[C++4OpenCL] Add clang extension for non-portable kernel parameters

[olestrohm]

Summary

This feature allows using non-portable types as kernel parameters. This allows bypassing the portability guarantees from the restrictions specified
in C++ for OpenCL v1.0 s2.4.

Currently this only disables the restrictions related to layout, as a programmer using the same compiler for host and device should get the same representation.
This could be extended to other things (like size_t) if desired in the future, but I think it's unlikely that someone would want that.

Previous discussion about the extension in https://bugs.llvm.org/show_bug.cgi?id=50081

[Anastasia]

clang/docs/LanguageExtensions.rst

1816

How about __cl_clang_unsafe_kernel_parameters to match the other extension naming scheme? Or we could use __cl_clang_non_portable_kernel_parameters, __cl_clang_non_portable_kernel_parameter_types to be more specific regarding the kind of safety that we allow to break?

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Let's add declarations of such types along in the example.

clang/lib/Sema/SemaDecl.cpp

8652

I would rather add an assert for this because we should not ever reach this function for the dependent types?

[olestrohm]

clang/lib/Sema/SemaDecl.cpp

8652

The function is actually called on dependent types

[olestrohm]

Improved the description and example per the feedback.

The check for dependent type is needed. If it is not included the diagnostic will get triggered when the extension is disabled, but not when it's enabled.

[Anastasia]

clang/docs/LanguageExtensions.rst

1820

Let's add references to relevant OpenCL C and C++ for OpenCL sections with restrictions.

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Let's add . at the end of every sentance. :)

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[olestrohm]

Added a link to the C++ for OpenCL specification and cleaned up the text according to the requests.

[olestrohm]

Fixed merge error

[Anastasia]

LGTM! Thanks!

[Anastasia]

Closed by https://reviews.llvm.org/rGe994e74bca49831eb649e7c67955e9de7a1784b6