Merge branch 'PHP-8.0'

* PHP-8.0:
  Fixed bug #81090

Author: nikic

Zend/zend_execute.c

@@ -1396,6 +1396,13 @@ static zend_never_inline void zend_binary_assign_op_typed_ref(zend_reference *re
 {
 	zval z_copy;
 
+	/* Make sure that in-place concatenation is used if the LHS is a string. */
+	if (opline->extended_value == ZEND_CONCAT && Z_TYPE(ref->val) == IS_STRING) {
+		concat_function(&ref->val, &ref->val, value);
+		ZEND_ASSERT(Z_TYPE(ref->val) == IS_STRING && "Concat should return string");
+		return;
+	}
+
 	zend_binary_op(&z_copy, &ref->val, value OPLINE_CC);
 	if (EXPECTED(zend_verify_ref_assignable_zval(ref, &z_copy, EX_USES_STRICT_TYPES()))) {
 		zval_ptr_dtor(&ref->val);
@@ -1409,6 +1416,13 @@ static zend_never_inline void zend_binary_assign_op_typed_prop(zend_property_inf
 {
 	zval z_copy;
 
+	/* Make sure that in-place concatenation is used if the LHS is a string. */
+	if (opline->extended_value == ZEND_CONCAT && Z_TYPE_P(zptr) == IS_STRING) {
+		concat_function(zptr, zptr, value);
+		ZEND_ASSERT(Z_TYPE_P(zptr) == IS_STRING && "Concat should return string");
+		return;
+	}
+
 	zend_binary_op(&z_copy, zptr, value OPLINE_CC);
 	if (EXPECTED(zend_verify_property_type(prop_info, &z_copy, EX_USES_STRICT_TYPES()))) {
 		zval_ptr_dtor(zptr);