[Bug fortran/81615] save-temps and gfortran produces *.f90 files instead of *.i or *i90 files

[barrowes at alum dot mit.edu]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=81615

--- Comment #12 from Ben Barrowes <barrowes at alum dot mit.edu> ---
I use these intermediate files during the software analysis process, but then
delete them later. They are useful for me to have.

When I am given a makefile, it is often 1000's loc. I am not sure I want to go
in and modify it such as you suggest below and tell the customer it is for
their own good. I'd rather be able to set a couple of switches to the
preprocessor and get what I want.

gfortran already allows to create a *.d file in each directory for each file.
Is that poor software design as well? And when gfortran files are preprocessed
all into a *.f90 file, except when they are not (see Thomas's email below), is
that poor software design?

ifort allows for the creation of these intermediate preprocessed files,
creating *.i and *.i90 files.

IBM XL allows this as well using the -d switch:
https://www.ibm.com/docs/en/xl-fortran-aix/16.1.0?topic=preprocessor-passing-fortran-files-through-c
And the intermediate filename becomes Ffilename.f*

Can gfortran be modified to have the option to do this as well?