[llvm] Deduplication of cyclic PHI nodes (PR #86662)

[Nikita Popov via llvm-commits]

nikic wrote:

> This is a continuation of a PR from https://reviews.llvm.org/D153014. There was a request by @nikic to benchmark the compile time for this change, which was done here: https://llvm-compile-time-tracker.com/index.php?config=Overview&stat=instructions%3Au&remote=mark-sed

Can you please rebase out the merge commits from this PR? Otherwise this is measuring the merge commit and not your change.

https://github.com/llvm/llvm-project/pull/86662