses cme.
+         * - caller classe's ccs->cme marks cc->cme.
+         * - if cc is invalidated (klass doesn't refer the cc),
+         *   cc is invalidated by `vm_cc_invalidate()` and cc->cme is
+         *   not be accessed.
+         * - On the multi-Ractors, cme will be collected with global GC
+         *   so that it is safe if GC is not interleaving while accessing
+         *   cc and cme.
+         */
         return;
       case imemo_constcache:
         {
@@ -10122,12 +10133,14 @@ gc_ref_update_imemo(rb_objspace_t *objspace, VALUE obj)
                 if (!is_live_object(objspace, cc->klass)) {
                     *((VALUE *)(&cc->klass)) = (VALUE)0;
                 }
-            }
 
-            if (cc->cme_) {
-                TYPED_UPDATE_IF_MOVED(objspace, struct rb_callable_method_entry_struct *, cc->cme_);
-                if (!is_live_object(objspace, (VALUE)cc->cme_)) {
-                    *((struct rb_callable_method_entry_struct **)(&cc->cme_)) = (struct rb_callable_method_entry_struct *)0;
+                // cc->cme_ is available if cc->klass is given
+
+                if (cc->cme_) {
+                    TYPED_UPDATE_IF_MOVED(objspace, struct rb_callable_method_entry_struct *, cc->cme_);
+                    if (!is_live_object(objspace, (VALUE)cc->cme_)) {
+                        *((struct rb_callable_method_entry_struct **)(&cc->cme_)) = (struct rb_callable_method_entry_struct *)0;
+                    }
                 }
             }
         }

iseq.c

@@ -282,6 +282,29 @@ rb_iseq_mark_and_move_each_value(const rb_iseq_t *iseq, VALUE *original_iseq)
     }
 }
 
+static bool
+cc_is_active(const struct rb_callcache *cc, bool reference_updating)
+{
+    if (cc) {
+        if (reference_updating) {
+            cc = (const struct rb_callcache *)rb_gc_location((VALUE)cc);
+        }
+
+        if (vm_cc_markable(cc)) {
+            if (cc->klass) { // cc is not invalidated
+                const struct rb_callable_method_entry_struct *cme = vm_cc_cme(cc);
+                if (reference_updating) {
+                    cme = (const struct rb_callable_method_entry_struct *)rb_gc_location((VALUE)cme);
+                }
+                if (!METHOD_ENTRY_INVALIDATED(cme)) {
+                    return true;
+                }
+            }
+        }
+    }
+    return false;
+}
+
 void
 rb_iseq_mark_and_move(rb_iseq_t *iseq, bool reference_updating)
 {
@@ -310,27 +333,11 @@ rb_iseq_mark_and_move(rb_iseq_t *iseq, bool reference_updating)
 
                 if (cds[i].ci) rb_gc_mark_and_move_ptr(&cds[i].ci);
 
-                const struct rb_callcache *cc = cds[i].cc;
-                if (cc) {
-                    if (reference_updating) {
-                        cc = (const struct rb_callcache *)rb_gc_location((VALUE)cc);
-                    }
-
-                    if (vm_cc_markable(cc)) {
-                        VM_ASSERT((cc->flags & VM_CALLCACHE_ON_STACK) == 0);
-
-                        const struct rb_callable_method_entry_struct *cme = vm_cc_cme(cc);
-                        if (reference_updating) {
-                            cme = (const struct rb_callable_method_entry_struct *)rb_gc_location((VALUE)cme);
-                        }
-
-                        if (cc->klass && !METHOD_ENTRY_INVALIDATED(cme)) {
-                            rb_gc_mark_and_move_ptr(&cds[i].cc);
-                        }
-                        else {
-                            cds[i].cc = rb_vm_empty_cc();
-                        }
-                    }
+                if (cc_is_active(cds[i].cc, reference_updating)) {
+                    rb_gc_mark_and_move_ptr(&cds[i].cc);
+                }
+                else {
+                    cds[i].cc = rb_vm_empty_cc();
                 }
             }
         }