[llvm] [ADT] Fix specialization of ValueIsPresent for PointerUnion (PR #121847)

[Nikita Popov via llvm-commits]

nikic wrote:

https://llvm-compile-time-tracker.com/compare.php?from=799e9883eaf7c7bdebfb8ddb3366d9137527b29d&to=7b0536794349734c8862fc140808e4e5a2ab8f8d&stat=instructions:u => It looks like GCC likes the new implementation and Clang hates it :)

If this isn't just perturbing some inlining heuristic, maybe we're missing some optimization...

https://github.com/llvm/llvm-project/pull/121847