[llvm] [llvm-profdata] Reject merging single-byte-coverage with count profiles (PR #213177)

[via llvm-commits]

gulfemsavrun wrote:

We have a use case where we merge single-byte counter profiles with 8-byte counter profiles for coverage. Single-byte counters are currently only supported in Clang; Rust does not support them yet, though there is an active proposal to add support (https://github.com/rust-lang/compiler-team/issues/1002).

Because our codebase includes C++ and Rust, we merge single-byte profiles from Clang with 8-byte profiles from Rust. We primarily care about line coverage (whether a line was hit) rather than exact hit counts. Therefore, we believe it is still valuable to allow merging these mixed-counter profiles rather than rejecting them.

https://github.com/llvm/llvm-project/pull/213177