Development/Intel Compiler

Description	Content
module load	compiler/intel
License	Commercial. See $INTEL_HOME/install-doc/EULA.txt. | Intel Product Licensig FAQ
Citing	n/a
Links	Intel C-Compiler Homepage
Graphical Interface	Yes (Intel Debugger GUI-Verison)
Included modules	icc | icpc | ifort | idb | gdb-ia

Introduction

The Intel Compiler of the Intel Composer XE Suite consists of tools to compile and debug C, C++ and Fortran programs:

icc	Intel C compiler
icpc	Intel C++ compiler
ifort	Intel Fortran compiler
idb	Intel debugger in GUI mode (until version 14 only)
gdb-ia	Intel version of GNU debugger in console mode (from version 15)
idbc	Intel debugger in console mode (until version 14 only)

The intel compiler suite also includes the TBB (Threading Building Blocks) and IPP (Integrated Performance Primitives) libraries.

More information about the MPI versions of the Intel Compiler is available here:

• Best Practices Guide for Parallel Programming.

Versions and Availability

A list of versions currently available on all bwHPC Clusters can be obtained from the cluster information system
Cluster Information System

On the command line interface of any bwHPC cluster you'll get a list of available versions by executing:

$ module avail compiler/intel

Loading the module

Default Version

You can load the default version of the Intel Compiler with the command

$ module load compiler/intel

If loading the module fails, check if you have already loaded the module with 'module list'.

Specific (newer or older) Version

If you wish to load a specific (older or newer) version (if available), add the specific version number of the intel compiler, e.g. for loading Intel compiler suite 17.0, execute:

$ module unload compiler/intel
$ module   load compiler/intel/17.0

Note: Only one compiler can be loaded in your active session, hence, before loading a new intel compiler version you must to unload the current loaded version.

For unloading the intel compiler the version number is not required:

$ module unload compiler/intel

unloads any currently loaded intel compiler version.

Intel Compiler Specific Environment Variables

To see a list of all Intel Compiler environment variables set by the 'module load' command execute:

module show compiler/intel

Documentation

Online documentation

• Intel® C-Compiler Documentation
• Intel® Software Documentation Library

Local documentation

For version specific documentation see the help page of the module. For example

$ module help compiler/intel

will show the information for the default version.

Manual Pages

For detailed lists of the different program options consult the particular man page

$ man icc
$ man icpc
$ man ifort
$ man idb
$ man gdb-ia

Debugger

Please use DDT. It is a parallel debugger with graphical user interface and can also be used for debugging serial programs. The description of the debugger can be found on the website
http://www.bwhpc-c5.de/wiki/index.php/DDT

Optimizations

You can turn on various optimization options to enhance the performance of your program. Which options are the best depends on the specific program and can be determined by benchmarking your code. A command which gives good performance and a decent file size is icc -xHost -O2 ex.c. With the option -xHost instructions for the highest instruction set available on the compilation host processor are generated. If you want to generate optimal code on bwUniCluster for both nodes with Sandy Bridge architecture and nodes with Broadwell architecture, you must compile your code with the options -xAVX -axCORE-AVX2 (instead of -xHost).
There are more aggressive optimization flags and levels (e.g. -O3 or -fast and implied options) but the compiled programs can get quite large due to inlining. Additionally the compilation process will probably take longer. Moreover it may happen that the compiled program is even slower -- or may require installation of additional statically-linked libraries. Such a command would be for example: icc -fast ex.c

Profiling

Profiling an application means augmenting the compiled binary with information on execution counts per source-line (and basic blocks) -- e.g. one may see how many times an if-statement has been evaluated to true. To do so, compile your code with the profile flag: icc -p ex.c -o ex.
Using the gprof tool, one may manually inspect execution count of each executed line of source code.
For compiler optimization, recompile Your source using icc -prof-gen ex.c -o ex then execute the most co]]mmon and typical use-case of your application, and then recompile using the generated profile count (and using optimization): icc -prof-use -O2 ex.c -o ex.

Further literature

A tutorial on optimization can be found at Compiler-Essentials.pdf and to get the different optimization options execute icc -help opt icc -help advanced
or the previously described catch-all option -v --help.