diff --git a/ext/standard/array.c b/ext/standard/array.c
index dc0d434d1883e..22afef7e96832 100644
--- a/ext/standard/array.c
+++ b/ext/standard/array.c
@@ -3825,6 +3825,56 @@ PHPAPI int php_array_replace_recursive(HashTable *dest, HashTable *src) /* {{{ *
 }
 /* }}} */
 
+/* Returns true if it's possible to do an in-place array modification, preventing a costly copy.
+ * It also modifies the CV to prevent freeing it upon assigning.
+ * If this returns true you need to add a ref at the end of the modification for the return value. */
+static bool prepare_in_place_array_modify_if_possible(const zend_execute_data *execute_data, const zval *arg)
+{
+	/* 2 refs: the CV and the argument; or 1 ref for a temporary passed as argument */
+	uint32_t refcount = Z_REFCOUNT_P(arg);
+	ZEND_ASSERT(refcount > 0);
+	if (refcount > 2) {
+		return false;
+	}
+	/* Immutable or persistent => no modification allowed */
+	if (GC_FLAGS(Z_ARRVAL_P(arg)) & (IS_ARRAY_IMMUTABLE | IS_ARRAY_PERSISTENT)) {
+		return false;
+	}
+
+	if (refcount == 2) {
+		const zend_op *call_opline = execute_data->prev_execute_data->opline;
+		const zend_op *next_opline = call_opline + 1;
+
+		/* Must be an assignment from the result of the call to a CV */
+		if (next_opline->opcode != ZEND_ASSIGN || next_opline->op1_type != IS_CV || next_opline->op2.var != call_opline->result.var) {
+			return false;
+		}
+
+		/* Must be an assignment to the same array as the input */
+		zval *var = ZEND_CALL_VAR(execute_data->prev_execute_data, next_opline->op1.var);
+		if (Z_TYPE_P(var) != IS_ARRAY || Z_ARRVAL_P(arg) != Z_ARRVAL_P(var)) {
+			return false;
+		}
+		/* Must set the CV to NULL so we don't destroy the array on assignment */
+		ZVAL_NULL(var);
+		/* Make RC 1 such that the array may be modified */
+		GC_DELREF(Z_ARRVAL_P(arg));
+	}
+
+	return true;
+}
+
+static bool set_return_value_array_dup_or_in_place(const zend_execute_data *execute_data, const zval *arg, zval *return_value)
+{
+	if (prepare_in_place_array_modify_if_possible(execute_data, arg)) {
+		RETVAL_ARR(Z_ARRVAL_P(arg));
+		return true;
+	} else {
+		RETVAL_ARR(zend_array_dup(Z_ARRVAL_P(arg)));
+		return false;
+	}
+}
+
 static zend_always_inline void php_array_replace_wrapper(INTERNAL_FUNCTION_PARAMETERS, int recursive) /* {{{ */
 {
 	zval *args = NULL;
@@ -3846,10 +3896,11 @@ static zend_always_inline void php_array_replace_wrapper(INTERNAL_FUNCTION_PARAM
 		}
 	}
 
-	/* copy first array */
+	/* copy first array if necessary */
 	arg = args;
-	dest = zend_array_dup(Z_ARRVAL_P(arg));
-	ZVAL_ARR(return_value, dest);
+	bool update_refcount = set_return_value_array_dup_or_in_place(execute_data, arg, return_value);
+	dest = Z_ARRVAL_P(return_value);
+
 	if (recursive) {
 		for (i = 1; i < argc; i++) {
 			arg = args + i;
@@ -3861,6 +3912,10 @@ static zend_always_inline void php_array_replace_wrapper(INTERNAL_FUNCTION_PARAM
 			zend_hash_merge(dest, Z_ARRVAL_P(arg), zval_add_ref, 1);
 		}
 	}
+
+	if (update_refcount) {
+		GC_ADDREF(dest);
+	}
 }
 /* }}} */
 
