[Bug libstdc++/110138] New: Extra constructor called when using basic_string::operator+

[wwwhhhyyy333 at gmail dot com via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110138

            Bug ID: 110138
           Summary: Extra constructor called when using
                    basic_string::operator+
           Product: gcc
           Version: 13.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: libstdc++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: wwwhhhyyy333 at gmail dot com
  Target Milestone: ---

Created attachment 55268
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=55268&action=edit
Simplified test

complied with -std=c++20 -O0

GCC 12.3/Clang 16 outputs:
Alloc: 3
Alloc: 6
Alloc: 9
Alloc: 12

GCC 13.1 outputs:
Alloc: 3
Alloc: 7
Alloc: 11
Alloc: 15