[llvm] [DFAJumpThreading] Add an early exit heuristic for unpredictable values (PR #85015)

[Nikita Popov via llvm-commits]

nikic wrote:

Note that with this patch, there is still a 20% compile-time regression in X86Disassembler.cpp, despite not performing a transform: https://llvm-compile-time-tracker.com/compare_clang.php?from=8c5e9cf737138aba22a4a8f64ef2c5efc80dd7f9&to=42c75d888058b35c6d15901b34e36251d8f766b9&stat=instructions%3Au&sortBy=interestingness

https://github.com/llvm/llvm-project/pull/85015