.. role:: ref(emphasis)

.. _futhark-opencl(1):

==============
futhark-opencl
==============

SYNOPSIS
========

futhark opencl [options...] <program.fut>

DESCRIPTION
===========


``futhark opencl`` translates a Futhark program to C code invoking
OpenCL kernels, and either compiles that C code with gcc(1) to an
executable binary program, or produces a ``.h`` and ``.c`` file that
can be linked with other code. The standard Futhark optimisation
pipeline is used, and GCC is invoked with ``-O``, ``-lm``, and
``-std=c99``. The resulting program will otherwise behave exactly as
one compiled with ``futhark c``.

``futhark opencl`` uses ``-lOpenCL`` to link (``-framework OpenCL`` on
macOS).  If using ``--library``, you will need to do the same when
linking the final binary.

OPTIONS
=======

-h
  Print help text to standard output and exit.

--library
  Generate a library instead of an executable.  Appends ``.c``/``.h``
  to the name indicated by the ``-o`` option to determine output
  file names.

-o outfile
  Where to write the result.  If the source program is named
  ``foo.fut``, this defaults to ``foo``.

--safe
  Ignore ``unsafe`` in program and perform safety checks unconditionally.

-v verbose
  Enable debugging output.  If compilation fails due to a compiler
  error, the result of the last successful compiler step will be
  printed to standard error.

-V
  Print version information on standard output and exit.

-W
  Do not print any warnings.

--Werror
  Treat warnings as errors.

EXECUTABLE OPTIONS
==================

Generated executables accept the same options as those generated by
:ref:`futhark-c(1)`.  For the ``-t`` option, The time taken to perform
device setup or teardown, including writing the input or reading the
result, is not included in the measurement. In particular, this means
that timing starts after all kernels have been compiled and data has
been copied to the device buffers but before setting any kernel
arguments. Timing stops after the kernels are done running, but before
data has been read from the buffers or the buffers have been released.

The following additional options are accepted.

--build-option=OPT

  Add an additional build option to the string passed to
  ``clBuildProgram()``.  Refer to the OpenCL documentation for which
  options are supported.  Be careful - some options can easily
  result in invalid results.

--default-group-size=INT

  The default size of OpenCL workgroups that are launched.  Capped
  to the hardware limit if necessary.

--default-num-groups=INT

  The default number of OpenCL workgroups that are launched.

--default-threshold=INT

  The default parallelism threshold used for comparisons when
  selecting between code versions generated by incremental flattening.
  Intuitively, the amount of parallelism needed to saturate the GPU.

--default-tile-size=INT

  The default tile size used when performing two-dimensional tiling
  (the workgroup size will be the square of the tile size).

-d, --device=NAME

  Use the first OpenCL device whose name contains the given string.
  The special string ``#k``, where ``k`` is an integer, can be used to
  pick the *k*-th device, numbered from zero.  If used in conjunction
  with ``-p``, only the devices from matching platforms are
  considered.

--dump-opencl=FILE

  Don't run the program, but instead dump the embedded OpenCL program
  to the indicated file.  Useful if you want to see what is actually
  being executed.

--dump-opencl-binary=FILE

  Don't run the program, but instead dump the compiled version of
  the embedded OpenCL program to the indicated file.  On NVIDIA
  platforms, this will be PTX code.

--load-opencl=FILE

  Instead of using the embedded OpenCL program, load it from the
  indicated file.

--load-opencl-binary=FILE

  Load an OpenCL binary from the indicated file.

-p, --platform=NAME

  Use the first OpenCL platform whose name contains the given string.
  The special string ``#k``, where ``k`` is an integer, can be used to
  pick the *k*-th platform, numbered from zero.

--print-sizes

  Print all sizes that can be set with ``-size`` or ``--tuning``.

-P, --profile

  Gather profiling data while executing and print out a summary at the
  end.  When ``-r`` is used, only the last run will be profiled.
  Implied by ``-D``.

--size=ASSIGNMENT

  Set a configurable run-time parameter to the given
  value. ``ASSIGNMENT`` must be of the form ``NAME=INT`` Use
  ``--print-sizes`` to see which names are available.

--tuning=FILE

  Read size=value assignments from the given file.

SEE ALSO
========

:ref:`futhark-test(1)`, :ref:`futhark-cuda(1)`, :ref:`futhark-c(1)`