Transitioning makefile from Visual Studio + ifort to gfortran? - visual-studio

Question

I need to use some Fortran code that was developed by a co-worker using Microsoft Visual Studio (it is a modified version of this groundwater flow model). However, I don't have an ifort license, and generally prefer to use open-source alternatives, so I am trying to transition to gfortran. After much googling and time on StackOverflow, I've successfully created a makefile, compiled the code, and run a simulation using gfortran. However, while benchmarking I found that the code I compiled with gfortran runs ~2.5x slower than my coworker's code compiled from Visual Studio (~30 seconds compared to ~13 seconds). Also, the size of the resulting .exe file from gfortran is about half that of Visual Studio.
I understand that there can be some differences in speed just due to switching compilers; however, the difference I observe seems extreme, leading me to believe there are certain compiler settings that differ between the two. I realize that the question, 'how can I optimize my Fortran code?' is vague and has been answered in detail elsewhere. Instead, my question is: What's the most efficient way to duplicate or approximate a compilation carried out using Microsoft Visual Studio (+ ifort) with gfortran?
My first instinct was to have my co-worker export a makefile from Microsoft Visual Studio (as described here), which I could then modify to work with gfortran by using equivalent settings where possible; however, it appears to be no longer possible to export a makefile from within Visual Studio. Second, I looked for a Fortran equivalent to MakeItSo, but didn't have any luck. I also had my co-worker send me screenshots of the Configuration Properties for Fortran in Visual Studio; however, there appear to be Visual Studio settings for which I cannot find clear analogs in gfortran (for example, the "Favor Size or Speed?" switch) seen here:
FWIW, I am running gfortran on Cygwin:
$ gfortran --version
GNU Fortran (GCC) 5.4.0
Copyright (C) 2015 Free Software Foundation, Inc.
After help in the comments section from #VladimirF, I have updated my makefile and can confirm that flags are being successfully passed to gfortran:
$ make SUTRA
gfortran -O3 -march=native -ffixed-line-length-72 -m64 -c -o slake_mods.o slake_mods.F
gfortran -O3 -march=native -ffixed-line-length-72 -m64 -c -o fmods_3_0.o fmods_3_0.F
gfortran -O3 -march=native -ffixed-line-length-72 -m64 -c -o slake.o slake.F
gfortran -O3 -march=native -ffixed-line-length-72 -m64 -c -o slake_blas.o slake_blas.F
gfortran -O3 -march=native -ffixed-line-length-72 -m64 -c -o slake_linpack.o slake_linpack.F
gfortran -O3 -march=native -ffixed-line-length-72 -m64 -c -o slake_slatec.o slake_slatec.F
gfortran -O3 -march=native -ffixed-line-length-72 -m64 -c -o ssubs_3_0.o ssubs_3_0.F
gfortran -O3 -march=native -ffixed-line-length-72 -m64 -c -o usubs_3_0_non-Jeff.o usubs_3_0_non-Jeff.F
gfortran -O3 -march=native -ffixed-line-length-72 -m64 -c -o sutra_3_0.o sutra_3_0.F
gfortran slake_mods.o fmods_3_0.o slake.o slake_blas.o slake_linpack.o slake_slatec.o ssubs_3_0.o usubs_3_0_non-Jeff.o sutra_3_0.o -m64 \
-O3 -march=native -ffixed-line-length-72 -m64 -o SUTRA
My co-worker is using Intel Visual Fortran Compiler XE 12.0.2.154 on IA-32 with Microsoft Visual Studio 2008.