Building with oneAPI for non-standard compiler installation

[oleksandr-pavlyk]

For the default value of --sycl-compiler-prefix option to develop/install setup commands we require ONEAPI_ROOT and do not set DPCTL_CUSTOM_DPCPP_INSTALL_DIR.

The logic is all built assuming that setting DPCTL_CUSTOM_DPCPP_INSTALL_DIR signals use of custom-built DPC++ toolchain.

When oneAPI compiler bits are installed into Python environment, we can not use ONEAPI_ROOT, since compiler's location is no longer ${ONEAPI_ROOT}/compiler/latest/linux but ${CONDA_PREFIX} instead, and must rely on --sycl-compiler-prefix which sets DPCTL_CUSTOM_DPCPP_INSTALL_DIR and CMake script starts assuming that we build with OS DPC++ toolchain.

@AndresGuzman-Ballen

[diptorupd]

I propose the following: in FindIntelSycl.cmake the option DPCTL_CUSTOM_DPCPP_INSTALL_DIR should only indicate the compiler root that may or may not be a oneAPI installation. We rename it to DPCTL_DPCPP_HOME_DIR

Next we add another CMake option: DPCTL_DPCPP_FROM_ONEAPI=ON that will indicate that the DPCTL_DPCPP_HOME_DIR is a oneAPI install. For using a truly custom Intel Sycl compiler, we will need to set DPCTL_DPCPP_FROM_ONEAPI=OFF.

[oleksandr-pavlyk]

I like the renaming idea. In #481 I implemented detection of oneAPI by matching for "dpcpp" in ${CMAKE_CXX_COMPILER}.

[diptorupd]

We will need to add a setup.py option too to setup the flag to indicate we use custom compiler.

[oleksandr-pavlyk]

In FindIntelSycl we query clang or dpcpp to query version. We can drop this branching. clang --version will give the right version. In oneAPI:

(idp) [10:15:53 ansatnuc04 dpctl-capi]$ clang --version
Intel(R) oneAPI DPC++ Compiler 2021.2.0 (2021.2.0.20210317)
Target: x86_64-unknown-linux-gnu
Thread model: posix
InstalledDir: /localdisk/intel/oneapi/compiler/2021.2.0/linux/bin

In DPC++ toolchain:

(build_sycl) [10:17:03 ansatnuc04 sycl_workspace]$ export PATH=$DPCPP_HOME/llvm/build/bin:$PATH
(build_sycl) [10:18:15 ansatnuc04 sycl_workspace]$ export LD_LIBRARY_PATH=$DPCPP_HOME/llvm/build/lib:$LD_LIBRARY_PATH
(build_sycl) [10:18:16 ansatnuc04 sycl_workspace]$ clang --version
clang version 13.0.0 (https://github.com/intel/llvm 9b61592812e3a58d8d1b995cc0fef730cd817d43)
Target: x86_64-unknown-linux-gnu
Thread model: posix
InstalledDir: /localdisk/work/opavlyk/sycl_workspace/llvm/build/bin

[oleksandr-pavlyk]

The only other branching is the minimum version we require.

[oleksandr-pavlyk]

Implemented in both DPCTL_DPCPP_HOME_DIR and DPCTL_DPCPP_FROM_ONEAPI in #481