Overview of Linux Compilers

This cluster has 3 different kinds of compilers

1. GNU
2. Portland Group (PGI)
3. Intel

Below is a table that shows the different compilers:

** Use these suffixes for code that needs preprocessing with cpp.

• • No one compiler works best for all kinds of code.
  • If you are interested in speeding up your application, you will want to test various compiler options and compilers to see which ones work the best for your application.
  • There is a man page for each compiler that lists the compiler options.
  • In general, gcc/g++ is the most flexible since it runs on a variety of different computer platforms.
  • Many people use gcc/g++ so it will be easy to port their code to other platforms.
  • g77 was previously the fortran77 GNU compiler and is now retired and replaced by gfortran.
  • The PGI compilers will compile f77,f90, C, and C++ codes.
    • • They compile a variety of codes with fewer errors than the Intel compilers.
      • Many Fortran codes use extensions to the language and the Portland Group compilers support those extensions.
    • Portland Group recommends that you use the pgf90 for both Fortran 90 and fortran 77 codes to gain additional code speed up.

• All of the compiler commands listed above are in the standard user path.

Useful Compiler Options

• • Here are some useful compilers optimizations options to know about for each of the three kinds of compilers.
  • All three kinds of compilers generate code that is optimized for the platform where they are compiled.
  • The comments below apply to both C/C++ and Fortran77/90 codes.

• These optimizations will not necessarily speed up all kinds of code and should be tested individually.

Portland Group: pgcc, pgCC, pgf77, pgf90

• • If you want to use a number of more aggressive optimizations that makes use of the features of the AMD  processors to speed up your code and use the options  -fastsse -O4.

• In addition, there are other optimization options to try.

GNU compilers: gcc, g++

Use option -O3 for the most aggressive optimization. Here are some optimization options.

Intel Compilers: ifort, icc

• • Use the option -O3 to obtain more aggressive optimization.
  • You can use the -parallel option to have the compiler insert multi-threaded code in loops that can be safely parallelized.

• Here are some other optimization options.