[cfe-dev] OpenCL types mangling.

[Bader, Alexey via cfe-dev]

Hi,

I'd like to discuss current mangling rules for OpenCL built-in types.

OpenCL specification defines number of built-in types:

-          Vector types e.g. int4, half8, etc.

-          Image types e.g. image2d_t, image

-          Sampler type - sampler_t

-          ...

All those types are mangled by clang using Itanium C++ ABI<https://mentorembedded.github.io/cxx-abi/abi.html>, which doesn't describe mangling of OpenCL types, but if we extend it naturally, OpenCL built-in types should be excluded from substitution as built-in type. BTW, it's the way how SPIR 1.2 defines it (appending A of https://www.khronos.org/registry/spir/specs/spir_spec-1.2.pdf).

Clang 3.6+ substitutes OpenCL built-in types although they were not compressed before this commit<https://github.com/llvm-mirror/clang/commit/76742aedda1189059fbc0a4c6af6d0285dbec9da>. This looks like unintentional change.
Unfortunately recovering original behavior will solve the problem only partially.
OpenCL built-in vector types are implemented not as Clang's built-in types, but as vector extension types, so they will require special case in mangler.

I'd like to have an agreement within clang community on how to handle substitution of OpenCL built-in types since it's not part of the OpenCL specification, but rather internal compiler design. Is it OK to disable OpenCL built-in type compression? The only con of this approach is the length of mangled types. If I get it correctly built-in types are exceptions because their compression will not reduce the size of the mangled name and for some types even increase.

Does it worth documenting mangling rules for OpenCL built-in types?

- Alexey


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