OpenMP (CPU) support

[breyerml]

Sorry, if this is the wrong place to ask such a question.

How can I enable OpenMP support using the SYCL Intel llvm branch?
I wanted to run a simple OpenMP program:

#include <iostream>

int main() {

  #pragma omp parallel for
  for (int i = 0; i < 10; ++i) {
    std::cout << "Round: " << i << std::endl;
  }

  return 0;
}

using clang++ -fopenmp main.cpp. However, this results in a linker error:

/usr/bin/ld: cannot find -lomp
clang-13: error: linker command failed with exit code 1 (use -v to see invocation)

(Full error message when using -v while compiling:

clang version 13.0.0 (https://github.com/intel/llvm.git ad46b641972b90da748768678daa7fae4dcc1b78)
Target: x86_64-unknown-linux-gnu
Thread model: posix
InstalledDir: /home/u75527/Programs/intel-llvm/build/bin
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/9
Selected GCC installation: /usr/lib/gcc/x86_64-linux-gnu/9
Candidate multilib: .;@m64
Selected multilib: .;@m64
 "/home/u75527/Programs/intel-llvm/build/bin/clang-13" -cc1 -triple x86_64-unknown-linux-gnu -emit-obj -mrelax-all --mrelax-relocations -disable-free -main-file-name main.cpp -mrelocation-model static -mframe-pointer=all -fmath-errno -fno-rounding-math -mconstructor-aliases -munwind-tables -target-cpu x86-64 -tune-cpu generic -debugger-tuning=gdb -v -fcoverage-compilation-dir=/home/u75527/Programs/hipsycl/build -resource-dir /home/u75527/Programs/intel-llvm/build/lib/clang/13.0.0 -internal-isystem /usr/lib/gcc/x86_64-linux-gnu/9/../../../../include/c++/9 -internal-isystem /usr/lib/gcc/x86_64-linux-gnu/9/../../../../include/x86_64-linux-gnu/c++/9 -internal-isystem /usr/lib/gcc/x86_64-linux-gnu/9/../../../../include/c++/9/backward -internal-isystem /home/u75527/Programs/intel-llvm/build/lib/clang/13.0.0/include -internal-isystem /usr/local/include -internal-isystem /usr/lib/gcc/x86_64-linux-gnu/9/../../../../x86_64-linux-gnu/include -internal-externc-isystem /usr/include/x86_64-linux-gnu -internal-externc-isystem /include -internal-externc-isystem /usr/include -fdeprecated-macro -fdebug-compilation-dir=/home/u75527/Programs/hipsycl/build -ferror-limit 19 -fopenmp -fopenmp-cuda-parallel-target-regions -fgnuc-version=4.2.1 -fcxx-exceptions -fexceptions -fcolor-diagnostics -faddrsig -D__GCC_HAVE_DWARF2_CFI_ASM=1 -o /tmp/main-e11f36.o -x c++ main.cpp
clang -cc1 version 13.0.0 based upon LLVM 13.0.0git default target x86_64-unknown-linux-gnu
ignoring nonexistent directory "/usr/lib/gcc/x86_64-linux-gnu/9/../../../../x86_64-linux-gnu/include"
ignoring nonexistent directory "/include"
#include "..." search starts here:
#include <...> search starts here:
 /usr/lib/gcc/x86_64-linux-gnu/9/../../../../include/c++/9
 /usr/lib/gcc/x86_64-linux-gnu/9/../../../../include/x86_64-linux-gnu/c++/9
 /usr/lib/gcc/x86_64-linux-gnu/9/../../../../include/c++/9/backward
 /home/u75527/Programs/intel-llvm/build/lib/clang/13.0.0/include
 /usr/local/include
 /usr/include/x86_64-linux-gnu
 /usr/include
End of search list.
 "/usr/bin/ld" -z relro --hash-style=gnu --eh-frame-hdr -m elf_x86_64 -dynamic-linker /lib64/ld-linux-x86-64.so.2 -o a.out /lib/x86_64-linux-gnu/crt1.o /lib/x86_64-linux-gnu/crti.o /usr/lib/gcc/x86_64-linux-gnu/9/crtbegin.o -L/usr/lib/gcc/x86_64-linux-gnu/9 -L/usr/lib/gcc/x86_64-linux-gnu/9/../../../../lib64 -L/lib/x86_64-linux-gnu -L/lib/../lib64 -L/usr/lib/x86_64-linux-gnu -L/usr/lib/../lib64 -L/home/u75527/Programs/intel-llvm/build/bin/../lib -L/lib -L/usr/lib /tmp/main-e11f36.o -lstdc++ -lm -lomp -lgcc_s -lgcc -lpthread -lc -lgcc_s -lgcc /usr/lib/gcc/x86_64-linux-gnu/9/crtend.o /lib/x86_64-linux-gnu/crtn.o
/usr/bin/ld: cannot find -lomp
clang-13: error: linker command failed with exit code 1 (use -v to see invocation)

)

I've build the current sycl branch on the Intel devcloud using:

python3 ~/Programs/intel-llvm/buildbot/configure.py
python3 ~/Programs/intel-llvm/buildbot/compile.py

as given here: https://intel.github.io/llvm-docs/GetStartedGuide.html#build-dpc-toolchain

I also tried to steps described in https://openmp.llvm.org/ to enable OpenMP support.
I added openmp as external project in the configure.py file and I build OpenMP as out-of-tree build with the CMAKE_INSTALL_PREFIX CMake variable set to ~/Programs/intel-llvm/build both without success.

What is the easiest way to enable OpenMP support alognside SYCL using Intel's llvm fork?
(I don't new offload capabilities using OpenMP. OpenMP should simply be usable in host CPU code.)

[vzakhari]

Please try using the following patch:

index 28f36c815bcb..7f59aed732d0 100644
--- a/buildbot/configure.py
+++ b/buildbot/configure.py
@@ -22,7 +22,7 @@ def do_configure(args):
     xptifw_dir = os.path.join(abs_src_dir, "xptifw")
     libdevice_dir = os.path.join(abs_src_dir, "libdevice")
     llvm_targets_to_build = 'X86'
-    llvm_enable_projects = 'clang;' + llvm_external_projects
+    llvm_enable_projects = 'clang;openmp;' + llvm_external_projects
     libclc_targets_to_build = ''
     sycl_build_pi_cuda = 'OFF'
     sycl_werror = 'ON'

And the following commands:
python $DPCPP_HOME/llvm/buildbot/configure.py
python $DPCPP_HOME/llvm/buildbot/compile.py
cmake --build $DPCPP_HOME/llvm/build -- omp
cmake --build $DPCPP_HOME/llvm/build -- install

[breyerml]

Thanks. Works like a charm now.

[jinz2014]

Can you add this to the getting started guide ?