[SYCL][NewOffload] Introduce specialization constants in clang-linker-wrapper

[maksimsab]

Add -sycl-spec-const-handling-mode command line option to clang-linker-wrapper.
processSpecConstants is moved from sycl-post-link to lib/SYCLLowerIR/SpecConstants.cpp and invoked from sycl-post-link and splitting library.

[maksimsab]

I need to check how "default_values" mode is handled in clang-linker-wrapper.

[sarnex]

Thanks for the PR!

My understanding of when we should clang-linker-wrapper args is when we need to communicate information from the driver to clang-linker-wrapper, where in most cases that happens for user specified command-line args that effect how clang-linker-wrapper needs to act.

For this case, I'm not sure I see why we need the new flag. I don't see any user visible option for Clang to effect spec consts, only logic to set the -spec-const flag to sycl-post-link, which seems to be a triple-based calculation.

Also in this PR I don't see any changes to the driver to set this new flag.

Could you go into detail on why we need this flag and how we plan to modify the driver to set it?

Thanks

[asudarsa]

+1 on @sarnex comment here about the need for this mode.
I see the related code here

llvm/clang/tools/clang-linker-wrapper/ClangLinkerWrapper.cpp

Line 646 in 9eaca2b

bool SpecConstsSupported = (!Triple.isNVPTX() && !Triple.isAMDGCN() &&

and the spec-const mode seems to rely on the target triple and nothing else and hence should be computed inside the clang-linker-wrapper.
@maksimsab please let me know if we are missing something here.

Thanks

[maksimsab]

You are right. It needs to be redesigned.

[github-actions]

This pull request is stale because it has been open 180 days with no activity. Remove stale label or comment or this will be automatically closed in 30 days.