When compiling MPICH 4.0.1 with GCC 11.2.0 (on Ubuntu) the configuration will abort with the following error message from MPICH’s configure:
checking whether gfortran allows mismatched arguments… yes, with -fallow-argument-mismatch
configure: error: The Fortran compiler gfortran does not accept programs that call the same routine with arguments of different types without the option -fallow-argument-mismatch. Rerun configure with FFLAGS=-fallow-argument-mismatch and FCFLAGS=-fallow-argument-mismatch
This was already discussed among gfortran/OpenCoarray team members some time ago:
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=91731
Whatever MPICH version I was trying out with gfortran/OpenCoarrays, the use of FFLAGS=-fallow-argument-mismatch with MPICH configure did always result into an extremely poor coarray performance pattern: The resulting coarray programs are not only slowly running, they also show a certain pattern where the execution does appear to hold at several times (with my test cases). The exactly same execution pattern is with ifort.
With gfortran/OpenCoarrays, compiling MPICH without using FFLAGS=-fallow-argument-mismatch with ./configure did always deliver an incredible high coarray performance with my test cases (with an highly optimized PGAS cost function and performance measuring only for the code execution within coarray teams and without counting times for allocating coarrays or any blocking synchronization process).
So far, avoiding
./configure FFLAGS=-fallow-argument-mismatch FCFLAGS=-fallow-argument-mismatch
with MPICH was all I had to do, to achieve high coarray performance with gfortran/Opencoarrays.