In order to support non-user-named kernels, SYCL needs some way in the
integration headers to name the kernel object themselves. Initially, the
design considered just RTTI naming of the lambdas, this results in a
quite unstable situation in light of some device/host macros.
Additionally, this ends up needing to use RTTI, which is a burden on the
implementation and typically unsupported.
Instead, we've introduced a builtin, __builtin_unique_stable_name, which
takes a type or expression, and results in a constexpr constant
character array that uniquely represents the type (or type of the
expression) being passed to it.
The implementation accomplishes that simply by using a slightly modified
version of the Itanium Mangling. The one exception is when mangling
lambdas, instead of appending the index of the lambda in the function,
it appends the macro-expansion back-trace of the lambda itself in the