Optimize SplFixedArray when magic methods aren't overridden

This decreases the memory usage of SplFixedArrays by 32 bytes per object
on 64-bit systems (use 1 null pointer instead of 5 null pointers)
If allocating a lot of arrays of size 1, memory usage was 19.44MiB before this
change, and 16.24MiB after the change.

Existing tests continue to pass.

Subclassing SplFixedArray is already inefficient and rarely done.
It checks for the existence of 5 methods every time a subclass is instantiated.
(and has to switch back from C to the php vm to call those methods)

Closes GH-6552

Author: TysonAndre

ext/spl/spl_fixedarray.c

@@ -41,17 +41,22 @@ ZEND_GET_MODULE(spl_fixedarray)
 
 typedef struct _spl_fixedarray {
 	zend_long size;
+	/* It is possible to resize this, so this can't be combined with the object */
 	zval *elements;
 } spl_fixedarray;
 
-typedef struct _spl_fixedarray_object {
-	spl_fixedarray       array;
+typedef struct _spl_fixedarray_methods {
 	zend_function       *fptr_offset_get;
 	zend_function       *fptr_offset_set;
 	zend_function       *fptr_offset_has;
 	zend_function       *fptr_offset_del;
 	zend_function       *fptr_count;
-	zend_object          std;
+} spl_fixedarray_methods;
+
+typedef struct _spl_fixedarray_object {
+	spl_fixedarray          array;
+	spl_fixedarray_methods *methods;
+	zend_object             std;
 } spl_fixedarray_object;
 
 typedef struct _spl_fixedarray_it {
@@ -222,6 +227,9 @@ static void spl_fixedarray_object_free_storage(zend_object *object)
 	spl_fixedarray_object *intern = spl_fixed_array_from_obj(object);
 	spl_fixedarray_dtor(&intern->array);
 	zend_object_std_dtor(&intern->std);
+	if (intern->methods) {
+		efree(intern->methods);
+	}
 }
 
 static zend_object *spl_fixedarray_object_new_ex(zend_class_entry *class_type, zend_object *orig, bool clone_orig)
@@ -252,26 +260,34 @@ static zend_object *spl_fixedarray_object_new_ex(zend_class_entry *class_type, z
 
 	ZEND_ASSERT(parent);
 
-	if (inherited) {
-		intern->fptr_offset_get = zend_hash_str_find_ptr(&class_type->function_table, "offsetget", sizeof("offsetget") - 1);
-		if (intern->fptr_offset_get->common.scope == parent) {
-			intern->fptr_offset_get = NULL;
+	if (UNEXPECTED(inherited)) {
+		spl_fixedarray_methods methods;
+		methods.fptr_offset_get = zend_hash_str_find_ptr(&class_type->function_table, "offsetget", sizeof("offsetget") - 1);
+		if (methods.fptr_offset_get->common.scope == parent) {
+			methods.fptr_offset_get = NULL;
+		}
+		methods.fptr_offset_set = zend_hash_str_find_ptr(&class_type->function_table, "offsetset", sizeof("offsetset") - 1);
+		if (methods.fptr_offset_set->common.scope == parent) {
+			methods.fptr_offset_set = NULL;
 		}
-		intern->fptr_offset_set = zend_hash_str_find_ptr(&class_type->function_table, "offsetset", sizeof("offsetset") - 1);
-		if (intern->fptr_offset_set->common.scope == parent) {
-			intern->fptr_offset_set = NULL;
+		methods.fptr_offset_has = zend_hash_str_find_ptr(&class_type->function_table, "offsetexists", sizeof("offsetexists") - 1);
+		if (methods.fptr_offset_has->common.scope == parent) {
+			methods.fptr_offset_has = NULL;
 		}
-		intern->fptr_offset_has = zend_hash_str_find_ptr(&class_type->function_table, "offsetexists", sizeof("offsetexists") - 1);
-		if (intern->fptr_offset_has->common.scope == parent) {
-			intern->fptr_offset_has = NULL;
+		methods.fptr_offset_del = zend_hash_str_find_ptr(&class_type->function_table, "offsetunset", sizeof("offsetunset") - 1);
+		if (methods.fptr_offset_del->common.scope == parent) {
+			methods.fptr_offset_del = NULL;
 		}
-		intern->fptr_offset_del = zend_hash_str_find_ptr(&class_type->function_table, "offsetunset", sizeof("offsetunset") - 1);
-		if (intern->fptr_offset_del->common.scope == parent) {
-			intern->fptr_offset_del = NULL;
+		methods.fptr_count = zend_hash_str_find_ptr(&class_type->function_table, "count", sizeof("count") - 1);
+		if (methods.fptr_count->common.scope == parent) {
+			methods.fptr_count = NULL;
 		}
-		intern->fptr_count = zend_hash_str_find_ptr(&class_type->function_table, "count", sizeof("count") - 1);
-		if (intern->fptr_count->common.scope == parent) {
-			intern->fptr_count = NULL;
+		/* Assume that most of the time in performance-sensitive code, SplFixedArray won't be subclassed with overrides for these ArrayAccess methods. */
+		/* Save 32 bytes per object on 64-bit systems by combining the 5 null pointers into 1 null pointer */
+		/* (This is already looking up 5 functions when any subclass of SplFixedArray is instantiated, which is inefficient) */
+		if (methods.fptr_offset_get || methods.fptr_offset_set || methods.fptr_offset_del || methods.fptr_offset_has || methods.fptr_count) {
+			intern->methods = emalloc(sizeof(spl_fixedarray_methods));
+			*intern->methods = methods;
 		}
 	}
 
