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Different compilers in Pyccel

Compilers supported by Pyccel

Pyccel provides default compiler settings for 4 different compiler families:

  • GNU : gcc / gfortran
  • Intel : icx / ifx
  • NVIDIA : nvc / nvfort

Warning : The GNU compiler is currently the only compiler which is tested regularly

Specifying a compiler

The default compiler family is GNU. To use a different compiler, the compiler family should be passed to either pyccel or epyccel. E.g.

pyccel example.py --compiler=intel

or

epyccel(my_func, compiler='intel')

It is also possible to change the default compiler family by setting the environment variable PYCCEL_DEFAULT_COMPILER.

User-defined compiler

The user can also define their own compiler in a JSON file. To use this definition, the location of the JSON file must be passed to the compiler argument. The JSON file must define the following:

  • exec : The name of the executable
  • mpi_exec : The name of the MPI executable
  • language : The language handled by this compiler
  • module_output_flag : This flag is only required when the language is Fortran. It specifies the flag which indicates where .mod files should be saved (e.g. '-J' for gfortran)
  • debug_flags : A list of flags used when compiling in debug mode [optional]
  • release_flags : A list of flags used when compiling in release mode [optional]
  • general_flags : A list of flags used when compiling in any mode [optional]
  • standard_flags : A list of flags used to impose the expected language standard [optional]
  • libs : A list of libraries necessary for compiling [optional]
  • libdirs : A list of library directories necessary for compiling [optional]
  • includes : A list of include directories necessary for compiling [optional]

In addition, for each accelerator (mpi/openmp/openacc/python) that you will use the JSON file must define the following:

  • flags : A list of flags used to impose the expected language standard [optional]
  • libs : A list of libraries necessary for compiling [optional]
  • libdirs : A list of library directories necessary for compiling [optional]
  • includes : A list of include directories necessary for compiling [optional]

Python is considered to be an accelerator and must additionally specify shared_suffix.

The default compilers can provide examples compatible with your system once Pyccel has been executed at least. To export the JSON file describing your setup, use the --export-compile-info flag and provide a target file name. E.g.

pyccel --compiler=PGI --language=c --export-compile-info=icc.json

Utilising Pyccel within Anaconda Environment

While Anaconda is a popular way to install Python as it simplifies package management, it can introduce challenges when working with compilers.

Upon installation Anaconda modifies your shell's environment variables.

This can lead to packages installed in conda/anaconda usurping the packages manually installed by the user.

This in turn easily leads to nasty surprises (e.g. using libraries compiled for serial execution instead of optimised parallel implementations).

To avoid these problems, Pyccel ignores Conda paths when searching for compilers in the system's PATH.

By using the expected compiler, the expected libraries are correctly linked.

Pyccel offers the --conda-warnings flag which takes one of the following options : off, basic, verbose. This controls the visibility of Conda-related warnings. The default value is basic which indicates when folders are ignored. The verbose option additionally outputs a list of all ignored folders. If these folders should not be ignored then this can be avoided by using a user-defined compiler file as described above. The off option suppresses all Conda-related warnings.