Convert rb_class_cc_entries.entries in a flexible array member

`rb_class_cc_entries` is little more than a `len` and `capa`.
Hence embedding the entries doesn't cost much extra copying and
saves a bit of memory and some pointer chasing.

Co-Authored-By: Étienne Barrié <etienne.barrie@gmail.com>

vm_callinfo.h

@@ -585,9 +585,15 @@ struct rb_class_cc_entries {
         unsigned int argc;
         unsigned int flag;
         const struct rb_callcache *cc;
-    } *entries;
+    } entries[FLEX_ARY_LEN];
 };
 
+static inline size_t
+vm_ccs_alloc_size(size_t capa)
+{
+    return offsetof(struct rb_class_cc_entries, entries) + (sizeof(struct rb_class_cc_entries_entry) * capa);
+}
+
 #if VM_CHECK_MODE > 0
 
 const rb_callable_method_entry_t *rb_vm_lookup_overloaded_cme(const rb_callable_method_entry_t *cme);

vm_insnhelper.c

@@ -1981,15 +1981,15 @@ static VALUE vm_mtbl_dump(VALUE klass, ID target_mid);
 static struct rb_class_cc_entries *
 vm_ccs_create(VALUE klass, VALUE cc_tbl, ID mid, const rb_callable_method_entry_t *cme)
 {
-    struct rb_class_cc_entries *ccs = ALLOC(struct rb_class_cc_entries);
+    int initial_capa = 2;
+    struct rb_class_cc_entries *ccs = ruby_xmalloc(vm_ccs_alloc_size(initial_capa));
 #if VM_CHECK_MODE > 0
     ccs->debug_sig = ~(VALUE)ccs;
 #endif
-    ccs->capa = 0;
+    ccs->capa = initial_capa;
     ccs->len = 0;
     ccs->cme = cme;
     METHOD_ENTRY_CACHED_SET((rb_callable_method_entry_t *)cme);
-    ccs->entries = NULL;
 
     rb_managed_id_table_insert(cc_tbl, mid, (VALUE)ccs);
     RB_OBJ_WRITTEN(cc_tbl, Qundef, cme);
@@ -1997,21 +1997,21 @@ vm_ccs_create(VALUE klass, VALUE cc_tbl, ID mid, const rb_callable_method_entry_
 }
 
 static void
-vm_ccs_push(VALUE cc_tbl, struct rb_class_cc_entries *ccs, const struct rb_callinfo *ci, const struct rb_callcache *cc)
+vm_ccs_push(VALUE cc_tbl, ID mid, struct rb_class_cc_entries *ccs, const struct rb_callinfo *ci, const struct rb_callcache *cc)
 {
     if (! vm_cc_markable(cc)) {
         return;
     }
 
     if (UNLIKELY(ccs->len == ccs->capa)) {
-        if (ccs->capa == 0) {
-            ccs->capa = 1;
-            ccs->entries = ALLOC_N(struct rb_class_cc_entries_entry, ccs->capa);
-        }
-        else {
+        RUBY_ASSERT(ccs->capa > 0);
         ccs->capa *= 2;
-            REALLOC_N(ccs->entries, struct rb_class_cc_entries_entry, ccs->capa);
-        }
+        ccs = ruby_xrealloc(ccs, vm_ccs_alloc_size(ccs->capa));
+#if VM_CHECK_MODE > 0
+        ccs->debug_sig = ~(VALUE)ccs;
+#endif
+        // GC?
+        rb_managed_id_table_insert(cc_tbl, mid, (VALUE)ccs);
     }
     VM_ASSERT(ccs->len < ccs->capa);
 
@@ -2143,7 +2143,7 @@ vm_populate_cc(VALUE klass, const struct rb_callinfo * const ci, ID mid)
     cme = rb_check_overloaded_cme(cme, ci);
 
     const struct rb_callcache *cc = vm_cc_new(klass, cme, vm_call_general, cc_type_normal);
-    vm_ccs_push(cc_tbl, ccs, ci, cc);
+    vm_ccs_push(cc_tbl, mid, ccs, ci, cc);
 
     VM_ASSERT(vm_cc_cme(cc) != NULL);
     VM_ASSERT(cme->called_id == mid);

vm_method.c

@@ -22,15 +22,6 @@ static inline rb_method_entry_t *lookup_method_table(VALUE klass, ID id);
 #define ruby_running (GET_VM()->running)
 /* int ruby_running = 0; */
 
-static void
-vm_ccs_free(struct rb_class_cc_entries *ccs)
-{
-    if (ccs->entries) {
-        ruby_xfree(ccs->entries);
-    }
-    ruby_xfree(ccs);
-}
-
 static enum rb_id_table_iterator_result
 mark_cc_entry_i(VALUE ccs_ptr, void *data)
 {
@@ -39,7 +30,7 @@ mark_cc_entry_i(VALUE ccs_ptr, void *data)
     VM_ASSERT(vm_ccs_p(ccs));
 
     if (METHOD_ENTRY_INVALIDATED(ccs->cme)) {
-        vm_ccs_free(ccs);
+        ruby_xfree(ccs);
         return ID_TABLE_DELETE;
     }
     else {
@@ -69,7 +60,7 @@ cc_table_free_i(VALUE ccs_ptr, void *data)
     struct rb_class_cc_entries *ccs = (struct rb_class_cc_entries *)ccs_ptr;
     VM_ASSERT(vm_ccs_p(ccs));
 
-    vm_ccs_free(ccs);
+    ruby_xfree(ccs);
 
     return ID_TABLE_CONTINUE;
 }
@@ -146,13 +137,13 @@ static enum rb_id_table_iterator_result
 vm_cc_table_dup_i(ID key, VALUE old_ccs_ptr, void *data)
 {
     struct rb_class_cc_entries *old_ccs = (struct rb_class_cc_entries *)old_ccs_ptr;
-    struct rb_class_cc_entries *new_ccs = ALLOC(struct rb_class_cc_entries);
-    MEMCPY(new_ccs, old_ccs, struct rb_class_cc_entries, 1);
+    size_t memsize = vm_ccs_alloc_size(old_ccs->capa);
+    struct rb_class_cc_entries *new_ccs = ruby_xmalloc(memsize);
+    memcpy(new_ccs, old_ccs, memsize);
+
 #if VM_CHECK_MODE > 0
     new_ccs->debug_sig = ~(VALUE)new_ccs;
 #endif
-    new_ccs->entries = ALLOC_N(struct rb_class_cc_entries_entry, new_ccs->capa);
-    MEMCPY(new_ccs->entries, old_ccs->entries, struct rb_class_cc_entries_entry, new_ccs->capa);
 
     VALUE new_table = (VALUE)data;
     rb_managed_id_table_insert(new_table, key, (VALUE)new_ccs);
@@ -173,21 +164,19 @@ rb_vm_cc_table_dup(VALUE old_table)
 static void
 vm_ccs_invalidate(struct rb_class_cc_entries *ccs)
 {
-    if (ccs->entries) {
     for (int i=0; i<ccs->len; i++) {
         const struct rb_callcache *cc = ccs->entries[i].cc;
         VM_ASSERT(!vm_cc_super_p(cc) && !vm_cc_refinement_p(cc));
         vm_cc_invalidate(cc);
     }
 }
-}
 
 void
 rb_vm_ccs_invalidate_and_free(struct rb_class_cc_entries *ccs)
 {
     RB_DEBUG_COUNTER_INC(ccs_free);
     vm_ccs_invalidate(ccs);
-    vm_ccs_free(ccs);
+    ruby_xfree(ccs);
 }
 
 void