[llvm] [InferAttrs] Mark errnomem-setting libcalls as such (PR #124742)

[Nikita Popov via llvm-commits]

https://github.com/nikic commented:

I'm pretty apprehensive about the heavy lifting "inaccessible memory" is doing in this patch -- things like locales, files etc are now modelled as inaccessible memory.

 * I'm not very confident there are no non-libcall ways to access all of these even within the defined API.
 * We also have to worry about accesses of implementation details in headers. If any library calls are implemented as inline functions in headers, they may access memory that is logically inaccessible.
 * This further increases the LTO risk, where this inaccessible memory may become accessible. Currently this problem is mostly limited to allocators, but this expands it to all of libc.

TBH I think that all this patch should be doing is change this one line to restrict to errnomem: https://github.com/llvm/llvm-project/blob/661daa22bfb678de3162369a34042a69b548e883/llvm/lib/Transforms/Utils/BuildLibCalls.cpp#L1415

That's the main case we're interested in handling. (Well, that and malloc, but I think that should only be added after the AA support is there.)

https://github.com/llvm/llvm-project/pull/124742