__enzyme_allocation_like fails to detect null pointer argument index

[pengmai]

Context: When registering a custom allocator via __enzyme_allocation_like as a global array, the second element is the index of the argument for the size of the memory allocation. This element must be an integer casted to a pointer.

If this index is 0, many frontends (including clang and mlir-translate) will emit a ConstantPointerNull instead of a ConstantInt in the array. This causes preserve-nvvm to fail to detect the metadata, which triggers a crash.

Is there a known workaround? If not, I believe the fix should be pretty simple and I'm happy to submit a PR.

[wsmoses]

Not that I'm aware of, fix is welcome!