[PATCH] D151087: [Clang] Permit address space casts with 'reinterpret_cast' in C++

Mon May 22 08:18:36 PDT 2023

jhuber6 added a comment.

In D151087#4360919 <https://reviews.llvm.org/D151087#4360919>, @arsenm wrote:

> In D151087#4360695 <https://reviews.llvm.org/D151087#4360695>, @jhuber6 wrote:
>
>> I don't think that's something we can diagnose here with just the address space number. it would require information from the underlying target for the expected pointer qualities to the address space.
>
> Yes, this is mandatory. Numbered address spaces are broken and just work by accident and I don't love seeing new code rely on whatever random behavior they have now. Right now they happen to codegen to something that appears to work, while bypassing any kind of sensible semantic checking for what you're doing with them. If you want to really use this, we need to find some way to map numbers back into language address spaces and make them fully aware of the target properties

How are they broken? The expectation is just that they line up with what the backend defines them as, which should be a stable target. We could potentially use target info to map the numbered address spaces into something sensible. E.g. `1 = opencl_lobal`, `3 = opencl_local`, `5 = opencl_private`. I think that's commend between NVPTX and AMDGPU. But I still don't think that we should be preventing from even doing wrong things with them if the user explicitly requests it.

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https://reviews.llvm.org/D151087