Available compiler suites
Four different compiler suites are installed on the machine:
|Compiler suite||Version||Module||Man pages||User guides|
|Portland Group (PGI) Default||10.2||PrgEnv-pgi||
man pgcc C
|PathScale Compiler Suite (path)||3.2||PrgEnv-pathscale||man pathcc C/C++
man pathf95 Fortran
man eko All flags
|GNU Compiler Collection (GCC)||4.4||PrgEnv-gnu||
man gcc C/C++
|Intel Compilers Professional Edition
|11.1||PrgEnv-intel||man icc C/C++
man ifort Fortran
The active compiler package when logging in is PGI. To use another compiler package, or another version of a particular compiler package, one should switch the active package using the module system (see Module environment):
module swap PrgEnv-pgi PrgEnv-gnu # swap PGI compiler to GNU compiler
Detailed information on the compilers is available in their respective user guides and man pages. To read a man page one should execute the man command after having switched to the relevant programming environment.
When compiling one should always use a generic command such as f95 or mpif90, which refer to the compiler of the loaded compiler package. The aliases are listed in the following table:
|Language||Serial/Parallel compiler||Parallel MPI compiler|
For more information on compiling parallel programs, see the subsection Using MPI.
Choosing a compiler
There are two important factors that should be taken into account when choosing between the compilers: correctness and performance of the compiled program.
- Some programs may only produce correct results when compiled with a particular compiler. It is also possible that the program produces wrong results when compiled using aggressive compiler optimizations. It is thus of key importance to always check that the compiled program actually produces correct results.
- One should choose the compiler gving the best performance, while still producing correct results. It is impossible to know ahead of time which compiler is the best for a particular program. One simply has to find the best compiler and its optimal compiler options using a 'generate and check' method.
Selecting compiler options
The options available for the PGI, PathScale, GCC, and Intel compiler suites can be found in their individual sections on this page, from their man pages when the corresponding programming environment is loaded, or in the compiler manuals on the Web (see the first table).
In the table below we have listed good optimization flags for the installed compilers. It is best to start from the safe level and then move up to intermediate or even Aggressive, while making sure that the results are corerct and that the program is quicker.
Finally the following table shows some options that are common for all the compilers:
|-c||Compiles only, produces unlinked object filename.o|
|-o filename||Gives the name filename for the executable. Default: a.out|
|-g||Produces symbolic debug information|
|-Idirname||Searches directory dirname for include files or module files|
|-Ldirname||Searches directory dirname for for library files specified by -l|
|-llibname||Searches the specified library file with the name liblibname.a|
|-O[level]||Specifies whether to optimize or not and at which level level|