@@ -3925,22 +3980,34 @@ static zend_always_inline void php_array_merge_wrapper(INTERNAL_FUNCTION_PARAMET
 
 	arg = args;
 	src  = Z_ARRVAL_P(arg);
-	/* copy first array */
-	array_init_size(return_value, count);
-	dest = Z_ARRVAL_P(return_value);
+	bool update_refcount = false;
+	/* copy first array if necessary */
 	if (HT_IS_PACKED(src)) {
-		zend_hash_real_init_packed(dest);
-		ZEND_HASH_FILL_PACKED(dest) {
-			ZEND_HASH_PACKED_FOREACH_VAL(src, src_entry) {
-				if (UNEXPECTED(Z_ISREF_P(src_entry) &&
-					Z_REFCOUNT_P(src_entry) == 1)) {
-					src_entry = Z_REFVAL_P(src_entry);
-				}
-				Z_TRY_ADDREF_P(src_entry);
-				ZEND_HASH_FILL_ADD(src_entry);
-			} ZEND_HASH_FOREACH_END();
-		} ZEND_HASH_FILL_END();
+		/* Note: If it has holes, it might get sequentialized */
+		if (HT_IS_WITHOUT_HOLES(src) && prepare_in_place_array_modify_if_possible(execute_data, arg)) {
+			update_refcount = true;
+			dest = src;
+			ZVAL_ARR(return_value, dest);
+		} else {
+			array_init_size(return_value, count);
+			dest = Z_ARRVAL_P(return_value);
+
+			zend_hash_real_init_packed(dest);
+			ZEND_HASH_FILL_PACKED(dest) {
+				ZEND_HASH_PACKED_FOREACH_VAL(src, src_entry) {
+					if (UNEXPECTED(Z_ISREF_P(src_entry) &&
+						Z_REFCOUNT_P(src_entry) == 1)) {
+						src_entry = Z_REFVAL_P(src_entry);
+					}
+					Z_TRY_ADDREF_P(src_entry);
+					ZEND_HASH_FILL_ADD(src_entry);
+				} ZEND_HASH_FOREACH_END();
+			} ZEND_HASH_FILL_END();
+		}
 	} else {
+		array_init_size(return_value, count);
+		dest = Z_ARRVAL_P(return_value);
+
 		zend_string *string_key;
 		zend_hash_real_init_mixed(dest);
 		ZEND_HASH_MAP_FOREACH_STR_KEY_VAL(src, string_key, src_entry) {
@@ -3967,6 +4034,10 @@ static zend_always_inline void php_array_merge_wrapper(INTERNAL_FUNCTION_PARAMET
 			php_array_merge(dest, Z_ARRVAL_P(arg));
 		}
 	}
+
+	if (update_refcount) {
+		GC_ADDREF(src);
+	}
 }
 /* }}} */
 
@@ -4574,7 +4645,7 @@ PHP_FUNCTION(array_unique)
 
 	cmp = php_get_data_compare_func_unstable(sort_type, 0);
 
-	RETVAL_ARR(zend_array_dup(Z_ARRVAL_P(array)));
+	bool update_refcount = set_return_value_array_dup_or_in_place(execute_data, array, return_value);
 
 	/* create and sort array with pointers to the target_hash buckets */
 	arTmp = pemalloc((Z_ARRVAL_P(array)->nNumOfElements + 1) * sizeof(struct bucketindex), GC_FLAGS(Z_ARRVAL_P(array)) & IS_ARRAY_PERSISTENT);
@@ -4620,6 +4691,10 @@ PHP_FUNCTION(array_unique)
 		}
 	}
 	pefree(arTmp, GC_FLAGS(Z_ARRVAL_P(array)) & IS_ARRAY_PERSISTENT);
+
+	if (update_refcount) {
+		GC_ADDREF(Z_ARRVAL_P(array));
+	}
 }
 /* }}} */
 
@@ -4744,6 +4819,7 @@ static void php_array_intersect(INTERNAL_FUNCTION_PARAMETERS, int behavior, int
 	zend_fcall_info *fci_key = NULL, *fci_data;
 	zend_fcall_info_cache *fci_key_cache = NULL, *fci_data_cache;
 	PHP_ARRAY_CMP_FUNC_VARS;
+	bool in_place = false;
 
