Gfortran compiling options

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1

My workflow involves importing Fortran subroutines into R to work with very large vectors and matrices. My gfortran compiling options are as follows:
gfortran -fimplicit-none -ffree-line-length-0 -fdefault-integer-8 -fdefault-real-8 -fpic -shared fortran_file.f95 -o fortran_file.so

I find these options very convenient to use. I would like to ask whether these options can bring unexpected errors. I am not concerned about portability since I only distribute the so files and other R users just call them from R.

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So the implicit none and free line length options are ok, right? Regarding the default bit options, what are the potential issues?

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It looks like you you are not sure whether you have sprinkled enough IMPLICIT NONE in your sources. Please do yourself a favour and do so.

It is also not clear whether you have enabled explicit interfaces for your subprogram references. Again, same advice applies.

The -fdefault-X-Y options are abhorrent to me, for reasons explained above.

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does the order of these options matter?

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Thanks! I like to use -finit-real=snan combined with the -ffpe-trap=ā€¦ to catch operations performed with variables that were not initialized.

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For ā€˜releaseā€™ use, I usually only use -Ofast -mach=native
If anyone have better flags for ā€˜releaseā€™ mode, please advise too.

For ā€˜debugā€™ use, possibly could just use whatever flags you want.

I usally use intel fortran first, then use gfortran to compile and to fix some possible issues which intel fortran is happy but gfortran is unhappy about.

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Thank you very much!

Do you have suggestions about what flags to use for ā€˜release modeā€™?

By the way, in my another topic,

It seems really the 8 times slow down is caused by my random number generator. Thank you very much for bring that to my attention!

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@CRquantum

-Ofast turns on -ffinite-math-only among (many) others. -ffinite-math-only orders the compiler to assume that all the numbers involved in the calculations are finite ā€” no Inf, no NaN. This is fine if you have only a few lines of code, and they deal with only numerically easy (well-conditioned) problems. Otherwise, Inf and NaN will likely pop out at places that we may not be able to imagine until we see them.

If -Ofast is intended, then it may be a good idea to put at least -fnofinite-math-only afterwards.

See:

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I understand that Fortran highly values backward compatibility. How about gfortran? Is it possible that some of these gfortran options be deprecated in the future?

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I also avoid the gfortran option -freal-M-real-N (where M = 4 or 8, N = 4, 8, 10 or 16, but N /= M) because it doesnā€™t do everything I wanted it to. Selected_real_kind ignored these options and so did literal constants with _kind, e.g. 1.0_4, when I last tried them a few years ago. I donā€™t know whether more recent gfortran versions have fixed those problems.