@@ -329,15 +345,15 @@ static zval *spl_fixedarray_object_read_dimension(zend_object *object, zval *off
 		return &EG(uninitialized_zval);
 	}
 
-	if (intern->fptr_offset_get) {
+	if (UNEXPECTED(intern->methods && intern->methods->fptr_offset_get)) {
 		zval tmp;
 		if (!offset) {
 			ZVAL_NULL(&tmp);
 			offset = &tmp;
 		} else {
 			SEPARATE_ARG_IF_REF(offset);
 		}
-		zend_call_method_with_1_params(object, intern->std.ce, &intern->fptr_offset_get, "offsetGet", rv, offset);
+		zend_call_method_with_1_params(object, intern->std.ce, &intern->methods->fptr_offset_get, "offsetGet", rv, offset);
 		zval_ptr_dtor(offset);
 		if (!Z_ISUNDEF_P(rv)) {
 			return rv;
@@ -380,15 +396,15 @@ static void spl_fixedarray_object_write_dimension(zend_object *object, zval *off
 
 	intern = spl_fixed_array_from_obj(object);
 
-	if (intern->fptr_offset_set) {
+	if (UNEXPECTED(intern->methods && intern->methods->fptr_offset_set)) {
 		if (!offset) {
 			ZVAL_NULL(&tmp);
 			offset = &tmp;
 		} else {
 			SEPARATE_ARG_IF_REF(offset);
 		}
 		SEPARATE_ARG_IF_REF(value);
-		zend_call_method_with_2_params(object, intern->std.ce, &intern->fptr_offset_set, "offsetSet", NULL, offset, value);
+		zend_call_method_with_2_params(object, intern->std.ce, &intern->methods->fptr_offset_set, "offsetSet", NULL, offset, value);
 		zval_ptr_dtor(value);
 		zval_ptr_dtor(offset);
 		return;
@@ -422,9 +438,9 @@ static void spl_fixedarray_object_unset_dimension(zend_object *object, zval *off
 
 	intern = spl_fixed_array_from_obj(object);
 
-	if (intern->fptr_offset_del) {
+	if (UNEXPECTED(intern->methods && intern->methods->fptr_offset_del)) {
 		SEPARATE_ARG_IF_REF(offset);
-		zend_call_method_with_1_params(object, intern->std.ce, &intern->fptr_offset_del, "offsetUnset", NULL, offset);
+		zend_call_method_with_1_params(object, intern->std.ce, &intern->methods->fptr_offset_del, "offsetUnset", NULL, offset);
 		zval_ptr_dtor(offset);
 		return;
 	}
@@ -462,12 +478,12 @@ static int spl_fixedarray_object_has_dimension(zend_object *object, zval *offset
 
 	intern = spl_fixed_array_from_obj(object);
 
-	if (intern->fptr_offset_has) {
+	if (UNEXPECTED(intern->methods && intern->methods->fptr_offset_has)) {
 		zval rv;
 		zend_bool result;
 
 		SEPARATE_ARG_IF_REF(offset);
-		zend_call_method_with_1_params(object, intern->std.ce, &intern->fptr_offset_has, "offsetExists", &rv, offset);
+		zend_call_method_with_1_params(object, intern->std.ce, &intern->methods->fptr_offset_has, "offsetExists", &rv, offset);
 		zval_ptr_dtor(offset);
 		result = zend_is_true(&rv);
 		zval_ptr_dtor(&rv);
@@ -482,9 +498,9 @@ static int spl_fixedarray_object_count_elements(zend_object *object, zend_long *
 	spl_fixedarray_object *intern;
 
 	intern = spl_fixed_array_from_obj(object);
-	if (intern->fptr_count) {
+	if (UNEXPECTED(intern->methods && intern->methods->fptr_count)) {
 		zval rv;
-		zend_call_method_with_0_params(object, intern->std.ce, &intern->fptr_count, "count", &rv);
+		zend_call_method_with_0_params(object, intern->std.ce, &intern->methods->fptr_count, "count", &rv);
 		if (!Z_ISUNDEF(rv)) {
 			*count = zval_get_long(&rv);
 			zval_ptr_dtor(&rv);