 	bucket_compare_func_t intersect_key_compare_func;
 	bucket_compare_func_t intersect_data_compare_func;
@@ -4828,12 +4904,15 @@ static void php_array_intersect(INTERNAL_FUNCTION_PARAMETERS, int behavior, int
 	} else if ((behavior & INTERSECT_ASSOC) && key_compare_type == INTERSECT_COMP_KEY_USER) {
 		BG(user_compare_fci) = *fci_key;
 		BG(user_compare_fci_cache) = *fci_key_cache;
+	} else {
+		in_place = true;
 	}
 
 	for (i = 0; i < arr_argc; i++) {
 		if (Z_TYPE(args[i]) != IS_ARRAY) {
 			zend_argument_type_error(i + 1, "must be of type array, %s given", zend_zval_value_name(&args[i]));
 			arr_argc = i; /* only free up to i - 1 */
+			in_place = false;
 			goto out;
 		}
 		hash = Z_ARRVAL(args[i]);
@@ -4870,8 +4949,12 @@ static void php_array_intersect(INTERNAL_FUNCTION_PARAMETERS, int behavior, int
 		}
 	}
 
-	/* copy the argument array */
-	RETVAL_ARR(zend_array_dup(Z_ARRVAL(args[0])));
+	/* copy the argument array if necessary */
+	if (in_place) {
+		in_place = set_return_value_array_dup_or_in_place(execute_data, &args[0], return_value);
+	} else {
+		RETVAL_ARR(zend_array_dup(Z_ARRVAL(args[0])));
+	}
 
 	/* go through the lists and look for common values */
 	while (Z_TYPE(ptrs[0]->val) != IS_UNDEF) {
@@ -4982,6 +5065,10 @@ static void php_array_intersect(INTERNAL_FUNCTION_PARAMETERS, int behavior, int
 
 	efree(ptrs);
 	efree(lists);
+
+	if (in_place) {
+		GC_ADDREF(Z_ARRVAL_P(return_value));
+	}
 }
 /* }}} */
 
@@ -5129,6 +5216,7 @@ static void php_array_diff(INTERNAL_FUNCTION_PARAMETERS, int behavior, int data_
 	zend_fcall_info *fci_key = NULL, *fci_data;
 	zend_fcall_info_cache *fci_key_cache = NULL, *fci_data_cache;
 	PHP_ARRAY_CMP_FUNC_VARS;
+	bool in_place = false;
 
 	bucket_compare_func_t diff_key_compare_func;
 	bucket_compare_func_t diff_data_compare_func;
@@ -5213,12 +5301,15 @@ static void php_array_diff(INTERNAL_FUNCTION_PARAMETERS, int behavior, int data_
 	} else if ((behavior & DIFF_ASSOC) && key_compare_type == DIFF_COMP_KEY_USER) {
 		BG(user_compare_fci) = *fci_key;
 		BG(user_compare_fci_cache) = *fci_key_cache;
+	} else {
+		in_place = true;
 	}
 
 	for (i = 0; i < arr_argc; i++) {
 		if (Z_TYPE(args[i]) != IS_ARRAY) {
 			zend_argument_type_error(i + 1, "must be of type array, %s given", zend_zval_value_name(&args[i]));
 			arr_argc = i; /* only free up to i - 1 */
+			in_place = false;
 			goto out;
 		}
 		hash = Z_ARRVAL(args[i]);
@@ -5255,8 +5346,12 @@ static void php_array_diff(INTERNAL_FUNCTION_PARAMETERS, int behavior, int data_
 		}
 	}
 
-	/* copy the argument array */
-	RETVAL_ARR(zend_array_dup(Z_ARRVAL(args[0])));
+	/* copy the argument array if necessary */
+	if (in_place) {
+		in_place = set_return_value_array_dup_or_in_place(execute_data, &args[0], return_value);
+	} else {
+		RETVAL_ARR(zend_array_dup(Z_ARRVAL(args[0])));
+	}
 
 	/* go through the lists and look for values of ptr[0] that are not in the others */
 	while (Z_TYPE(ptrs[0]->val) != IS_UNDEF) {
@@ -5365,6 +5460,10 @@ static void php_array_diff(INTERNAL_FUNCTION_PARAMETERS, int behavior, int data_
 
 	efree(ptrs);
 	efree(lists);
+
+	if (in_place) {
+		GC_ADDREF(Z_ARRVAL_P(return_value));
+	}
 }
 /* }}} */