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Compiler options

Several compilers are available to Lunarc users. Here we list the command names and options that often produce good performance for the most used compilers. More may be found by looking through the list of available modules obtained by the command

module avail 

Before running production runs, it is a good idea to test a program by running it with various checks turned on, for example to see that arrays are not indexed out of bounds. When the program has passed the test, it may be recompiled with optimization flags to get the best performance.

The compiler options given here are only suggestions of useful combinations, but not guaranteed to be optimal in all cases. To see what options are available check the man pages

man compiler-command 

In terms of optimized performance, the Intel compilers usually give good results (fast programs) for both Intel (Sigrid) and AMD processors (Docenten, Sweet16). PathScale and Portland Group compilers are in some cases superior on AMD. The GNU compilers generally work, but are usually outperformed by other compilers.

Compiler commands and switches

Intel compiler commands:

Adding the gnu compiler module:

module add intel 

Fortran 77/90/95 compiler:

C compiler:

C++ compiler:


Compiler Options:

Checking for mistakes

-check all -g -traceback 

Optimization flags:

-O3 -xW 

-O3 -ipo -unroll 


Problem solving

By default, the Intel compiler puts arrays on the stack and if they are too large, the program may crash with segmentation fault. A solution is to instruct the compiler to put the arrays on the heap instead.


This may reduce performance and it is therefore possible to specify a minimum size of arrays to be put on the heap instead of the stack, when the size is known at compile time.

-heap-arrays <size in kilobytes> 

GNU Compiler commands

Adding the gnu compiler module:

module add gcc

Fortran 77/90/95 compiler:


C compiler:


C++ compiler:


Compiler Options:

Checking for mistakes:

-fbounds-check -g 

Optimization flags:

-O3 -funroll-loops 

PathScale compiler commands:

Adding the pathscale module:

module add pathscale 

Fortan 77/90/95 compiler:


C compiler:


C++ compiler


Compiler Options:

Checking for mistakes

-C -g 

Optimization flags:


Portland compiler commands

Adding the portland compiler module:

module add pgi 

Fortran 77 compiler:


Fortran 90/95 compiler:


C compiler:


C++ compiler:


Compiler Options:

Checking for mistakes:

-Mbounds -g 

Optimization flags:

-O3 -fastsse -Mvect 

Problem solving:

By default, objects, such as arrays, are limited to 2 GB. The option to allow larger objects is


Author: (LUNARC)

Last Updated: 2022-10-05