Support open source DPC++ compiler

[dvrogozh]

With: a928b93

Install the following dependencies:

$ docker run -it --rm ubuntu:26.04
$ apt-get update && apt-get install git cmake make g++ gcc pkg-config python3 libze-dev
# apt-get install dpclang-6

The last command installs open source DPC++ compiler packaged in Ubuntu 26.04. Please:

1. Add support for this compiler within the PTI project
2. Clarify how project needs to be built with this compiler:
   1. By specifying -DCMAKE_C_COMPILER=dpclang -DCMAKE_CXX_COMPILER=dpclang++, i.e. using dpclang to build C/C++/SYCL
   2. Or project will build C/C++ with regular compilers (gcc/clang) and use dpclang only for the SYCL code. How project will find the dpclang in this case?

CC: @mschilling0

[mschilling0]

1. TBD. However, I was able to compile PTI with it. Without XPTI, this compiler would just be needed for the tests and samples to build completely e.g., dpc_gemm sample needs a SYCL compatible compiler otherwise it will not build.
2. i. This seems to work. ii. is not supported because I don't believe CMake supports using multiple compilers in the build unless its a new "language" e.g., CUDA. I've seen projects do this: https://github.com/arrayfire/arrayfire/tree/master/CMakeModules i.e., make a new language called "SYCL"

[dvrogozh]

For 1. I was ablet to build PTI with the dpclang as well though indeed that's not a complete exercise due to currently missing XPTI, but as you know we are working to get it:

• xpti library miss Linux versioning and pkgconfig/cmake configurations llvm#21507

Question is whether we need any other fixes specific to dpclang? One obvious thing to check is verify compiler insource identification which is that it does not define __INTEL_LLVM_COMPILER (__DPCPP__ and __dpcpp_major__ should be used instead). Here is a grep for that:

# fgrep -rsn __INTEL_LLVM_COMPILER
test/sycl_queue_id.cc:532:#if __INTEL_LLVM_COMPILER >= 20240101 || __LIBSYCL_MAJOR_VERSION >= 8
test/sycl_queue_id.cc:566:#if __INTEL_LLVM_COMPILER >= 20240101 || __LIBSYCL_MAJOR_VERSION >= 8
test/sycl_queue_id.cc:573:#if __INTEL_LLVM_COMPILER >= 20240101 || __LIBSYCL_MAJOR_VERSION >= 8
test/sycl_queue_id.cc:609:#if __INTEL_LLVM_COMPILER >= 20240101 || __LIBSYCL_MAJOR_VERSION >= 8
test/main_urgemm_fixture.cc:48:// instead rely on  __INTEL_LLVM_COMPILER that provided by oneAPI compiler
test/main_urgemm_fixture.cc:61:#if (defined(__INTEL_LLVM_COMPILER) && (__INTEL_LLVM_COMPILER >= 20250300))
test/main_urgemm_fixture.cc:69:#if (defined(__INTEL_LLVM_COMPILER) && (__INTEL_LLVM_COMPILER >= 20260000))
test/main_urgemm_fixture.cc:79:// For oneAPI compiler we rely on  __INTEL_LLVM_COMPILER check.
test/main_urgemm_fixture.cc:80:#if defined(__INTEL_LLVM_COMPILER) && (__INTEL_LLVM_COMPILER < 20250300)
grep: test/.main_urgemm_fixture.cc.swp: binary file matches
samples/vector_sq_add/vector_sq_add.cc:312:#if __INTEL_LLVM_COMPILER >= 20240000
samples/onemkl_gemm/onemkl_gemm.cc:62:#if __INTEL_LLVM_COMPILER >= 20240000

@mschilling0 , can you, please, check if we will need to adjust any of the above?

For 2. Using -DCMAKE_C_COMPILER=dpclang -DCMAKE_CXX_COMPILER=dpclang++ should probably be fine for now. Is that's the way how the project is built by the ICX compiler at the moment? Doing ii) can possible even nowadays, but requires manual setup for the compiler which is a pain and better to avoid. Going forward I believe we will have a way to have the granularity to build only SYCL related files with the SYCL enabled compiler as that work is being currently done in cmake as far as I know, but it's not ready yet.