[SYCL][DOC] Add build instructions for Windows to GetStartedWithSYCLC…

[v-klochkov]

…ompiler.md

1. Fixed an error in cmake command for Linux.
2. Added steps for OpenCL-Headers and OpenCL-ICD-Loader components, which
   are required.
3. Added Windows build instructions.
4. Made the build process more verbose and clear. You can literally follow
   the guide step-by-step to build compiler and tools and run a simple test.

Signed-off-by: Vyacheslav N Klochkov [email protected]

[v-klochkov]

See the final result as it appears in browser (not in editor) here: https://github.com/v-klochkov/llvm/blob/public_windows_getting_started/sycl/doc/GetStartedWithSYCLCompiler.md

[mibintc]

LGTM, I added a few inline comments. Thanks for documenting this!

[bader]

Please, clarify that this is an optional step.
CMake will automatically configure OpenCL headers and ICD loader if OpenCL_INCLUDE_DIR and OpenCL_LIBRARY variables are not set.

BTW, these part of the instructions are not related to Windows enabling, so it would be better to have it committed separately. It should be okay to have a separate commit in this PR as long as it documentation only.

[v-klochkov]

I did not know that OpenCL-Headers and ICD-Loader parts were optional. Probably because I started SYCL build on some older machine with DLLVM_TEMPORARILY_ALLOW_OLD_TOOLCHAIN=1, etc.

Thank you. I am removing these 2 big blocks now.

[v-klochkov]

Now I am not so sure that removing those two optional blocks (download OpenCL_Headers and download/build OpenCL-ICD-Loader) was good idea.
I am going to put them to this guide again.

The reason: even with this patch (that is in code-review now): #528 nmake and make work perfectly without those optional steps/blocks, while 'ninja' does not. Ninja (or our build scripts) have some problems with dependencies. Ninja does not build ICD-Loader before building sycl.lib. SYCL CMakeLists.txt look good to me.

[bader]

I'd like to improve this document further including these changes, but we need to get them in first.

[v-klochkov]

I updated the doc (added again those 2 optional steps for Headers and ICD-Loader).

BTW, The doc says:

clang++ -fsycl simple-sycl-app.cpp -o simple-sycl-app.exe -lOpenCL

Do we really need -lOpenCL now after we've got the PluginInterface. If there are no more direct calls of OpenCL functions, then -lOpenCL is not needed, right?

Edited (Aug21): I skip my question because from PRs like this (#517) I can see that direct calls of OpenCL functions are still exist in our sources.