[SYCL] Move implementation details under sycl_private namespace

[alexbatashev]

ABI tests require a way to differentiate private and publicly accessible
symbols. Wrap symbols that are not be accessible from user application
in sycl_private namespace to exclude them from ABI checks.

Signed-off-by: Alexander Batashev [email protected]

[bader]

What is "private symbol"?
How can I decide which symbol is private?

[alexbatashev]

What is "private symbol"?
How can I decide which symbol is private?

Does it sound better now?

[bader]

We have "detail" namespace for "implementation details".
How can I decide which symbol should be "sycl_private" namespace and which symbol in "detail"?

[alexbatashev]

We have "detail" namespace for "implementation details".
How can I decide which symbol should be "sycl_private" namespace and which symbol in "detail"?

detail is used for many things across the project. It hides both host- and device-side implementation details, and user application still link againts those symbols. sycl_private only wraps the contents of source directory: those symbols can not be accessed from user applications, because the declarations are unknown.

[bader]

What is wrong with anonymous namespace?
Can we use it to hide symbols?

[bader]

sycl_private only wraps the contents of source directory: those symbols can not be accessed from user applications, because the declarations are unknown.

I see sycl_private uses in SYCL headers. Is this intentional?

[alexbatashev]

sycl_private only wraps the contents of source directory: those symbols can not be accessed from user applications, because the declarations are unknown.

I see sycl_private uses in SYCL headers. Is this intentional?

Yes, we still need to keep pointers to impl object. To fill in template arguments I needed forward declarations of classes. But pointers and forward declarations are not linkable symbols, so, those are not really "uses". And we still have a differentiation between accessible and inaccessible pieces of code.

[bader]

What is wrong with anonymous namespace?
Can we use it to hide symbols?

@alexbatashev, could you answer these questions, please?

[alexbatashev]

What is wrong with anonymous namespace?
Can we use it to hide symbols?

@alexbatashev, could you answer these questions, please?

I doubt I can reliably filter out everything that is inside cl::sycl::detail::(anonymous) namespace, but I’ll experiment a bit more with that.

[alexbatashev]

What is wrong with anonymous namespace?
Can we use it to hide symbols?

@bader while I can reliably detect anonymous namespaces on Linux, Windows is a bit trickier. But that's not the main problem. The main problem is that anonymous namespace implies internal linkage. And it breaks our tests:

In file included from /repos/sycl_private/sycl/unittests/scheduler/MemObjCommandCleanup.cpp:10:
/repos/sycl_private/sycl/unittests/scheduler/SchedulerTestUtils.hpp:76:6: error: function 'addEdge' is used but not defined in this translation unit, and cannot be defined in any other translation unit because its type does not have linkage

Can we keep sycl_private?