[llvm] ConstraintElim: add dry-run routine to fail early (PR #99670)

[Ramkumar Ramachandra via llvm-commits]

artagnon wrote:

New results look good: http://llvm-compile-time-tracker.com/compare.php?from=c5ee3c05ca61f3fae11337c5853aee7b450a9dc6&to=50c2e95b9a66395d5f6b62a99e67fec1a874f8f5&stat=instructions%3Au.

@dtcxzyw Could you kindly check the latest commit against your data set?

https://github.com/llvm/llvm-project/pull/99670