[llvm] Fix uninitialized variable (PR #89040)

[Chris B via llvm-commits]

llvm-beanz wrote:

Even if that were true (which it isn’t, we create a std::variant of the four versions), the change still doesn’t make sense. Why would we want to only initialize the last field of a large data structure?

Is there an actual case where this caused an uninitialized value to be used, or is this just a speculative problem?

https://github.com/llvm/llvm-project/pull/89040