Compiling Programs (and using the optimization flags)
Compiling
| COMPILER | USAGE EXAMPLE | NOTES ON EXAMPLE |
|---|---|---|
| C/C++ | ||
| GNU C | gcc myprogram.c -o myprogram.exe | The gcc compiler will compile the myprogram.c “c” code to the executable myprogram.exe |
| GNU C++ | g++ myprogram.cpp -o myprogram.exe | The g++ compiler will compile the myprogram.cpp C++ code to the executable myprogram.exe |
| Intel C | icc myprogram.c -o myprogram.exe | The icc compiler will compile the myprogram.c “C” code to the executable myprogram.exe |
| Intel C++ | icc myprogram.cpp -o myprogram.exe | The icc compiler will compile the myprogram.cpp c++ code to the executable myprogram.exe |
| FORTRAN | ||
| Intel Fortran | ifort myprogram.f -o myprogram.exeifort myprogram.f90 -o myprogram.exeifort myprogram.f95 -o myprogram.exe | The ifort compiler will compile the myprogram.f (or *.90 or *.95) fortran code to the executable myprogram.exe |
| GNU FortranNote: you will need to load the gnu-gcc-4.8.1 or gcc-fortran module, before the gfortran compiler is available. | gfortran myprogram.f -o myprogram.exegfortran myprogram.f90 -o myprogram.exegfortran myprogram.f95 -o myprogram.exe | The gfortran compiler will compile the myprogram.f (or *.90 or *.95) fortran code to the executable myprogram.exe |
| MPI | ||
| C/C++ for MPI (GNU Compiler) | mpicc myprogram.c -o myprogram.exe | The gcc compiler will compile the myprogram.c “C” code to the executable myprogram.exe using the mpi wrapper mpicc |
| C/C++ for MPI (Intel Compiler) | icc myprogram.c -o myprogram.exe -lmpi | The icc compiler will compile the myprogram.c “C” code to the executable myprogram.exe using the mpi wrapper mpiicc |
| ADA | ||
| GNU ADA(Note – ADA not currently available on Login Node)Can provide access to compiler if needed | gnatmake myprogram -o myprogram.exe | The gcc compiler will compile the myprogram.adb ADA code to the executable myprogram.exe using the gnatmake program |
Optimization
The selection and modification of variables and options during the compile process can have a significant effect on program execution and results. One simple technique is to use optimization flags when compiling the code. Optimization flags encourage the compiler to improve upon performance (however this can come at the expense of correct results). Optimization flags are represented in syntax as “-O#” (The letter O and then a number), which are the compiling flag option used to select the level of optimization applied to produce an executable.
An example of compile syntax would be:
g++ (or icc) -O2 myprogram.cpp -o myprogram.exe
Programs initially compiled using the default compile options for each compiler are set to the following levels of optimization, GNU compilers use no optimization (“-O0”) and the Intel compiler uses level 2 optimization (“-O2”).
Example compile syntax include:
| OPTIMIZATION LEVEL | FLAG | COMPILING EXAMPLE |
|---|---|---|
| GNU COMPILER | ||
| No Optimization | -O0 | g++ -O0 myprogram.cpp -o myprogram.exe. |
| Level 1 | -O1 | g++ -O1 myprogram.cpp -o myprogram.exe. |
| Level 2 | -O2 | g++ -O2 myprogram.cpp -o myprogram.exe. |
| Level 3 | -O3 | g++ -O3 myprogram.cpp -o myprogram.exe. |
| Fast | -fast | g++ -fast myprogram.cpp -o myprogram.exe. |
| INTEL COMPILER | ||
| No Optimization | -O0 | icc -O0 myprogram.cpp -o myprogram.exe. |
| Level 1 | -O1 | icc -O1 myprogram.cpp -o myprogram.exe. |
| Level 2 | -O2 | icc -O2 myprogram.cpp -o myprogram.exe. |
| Level 3 | -O3 | icc -O3 myprogram.cpp -o myprogram.exe. |
| Fast | -fast | icc -fast myprogram.cpp -o myprogram.exe. |