Today, there are at least 9 production-level surviving Fortran compilers (GNU Fortran, IFX, nagfor, nvfortran, XLF, Cray/HPE's ftn, Fujitsu's frt, old Flang-based Arm/AMD, and flang-new). This situation has advantages and disadvantages for our users. Their Venn diagram of equivalently implemented features is very much not a circle, and portability across compilers is really tough. The ISO standard is hardly clear and doesn't have a test suite or reference implementation, so it's been a very challenging task to make flang-new as easy to port existing codes to as possible.