Nomp Examples

Make sure both libnomp and nompcc is built and NOMP_INSTALL_DIR and NOMP_CLANG_DIR are set before trying this section. Follow the instructions in Build Instructions to build and set these variables correctly.

This example requires creating three files in your working directory. First, let’s create foo.c file which contains the C program annotated with nomp pragmas.

foo.c

#include <stdio.h>

void foo(double *a) {
#pragma nomp for transform("transforms", "foo")
  for(int i = 0; i < 100; i++)
    a[i] = i;
}

int main(int argc, const char *argv[]) {
#pragma nomp init(argc, argv)
  double a[100] = {0};
  for (int i = 0; i < 100; i++)
    printf("a[%d] = %f \n", i, a[i]);

#pragma nomp update(to : a[0, 100])
  foo(a);
#pragma nomp update(from : a[0, 100])

  for (int i=0; i<100; i++)
    printf("a[%d] = %f \n", i, a[i]);

#pragma nomp update(free : a[0, 100])
#pragma nomp finalize

    return 0;
}

Then let’s create the transforms.py file which contains the foo Python function that is called by libnomp during the creation of accelerator kernel. This file has the loopy transformations that are applied to the kernel.

transforms.py

import loopy as lp

LOOPY_LANG_VERSION = (2018, 2)

def foo(knl, context):
    (iname,) = knl.default_entrypoint.all_inames()
    i_inner, i_outer = f"{iname}_inner", f"{iname}_outer"
    knl = lp.split_iname(
        knl, iname, 32, inner_iname=i_inner, outer_iname=i_outer
    )
    knl = lp.tag_inames(knl, {i_outer: "g.0", i_inner: "l.0"})
    return knl

Finally, let’s create nompcc which is a helper script that links libnomp installation to the clang compiler during compilation.

nompcc

#!/bin/bash

if [ -z "${NOMP_INSTALL_DIR}" ]; then
    echo "Error: NOMP_INSTALL_DIR is not defined !"
    exit 1
fi
if [ -z "${NOMP_CLANG_DIR}" ]; then
    echo "Error: NOMP_CLANG_DIR is not defined !"
    exit 1
fi

NOMP_LIB_DIR=${NOMP_INSTALL_DIR}/lib
NOMP_INC_DIR=${NOMP_INSTALL_DIR}/include

${NOMP_CLANG_DIR}/clang -fnomp -include nomp.h -I${NOMP_INC_DIR} "$@" -Wl,-rpath,${NOMP_LIB_DIR} -L${NOMP_LIB_DIR} -lnomp

Now, compile foo.c containing nomp pragmas using nompcc script as follows:

chmod +x nompcc
./nompcc foo.c -o foo

You can now run the compiled executable by simply providing commnad line arguments to initialize and use backends, devices, etc.

./foo --nomp-backend opencl --nomp-device 0

Read more about arguments accepted by nomp_init() under User API.